Abstract:
A knee brace is provided for supporting an injured interior cruciate ligament by using straps that produce a forced couple on the knee joint to keep the tibia properly behind the femur (anti-drawering) while allowing for adjustment of the amount of anti-drawering to fit the individual needs of the patient. The knee brace may utilize a quadricentric hinge that closely approximates the natural movement of the knee joint and allows for adjustment of the knee brace to account for the natural curvature of the individual patient&#39;s leg bones. The quadricentric hinge can include four gears. Typically, these gears may be two drive gears and two idler gears.

Description:
FIELD OF THE INVENTION 
     This invention relates to a device for supporting an injured knee that acts as the anterior cruciate ligament. 
     BACKGROUND OF THE INVENTION 
     The human knee joint is supported by four major ligaments, including: 
     1. the fibular collateral ligament, arranged on the outer (lateral) side of the knee. This ligament is attached to the outer prominence of the thigh bone (the lateral femoral epicondyl) and stretches to the lateral side of the shin bone (tibia); 
     2. the medial collateral ligament, arranged on the inner (medial) side of the knee. This ligament is attached above to the inner prominence of the thigh bone (the medial femoral epicondyl) and below to the medial aspect of the tibia; 
     the central (cruciate) ligaments which cross in the center of the joint, including 
     3. the anterior cruciate ligament attached from the femur to the front of the tibia; and 
     4. the posterior cruciate ligament attached from the femur to the rear of the tibia. 
     The knee ligaments prevent abnormal motion of the knee and permit normal motion of the knee. All ligaments are taut when the knee is straight (extension) and are lax when the knee is bent (flexion). The anterior cruciate ligament prevents excessive forward displacement of the tibia in relation to the femur. 
     Excessive stress on the outside or inside of the knee joint will tear the ligaments. Athletic injuries, some of the most common knee injuries, occur when the foot is fixed on the ground while the thigh rotates inward and the leg outward, creating stress on the ligaments on the inner side of the knee. The anterior cruciate ligament may also be injured when the tibia is pushed too far forward on the thigh bone. 
     In most mild injuries to the knee ligaments, complete mobility may be restored if the joint is immobilized to allow the ligament time to heal. However, more severe injuries may leave permanent stiffness or lack of complete mobility, but the chance for recovery is increased if the ligament can be immobilized for a period of time. 
     It has been well known to use a knee brace to support an injured knee joint. Previous knee braces have been mainly concerned with providing support and preventing abnormal movement of the knee, such as over-extension, over-flexion or rotation of the joint. To accomplish this effect, previous devices have been constructed to include means on both the lateral and the medial sides of the leg to attach the brace to the leg and a hinge located at the center of the axis of rotation of the knee joint. 
     A known type of hinge used in prior knee braces consists of a bicentric geared hinge where there are often stops associated with the hinge gears for limiting the extent of flexion and extension. 
     The problems associated with these types of knee braces include the fact that they do not provide the forces necessary to act as the anterior cruciate ligament in order to prevent the tibia from moving forward of the femur. Anti-drawering is the term given to the effect of preventing the tibia from moving forward of the femur. The treating physician will often want to control the amount of anti-drawering effect of a knee brace depending on the severity of the injury and the individual characteristics of the patient&#39;s bone structure. Most of the previous devices include straps that encircle the leg to attach the brace to the leg. Some braces include rigid shells that are held onto the leg by straps. Neither of these arrangements provide the forces on the various parts of the leg necessary to keep the tibia in proper alignment. 
     The device disclosed in U.S. Pat. No. 4,697,583, to Mason et al. (&#34;Mason&#34;), purportedly provides the forces necessary to act as a substitute for the anterior cruciate ligament. The device disclosed in Mason includes strategically placed rigid and adjustable straps attached to rigid bars on either side of the leg both above and below the knee that create a force couple on the knee joint which forces the tibia backward into alignment in relation to the femur. The bars are designed to conform to the general shape of the bones, including a curved portion which is immediately adjacent to the knee. The Mason patent also discloses a bicentric hinge to provide for movement and the hinge includes stop means to control the extent of knee extension and flexion. The device disclosed in Mason does not, however, allow for any adjustment of the anti-drawering effect and therefore, no adjustment of the relative position of the tibia and the femur. Because of its arrangement, with the attachment bars having a set curvature to account for the natural position of the bones, the device disclosed in Mason cannot be adjusted to fit the particular anti-drawering needs of an individual patient, especially with respect to the patient&#39;s changing anti-drawering needs as the postsurgical healing process progresses. 
     The straps of Mason which attach the brace to the leg only encompass a portion of the leg and therefore, the rigid straps must be individually formed to fit an individual&#39;s particular leg size or the straps must be made in general leg sizes which may cause discomfort to the patient. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems of prior devices by providing a knee brace with a quadricentric hinge that allows the orthopedist to adjust the amount of anti-drawering effect to fit the individual needs of each patient. 
     In accordance with one aspect of the present invention, a knee brace is provided for supporting an injured anterior cruciate ligament by using straps that produce a force couple on the knee joint to keep the tibia properly behind the femur (anti-drawering), while allowing for adjustment of the amount of anti-drawering to fit the individual needs of the patient. 
     In accordance with another aspect of the present invention, a knee brace is provided for supporting an injured anterior cruciate ligament with a quadricentric hinge that closely approximates the natural movement of the knee joint and allows for adjustment of the brace to account for the natural curvature of the individual patient&#39;s leg bones. 
     In accordance with yet another aspect of the present invention, a knee brace is provided for supporting an injured anterior cruciate ligament that may be mass produced and yet may be adjusted to fit the needs of individual patients. 
     The knee brace of the present invention includes at least two bars to be attached above the knee joint and at least two bars attached below the knee joint. These bars not only stabilize the knee joint, but also prevent any unnatural rotational movement of the knee. These bars are attached to the patient&#39;s leg at four points. The first point is at the top of the thigh where an anterior thigh cuff is attached. The anterior thigh cuff provides a force backward on the front of the upper thigh. 
     The second point of contact is at the lower thigh just above the knee joint. There, a distal posterior thigh strap applies a force forward on the back of the leg. 
     The lower bars are attached to the leg by an adjustable tibia strap just below the knee joint. The tibia strap applies a force backward on the front of the shin. 
     The final strap is a rigid distal shin cuff which applies a forwardly directed force to the back of the lower calf. 
     The upper and lower rigid bars are joined by a quadricentric hinge. A quadricentric hinge is one which contains four axes of pivotable rotation. The quadricentric hinge is adjustable to allow for adjustment of the tibia in relation to the femur. 
     The quadricentric hinge can comprise four gears, two drive gears and two idler gears. The drive gears are attached to the ends of the rigid bars and have structure sufficient to allow for adjustment of the amount of anti-drawering effect and the amount of extension and flexion of the knee. The idler gears, on the other hand, have fixed pivot points and intermesh at the anatomical center of the knee. 
     The quadricentric hinge allows the position of the drive gears to be adjusted to account for the natural curvature of the leg bones for each individual patient without changing any parts on the brace. This overcomes the problems in the previous devices where doctors were required to either change the rigid bars to fit the individual patient or use rigid bars that only approximated the individual&#39;s natural bone structure. Now, one device may be used on a wide variety of patients, thus reducing cost and facilitating mass production. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the knee brace; 
     FIG. 2 is a front view of the knee brace; 
     FIG. 3 is a plan view of the quadricentric hinge joint showing the hinge set at the minimum anti-drawer setting; 
     FIG. 4 is a plan view of the quadricentric hinge joint showing the hinge set at the minimum anti-drawer and also set for a 15° extension stop; 
     FIG. 5 is a plan view of the quadricentric hinge joint showing the hinge set at the maximum anti-drawer setting; 
     FIG. 6 is a plan view of the quadricentric hinge joint showing the hinge set at the maximum anti-drawer and also set for a 20° extension stop; 
     FIG. 7 is a plan view of the quadricentric hinge joint; 
     FIG. 8 is a plan view of the quadricentric hinge joint showing the engagement of the gears as the knee joint moves; 
     FIG. 9 is a cross-sectional view of the quadricentric hinge joint; and 
     FIG. 10 is a plan view of the quadricentric hinge joint showing spur idler gears with flexion and extension stops. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures generally and in particular to FIG. 1, a novel knee brace 11 is illustrated which supports an injured knee joint, specifically providing support for an injured anterior cruciate ligament by providing a force couple on the person&#39;s leg L. More specifically, brace 11 is designed to produce a first force A on the upper front portion of a person&#39;s thigh T, a second force B on the lower rear portion of the person&#39;s thigh T, a third force C on the upper front portion of the person&#39;s shin S, and a fourth force D on the lower rear portion of the person&#39;s shin S. Together with the quadricentric hinge joint 36, these forces allow the treating physician to adjust the alignment of the person&#39;s tibia relative to his or her femur. 
     Now referring to FIG. 1 and FIG. 2 in combination, knee brace 11 may comprise a lateral femoral bar 12, a medial femoral bar 14, a lateral tibia bar 16 and a medial tibia bar 18. The femoral bars are connected by a rigid proximal anterior thigh cuff 20 which extends across the front of the person&#39;s leg L. Anterior thigh cuff 20 is held firmly in place against the person&#39;s leg L by use of an adjustable proximal posterior thigh strap 24, which may be adjusted to insure that the curvature of anterior thigh cuff 20 corresponds to the curvature of the person&#39;s thigh T. The adjustment may be accomplished through known means such as a buckle. Proximal posterior thigh strap 24 may also be used to adjust the amount of force A that anterior thigh cuff 20 exerts on the front of the person&#39;s thigh T. 
     Femoral bars 12 and 14 are also connected by a reinforced adjustable distal posterior thigh strap 26. Distal posterior thigh strap 26 exerts a force B on the back of the person&#39;s thigh T. Distal posterior thigh strap 26 is held firmly in place against the person&#39;s leg by use of a reinforced anterior thigh strap 28, which may be adjusted to insure that the curvature of distal posterior thigh strap 26 corresponds to the curvature of the person&#39;s leg. Anterior thigh strap 28 may also be used to adjust the strength of force B which distal posterior thigh strap 26 exerts on the back of the person&#39;s leg. 
     Lateral tibia bar 16 and medial tibia bar 18 are connected by an adjustable proximal tibia strap 30. Proximal tibia strap 30 exerts a force C on the front of the person&#39;s shin S. 
     Tibia bars 16 and 18 are also connected by a rigid distal tibia cuff 32, which exerts a force D on the back portion of the person&#39;s calf G. The curvature of distal tibia cuff 32 is adjustable by use of an adjustable distal anterior shin strap 34. Distal anterior shin strap 34 may also be used to adjust the strength of force D exerted on the back of the person&#39;s leg L. 
     Lateral femoral bar 12 and lateral tibia bar 16 are joined at the knee joint by a quadricentric hinge joint 36. Likewise, medial femoral bar 14 and medial tibia bar 18 are joined at the knee joint by a quadricentric hinge joint 38 similar to quadricentric hinge joint 36. 
     Referring to FIGS. 7-9, quadricentric hinge joint 36 comprises a femoral drive gear 40, a tibia drive gear 42, an anterior idler gear 44, a posterior idler gear 46, an outer cover 48 and an inner cover 50. Femoral drive gear 40 is an extension of femoral bar 12. Likewise, tibia drive gear 42 is an extension of tibia bar 16. Femoral drive gear 40 intermeshes with anterior idler gear 44. Similarly, tibia drive gear 42 intermeshes with posterior idler gear 46. Knee brace 11 is preferably designed so that idler gears 44 and 46 intermesh at the anatomical center of the knee joint. The gear teeth on the gears do not extend around the entire circumference of the gears, thus creating limits of flexion and extension at the ends of the gear teeth, as is shown in FIG. 8. 
     Anterior idler gear 44 is fixed about an axis of rotation by a pin 52. Likewise, posterior idler gear 46 is fixed about an axis of rotation by a pin 54. On the other hand, femoral drive gear 40 has an axis of rotation which is movable along a generally arcuate path circumscribed by a groove 56 in outer cover 48 and a groove 58 in inner cover 50. In a similar fashion, tibia drive gear 42 has an axis of rotation which is movable along a generally arcuate path circumscribed by a groove 60 in outer cover 48 and a groove 62 in inner cover 50. The axis of rotation of femoral drive gear 40 may be moved and fixed at any point along the generally arcuate path by loosening and tightening a screw 64 and a complementary nut 66. The axis of rotation of tibia drive gear 42 may also be moved and fixed at any point along the generally arcuate path by loosening and tightening a screw 68 and a complementary nut 70. 
     Referring to FIGS. 3-6, in operation the amount of anti-drawering effect desired may be adjusted to fit the individual patient&#39;s needs. Specifically referring to FIG. 3, knee brace 11 may be adjusted to allow for a minimum amount of anti-drawering. By adjusting the position of screws 64 and 68 in grooves 56 and 60, respectively, knee brace 11 may be affixed in a position where the distance &#34;E,&#34; the offset, between the relative position of tibia bar 16 and femoral bar 12, is at a minimum. 
     FIG. 5 shows knee brace 11 adjusted to a position wherein the distance &#34;F,&#34; the offset, between the relative position of the tibia bar 16 and the femoral bar 12, is at a maximum. This position provides the maximum amount of anti-drawering effect. 
     FIG. 4 shows knee brace 11 where screw 68 has been adjusted in grooves 60 and 62 to allow for a 15° extension stop of leg L. Likewise, as shown in FIG. 6, screw 64 may be adjusted in grooves 56 and 58 to allow for a certain amount of extension stop, here about 20°. 
     FIG. 10 shows an alternative construction of a brace 110 and a quadricentric hinge joint 136, wherein an anterior idler gear 144 includes a flexion adjustment spur 172. Likewise, a posterior idler gear 146 includes an extension adjustment spur 175. Flexion adjustment spur 172 engages a flexion adjustment pin 174 which extends through one of a plurality of flexion adjustment apertures 176 in outer cover 148. Flexion adjustment apertures 176 are preferably spaced to allow for adjustment of the amount of allowable flexion at regular intervals, such as about 15° intervals. Similarly, extension adjustment spur 175 engages an extension adjustment pin 178 which extends through one of a plurality of extension adjustment apertures 180 in outer cover 148 and a complementary aperture in the corresponding inner cover (not shown). Again, extension adjustment apertures 180 are spaced to allow for adjustment of the allowable extension at regular intervals. 
     Also shown in FIG. 10, outer femoral drive gear adjustment groove 156, inner femoral drive gear adjustment groove (not shown), outer tibia drive gear adjustment groove 160, and inner tibia drive gear adjustment groove (not shown), may be constructed to comprise finite positions for screws 64 and 68. In this way, the axes of rotation of femoral drive gear 140 and tibia drive gear 142 may be fixed at predetermined finite positions along a generally arcuate path to provide for adjustment of the amount of anti-drawering effect provided by the knee brace 110. 
     Preferably, both outer drive gear adjustment grooves 156 and 160 include a plurality of indents 182 and 184. These indents can fix the axes of drive gears 140 and 142 in specified positions defined by indents 182 and 184. Additionally, the defined indents allow a specified anti-drawer setting to be readily achieved. Similar indents may be provided in both inner drive gear adjustment grooves (not shown). 
     When the brace 110 or 11 is affixed to a person&#39;s leg, the circumference of the various straps will be adjusted to fit the circumference of the person&#39;s leg. For example, brace 11 is affixed by adjusting proximal posterior thigh strap 24, distal anterior thigh strap 28, and distal anterior shin strap 34. This will also adjust the amount of forces A, B, C, and D exerted on the person&#39;s leg L. The amount of anti-drawering effect provided by quadricentric hinges 36 and 38 will then be adjusted. By doing this, injury or aggravation of injury to the anterior cruciate ligament can be prevented by forcing the tibia to remain in a position posterior to the femur. In order to adjust the amount of anti-drawering effect, screw 64 is loosened and positioned along grooves 56 and 58, and then screw 68 is loosened and positioned along grooves 60 and 62. Screws 64 and 68 can be positioned to provide an anti-drawering effect so that the tibia is positioned anywhere from a minimum distance &#34;E&#34; behind the femur, to a maximum distance &#34;F&#34; behind the femur. 
     The amount that the knee joint may be flexed can then be adjusted by positioning flexion adjustment pin 174 in the desired flexion adjustment aperture 176 to provide a predetermined amount of flexion stop. The amount that the knee joint may be extended can be adjusted by positioning the extension adjustment pin 178 in the extension adjustment apertures 180 to provide a predetermined amount of extension.