Abstract:
Methods and devices for distraction osteogenesis are disclosed employing an energy storage device and a controlled release of energy to provide a separating force. For example, bone expansion devices can include a first anchor element attachable to a first segment of bone, a second anchor element attachable to a second segment of bone, and an actuator for applying a separating force between the first and second anchor elements. The actuator can include a potential energy storage device and a controller for releasing energy from the energy storage device to provide the separating force.

Description:
FEDERALLY SPONSORED RESEARCH 
     This invention was made with government support from the National Institutes of Health under Grant No. 1 R43DE014803-01A1. The government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The technical field of this invention is distraction osteogenesis and, in particular, methods and devices for expansion of bone and skeletal structures, such as the mandible. 
     BACKGROUND OF THE INVENTION 
     Skeletal expansion to treat deformities, such as maxillofacial deformities, is accomplished conventionally through multiple bone grafts. However, a new approach is distraction osteogenesis, a technique which employs the body&#39;s bone regeneration ability to fill a gap in the bone. The gap is gradually expanded with a mechanical distractor as new bone tissue is grown, thus reducing or eliminating the need for bone grafts. 
     However, existing distractors typically are manually operated devices that require daily adjustment by the patient or a healthcare professional. Such adjustments are typically done empirically or based on a predetermined schedule that may bear little relationship to a patient&#39;s actual tissue regenerating capabilities. Moreover, conventional distractors are linear devices that usually only permit bone expansion in a straight line while optimal bone reconstruction, especially facial bone reconstruction, may require non-linear, e.g., curved, expansion techniques. 
     Accordingly, there exists a need for better bone distraction methods and devices. Better control mechanisms, especially automated systems and devices that permit greater degrees of dimensional freedom would satisfy long-felt needs in the art. 
     SUMMARY OF THE INVENTION 
     Methods and devices are disclosed for distraction osteogenesis employing an energy storage device and a controlled release of energy to provide a separating force. Bone expansion devices according to the invention can include a first anchor element adapted to be attached to a first segment of bone, a second anchor element adapted to be attached to a second segment of bone, and an actuator for applying a separating force between the first and second anchor elements, the actuator further comprising a potential energy storage device and a controller for releasing energy from the energy storage device to provide the separating force. 
     In one embodiment the first anchor element can include a rail and the second anchor element can be mechanically linked to the rail of the first anchor element, e.g., such the second anchor element is slidably coupled to the rail of the first anchor element. In further embodiments, the rail can be either straight or curved, depending upon the application. Alternatively, the rail can be slidably coupled to the second anchor element such that the rail can slide between a contracted and an extended position. In further embodiments, the rail can be either straight or curved, depending upon the application. 
     The actuators of the invention can be hydraulic actuators, e.g., a chamber coupled to one of the anchor elements and a piston disposed within the chamber and mechanically linked to the other anchor element such that a fluid within the chamber can apply a separating force. In one embodiment, the actuator can further include an energy source for pressurizing the fluid within the chamber. For example, the energy source can include a reservoir of pressurized fluid and the reservoir can be pre-charged with the pressurized fluid. In another embodiment, the energy source can include a spring that applies pressure to the fluid. 
     The actuator can further include a valve for regulating fluid transfer (volume and/or pressure) from the reservoir to the chamber. Additionally, the invention can include one or more sensors for measuring separation of the first and second anchor elements and the controller can further include a microprocessor. 
     In another aspect of the invention, kits are disclosed for distraction osteogenesis that can include a plurality of base elements adapted to be attached to a first segment of bone, each of said base elements having a rail of a different shape, at least one rail receiving element adapted to be attached to a second segment of bone and further adapted to have a base element rail slidably coupled thereto, and a actuator for applying a separating force between a base element and a slider element, the actuator further comprising a potential energy storage device and a controller for incrementally releasing energy from the energy storage device to provide the separating force. 
     In a further aspect of the invention, methods for distraction osteogenesis are disclosed that can include the steps of providing a first anchor element, a second anchor element, and a actuator for applying a separating force between the first and second anchor elements. Preferably, the actuator can further include a energy source and a controller for incrementally releasing energy from the source to provide the separating force. The method can be practiced by attaching the first anchor element to a first segment of bone, attaching the second anchor element to a second segment of bone, applying a separating force for a first period of time, measuring a change in distance between the first and second segments of bone, and modifying either the magnitude of the separating force or the period of time to maintain a desired distraction protocol. 
     In yet another aspect, the invention can use miniature hydraulics to produce a fully buried actuator capable of producing curved distraction trajectories. The methods and devices of the present invention can reduce patient responsibility by automating the motion process, permit clinicians to alter the distraction rate as treatment progresses, and reduce distraction time by making the motion virtually continuous. 
     Further aspects of the invention can include automation of motion, hydraulic motion power, e.g., driven by a spring-loaded hydraulic pump, the use of micro-dispensing valves to control motion, and constructions that permit full implantation of all components. To eliminate the need for large batteries to store electrical energy, the invention can store hydraulic energy in a spring-loaded cylinder. The bone distraction can be performed by small hydraulic actuators. Miniature valves can control flow of fluid to the actuators. All of the motion can be controlled by a small microcontroller which can be accessed directly or through a radio-frequency (RF) link. 
     Additional objects, advantages, and novel features of the invention will be set forth in part in the description as follows and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic illustration of a mandibular distraction system according to the invention; 
         FIG. 2  is an exploded view of one embodiment of a hydraulically-actuated mandibular distractor according to the invention; 
         FIG. 3  illustrates side and top views of the distractor of  FIG. 2  in a contracted position; 
         FIG. 4A  is a side view of one embodiment of a curved distractor according to the invention in a contracted position; 
         FIG. 4B  is a side view of the curved distractor of  FIG. 4A  in an extended position; 
         FIG. 5  is a schematic illustration of two curved distractors having different radii of curvature; 
         FIG. 6A  is a perspective view of another embodiment of a curved distractor according to the invention; 
         FIG. 6B  is an exploded view of the curved distractor of  FIG. 6A ; 
         FIG. 7  illustrates side and top views of the curved distractor of  FIG. 6A  in a contracted position; 
         FIG. 8  is an exploded view of one embodiment of a hydraulic power supply with a spring-loaded reservoir; 
         FIG. 9  is a cross-sectional view of another embodiment of a hydraulic power supply with a spring-loaded reservoir; and 
         FIG. 10  is a schematic illustration of one embodiment of a system for distracting bones. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. 
     The present invention generally provides for methods and devices that can be used to treat skeletal deformities by way of distraction osteogenesis. The devices disclosed herein allow for the controlled distraction between two bone surfaces so that new bone can be formed of generated between the two surfaces. The device can store potential energy, and the stored potential energy can be used to operate the device, thereby separating the two bone surfaces. The amount of distraction can be controlled by the device internally, externally, or by a combination of the two. The bone surfaces can be separated so that the nearest edges remain approximately parallel, or alternatively, the bone surfaces can be separated so that the nearest edges form an angle therebetween. A person having ordinary skill in the art would recognize that although the disclosed methods and devices generally discuss distracting bone surfaces, the devices and methods can also be used to contract bone surfaces, for instance to close a gap between two surfaces. 
     While the methods and devices taught can be used in a variety of locations in the body, one place in particular it can be beneficial to use the devices and practice the methods is in the area of the mandible. As illustrated in  FIG. 1 , a distractor  20  can be anchored to two bone surfaces  102 ,  104  of a mandible  100  and can be adapted to distract the two surfaces  102 ,  104  so that new bone  106  can be formed or generated therebetween. In the illustrated embodiment movement of the distractor  20  is caused by an actuation system  200 . The actuation system  200  can be disposed in the body and configured to operate based on programmed parameters or operate based on parameters directed to the actuation system  200  from outside of the body. Alternatively, the actuation system  200  can be disposed outside of the body and can be configured to move the distractor  20  remotely. While a number of different components can be used to actuate the distractor  20 , the actuation system  200  includes a hydraulic power supply or actuator  202  and a valve  204 . The hydraulic power supply  202  can be configured to deliver a fluid to the distractor  20 , for example via a tube  206 , and the delivery of the fluid can be regulated by the valve  204 . The tube  206  can be made of a number of different materials, but in one embodiment it is made of polytetrafluoroethylene. As the amount of fluid delivered to the distractor  20  increases, the distractor  20  moves to further distract the bone surfaces  102 ,  104 . 
     The amount of fluid that is delivered to the distractor  20  by the actuation system  200  can be controlled in a number of different ways, but in the illustrated embodiment a regulation system  210  is used. As shown, the regulation system  210  and the actuation system  200  are disposed in the same component, control pack  10 . Alternatively, the actuation system  200  and the regulation system  210  can be separate components, each being selectively disposed inside or outside of the body. Each of the actuation system  200  and the regulation system  210 , or if housed together the control pack  10 , can be disposed inside or outside of the body. In one exemplary embodiment, the distractor  20  is disposed inside the body and the control pack  10 , including both the actuation system  200  and the regulation system  210  therein, is disposed outside of the body and is configured to communicate signals and/or force to the distractor  20  to distract bone surfaces  102 ,  104 . In the illustrated embodiment, the actuation system includes a controller  211  having a position sensor interface  212 , a control circuit  214 , a wire  216 , and a power supply  218 . The position sensor interface  212  can determine the location of at least one of the bone surfaces  102 ,  104  and a relevant component of the distractor  20 , and the control circuit  214  can communicate with the valve  204  of the actuation system  200  to regulate an amount of fluid delivered to the distractor  20 . The location of at least one of the bone surfaces  102 ,  104 , and the relevant component of the distractor  20  can be communicated to the position sensor interface  212  in a number of ways, but in the illustrated embodiment wire  216  is connected to a sensor (not illustrated) disposed in the distractor  20  and communicates the location of the distractor  20  to the regulation system  210 . The wire  216  can be disposed in the tube  206 , separate from the tube  206 , or both the tube  206  and the wire  216  can be disposed together in a separate tube. In alternative embodiments, the distractor  20 , or one of the bone surfaces  102 ,  104 , can be adapted to communicate a position thereof wirelessly. The power supply  218  can be used to power at least one of the position sensor interface and the control circuit, and can also be used to power components of the actuation system  200  when components of the actuation system  200  may require a power supply. 
     One exemplary embodiment of a distractor  120  is illustrated in  FIGS. 2 and 3 . The distractor  120  is hydraulically-driven by placing a hydraulic force on a piston  122  disposed in a cylinder  124 . An o-ring or other sealing device can be used as a seal between the piston  122  and a bore  123  of the cylinder  124 . The cylinder  124  can be configured to receive a fluid such that as fluid enters the cylinder  124 , the piston  122  is driven out of the cylinder  124  in a distal direction D. In one embodiment, the cylinder  124  is machined to accept MINSTAC (Miniature Inert System of Tubing and Components) fittings to allow fluid to enter the cylinder  124 . MINSTAC fittings are commercially available from the Lee Company in Westbrook, Conn. and are discussed in further detail below with respect to  FIGS. 5A and 5B . The cylinder  124  can be coupled to a rail receiving element or slider  126  which is slidably operative to move two bone surfaces with respect to each other that are attached to the distractor  120 . The rail receiving element  126  can include features for mating the rail receiving element  126  to a bone surface, such as openings  128 . Cortical screws or pins, or other attachment mechanisms, can be disposed through the openings  128  to mate the rail receiving element  126  to a bone surface. In the illustrated embodiment, a saddle  130  is coupled to the cylinder  124  and the saddle  130  is also coupled to the rail receiving element  126 , for example by way of a pivot pin  132 . The pivot pin  132  can allow some freedom of motion between the cylinder  124  and the rail receiving element  126 . The rail receiving element  126  can move two bone surfaces with respect to each other by translating along a rail  134  that is fixed. The rail  134  can be substantially straight and can include features for mating the rail  134  to a bone surface, such as openings  136 . Cortical screws or pins, or other attachment mechanisms, can be disposed through the openings  136  to mate the rail  134  to a bone surface. Further, the piston  122  can be coupled to the rail  134  by way of a pivot pin  138 . In the illustrated embodiment, as the piston  122  is driven out of the cylinder  124  in the distal direction D, the rail receiving element  126  translates along the rail  134  in the proximal direction P. In an alternative embodiment, the rail receiving element  126  is not operative to slide and instead is configured to be fixed while the rail  134  is not fixed and instead is operative to slide. Accordingly, in such an embodiment, as the piston  122  is driven out of the cylinder  124  in the distal direction D, the rail  134  is also driven in the distal direction D, away from the rail receiving element  126 . 
     While each of the components of the distractor  120  can be made of a variety of materials, and each component can be made of a different material, in one exemplary embodiment each of the piston  122 , the cylinder  124 , the rail receiving element  126 , the saddle  130 , the pivot pins  132 ,  138 , and the rail  134  is machined from Titanium 6A1-4V. Further, while the size of the components can vary, based at least in part on the intended use, in one embodiment particularly useful for distracting mandibles the cylinder  124  has a length L C  of approximately 31 mm and a diameter D C  of approximately 5 mm, while a bore  123  for receiving the piston  122  has a diameter D B  of approximately 4 mm. Further, the rail can have a length L R  of approximately 33 mm and can have a width W R  of approximately 6.35 mm, which can allow for a linear displacement of approximately 25 mm. In one embodiment a height H of the distractor  120  is approximately 8 mm. 
       FIGS. 4A and 4B  illustrate another embodiment of a distractor  220 . The distractor  220  is similar to the distractor  120  in that it includes a piston  222  disposed in a cylinder  224  that is configured to receive a fluid such that as fluid enters the cylinder  224 , the piston  222  is driven out of the cylinder in a distal direction D′. Further, the distractor  220  can include a rail receiving element  226  disposed over a rail  234 , however rather than the rail receiving element  226  translating over the rail  234 , in the illustrated embodiment the rail  234  is coupled to and moves with the piston  222  to move two bone surface with respect to each other while the rail receiving element  226  remains substantially stationary. As illustrated, the rail  234  can pass through rail receiving element  226 . The rail  234  can include openings  236  to mate to a bone surface, and the rail receiving element  226  can include openings  228  to mate to another bone surface, for example by inserting cortical screws through the openings  236 ,  228  and into the respective bone surfaces. While in the distractor  120  the rail  134  is substantially straight, the rail  234  of the distractor  220  is curved, which allows for curvilinear distraction trajectories.  FIG. 4A  shows the distractor  220  in a contracted position and  FIG. 4B  shows the distractor  220  in an extended position. As illustrated, the curved rail  234  allows the distractor  220  to displace the nearest edges of bone surfaces at a non-parallel angle, defined herein as an angle of distraction A. More specifically, a distal end  234   d  of the curved rail  234  can extend outside of an axis C defined by the cylinder when the distractor  220  is moved from the contracted position to the extended position. While the curved rail  234  can have any length and any angle of distraction A, which will depend at least in part on the desired location of the bone surfaces to which the distractor  220  will be mated, in one embodiment the rail  234  has a radius R R  of approximately 50 mm over an angle of distraction A of approximately 32°. Selection of a different angle of distraction A may require a shorter or longer piston  222 , cylinder  224 , and/or rail  234 . 
     As illustrated in  FIG. 5 , a curved rail  234 ′,  234 ″ of a distractor  220 ′ can be defined by a radius of curvature. Adjusting a radius of curvature of the curved rail  234 ′,  234 ″ can change the angle of distraction A. In the illustrated embodiment, the curved rail  234 ′ has a radius of curvature R C ′ of approximately 50 mm, while the curved rail  234 ″ has a radius of curvature R C ″ of approximately 75 mm. As shown, the greater the radius of curvature, the less curved the rail  234 ′,  234 ″ is. Each of the curved rails  234 ′,  234 ″ is configured to slide along pivot pins  231 ′, as discussed in further detail with respect to pivot pins  331  in  FIGS. 6A and 6B . Selection of a different radius of curvature, like selecting a different angle of distraction, may require a shorter or longer piston, cylinder, and/or rail. 
     Further, rails of a distractor can be selectively interchangeable such that a kit can be formed that includes a distractor having multiple rails. Each rail can be substituted into the distractor based on the need for a rail having particular dimensions. The rails can be substantially straight and/or curved and can have varying dimensions, for example varying lengths and radii of curvature, to allow for a diverse selection of rails for use with the distractor. The same rail can be used for an entire procedure, or alternatively, rails can be substituted for each other during the course of a procedure, whether the same day or over an extended period of time. Similarly, other components of the distractor can be interchangeable, such as, by way of non-limiting example, the rail receiving element. 
     Another exemplary embodiment of a distractor  320  is illustrated in  FIGS. 6A and 6B . The distractor  320  is hydraulically-driven by placing a hydraulic force on a piston  322  disposed in a housing  324 . An o-ring or other sealing device can be used as a seal between the piston  322  and a fluid chamber  323  of the housing  324 . The fluid chamber  323  can be configured to receive a fluid such that as fluid enters the chamber  323 , the piston  322  is driven out of the chamber  323  in a distal direction D″. In the illustrated embodiment, the chamber  323  is also adapted to accept MINSTAC fittings  350 . The MINSTAC fittings can include a ferrule  352 , a collet  354 , and a coupling  356 , which together allow the tube  206  of the actuation system  200  (not pictured) to be in fluid communication with the fluid chamber  323  of the housing  324 . The housing  324  can be configured to mate to a bone surface. In the illustrated embodiment the housing is coupled to a rail receiving element  326  that includes features for mating the rail receiving element  326 , and thereby the housing  324 , to a bone surface. In the illustrated embodiment the features for mating the rail receiving element  326  to a bone surface are openings  328 . The openings  328  can be offset from each other. Cortical screw or pins, or other attachment mechanisms, can be disposed through the openings  328  to mate the rail receiving element  326  to a bone surface. 
     The housing  324  can include a pivot  330  such that a pivot pin  332  can mate the rail receiving element  326  to the housing  324  by way of the pivot  330 . The pivot pin  332  can allow some freedom of motion between the housing  324  and the rail receiving element  326 . A rail  334  can be coupled to each of the piston  322  and the housing  324  such that as the piston  322  moves in the distal direction D″, the rail  334  also moves away from the housing  324  to increase a gap between a distal end  334   d  of the rail  334  and the housing  324 . The rail receiving element  326  can further include one or more pin-receiving apertures  329 . As illustrated, the rail  334  can pass through rail receiving element  326  and can pivot along one or more pivot pins  331  disposed in the one or more pin-receiving apertures  329 . In embodiments that utilize more than one rail, the rails can each be configured to slide on the same pivot pins  331  without requiring movement of the pivot pins  331 , as shown in  FIG. 5  with respect to rails  234 ′,  234 ″. The distal end  334   d  of the rail  334  can include features for mating the rail  334  to a bone surface, such as openings  336 . The openings  336  can be offset from each other. Cortical screw or pins, or other attachment mechanisms, can be disposed through the openings  336  to mate the rail  334  to a bone surface. Further, a piston anchor  340  having a pivot  342  can couple the piston  322  to the rail  334  by way of a pivot pin  338 . The pivot pin  338  can allow some freedom of motion between the piston  322  and the rail  334 . In the illustrated embodiment, as the piston  322  is driven out of the cylinder  324  in the distal direction D″, the rail  334  travels along the pivot  330  of the housing  324  such that the distal end  334   d  of the rail  334  moves away from the housing  324  at an angle because the rail  334  is curved. In an alternative embodiment, the rail  334  is fixed and instead the rail receiving element  326  is configured to translate along a length of the rail  334 . In such an embodiment, the rail  334  can be substantially straight or curved and the rail receiving element  326  can be specifically designed to slide across the shape of the rail  334 . Accordingly, as the piston  322  is driven out of the cylinder  324  in the distal direction D″, the rail receiving element  326  translates along the fixed rail  334  away from the distal end  334   d  of the rail  334 . 
     The illustrated embodiment also includes a sensing mechanism  370  configured to determine a location of a relevant component of the distractor  320 . While in the illustrated embodiment the relevant components include the piston  322  and the rail  334 , in other embodiments, such as an embodiment in which the rail receiving element  326  translates across the rail  334 , the rail receiving element  326  can be a relevant component for determining a location. As shown, the sensing mechanism  370  includes a transducer core  372  coupled to a transducer coil  374 . The transducer core  372  is coupled to both the piston  322  and the rail  334  such that movement of the piston  322 , and thereby the rail  334 , causes movement of the transducer core  372 . As the core  372  moves in the distal direction D″, the core  372  moves away from the coil  374 , thereby reducing the inductance of the coil  374 . In the illustrated embodiment, the transducer core  372  and the transducer coil  374  are at least partially disposed in a sensing chamber  325  of the housing  324 . Further, as shown, a shield  376  is coupled to the transducer core  372  and the combination of the shield  376  and the transducer core  372  is coupled to both the piston  322  and the rail  334  by the piston anchor  340 . A distal core anchor  378  can be used to maintain the shield  376  and the transducer core  374  in the sensing mechanism attachment anchor  340 , while a proximal core anchor  380  can be used to maintain the transducer coil  374  in a desired location of the sensing chamber  325 . The transducer coil  374  can be configured to communicate the location of the transducer core  372  to a location remote from the distractor  320 . For example, as the inductance of the transducer coil  374  changes, the coil  374  can be wired to a position sensor interface of a regulation system, such as the position sensor interface  212  of the regulation system  210  (not pictured), which can in turn regulate an actuation system, such as actuation system  200  (not pictured), to allow for further distraction as desired. Alternatively, the transducer coil  374  can be configured to communicate wirelessly with a regulation system and/or an actuation system like the regulation system  210  and the actuation system  200 . 
     Similar to the distractor  120 , the distractor  320  can be made of a variety of different materials, including Titanium 6A1-4V, and each component of the distractor  320  can be made of a different material. In one exemplary embodiment, each of the piston  322 , the cylinder  324 , the rail receiving element  326 , the pivot pins  331 ,  332 , and  338 , the rail  334 , the piston anchor  340 , the collet  354 , the coupling  356 , and the shield  376  is machined from 316L stainless steel, the ferrule  352  is machined from polytetrafluoroethylene, and each of the core anchors  378 ,  380  is machined from ultra high molecular weight polyethylene. Further, while the size of the components can vary, based at least in part on the intended use, in one embodiment particularly useful for distracting mandibles a length L D  from a proximal end of the housing  324  to a distal end  334   d  of the rail  334  in the contracted position is approximately 46.5 mm, a height H D  from a tip of the rail  334  to a bottom of the rail receiving element  326  is approximately 20 mm, a height H H  of the housing  324  is approximately 8.75 mm, a thickness T D  of the distractor  320  is approximately 7.25 mm, and a thickness T R  of the rail  334  is approximately 1.5 mm. 
       FIGS. 8 and 9  illustrate exemplary embodiments of a hydraulic power supply or actuator  202 ′,  202 ″ having a spring-loaded reservoir for use in an actuation mechanism, like the actuation mechanism  200 , with a distractor, such as the distractors  20 ,  120 ,  220 , and  320 . In particular, the hydraulic power supplies  202 ′,  202 ″ are configured to be driven by pressurized fluid, such as water, provided from the spring-loaded reservoir. In the illustrated embodiments, the hydraulic power supplies  202 ′,  202 ″ include a housing  205 ′,  205 ″ a piston  207 ′,  207 ″ at least partially disposed in the housing  205 ′,  205 ″, a spring  209 ′,  209 ″ disposed in the housing  205 ′,  205 ″ and configured to apply a force to the piston  207 ′,  207 ″, and a cap  208 ′,  208 ″ configured to keep the spring  209 ′,  209 ″ disposed in the housing  205 ′,  205 ″ and further configured to allow a force being supplied to the spring  209 ′,  209 ″ to be adjusted, either by the cap  208 ′,  208 ″ itself or by an outside agent. As shown in  FIG. 9 , the cap  208 ″ is integrally formed with the housing  205 ″. Optionally, the piston  207 ′,  207 ″ can be sealed with one or more seals  203 ′,  203 ″, such as an o-ring made of silicone or a Viton o-ring. The piston  207 ′,  207 ″ can also optionally be lubricated with a surgical lubricant. With respect to the hydraulic power supply or actuator  202 ′ of  FIG. 8 , an adjustment mechanism, such as a threaded rod, can be introduced into the housing  205 ′ through an opening  213 ′ of the housing  205 ′ to charge the supply, i.e. to pull the piston  207 ′ toward the cap  208 ′, thereby drawing in a fluid and compressing the spring  209 ′. As shown, a force being applied to the spring  209 ′ can be adjusted by turning the cap  208 ′. As the force on the spring  209 ′ increases, a force being applied to the piston  207 ′ by way of the spring  209 ′ also increases, which in turn can cause fluid to be displaced out of the housing  205 ′. A tube  206 ′ can be coupled to the housing  205 ′ to receive the displaced fluid and direct it to the distractor. As illustrated in particular by  FIG. 9 , the piston  207 ″ can extend out of the housing  205 ″ such that an adjustment mechanism does not have to be introduced into the housing  205 ″. As shown by  FIG. 9 , the location of the piston  207 ″ can be adjusted directly from outside of the housing  205 ″. The piston  207 ″ can also be generally configured to stay in place. Further, the piston  207 ″ can include a fluid passage  215 ″, which can be configured to add or remove fluid from the housing  205 ″ as desired. 
     As discussed generally with respect to the actuation system  200 , a hydraulic power supply or actuator  202  can be regulated by a valve  204 . Likewise, the hydraulic power supply  202 ′,  202 ″ can also be regulated by one or more valves. More than one valve can be used in instances where it may be desirable to either add or remove fluid from a distractor. The one or more valves can be coupled to the hydraulic power supply  202 ′,  202 ″ to control the flow of fluid therefrom. Various valves can be employed. For example, a micro-dispensing valve configured to operate with the MINSTAC fittings discussed above, such as model INKX0520950AA from the Lee Company, can be used. In one embodiment, the valve can be coupled to the hydraulic power supply  202 ′,  202 ″ with a tube, such as 1/16 inch polytetrafluoroethylene tubing. Further, any sort of circuit can be used to operate the valve. For example, a simple single-transistor switch circuit can be used to control current to the valve from a TTL-level input. 
       FIG. 10  illustrates a schematic view of a distractor  520  coupled to an actuation system  500  and a regulation system  510 . The actuation system  500  and the regulation system  510  can be disposed within a control pack, like the control pack  10 . Each of the distractor  520 , the actuation system  500 , and the regulation system  510  can include components similar to the components discussed herein. By way of non-limiting example, the distractor  520  can be similar to the distractors  20 ,  120 ,  220 , and  320 . As shown, the distractor  520 , which includes a piston  522 , a rail  534 , a piston anchor  540 , and a sensing mechanism  570 , is disposed between two bone surfaces  602 ,  604  of a mandible  600 . The distractor  520  is in fluid communication with the actuation system  500 , and in particular a hydraulic power supply  502 , by way of a tube  506 . Disposed therebetween can be one or more valves  504 ,  505  of the regulation system  510 , which are configured to regulate a flow of fluid from the hydraulic power supply  502  to the distractor  520 . In the illustrated embodiment, the valve  504  is configured to allow fluid to flow toward the distractor  520  while the valve  505  is a reverse valve which allows fluid to be evacuated from the distractor  520 . While the reverse valve  505  can be configured to allow fluid removed from the distractor  520  to go back to the hydraulic power supply  502 , in the illustrated embodiment fluid received from the distractor  520  is removed from the system. The valves  504 ,  505  can be controlled based on feedback received from the sensing mechanism  570 . More particularly, the sensing mechanism  570  can be wired to communicate with a controller  511 , for example a DSPIC30F6012A microcontroller from the Lee Company, to analyze a location of the rail  534 . Although not illustrated, similar to the controller  211 , the controller  511  can include components such as a position sensor interface, a control circuit, a wire, and a power supply. Based on the feedback received from the sensing mechanism  570  and analyzed by the controller the valves  504 ,  505  can be operated to control fluid flow between the actuation system  500  and the distractor  520 . Such control can be programmed to occur automatically, or alternatively, can be performed manually. 
     A person having ordinary skill in the art would recognize that the system discussed with respect to  FIG. 10  is merely one of many systems that can be designed based on the teachings herein. By way of non-limiting example, although the controller  511  is configured to control the valves  504 ,  505 , in an alternative embodiment the controller  511  can be configured to control a force being applied to a spring of the hydraulic power supply  502 . By further way of non-limiting example, although the system as illustrated shows only the distractor  520  being an internal device, in alternative embodiments the components of the actuation system  500  and the regulation system  510  can be configured to be disposed internally. 
     A system similar to the one described with respect to  FIG. 10  was used in tests of the distractor  320  and the hydraulic power supply  202 ′. In particular, the controller  511  measured the inductance of the coil  374  at fifteen minute intervals and opened a valve  504 , which happened to be a solenoid valve, for a time interval proportional to the error between the desired and measured position. 
     At full compression of the spring  209 ′ the fluid pressure was approximately 3.5 MPa, producing a force of the piston  322  of approximately 40 N. At full extension of the spring  209 ′ the fluid pressure was approximately 2.0 MPa, producing a force of the piston  322  of approximately 25 N. These tests demonstrated that the hydraulic power supply  202 ′, the MINSTAC fittings, valves  504 ,  505 , tubes  206 ′, and distractor  320  can survive the required pressures. 
     The system described with respect to  FIG. 10  was further used to test the distractor  320  in pig cadavers and live animals to evaluate surgical installation and operation. During the course of the testing, the system functioned for several days in live animals and was able to produce forces necessary to complete a distraction to approximately 11 mm. 
     In an 11 day-1 millimeter per day distraction performed on one pig cadaver using the system described with respect to  FIG. 10  with the distractor  320 , the controller  511  was able to follow a programmed motion with a root-mean-squared error of approximately 0.086 mm. Further, in a live animal, surrounding tissue grows and stretches to accommodate new bone. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.