Disorders of the Hip in Horses
Disorders of the coxofemoral joint are relatively rare causes of lameness in horses. Most cases are traumatic in origin, secondary to falls or being cast (within a stall) in recumbency, although septic arthropathies and developmental disorders of the joint have been occasionally reported. Regardless of the etiology of the primary disease, secondary osteoarthritis of the coxofemoral joint is a common sequela, which will frequently result in permanent lameness.
Lameness is the predominant presenting clinical sign of any coxofemoral disease. Although the lameness can be subtle, more frequently a moderate to severe lameness (non-weight-bearing) is seen at presentation. In severe cases, the horse will often stand with the limb partially flexed. With any degree of chronicity, atrophy of the muscles of the hindquarters, such as the gluteals and quadriceps, is often moderate to marked. In cases of coxofemoral subluxation, the leg will be held in a semi-flexed position with an obvious outward rotation of the stifle and toe and an inward rotation of the point of the hock. In complete coxofemoral luxations, the same rotational abnormality in limb position is observed, and additionally the leg will appear shorter, which is best identified by the point of the hock being displaced proximal to that of the contralateral limb. Most horses with coxofemoral pathology show some pain on proximal limb flexion or abduction. Rectal examination is generally unrewarding, although in some cases of acute fracture, a hematoma or alteration in the bony architecture is palpable per rectum. Intra-articular local anesthesia of the coxofemoral joint is frequently used to identify the joint as the cause of lameness, particularly in cases of chronic lameness. Although this technique can be technically challenging, ultrasonography can help guide needle placement.
Definitive diagnosis of coxofemoral pathology usually requires some form of diagnostic imaging. Bone scanning (nuclear scintigraphy) is commonly used to identify the coxofemoral joint as the site of pathology. This technique is highly sensitive for identification of the involvement of the joint but has a low specificity for identification of the pathology within the joint. Percutaneous ultrasonography can provide considerable information on the coxofemoral joint, although its use at this site is technically challenging. Radiography can be very rewarding, especially in smaller horses and ponies, although optimal views require general anesthesia. Because of the risk of using general anesthesia in horses with serious limb injuries, such imaging is only rarely performed. A number of techniques are available to radiograph the coxofemoral joint in the standing horse, using either a ventrodorsal or lateral oblique views. Arthroscopy of the coxofemoral joint is possible, although it is technically challenging in most adult horses and ponies; acceptable joint visualization can be obtained by most operators in foals.