Collateral Desmitis of the Coffin Joint

CHAPTER 126 Collateral Desmitis of the Coffin Joint

Collateral desmitis of the coffin joint has long been ignored as a potential cause of foot lameness in horses because of practitioners’ inability to image the collateral ligament with radiography and the absence of telling clinical signs. First ultrasonography—and later magnetic resonance imaging (MRI)—have focused attention on this important structure and its appearance in health and disease. The frequency with which collateral desmitis has been diagnosed has therefore increased dramatically in recent years. In one study it was considered to be the second most important single injury responsible for foot lameness in horses without radiographic abnormalities (behind digital deep digital flexor tendonitis), whereas in another study it was found to be the most common injury in Warmblood sport horses.

The collateral ligaments of the coffin joint originate from depressions on the distal aspect of the medial and lateral epicondyles of the middle phalanx. In the standing horse, the collateral ligaments course in a vertical direction, perpendicular to the ground, toward their insertion on small depressions on the dorsoproximomedial and dorsoproximolateral aspects of the distal phalanx. These depressions are adjacent to the lateral and medial margins of the coffin joints, and they lie immediately dorsal to the medial and lateral ungular cartilages. The function of the ligaments is to support the coffin joint during movement in the sagittal, frontal, and transverse planes. It has been determined that asymmetric foot placement, with the hoof quarters at different heights, results in rotation and sliding of the distal and middle phalanges in both the transverse and frontal planes. This type of collateral motion is encountered mainly during the stance phase of asymmetric propulsion, such as when the horse is moving in circles, and places particular stress on the collateral ligaments of the coffin joint.


Horses of all breeds or disciplines can be affected, but horses used for jumping appear to be at increased risk. Knowledge of an acute injury is rarely reported in the history. In one report, however, nearly 20% of horses with a diagnosis of collateral desmitis had a history of being treated for a foot abscess before referral for diagnosis.

Regional Anesthesia

In a study in which the first author was involved, only 24% of 21 horses with MRI evidence of collateral ligament disease had significant improvement in lameness after intra-articular anesthesia of the coffin joint. However, other practitioners who relied on ultrasonography for diagnosis of desmitis have suggested that 80% of affected horses became sound after anesthesia of the coffin joint. It is useful to know that anesthesia of the navicular bursa does not result in improvement in lameness caused by collateral desmitis. A palmar digital nerve block, however, improved lameness significantly in 72% of 21 horses with MRI evidence of collateral ligament disease. In that study, all horses with collateral ligament disease became sound after an abaxial sesamoid nerve block. Lameness will also improve significantly in most cases if a palmar digital nerve block or abaxial sesamoid nerve block is only performed uniaxially on the side of the affected ligament.

Not all horses suspected of having soft tissue injury in the foot have the benefit of undergoing MRI examination. In these instances, the response to different anesthetic techniques in the foot can help to distinguish between the two most common soft tissue injuries, collateral desmitis and digital tendonitis of the deep digital flexor tendon (Table 126-1).

May 28, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Collateral Desmitis of the Coffin Joint

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