Abstract:
A joint-supporting device comprises tensile members extending from above the joint to below it, supplementing the tensile characteristics of the joint&#39;s tendons, ligaments, and other structure. The tension members extend between a proximal cuff above the joint to a distal cuff below it, and pass over a pad at the apex of the joint, redirecting the tension members. In order that the cuffs are supported in position so that the tension members can effectively support the joint, they are spaced away from the joint by compression members bearing on proximal and distal bolsters, in turn located positively by the boney structure of the joint. 
     In order that the structure of the invention not interfere overly with the normal function of the joint, the device employs dilatant materials having the property of varying their hardness upon motion. The dilatant material is disposed so as to limit the relative angular velocity of the members of the joint. The dilatant material can be disposed in pad form, arranged to be compressed by the tensile members as the joint is extended, and/or as the core of a composite tensile member, sheathed in a cover woven of high tensile strength filaments or yarns.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Provisional Patent Application Ser. No. 61/321,212, filed Apr. 6, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention herein relates to a device to prevent damage to body joints. The invention is described in an embodiment for prevention of equine lower limb injuries during athletic activity, but is not limited thereto. 
       BACKGROUND OF THE INVENTION 
       [0003]    Horses are large running mammals, typically weighing 450-500 kg (990-1100 lbs), and sometimes much more. They are capable of rapid acceleration and attaining speeds of 20 ms −1  (44 mph). Evolution and careful breeding have left horses, particularly horses bred for racing and other athletic contests (as opposed, for example, to draft horses) with comparatively slender and fragile legs comprised substantially of long bones articulated by several series of compact muscles, tendons, and ligaments. The latter three soft tissue structures (as opposed to bone and cartilage, that is) are principally responsible for enabling locomotion either by providing propulsive forces (e.g., upper hind limb musculature), by storing energy (e.g., in the superficial digital flexor tendon (“SDFT”), by abating vibration (e.g., upper forelimb muscles), and by one or more further mechanisms. 
         [0004]    The horse&#39;s large body size, slender limb structure and occasional need for high speed or rapid acceleration expose the lower limbs, in particular, to risk of injury, either from a single traumatic event such as blunt force trauma or a mis-step of the hoof, or from accumulated micro-damage sustained, for example, during repeated loading of the limb during race training. This can include exposure to too many cycles (frequency) or cycles of excess magnitude (force). 
         [0005]    Injury arising from a single incident can affect any of the limb&#39;s constituent structures, although the more distal (lower limb) components are generally at greater risk by virtue of their proximity to the ground and ground obstructions. Lower limb structures are placed at greater risk by the paucity of enveloping muscle which, higher up the limb, serves as a ‘fleshy’ buffer to external trauma. As one progresses toward the foot, the limb is increasingly composed solely of bone and adjacent tendon and ligament fibers covered by skin. 
         [0006]    Injury resulting from accumulated micro-damage also has preferred sites of incidence. For example, the dorsal (front) surface of the horse&#39;s third metacarpal (cannon) bone or the mid-metacarpal region of the SDFT are locations frequently affected in racing thoroughbreds. In particular, the fetlock joint, at which the cannon bone meets the pastern bone, is extremely vulnerable to injury, often with catastrophic results. The device of the preferred embodiment of the present invention (although as noted the invention is not limited thereto) is directed to reduction of the likelihood of injury to the fetlock, as well as to related anatomical structures that are not part of the fetlock per se, such as the superficial digital flexor tendon and the proximal suspensory ligament. 
         [0007]    As will be appreciated by those of skill in the art, the corresponding joints in fore and rear legs, and the related structures, are called by the same names as a matter of lay use. When one gets scientific, the terminology changes between fore and hind limb. For example, the fetlock of the forelimb—the metacarpo-phalangeal joint, becomes the metatarso-phalangeal joint in the rear limb. The lay terminology is used herein for simplicity. It will be appreciated that the invention is not thus limited. 
         [0008]    It should also be noted that the stiffness of biological, soft tissue structures, including tendons and ligaments, increases at very high rates of deformation. Thus, if the fetlock flexor tendons are stretched very quickly (e.g. due to a misstep or fatigue), they can develop much higher resistive loads than if stretched more slowly, even if the joint is not hyperextended per se. This higher load may lead to injury, especially if it occurs repetitively. 
         [0009]    Once sustained, injury—be it to bone or soft tissue—requires substantial periods of complete rest or much reduced exercise before the animal can return to normal activity, and in some cases the recovery is never complete. Man&#39;s competitive use of horses—which frequently exceeds ‘normal activity’—places additional and frequently unreasonable demands on the healing tissues. As a result, the healing process can be exacerbated and the injury will fail to fully resolve, causing a chronic and sometimes life-long limitation of use. Additionally, while bone is unusual in being able to completely heal itself, soft tissues generally heal with some degree of scar formation which results in added compromise of ambulatory ability, mediated, for example, by pain or adhesions. Scar tissue (unspecialized fibrous tissue in an orientation that is mechanically inferior and/or predisposed to forming adhesions to adjacent structures) is also invariably less strong than undamaged tissue, placing the injured tissue(s) at risk of re-injury. 
         [0010]    Recognizing the substantial cost of limb injury to the animal (distress, reduced ambulation, risk of re-injury, etc.) and society (lost use, veterinary bills, investment loss, etc.), researchers have long sought means for reducing the incidence of lower limb injury. Many approaches have been taken including but by no means limited to alteration of ground surface, modification of training techniques, and use of drugs and nutraceuticals. Others have sought to ameliorate the demands placed on the horse&#39;s locomotor system during competition by reducing the severity of competitive courses and easing schedules. 
         [0011]    Yet another approach has clinicians and researchers attempting to positively impact lower limb biomechanics by limiting extremes of motion, so as to protect both soft and hard tissue structures from being overstressed. The situation is complicated by an incomplete understanding of lower limb mechanics, sometimes resulting in contradictory data findings or theorems. The situation is further exacerbated by the extreme forces occurring within the lower limb during competitive activity—forces which have so far exceeded the ability of the art to positively yet practically prevent extremes of limb motion, for example, by placing the lower limb within protective bandages or boots. 
         [0012]    Referring more specifically to the prior art US patents and applications known to the inventors that are directed to protection of the fetlock, and in related fields, Lewis U.S. Pat. No. 121,880 shows a “Stocking for Horses” that is made of rubber and features stiffening ribs to prevent the stocking from working downwardly as the horse moves. 
         [0013]    Hyman U.S. Pat. No. 3,209,517 shows a leg support for horses made of closed-cell foam and secured by Velcro straps. 
         [0014]    Pomeranz U.S. Pat. No. 4,471,538 is broadly directed to shock-absorbing devices (not specifically for equine applications) employing “rheoprexic fluid” which appears to generically describe a component of a composite “dilatant” material that is used in the preferred embodiment of the invention. 
         [0015]    Boyd U.S. Pat. No. 5,107,827 discloses a protective bandage for the fetlocks of horses that is made of Neoprene synthetic rubber, cut out in a complicated fashion and provided with numerous Velcro strips so that the bandage is secured together at numerous points as it is wrapped around the horse&#39;s leg. 
         [0016]    Hayes et al U.S. Pat. Nos. 5,545,128 and 5,599,290 disclose methods and garments for reducing bone injury due to impact by provision of “shear thickening”, i.e., dilatant, material “in a manner to permit the shunting of impact energy away from the vulnerable [bone] region to the soft tissue region” (claim 1 of the &#39;128 patent). 
         [0017]    Walters et al U.S. Pat. Nos. 5,861,175 and 6,368,613 and application 2002/0077368 disclose a method for treatment of articular disorders by injection of fluorocarbons to replace lost synovial fluid. 
         [0018]    Chambers U.S. Pat. No. 6,883,466 discloses an animal leg wrap comprising a soft, resilient filler material. 
         [0019]    Springs U.S. Pat. No. 6,918,236 shows a breathable equine leg wrap of specific construction. Of interest is the use of phase-change materials for heat removal. 
         [0020]    Allen U.S. Pat. Nos. 7,402,147 and 7,789,844 show body limb movement limiters involving a tether paid off a reel, the movement of which is limited by a dilatant fluid. 
         [0021]    Greenwald et al U.S. Pat. No. 7,837,640 discloses a joint protective device including an engineered textile including fibers that slide freely over one another at low loads but with increased friction at higher loads, so that the device provides increased resistance to motion at higher loads. The device is also to comprise a “strain rate dependent damping material . . . so that stiffness in the engineered textile is a non-linear function of displacement, velocity or acceleration”. See claim 1. This material can be one exhibiting “dilatant non-Newtonian behavior such that material stiffness increases with strain rate”—see col. 6, lines 40-42. 
         [0022]    Bettin et al U.S. Pat. No. 7,896,019 shows control of the viscosity of a dilatant fluid by application of oscillatory stress, e.g., by way of a piezoelectric transducer, so as to tune the material&#39;s characteristics to the application. 
         [0023]    Clement patent application 2004/0055543 shows a protective device for a horse&#39;s leg that comprises a rigid casing and a padded lining. 
         [0024]    White patent application 2006/0107909 shows a tendon and ligament support for the legs of a horse that comprises a gel layer, a dry flex layer, and a Lycra outer layer. 
         [0025]    Lindley patent application 2006/0231045 shows a horse leg protector comprises an impact-absorbing inner layer of rubber or foam and a rigid outer housing. Ventilating passages are provided throughout. 
         [0026]    Heid et al patent applications 2009/0094949 and 2009/0288377 show equine support boots including sling straps providing support to the fetlock. 
         [0027]    Farrow et al patent application 2010/0056973 shows a therapeutic compression device to fit around a limb of a patient. 
         [0028]    Green et al patent application 2010/0132099 shows “energy absorbing blends” where a dilatant fluid is entrapped in a solid matrix of a polymer material. It appears possible that this application is directed to a material known to the art as “d3o”. This material is employed in the preferred embodiment of the invention, as discussed in detail below. 
         [0029]    Husain patent application 2010/0192290 shows a neck protection collar. 
         [0030]    Lutz patent application 2011/0034848 shows a compression bandage for horses involving specific closures. 
         [0031]    Eggeman U.S. Pat. No. 2,512,925 shows a skid boot for horses, designed to protect the fetlock from contact. 
         [0032]    Dever U.S. Pat. No. 2,937,487 shows a protective leg sheath for horses. 
         [0033]    Schubert U.S. Pat. No. 3,193,984 shows an inflatable leg sheath for horses. 
         [0034]    Porner U.S. Pat. No. 4,099,269 shows a leg sheath for horses with air pockets built into it for impact resistance. 
         [0035]    Shapiro U.S. Pat. No. 4,538,602 shows a spirally-wrapped leg protector for horses. 
         [0036]    Scott U.S. Pat. No. 5,115,627 shows a horse boot made up of several specified materials. 
         [0037]    Gnegy U.S. Pat. No. 5,152,285 shows a horse boot with pockets for insertion of hot or cold packs to treat the horse&#39;s leg. 
         [0038]    Amato U.S. Pat. No. 5,363,632 shows a boot with an inflatable bladder to support the underside of the fetlock. 
         [0039]    Vogt U.S. Pat. No. 5,579,627 shows a support wrap for a horse&#39;s leg, including a fetlock-supporting sling strap. 
         [0040]    Vogt U.S. Pat. No. 5,816,032 is a continuation-in-part of the above and claims a tendon support member. 
         [0041]    Wilson U.S. Pat. No. 5,910,126 shows a support wrap for a horse&#39;s leg. 
         [0042]    Farley U.S. Pat. No. 5,441,015 discloses a method for treatment of an injured horse&#39;s leg involving a split rigid cast-type device. 
         [0043]    Daly U.S. Pat. No. 7,559,910 discloses a device for preventing over-articulation of the fetlock including an articulated joint including a “pivot arrangement”. 
         [0044]    Rogers U.S. Pat. No. 6,151,873 shows a legging for horses including fly netting. 
         [0045]    Bard U.S. Pat. No. 6,553,994 shows an orthopedic support molded so as to provide ventilation channels and passages. 
         [0046]    Finally, Detty U.S. Pat. No. 5,871,458 shows an equine ankle brace including a cup-like member for fitting over the fetlock. 
         [0047]    None of the prior art devices shown in the patents and applications mentioned above has been fully successful. As will be apparent, most of these are simply intended to protect the horse&#39;s legs from direct impact damage, which, while doubtless beneficial, is insufficient to protect against damage due to repetitive loading, overexertion, hyperextension of the joint, and the like. These damage mechanisms are discussed more fully below. Of the art discussed above, only the device shown in the Daly patent is explicitly intended to prevent hyperextension by mechanical means, and this device would appear to interfere with the normal motion of the horse. 
         [0048]    More specifically, it is an object of the invention to provide a device that provides actual mechanical support to the fetlock, in essence providing additional support to the articular interface, joint capsule, tendons, ligaments, and other periarticular structures without unduly interfering with the normal motion of the joint. Still more particularly, it is desired to provide a device that comes into play primarily as the horse fatigues, for example, towards the end of a race, when it is most vulnerable to damage. Several different and complementary ways in which this can be accomplished are disclosed herein. 
         [0049]    Referring now to the typical damage mechanisms experienced by horses, injuries resulting from accumulated micro-damage, which from a clinical perspective are equally if not more prevalent than injuries from a single traumatic event, have predilection sites, which are in turn linked to specific athletic activities. For example, the SDFT in the mid to proximal metacarpal region of the front limb is the most frequently injured locus in racing thoroughbreds while the suspensory ligament (SL) is more frequently injured in racing standardbreds. Deep digital flexor tendon (DDFT) injury is most commonly encountered in jumping horses while hind limb proximal suspensory injury is more common in dressage horses. Similarly, bone and cartilage injury secondary to accumulated microdamage have predilection sites, for example, the proximal-dorsal aspect of the first phalanx within the fetlock joint. In each case, the likelihood of injury appears to increase with fetlock hyperextension. 
         [0050]    The specific device according to the present invention that is described in detail herein is a protective device to be worn by the horse during exercise which will eliminate or ameliorate motion-related injuries which occur between the distal-most aspect of the carpus (knee) and the coronary band of the hoof. As noted, however, the invention is not limited to this specific embodiment, nor to the fetlock, nor to devices to be worn only by horses, nor only by animals. The device may also be usefully worn during recovery from injury. 
         [0051]    Referring now specifically to the equine fetlock, within that region lie three particularly ‘at-risk’ principal soft tissue support structures (the SDFT, the DDFT and the SL) on the palmar/plantar (back) aspect of the bones, which work in unison with the limb&#39;s many other soft tissue components (e.g., the joint capsule, annular ligaments, and extensor tendons) to effect locomotion. 
         [0052]    To best understand how the current invention will prevent injury to the SDFT, DDFT and SL, their anatomical and functional characteristics will be reviewed. 
         [0053]    Collectively, the SDFT, DDFT and SL are substantially modified muscles, possessing short muscle fibers, a pennate structure (that is, comprising a muscle in which fibers extend obliquely from either side of a central tendon) and significant passive elastic properties. The SL, an evolutionary modification of the interosseus muscle, is completely fibrous with only remnants of muscle fibers to be found. The superficial digital flexor muscle (proximal to but contiguous with the SDFT) is also almost completely fibrous in the hind limb and in the forelimb has short muscle fibers of 2-6 mm length. These are primarily ‘slow’ muscle fibers best suited to supportive rather than propulsive functions by means of constant or extended length activity. The deep digital flexor muscle has three heads or muscle compartments (humeral, radial and ulnar) composed of varying numbers of short, intermediate, and long muscle fibers. It combines slow muscle fibers with a substantial population of ‘fast’ fibers which are better suited to propulsive functions. The SDFT and DDFT muscles are protected by accessory ligaments that link the tendon, distal to the muscle belly, to bone, effectively protecting the muscle and limiting the overall stretch (strain) that can be effected through the structure. 
         [0054]    Once a horse has expended substantial energy in accelerating to a constant speed, a primary goal is to maintain that speed while minimizing the subsequent use of energy. The SDFT and DDFT have a major role in this process wherein their largely tendinous composition allows them to store and then return elastic energy, in the manner of a spring being stretched to store energy and then released to expend the stored energy. The SDFT and DDFT do this with remarkable efficiency, returning about 93% of the energy stored, much of the rest being dissipated as heat. 
         [0055]    During the energy storage process at the time of weight-bearing, the tendons are substantially stretched. Under normal circumstances, the amount of stretch which they sustain (which may be as much as 8-12% of the resting length) remains within physiologically normal limits, allowing the tendons to recover their original form without injury. This elastic increase in length is the very means by which energy is efficiently stored in the same way that a spring stores energy by stretching, as above. 
         [0056]    However, during extremes of activity the tendon or ligament can be stretched so much, particularly as the horse fatigues, that micro- and sometimes macro-damage occurs. Progressive degenerative changes within the tendon or ligament may precede and predispose to this injury. Given sufficient recovery time, micro-damage can often be repaired. If not, micro-damage can accumulate leading to macro-damage. The dividing line between the tendon strains (that is, the amount by which it is stretched) required to achieve efficient elastic energy storage and those which result in disruption of the tendon microstructure is very fine. If disruption does occur but is limited to a very small volume, the damage can be accommodated without compromising function, but when the injury is more widespread, clinical unsoundness can result. 
         [0057]    At rest the SL is fully capable of passively resisting change in fetlock angle. At speed, however, the SDFT and DDFT provide additional support for the fetlock, countering the substantial weight-bearing forces, which tend to hyper-extend the joint. A controlled increase in joint extension is preferred. Towards extremes of exertion, however, the fast muscle fibers of the DDFT become fatigued and, with the passive SL limited in its ability to provide additional support as determined by its architecture, the SDFT is increasingly responsible for countering hyper-extension of the fetlock. Eventually, the SDFT can also be overloaded, the joint progresses to hyperextension, and damage ensues. 
         [0058]    The SDFT and DDFT have additional roles, including the damping of the high-frequency (30-50 Hz) vibrations that occur at foot impact and which otherwise would cause increased onset of structural fatigue damage within bone and soft tissue, by increasing the number of loading cycles and the loading rate experienced by the limb. 
         [0059]    Other comments regarding modes of injury include the following: 
         [0060]    In addition to injury of the principle flexor soft-tissue structures (SL, SDFT and DDFT), fetlock hyperextension can also cause injury of hard tissue structures of the lower limb. For example, with fetlock hyperextension, the increasing forces exerted on the cartilage and underlying bone of the dorsal peripheral margin of the fetlock joint can cause microfracture. If given insufficient time to heal, accumulated microdamage eventually results in clinical injury caused, for example, by cartilage cracking and associated osteoarthritis or even bone fracture. 
         [0061]    While the etiology (i.e., cause) of some SDFT, DDFT, and SL injuries are better understood than others, the final common pathway is one of mechanical disruption of collagen, the principal component of tendon and ligament, at a microscopic and sometimes macroscopic level. Concurrent with the disruption of the individual collagen fibers or bundles of fibers is local bleeding and resultant inflammation. Clinically this is characterized by pain, heat and swelling. The blood clot is subsequently resorbed and/or replaced by new collagen fibers laid down in a new extracellular matrix (bed), initially in random configuration. Finally, the collagen undergoes remodeling and is realigned to best offset the loading forces extant at that location. The process in its entirety takes up to one year to complete. As stated previously, the scar tissue thus formed is generally inferior in its mechanical qualities to uninjured tendon, predisposing the limb to reinjury. 
         [0062]    Which of the support structures of the limb that is injured in any particular case, and where the injury might occur along its length, is predicated on multiple factors including but not limited to blood supply, pre-existing injury, degenerative disease, point of focal loading, activity type and quite possibly a series of mechanical parameters with pertinence to joint dynamics as well as the visco-elastic nature of tendons and ligaments. 
         [0063]    It will be apparent that to the extent the fetlock joint can be prevented from being hyperextended, loading the support structures beyond their normal elastic limits, injury can be limited. Intuitively, limiting extremes of fetlock motion would appear to be most easily achieved by physically restricting the upper limits of flexion and particularly extension in the longitudinal axis (forward and backward). Various types of boot and bandage have been studied with this goal in mind in previous reports. The data is often contradictory. Crawford et al. (1990a,b) found that different bandaging techniques and materials significantly influenced the energy absorption capacity of these bandages. Keegan et al. (1992) showed that support bandages did not alter mean strain in the suspensory ligaments while the horses were standing or walking. Using a tensile testing machine, Balch et al. (1998) demonstrated in an in vitro setting that certain types of support boots could absorb up to 26% of total force. However, in a similar set-up, Smith et al. (2002) found no difference between limbs with and without neoprene support boots. Kicker et al (2004) found some support boots to provide a significant reduction in total joint extension of up to 1.44 degrees at the trot, the practical implications of which have yet to be determined. Ramon et al (2007) found that athletic taping of the fetlock did not alter the kinematics of the forelimb during stance, but does limit flexion of the fetlock by approximately 5 degrees during the swing phase. A decreased peak vertical force also resulted, quite possibly due to an increased proprioceptive effect. Finally, Swanstrom (2005) shows soft tissue strain with fetlock angle for SDFT, DDFT and SL. The inventors estimate from this data that limiting the fetlock extension by 8 degrees is required to achieve a 10% reduction in extension of the SDFT, DDFT, and SL. 
         [0064]    Similarly, it will be self-apparent that limiting the angular velocity of the joint will be useful in preventing injury. 
         [0065]    The objects of the invention are therefore to address the following biomechanical protection strategies:
       1. Limitation of longitudinal or mediolateral ultimate joint flexion or extension.   2. Limitation of longitudinal or mediolateral rate of joint flexion or extension.   3. Limitation of flexor apparatus ultimate load.   4. Limitation of flexor apparatus load rate.   5. Re-distribution of ground reaction forces away from bone to more superficial soft tissues.   6. Dissipation of concussive forces.   7. Dissipation of vibratory impact forces.   8. Cooling effect.       
 
         [0074]    Furthermore, it is important that these be accomplished without adversely affecting the horse&#39;s proprioceptive ability, and while interfering with the horse&#39;s normal motion as minmally as possible. 
       SUMMARY OF THE INVENTION 
       [0075]    According to the invention, a fetlock-supporting device is provided comprising tensile members extending from above the joint to below it, which serve to add additional tensile capability, supplementing the tensile characteristics of the SDFT, DDFT, and SL. The tensile members extend between a proximal cuff above the fetlock to a distal cuff at the hoof, and pass over a fetlock pad at the rear of the joint, redirecting the tensile members. In order that the cuffs are supported in position, so that the tensile members can effectively support the joint, the cuffs are spaced away from the joint by compression members bearing on proximal and distal bolsters, in turn located positively by the boney structure of the fetlock. In this way the tensile members can effectively support the fetlock without the need for constricting cuffs, which would be painful and tend to reduce blood circulation if made tight enough to be effective as anchors for tension members. 
         [0076]    As mentioned, it is important that the structure of the invention not interfere overly with the normal function of the fetlock, but provide support when the horse fatigues and is most susceptible to injury of any or all of the SDFT, DDFT, and SL, as well as the bone and cartilage structures of the joint. There are several ways in which this can be accomplished, all of which are considered to be within the scope of the invention. One comprises use of dilatant materials, which have the property (as discussed briefly above) of varying their hardness upon motion. More specifically, there is now available a material known as “d3o”, which comprises a dilatant fluid confined in a matrix of a polymer, so that the dilatant fluid can be disposed as needed. In the present context, the dilatant material is disposed so as to prevent further motion if the angular motion of the fetlock becomes too rapid, or if its range of motion becomes close to hyperextension, either of would tend to occur during transient instabilities or missteps or as the horse fatigues. The dilatant material can be disposed as the core of a composite tension member, sheathed in a cover woven of high tensile strength filaments or yarns. 
         [0077]    In a further embodiment, the dilatant material can be controlled responsive to an external signal. For example, the range and rate of angular rotation of the fetlock can be monitored as the horse exercises, for example, in a race, and compared to reference values for safe exercise determined during testing. Where the rate and/or range of fetlock angular rotation approach unsafe levels as the horse becomes fatigued during exercise, the dilatant material can be controlled to become stiffer (possibly using the piezoelectric technique disclosed in the Bettin et al patent discussed above) and thereby resist hyperextension of the joint, to avoid injury. 
         [0078]    Further aspects of the invention will become apparent from the detailed discussion below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0079]    The invention will be better understood by reference to the accompanying drawings, in which: 
           [0080]      FIG. 1  shows a graph of fetlock angle versus strain in the SL, DDF, and SDF structures discussed above; 
           [0081]      FIG. 2  shows schematically the way in which the device of the invention is intended to increase the natural spring constant provided by the stretch in the SL, DDF, and SDF structures; 
           [0082]      FIG. 3  shows the fetlock moment in Newton-meters as a function of fetlock angle, and illustrates the manner in which the device of the invention is to operate to limit the maximum extension of the fetlock; 
           [0083]      FIG. 4  shows the external features of the device, in a side view; 
           [0084]      FIGS. 5 and 6  show, respectively, side and rear views of the device of the invention illustrating key structural components thereof; 
           [0085]      FIG. 7  shows one way in which tensile members comprised by the device of the invention can be affixed to cuffs thereof, and  FIG. 8  shows a detail thereof; 
           [0086]      FIGS. 9 and 10  show respectively elevation and side views of a ratchet-and-pawl mechanism for adjusting the tension in the tensile members; 
           [0087]      FIG. 11  shows a more detailed rear view of the device of the invention; 
           [0088]      FIG. 12  shows another means for affixing the tensile members to the cuffs; 
           [0089]      FIG. 13  shows a detailed side view of a fetlock pad comprised by the device of the invention; 
           [0090]      FIG. 13A  shows a cross-section along the line  13 A- 13 A of  FIG. 13 ; 
           [0091]      FIGS. 14 and 15  show, respectively, side and rear views of a goniometer to be affixed to the leg of the horse for measuring fetlock angle as the horse moves; and 
           [0092]      FIG. 16  shows a composite tensile member. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0093]      FIG. 1  shows the strain experienced by the SL, DDF and SDF as the fetlock is flexed during the weight bearing phase of gait. As above, the available data indicates that an eight degree reduction in fetlock angle is required to achieve a ten percent reduction in peak tendon strain. Achieving this eight degree reduction in fetlock extension is accordingly one of the desired design goals of the invention. Along with this reduction in peak fetlock angle, the peak angular velocity will be reduced accordingly. The peak angle will be reduced by adding a parallel load path having the capability of storing and releasing energy, increasing the “springiness” of the fetlock, thereby increasing the overall stiffness of the fetlock joint. Specifically, fetlock stiffness will be increased toward the end of its extension.  FIG. 2  shows the approach schematically: The device adds another spring structure in parallel with the SL, DDF and SDF, increasing the effective spring constant experienced by the fetlock, and thereby limiting its maximum extension in response to a given force applied. The device function can be fine tuned in order to control the device stiffness, in particular to achieve non-linear increase in resistance to motion as the joint becomes fully-extended and to angular velocity. Use of both elastic and viscoelastic elements will allow a close match to the normal fetlock stiffness, that is, as exhibited without a device. 
         [0094]      FIG. 3  shows graphs of fetlock maximum angle versus the moment (i.e., torque applied). The curves marked A and A′ show measured data for fetlocks with no additional device provided; as noted above, in this particular case the joint can operate up to about 56 degrees. In order to limit damage, it is desired as above to limit this to about 48 degrees. This absolute angle may vary from animal to animal, of course, and the individual examples of the device of the invention will be able to accommodate changes to this preferred angle. The curve marked B shows performance with linear increase in stiffness with angle and curve C shows performance with a non-linear increase in stiffness. Both devices achieve the desired eight degree reduction in fetlock extension, but the non-linear stiffness device of curve C will allow more normal motion until the fetlock reaches hyperextension. Accordingly, a primary goal of the present invention is to provide non-linear increase in additional tension applied to the joint, so as to allow normal fetlock motion insofar as possible while restricting pathologic hyperextension, and likewise to limit the maximum rate of joint rotation without unduly restricting motion. 
         [0095]    Another goal of the present invention is to protect the fetlock region from impact damage, to provide cooling and moisture wicking insofar as possible, to damp vibration, and to provide abrasion resistance to the fetlock.  FIG. 4  shows the outer structure of the device according to the invention, which provides these features. The structural elements that are directed to the other objects of the invention mentioned above are disposed within the outer structure of  FIG. 4 , or between the inner and outer sleeves thereof, and are discussed more fully below. 
         [0096]    Thus, as illustrated in  FIG. 4 , the device of the invention comprises an inner sleeve  10  made of a moisture-wicking breathable material (such as that known as Coolmax, or possibly that known as X-static) extending the length of the device, which is shown in use, that is, installed over a horse&#39;s fetlock. The lower end of inner sleeve  10  is terminated by an elastomeric seal  12 , sealing sleeve  10  to the upper portion of the horse&#39;s hoof H, to prevent entry of dirt, sand, and moisture. An outer sleeve  14  is also provided of a breathable, lightweight, durable elastic material (such as that known as Drytex). A protective pad  16  of a viscoelastic material (such as that known as Sorbothane) is provided on the forward portion of the cannon bone, for vibration damping. Pad  16  can be secured to either the inner sleeve  10  or outer sleeve  14 . Similarly, a protective member of abrasion resistant textile  17  can be provided on the rear of the fetlock, to protect the joint in case of “rundown”, where the fetlock is hyperextended so far that the rear of the fetlock contacts the ground. 
         [0097]      FIGS. 5 and 6  show the principal components of the device of the invention which serve to strengthen and stiffen the fetlock joint. These include a proximal cuff  20 , a distal cuff  22 , a proximal fetlock bolster  24 , a distal fetlock bolster  26 , a fetlock pad  28  over the proximal sesamoid bones, proximal and distal compression members  30  and  32 , and tensile members  34  connecting the proximal and distal cuffs  20  and  22  and passing behind the fetlock pad  28 . 
         [0098]    As mentioned above, one of the primary objectives of the structure of  FIGS. 5 and 6  is to limit the degree to which the fetlock joint can be extended, which occurs in the direction of arrow D in  FIG. 5 ; that is, as the horse runs, and the hoof hits the ground, the fetlock rotates in the direction of arrow D, stretching the tendons, ligaments, and muscles. When the collective strength of the muscles and tendons equal and then exceed the opposing forces, they pull the fetlock back toward the static position shown in  FIG. 5 . In this way the horse&#39;s leg exerts force on the ground, propelling it forward. 
         [0099]    As mentioned above, hyperextension of the fetlock is to be prevented by the structure shown. This requires that the tensile members  34  carry tension from the distal cuff  22  to the proximal cuff  20 . It will be apparent that in order to do so the cuffs must be retained in their respective positions. It would not be desirable to make the cuffs fit so tightly that friction alone would hold them in place, as this would require so much clamping pressure as to be very uncomfortable for the horse and impede blood circulation. 
         [0100]    Therefore, according to an important aspect of the invention, the proximal and distal cuffs  20  and  22  are retained in position by respective compression structures  30  and  32  bearing against respective bolsters  24  and  26 . Bolsters  24  and  26  are in turn retained in position by bearing against the boney anatomy of the fetlock, which is sufficiently non-uniformly cylindrical that properly-fitted bolsters will not tend to be drawn toward one another by tension in the tensile members  34 . The cuffs, compression structures, and bolsters can be adhesively bonded to one another, e.g., in an initial fitting of a particular device to a particular horse, or the assembly can be provided in a variety of sizes to suit different horses. 
         [0101]    Thus, as the horse runs, and the fetlock is repeatedly extended and relaxed, the tensile members  34  will be repeatedly tensioned and released. (The degree to which tensile members  34  are tensioned will depend on the degree they are tensioned at installation of the device; this can be made adjustable in a manner discussed below.) Tension from the tensile members  34  is taken up by the cuffs, which are accordingly urged toward one another. The relative motion of the cuffs is resisted by the compression structures, in turn supported by the bolsters, in turn spaced apart by the boney structure of the fetlock. 
         [0102]    The tensile members  34  are arranged so as to pass over the rear of the fetlock pad  28 . This may comprise a molded thermoplastic saddle against which the tensile members  34  bear, with a resilient or dilatant member between the saddle and the skin over the fetlock. Presently preferred structures of the fetlock pad is shown in detail by  FIG. 10  and  FIGS. 13 and 13A . In this way the direction of the tension in the tensile members  34  is redirected around the rear of the fetlock, from the proximal cuff  20  to the distal cuff  22 , generally parallel to the orientation of the tendons and ligaments. 
         [0103]      FIGS. 7 and 8  show one way in which the tensile members  34  can be secured to the proximal and distal cuffs  20  and  22  in order that the tension in tensile members  34  can be transferred to the anatomy of the horse and thus effectively help to support the fetlock. The tensile members  34  comprise elongated filaments, strands or yarns of light, flexible material of high tensile strength, such as a liquid crystal polymer material, one example of which is commercially available as Vectran.  FIG. 16  shows a preferred construction of these tensile members, also incorporating dilatant material. The high point loads occasioned by the attachment of such slender members to a cuff can be accommodated as illustrated. 
         [0104]    The cuffs (proximal cuff  20  in the illustration) will comprise an outer shell  40  of a relatively hard material lined with a pad  42  of a resilient material so as not to irritate the horse&#39;s skin. A molded thermoplastic outer shell  40  lined with a pad  42  of a material such as that sold as Sorbothane may suffice. The constraint is that the outer shell  40  of the cuff  20  must be C-shaped and have sufficient flexibility to be able to be temporarily deformed and slipped over the horse&#39;s leg from the front or over the hoof, from below. The two ends of the “C” can then be affixed to one another by a buckle, snap fitting, “Velcro” or the like. See  FIG. 11 . The structure of distal cuff  22  is similar. The structure of the bolsters will be generally similar, although these of course will not require terminations for tensile members. The compression structures will likewise comprise an outer shell molded of a relatively hard material, lined with a resilient pad. 
         [0105]    As shown, the outer shell  40  may be molded to comprise one or more recesses  44  with surrounding lips  46  to retain a ball  48  crimped on to the end of a strand  50  of the tensile member  34 . A generally tubular grommet or interface member  49  ( FIG. 8 ) of resilient material, possibly having metallic washers (not shown) on either side, may be interposed between the shell and ball; as tension is applied to the tensile member  34 , this grommet  49  will compress, further tensioning the tensile member  34  and restricting overall movement and angular velocity of the fetlock. Grommet  49  may also be formed of dilatant material, hardening as it is compressed by tension applied by the tensile member  34 , so as to increase tension in the tensile members  34  in a non-linear fashion. 
         [0106]    Numerous other means of terminating the strands  50  of the tensile members  34  to the cuffs are within the skill of the art. For example, numerous smaller strands of the tensile material could be wrapped in a separate operation around metallic end fittings, so that the individual strands do not themselves experience excessive tension; the end fitting might then be riveted to the outer shell  40  of the cuff.  FIGS. 11 and 12  show an alternative where the tensile members are wrapped around the cuffs, largely avoiding the problem of terminating the tensile members at the cuffs. Various specific orientations of the tensile members are also within the scope of the invention, as illustrated. 
         [0107]      FIGS. 9 and 10  show one possible method of adjustment of the tension of the tension members between the proximal and distal cuffs. Here, the fetlock pad assembly  28  comprises a member  56  of material chosen to harden when subjected to compression loads, such as the material known as d3o, which, as above, comprises a dilatant polymer confined in a matrix of a closed-cell polymer. This material (which may be encased in a further sheath (not shown) of a friction-reducing material (e.g., that sold as Spandex)) contacts the horse&#39;s fetlock. Affixed to this member  56  is a molded plastic saddle member  58 . An internally-toothed gear  62  is molded integrally with saddle member  58 . A take-up spool  60  is pivoted to saddle member  58  at  64 . A pawl  66  is spring-biased outwardly with respect to, and is carried by take-up spool  60 , so as to engage the teeth of gear  62 . Tension members are wound around the take-up spool  60  from opposite sides, as shown. 
         [0108]    Thus, when spool  60  is rotated in the counter-clockwise direction (in the view of  FIG. 9 ), the tension members are drawn onto spool  60 , tightening the tension therein. The pawl  66  interacts with the gear  62  to retain the desired tension. This can be done upon initial fitting of the device to the horse, or upon each use. Other methods of adjusting the tension of the tensile members are within the skill of the art. 
         [0109]      FIG. 11  shows a rear view of one preferred embodiment of the device of the invention, providing additional details. As previously, the tensile members  34  connect the proximal cuff  20  to the distal cuff  22 , while the compression members  30  and  32  space the cuffs from the respective bolsters  24  and  26 . In this embodiment, as shown further by  FIG. 12 , the tensile members  34  are wrapped around the cuffs, avoiding the necessity of fixing points as described above, and pass through channels or tunnels formed on the rear of the fetlock pad assembly  28 . As indicated at  70 , the cuffs and bolsters can be secured in place over the horse&#39;s leg by buckles, snaps, Velcro, or the like. With the tensile members slack, the cuffs and bolsters will be “opened” (as one spreads open a tight fitting shoe to insert one&#39;s foot), allowing the device to be slipped over the hoof and slid up the leg into position. 
         [0110]      FIGS. 13 and 13A  show further details of the fetlock pad assembly  28 , and illustrates an embodiment differing somewhat from that of  FIG. 10 . As illustrated, the fetlock pad assembly  28  may comprise a saddle member  29  molded of a hard plastic material, having grooves  29   a  or tunnels (not shown) molded therein to receive the tensile members  34 . A dilatant pad  31  is affixed to saddle member  29 , e.g. by cooperating hook structures (not shown). Dilatant pad  31  may comprises a deformable container  31   a  containing a quantity of the dilatant material, e.g., the d3o material discussed previously. As shown, the dilatant pad  31  may be of generally toroidal or “donut” shape, to better fit over the fetlock, and specifically to fit over and provide support to the sesamoid bones. 
         [0111]    As the horse runs, as noted, the tensile members  34  will repetitively become increasingly taut, and will then be relaxed. As the tension in tensile member  34  increases, the pad member  56  (or  31 , in the embodiment of  FIGS. 13 and 13A ) will be under increasingly more compression. Due to the properties of the dilatant material, as the pad  56  (or  31 ) is increasingly rapidly compressed, it effectively stiffens. Similarly, if grommet  49  is provided and made of the d3o material, it will likewise repetitively become harder upon each stride, as the horse runs. Accordingly, as the horse runs and becomes fatigued, so that its own tendons stretch, and the fetlock becomes more extended, the d3o material will be increasingly compressed, and will become stiffer. 
         [0112]    In this way the device of the invention provides increasing tensile support to the fetlock as the horse becomes fatigued, providing more support against hyperextension of the fetlock as the horse fatigues. Providing the fetlock pad with the dilatant material as described would also serve to limit the maximum angular velocity of the fetlock; as the dilatant material is deformed by compression of the tension members, it stiffens, limiting the angular velocity of the fetlock. Further, the structure shown will provide additional support to the fetlock in a non-linear fashion; that is, while the horse&#39;s fetlock motion is normal, the device of the invention will interfere minimally with its normal motion, but as the horse fatigues, the device will exert more and more resistance to limit both the range of motion and the angular velocity of the joint, preventing injury from both hyperextension and excessive angular velocity. 
         [0113]    Another method of limiting the angular velocity of the fetlock which seems very promising is to provide the dilatant material in a polymer matrix as the core of a small-diameter composite tension member, with this core being sheathed in a braided cover made of yarns of high-tensile strength flexible material, such as the Vectran liquid crystal polymer discussed above. This composite tension member could be used as the tensile members  34  of the device of the invention, as discussed above. 
         [0114]    For example, as shown schematically in  FIG. 16 , the dilatant material  90  could be contained in a series of small tubular compartments  92  formed by crimping a tube  94  of a polymer under conditions of heat and pressure so as to seal the compartments. This assembly could then be sheathed in a braided cover  96  woven of a high-tensile yarn, e.g., of the Vectran material discussed above. As tensile members  34  of this construction are placed under increasing tension as the horse runs, the braided cover  96  would be reduced in diameter, compressing the dilatant material  90  and stiffening the tensile member. Likewise, as the tensile members  34  bend over the back of the fetlock pad, the dilatant material will be further stiffened. This stiffening of the tensile members, particularly as they pass over the back of the fetlock pad, would prevent the fetlock from excessive angular velocity. 
         [0115]      FIGS. 14 and 15  show a goniometer, that is, a device for measuring angles, which can be attached to the horse&#39;s leg for measuring fetlock extension. The goniometer can be used in a first stage for determining the horse&#39; normal range of motion (ROM), and, in one possible embodiment, for limiting the ROM to prevent injury. The goniometer comprises first and second arms,  80  and  82  respectively, that are attached to the cannon and pastern part of the leg, that is, above and below the fetlock. Arms  80  and  82  are joined at a pivot point  84  arranged to be aligned with the joint of the fetlock. A potentiometer  86  is arranged to have its body fixed to one of arms  80  and  82  and its shaft to the other, so that as the horse moves the resistance of the potentiometer  86  varies as the angle of the fetlock. The potentiometer is connected to a data logger (not shown) by wire  88 , so as to collect fetlock-extension data as the horse exercises. 
         [0116]    For example, the horse can be exercised on a treadmill to determine its normal ROM. This data can be used to optimize the tension in the tensile members to limit the ROM. In a further embodiment, the goniometer can be worn by the horse when exercising and normal ROM data compared with ROM data collected during exercise and used to limit the ROM accordingly as the horse fatigues, by altering the dynamic characteristics of the device and reduce the chance of injury. This can be accomplished by stiffening the dilatant material in response to an external signal, as suggested by the Bettin et al patent, discussed above. This could possibly also be combined with the “engineered textiles” of the Greenberg et al patent discussed above; these use a “viscoelastic” material that comprises some degree of “springiness” in that it can store and release energy, as a spring does. 
         [0117]    While the invention has been disclosed in terms of preventing injury to the equine fetlock, the principles of the invention can be used by those of skill in the art to prevent injury to other joints, as well as those of other animals and of humans. It will be appreciated that the structure of the device can vary somewhat in such differing uses; for example, in some case it may be possible to dispense with the compression structures, so that the cuffs bear directly on the bolsters, and indeed in some cases the function of the cuffs and bolsters may be performed by unitary proximal and distal members on either side of the joint to be protected. Further, the distal cuff could be attached to the hoof, eliminating the distal bolster and compression structure; indeed the tensile members could be attached to the hoof, eliminating the distal cuff as well. 
         [0118]    It should also be recognized that while the invention has been disclosed in an embodiment that both limits the maximum extension of the fetlock and limits its maximum angular velocity, which is anticipated to be the preferred embodiment, there may be cases wherein only one of these functions is desired. 
         [0119]    Accordingly, while a preferred embodiment of the invention has been disclosed in detail, the invention is not to be limited thereto but only by the following claims.