Abstract:
A surgical distraction apparatus is disclosed. The surgical distraction apparatus includes a tissue distraction device adapted for implantation, the tissue distraction device including a plurality of distraction members, one or more actuators adapted for implantation and operatively coupled to the tissue distraction device, the one or more actuators being configured to drive the tissue distraction device and adjust the alignment of the plurality of distraction members, and an activator adapted to deliver one or more pulses to at least one actuator in the one or more actuators.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/828,656, filed May 29, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Distraction systems are utilized for altering body configuration and skeletal malformation. Progressive distraction is critical to many craniofacial, orthopedic and surgical interventions, such as for scoliosis, which is a three-dimensional deformation of the spine. Idiopathic scoliosis is typically corrected by the surgical insertion of rods attached to two or more vertebrae. During traditional surgery, high forces are applied, distracting the vertebrae from their initial position so as to partially or fully correct the scoliosis. This sudden mechanical stretching of the tissues is traumatic and painful and results in high stresses in the implanted rod system. 
         [0003]    As another illustrative example, pectus excavatum is the most common congenital deformity of the anterior chest wall in which the sternum and costochondral cartilages are abnormally formed. Previously, rigid metal bars were typically inserted to distract the chest wall and correct the deformity in a single operation. 
         [0004]    Craniosynostosis is a condition in which the sutures of an infant&#39;s skull are prematurely closed. Currently these sutures are surgically opened by one or more operations in which the bones of the skull are removed or reshaped. 
         [0005]    Common to most prior distraction systems is a mechanism based on the physical manipulation of the system by the surgeon. Such systems generally necessitate open access to the implanted device to alter its configuration. Frequently these systems are applied externally or internally with external exposure of the unit and are fraught with an increased morbidity and risk of infection. Many such systems are limited by the inability to change the configuration of the implanted hardware as the patient&#39;s habitus changes. Non-static systems are even more germane to changes with growth observed in a pediatric population. 
         [0006]    Current techniques for surgical correction of malformations often require sudden, radical stretching and correction of the tissue configuration in each operation so as to minimize the number of invasive surgical procedures required. In some cases there is a need for multiple operations, for example, to allow for growth or for swelling to subside. Often this entails severe postoperative trauma and pain. It also places a strain on resources for both the patient and society. 
         [0007]    A small number of surgical distraction devices have been developed which can be externally activated once the incisions are closed. 
         [0008]    Typically these systems depend on the ability to place a toroidal magnet around the limb for the purpose of moving the internal elements of the device as in a conventional electric motor with a rotor and a stator. Due to these spatial constraints such systems are limited in application to use in extremities, such as the femur. They can&#39;t be employed within the chest or abdomen, for example. 
         [0009]    Other devices employ implanted electric motors or components containing rare earth elements that are potentially toxic within the human body. 
         [0010]    Several systems have been developed in which an implanted actuator lengthens or shortens a rod or cable. Tissue distraction is intended to occur due to axial compression or tension forces in the rod or cable transmitted in-line to the tissues. 
         [0011]    Treatment of scoliotic diseases is typically accomplished by spine fixation using specially designed pedicle screws or other devices. These are attached to suitable points on several of the vertebral bodies and to rigid spinal rods by means of a variety of specialized connection devices. Many of these fixation devices provide adjustable degrees of freedom that allow the surgeon some intra-operative leeway to adjust the positions of the vertebrae relative to one another in the coronal, sagittal, and transverse planes. However a common characteristic of most such spinal fixation systems is that postoperatively there is no possibility of making minor adjustments to the geometry of the fixation system to correct for growth or to accommodate changes in the anatomy due to the presence of the fixation system over a period of time. 
         [0012]    During surgery, the fixation system is generally pre-tensioned to urge the spine into a more desired configuration. Unfortunately, once the vertebrae have relaxed in the desired direction a state of equilibrium is attained in which there are no longer any significant restoring forces to further coerce the tissues and further correct the deformity. 
         [0013]    In fact, the presence of the implanted rigid fixation system can eventually begin to have an adverse effect, constraining growth and necessitating further operations to shift the rod connections to new spatial locations where they can again provide the desired corrective loads on the spinal column. 
         [0014]    “Dynamic” or semi-constrained vertebral couplings have been used in the past, for instance with Harrington rods. Using screws in slots or cylindric joints sliding between stops, these dynamic couplings allow axial or angular motions to compensate for subsidence or settling. 
         [0015]    Telescoping rod systems have also been developed. Most of these are extended by surgical intervention with accompanying trauma and risks. 
         [0016]    Kiester, U.S. Pat. No. 7,955,357, describes an externally adjustable expandable rod system for the treatment of scoliosis. This utilizes an implanted Nitinol muscle wire ratchet actuator to lengthen an implanted rod. Electrically heating and cooling the Nitinol wire via an implanted power pickup causes the Nitinol wire to alternately stretch and shrink. This motion incrementally rotates a screw system which telescopically lengthens the rod over a period of time. In this way, the rod is loaded in compression thereby gradually forcing apart the vertebrae attached to the two ends of the rod. Scoliosis correction with this device is primarily obtained by axial (compressive) forces in the rod rather than lateral bending (side to side) forces on the vertebrae as is done in the present system. 
         [0017]    Nuss, U.S. Pat. No. 6,024,759, describes a minimally invasive treatment for pectus excavatum in which one or more bowed steel bars are inserted under the deformed sternum with their convexity facing posteriorly. Subsequently, in the same operation, the bars are rotated  180  degrees so that the ends of the bars follow the curvature of the chest and the deformed sternum is forced outwards towards its final position in a single operation. Unfortunately, this sudden surgical correction of the deformity is generally accompanied by severe postoperative trauma and pain. 
         [0018]    Distraction osteogenesis is the process of gradually correcting deformities by stretching bones and tissues such as the long bones of the leg or craniofacial bones. A variety of devices have been developed for this purpose, including external fixators, internal nails, and motorized implants. 
         [0019]    Intramedullary nails driven by electric motors and control systems have been designed for elongating long bones separated by an osteotomy. Such systems require implantation of electric motors with potentially toxic rare earth magnetic materials and are tailored to use in the long bones of the extremities. 
         [0020]    Stepping motors, pawls, and ratchet devices have long been applied in non-medical applications such as clock escapements, typewriters, printers, odometers, toys, wrenches, motion picture projectors, rotary telephone switchboards, production machinery and the like. 
         [0021]    Magnetically activated clock escapements and single cycle clutches have been employed to incrementally release a pre-tensioned spring or a shaft driven by some other power source. Solenoid driven ratchet stepping motors have also been used but such devices require a source of electricity to drive the ratchet. Further, the solenoid magnet that is built into the assembly depends on precise alignment and a small controlled gap to insure proper functioning of the device. 
         [0022]    Similarly, electrical stepping motors generally utilize a rotor and a stator. They incorporate multiple pole pieces and windings and require an electrical power source to sequentially energize the windings. They generally depend on a small carefully controlled air gap between the rotor and the stator so as to reduce the length of the flux lines between the fixed and moving pole pieces. A rotating magnetic field generated within the windings causes the rotor to index relative to the stator. To get a significant amount of torque, either the rotor or the stator must be energized or else a permanent magnet is employed. Strong permanent magnets generally are highly toxic due to their rare earth element composition. 
       BRIEF SUMMARY 
       [0023]    A system and apparatus is described that provides a distraction system that can be externally adjusted and manipulated after the incisions are closed and without necessitating further surgical intervention. The ability of the present system to gradually make the transition from an initial to the planned final configuration can radically change the feasibility and efficacy of surgical distraction. In many cases it can greatly speed recovery while also reducing pain, trauma, number of surgical interventions required, and costs both to the patient and to society. 
         [0024]    The present system provides a distraction apparatus with a final configuration that can be preoperatively planned so as to produce the intended corrected geometry, optionally over an extended period of time but with an initial configuration that can closely conform to the preoperative geometry of the patient. 
         [0025]    The present system provides a distraction apparatus that can be reconfigured through a minimally invasive incision. 
         [0026]    The present system also provides a minimally invasive distraction apparatus that can synchronously provide desired amounts of progressive correction at multiple points using a single externally controlled actuator. In many cases, the proportional amounts of displacement to be applied at each point during each treatment can be preoperatively determined. 
         [0027]    The present system describes a spinal fixation apparatus that can be adjusted postoperatively over a period of time, requiring a minimum of surgical intervention and minimizing the associated trauma, such as the trauma traditionally associated with correction of Idiopathic scoliosis. 
         [0028]    Similarly, the present distraction apparatus describes a system that can slowly correct various other malformations or deformities thereby allowing the tissues to relax and equilibrate over time. In this way, use of the present apparatus can avoid much postoperative pain and discomfort, such as that normally associated with treatment of pectus excavatum, pectus carinatum, or craniosynostosis. 
         [0029]    The present system is directed to a family of cable coupled surgical distraction apparatuses and systems that use an externally controlled implanted incremental actuator. These apparatuses and systems allow slow progressive alteration of the patient&#39;s physical configuration via external control such as by an externally controlled electromagnetic field or physical pressure on the skin. The present system aids in minimally invasive surgical procedures. 
         [0030]    The system includes one or more implantable ratchet-driven actuators, an implantable tissue distraction means coupled to and driven by said actuators, and an external actuation means for incrementally activating said actuators by delivering a sequence of magnetic or mechanical pulses. Other forms of actuator and actuation means can also be employed. Such means can utilize electric motors controlled by means of wireless telemetry, induction coils, or other modalities or means such as manually operated levers or threaded devices. 
         [0031]    The system also includes surgical distraction apparatuses with segmented cable-tensioned distraction members. These members are so arranged and disposed as to provide a multiplicity of lateral (bending) forces at right angles to the members and at multiple locations and not just axial forces along the members. These combined forces gradually urge the distracted tissues in planned directions as the cable tension is increased. Such cable-tensioned distraction members can include segmented rods or bars adapted to insertion through relatively small surgical openings. These segmented structures can be tensioned into their final rigid configuration. Such tensioning can be done progressively over a period of time using the externally controlled actuator means of the present system. 
         [0032]    Such tensioning can also be achieved surgically using an implanted adjusting means rather than with an externally controlled tensioning actuator. Tensioning can be done either prior to closing the initial incision or progressively over a period of time using a minimal incision to gain access to the tensioning means. 
         [0033]    A compliant spring means can be incorporated in series with the cable system. This spring means can be designed to protect against accidental overloads of the mechanism or of the tissues being distracted. It can also be designed so as to provide a consistent or preferred level of tension in the cables independent of perturbations caused by relative motions of the bones or other structures. Flexural properties can be built into the system&#39;s attachments or anchors, into selected links, or into the tensioning cables themselves. 
         [0034]    The present system is particularly suited to minimally invasive surgical procedures, since many of the components are adapted to insertion through relatively small surgical openings and then can be tensioned into their final configuration while working through the same surgical incision proximal to the actuator itself. 
         [0035]    The implanted actuators can be powered by a pulsed magnet system external to the patient, optionally directed by computer control. 
         [0036]    Post-surgery, the implanted actuators can be externally activated in a controlled fashion without further surgical intervention and without any penetration of the skin by wires or other devices. 
         [0037]    The magnetically controlled actuator of the present system uses neither implanted magnets nor implanted power sources or heating elements. It also does not depend on having a small, carefully aligned air gap or the ability to completely surround the actuator motor with a rotating magnetic field. Thus, the present distraction system can be used on portions of the anatomy such as the chest or abdomen where the actuator is only proximal to one surface of the body. 
         [0038]    The system does not require implantation of any rare earth elements, batteries, electric motors, or other toxic substances. The implanted parts are purely passive mechanical components. Additionally, many variations of the system and apparatus described can be utilized. The ratchet actuators can be driven by mechanical pressure applied to portions of the actuator through the tissues of the skin. Actuation of the cable-tensioned distraction system can be achieved surgically through a minimally invasive incision. Actuators of the present system can be configured to produce either rotary or linear incremental motions. 
         [0039]    These rotary or linear motions from the actuator are mechanically coupled to what will herein be referred to as “end effector” members that in turn push or pull on the actual tissues of the patient thereby performing the actual distraction. 
         [0040]    A number of such novel coupling means can be used together with a number of such novel end effector distraction devices. For example, the actuators can be used to stiffen a segmented cable-tightened system of link elements. In the slack, unstressed configuration, these links can be threaded through contorted anatomical regions so as to conform to the basically uncorrected pre-surgical deformity. 
         [0041]    The geometry of the contact points or joints between the link elements is arranged so that as the links are progressively pulled into the stiffened configuration by means of the aforementioned actuator, one or more points on the various links applies pressure to the tissues urging them into the desired final distracted configuration. 
         [0042]    Construction of the joints between the tensioned segments can be adjusted to constrain the direction of flexing at that joint and to allow preferred combinations of distraction forces on the tissues or bones being distracted. These can consist of a mix of lateral forces (perpendicular to the segments) and axial forces (along the segments). The directions and magnitudes of these forces can vary from segment to segment and also over time with the progression of the treatment as the system is incrementally tensioned postoperatively. 
         [0043]    The present system teaches both planar and non-coplanar constructions for the distraction apparatus. Non-coplanar distraction displacements, forces, and torques can be produced using either the planar or non-coplanar apparatus constructions taught herein. 
         [0044]    The present system also teaches how the geometry of the joints between the tensioned segments can be tailored so that the joints between adjacent segments become stiffer and more rigid as the tensioning cable is shortened. In effect, the individual links behave more like a single member better able to resist transverse and bending loads as the treatment progresses. 
         [0045]    The final end effector action between the links and the tissues can be accomplished by means of a number of devices, such as pedicle screws, sutures, wires, adjustable rod mounts, and so forth; by direct contact pressure between various bearing surfaces on the links and the tissues; or by other coupling means allowing desired directions of freedom and constraint. Elastically compliant elements can be incorporated into some end effectors to control the force levels at that interface between the tissues and the distraction device. 
         [0046]    One or more of said end effector coupling means can be engaged to said actuator in such a way as to simultaneously apply corrective forces or pressures to several areas of the patient&#39;s anatomy as needed. 
         [0047]    These can include original end effector coupling means tailored to the needs of a particular patient or surgical operation or such well-known means as pedicle screws, sutures, cables, rods, ball joints, compliant couplings, point, line, or surface contacts, and so forth. Depending on the particular application of the system a plurality of such end effector couplings can be used at the same time. 
         [0048]    The present system also teaches construction of some new end effector pedicle attachment devices for transferring forces between the jointed distraction rod members and the vertebrae in the treatment of scoliosis. 
         [0049]    The actuator of the present system can be used to drive one or more screws and nuts or turnbuckle-type devices to pull together or push apart bony structures such as vertebrae, skull sutures, or for other tissue distraction purposes. Again, the final attachment of these nuts or turnbuckles to the tissues can be attained by various devices. 
         [0050]    Coupling between the rotary actuator and these turnbuckles, cables, or other devices can be accomplished by a variety of mechanisms providing the necessary amount of torsional or rotational stiffness. However said coupling can also be so configured as to allow flexibility and out of plane motions where desired or when the actuator is not proximal to the distraction end effector. For instance, rigid rods or shafts can be used but there can also be flexible shafts, telescoping prismatic joints, bellows, bell cranks, universal joints, or other equivalent means used to provide needed flexibility and room for growth or to accommodate the internal motions of the anatomy while still providing and constraining the desired distraction. 
         [0051]    A single rotary actuator can drive multiple distractor end effectors. Distraction performance can be tailored to attain a differential action at various points along the mechanism by a variety of means. For example, linkages or different screw pitches can be employed at different points in the system thereby tightening some points while loosening others. 
         [0052]    Some of these turnbuckles or nuts can employ a variety of left or right-hand screw pitches providing a differential action as needed so that a unidirectional rotation of the actuator can cause various forms of distraction at different points in the body. For instance in the case of the spine, some points can be spread apart while others were drawn together. 
         [0053]    The actuator can be used to drive a flexible rotary coupling system such as a flexible shaft, telescoping prismatic joints, bellows, or universal joints, thereby conveying the rotary motion to remote sites within the body where it can be needed for tissue distraction or other purposes. 
         [0054]    It will be appreciated that the actuator can have single or double-ended shafts as needed. Further, it can be coupled via gear trains, levers, cables, push-pull shafts, power screws, or other devices so as to obtain increased mechanical advantage if needed. 
         [0055]    It will be further noted that a variety of end effector means can be used to couple the tissue distraction motions of the actuator-driven components of the present system to the anatomy of the patient so as to most effectively utilize the distraction system in a particular application. 
         [0056]    For example, in correction of pectus excavatum, a multi-link cable-tensioned hinged assembly of rods or bars can be passed beneath the sternum from one side of a patient to the other. This initial operation can be performed in a minimally invasive manner using tapes or cords to pull the loosely coupled link members beneath the tissues following the curvature of the uncorrected anatomy. A protective flexible sleeve can be used as a passageway to assist in guiding these components into position and to provide protection to the tissues, both during the initial operation and optionally for the duration of the progressive treatment. One or more incremental or other rotary actuators or terminal fixation devices can then be coupled to the ends of this cable system and sutured beneath the skin on the patient&#39;s sides. Initially, the link assembly can conform to the patient&#39;s deformity and can be relatively unstressed. 
         [0057]    Postoperatively, over a period of time, the actuators in the present system can be externally activated, incrementally tensioning the link system without further surgical interventions. The geometry of the links and their coupling joints can be so configured as to gradually apply necessary corrective distraction forces to the sternum as the link assembly becomes stiffer. In this situation, the end effectors conveying the distraction forces to the tissues can be the contact surfaces of the actual links themselves or a sleeve or other surface between the tissues and said links. 
         [0058]    Controlling the number of incremental activations of the actuators can provide a measure of the amount of correction being delivered during any particular postsurgical treatment and, indirectly, the change in distraction forces that can be expected as a result. Over a period of weeks or months these forces can slowly urge the tissues into the desired final form without the sudden pain and discomfort of the traditional open surgical procedure. 
         [0059]    As another typical application of the present system, in surgical correction of scoliosis a multi-link cable-tensioned hinged assembly of rods can be tunneled or implanted alongside the spine and attached to two or more selected vertebrae using pedicle screws or other devices as described earlier. Initially, the slack joints between these rod segments can allow them to somewhat conform to the spine&#39;s initial deformity. 
         [0060]    An actuator of the present system can be attached to the cables at one distal end of the cables. Over a period of time the cables can be tensioned. Contact forces between adjacent links can cause the links to move towards a final predetermined configuration. The geometry of the various joints between the links and the shape of the links themselves can determine the final three-dimensional shape of the distraction device. The end effectors acting on the various vertebrae (pedicle screws, compliant or sliding connectors, or other devices) can apply relatively gentle loads on the spine over a period of time, thereby urging the ligamentum flavum to stretch so as to alleviate the scoliosis. 
         [0061]    Selected vertebral attachments can be coupled to jointed links by slack motion couplings of the present system utilizing slots, cams, or pivots together with mechanical limit stops. These limit stops can be positioned so as to allow some parts of the distraction system to move freely in certain directions when treatment begins and only begin applying distraction force to the connected structures at a later point in the progressive treatment protocol. In another illustrative example, they can also be configured to provide initial corrective forces and displacements at certain locations that taper off and diminish later in the progressive treatment while other portions of the distractor apparatus might come into engagement or continue to apply loads at other locations. 
         [0062]    In some situations a pair of cable-tensioned apparatuses can be implanted on either side of the spine to apply more control and a higher corrective force. In this case, actuators of the present system can be offset from one another to allow each cable system to be independently controlled and tensioned. 
         [0063]    Cross members coupling selected jointed members of the two rod assemblies can be provided with needed pivots or other joints allowing needed flexibility in desired planes and stiffness and constraint in other directions. These cross members can also provide fixation supports for pedicle screws and similar hardware. 
         [0064]    A variety of other mechanisms can be driven by the incremental actuator system and used to provide the distraction forces. For instance: single or multiple cables can be employed; the link members can be hinged together or keyed to interlock by the shape of their contacting surfaces; a single flexible spline member with controllable stiffness can be used in place of the multiple links; the links can be bent or have varying cross-sections; there can be intermediate guides or attachments; and so forth. 
         [0065]    Further, a variety of motor devices with suitable gear reductions and control systems can possibly be utilized in place of the incremental actuator to activate the mechanical distraction system. When utilizing such motors, power and control devices can be implanted along with the motor actuator. Inductive coupling or other means can be used to power the implanted motor to avoid the use of skin penetrating wires. Additionally, Nitinol or electric motor drive systems can be used in place of the ratchet actuators described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0066]      FIG. 1  is a schematic conceptual overview showing the main elements of the system as it can be configured for treating scoliosis. 
           [0067]      FIG. 2  illustrates a distraction system for treating pectus excavatum according to an exemplary embodiment. 
           [0068]      FIG. 3  illustrates the system&#39;s segmented cable-tensioned distraction members according to an exemplary embodiment. 
           [0069]      FIG. 4  is an illustration of how the present system guides the distraction members into alignment as the cables bring the mating surfaces into contact. 
           [0070]      FIGS. 5-6  illustrate how the tubular links of the present system can be configured with one or more cables and specialized joint geometry to better control the relative motion between the distraction members. 
           [0071]      FIGS. 7-8  illustrate how substantially bar-shaped links of the present system can be configured to “nest” and come into rigid alignment in a two-dimensional application. 
           [0072]      FIG. 9  illustrates an overview of the geometry needed to understand the principles underlying operation of the joints of the present system. 
           [0073]      FIG. 10  is a two-dimensional example illustrating how joint geometry of the present system can force proper self-assembly by restricting possible translational freedoms between links. 
           [0074]      FIGS. 11-13  show how the instantaneous joint configuration of the same two links insures proper self-assembly by forcing the links into rotational alignment. 
           [0075]      FIG. 13  details the overall rotational freedom and constraint provided by joints of the present system. 
           [0076]      FIG. 14  illustrates a simplified diagram of the forces acting at a typical joint of the present system as the cables are tightened. 
           [0077]      FIG. 15  illustrates the polygon of forces at the joint in  FIG. 9 . The cable tension is in equilibrium with the forces at the contact patches between the links 
           [0078]      FIGS. 16-18  illustrate how the principles taught in the  FIGS. 7-15  can be generalized and extended to three-dimensional alignment variations. 
           [0079]      FIG. 17  illustrates how the links of the present system can be inserted and threaded along a curved guide cable prior to tensioning. 
           [0080]      FIG. 18  illustrates how the links of the present system can be straight or curved and how asymmetrical joint geometry can coerce adjacent links into alignment as the joints are mated together. 
           [0081]      FIG. 19  gives a schematic overview of the present system. 
           [0082]      FIG. 20  illustrates an external pulse generator used to incrementally drive the implanted distraction actuator system according to an exemplary embodiment. 
           [0083]      FIG. 21  outlines a control computer that can be used to operate the present system. 
           [0084]      FIG. 22  is a block diagram of key elements of the power switching and control system according to an exemplary embodiment. 
           [0085]      FIG. 23  is an exterior view of an actuator of the present system according to an exemplary embodiment. 
           [0086]      FIG. 24  illustrates an exemplary embodiment of the incremental actuation surgical motor of the present system. 
           [0087]      FIG. 25  is an exploded view of the wrap spring actuator of  FIG. 24 . 
           [0088]      FIG. 26  illustrates an exemplary embodiment of the present ratchet actuator system as it can be arranged for treatment of pectus excavatum and which uses a multiplicity of pawls to produce micro-stepping despite limited angular rotation of the input lever. 
           [0089]      FIG. 27  illustrates the  FIG. 26  device mounted in a case with typical suture attachments, a coupling system for connecting the actuator to tension cables, and an adjusting provision for positioning the actuator relative to a reaction member against which the cables are tensioned. 
           [0090]      FIG. 28  illustrates a manually actuated reversible ratchet actuator using a wrap spring clutch which can be activated by external pressure on the skin of the patient. 
           [0091]      FIG. 29  illustrates a dual ended system of the actuators according to an exemplary embodiment. 
           [0092]      FIG. 30  illustrates how gearboxes can be employed to drive end effectors in other planes, at different speeds, at right angles to the primary actuator shaft, or to increase the available torque. 
           [0093]      FIGS. 31 and 32  illustrate how multiple distractors of the present system can be staggered for use in treatment of scoliosis. 
           [0094]      FIG. 33  illustrates how the distraction apparatus of the present system can be coupled to vertebrae. 
           [0095]      FIG. 34  illustrates a pedicle attachment of the present system allowing angular compensation during the course of treatment. 
           [0096]      FIG. 35  illustrates how the pedicle attachment system of the present system can allow selective limited axial or angular motion with respect to the distractor links during the course of treatment. 
           [0097]      FIG. 36  details a split pedicle attachment system of the present system. 
           [0098]      FIG. 37  illustrates how limit stops of the present system can be incorporated to further control the timing and the distraction applied at different points during the course of treatment. 
           [0099]      FIG. 38  illustrates a dual distractor system and how limit stops of the present system can be incorporated to control when during treatment a particular distractor force becomes active. 
           [0100]      FIGS. 39 and 40  show a collar illustrating how a limit stop of the present system can control when during treatment a particular axial distractor force becomes active. 
           [0101]      FIG. 41  illustrates the present system using a turnbuckle end effector distraction device coupled to the actuator by means of a flexible shaft. Right or left-handed screw threads can be chosen for the turnbuckle&#39;s threaded members allowing the end effector distractor to draw together or separate as needed, for a given direction of rotation of the driving actuator. 
           [0102]      FIG. 42  illustrates a turnbuckle end effector distractor of the present system that can be applied to craniosynostosis or other surgical procedures requiring separating or drawing together bony structures, and in which differential screw threads can be chosen to provide high forces and fine distraction adjustments. 
           [0103]      FIG. 43  illustrates an exemplary embodiment of the present system in which telescoping or universal joints are chained together to permit the actuator to be remotely mounted relative to the distractor end effector and illustrates the variations allowed by the interchanging modular components of the system. 
           [0104]      FIG. 44  illustrates an exemplary embodiment of the present system in which a tension cable is employed as the terminal end effector distraction device. 
           [0105]      FIG. 45  illustrates the present system employing a turnbuckle actuated hinged distractor according to an exemplary embodiment. 
           [0106]      FIG. 46  illustrates the present system wherein multiple distraction devices are serially coupled together by flexible shafts or other devices and driven by a single implanted actuator according to an exemplary embodiment. 
           [0107]      FIG. 47  is a chart showing possible variations of the design of the implantable surgical distraction apparatus and conditions which can be treated using the apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0108]    The present system and apparatus is directed to an implantable surgical distraction device suited to application for correction of a wide variety of anatomical malformations. The device is particularly directed towards use in protracted treatments extending over long periods where the degree of distraction can benefit by being incrementally altered long after the original surgical operation has ended. Scoliosis and pectus excavatum are typical examples of such surgeries where a capability for making post-surgical adjustments can be beneficial. 
         [0109]    Implantable elements of the current system are particularly suited to insertion by minimally invasive surgical procedures. In many cases they can be threaded into the body through relatively small incisions, pulled or pushed through like beads on a string and then erected in place by tensioning a device at the terminal end of the assembly. 
         [0110]    Elements of the present system are modular in concept and can be employed in various combinations as needed to meet the surgical situation at hand. Further, some of these components can be custom-shaped to meet the size and needs of a particular patient. Certain components are adapted to receive custom attachments and ancillary hardware for purposes such as anchoring sutures or fixating pieces to various bony structures such as pedicles of the vertebral bodies or ribs. 
         [0111]    The current system is adapted to progressively changing its spatial arrangement from an initial configuration somewhat following the contours of the patient&#39;s malformation at the time of surgery to a final corrected configuration. As the distraction device changes shape, the change of shape is communicated to the patient&#39;s tissues via “end effectors” which press on selected portions of the anatomy and cause the tissues to relax towards a preferred corrected arrangement. 
         [0112]    This change of geometry can be controlled by means external to the patient without necessitating further surgery for each adjustment. For instance, in many cases it can be done during a series of office visit treatments. 
         [0113]    The features which correspond to the numerals in the figures in an exemplary embodiment are listed below and are discussed in greater detail with respect to each figure.
     10 —Surgical motor     20 —Typical distraction device and coupling mechanism     21 —Before treatment     22 —After treatment     23 —Transverse section of abdomen     30 —External actuator drive means     40 —Control system     50 —Link segment     55 —End Effectors     60 —Tensioning cables     70 —Contact between members     72 —Contact surfaces between members     74 —Cable passageways     76 —Hinge axis     80 —Cylindrical tubular link assembly     90 —Cylindrical tubular link body     100  —Hinging joint members prior to tensioning     110  —Hinging joint members post tensioning     120  —Female joint half     130 —Male joint half     135 —Sliding cylindric surfaces     140 —Rigidly aligned nesting joints     150 —Contact surfaces between members     160 —Links brought into alignment by joint geometry     170 —Female keyed joint half     180 —Male keyed joint half     190 —Keyed and fully mated joint     200 —Curved link     210 —Straight link     220 —Mated pair of links     230 —Tensioning cable passages     240 —Contact as joints start to close     250 —Fully closed joint     260 —Rounded nose     262 —Rounded trailing edge     270 —Wedge surfaces     280 —Parallel locking surfaces     290 —Final seating surfaces     300 —Reference link     310 —Link moving with respect to reference link     320 —Contact patch at O 1        330 —Contact patch at O 2        340 —Common normal at contact patch O 1        350 —Common normal at contact patch O 2        360 —Common tangent at contact patch O 1        370 —Common tangent at contact patch O 2        380 —Field of translational restraint due to contact at O 1        390 —Field of translational freedom due to contact at O 1        400 —Field of translational restraint due to contact at O 2        410 —Field of translational freedom due to contact at O 2        420 —Overall field of translational freedom in joint     430 —Fields of Clockwise Rotational Freedom allowed by contact at O 1  (Solid curved arrows)     440 —Fields of Counter-Clockwise Rotational Freedom allowed by contact at O 1  (Solid curved   arrows)     450 —Fields of Clockwise Rotational constraint allowed by contact at O 1  (Dashed curved arrows)     460 —Fields of Counter-Clockwise Rotational constraint allowed by contact at O 1  (Dashed   curved arrows)     470 —Fields of Clockwise Rotational Freedom allowed by contact at O 2  (Solid curved arrows)     480 —Fields of Counter-Clockwise Rotational Freedom allowed by contact at O 2  (Solid curved   arrows)     490 —Fields of Clockwise Rotational constraint allowed by contact at O 2  (Dashed curved arrows)     500 —Fields of Counter-Clockwise Rotational constraint allowed by contact at O 2  (Dashed   curved arrows)     510 —Overall remaining field of Rotational Freedom (Clockwise within angle)     520 —Tensioning cable     530 —Normal force at O 1        540 —Normal force at O 2        550 —Cable tension pulling moving link with respect to fixed reference link     560 —Pulse transmitter     570 —Face of pulse transmitter     580 —Grip of pulse transmitter     590 —Coupling to control computer     600 —Control computer     610 —Treatment programming or selection     620 —Treatment status display     630 —Treatment delivery switch     640 —Case of actuator     650 —Mounting means for distractor to motor     660 —Adjustment means     670 —Anti-rotation means     680 —Main drive shaft     690 —Bearings     700 —Lever arm     710 —Ratchet mechanism     720 —Return spring means     730 —Nut     740 —Threaded portions of shaft     750 —Unthreaded portions of shaft     760 —Key slot     770 —Cable setscrews     780 —Cable passages     790 —Wrap spring clutches     800 —Backstop wrap spring clutch     810 —Return spring     820 —Bushing     830 —Pawls     840 —Ratchet wheel     850 —Base link     860 —Stitch anchors     870 —Spring arm     880 —Spring arm     890 —Wrap spring clutch     900 —Drum portion     910 —Bearing     920 —Antirotation surface     930 —Double ended shafts     940 —Gearbox     950 —Primary shaft     960 —Secondary shaft     970 —Staggered locations     980 —Offset distractor parts     990 —End Effectors     1000 —Link Attachment member     1010 —Bore hole     1020 —Mounting Screw     1030 —Fixation plate     1040 —Locking setscrew     1050 —Pedicle Screw     1060 —Angular freedom compensation     1070 —Axial compensation     1080 —Rotational compensation     1090 —Locking Collar     1100 —Collar setscrew     1110 —Slotted joint     1120 —Side to side compensation     1130 —Cover component     1140 —Base component     1150 —Mounting screw     1160 —Mounting Screw hole     1170 —Interlocking edge     1180 —Tapped hole     1190 —Face piece hole     1200 —Flexible shaft     1210 —Turnbuckle distractor     1220 —Remote distractor     1230 —Turnbuckle shaft     1240 —Left and right hand threads     1250 —Attachment points     1260 —Prismatic joint chain     1270 —Universal joint chain     1280 —Threaded tension member     1290 —Nut     1300 —End loop     1310 —Tension cable     1320 —Rotary bearing     1330 —Distractor links joint     1340 —Distractor links     1350 —Turnbuckle shaft     1360 —Turnbuckle ends     1370 —Turnbuckle nut     1380 —Turnbuckle nut     1390 —Articulated distractor     1400 —Drive train     1410 —Different threads     1420 —Lever arm   
 
         [0269]      FIG. 1  gives a pictorial overview of key elements of the present system as it can be applied in correcting deformities of the spine. 
         [0270]    Part  10  represents an implantable rotary or linear actuator that can be controlled by pulses delivered through the skin or other tissues of the patient. 
         [0271]    Typically, the number and duration of these pulses for a particular treatment can be planned and programmed into a control computer (part  40 ) and then delivered to the internal actuator  10  by a transmitting device such as an electromagnet, shown here as part  30 . The pulses can be mechanically communicated to the internal actuator by pressure on the skin or through another intermediate implanted transmission medium such as a fluid filled bladder, such as by using the actuator of  FIG. 28 . 
         [0272]    Part  30  is a pictorial representation of such a magnetic pulse source or other external transmitting device. It can be positioned in proximity to  10  but external to the patient. The alignment and air gap are such that a pulse from  30  can result in an incremental indexing rotation of the implanted actuator. 
         [0273]    Part  40  illustrates the power, control, and computer system that can be used in conjunction with  30  to deliver a desired train of pulses to the actuator  10 . Part  40  can incorporate computer or other means to allow the physician to preset such variables as the number of pulses to be delivered, their strength, their duration, and the timing between pulses. It can contain the trigger mechanisms for actually delivering the treatment pulses. It can also incorporate a display or other feedback mechanisms to convey to the operator the extent and status of the present treatment. 
         [0274]    Part  40  also symbolically represents the power switching and control system that converts the low-level control logic information to the voltages and current levels needed to drive the treatment transmitter  30 . Typically it can incorporate a solid-state relay, surge suppressor circuitry, and the like. 
         [0275]    Finally,  20  typifies one of many possible deformable tissue distractor systems whose geometry can be gradually altered during the course of the treatment by means of the incremental actuator  10 . 
         [0276]    For instance, in  FIG. 1 , distractor  20  consists of a series of somewhat cylindric jointed link members  50  coupled together by internal cables. The joints between the somewhat cylindrical links are so disposed as to cause the link elements of distractor  20  to attain a predetermined final three-dimensional shape when the cables are tensioned. This shape correction is transmitted to the patient&#39;s tissues via a variety of end effector devices  55 .  FIG. 1  shows how the present system can be configured for treating scoliosis. 
         [0277]      FIG. 2  shows how the present system can be utilized in treating pectus excavatum. (A transverse radiographic image of the patient&#39;s untreated sunken abdomen is shown in the background for context.) Here, the distractor  20  is comprised of a cable-tensioned system of jointed link members but they are flattened bar-like members rather than substantially cylindrical members as in  FIG. 1 . 
         [0278]    In the case of pectus excavatum, this flexible cable-coupled system of links can be threaded beneath the sternum through small incisions proximal to the actuators  10  on either side of the patient. This can be facilitated using tapes or other guides. A flexible protective sleeve can be used over the cable distractor links to serve as a guide and also to prevent their accidentally pinching the patient&#39;s tissue. In some situations the cables can be introduced before the actual links to serve as guides. Then the individual links can be slipped along the cables, possibly working in from the two sides. The sleeve can have markings to aid a surgeon. 
         [0279]    Mounting holes  860  in  FIG. 2  represent typical means by which the distraction system can be sutured or otherwise anchored or attached in position. 
         [0280]    In different applications of the present system, the length and curvature of the individual distractor links to be used can be preoperatively chosen by the physician so as to minimize trauma and obtain the best final geometry. Well-known imaging modalities and computer modeling can be developed to facilitate this preoperative treatment visualization process. 
         [0281]    Shorter distractor links with joints closer together can be employed in the areas requiring the most correction of curvature. Similarly, distractor joints can be spaced further apart in areas where less correction is needed. 
         [0282]    After insertion, the cables and links can then be pre-tensioned and fastened to anchor nut devices on the incremental surgical actuators  10 .  FIG. 1  shows an application with a single such actuator device for correcting spine curvature.  FIG. 2  shows a chest wall deformity application using a pair of these actuators  10  attached beneath incisions on either side of the torso. 
         [0283]    Postoperatively, the incremental actuators can be progressively tightened over a period of time. The present system teaches how the geometry of the mating surfaces between the links can cause them to gradually move into a preferred final alignment with one another. As the joints approach their final alignment, the distractor system becomes stiffer so it can better resist bending. As the transition takes place, the end effectors attached to the links of the distractor gradually apply increased corrective forces on the anatomical structures. This gradual change can alleviate much of the pain and discomfort associated with present more abrupt surgical treatments. 
         [0284]      FIG. 2 , for example, shows how the present system can gradually make such a transition. At the start of treatment, the un-tensioned distractor can follow the general shape of the patient&#39;s chest wall as shown in initial configuration  21 . 
         [0285]    During treatments spread out over a period of time, when the physician activates the pulse generator  30 , the incremental rotations of the actuator  10  increase the tension in the cables and cause the distractor device  20  to transition from a starting configuration  21  compatible with and somewhat conforming to the initial shape of the deformity being treated to a final desired shape such as  22 . 
         [0286]    In the illustrative example of pectus excavatum treatment (shown in  FIG. 2 ) the sternum and ribs can be gently forced into a more natural orientation near the end of treatment. Once the tissues had adapted to the new chest wall configuration, the link distraction system can be surgically removed. 
         [0287]    The present system differs from other devices because this change in configuration is primarily due to angular bending in the joints between adjacent cable connected link elements and not due to telescoping of said links. 
         [0288]    As the distraction device makes this shape transition, the distractor  20  will provide forces on the actual tissues of the patient via a variety of end effector elements  55  attached to said distractor links. These end effectors are chosen and arranged so as to preferentially coerce the tissues in desired directions thereby providing correction to the deformity. 
         [0289]    These end effectors  55  serve to interface the progressively reshaping distraction apparatus to the patient&#39;s tissues. End effectors  55  can comprise such well-known devices as surgical screws or other pedicle attachments. Specialized end effectors  55  are also described in and as part of the present system. 
         [0290]    End effector action in the present system can also take place as a result of shaped surfaces or coverings on the distractor link elements themselves that can bear directly against the tissues. This mechanism for tissue distraction is employed as shown in  FIG. 2 . 
         [0291]    In  FIG. 2  for example, the outward facing flattened faces of the jointed links of distractor  20  serve as the end effectors. These bearing surfaces are so disposed as to push outward on the chest wall when the cables are tightened, thereby correcting the deformity when treating pectus excavatum. 
         [0292]    The final shape that the stiffened distractor  20  will attain is controlled by the chosen distractor link shape and dimensions, the tension cable arrangement, and by the joint geometry. Custom or standardized distractor  20  and end effector components can be chosen or manufactured to meet the particular needs at hand and forces required. 
         [0293]    The present system teaches how a variety of joint geometries can be selected so as to produce desired forces, rotations and translations at various points along the distractor  20 . Some joints can have stops allowing limited angular rotations, say, while others can permit free motions in certain directions but constrain motion in other directions. In this manner the final post-tensioned shape and curvature of distractor  20  can be controlled along its length in three dimensions. 
         [0294]      FIG. 3  shows an exemplary embodiment of the present system using a pair of tensioned cables  60  to draw the links  50  into alignment. The cables  60  are attached to a common draw nut assembly at the actuator end and a common actuator or anchor means at the other end so they act in concert to draw the links  50  into tighter contact with one another and with a desired final alignment. 
         [0295]    As the slack is taken out of the system, adjacent pairs of links will be drawn together as at  70 . The cables running through lengthwise passageways  74  in the links also press against and are in contact with various areas on the periphery of the passageways through the links. 
         [0296]    Due to the small clearances, the net effect of this fairly complex interaction of slipping, sliding, and rubbing between parts will be to coerce the links towards a configuration where the contacting surfaces  72  between adjacent links are pulled towards coincidence. Effectively there will be an approximate hinging motion between the links with the pair of cables acting to constrain the direction of this hinge axis as shown by arrow  76  in  FIG. 3 . 
         [0297]      FIG. 3  also shows how the links of the present system can be either straight or curved. They can also be twisted in three dimensions, so as to produce distractions in multiple planes. 
         [0298]      FIG. 3  further shows how the links can have flattened bar-like cross sections if that is beneficial, say for strength reasons or to better fit the patient or to provide more comfortable bearing surfaces against anatomical structures. Link edges can be rounded with fillets as shown and the links and joints can also have a flexible protective tubular sleeve or cover to prevent tissue from growing or being pinched in the joints. 
         [0299]      FIG. 4  shows how the links of the present system can also be constructed with a cylindrical or other cross-section. 
         [0300]      FIG. 5  shows a joint for the present system that will aid the links in following a desired hinge axis as they come into alignment. Here, the two halves of joint  100  have mating male and female sliding surfaces that align the link bodies and guide the hinging action as the cables are tightened. 
         [0301]      FIG. 5  also shows how the joints of the present system can either be made as integral parts of the links or as separate components attached to and functioning as part of the links.  80  gives an example of a complete link assembly with a tubular link body  90  and joint halves such as the male and female pair  100  attached at both ends. Such a construction can allow a smaller inventory of components to be customized to meet the needs of a particular patient. For instance, the tubular bodies  90  can be stocked in various lengths or bends and combined with standard joints  100 . The joints at the two ends of  80  can be pressed or keyed into the tubular members  90 . They can also be rotated slightly with respect to one another to provide out of plane distraction. 
         [0302]    The joints can also have their hinge axes oriented in different planes and have their colliding surfaces so arranged as to provide a desired amount of spatial rotation at each joint. They need not be manufactured to result in an in-line orientation of the coupled links but can be customized as needed for a particular distraction purpose. Further, modifications can be incorporated within the spirit of this system, for instance to allow one or more cables or multiple passages for cables. 
         [0303]      FIG. 6  details how the joints of the present system can be made with male and female portions  120  and  130 . These portions can have sliding surfaces  135  in the form of partial cylinders that will guide the attached links with a hinging action. When the cables are fully tensioned and the links are in their final positions, this hinging action is arrested by the substantially flat surfaces  72  coming into face-to-face contact. The part-to-part contact between the sides of the cables  60  and the axial passageways  74  through the joints will result in a strong, relatively stiff final configuration where side-to-side loads on the distractor of the present system will be primarily absorbed as shear loads in the cables rather than as tensile loads. For clarity, the cables are not shown in the  FIG. 6  illustration but are understood to run through the passageways  74 . 
         [0304]    It will be appreciated that a variety of mating surface geometries can be used for the two halves of the joints to control the final tensioned positions of the cable-coupled links. Further, a multiplicity of cables can be used as shown in  FIG. 6  or a single cable can be employed to pull the halves of the joints into alignment. 
         [0305]      FIGS. 7 and 8  show other variations for constructing the joints of the present system. The joint geometry shown in  FIGS. 7 and 8  provides positive spatial alignment between adjacent links, correction of misalignment, and higher bending strength then can be otherwise achieved by depending on the cable tension alone. This joint geometry can be particularly well suited to distractors for the treatment of pectus excavatum or pectus carinatum, as illustrated in  FIG. 2 . 
         [0306]    The links shown in  FIGS. 7 and 8  have male and female mating coupling surfaces. As seen in the cross-sectional projected views, the coupling surfaces of are characterized by rounded surfaces  260  and  262 , and wedge-like surfaces  270  which make a smoothly curved transition into parallel flat surfaces  280 . (It will be appreciated that the cables that draw the links together are omitted from  FIGS. 7 and 8  for clarity. These cables pass through the cable passages  230 .) 
         [0307]    When loosely assembled so as to follow the curvature of the deformity at the time of surgery, the coupling surfaces of one or more adjacent links can be only partially engaged as seen at  240 . Line or surface contact can occur, say between the male or female rounded surfaces  260  or  262  and the male or female round or flat surfaces as seen at  240 . 
         [0308]    As the cables are tightened, either because they were shortened by means of the ratchet actuator or because of motion or growth of the patient, vibrations, or other disturbances, the geometry shown in  FIG. 7  forces adjacent links into proper alignment. Wedging action between the joints straightens the connections and amplifies the effectiveness of the cable tension in resisting side bending loads on the joints. Finally, once the mating parallel surfaces  280  are engaged, the cable is relieved from providing any of the bending stiffness to that portion of the distractor link assembly. The cable&#39;s main function then is to simply keep the links engaged. 
         [0309]      FIG. 7  shows a preferred configuration with provision for two cables running through the passageways  230  shown. One or more cables can be used within the spirit of this system. Again, for clarity of illustration, the cables have been omitted from the  FIG. 7  illustration. 
         [0310]    It will be seen that the cable-connected links  220  in  FIG. 7  can be made in different lengths and different curvatures to meet the needs of a particular patient or operation. 
         [0311]    Further, one can employ a variety of attachments and fittings on the various links  220  as needed for such purposes as providing intermediate stiffening, support, stabilization, suture attachments, and so forth. 
         [0312]      FIGS. 9 through 15  teach in two-dimensions several underlying theoretical principles of the present system. These joint design principles can be extended into three-dimensional geometries for other distractor applications as is shown in  FIGS. 16 through 18 . In  FIGS. 9-15  the common normals and common tangents at the contact patches between links control the relative positions of the links and how they can move as the cables are tightened in the present system. 
         [0313]    It will be understood that the two links  300  and  310  of  FIG. 9  are being pulled together by tensioned cables running through passageways within the links. These passageways run substantially down the centerline of the links as seen in these views and in the  FIG. 8  projected view. The coupling cables and passageways are not shown in these diagrams for reasons of clarity. 
         [0314]    When the cable is snug and the joint is partially assembled as shown in  FIG. 9  there will typically be contact between the male and female portions of the joint at several points such as  320  and  330 . The number of these contact points together with their locations and inclinations relative to one another determines the relative motions possible between the two links  300  and  310 . 
         [0315]    As seen in  FIG. 9 , at each contact point one can construct an instantaneous common normal to the two halves of the joint and a common tangent. At  320  the common normal is  340  and the common tangent is  360 . At  330  the common normal is  350  and the common tangent is  370 . 
         [0316]    Considering just the instantaneous contact between the two bodies at point  320  of  FIG. 9 , it will be seen that the only directions in which body  310  can move relative to body  300  is shown by the illustrative arrows  390 . Motion towards the other side of the common tangent at  360  is blocked by the fact that the two links would collide at  320  if link  310  were to try to move in that direction. Given this one point of contact at point  320 , motion in any of the directions suggested by the arrows  390  is possible because it would tend to open the gap and separate the contact at  320 . Thus on one side of the common tangent at  320  we can say there is a “field of translational freedom” and on the other side is a “field of translational restraint”. This instantaneous “field of translational restraint” caused by the contact at  320  is shown by the cross-hatched region  380 . 
         [0317]    If we have two or more simultaneous points of contact ( 320  and  330  in this case) then each common tangent produces a field of possible translational freedom (fields  390  and  410 ) and a field of translational restraint ( 380  and  400 ). Whether or not one body can translate relative to the other is determined by whether or not there is any residual field of translational freedom once all such contact points have been taken into account. 
         [0318]      FIG. 10  shows how the two contact points shown in  FIG. 9  limit the ability of link  310  to translate relative to link  300 . At this instant, link  310  can only translate out of the wedge-shaped region shown. The cross-hatching shows the fields of translational restraint in which one or the other or both contact points are colliding thereby preventing translational motion. 
         [0319]    If the links were initially separated but being pulled together by a cable then the rounded nose of link  310  can translate towards the female socket region of link  300  until contact occurred between the two links, say at point O 1  or O 2 . When that happens, sliding along the common tangent at the contact point can further guide the moving link within the field of translational freedom towards the nested configuration until a second contact point became active and further translation was blocked as is shown in  FIG. 10 . Tension in the cable can prevent translation out of that residual wedge-like field of translational freedom so all translatory motion would be blocked once the two contacts at O 1  and O 2  occurred. 
         [0320]    Similarly,  FIGS. 11 and 12  teach how the common normal between two colliding bodies determines how they can rotate relative to one another. For instance, in  FIG. 11  again consider the upper body ( 300  shown here with the light outline) as being the fixed reference body and see how the contact at point O 1  limits the ability for the lower body ( 310  shown here with the heavy outline) to rotate relative to the reference body. (Ignore for the moment the contact at point O 2 .) 
         [0321]    The common normal at the contact point O 1  is the line  340  (E O 1  F). Clockwise or counter-clockwise rotation of body  310  relative to body  300  is possible or restricted depending on whether the instantaneous center of rotation is located on one side or the other relative to this common normal. 
         [0322]    In  FIG. 11 , if the center of rotation is above the normal  340  then a counterclockwise rotation of the body  310  is possible because rotation in that direction would tend to open the gap at O 1 . In other words, there is a counterclockwise field of rotational freedom as shown by the solid curved arrows sketched above line  340 . 
         [0323]    Similarly, if the center of rotation is below the normal  340  then a then a clockwise rotation of the body  310  is possible because it would also tend to open the gap at O 1 .  FIG. 11  shows this field of clockwise rotational freedom by means of the solid curved clockwise arrows in the region below the normal  340 . 
         [0324]    Conversely, body  310  is blocked from rotating in the clockwise direction about any center of rotation lying above the normal  340  because such a rotation would tend to bring the contacting surfaces closer together into a collision at O 1 . The dashed clockwise curved arrows of 
         [0325]      FIG. 11  show that clockwise rotation is impossible about centers of rotation in that region. We can refer to the region above the common normal  340  as the “field of clockwise rotational restraint” produced by contact at O 1 . 
         [0326]    Similarly the region below the common normal  340  is the “field of counterclockwise rotational restraint” produced by contact at O 1 , as shown by the counterclockwise dashed curved arrows of  FIG. 11 . 
         [0327]      FIG. 12  shows the similar rotational constraints produced by the contact at point O 2 . Common normal  350  divides the plane into a region of clockwise rotational freedom above line  350  and counterclockwise rotational freedom on the other side of the common normal. Similarly, contact at O 2  causes a field of clockwise rotational restraint below the normal  350  and counterclockwise rotational restraint above the normal. 
         [0328]    All of these fields are instantaneous properties and change as the contact points shift position and direction. 
         [0329]      FIG. 13  shows that with simultaneous contact between links  300  and  310  at the two points O 1  and O 2  shown in  FIG. 25  these common normals and common tangents define overlapping regions of clockwise and counterclockwise rotational freedom and restraint. In order for body  310  to rotate at all it must rotate about a center of rotation in a field of rotational freedom that is not blocked in both the clockwise and counterclockwise directions. 
         [0330]      FIG. 13  shows that body  310  can only rotate in a clockwise direction relative to body  300  and only about a center of rotation inside the acute angle P Q R defined by the instantaneous common normals at the two contact points. All other rotations are blocked. 
         [0331]    When contact at O 1  or O 2  temporarily prevents the male link  310  from translating further into a nesting position with the female socket in link  300  it forces link  310  to rotate into alignment in response to tension from the cable. Similarly, when link  310  has rotated into proper alignment and there is no further field of rotational freedom, the parallel tangent surfaces defining the field of translational freedom will allow it to be pulled further into the nesting position until it is firmly seated and additional contacts block further nesting motion. 
         [0332]    Thus, the geometry illustrated by this provides that the joint can only move in such a way as to close the joint and rotate into proper alignment when the joint halves are constrained from separation by a tensile cable. Since there is no side-to-side field of translational freedom once the links are nested, the effective side-to-side bending strength of the joint is primarily a function of the strength of the link materials and thicknesses and not of the tension in the cable. 
         [0333]    This closing of the gap between the two halves of the joint can be urged or caused by the tension in the cable but it can also result from any other disturbance such as random jiggling motions within the joint. However, once it occurs, if the cables are able to hold the joint from again separating then the only possible motions will be in the desired direction and tend to close the joint. 
         [0334]      FIG. 14  is a simplified free-body diagram showing the principal forces active in the joint just discussed during the period before the links are fully engaged. Vector  550  represents the cable tension pulling link  310  towards link  300 . Vector  530  represents the normal force which link  300  is exerting on link  310  at contact O 1 . Vector  540  represents the normal force link  300  is producing at contact O 2 . 
         [0335]    It will be seen that forces  530  and  540  produce a clockwise couple tending to rotate link  310  into alignment with the joint. 
         [0336]      FIG. 15  is a polygon of forces showing the force equilibrium between these forces. (Frictional forces have been ignored for clarity.) It shows that the construction taught by the present system can produce or resist fairly significant side forces  530  and  540  with a relatively small cable tension  550 . As the links come closer to being in alignment the tensile loads in the cable (and that must be produced by the actuator) dramatically decrease. 
         [0337]    These same general principles apply to joints constructed by the teachings of this patent when extended to three dimensions, say by rotating the two-dimensional profiles of  FIG. 9  about an axis so as to form a swept male or female joint somewhat like a wine glass or goblet, as illustrated in  FIGS. 16-18 . 
         [0338]      FIG. 16  illustrates how these principles taught in connection with the  FIG. 9  planar joint also work when generalized and extended into three dimensions. The analogy with the planar device is as follows: In three dimensions, the points of contact between the joints become contact patches and the tangent lines become tangent surfaces. The spatial translational and rotational freedoms permitted by the joints are now constrained by half-spaces defined by the common tangent planes and by the directions of the common normals at the contact points. 
         [0339]    When the planar joint geometry of  FIG. 9  is swept about an axis into a surface of revolution, links such as those shown in  FIGS. 16 and 17  can be generated. Those links will be constrained by the contact patches between the male and female joint components to rotate and align into a stiffened member as the cables are tightened. However they can still have a rotational freedom about an axis aligned with a cable passing through the joint. Depending on the specific application of the present system that extra freedom can or can not be important. 
         [0340]      FIG. 18  shows how that remaining rotational freedom can be removed by sweeping the planar joint about a non-circular cross-section such as an ellipse. Here, the male joint half  180  and the female joint half  170  are shown as having elliptical cross-sections although other mating non-symmetrical geometries can also work. Such joints can nest or key together in a manner that can eliminate all relative freedoms of motion as the cables pull the joint halves together. Other asymmetric geometries can also be used within the spirit and teaching of this patent to cause the joint haves to key into alignment as they pull together. 
         [0341]    The remaining rotational freedom can also be removed by employing two or more tensioning cables running through side-by-side passageways as shown in  FIG. 5 . 
         [0342]    In addition, as the joint closes into the regime in which the plug and socket are substantially prismatic rather than conical, the bending stiffness of that portion of the distractor is greatly increased. There is an increasing wedging action that enhances the mechanical advantage of the distractor as was taught in  FIG. 15 . The system makes a transition from producing distractor forces primarily because of the tension in the cable and the effective lever arm at which the cable tension acts to a configuration where the distractor can produce or resist forces primarily because of the geometry and material properties of the links themselves. When the joint is fully drawn together, the cable tension is only needed to resist axial loads and maintain axial assembly of the distractor links. 
         [0343]      FIG. 18  also illustrates how the links of the cable-tensioned distractor can be bent (as shown by link  200 ) or twisted along their lengths as needed to achieve distraction in different planes and directions at different joint locations. 
         [0344]      FIGS. 19 through 22  show suitable electronic and control circuitry for driving the imbedded actuator  10  of the present system. Other circuitry can also be used. 
         [0345]      FIG. 19  shows a representation of how a physician can actuate the present system during a distraction treatment. The physician can initiate an incremental reshaping of the distractor  20  by placing an external transmission device  30  in a position where it can communicate one or more pulse signals to the implanted incremental actuator  10 . The physician can use a control system represented by  40  to send a desired series of pulses to the implanted actuator  10 . Suitable electronic computer and control circuitry can be integrated with and activated by parts  30  and  40 . 
         [0346]      FIG. 20  represents a typical external pulse transmitter  30  that can be used with the present system. It will be appreciated that the particular shape shown in  FIG. 20  is unimportant but is just used for illustrative purposes. 
         [0347]    The shape of transmitter  30  is such that it can be positioned by means of a handle  580  or other device with a face  570  near or against the skin of the patient in the vicinity of the implanted rotary ratchet actuator  10 . Control switches and other devices can be incorporated into the unit as desired along with needed safety devices such as thermal and electrical insulation. 
         [0348]    Transmitter  30  can have a first surface  570  so disposed as to aid in properly positioning the pulse generator  560  with respect to the implanted actuator. 
         [0349]    Transmitter  30  can comprise an electromagnet with windings and pole pieces capable of producing a magnetic pull strong enough to act through the tissues and air gap near face  570  and thereby index the implanted magnetically activated ratcheting rotary actuators  10  taught in this patent. 
         [0350]    It will be understood that other forms of transmitter device can be used within the spirit of this system to drive other forms of implanted actuator motors. These can include wireless transmitters to drive implanted actuator motors with internal power supplies, induction coils to transmit pulses to implanted receiving coils, and other devices. 
         [0351]    Transmitter  30  can also have a handgrip or other means  580  suited to aiding the physician in aligning and positioning the device with respect to the patient and a means  590  for connecting device  30  to necessary power and control devices  40 . It will be understood that elements of  40  can be integrated into  30 . They are shown as separate component modules simply for illustrative purposes. 
         [0352]    Switch  630  of  FIG. 21  represents a typical means that can be used by the physician to deliver a predetermined number of electromagnetic pulses to the implanted actuator. An associated microprocessor or computer (represented by box  600 ) can be programmed to convert the desired treatment protocol from terms most useful to the physician to the needed number of pulses to drive the implanted actuator. For instance, the physician can specify to the computer the length of cable to be retracted by the actuator and the computer can convert that into the number of pulses needed to achieve that distraction. 
         [0353]    As an example, a display means  620  can be used as a human interface to aid in presetting the number of pulses to be delivered, to indicate the number of pulses currently delivered, or to graphically show the status of the present treatment. Such a display means can optionally even be coupled to real-time imaging hardware to show how the patient or the implanted distractor system is actually responding to the current treatment. 
         [0354]    Similarly, there can be interface devices coupled to the control computer to change the planned treatment. For instance, devices like switch  610  can be used to preset such things as the number of pulses to be delivered, their timing or duration, the total angular rotation to be attained, or the linear distance through which the distractor is to move. Sensors and feedback devices can also be incorporated within the distractor system to communicate to the external control system  40  internal parameters within the patient such as tension in the cables or forces on the distractor. 
         [0355]      FIG. 22  is a flow chart schematic showing the logic and general arrangement of how the control system  40  and electromagnet  30  of the present system can be configured. 
         [0356]      FIG. 23  shows elements of a typical actuator of the present system. Here,  640  is the outer non-magnetic housing or case of a rotary incremental actuator  10  operated by the external pulse source  30 . Part  650  shows a possible mounting means via which said actuator  10  can be attached to distractor  20 . 
         [0357]    Setscrews  660  in  FIG. 23  represent a possible assembly and adjustment means by which the relative positions of actuator  10  and distractor  20  can be initially adjusted as needed during the open surgical procedure to implant the present system. 
         [0358]    Part  670  represents a typical anti-rotation means by which the rotation produced by actuator  10  can be blocked from transmission to other parts of the system. It shows one means by which reaction forces can be absorbed internally within the system. 
         [0359]      FIG. 24  shows an internal view of actuator  10 .  680  is a shaft rotationally mounted on the actuator case via bearings  690 . Shaft  680  has threaded portions  740  and unthreaded portions  750  of various diameters. Said bearings  690  allow shaft  680  to rotate but provide thrust resistance along the axis of the shaft.  700  is a lever arm made of ferrous or other material that can be magnetically pulled by external electromagnet  30 .  710  shows a ratchet mechanism whereby angular rotation of arm  700  can be transmitted to shaft  680 .  720  is a return spring means capable of returning arm  700  to its rest position when the magnetic field is removed. 
         [0360]    In  FIG. 24 ,  730  is a nut assembly threaded onto shaft  680  and so disposed as to convert the rotation of shaft  680  into axial motion of the nut assembly  730  along the shaft. Suitable keying means such as pin  670  sliding in a groove  760  in the nut are used to prevent the nut from rotating with the shaft. Setscrews or other means  770  are used to couple the translating nut to cables or other devices moving elements of the distractor  20  relative to the actuator body  640 . In  FIG. 24  the cables can be held in the nut by means of the cable passages  780  through which the ends of the cable can enter the nut assembly and by the setscrews  770  pinning them within the nut assembly. Other well-known cable clamping means can also be employed to hold the cables to the nut assembly. 
         [0361]      FIG. 25  is an exploded view of the inside of actuator  10  which uses wrap-spring clutches as an illustrative example of the ratchet actuator principles taught in the present system. 
         [0362]    Arm  700  pivots around shaft  680 . Wrap spring clutches  790  produce incremental rotation of shaft  680  when arm  700  swings in one direction but allow the arm  700  to rotate independently of shaft  680  during the return swing. Backstop wrap spring ratchet  800  acts between the case  640  and shaft  680  and is used to prevent shaft  680  from being rotated in the reverse direction. Torsional return spring  810  is used to reposition the arm between pulses. It will be appreciated that other return means can be employed. Here, bushing  820  provides bearing surfaces to prevent the various mechanism components from jamming. 
         [0363]    It will be appreciated that other ratchet means can be employed in place of the wrap spring clutches illustrated in  FIG. 25 . The wrap spring clutches are particularly advantageous, however, due to their compact size and their ability to function with small input swing angles of arm  700 . Further, rectangular shaped wire can be advantageously used for the wrap spring clutches, to minimize the tendency of the clutches to try to move axially on the shaft  680 . 
         [0364]    Other well-known ratchet means can be substituted for the wrap spring drive clutches  790  or for the wrap spring back stop  800 . Some such devices include: toothed ratchets and pawls, sprag clutches, roller clutches, multi pawl ratchets, spiral band clutches, expanding nitinol wire clutches, escapements, or other forms of overrunning clutches. Use of any such devices can still be within the spirit of the present system. 
         [0365]      FIG. 26  shows one such variation. Here, multiple pawls  830  acting on a toothed ratchet wheel  840  are used to obtain fine pitch incremental rotation of shaft  680  in response to a small angular swing of arm  700  as previously described. Spring means not shown keep the various pawls lightly pressed against the ratchet wheel. The pawls are staggered and so arranged that the effective number of teeth on the ratchet wheel is the actual pitch multiplied by the number of pawls in use. 
         [0366]    Not shown in  FIG. 26  is the backstop prevention mechanism that can consist of a similar set of pawls pivoted on the actuator case and acting between the ratchet wheel  840  and the case. 
         [0367]      FIG. 26  also illustrates an exemplary embodiment in which  730  is a nut threaded on shaft  680  (the threads are not shown in this Figure). The shaft rotates in bushings or bearings also not shown which prevent it from shifting axially within the housing or case  640 . 
         [0368]      FIG. 26  shows the present system as it can be configured for treating pectus excavatum with distractor links of the flattened bar type shown in  FIG. 7 . Base link  850  is rigidly attached to the actuator case  640  and serves as a reaction member against which the chain of distractor links is drawn as the cables are tensioned. 
         [0369]    Rotation of threaded shaft  680  causes nut  730  to translate away from stationary component  850 . In doing so it tensions cables  60  that are rigidly affixed to the nut  730  by set screws or other such devices. 
         [0370]      FIG. 27  shows an alternate cut-away view of  FIG. 26 . Here actuator case  640  is held fixed relative to the patient by suitable means such as stitch anchors  860 . The reference base link  850  of the distractor mechanism is initially installed and positioned relative to the actuator case by means such as the setscrews  660 . Using this means, the surgeon can pretension the cables as needed and take out initial slack in the distractor chain of links prior to closing the surgical incisions. 
         [0371]    In  FIG. 27 , the nut  730  is shown with a substantially rectangular cross-section and slides in a mating prismatic slot in the case  640  so as to prevent rotation of the nut. 
         [0372]    Relatively high tension can be achieved in the cables by using a fine pitch thread on shaft  680 . 
         [0373]    Shaft  680  rotates in one or more bearings or bushings such as at  690 . The axial force due to the cable tension is taken up by a thrust bearing means acting between the rotating shaft and the case. For instance, said thrust bearing can be a rotating conical bushing or joint between shaft  680  and fixed link  850  attached to case  640 . 
         [0374]      FIG. 28  shows a form of the incremental actuator  10  that is activated by mechanical pressure on the two arms  870  and  880  of the wrap spring clutch  890 . This does not require the electromagnet  30  or the electromechanical control system  40  but is purely mechanical. It is suited to use in situations such as pectus excavatum where the actuator can be mounted just beneath the skin and where the surgeon can actually press on the actuator from outside the body. 
         [0375]    In this situation, a flexible diaphragm (not shown) can cover the wrap spring clutch portion of the case  640 . Wrap spring clutch  890  is a loose fit on drum portion  900  of shaft  680 . 
         [0376]    Pressing simultaneously on arms  230  and  240  tightens the clutch coil  890  on the drum  260 . Rocking one way or the other while doing so will incrementally rotate the shaft  680 . In this way the surgeon can cause nut assembly  730  to advance or retract as desired along the screw threads  740  affixed to the shaft  680 . A surface of the nut assembly  730  can slide against a guide surface such as  920  to keep the nut from rotating with respect to the case. 
         [0377]    As described before, the shaft  680  is constrained to rotate on fixed bearings relative to the stationary members. In this case, a suitable socket at  910  can serve as such a rotating and thrust bearing device. Cables or other devices can be coupled to the actuator via means such as the nut assembly  730  and setscrews  770 . These cables can then move the elements of the distractor  20  during the course of the treatment applied postoperatively. 
         [0378]    Stitch anchors  860  or other attachment devices can be suitably disposed to aid in attaching the case  640  to the patient. A stationary base link member  850  can be fixed relative to the case to provide a reaction member to align and constrain the remainder of the distractor chain relative to the case as the nut assembly is progressively advanced during the course of treatment. 
         [0379]      FIG. 29  shows how the incremental rotary actuator of the present system can be configured with double-ended shafts  930  if so desired for a particular surgical application. Each of these shafts can be used to drive distractor devices as previously described. 
         [0380]    Other implanted medical devices suited to being driven by a periodically activated externally controlled rotary actuator can also be coupled to the actuator of the present system. Such devices can include specialized pumps or medicine release devices for example. 
         [0381]      FIG. 29  also shows how attachment devices such as  860  can be added to the actuator to aid in suturing the actuator case to the patient or otherwise stabilizing it relative to the patient or the distractor mechanism. 
         [0382]      FIG. 30  illustrates how a gearbox  940  can be employed in conjunction with the rotary actuator of the present system. Such a device can be used to change the speed, direction of rotation, or mechanical advantage or to obtain a rotary output on a secondary shaft  960  at an angle inclined in relation to the primary actuator shaft  950 . 
         [0383]      FIG. 31  shows how multiple distractors of the present system can be used, for example, in correcting scoliosis. With proper choice of end effectors, multiple distractors can be arranged to work cooperatively so as to give higher forces or better control of the distraction. The two distractor systems can need to have appropriate degrees-of-freedom and enough compliance so that each can be slightly adjusted with respect to the other without binding. 
         [0384]    In this example, a pair of actuators is arranged at staggered locations  970 . This spatial separation can allow them to be individually activated by the external transmitter  30 . If the present system is used with other types of actuators then they can be individually addressed and controlled without being spatially separated. 
         [0385]      FIG. 32  shows what this configuration of distractors can look like after treatment. It can be seen, for example at  980 , that there can be provisions for some of the distractor links to slide or rotate in certain dimensions relative to their counterpart links on the second distractor and relative to the vertebrae as the correction took place. End effectors allowing such differential motion to occur are described as part of the present system. 
         [0386]      FIG. 33  illustrates some possible end effectors  55  of the present system. Many fixation devices, such as pedicle screws  1050 , can also be adapted for use with this distraction system but a number of variations are described in the following figures. These new end effector variations of the present system are also adaptable for use with other distraction systems. 
         [0387]    Conventional spinal fixation devices are designed to work with a static system of distraction rods rather than a hinged, changing distraction structure. The present system describes a dynamically reconfiguring jointed structure  20  where the slopes and positions of individual rod segments progressively change during the course of treatment. 
         [0388]    “Dynamic” or semi-constrained couplings have been used in the past, but for the purpose of allowing the vertebrae to settle or move with respect to a stationary rod system, rather than in conjunction with a dynamically changing distractor  20  as described in the present system. The present system describes dynamic couplings and mechanical limit stops that not only meet those requirements but can additionally be configured to perform tasks unique to the requirements of the jointed link distractor  20  of the present system. 
         [0389]    Individual links of distractor  20  must be able to preferentially bear on the tissues in certain directions and allow the tissues to shift with respect to the distractor links in certain other desired directions. End effector constraints needed at various points can also vary along the length of the distractor mechanism. 
         [0390]    Certain distractor links can require semi-rigid anchoring to an anatomical structure such as a particular vertebra for example. Other links can require no coupling whatsoever to the anatomy, and others can, for example, require only side-to-side force transmission and need somewhat free motion in all other dimensions. This freedom can be needed to accommodate motion due to correction of the deformity, to allow growth of the patient, or to accommodate changes in the geometry of the distractor  20  itself. Constructions described in the present system can satisfy each of these varied requirements. 
         [0391]    End effectors of the present system can be rigidly coupled to the jointed distractor links or coupled by slack motion couplings utilizing cam slots, cylindric joints, or pivots with controlled clearances.  FIGS. 34 through 40  show such end effector variations of the present system particularly adapted to coupling links of the jointed distractor mechanism to individual vertebrae with selectable degrees of freedom or constraint. 
         [0392]    In  FIG. 34 , part  1000  comprises a member that can be mounted to a particular distractor link  50 , either by bolting to the link or by wrapping around the link as shown. Part  1000  can be rigidly fastened to the distractor link  50  or it can be coupled to the link by a bearing allowing motion in one or more directions. Bore  1010  in part  1000  can be a tight fit rigidly holding  1000  to link  50  or it can be oversize to form a bearing allowing rotational motion such as  1080  or axial translational motion such as  1070  with respect to  50 . A setscrew such as  1040  can be used to lock part  1000  in position with respect to  50  and suitable stops such as collar  1090  held in place by a setscrew  1100  can be used to limit the range of motion allowed. 
         [0393]    As illustrated in  FIG. 38 , limit stops can be arranged to allow portions of the distraction system to move freely in certain directions such as  1070  when treatment begins. In this example, the connected end effectors only begins applying distraction force to the connected anatomical structures when the stop  1090  hits its limits and begins pressing upwards on the bottom of  1000 . This aspect of the present system can minimize initial loads on the distractor system and allow the distractor  20  to selectively engage and exert certain forces at a planned later point in the progressive treatment protocol when it is desirable to do so, either for medical or for structural mechanical reasons. For instance, as the joints of the distractor near collinearity, (a “toggled” position) the distractor mechanism  20  will be able to generate higher axial forces than when there is more freedom for angular articulation in the joints. 
         [0394]      FIG. 35  shows how part  1000  can be mounted to a connecting bracket or plate  1030  by means of a bolt  1020  passing through a hole  1160  or other suitable mounting means. Fixation bracket  1030  can in turn be mounted to a vertebra by pedicle screws  1050  or other suitable devices. 
         [0395]    Attachment  1020  can either provide a rigid coupling or one or more degrees of freedom. For instance, if bolt  1020  is slack it can serve as a hinge joint allowing rotation about its axis as shown by  1060 . The coupling between the bolt  1020  and the fixation plate  1030  can also be designed with more freedom, allowing it to function as a ball joint. Further,  1160  can be designed as an elongated slotted coupling as shown by  1110  in  FIG. 37 . As shown in this illustrative example,  1020  moving in the slot can provide constraint in the axial direction but limited freedom of motion from side-to-side. When the bolt reached the end of the slot  1110  it can begin exerting sideways force in the side-to-side direction  1120 . 
         [0396]      FIG. 36  shows an exemplary embodiment of this end effector in which part  1000  comprises two components  1130  and  1140 . Cover member  1130  and inner member  1140  snap together, keyed by the mating edges as at  1170 . They are then locked in position by bolt  1150  passing through hole  1190  in cover member  1130  and threaded into mating hole  1180  in the inner member  1140 . 
         [0397]    This construction clears up the surgical field and simplifies the assembly of the distractor system  20  during surgery. Parts of the distractor system lying near the spine can be attached to the vertebrae without interference from the distractor links  50 . Then, the distractor links  50  can be positioned, and finally the cover member  1130  can be bolted in place. 
         [0398]      FIGS. 38 and 40  illustrate how the present system can be adapted to work with a pair of distractor links on either side of the spine. 
         [0399]    Further control of the distractor system  20  of the present system can be achieved by incorporating flexural elements such as springs into the links, joints, or end effectors of the present system. Such compliant elements can also be arranged to provide protection against accidental overloads, say due to an unforeseen motion, impact, or load on the tissues. 
         [0400]      FIGS. 41 through 46  show the present system with the incremental actuator  10  of the present system remotely coupled to an implanted end effector distraction device  1220  means by use of flexible shafting  1200  or a variety of other flexible coupling devices. In  FIG. 41 , the remote end effector  1220  comprises a turnbuckle assembly. Shaft  1230  of the turnbuckle end effector mechanism  1220  has portions with left and right hand screw threads  1240 . These engage matching left and right hand threaded end effector nut members  1210  that can be shaped as needed and can be sutured, screwed, or otherwise attached to the bones or other tissues being distracted using suitable attachment features like the holes  1250 . 
         [0401]    For instance, in one possible application of use of this system in craniofacial surgery, this system can be adapted for use in distracting skull sutures in an infant. Actuator  10  can be remotely located beneath the skin. 
         [0402]    The flexible shaft  1200  can be designed to have torsional stiffness in the direction of the actuator rotation. 
         [0403]      FIG. 42  shows an illustrative turnbuckle-style distractor mechanism that can be used in conjunction with an implanted rotary actuator such as  10 . Clockwise and counterclockwise screw threads or screws of different pitches can be employed to cause the end effectors  1210  to move together or apart as needed, even though the input rotation is unidirectional. High axial forces can be obtained by utilizing the differential action of such a mechanism. If desired, a rotary bearing can be employed in place of one of the threaded connections since a rotary bearing is kinematically equivalent to a screw thread of zero pitch. 
         [0404]      FIG. 43  illustrates an apparatus in which a flexible drive train  1400  comprising a chain of prismatic  1260  and universal joints  1270  is used to couple the actuator  10  to the remote turnbuckle end effector system  1220 . In this way the actuator can be located in a convenient preferred location remote from the region in which the distraction is required, such as where there is more available space within the patient or where the magnetic pulses can be better transmitted to the actuator. 
         [0405]    It will be appreciated from  FIGS. 41 and 43  that within the spirit of this system the flexible drive train  1400  can comprise shafts, bellows, flexible couplings, universal joints, and similar devices as needed to transmit the rotary motion from the actuator  10  to the actual distractor end effector mechanism  1220 . 
         [0406]      FIG. 44  shows the present system with an end effector distractor which comprises a tensioned cable  1310 . As illustrated, a flexible shaft  1200  couples the rotary actuator  10  to a threaded member  1280 . Threaded nut component  1290  comprises one half of the end effector system and is screwed or sutured in position as described earlier in connection with the turnbuckle. 
         [0407]    Rotation of said threaded member  1280  in the matching threaded nut component  1290  causes the threaded member  1280  to move axially with respect to the nut  1290 . This axial motion can be used to tighten or loosen a cable  1310 . Said cable is attached between nut end effector member  1290  and end effector  1300  affixed to the tissues to be distracted with respect to those affixed to  1290 . The loop  1300  just shows one of many ways the cable can be attached to the tissues or bones at the distal end of the cable  1310 . If desired there can be an intermediate rotary bearing  1320  so as to avoid producing a twist in the cable  1310 . 
         [0408]      FIG. 45  shows another style of articulated distractor  1390  that can be driven by the rotary actuator  10  of the present system using a flexible drive shaft  1200  or other flexible drive train coupling such as  1400  taught in this patent. 
         [0409]    Shaft member  1350  has clockwise and counterclockwise threaded distal portions mated with threads in pivoted block members  1370  and  1380 . Rotation of shaft member  1350  effectively pushes apart or pulls together points  1360  thereby causing the joint between links  1340  to hinge about point  1330 . Motion of the distractor links  1340  is then coupled to the tissues by suitable end effectors or shaped surfaces built into or attached to members  1340 . 
         [0410]    It will be appreciated that other differential screw configurations and linkage geometries can be employed to similarly achieve articulation between links  1340  of a distractor of the present system. 
         [0411]      FIG. 46  shows how multiple articulated distractor joints  1390  can be chained together and serially driven by a single rotary actuator  10 . By using different choices of screw threads on the different joints  1410  or by using different lever arms  1420  one can obtain differential action along the length of the distractor assembly. Joints can be designed to rotate in different planes, in opposite directions, and by different amounts as needed. High mechanical advantages can be attained by having rotation of the actuator driving fine pitch threaded connections to the output end effector members or by having longer effective lever arms  1420 . The link construction shown where the two links  1340  are co-linear is merely illustrative. The links can be made like bell cranks with the joint halves at right angles to one another or at another desired angle, depending on the anatomical needs of the particular application. 
         [0412]      FIG. 47  shows a chart illustrating possible variations of the implantable surgical distraction apparatus, including variations of components of the apparatus, variations of the features, variations of applications of the apparatus, and combinations of the different variations. These include bent coupling, segmented tensioned, hinge axis, joint geometry control, surfaces glide, tension independent, for pectus, for scoliosis, bending not telescoping, end effectors, end effector variants, limit stops, limit stops force, limit stops motion, sleeves, sleeve guides, pulse types, electric motor, nitinol ratchet, magnetic actuators, arm pulled, backstop, return spring, wrap spring, nut assembly on the cable, nut adjusts tension, mechanical pressure, coupled to ratchet, ratchet wrap spring, mechanical double clutch, operative coupling set, turnbuckle, skull sutures, cable and nut, turnbuckle hinged, no pulses, minimally invasive surgical tools, and surgical options.