Aching Equine Knees: Carpal Lesions in the Non-Racehorse

Sue Dyson, VetMB, PhD, FRCVS, head of clinical orthopedics at the Animal Health Trust in Newmarket, England, discussed a variety of lesions in the carpal region (knee) of the non-racehorse at the AAEP Focus seminar in Ft. Collins, Colo., on July 31, 2007. She prefaced her presentation by saying lesions in this area can be quite challenging to identify.

One common injury is that of the superficial flexor tendon (SDFT), usually in older competition horses aged 12-15 years. She noted that an abnormality is not always found on palpation or related to thickening of the tendon. Making this syndrome even more frustrating is that the lameness might be exacerbated by work, but it could only be intermittent in occurrence, with prompt resolution after rest.

Carpal flexion might exacerbate the horse's lameness when already lame, but if the horse is not lame at the time of the exam, the flexion test won't produce lameness. Diagnostic anesthesia using upper limb nerve blocks will abolish the lameness when the horse is demonstrating lameness and pain. Pain can be identified with careful palpation of the superficial digital flexor tendon. There are no particular characteristics of the associated lameness in this area.

It is noteworthy that often the lesions are bilateral (in both forelimbs) despite lameness only appearing in one limb. These SDFT injuries near the carpus do not do well with conservative treatment--either the lameness persists or improves only to relapse. It is possible this might be a degenerative lesion seen only in teenage horses.

Imaging of the lame limb should be accompanied by imaging of the opposite limb; it is not unusual to see pathology in the non-lame leg also. Dyson believes many of these lesions are bilateral in spite of having a unilateral lameness. Conservative treatment does not typically resolve the problem, as the horse might seem fine until put back into regular work, and ultrasonic abnormalities persist. Surgical treatment of cutting the carpal retinaculum is one procedure to try to provide some relief.

Another lesion of the SDFT in the carpal or proximal metacarpal (hock) region occurs in the 15-20-year-old horse, with a sudden onset of severe lameness. These are degenerative lesions that are accompanied by pronounced swelling in the carpal canal region. These horses do not respond well to therapy, and Dyson reports they will stay lame. Cutting of the carpal retinaculum only provides a very slight relief.

Tearing of the SDFT at the tendon- muscle junction is another syndrome that Dyson reports has a poor prognosis with no recovery.

Dyson discussed another carpal lesion seen in sport horses and pleasure horses--that of the antebrachialcarpal joint. The horses are often tolerant of relatively advanced disease prior to onset of lameness. There might be a history of fidgeting with the farrier, or of stumbling or reduced knee flexion over rails causing them to be knocked down. Usually there is distention of the joint capsule, pain with passive flexion, and a positive carpal flexion test. Diagnostic anesthesia of the carpal joint usually improves lameness and range of motion, although lameness is not entirely abolished. Radiographic changes are usually significant. Treatment is palliative using intra-articular medications of anti-inflammatory drugs or IRAP to manage an advanced stage of osteoarthritis.

Osteoarthritis of the carpal-metacarpal joint is not common and can be difficult to diagnose. Often it is associated with moderate lameness, but not necessarily any localizing signs nor restriction of range of motion. There might only be partial response to diagnostic anesthesia. Radiographic findings usually show osteoarthritis restricted to one side of the joint. This form of degenerative joint disease responds poorly to intra-articular treatment, necessitating additional management with systemic NSAIDs.

Bone disease of the third carpal bone is a situation seen in endurance or event horses. Dyson notes that there is an episodic lameness following long-distance endurance exercise that resolves spontaneously within 24 hours. She said one such horse could be ridden for less than 25 miles, but if work progressed beyond 25 miles, the horse immediately went lame.

Lameness in an event horse tends to be more persistent. Nuclear scintigraphy is the best diagnostic technique, along with specialized radiographic views to detect sclerosis of the third carpal bone. Fracture potential exists, and in that case, one treatment option is to transfix the bone with a screw. Tildren has been used to manage bone disease. (Tildren, or tiludronic acid, is not approved for use in the United States, but your veterinarian can get permission to import this drug. It inhibits bone reabsorption. It has been effective for some cases of navicular syndrome and is similar to a drug women take to inhibit osteoporosis.)

Episodic recurrent lameness related to the carpus can be present for various reasons, such as bone spikes on the radius, an osteochondroma, or bleeding in the joint or sheath. Depending on the problem, sometimes there is no palpable abnormality, and it might be difficult to reproduce lameness or to affect a change with diagnostic anesthesia; nuclear scintigraphy is not always helpful to diagnose the problem. Carpal sheath pain can be present with no palpable abnormality.

Dyson's concluding remarks about carpal lesions urged the practitioner to marry together a good history and clinical signs with localizing anesthesia and imaging techniques. Distention of the joint capsule or carpal sheath is usually significant, particularly when coupled with diminished range of motion of the knee. Remember, absence of clinical signs related to the carpus does not eliminate it as a suspicious area of lameness investigation.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More