Surgical management of specific equine lameness disorders (Proceedings)

Most cases of equine lameness are treated with a combination of medical and other non-surgical methods. However, there are a few specific cases in which surgical management is the treatment of choice. The surgical procedures that will be discussed in this paper include arthroscopy/tenoscopy/bursoscopy, palmar digital neurectomy, plantar fasciotomy with or without neurectomy of the deep branch of the lateral plantar nerve, pastern arthrodesis, and tarsal arthrodesis.

Arthroscopy involves the surgical exploration of a joint using a small telescope enabling a thorough examination of the joint without the need for a large surgical approach. Tenoscopy/bursoscopy involves the surgical exploration of tendon sheaths and bursae using the same surgical method. Using a technique called triangulation, additional small portals can be made that allow for surgical instruments to be placed within the synovial structure. The most common condition for the utilization of arthroscopy is for fragment removal. Fragments in equine joints arise from 2 main sources: traumatic injury and osteochodritis dissecans. The most common instances of traumatically induced osteochondral chip fragmentation are in the carpal and fetlock joints. Although chip fractures have been frequently considered acute injuries and recognized with acute clinical signs, it has been suggested that they are a secondary complication affecting joint margins previously altered by subchondral bone disease. Exercise causes microdamage within the joint which can lead to microcracks, more diffuse microdamage, and subchondral bone sclerosis. Therefore the ÒacuteÓ chip fracture typically occurs through this abnormal bone.

When accompanied by lameness, joint effusion, and pain upon flexion, the management of intra-articular joint fragments is relatively straight forward. These types of cases are most common in horses that perform at speed (race horses). In these cases, arthroscopic fragment removal and joint exploration is indicated. If not treated in a timely fashion, the inflammatory mediators that are released from the damaged bone and cartilage can lead to further cartilage damage, chronic proliferative synovitis, and joint capsule fibrosis leading to a decreased range of motion. When the lameness and effusion are significant, usually there is damage to the joint in addition to the fragmentation seen radiographically. Therefore, a thorough exploration of the joint should be performed.

In many cases of intra-articular fragmentation, the management may not be straight forward. In my practice, there are many sound horses with intra-articular chip fragments that are found incidentally on pre-purchase examinations or in lameness examinations where the lameness is being caused by a different problem. Sometimes it is hard to recommend surgery and the accompanying down time in an otherwise sound horse that has been competing regularly. Decision making depends on the specific joint involved or the location of the fragment. I find that chip fragments in low motion joints, such as the pastern joint, rarely cause lameness problems and therefore are usually left in place, unless diagnostic intra-articular anesthesia confirms that the lameness is originating from the fragment. In high motion joints, such as the fetlock joint, I feel that location within the joint is particularly important, in addition to the discipline of the horse. I recommend that dorsal articular chip fragments within the fetlock joint be removed, even in the absence of clinical disease. These fragments over time can cause articular surface damage to the adjacent metacarpal condyle leading to osteoarthritis in the athletic horse. They also serve as point to decline purchase when found on a pre-purchase examination. Despite this recommendation, I have seen several horses with dorsal fetlock osteochondral fragments that have maintained athletic careers for years in the absence of clinical lameness. This is particularly true in horses that perform at low speeds (western performance horse). Palmar or plantar osteochondral fragmentation off of the proximal palmar or plantar eminence of the first phalanx are also common incidental findings in otherwise sound horses. Again, these are generally removed in horses that perform at speed. However, in horses involved in other disciplines, particularly those that work at lower speeds, I generally do not recommend surgical removal when there is clinical soundness. If lameness is present, the palmar/plantar fetlock fragment must be confirmed as the cause of the lameness using intra-articular anesthesia prior to recommending surgical removal. This is because these fragments are embedded within the distal sesamoidean ligaments in an area of the joint that is difficult to surgically access. The surgical removal of these fragments can be associated with some damage to the articular surface as well as to the distal sesamoidean ligaments, resulting in a longer post-operative convalescent periods. There are many horses in my practice that perform in disciplines at lower speeds that have these palmar/plantar osteochondral fragments with no apparent lameness or performance problems. Many of these fragments may have been present in the joint since they were yearlings or even weanlings.

Osteochondral fragmentation within the carpal joints are almost always cases where arthroscopic fragment removal is recommended. This is because most of these are traumatic in origin. Osteochondral fragments within the hock and stifle joints can either be traumatic or developmental in nature. Traumatic causes of fragmentation in these joints is usually accompanied by lameness and joint effusion, and are good candidates for arthroscopic joint surgery. Many developmental causes of osteochondral fragmentation in the hock and stifle joints have joint effusion as the only clinical sign (no clinical lameness). In these cases the defective cartilage and exposed subchondral bone serve as inflammatory mediators that will lead to persistent joint effusion if not operated on. There are also cases where these osteochondrosis lesions are clinically silent (no joint effusion), and found incidentally on an otherwise sound horse. In this situation, if the horse is an adult and has an athletic record with no history of lameness or joint effusion, surgery is generally not recommended. Therefore, I generally use joint effusion as my chief decision maker when determining the proper management of osteochondrosis lesions in the hock or stifle.

In addition to osteochondral fragmentation, other indications for arthroscopic, tenoscopic, or bursoscopic surgical intervention include debridement of a surface defect, internal fixation, lavage and decontamination of the joint (septic arthritis), and removal of soft tissue masses.

Palmar digital neurectomy is the surgical severing of the lateral and medial palmar digital nerves to remove neural sensation to the palmar heel region. Most surgical techniques involve removing a section of the nerve, which prolongs the length of time it takes for the nerves to regenerate. The surgical method that I typically utilize is the guillotine technique in which a 2-3 cm section of nerve is removed by sharp severing of the nerve. The nerve is stretched over the scalpel blade allowing the tension of the nerve to sever its fibers. This allows the proximal and distal nerve stumps to be retracted into the soft tissues so as to not be incorporated into the incision. This should be done as atraumatically as possible. A neuroma at the cut end of the nerve is the most common surgical complication and can cause pain and lameness. Good surgical technique is the most effective means of minimizing the occurrence of neuromas. Other surgical techniques have been developed, however they all seem to be equivalent when comparing the incidence of neuroma formation.

Palmar digital neurectomy is generally performed in cases of end stage navicular disease, when all other treatment options have failed. Most of the time, palmar digital neurectomy is performed bilaterally. As neurectomy removes the protective pain mechanism, case selection is important. Cases in which there is severe roughening and remodeling of the flexor surface of the navicular bone are generally not good candidates for surgical neurectomy, as they are prone to complete rupture of the deep digital flexor tendon. Also, bilateral diagnostic anesthesia of the palmar digital nerves at the same level as the proposed neurectomy should be performed in front of the owner and trainer, as the clinical improvement post nerve block will be similar post neurectomy. Many horses may be significantly improved post neurectomy, but yet still maintain a subtle clinical lameness. Allowing the owner and trainer to evaluate the horse after bilateral blocking will ensure customer satisfaction after the surgical procedure.

Following palmar digital neurectomy, the horse is rested for approximately 30 days. Continued foot care is essential post surgery. I consider 2 years of clinical soundness a surgical success, but this can be highly variable. For this reason, older horses with only 1-2 years remaining on their athletic careers are the best surgical candidates.

Proximal suspensory desmitis of the rear limb is a particularly challenging cause of lameness in the athletic horse. A big reason for the failure of therapy of this disease is the unique anatomy of the proximal suspensory area. The proximal part of the suspensory in the rear limb is located within a confined tunnel that is made up of the plantar part of the third metatarsal, the axial parts of the second and fourth metatarsal bones, and an inelastic band of connective tissue or retinaculum around the plantar part. Therefore injury to the proximal part of the rear suspensory that results in swelling can cause a compartment type syndrome leading to additional pain because of pressure within this inelastic structure. This can cause a vicious cycle of pain and swelling resulting in a chronic painful condition. Therefore, in lameness cases caused by rear limb proximal suspensory desmitis, successful medical treatment is difficult. Medical therapy consisting of peri-ligamentous injections with anti-inflammatories and extracorporeal shock wave therapy combined with rest is initially tried. When the results of medical therapy is unsatisfactory, surgical transection of the plantar fascia or retinaculum may be indicated, particularly when there is gross enlargement in the cross sectional area of the proximal suspensory as seen on ultrasound. The horse is placed in dorsal recumbency, and a 4-6 cm incision is made in the proximal medial metatarsus just distal to the chestnut. The thick subcutaneous fascia is incised to expose the tendons and proximal suspensory ligament. The plantar fascia can be ascertained as its fibers are oriented in a transverse plane. Using curved kelly hemostats, the plantar fascia can be separated from the proximal suspensory ligament and incised. I prefer to remove several millimeters of the fascia if possible. Incision of the most proximal and distal part of the plantar fascia can be completed with surgical scissors without extending the skin incision. Once the plantar fascia is incised, the proximal suspensory ligament will usually bulge out of the fascial incision indicating the compression caused by the structure. Depending on the case, I will often combine the plantar fasciotomy with ligament splitting and intralesional injection with stem cells. Using a number 11 scalpel blade, the proximal part of the ligament is split longitudinally down to the proximal third metatarsal bone. The area can then be infiltrated with stem cells through pre-placed needles. The subcutaneous fascia is closed followed by a subcuticular skin closure. This procedure can be performed unilaterally or bilaterally, depending on the case.

In certain cases, plantar fasciotomy is combined with neurectomy of the deep branch of the lateral plantar nerve. This surgical technique is performed similarly, although through a lateral approach rather than the previous described medial approach. The deep branch of the lateral plantar nerve is incised as is enters the proximal suspensory ligament. This technique is used in cases where diagnostic anesthesia localizes the source of lameness to the proximal suspensory ligament, but there is no apparent ultrasonographic lesions. When there is ultrasonographic evidence of lesions within the proximal suspensory ligament, neurectomy of the deep branch of the lateral plantar nerve is contraindicated, as progression of the lesion can occur post surgically.

Following plantar fasciotomy over the proximal suspensory ligament, 60 days of controlled exercise is given. An additional 60 days of rest is usually given, but a clinical improvement or soundness at 60 days is a good prognostic indicator for the future athletic soundness of the horse.

Surgical arthrodesis of the proximal interphalangeal joint is generally performed in cases of osteoarthritis, osteochondrosis, or fracture. As this is a low motion joint, surgical joint fusion can still preserve athletic soundness. Osteoarthritis of the pastern joint is a common cause of lameness in both the fore and hindlimb, particularly in the western performance horse. Medical management of the lameness using both systemic and intra-articular anti-inflammatories is attempted as long as possible. When the lameness persists despite medical therapy, surgical arthrodesis is indicated.

Surgical approach to the dorsal aspect of the proximal interphalangeal joint is made using an inverted єѠincision. This incision must be made in close proximity to the hoof capsule, so careful foot preparation and surgical draping should be made. The joint is dorsally subluxated by incising the lateral and medial collateral ligaments to allow for complete debridement of the articular surface. In cases where there is severe osteoarthritis involving significant proliferation of bone, excess bone may need to be removed to provide a smooth dorsal surface of the first and second phalanx. The arthrodesis is completed using a combination of dynamic compression plate and screws. In cases of second phalanx fracture, 2 dynamic compression plates may have to be used. The leg is placed in a distal limb cast following the surgical procedure.

The literature supports approximately 60% and 80% success rates on the fore and hind limbs, respectively. My experience has been similar in cases where the only lesion is in the proximal interphalangeal joint. Many horses that have osteoarthritis of the pastern joint have concurrent problems in other locations, particularly the distal interphalangeal joint. Potential complications post surgery include the formation of osteoarthritis in the distal interphalangeal joint due to inadvertent distal placement of the implants causing interference with the extensor process of the coffin bone. Therefore particular care and intra-operative imaging should be used when placing implants. Similarly, the implants should not extend beyond the palmar/plantar cortex of the first or second phalanx, as bony callous and remodeling can lead to post-arthrodesis lameness from interference with the soft tissue structures in this area. The typical time frame necessary for complete joint fusion is approximately 4 months, however clinical soundness may take 6-12 months to occur.

Arthrodesis of the distal tarsal joints is more appropriately named facilitated ankylosis. Osteoarthritis of the distal intertarsal and tarsometatarsal joints are one of the most common causes of rear limb lameness in athletic horses. Similar to the proximal interphalangeal joint, osteoarthritis in these low motion joints can usually be managed medically via intra-articular injections of anti-infammatories. When this is not effective, fusion of these joints will eliminate the pain while having no effect on the range of motion of the joint. With natural disease and medical management, occasionally these joints will ankylose on their own. However, sometimes the ankylosis is incomplete, causing a lameness that will not respond any more to medical treatment. This may be due to an increase in intra-articular or intra-osseous pressure. Several surgical arthrodesis techniques have been described as well as methods for medical facilitated ankylosis.

The most popular method for surgical facilitated ankylosis of the distal tarsal joints involves a drilling technique where 3 divergent drill tracts are made through the articular surfaces of both the distal intertarsal and tarsometatarsal joints. Intra-operative imaging is used to control positioning of the drill bit. No surgical stabilization in the form of implants is usually necessary. The drill tracts will eventually fill in with osseous and fibrous tissue to complete the ankylosis. This process usually takes 6-12 months to complete, however, clinical improvement usually occurs faster. In some cases a dramatic improvement in lameness will occur very rapidly, probably due to relieving the increased intra-osseous pressure by the drill tract. An alternative technique using a laser fiber to vaporize the articular cartilage has also been developed and has similar results. Medical facilitated ankylosis of the distal tarsal joints can also be achieved with intra-articular injections of ethyl alcohol. This method is relatively non-invasive and can have satisfactory results in less time than the surgical methods. Horses that are good candidates for this procedure are those where there is a marked increase in radiopharmaceutical uptake in the distal hock joints on nuclear scintigraphy but with minimal detectable radiographic changes. I prefer to place the horse in dorsal recumbency under general anesthesia and use fluoroscopy to guide my needles into the joints. Approximately 3-4 mL of ethyl alcohol is injected into each joint. Post-injection pain has been negligible to non-existent in my experience. Many horses can be started back into work in 60-90 days following this technique.

The surgical management of certain lameness disorders can be used alone or in combination with other therapies to achieve soundness. An accurate diagnosis and case selection are the most important factors in achieving success with any therapy.