Injuries of the suspensory ligament (superior sesamoidean ligament or interosseous muscle) are common injuries in both forelimbs and hindlimbs of horses. Lesions are frequently restricted to the proximal one-third of the ligament, to the body or middle one-third, or to one or both branches.
Proximal Suspensory Desmitis
The term proximal suspensory desmitis is restricted to lesions confined to the proximal one-third of the metacarpus (or metatarsus). It is relatively common and affects both forelimbs and hindlimbs of horses of all ages. In contrast to lesions involving the body or branches (or both) of the suspensory ligament, there is usually associated lameness, poor performance, or poor action. The condition may be unilateral or, less commonly, bilateral. It sometimes is seen in association with more distal limb pain (eg, navicular disease) and is frequently seen in horses with poor mediolateral or dorsopalmar foot balance. Straight hock conformation or hyperextension of the metatarsophalangeal joints may predispose to this type of injury.
Lameness can vary in degree from mild to severe and, in early cases, is generally exacerbated by work and improved by rest. Forelimb lameness may be accentuated by flexion of the fetlock and interphalangeal joints but is generally unaffected by carpal flexion, whereas hindlimb lameness may be increased by flexion of the fetlock and interphalangeal joints or by flexion of the hock and stifle joints.
In acute cases, there may be localized heat in the proximal metacarpal (or metatarsal) region with or without periligamentous soft-tissue swelling. In more chronic cases, frequently no palpable abnormality can be detected.
Diagnosis is made by local anesthesia and ultrasonographic examination, which usually demonstrates diffuse or central hypoechoic areas with hyperechogenic foci in chronic cases. Treatment in the forelimb is commonly conservative (with intralesional injection of bone marrow-derived stem cells and shock wave therapy being more commonly used). In the hindlimb, these techniques are less successful, although shock wave therapy has improved the overall success rate. Most recently, the use of fasciotomy and neurectomy of the deep branch of the ulnar nerve has become popular. Adjunctive treatments include a graduated program of exercise combined with correction of foot imbalance.
Desmitis of the Body of the Suspensory Ligament
This is principally an injury of racehorses. Injuries usually affect the forelimb of Thoroughbreds, and both forelimbs and hindlimbs in Standardbreds. Soreness on palpation of the forelimb suspensory ligament is quite common in horses with lameness associated with a more distal limb problem; however, only rarely is any structural abnormality of the ligaments identifiable ultrasonographically. The clinical signs vary and involve enlargement of the ligament, local heat, swelling, and pain. Diagnosis is usually based on clinical signs and can be confirmed ultrasonographically. Treatment is aimed at reducing inflammation by systemic NSAID, hydrotherapy, and controlled exercise. Shock wave therapy and stem cell therapy have also been used for these lesions.
Desmitis of the Medial or Lateral Branch of the Suspensory Ligament
This relatively common injury is seen in all types of horses in both forelimbs and hindlimbs. Usually only a single branch in a single limb is affected, although both branches may be affected, especially in hindlimbs. Foot imbalance is often recognized in affected horses, and this may be a predisposing factor.
The clinical signs depend on the degree of damage and the chronicity of the lesion(s) and include localized heat and swelling. Swelling is often due to local edema of the affected branch. Pain is usually elicited either by direct pressure applied to the injured branch or by passive flexion of the fetlock. Lameness is variable and may be absent.
Diagnosis is based on clinical signs and ultrasonographic examination. Only rarely are local analgesic techniques required. Ultrasonography can detect a range of abnormalities, including enlargement, alteration of shape, and alterations in echodensity.
Management depends on the severity of the signs and on the breed and use of the horse. Shock wave therapy, as well as stem cell therapy have been used. Strict attention to foot balance is also critical in the management of these lesions. The clinical signs may take many months (≥6) to improve. The condition may recur.
Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; James K. Belknap, DVM, PhD, DACVS; Jane C. Boswell, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS; Peter Clegg, MA, Vet MB, PhD, CertEO, DECVS, MRCVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; Jean-Marie Denoix, DVM, PhD, Agregé; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVS, MRCVS; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD