Helping Foot Pain: Blocking Tendon Sheath Might Aid Diagnosis

At the AAEP Blue-Ribbon Panel Research Meeting in Ft. Collins, Colo., on Aug. 1, Michael Schramme, DVM, CertE, PhD, Dipl. ECVS, of North Carolina State University, discussed analgesia of the tendon sheath and its significance to digital flexor tendon pain in the foot.

His research was conducted with three models--one involved tightening set screws against the sole or heel to induce moderate to severe lameness in specific areas of the foot, another used toxin injection into the coffin joint, and the third injected toxin into the navicular bursa. Following induction of lameness, each horse received anesthetic into the digital flexor tendon sheath to see if lameness could be abolished. Videos were taken of the horses before anesthetic and at 10 and 20 minutes following injection. The lameness was scored by evaluators using a consistent scale.

For all three groups--heel pain, coffin joint pain, and navicular pain--there was no significant improvement in median lameness scores at either 10- or 20-minute evaluations. The researchers concluded that analgesia of the digital flexor tendon sheath has little effect on lameness caused by pain originating in the sole, coffin joint, or navicular bursa. Anesthesia in the digital flexor tendon sheath limits pain only to structures within the sheath, such as the flexor tendon or distal sesamoidean ligaments. This study suggests that analgesia of the digital sheath is a useful alternative diagnostic tool for identifying tendonitis in the foot instead of relying on a more expensive MRI.

Another suggestion that arose from this study is that improvement in sole pain in the toe 20 minutes following anesthesia might be due to partial desensitization of the palmar digital nerve distal (the farther away--in this case from the horse's body) to the origin of the branches that provide heel sensation. The digital sheath and coffin joint might be intimately related with the sheath lying close to the neurovascular bundle, particularly when the distal limb is held up in flexion as one might do when infusing a palmar digital nerve block.

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 recent book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care (available at or by calling 800/582-5604). 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.

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