Collateral ligament (CL) desmopathy of the distal interphalangeal joint (DIP joint) is frequently diagnosed in horses that exhibit lameness isolated to the foot.
Most CLs of the DIP joint lie deep to the hoof capsule. They originate from depressions on the distal medial and lateral aspects of the middle phalanx, and they insert in depressions on the dorsomedial and dorsolateral aspects of the distal phalanx, close to the joint margins and the dorsal aspect of the medial and lateral cartilages of the foot. The CLs support the DIP joint in its movements in the sagittal, dorsal, and transverse planes.
Etiology and Pathophysiology of DIP Joint CL Desmopathy in Horses
Collateral ligaments may become injured during the stance phase of the inner limb as a horse moves in a circle where the DIP joint undergoes lateral motion and medial rotation. Uneven footing and hoof imbalance are thought to increase the likelihood of injury.
Clinical Findings of DIP Joint CL Desmopathy in Horses
Horses with desmopathy of the CL of the DIP joint usually do not have specific localizing clinical signs. Most patients have moderate acute or chronic lameness that often varies in severity depending on the direction of movement and the footing.
Diagnosis of DIP Joint CL Desmopathy in Horses
Analgesia of the palmar digital nerves improves the lameness in most horses with an injury to the CL of the DIP joint. Intra‐articular anesthesia of the DIP joint can also improve the lameness in some horses with an injury to the CL of the DIP joint.
Radiography intended to reveal characteristic changes such as remodeling of the collateral fossa of the distal phalanx or ossification of the ungual cartilages has low sensitivity for detecting CL desmopathy. Nuclear scintigraphy intended to reveal abnormally increased radioisotopes in the region of CLs has low specificity for desmopathy of the CL.
The proximal portion of the CL may be evaluated by ultrasonography, which has good sensitivity and specificity for proximal lesions of the CL. However, many lesions occur only in the distal portion of the ligament, which is not accessible for ultrasonographic imaging, because of interference by the hoof capsule.
MRI has the highest sensitivity and specificity and is therefore considered the gold standard for diagnosing CL desmopathy of the DIP joint in horses.
Differential diagnoses for DIP joint CL desmopathy in horses include all other causes of mild to moderate lameness in the foot.
Treatment and Management of DIP Joint CL Desmopathy in Horses
The main goal in the treatment of CL desmopathy of the DIP joint is to provide the ligament with an environment conducive to healing. To decrease stress on the CL, the horse is rested for a variable period of time that depends on recheck evaluations.
A horseshoe with a wider branch on the side of the injured ligament can decrease sinking of that side of the foot in deformable surfaces, in theory decreasing strain on the ligament. If a horse is standing on a flat, nondeformable surface during the rest period, the type of shoe applied is probably irrelevant.
If the lesion is in the proximal aspect of the ligament, imaging-guided injections of therapeutic biologics or extracorporeal shock wave therapy may aid the healing process.
The prognosis is good for return to athletic use in horses with CL desmopathy of the DIP joint.
