Patent Description:
Joint replacement is one of the most common and successful operations in modern orthopaedic surgery. It consists of replacing painful, arthritic, worn or diseased parts of a joint with artificial surfaces shaped in such a way as to allow joint movement. Osteoarthritis is a common diagnosis leading to joint replacement. Such procedures are a last resort treatment as they are highly invasive and require substantial periods of recovery. Total joint replacement, also known as total joint arthroplasty, is a procedure in which all articular surfaces at a joint are replaced. This contrasts with hemiarthroplasty (half arthroplasty) in which only one bone's articular surface at a joint is replaced and unincompartmental arthroplasty in which the articular surfaces of only one of multiple compartments at a joint (such as the surfaces of the thigh and shin bones on just the inner side or just the outer side at the knee) are replaced. Arthroplasty as a general term, is an orthopaedic procedure which surgically alters the natural joint in some way. This includes procedures in which the arthritic or dysfunctional joint surface is replaced with something else, procedures which are undertaken to reshape or realigning the joint by osteotomy or some other procedure. As with joint replacement, these other arthroplasty procedures are also characterized by relatively long recovery times and are highly invasive procedures. A previously popular form of arthroplasty was interpositional arthroplasty in which the joint was surgically altered by insertion of some other tissue like skin, muscle or tendon within the articular space to keep inflammatory surfaces apart. Among other types of arthroplasty are resection(al) arthroplasty, resurfacing arthroplasty, excisional arthroplasty, mold arthroplasty, cup arthroplasty, silicone replacement arthroplasty, and osteotomy to affect joint alignment or restore or modify joint congruity. When it is successful, arthroplasty results in new joint surfaces which serve the same function in the joint as did the surfaces that were removed. Any chondrocytes (cells that control the creation and maintenance of articular joint surfaces), however, are either removed as part of the arthroplasty, or left to contend with the resulting joint anatomy. Because of this, none of these currently available therapies are chondro-protective.

Other approaches to treating osteoarthritis involve an analysis of loads which exist at a joint. Both cartilage and bone are living tissues that respond and adapt to the loads they experience. Within a nominal range of loading, bone and cartilage remain healthy and viable. If the load falls below the nominal range for extended periods of time, bone and cartilage can become softer and weaker (atrophy). If the load rises above the nominal level for extended periods of time, bone can become stiffer and stronger (hypertrophy). Finally, if the load rises too high, then abrupt failure of bone, cartilage and other tissues can result. Accordingly, it has been concluded that the treatment of osteoarthritis and other bone and cartilage conditions is severely hampered when a surgeon is not able to precisely control and prescribe the levels of joint load. Furthermore, bone healing research has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of load over time, e.g. during a particular treatment schedule. Thus, there is a need for devices which facilitate the control of load on a joint undergoing treatment or therapy, to thereby enable use of the joint within a healthy loading zone.

Certain other approaches to treating osteoarthritis contemplate external devices such as braces or fixators which attempt to control the motion of the bones at a joint or apply cross-loads at a joint to shift load from one side of the joint to the other. A number of these approaches have had some success in alleviating pain but have ultimately been unsuccessful due to patient discomfort or the inability of the devices to facilitate and support the natural motion and function of the diseased joint.

One new approach to treating osteoarthritis involves implantation of an extra-articular implantable joint unloading device which is positioned alongside the painful joint and bears some of the load normally borne by the joint. This unloading device reduces pain by cushioning the joint from excessive loading. Since the device is extra-capsular and extra-articular, no bone, ligament, or cartilage is removed and future treatment options, such as joint replacement, are still available if needed. However, for some patients a more temporary solution may be more attractive. Patients and physicians may also be interested in providing an unloading device in which a portion of the device is external for ease of adjustment and removal.

With the foregoing applications in mind, it has been found to be desirable to develop temporary joint unloading structures for mounting to body anatomy with at least a portion of the unloading structure external and removable. Such structures should conform generally to body anatomy and cooperate with body anatomy to achieve desired load reduction, energy absorption, energy storage, and energy transfer. For these implant structures to function optimally, they must not cause an adverse disturbance to joint motion. Therefore, what is needed is an approach which addresses both joint movement and varying loads as well as complements underlying or adjacent anatomy.

<CIT> discloses an apparatus for controlling the load on articular cartilage of a human or animal joint comprising: a first fixation assembly for attachment to a first bone; a second fixation assembly for attachment to a second bone; and a link assembly coupled to the first fixation assembly by a first pivot and coupled to the second fixation assembly by a second pivot, the link assembly including a compression spring configured to counteract the natural compressive forces experienced by the joint.

<CIT> discloses an external fixation system for a joint having a first bone and a second bone and an anatomical axis of rotation comprising: a proximal frame couplable to the first bone; a distal frame couplable to the second bone; a first connector having a first member pivotally coupled to a second member at a first pivot axis; and a second connector having a third member pivotally coupled to a fourth member at a second pivot axis; wherein the first and second connectors are mountable between the proximal and distal frames at a location such that the first and second pivot axes are coaxial with the anatomical axis of rotation.

<CIT> discloses an external artificial joint, wherein supporting members are linked on both sides of a hinge, one of the supporting members has rods and an angle adjusting section and is connected to a clamper, and another of the supporting members has such a structure that a rod is put through a cylinder on which an adjusting ring is screwed and a spring receives a force in the expanding direction, and is connected to the clamper.

<CIT> discloses an orthopaedic fixation apparatus comprising: a first rod member having a pair of opposed end portions, at least one of the end portions being generally hemispherically shaped; a second rod member having end portions, at least one of which is generally hemispherically shaped, the two rods being positioned end-to-end during use with the corresponding hemispherically-shaped portions abutting; a flexible shaft coupler that forms a connection between the hemispherically shaped respective end portions of the rod members; a plurality of bone pins for forming connections to first and second bone parts at spaced apart positions generally on opposite sides of the flexible shaft coupler; and clamps for forming an interface in between each of the bone pins and the rod members.

Briefly and in general terms, the present disclosure is directed towards treating diseased or mal-aligned body joints, typically affected by osteoarthritis, using a transcutaneous joint unloading device without limiting the range of motion of the patient's articulating joint. The devices of the present invention accomplish one or more of: absorbing energy during normal gait, reducing load on at least a portion of the natural joint, load transferring or bypassing, energy cushioning, and load sharing, unloading or load redistribution. In addition, both energy dampening and shock absorption are considered in effecting such load manipulations. Further, the particular anatomy of a patient is considered in the contemplated approaches in that loads on desired portions of anatomy are manipulated without overloading healthy surfaces. In a preferred aspect, the present invention adds an energy absorber to the joint to reduce energy transferred through the natural joint. One aspect includes a system for manipulating or absorbing energy transferred by members defining a joint.

A transcutaneous unloading device for a joint according to the invention is defined in claim <NUM>.

The invention may be used in a method of treating a joint comprises attaching a first anchor portion of a first percutaneous anchor to a first member of the joint, attaching a second anchor portion of a second percutaneous anchor to a second member of the joint, and attaching a load absorber to the first and second anchors so that a load absorbing portion of the load absorber is disposed externally of a user's skin by attaching a first and a second mating portion of the load absorber to first and second anchor mating portions of the first and second anchors, the load absorbing portion being disposed between the first and the second mating portions, the load absorbing portion comprising a single load absorbing pivot, the load absorber being attached so that the load absorbing pivot is pivotable at least about an axis substantially aligned with an axis of rotation of the first and second members of the joint.

Other features of the unloading device and device will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the embodiments.

The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which:.

Referring now to the drawings, which are provided by way of example and not limitation, the disclosed embodiments are directed to apparatus for treating the knee joint. However, these embodiments may also be used in treating other body joints, and to alleviate pain associated with the function of diseased or misaligned members forming a body joint while preserving range of motion of the joint. The embodiments described below relate to apparatuses for reducing the amount of load carried by the natural joint anatomy.

Certain of the embodiments include joint unloading devices designed to minimize the loading of the anatomy of the body, such as that found at a body joint. It has been postulated that to minimize pain, unloading or load absorption of <NUM>-<NUM>% of the forces on the joint, in varying degrees, may be necessary. Variable unloading or energy absorption in the range of <NUM>-<NUM>% can be a target for certain applications.

It has also been found that a medial compartment of a knee of an average person with osteoarthritis can benefit from an absorber set for compression between <NUM> and <NUM>, and preferably <NUM>-<NUM> with a spring or absorber element that accommodates a range from <NUM>,<NUM>-<NUM>,<NUM> N (<NUM>-<NUM> pounds), preferably <NUM>,<NUM>-<NUM>,<NUM> N (<NUM>-<NUM> pounds). In a preferred embodiment, the absorber is set for about <NUM> of such compression and a pre-determined load of about <NUM>,<NUM>-<NUM>,<NUM> N (<NUM>-<NUM> pounds).

When a joint unloading device is attached to a joint as described below, less force is transferred through the bones and cartilage of the joint, and a degree of the force between bones of the joint is absorbed by the unloading device. In one embodiment, the joint unloading device can be initially configured to eliminate, variably reduce or manipulate loads at a first desired amount, and to be later adjusted or altered as patient needs are better determined or change to a second desired amount. The unloading device can be adjusted periodically or can be automatically adjusting based on feedback provided by the device.

In applications to the knee joint, the unloading device can be positioned only on the medial side of the knee and designed to absorb medial compartment loads in a manner that completely preserves the articulating joint and capsular structures. In other application, the unloading device can be positioned and designed for unloading the lateral compartment of the knee joint or both the medial and lateral compartments of the knee.

The present invention relates to a transcutaneous knee unloading device comprised of an external kinematic load absorber including at least one spring attached to transcutaneous bone anchors. Although the illustrated embodiment is designed for use with a knee joint, the device can be applied to the ankle, hip, and other joints.

A transcutaneous knee unloading device <NUM> according to the invention for a knee joint <NUM> is seen in <FIG>. The knee joint <NUM> comprises a first member <NUM>, which may be a femur, and a second member <NUM>, which may be a tibia. The device <NUM> shown in <FIG> is shown as having an external component on a medial side of a left knee joint <NUM>, but it will be appreciated that an external component of the device may be disposed on the lateral side of the joint, or on a right joint. As shown in phantom in <FIG>, an external component of the device <NUM> may be disposed bilaterally, i.e., on both the lateral and medial sides of the joint <NUM>.

The device <NUM> comprises a load absorber <NUM> that is ordinarily entirely or at least substantially outside of the user's skin. The load absorber <NUM> has a central load absorbing portion disposed between first and the second mating portions. The device <NUM> further comprises first and second transcutaneous anchors <NUM> and <NUM> in the form of bone screws each having a first threaded end configured to be affixed to the first member <NUM> of the knee joint <NUM>, and a mating end for mating with the first mating end of the load absorber <NUM>. The device also comprises a third transcutaneous anchor <NUM> having a threaded end configured to be affixed to the second member <NUM> of the knee joint <NUM>, and a mating end for mating with the second mating end of the load absorber <NUM>.

The load absorber <NUM> and the first, second and third anchors <NUM>, <NUM> and <NUM> are configured so that at least a portion of the load absorber is disposed externally of a user's skin S (shown by dotted lines in <FIG>). Thus, the load absorber <NUM> can be attached and detached from the first, second and third anchors <NUM>, <NUM> and <NUM> which are secured in the bone. The attachment and detachment of the load absorber <NUM> can be accomplished by the patient or physician and depending on the type of attachment can be done with or without tools. The patient may remove the absorber <NUM> during times of inactivity, such as when sleeping, bathing or sitting at a desk and may attach the absorber during all waking hours or only during active time periods.

As the bone anchors <NUM>, <NUM> and <NUM> are designed to traverse the skin of the patient, certain precautions can be implemented to prevent the transmission of microorganisms at the skin penetration site. In one embodiment, the anchors <NUM>, <NUM> and <NUM> can have a coating to reduce the possibility of infections, for example, titanium anchors can be provided with a silver anti-infective coating. Other known coatings and precautionary methods can also be used. Other precautions for prevention of infection can include specific cleaning and maintenance steps to be performed by the patient. For example, adhesive coverings may be provided for the exposed ends of the bone anchors when they are not in use.

In another embodiment, a porous tissue cuff can be secured around the bone anchors <NUM>, <NUM>, <NUM> to prevent infection at the tissue penetration site. A tissue cuff <NUM> as shown in <FIG> is secured to the bone anchor <NUM> and promotes skin growth into the cuff to provide a barrier to microorganisms. Attachment of the skin to the tissue cuff <NUM> can be initially preformed by suturing, followed by tissue growth. The secure attachment between the cuff <NUM> and the skin eliminates pathways for microorganisms to enter the body. Examples of materials for use in the tissue cuff <NUM> include ePTFE, PTFE and other materials used for synthetic vascular grafts. The material of the tissue cuff <NUM> should be flexible and avoid irritation of adjacent tissue.

The bone anchors can also include flanges or other anchoring structures which allow suturing to the skin. The flanges <NUM> shown on each of the anchors are arranged to lie just below the surface of the patient's skin. The flanges <NUM> can be provided with small openings to accommodate sutures for securing the skin around the anchors. Alternatively, other known skin securing systems can be used to secure the skin to the anchors.

The bone anchors <NUM>, <NUM> and <NUM> as shown in the present application are designed to have a top surface which do not protrude from the surface of the skin to prevent any discomfort of protruding parts when the device is removed. Alternately, other anchor structures can be used which protrude somewhat from the bone, however, preferably the bone anchors do not protrude more than about <NUM> from the skin surface.

The unloading device <NUM> comprises an energy absorber <NUM> and an arm <NUM> that are pivotably attached to each other via one or more pivot links. A first pivot link <NUM>, shown in <FIG>, is mounted in a recess in the lower end of the arm <NUM> and also includes a pivot post 47a that extends in an anterior direction and is secured in and pivotable relative to an opening <NUM> in the energy absorber <NUM>. The first pivot link <NUM> permits pivoting of the arm <NUM> relative to the energy absorber <NUM> in two dimensions including about a first axis normal to the user's coronal plane and a second axis perpendicular to the first axis direction.

As shown in <FIG> first pivot link <NUM> includes the pivot post 47a which permits angulation of the external surfaces of the arm <NUM> and absorbing portion <NUM> with respect to one another. Rotation about the pivot post 47a accommodates varus/valgus angulation of the joint. The first pivot link <NUM> also provides relative pivoting of the absorber <NUM> and the arm <NUM> at least about a pivot post <NUM> which is arranged along an axis substantially normal to the user's sagittal plane and extends through the pivot link <NUM>. The pivot post <NUM> allows flexion/extension motion of the joint <NUM> and provides the largest range of motion of the unloading device <NUM>. The pivot post <NUM> is ordinarily arranged to be located substantially parallel with an axis of rotation of the first and second members <NUM> and <NUM> of the joint <NUM>. Positioning the pivot post <NUM> directly on the axis of rotation of the joint provides for unloading force throughout rotation of the joint and throughout the gait of the patient. However, the device <NUM> facilitates positioning the pivot point <NUM> in a variety of locations relative to the axis of rotation of the knee joint <NUM> to obtain various unloading responses. A pivot point <NUM> just slightly anterior and superior of the axis of rotation of the joint provides an unloading device which unloads the joint in full extension and provides no unloading when the knee is beyond some predetermined amount of flexion. Other locations of the pivot point <NUM> can be used to achieve other unloading profiles during the motion of the joint.

It is presently believed that the first pivot link <NUM> should be arranged to permit at least <NUM> degrees or more of hyperextension of the knee joint <NUM> and at least <NUM> degrees or more of flexion, it being further believed that <NUM> degrees of hyperextension and <NUM>-<NUM> degrees of flexion will be sufficient for the vast majority of users and still allow for significant surgical variation. The first pivot link <NUM> also allows for varus/valgus rotation of the knee joint of at least <NUM> degrees and preferably at least <NUM> degrees.

The first and second anchors or bone screws <NUM> and <NUM> are connected to the arm <NUM> by upper and lower links <NUM> and <NUM>. The lower link <NUM> is rotatably attached at a first end thereof to the lower screw <NUM> and at a second end is adjustably attached to the arm <NUM>. The upper link <NUM> is rotatably attached at a first end thereof the upper screw <NUM> and at a second end is rotatably attached to the arm <NUM>. The first ends of the upper and lower links <NUM> and <NUM> are ordinarily attached to the upper and lower screws <NUM> and <NUM> in a manner such the links are substantially unable to transmit moment to the upper and lower screws, such as that the links are attached in a manner so that they are freely rotatable relative to the screws. The links are also preferably detachable from the bone screws <NUM> and <NUM> to allow the unloading device to be removed from the bone anchors. One such connection will be described in further detail below with reference to <FIG>.

The links <NUM> and <NUM>, shown most clearly in <FIG>, may be the same length but, ordinarily, are of different lengths an allow adjustment of unloading device to a particular patient. Ordinarily, it is desirable for a longitudinal axes of the arm <NUM> and the femur <NUM> to be parallel, as shown in <FIG>, and the device is adjustable to achieve this arrangement as will be described below.

The lower link <NUM> is adjustable and lockable relative to the arm <NUM> at one of a plurality of locking points. As shown in <FIG>, the arm <NUM> comprises a longitudinal slot <NUM> and the lower link <NUM> comprises fastener <NUM> at the second end of the lower link. The fastener extends through the slot <NUM> and threads into an internally threaded hole in the lower link <NUM> to secure the link <NUM> to the arm <NUM> at any locking position along the length of the slot. Ordinarily, the fastening arrangement between the arm <NUM> and the lower link <NUM> will be one that will prevents relative angular between the longitudinal axes of the arm and the lower link once the fastener <NUM> has been tightened. Changing the locking point of the lower link <NUM> relative to the arm <NUM> changes a location of the absorber pivot point <NUM> relative to the knee joint <NUM> and can change the overall function of the device.

While locking the lower link <NUM> to the arm <NUM> in this fashion can serve to also set the relative position of the upper link <NUM> relative to the arm, ordinarily, the upper link is also locked to the arm, such as by a threaded fastener <NUM> extending through the upper end of the arm <NUM> and into a threaded hole in the upper link <NUM>. When at least the lower link <NUM> is locked relative to the arm <NUM>, the upper and lower links <NUM> and <NUM> form a plurality of pairs of upper and lower link angles relative to the arm. Changing the upper and lower link angles ordinarily changes a location of the pivot point <NUM> relative to the first and second members <NUM> and <NUM> of the knee joint <NUM>. Selection of the length of the lower link <NUM> relative to the length of the upper link <NUM> can impact the variety of angles that the arm <NUM> can form with the first member <NUM> of the knee joint <NUM> and the position of the pivot point <NUM>. Longitudinal axes of the upper and lower links <NUM> and <NUM> ordinarily extend substantially perpendicularly to longitudinal axes of the upper and lower screws <NUM> and <NUM> when the screws are parallel.

The energy absorber, also called a load absorber <NUM> is ordinarily pivotably attached to the third anchor <NUM>, by a second pivot link <NUM> that permits pivoting of the absorber relative to the second anchor in two dimensions. Similar to the first pivot link <NUM>, the second pivot link <NUM> has a pivot post <NUM> which extends in an anterior direction from the third anchor <NUM> and is received in an opening in the lower end of the energy absorber <NUM>. The pivot post <NUM> pivotably connects the second pivot link <NUM> to the energy absorber allowing varus/valgus rotation of the joint.

Ordinarily, the second pivot link <NUM> is removably attached to the third bone anchor screw <NUM> in a manner that at least substantially precludes transmission of moment to the screw <NUM>, i.e., the second pivot link is ordinarily freely rotatable relative to the anchor screw. It is desirable for the second pivot link <NUM> to be easily attached to and detached from the anchor screw <NUM>, such as by providing suitable quick-release fittings as discussed below with reference to <FIG>. The second pivot link <NUM> can be provided in different sizes to facilitate offsetting the absorber <NUM> a desired distance from a user's skin.

The bone screws <NUM>, <NUM> and <NUM> are ordinarily bicortical screws which pass through the cortical (harder exterior bone) on two opposite sides of the bone to achieve secure and lasting fixation. Although the screws are shown extending out of the opposite side of the bone in <FIG>, they do not need to pass out of the bone. In the case of the bilateral embodiment of <FIG>, the screws <NUM>, <NUM> and <NUM> pass through the bones and are provided with a fitting to allow securing of the absorber on both sides of the joint with the same bone screws.

The load absorber <NUM> ordinarily comprises a spring <NUM> and a telescoping piston and arbor assembly. Alternatively, the spring <NUM> can serve as the arbor with a piston translating in the interior bore of the spring to accommodate the variable distance between the bones of the joint during rotation. <CIT> and <CIT> and <CIT> disclose embodiments of spring, piston and arbor assemblies that are suitable for use in connection with the present invention. The load absorber <NUM> is arranged so that as a user applies load to the knee joint <NUM>, such as by standing, walking or running, the spring <NUM> will tend to absorb some or all of the force and thereby reduce load on the knee joint.

As seen in <FIG>, when the knee joint is bent, a piston <NUM> and arbor (beneath the spring) telescope to allow the absorber <NUM> to extend to accommodate an increasing distance between the first pivot link <NUM> and the second pivot link <NUM>. Thus, the absorber spring <NUM> acts in compression to apply a force when the knee joint is in extension and the spring applies no force to the bones in tension when the joint is positioned in flexion as shown in <FIG>.

The absorber <NUM> can be provided with quick connection mechanisms (not shown) at both ends for quick attachment to and removal from corresponding connection mechanisms in the upper and lower pivot links <NUM> and <NUM> to facilitate changing the absorber <NUM> for a particular user. For example, absorbers may be provided in different lengths and different spring forces depending on the patient anatomy.

In the bilateral embodiment, as seen in <FIG>, the unloading device <NUM> is positioned on the medial side of the knee joint <NUM> while a second unloading device <NUM> is positioned on the lateral side of the joint. The bone screw anchors <NUM>, <NUM> and <NUM> extend through the bone and are attached to the corresponding upper and lower links <NUM> and <NUM> and pivot link <NUM>. A second absorber <NUM> and second arm <NUM> can be formed with the same features as those in the medial side device or can be modified for the lateral side of the joint.

<FIG> illustrates one example of a quick disconnect fitting for connection to the bone anchors in a removable manner. It is desirable for the upper and lower links <NUM> and <NUM> and the pivot link <NUM> to each be easily attached to and detached from the corresponding bone anchors <NUM>, <NUM> and <NUM> either by a physician or a patient. Fittings such as quick-disconnect fittings can be provided to facilitate attachment and removal of the external load absorber <NUM> from the bone anchors by the user with or without assistance. Examples of quick disconnect fittings include snap lock fittings, taper lock fittings and interference fittings. In one example, as shown in <FIG>, the quick-disconnect fitting for attaching the pivot link <NUM> to the bone screw <NUM> secured in the tibia includes a tapering central bore <NUM> in the external end of the screw <NUM> and a corresponding tapered peg <NUM>. The tapered peg <NUM> also has a mating end for rotatably mating with the pivot link <NUM>. The connections to the first and second bone screws <NUM> and <NUM> can also include similar quick connections with tapered pegs <NUM> and <NUM>. In the event that a physician prefers for the unloading device to be removed only in the doctor's office, more secure fasteners including screws or locking screws can be used.

<FIG> illustrate an alternative unloading device <NUM>, which is not in accordance with the present invention, in which an external cam base <NUM> is secured to the femur <NUM> by one or more transcutaneous anchors <NUM>. The cam base <NUM> cooperates with a follower <NUM> provided on a follower base <NUM> which is also positioned external of the knee and secured to the tibia <NUM> by transcutaneous anchors <NUM>. The follower <NUM> is shown in the form of a small roller, however, other moving and non-moving followers may also be used. The follower <NUM> is mounted on the end of an absorber <NUM> which operates in a manner similar to the absorbers described above to absorb a portion of the forces normally transmitted by the natural knee joint. The cam and follower unloading device <NUM> provides an external discontinuous unloading device in which one or both bases <NUM>, <NUM> can be removed to deactivate the device.

A method of treating a knee joint <NUM> is described with reference to the device <NUM> shown in <FIG>. According to the method, first and second transcutaneous anchors <NUM> and <NUM> is attached to a first member <NUM> of the knee joint <NUM>, such as by screwing upper and lower screws <NUM> and <NUM> into holes that have been drilled in a femur. A third transcutaneous anchor <NUM> is attached to a second member <NUM> of the knee joint <NUM>, such as by screwing into a hole drilled in a tibia. Although two anchors are illustrated on the femur and one on the tibia, other numbers and types of anchors can also be used. The positions of the anchors may be determined by one or more templates or by using the absorber <NUM> and arm <NUM> as a guide to determine the proper positioning for the anchors.

A load absorber <NUM> is attached to the anchors <NUM>, <NUM> and <NUM> so that the load absorbing portion is disposed externally of a user's skin. The position of the pivot point <NUM> relative to the axis of rotation of the first and second members <NUM> and <NUM> of the knee joint <NUM> is adjusted by changing an angle of the lower link <NUM> in the manner described above.

Because the femur has six degrees of freedom relative to the tibia, it is desirable that a load absorbing device have at least four degrees of freedom, and preferably at least six degrees of freedom. The device <NUM> according to an aspect of the invention has six degrees of freedom as follows. The two pivot links <NUM> and <NUM> with each provide two degrees of freedom; about the pivot posts 47a, <NUM> and <NUM> and about the peg <NUM>; linear movement of the piston <NUM> relative to the spring <NUM> provides one degree of freedom; and rotational movement of the piston <NUM> relative to the spring and arbor provides one degree of freedom. While the device <NUM> illustrated in <FIG> provides motion with rotational joints, it will be appreciated that other types of joints and bearings, such as three degree of freedom spherical bearings, can be used instead.

The unloading device <NUM> according to the invention can be useful where the bones proximate the knee joint limit the locations in which femoral and tibial anchors can be provided. Even if it is necessary to provide the anchors at a distance from a location at which they would normally be installed, simple external adjustments can ensure that the pivot points of the device will be at desired locations. These adjustments can be accomplished after attachment of the anchors. In this case, the arm <NUM>, links <NUM> and <NUM>, pivot link <NUM>, and absorber <NUM> can be selected among elements provided in varying lengths.

The unloading device <NUM> according to the invention can be versatile. The device shown in <FIG> is illustrated used on a left medial knee, however, it could also be used on a right medial knee with the same parts rotated about various pivots. A device for use on left or right lateral knees, such as the device <NUM> of <FIG>, will be similar to the device <NUM>, however, somewhat different anatomical considerations may require alterations.

The unloading device <NUM> according to the invention can be used as a more temporary version of devices that are normally provided subcutaneously. This can be particularly useful for temporary unloading of the knee joint after another surgical procedure including cartilage repair or regeneration to allow the surgical site to heal under reduced loading conditions. The device may also be useful for users who are hesitant to undergo a procedure to have a fully implantable system. The device can be implanted minimally invasively with only a few load bearing screws inserted into the bone.

The device can be intraoperatively or post-operatively adjusted. For example, the device can be adjusted post-operatively as further or less load manipulation becomes necessary. Moreover, the device can be activated and adjusted to absorb energy to desired degree or can be deactivated so that no energy absorbing occurs, such as just subsequent to implantation during a period of healing. In this way, a natural healing process where tissue and bone at the interventional site grows to help in fixation of the structure can be allowed to progress prior to activating the load manipulating capabilities of the absorber.

The device can be used to provide load manipulation throughout a wide spectrum of joint unloading from complete unloading and even distraction of the joint to lower levels of partial unloading depending on the clinical situation of the patient. Advantageously, the external unloading device allows for changing clinical needs during the healing process or progression of a clinical condition. For patients seeking pain relief from osteoarthritis pain in a joint, it has also been found that a medial compartment of a knee of an average person with osteoarthritis can benefit from an absorber element that unloads the joint in a range from <NUM>,<NUM>-<NUM>,<NUM> N (<NUM>-<NUM> pounds), preferably <NUM>,<NUM>-<NUM>,<NUM> N (<NUM>-<NUM> pounds). However, this unloading may be adjusted further depending patient specific factors including patient size, pain level and activity level. Adjustments can be made by periodically by a physician to address patient reported pain or can be made by the patient at a physician's instruction during changing daily activity. For pain relief, the unloading is desired through only a portion of the gait cycle including the stance phase of the gait cycle.

The device can also be used for temporarily for complete unloading or distraction to facilitate tissue regeneration in patients recovering from joint surgery or trauma. Although permanent complete unloading would be negative to joint vitality, temporary unloading of <NUM>% of the joint forces or even distraction of the joint can facilitate biological regeneration. When distraction is provided, unloading sufficient to provide a space of about <NUM> to <NUM> between the regenerating joint tissues is desired. The <NUM>% unloading or distraction can be maintained for a period of about <NUM>-<NUM> months, preferably about <NUM> months to allow regeneration without significant negative effects on joint vitality. This complete unloading or distraction should be followed by a reduction in the percent of unloading (joint reloading) over the subsequent <NUM>-<NUM> years. The gradual reloading of the joint can be done in a gradual or stepwise manner with the goal of eliminating the unloading device completely over a period of time. Although complete unloading or distraction are described for promoting tissue regeneration, less than <NUM>% unloading may also be used to promote tissue regeneration. In one example <NUM>% to <NUM>% unloading can be provided to promote tissue regeneration.

In the case of complete or near complete unloading to allow tissue regeneration, unloading may be needed throughout the entire gait cycle or for only a portion of the gait cycle depending on the location of the damaged tissue within the joint. Examples of use of load reducing devices, such as the external unloading devices <NUM> and <NUM> of the present invention for load reduction during healing from other surgical procedures is described in U. patent application entitled "Methods and Devices for Partial Joint Offloading During Healing of Joint Tissue," filed on even date herewith.

The device can also incorporate an adjustable energy absorber which can be easily adjusted as the patient's need for unloading of the joint changes. Examples of adjustable energy absorbing devices are described in <CIT>. Such adjustable absorbers allow the patient of physician to adjust the energy absorbing or absorption device to alter the load manipulating or absorbing function of the device. For example, the physician may adjust the device <NUM> based on external or internal measurement of the load on the joint or on the absorber. Alternatively or additionally, the patient may adjust the absorber based on a current activity level, leaving the device on a low unloading setting while sitting at a desk and changing to a high unloading setting when exercising.

Moreover, feedback systems can be incorporated into the device to indicate the past performance of the device and help in adjustment for better performance. For example, the device may record data including loading, cycling and time worn.

In each of the disclosed embodiments, various features can be incorporated such as audible and textile feedback sub-systems can be incorporated to both indicate translation of load adjustment structure as well as to exhibit locking and unlocking of subcomponents.

Moreover, the device can include springs machined to provide desirable energy absorbing which varies as the spring is compressed during various degrees of flexion and extension of joint markers to which the unloading device is attached.

The term "spring" is used throughout the description but it is contemplated to include a variety of conventional springs including coil springs, leaf springs and other springs as well as other energy absorbing structures, such as resilient materials can be used to accomplish the functions of the invention. Magnetic, hydraulic, pneumatic or piezoelectric systems can also serve the unloading function of the spring.

In the present application, the use of terms such as "including" is open-ended and is intended to have the same meaning as terms such as "comprising" and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as "can" or "may" is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

Claim 1:
A transcutaneous unloading device (<NUM>) for a joint (<NUM>), comprising:
a load absorber (<NUM>) having a first and a second mating portion, a load absorbing portion disposed between the first and the second mating portions, and the load absorbing portion comprising a load absorbing pivot;
a first percutaneous anchor (<NUM>, <NUM>) having a first anchor portion configured to be affixed to a first member (<NUM>) of the joint, and a first anchor mating portion for mating with the first mating portion; and
a second percutaneous anchor (<NUM>) having a second anchor portion configured to be affixed to a second member (<NUM>) of the joint, and a second anchor mating portion for mating with the second mating portion,
wherein the first and second mating portions and the first and second anchors are configured so that, in use, the load absorbing portion is disposed externally of a user's skin and so that, in use, the load absorbing pivot is pivotable at least about an axis substantially aligned with an axis of rotation of the first and second members of the joint,
wherein the load absorbing portion comprises an absorber (<NUM>) and an arm (<NUM>) pivotably attached to the absorber at a pivot point,
characterized in that the first anchor comprises upper and lower screws (<NUM>, <NUM>) and upper and lower links (<NUM>, <NUM>) adjustably attached at first ends thereof to the upper and lower screws, respectively, and, at second ends thereof, to the arm.