Injuries of the suspensory ligament (interosseous muscle) are common in the forelimbs and hindlimbs of horses. Lesions are typically classified as affecting the proximal region, body, or branches of the suspensory ligament.
Proximal Suspensory Desmitis in Horses
Proximal suspensory desmitis (PSD) lesions are confined to the proximal one-third of the metacarpus. PSD can occur unilaterally or bilaterally and is common in all types of athletic horses.
Injury to the proximal suspensory ligament and/or its attachment to the proximal palmar aspect of the third metacarpal bone typically results in sudden-onset lameness that improves within a few days. Lameness varies from mild to moderate and is typically not severe, unless there is substantial involvement of the ligament and its attachment (avulsion of the palmar cortex).
A horse with bilateral PSD might have less overt lameness but more loss of action. Lameness is typically more noticeable on soft ground and with the affected leg on the outside, if the horse is moving in a circle. Response to distal limb and/or carpal flexion tests varies. Pressure applied to the proximal palmar metacarpal region might elicit pain; however, this response should be compared with that of the other limb to determine its importance.
Diagnosis of PSD usually requires localization with diagnostic analgesia. There are multiple techniques to desensitize the proximal aspect of the palmar metacarpus; some interpretation and follow-up diagnostics to exclude the carpus or tarsus might be necessary, because there is some overlap in local anesthetic effects in this region.
After lameness has been localized, both radiographic and ultrasonographic examination of the region should be performed. Ultrasonographic images of the proximal suspensory ligament should be critically compared with those of the other limb, bearing in mind that bilateral lesions do exist.
Nuclear scintigraphy can help detect concurrent or primary osseous injury at the proximal suspensory attachment. MRI is also extremely useful to detect subtle changes in the proximal suspensory ligament that might not be visible or conclusive with ultrasonography (see MRI images), and MRI allows concurrent examination of bony structures.
Courtesy of Dr. Matthew T. Brokken.
In contrast to horses with hindlimb PSD, most horses with acute forelimb PSD respond well to rest and a controlled exercise program for 3–6 months, showing approximately 90% return to function. Premature return to work typically results in recurrence or persistence of lameness. Horses with chronic PSD might require a longer rehabilitation program or adjunct therapy (NSAIDs, shock wave therapy, regenerative therapies) to return to consistent work.
The prognosis for horses with hindlimb PSD is guarded to fair for return to performance.
Desmitis of the Suspensory Ligament Body in Horses
Desmitis of the suspensory ligament body is principally an injury of racehorses. This injury usually affects the forelimbs of Thoroughbreds and the forelimbs and hindlimbs of Standardbreds.
Pain on palpation of the forelimb suspensory ligament is quite common in horses with other primary problems, and it is not diagnostic for suspensory desmitis. Clinical signs of desmitis of the suspensory ligament body vary and involve enlargement of the ligament, local heat, swelling, and pain. Diagnosis is usually based on clinical signs and can be confirmed by ultrasonographic examination.
Treatment of desmitis of the suspensory ligament body is aimed at decreasing inflammation with systemic NSAIDs, hydrotherapy, and controlled exercise. Shock wave therapy, platelet-rich plasma, and stem cell therapy have also been used.
The prognosis for horses with suspensory desmitis depends on the lesion severity but is generally good.
Desmitis of the Suspensory Ligament Branches in Horses
Desmitis of the suspensory ligament branches is a relatively common injury that occurs in all types of horses, in forelimbs and hindlimbs. Usually, only a single branch in a single limb is affected; however, both branches can be affected, especially in hindlimbs. Foot imbalance, which is often observed in affected horses, might be a predisposing factor.
Clinical signs of desmitis of the suspensory ligament branches depend on the extent of damage and the chronicity of the lesions; these signs include localized heat and swelling. Swelling is often caused by local edema of the affected branch. Effusion can be present in the adjacent palmar/plantar fetlock joint and/or the digital flexor tendon sheath. Pain is usually elicited either by direct pressure applied to the injured branch or by flexion of the fetlock. Lameness varies and might be absent.
Diagnosis of desmitis of the suspensory ligament branches is based on clinical signs and ultrasonographic examination. Radiography should also be performed to evaluate the attachment of the suspensory branch on the proximal sesamoid bones.
Low four-point diagnostic analgesia, and usually intra-articular analgesia of the fetlock joint, improves the lameness.
Ultrasonographic examination can reveal a range of abnormalities in the suspensory ligament branches, which might or might not be active lesions, including enlargement, alteration of shape, and alterations in echogenicity (see ultrasonographic images).
Courtesy of Dr. Matthew T. Brokken.
Treatment of desmitis of the suspensory ligament branches depends on the severity of the clinical signs and on the breed and use of the horse. Shock wave therapy, local anti-inflammatories, ligament splitting, and regenerative therapy have all been used, with varying results. Strict attention to foot balance is also critical in treating these lesions.
Clinical signs can take ≥ 6 months to improve, and the condition can recur. The prognosis for reinjury or persistence of lameness is worse in horses that are hyperextended in their fetlocks at rest or in horses with marked periligamentous fibrosis around the branch on ultrasonographic examination.
For More Information
Also see pet owner content regarding disorders of the carpus and metacarpus in horses.
