DEVICES FOR PASSIVE MOTION OF JOINTS UNDER TRACTION

Abstract: A device (10) for generating passive motion of a joint while applying traction has a proximal bracket (12) for engaging a pin (14) drilled into a proximal bone adjacent to the joint and a distal bracket (16) for engaging a pin (18) drilled into a distal bone adjacent to the joint. The two brackets (12, 16) are connected by a tension hinge mechanism (22) which includes a hinge (20) for permitting relative rotational movement of the brackets (12, 16) and an adjustment mechanism (22). The adjustment mechanism (22) is configured to allow substantially continuous adjustment of the distance between the hinge (20) and at least one of the brackets (12 or 16) so as to apply tension across the joint. The adjustment mechanism (22) also includes a number of elastic elements (24) deployed so as to allow elastic variation of the distance between the two brackets (12, 16).

Description: Devices for Passive Motion of Joints Under Traction FIELD AND BACKGROUND OF THE INVENTION The present invention relates to orthopedic surgical devices and, in particular, it concerns devices for moving joints while maintaining traction across the joint. It is known to employ traction across a joint in the treatment of conditions such as intra-articular fractures. Especially where the bones are fragmented to an extent which precludes direct surgical procedures to stabilize the fragments, traction is known to induce ligamentotaxis in which the fragments re-align due to forces on their capsule, ligamentous and volar plate attachments. Traction across a fractured joint can be applied by pushing apart pins implanted in each of the adjacent bones. An example of a simple system for applying traction in this manner is the "S Quattro Flexible Mini External Fixator" commercially available from Surgicraft Ltd., England. It has been found, however, that prolonged application of traction across a fractured joint without movement of the joint frequently results in loss of joint mobility due to irregular re-molding of the joint surfaces. A number of attempts have therefore been made to develop traction systems which permit freedom of movement of the joint, referred to as "dynamic traction" systems. One approach to dynamic traction is set out in an article entitled "The Dynamic Traction Method: Combining Movement and Traction for Intra- Articular Fractures of the Phalanges" by Robert R. Schenck, MD (Hand Clinics 10 (2) May 1994). This describes a system in which rubber bands are mounted between a transosseous wire located in the distal head of the middle phalanx and an external frame. In the primary example, the frame is formed as a large loop in the plane of movement of the joint. The point of connection of the rubber bands can then be slid manually around the loop to flex the joint while maintaining the applied traction. Also discussed are adaptations of existing continuous passive motion devices to apply tension, also by use of rubber bands. A particular shortcoming of the dynamic traction systems discussed by Schenck is the imprecision and inconvenience of adjustment of the tension applied. Adjustment is achieved primarily by adding or removing rubber bands, thereby giving large discrete jumps in the amount of tension. Although a possibility of twisting the rubber bands is mentioned, no mechanism is provided for such an adjustment. The systems also require professional supervision, making them unsuitable for home-treatment. A second approach to dynamic traction systems is represented by a proximal interphalangeal joint hinge commercially available under the tradename Compass from Smith & Nephew Richards Inc., USA. This hinge is secured by five pins drilled into the bones. Once positioned, an adjustment screw allows distraction of the joint. Once the desired degree of distraction is achieved, the pin blocks are fixed in position relative to the hinge. During normal operation of the hinge, no flexibility or elasticity is exhibited. Although the Compass system provides effectively continuously variable adjustment of the degree of distraction of the joint, the lack of flexibility in the system causes other shortcomings. Firstly, the hinge is extremely sensitive to misalignment. For this reason, a superfluous axial pin is drilled into the bone for alignment of the hinge. However, even with the extra pin, sufficiently precise positioning of the hinge is difficult to achieve. Additionally, even within the operative range of accuracy, a slight misalignment of the hinge may result in a large variation in the distraction of the joint during movement. The lack of flexibility also potentially makes the system breakable. Finally, passive movement of the joint is achieved by labor intensive manual operation of a worm-gear mechanism. It is also interesting to note that none of the available systems is suitable for use with injuries to the wrist joint. There is therefore a need for a dynamic traction device for treatment of conditions such as intra-articular fractures which provides substantially continuous adjustability of traction applied elastically across the joint. It would also be advantageous to provide such a device in which passive motion is automated, without depending upon active patient compliance. Furthermore, it would be useful to provide a device of this kind which is suited for use with wrist joints. SUMMARY OF THE INVENTION The present invention is a dynamic traction device for treatment of conditions such as intra-articular fractures which provides substantially continuous adjustability of traction applied elastically across the joint. Preferred embodiments of the mvention allow fully programmable control of a wide range of parameters relating both to the amount of traction applied and the range, speed and frequency of passive movement of the joint. According to the teachings of the present invention there is provided, a device for generating passive motion of a joint while applying traction, the joint having been prepared by insertion of pins into a proximal and a distal bone adjacent to the joint, the device comprising: (a) a proximal bracket for engaging the pin of the proximal bone; (b) a distal bracket for engaging the pin of the distal bone; and (c) a tension-hinge mechanism connecting between the proximal bracket and the distal bracket, the tension-hinge mechanism including: (i) a hinge for permitting rotational movement of the distal bracket relative to the proximal bracket, and (ii) an adjustment mechanism for allowing substantially continuous adjustment of the distance between the hinge and at least one of the proximal bracket and the distal bracket so as to apply tension across the joint, the adjustment mechanism including an elastic element deployed so as to allow elastic variation of the distance between the proximal bracket and the distal bracket. According to a further feature of the present invention, each of the proximal and the distal brackets is configured for engaging two pins inserted in each of the proximal and distal bones, respectively. According to a further feature of the present invention, there is also provided a volar-dorsal displacement bracket configured to releasably engage a part of the device, the volar-dorsal displacement bracket including an adjustable actuator configured to displace a part of the body adjacent to the joint in a lateral direction before insertion of at least one of the pins. According to a further feature of the present invention, at least one of the proximal and the distal brackets features a high tolerance pin clamp configured to provide at least one degree of freedom of at least a few millimeters in positioning of the at least one bracket relative to the pin. According to a further feature of the present invention, there is also provided an actuator mechanism deployed between the proximal bracket and the distal bracket for generating relative rotation between the proximal bracket and the distal bracket about the hinge. The actuator mechanism may include a gear member attached to one of the proximal bracket and the distal bracket and a worm gear mounted with an axis of rotation fixed relative to the other of the proximal bracket and the distal bracket, the worm gear being engaged with the gear member. According to a further feature of the present invention, there is also provided a drive unit coupled through a cable so as to drive the actuator mechanism, the cable being connected to the actuator mechanism through a safety clutch mechanism. The safety clutch mechanism may include a first portion including at least one rounded element biased radially so as to engage a corresponding rounded recess in a second portion of the safety clutch mechanism. According to a further feature of the present invention, the adjustment mechanism includes a counter-threaded bolt, the counter-threaded bolt serving as a central pin for the hinge. The counter-threaded bolt may form part of a scissors mechanism. According to a further feature of the present invention, the adjustment mechanism includes a gauge for indicating an extent of opening of the adjustment mechanism. According to a further feature of the present invention, there is also provided: (a) a plurality of adapter pins engaged directly with the proximal and the distal brackets; and (b) a plurality of angle adapters constructed to allow clamping of the inserted pins to the adapter pins such that the inserted pins and the adapter pins form therebetween any one of a plurality of predefined angles. According to a further feature of the present invention, the joint is a wrist joint, the proximal bracket including upper and lower abutment surfaces for abutting upper and lower surfaces of a forearm of a patient and the distal bracket includes upper and lower abutment surfaces for abutting upper and lower surfaces of a hand of the patient. BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is an isometric view of a first embodiment of a dynamic traction device, constructed and operative according to the teachings of the present invention, for use in surgical treatment of conditions such as intra-articular fractures in a wrist joint; FIG. 2 is a partially exploded isometric view of the device of Figure 1; FIG. 3 is a plan view of the device of Figure 1; FIG. 4 is a schematic isometric view of the device of Figure 1 in use; FIG. 5 is an isometric view of a second embodiment of a dynamic traction device, constructed and operative accordmg to the teachings of the present invention, for use in surgical treatment of conditions such as intra- articular fractures in a wrist joint; FIG. 6 is a schematic isometric view of the device of Figure 5 in use; FIG. 7 is a side view of a third embodiment of a dynamic traction device, constructed and operative according to the teachings of the present invention, for use in surgical treatment of conditions such as intra-articular fractures; FIG. 8 is a plan view of the device of Figure 7; FIG. 9 is a partially cut-away plan view of the device of Figure 7; FIG. 10 is a cross-section taken through a fixation pin clamp from the device of Figure 7; FIG. 11 is a schematic isometric view of the device of Figure 7 in use; FIG. 12 is an isometric view of the underside of the device of Figure 7 fitted with a number of angle adapters for altering the angle of motion of the joint; FIG. 13 is a cross-sectional view through an angle adapter from Figure 12; FIG. 14 is a schematic isometric view of the device of Figure 12 in use; FIG. 15 is a first exploded isometric view of a fourth embodiment of a dynamic traction device, constructed and operative according to the teachings of the present invention, for use in surgical treatment of conditions such as intra-articular fractures in an inter-phalangeal joint; FIG. 16 is a second exploded isometric view of the device of Figure 15; FIG. 17 is a plan view of the device of Figure 15; FIG. 18 is a side cross-sectional view of the device of Figure 15; FIG. 19 is an enlarged view of a region of Figure 18; FIG. 20 is an isometric view of a template for use in locating pins for use with the device of Figure 15; FIG. 21 is a schematic isometric view of the device of Figure 15 in use; FIG. 22 is an isometric view of an alternative spring element for use in the device of Figure 15; FIG. 23 is a side view of a fifth embodiment of a dynamic traction device, constructed and operative according to the teachings of the present invention, for use in surgical treatment of conditions such as intra-articular fractures in an inter-phalangeal joint; FIG. 24 is a side cross-sectional view through the device of Figure 23; and FIG. 25 is an isometric view of an alignment bracket for use with the device of Figure 23. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a dynamic traction device. The device is useful for treatment of a range of conditions such as intra-articular fractures and any other pathological or post-operative condition (arthroplaty) in which traction and/or early passive motion of the joints is indicated. The principles and operation of devices according to the present invention may be better understood with reference to the drawings and the accompanying description. Referring now to the drawings, Figures 1-4 show a first embodiment of a device, generally designated 10, constructed and operative according to the teachings of the present invention, for generating passive motion of a joint while applying traction. Generally speaking, device 10 has a proximal bracket 12 for engaging a pin 14 drilled into a proximal bone adjacent to the joint, and a distal bracket 16 for engaging a pin 18 drilled into a distal bone adjacent to the joint. Brackets 12 and 16 are connected by a tension-hinge mechanism which includes a hinge 20 for permitting relative rotational movement of the brackets, and an adjustment mechanism 22. Adjustment mechanism 22 is configured to allow substantially continuous adjustment of the distance between hinge 20 and at least one of brackets 12 and 16 so as to apply tension across the joint. Adjustment mechanism 22 also includes a number of elastic elements 24 deployed so as to allow elastic variation of the distance between brackets 12 and 16. It will be appreciated that the combination of continuous adjustability and elasticity provides considerable advantages over the prior art references described above. Specifically, the adjustment may be performed quickly and precisely to achieve the desired traction. At the same time, the elasticity renders the precise location of hinge 20 much less critical. It is a preferred feature of most embodiments of the present invention that most or all of the device is produced from X-ray transparent materials to allow imaging of the injured joint while the device is in place. A range of suitable plastics and other polymer materials generally known in the art may be used. Turning now to the features of device 10 in more detail, adjustment mechanism 22 includes a counter-threaded bolt 26 which serves as a central pin for hinge 20. "Counter-threaded" is used in this context to refer to a bolt which is threaded in a right-handed sense in one region and a left-handed sense in another region. Mounted on bolt 26 are two oppositely threaded locating collars 28, each engaged between the rings of a double ring washer bracket 30. Attached to locating collars 28 are a first pair of centrally pivoted scissor arms 32. A second pair are attached to brackets 30. The free ends of scissor arms 32 have downwardly projecting pins which engage transverse slots 34 in proximal and distal brackets 12 and 16. This structure functions as a double scissors mechanism so that rotation of an adjustment knob 36 formed at the end of bolt 26 simultaneously pushes brackets 12 and 16 towards or away from hinge 20. As mentioned above, adjustment mechanism 22 includes a number of elastic elements 24 deployed so as to allow elastic variation of the distance between brackets 12 and 16. In this embodiment, elastic elements 24 are preferably implemented as the entirety of one or both pairs of scissor arms 32. In other words, the material and design of the scissor arms are chosen to provide the required degree of flexibility. Thus, as knob 36 is tightened, brackets 12 and 16 move apart until mechanical resistance is encountered. Further tightening of knob 36 beyond this point causes some elastic deformation of arms 32, thereby elastically applying tension (traction) between brackets 12 and 16. The amount of tension is controlled in a continuous manner by the angle through which knob 36 is turned. Alternatively, localized flexible regions or spring elements may be incorporated within one or both pairs of arms 32 to provide the required elasticity. Preferably, device 10 also features an actuator mechanism 40 deployed between proximal bracket 12 and distal bracket 16 for generating relative rotation between them about hinge 20. This allows application of passive motion therapy while maintaining traction across a joint. Actuator mechanism 40 preferably includes a gear member 42, rotatably mounted near hinge 20. Gear member 42 has a fork-like extension 44 which engages a projection 46 from one of the brackets, in this case, distal bracket 16. Engaged with gear member 42 is a worm gear 48 the axis of which is mounted relative to the other bracket, in this case, proximal bracket 12. Rotation of worm gear 48 causes gear member 42, and hence distal bracket 16 to rotate relative to proximal bracket 12. Preferably, gear member 42 has an arcuate slot 43 (see Figure 2) at constant radius from the center of the gear member which is engaged by a pin of the worm gear housing. This ensures that the movement of the actuator mechanism is limited to an arcuate path, preventing any linear displacement between brackets 12 and 16 which could otherwise be caused. Preferably, worm gear 48 is driven through a flexible drive cable 50 by a portable control unit 52 which can be strapped to the arm 54 of a patient (see Figure 4). Control unit 52 typically includes an electric motor driven from batteries under the control of a programmable microprocessor unit. This allows a surgeon to set and modify parameters of a passive exercise treatment program, including the extent and speed of rotation about an axis of rotation, the delay between successive movements, the length of each treatment session and the time between sessions. All of these parameters may be programmed to change progressively or in steps during the course of the treatment. Optionally, control unit 52 may include a connection device, preferably in the form of a modem or tone-dialing connection to a telephone network, configured to form a connection with a central reprogramming station. This allows adjustment or reprogramming of the parameters of the treatment program within a home-care program without requiring the patient to attend a hospital or clinic. In an alternative implementation, worm gear 48 may be manually operated to achieve passive movement of the joint. As mentioned above, device 10 is skeletally anchored by pins 14 and 18 which are inserted into a proximal and a distal bone adjacent to the damaged joint. In order to prevent angular distortion of the joint under traction, pins 14 and 18 are preferably mounted in elongated plugs 56 which are received within corresponding elongated sockets 58 of brackets 12 and 16. Although device 10 can be used with minor adaptations for a wide range of different joints, the particular example shown here is designed for use with a wrist joint. In order to impart movement to the joint for passive motion therapy, brackets 12 and 16 provide upper and lower abutment surfaces 60 and 62 which apply pressure against the forearm and hand of the patient. A similar structure may be used in implementations for use with the elbow joint. Turning now to Figures 5 and 6, there is shown a second embodiment of a device, generally designated 70, constructed and operative according to the teachings of the present invention, for generating passive motion of a joint while applying traction. Device 70 is similar in principle to device 10, but employs a different design of adjuster mechanism 72 mounted directly between pins 14 and 18. Specifically, adjuster mechanism 72 also has a central bolt 74 which serves as a hinge. Between bolt 74 and each of pins 14 and 18, two spring rods 76 and 78 are mounted at an angle. The attachment of the spring rods to bolt 74 is through threaded collars 80, while the attachment to the pins is at sleeves 82 fixed by pressure fitting. Rotation of bolt 74 causes collars 80 to move along the bolt, thereby changing the angle of spring rods and hence urging pins 14 Spring rods 76 which are closer to the proximal and distal brackets are preferably relatively stiff, whereas rods 78, closer to the outer ends of the pins, are preferably relatively flexible. As a result, when adjustment mechanism 72 is tightened, the outward force caused by rods 76 is greater than that caused by rods 78, tending to force the implanted ends of the pins apart. This counters the tendency of the adjustment system to generate angular distortion in the joint. The thread of bolt 74 may be opposite for the two collars 80, causing them to push outwards simultaneously. Alternatively, co-directional threading can be used. This causes spring rods 78 to draw the ends of pins 14 and 18 inwards while stiffer spring rods 76 push outwards, thereby further enhancing the angular distortion compensation of adjustment mechanism 72. Device 70 also features an actuator mechanism 84. Actuator mechanism 84 is similar to mechanism 40 described above, except that the gear element is here implemented as an arched rack 86. In all other respects, the features and operation of device 70 will be fully understood by analogy to that of device 10 described above. Turning now to Figures 7-14, there is shown a third embodiment of a device, generally designated 200, constructed and operative according to the teachings of the present invention, for generating passive motion of a joint while applying traction. Device 200 is similar in principle to devices 10 and 70, but provides a number of structural and functional improvements. Most notably, it has been found valuable to employ two fixation pins 201 to positively align the bone on each side of the joint. To this end, at least one and preferably both of the proximal and distal brackets 204 and 206 are configured for engaging two pins inserted in the corresponding bones. Specifically, in the example illustrated, proximal bracket 204 features one pin clamp 210 while a second pin, required only for alignment, is accommodated within an elongated slot 212. In distal bracket 206, on the other hand, two pins are mounted in separate pin clamps 214, thereby both contributing to the alignment and rigidity of clamping. Preferably, some or all of pin clamps 210 and 214 are implemented as high tolerance pin clamps configured to provide at least one degree of freedom of at least a few millimeters in positioning of the bracket relative to the pin. This makes the precision of positioning of the fixation pins less critical and renders attachment of the device particularly easy. An example of a high tolerance pin clamp structure is shown in Figure 10. Here, a pin 201 may be clamped in any desired position within a slot or enlarged aperture 216 by tightening a knob 218 with an internally threaded bore onto a clamping sleeve 222 with a wide flange 224. The size of the base of knob 218 and flange 224 are sufficient to ensure secure alignment of pin 201 at any position across the width of aperture 216. A further improvement of this embodiment lies in the simplicity, reliability and performance of the adjustment mechanism, best seen in the cutaway view of Figure 9. Here, the major distal portion 226 of device 200 is connected at simple rigid hinges 228 to proximal bracket 204. The relatively small distal bracket 206 which directly engages the distal pins is attached to distal portion 226 by an adjustable spring-loaded mounting 230. Specifically, spring-loaded mounting 230 includes a partially-threaded adjustment rod 232 which is aligned within bores through two support blocks 234, 236 so as to be free to slide axially. Rod 232 is biased by an elastic element, preferably a helical spring 238 towards a distally displaced resting position as shown. Bracket 206 has a threaded inner bore (not visible) within which a threaded part of rod 232 is engaged. Thus rotation of rod 232 by means of adjuster 240 either adjusts the position of bracket 206 between the two support blocks or, if bracket 206 is held still, adjusts the tensile force exerted on bracket 206 by spring 238. Preferably, adjuster 240 is configured as a removable key to prevent unauthorized adjustment of the device after it is positioned. Additionally, a highly compact structure is achieved by replacing arched rack 86 with a linear rack 202. Variations in alignment of rack 202 during relative rotation of proximal and distal brackets 204 and 206 is accommodated by a pin-and-slot coupling 208. Referring now specifically to Figures 12-14, it has been found that, in certain cases, it is desirable to generate flexing motion of the joint in directions other than the flexion and extension (up-down) motion illustrated thus far. Clearly, a new device accordmg to the principles of the present invention could be designed for each intended application. However, to provide maximum convenience and flexibility of application, the present invention may also provide angle adapters 242 to allow selection of the angle of hinge 228 relative to pins 201. A preferred structure of angle adapter 242 is shown schematically in Figure 13. Angle adapter 242 is formed from first and second roughly cylindrical elements 244 and 246, each of which has a bore 248, 250 for receiving a pin 201 which is clamped in position by a clamping bolt 252 engaged in a threaded clamping recess 254. Abutting surfaces of first and second elements 244 and 246 are formed with a rotationally symmetric pattern of complementary projections and recessions 256 which, when the elements are clamped together, allows their relative rotational position to be fixed at any desired angle (subject to the angular step chosen between adjacent projections). First element 244 features a round axial shaft 258 with an annular recess 260 near its extremity. Second element 246 features a corresponding cylindrical axial recess for receiving shaft 258. Bore 250 is positioned such that, when first and second elements 244 and 246 are closed tightly together, bore 250 aligns with annular recess 260 so that insertion of pin 201 through bore 250 locks the elements tightly together. It will be appreciated that angle adapters 242 provide a convenient way of converting any device according to the present invention to provide flexing around axes at a wide range of angles to the direction of insertion of the fixation pins. Before insertion of the pin through second element 246, the two elements can be prized slightly apart to allow the adapter to be set to whatever angle is required. Once the elements are pushed back together and the pin is inserted through bore 250, the angle becomes securely and rigidly fixed. The pins are then clamped firmly by tightening of clamping bolts 252. As will now be clear, angle adapters 242 allow clamping of two pins at any one of a number of predefined angles. Figure 12 shows device 200 fitted with four angle adapters 242 all set to about 90°. As seen here, angle adapters 242 are generally used in conjunction with a number of adapter pins 262 which replace pins 201 for engagement directly with the proximal and the distal brackets The use of such a configuration for in-plane passive motion of the wrist is illustrated in Figure 14. Turning now to Figures 15-22, there will be described a fourth embodiment of a device, generally designated 90, constructed and operative according to the teachings of the present invention, for generating passive motion of a joint while applying traction. This embodiment employs similar principles to those of the embodiments described above, but in a design particularly suited for inter-phalangeal joints. An additional feature illustrated by this embodiment is the provision of a gauge for indicating the extent of opening of the adjustment mechanism. As in the previous embodiments, device 90 is skeletally anchored by two pins 92 and 94, in this case, inserted transosseously. The two brackets and the tension-hinge mechanism are all formed as an articulated hollow housing 96 which is mounted around the finger. A proximal section 98 of housing 96 features sockets 100 within which proximal pin 92 engages. Projections 102 from proximal section 98 engage hinge sockets 104 of an elongated distal section 106 of housing 96, thereby forming a hinge. Distal section 106 is formed with cut-out walls to as to form a spring structure. In the case illustrated here, a spiral cut-out 108 is formed to give distal section 106 a helical spring structure. Parenthetically, it should be noted that the term "cut-out" is used here to describe the final structure independent of the method used to generate it. Thus, distal section 106 may be produced directly with the required cut-outs by a range of conventional production techniques including, but not limited to, injection molding. Alternatively, a subsequent "cutting" procedure may be employed. The ends of distal pin 94 are secured by hooks 110 at the ends of a fork 112 which is designed to extend along the sides of a patient's finger. The central region of fork 112 features a threaded opening 114 which receives the threaded end of an adjustment bolt 116 which is seated in a cap assembly 118 at the end of distal section 106. It will now be appreciated that device 90 provides continuously adjustable elastic traction across a joint while permitting freedom of motion. Specifically, tightening of adjustment bolt 116 draws fork 112, and hence pin 94, towards cap assembly 118. This movement applies compression to the spring structure of distal section 106. This compressive force is transferred through the hinge to proximal section 98 and proximal pin 92. The result is traction applied between pins 92 and 94 corresponding to the extent of elastic compression in distal section 106. It is a preferred feature of this and other embodiments of the device of the present invention that a gauge is provided for indicating the extent of opening of the adjustment mechanism. A simple example of such a gauge, illustrated here as part of cap assembly 118, will now be described with reference particularly to Figures 15, 16 and 19. Thus, cap assembly 118 has an inner cap 120 which clips firmly onto a projecting rim of distal section 106. Inner cap 120 has a central opening 122 with a recessed rim which forms a seat for the flange of adjustment bolt 116. Three projections 124 provide central mounting points for three gear wheels 126 which form a planetary gear arrangement with a toothed head 128 of adjustment bolt 116. Engaged around the outer periphery of gear wheels 126 is an internally toothed wheel 130 on which an outer cover 132 sits. A projecting adjustment knob 134 engages a non-circular hole in the head of adjustment bolt 116 to facilitate manual rotation of the bolt. The step-down effect of the planetary gear arrangement is such that outer cover 132 turns a small fraction of a revolution for each full revolution of adjustment bolt 116. By providing a pointer and scale arrangement between outer cover 132 and the adjacent part of distal section 106, the extent of rotation of outer cover 132 serves as a gauge for indicating the extent of tightening of the device. Optionally, part or all of outer cover 132 can be designed to be easily turned by hand to allow calibration of the gauge. In this case, knob 134 is turned through its range of free movement to take up any slack until the first mechanical resistance is felt. The scale is then set to its zero mark. The subsequent tightening indicated by the gauge is then a true indication of the traction being applied across the joint. Preferably, device 90 also features an actuator mechanism 136 and control unit 138, structurally analogous and functionally equivalent to actuator mechanism 84 and control unit 52 described above. Turning now briefly to Figure 20, this shows a template 140 which is preferably used for precise positioning of the pins 92 and 94. As mentioned earlier, the elasticity of the devices of the present invention makes the positioning of the pins much less critical than in the prior art devices. However, particularly in the case of an injured finger where the entire region surrounding the injury is typically sensitive, it is important to position the pins centrally so that the device does not touch the skin near the injured joint. For this purpose, template 140 is produced with alignment bores 142 and 144 spaced on either side of a hinge 146 to correspond to the desired initial spacing of pins 92 and 94. Alignment bores 142 and 144 serve as drill guides for proper insertion of the pins. With brief reference to Figure 22, it should be appreciated that the spring structure of distal section 106 need not be helical and may take any of a wide range of forms. By way of example, Figure 22 shows an alternative spring structure 150 for use as part of distal section 106. The open sides of this structure minimize the bulk of device 90 between the injured finger and adjacent fingers, making the device more comfortable for the patient. Turning finally to Figures 23-25, there will be described a fifth embodiment of a device, generally designated 300, constructed and operative according to the teachings of the present invention, for generating passive motion of a joint while applying traction. This embodiment is generally similar to device 90 described above but replaces the external spring structures with a rigid external casing and employs a compact internal tensioning mechanism. This embodiment also provides for the preferred two-pin mounting on either side of the joint. These and other features of device 300 and its use will be clear from the following description. In a manner analogous to device 200 described above, device 300 employs a major distal portion 302 connected at simple rigid hinges 304 to proximal bracket 306 while the adjustment mechanism is implemented as a rod 308 axially biased by a spring 310 and engaged via a threaded connection 312 to distal bracket 314. Rotation of rod 308 by means of a preferably removable adjuster 316 either displaces distal bracket 314 axially or, if it is held in place, adjusts the tensile force exerted on distal bracket 314 by spring 310. As already mentioned, it has been found advantageous to employ two pins inserted in each bone adjacent to the joint to provide fully defined and constant alignment of the bones relative to the proximal and distal brackets. To this end, proximal bracket 306 features two hook-shaped pairs of recesses 318 for latching onto two pins on one side of the joint while distal bracket 314 in this case features one pair of hook-shaped recesses 320 and a pair of slots 322 for receiving two pins on the second side of the joint. The pins engaged by recesses 318 and 320 are optionally inserted using an appropriately formed template analogous to that of Figure 20. The significance of slots 322 will now be explained. In addition to the tension applied across the joint by the devices of the present invention, it has been found advantageous to provide slight lateral and/or angular volar-dorsal adjustment of the bones adjacent to the joint. This may be particularly useful for maintaining the reduced position of a sub-luxated or dislocated inter-phalangeal joint. To this end, only some of the intended number of pins, in this case three out of four, are inserted prior to positioning of the device. A volar-dorsal displacement bracket, such as bracket 324 of Figure 25, is then preferably used to displace a part of the body adjacent to the joint in a lateral direction before insertion of the remaining pin or pins. Bracket 324 is preferably configured to releasably engage a part of the corresponding device. In this case, bracket 324 is formed as a hollow cylinder with an internal bore 326 sized to fit closely around distal portion 302. Bracket 324 also includes an adjustable actuator which may be as simple as a bolt 328 engaged in a lateral hole 330. Bracket 324 is designed so that the actuator can be aligned with an open part of the device so as to push against a part of the limb adjacent to the joint and displace it laterally, i.e., roughly perpendicular to the extensional direction of the limb. Once the required position and/or angle is achieved, the remaining pin or pins are inserted so as to fix the position of the bones relative to the device. Bracket 324 may then be removed. Finally, it was mentioned earlier that the actuator mechanisms of devices according to the present invention are preferably driven by a drive unit such as within control unit 52 through a flexible drive cable 50. It is a particular feature of certain preferred implementations of the present invention that the drive cable is connected to the actuator mechanism through a safety clutch mechanism 332. An example of one suitable safety clutch mechanism 332 equally applicable to all embodiments of the present invention is seen in Figure 24. A first portion 334 includes at least one rounded element 336 biased radially so as to engage a corresponding rounded recess 338 in a second portion 340 of the safety clutch mechanism. In this case, two ball-bearings 336 are biased radially outwards by a helical spring 342 located within a transverse bore 344. Clearly, if any excess resistance is encountered, the applied torque will be sufficient to displace ball-bearings 336 inwards against spring 342, thereby momentarily breaking the driving relation between the drive cable and the actuator mechanism. The mechanism described has an added advantage that it allows instant connection and disconnection of the drive cable. Second portion 340 is here formed as a female connector which can simply be pulled off the male first portion 334 as required. Ball-bearings 336 are preferably retained within bore 344 by a retaining collar 346 which has apertures of diameter slightly less than the diameter of the ball-bearings. It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope of the present invention.

Claims: WHAT IS CLAIMED IS: 1. A device for generating passive motion of a joint while applying traction, the joint having been prepared by insertion of pins into a proximal and a distal bone adjacent to the joint, the device comprising: (a) a proximal bracket for engaging the pin of the proximal bone; (b) a distal bracket for engaging the pin of the distal bone; and (c) a tension-hinge mechanism connecting between said proximal bracket and said distal bracket, said tension-hinge mechanism including: (i) a hinge for permitting rotational movement of said distal bracket relative to said proximal bracket, and (ii) an adjustment mechanism for allowing substantially continuous adjustment of the distance between said hinge and at least one of said proximal bracket and said distal bracket so as to apply tension across the joint, said adjustment mechanism including an elastic element deployed so as to allow elastic variation of the distance between said proximal bracket and said distal bracket. 2. The device of claim 1, wherein each of said proximal and said distal brackets is configured for engaging two pins inserted in each of said proximal and distal bones, respectively. 3. The device of claim 2, further comprising a volar-dorsal displacement bracket configured to releasably engage a part of the device, said volar-dorsal displacement bracket including an adjustable actuator configured to displace a part of the body adjacent to the joint in a lateral direction before insertion of at least one of the pins. 4. The device of claim 1, wherein at least one of said proximal and said distal brackets features a high tolerance pin clamp configured to provide at least one degree of freedom of at least a few millimeters in positioning of said at least one bracket relative to the pin. 5. The device of claim 1, further comprising an actuator mechanism deployed between said proximal bracket and said distal bracket for generating relative rotation between said proximal bracket and said distal bracket about said hinge. 6. The device of claim 5, wherein said actuator mechanism includes a gear member attached to one of said proximal bracket and said distal bracket and a worm gear mounted with an axis of rotation fixed relative to the other of said proximal bracket and said distal bracket, said worm gear being engaged with said gear member. 7. The device of claim 5, further comprising a drive unit coupled through a cable so as to drive said actuator mechanism, said cable being connected to said actuator mechanism through a safety clutch mechanism. 8. The device of claim 7, wherein said safety clutch mechanism includes a first portion including at least one rounded element biased radially so as to engage a corresponding rounded recess in a second portion of said safety clutch mechanism. 9. The device of claim 1, wherein said adjustment mechanism includes a counter-threaded bolt, said counter-threaded bolt serving as a central pin for said hinge. 10. The device of claim 9, wherein said counter-threaded bolt forms part of a scissors mechanism. 11. The device of claim 1, wherein said adjustment mechanism includes a gauge for indicating an extent of opening of said adjustment mechanism. 12. The device of claim 1, further comprising: (a) a plurality of adapter pins engaged directly with said proximal and said distal brackets; and (b) a plurality of angle adapters constructed to allow clamping of the inserted pins to said adapter pins such that the inserted pins and said adapter pins form therebetween any one of a plurality of predefined angles. 13. The device of claim 1, wherein the joint is a wrist joint, wherein said proximal bracket includes upper and lower abutment surfaces for abutting upper and lower surfaces of a forearm of a patient and said distal bracket includes upper and lower abutment surfaces for abutting upper and lower surfaces of a hand of the patient.

Inventors: LUBOSHITZ SHMUEL, SELA ITAY, SHEKALIM AVRAHAM, LUBOSHITZ, SHMUEL, SELA, ITAY, SHEKALIM, AVRAHAM
Applicants: FRIEDMAN MARK M, LUBOSHITZ SHMUEL, RIMLON LTD, SELA ITAY, SHEKALIM AVRAHAM, FRIEDMAN, MARK, M., LUBOSHITZ, SHMUEL, RIMLON LTD., SELA, ITAY, SHEKALIM, AVRAHAM
Application year: 1998
Main classification: A61B17
IPC codes: A61B17, A61F2, B25J15, B25J17