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. Occasionally, however, septic arthropathies and developmental disorders of the joint have been reported. Regardless of the etiology of the primary disease, secondary osteoarthritis of the coxofemoral joint is a common sequela that frequently results 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 evident. In severe cases, the horse often stands with the limb partially flexed. With any amount of chronicity, atrophy of the muscles of the hindquarters, such as the gluteus muscles and quadriceps, is often moderate to marked.
In cases of coxofemoral subluxation, the leg is held in a semiflexed position with an obvious outward rotation of the stifle and toe and an inward rotation of the point of the hock. Complete coxofemoral luxations show the same rotational abnormality in limb position. In addition, the leg appears shorter, as is best reflected 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; with some acute fractures, however, a hematoma or alteration in the bony architecture can be palpated.
Intra-articular local anesthesia of the coxofemoral joint is frequently used to identify the joint as the cause of lameness, particularly in chronic cases. Although this technique can be technically challenging, ultrasonography can help guide needle placement. Because of the difficulty of this technique, when other regions of the limb have been ruled out as the source of lameness, intra-articular anesthesia and corticosteroids are sometimes injected simultaneously to avoid repeated arthrocentesis of the joint.
Definitive diagnosis of coxofemoral pathology 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 detecting involvement of the joint; however, it has low specificity for identifying the pathology within the joint.
Percutaneous ultrasonography can provide considerable information about the coxofemoral joint; however, its use at this site is technically challenging.
Radiographic evaluation can be very rewarding, especially in smaller horses and ponies; however, optimal views require general anesthesia. Because of the risk of administering general anesthesia to 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 to produce either ventrodorsal or lateral oblique views; depending on the size of the patient, these images can sometimes be diagnostic.
Arthroscopy of the coxofemoral joint is possible; however, it is technically challenging in most adult horses and ponies. Most clinicians can obtain acceptable joint visualization in foals.
CT can produce high-quality diagnostic images of the coxofemoral joints in foals and small ponies.
Luxation of the Coxofemoral Joint in Horses
Luxation (dislocation) of the coxofemoral joint is relatively rare in horses because of the strong support provided to the joint by the ligament of the femoral head (round ligament) and the accessory femoral ligament, as well as by the fibrocartilaginous acetabular rim. In horses, this injury is usually secondary to trauma.
Dislocations are much more common in small ponies, such as Shetland ponies, in which luxation of the coxofemoral joint has been frequently described secondary to upward fixation of the patella. Fracture of the dorsal acetabular rim may accompany the dislocation.
Non-weight-bearing (toe-touching) lameness, higher point of the hock compared to the contralateral limb, external rotation of the limb, and an asymmetrical pelvis are the most common clinical signs in horses with luxations of the coxofemoral joint.
Differential diagnoses for coxofemoral joint luxations include femoral capital physeal fracture, rupture of the round ligament, and fracture of the pelvis or femur.
Standing dorsolateral, 20°-to-30° ventral oblique radiography of the affected limb is useful to confirm the luxation (see standing radiograph). Usually the head of the femur is displaced dorsocranially from the acetabulum. Ventrodorsal radiographs (see ventrodorsal radiograph) can also be obtained under general anesthesia or, in some facilities, with the patient standing.
Courtesy of Dr. Albert Sole Guitart.
Courtesy of Dr. Louise Cosgrove.
Luxations of the coxofemoral joint are best managed by closed reduction under general anesthesia; however, reduction is unlikely to be successful if not performed soon after the injury. Reduction can be difficult to maintain through recovery from general anesthesia, and although the use of surgical techniques or Ehmer slings has been advocated, no single technique has been shown to be successful.
The prognosis for return to athletic function after coxofemoral joint luxation is very guarded. Closed reduction is possible in some small ponies and can enable them to be comfortable at pasture.
Ostectomy of the femoral head appears to be a reasonable treatment option with low complication rates in chronic cases of luxation in small horses, donkeys, or ponies (< 230 kg). The eventual outcome is usually a mechanical lameness with an acceptable comfort level and the ability to trot and gallop.
Pelvic Fractures in Horses
Pelvic fractures in horses can result from trauma (in which case the fractures are generally complete) or, in Thoroughbred racehorses, can be incomplete stress fractures of the ilium resulting from the repetitive stress of training/racing cycles. If they are not diagnosed, these incomplete fractures can progress to complete catastrophic fractures if the horse returns to speed work prematurely.
The most frequent fatigue pelvic fractures in Thoroughbred racehorses are the ilial and ischial fractures. Although most of these fractures involve the ilial wing, they can also occur in other areas of the pelvis, such as the tuber ischiadicum, ilial shaft, and potentially the pubis. It is common for horses with fractures of the tuber ischiadicum and tuber coxae to return to athletic activity. Fractures involving joints, especially the coxofemoral joint, typically carry a worse prognosis.
Fractures involving the acetabulum commonly result from trauma and usually present as severe, frequently non-weight-bearing lameness immediately after the injury. The amount of pain can be severe and sometimes difficult to control initially in horses with acute pelvic fractures. In most cases, however, the lameness improves markedly during the days after the injury.
Acetabular fractures are usually diagnosed in foals and young yearlings, probably because the acetabulum is the weakest point until the three bones forming it (ilium, ischium, and pubis) are completely fused (at approximately 1 year old).
Crepitus may be difficult to appreciate, even during passive flexion of the limb or rectal examination. Radiographic evaluation can be diagnostic; however, the difficulties of obtaining such images mean that diagnosis is usually achieved by a combination of nuclear scintigraphic and ultrasonographic evaluation. Ultrasonographic diagnosis of pelvic fractures has advanced considerably and is now considered the first-line method to assess pelvic fractures.
Fractures of the acetabulum, in contrast to other types of pelvic fractures, carry a poor prognosis for return to athletic function because they are frequently displaced and invariably lead to osteoarthritis (see below). The only treatment is prolonged rest (6–9 months) followed by supportive care for any resultant osteoarthritis.
Osteoarthritis and Other Coxofemoral Joint Diseases in Horses
Osteoarthritis of the coxofemoral joint is usually secondary to major trauma, such as luxation or fracture of the joint. Occasionally, osteoarthritis is diagnosed as a cause of chronic lameness, usually by positive response to intra-articular anesthesia, without a known prior incident of specific hip trauma.
Horses with severe osteoarthritis usually present with a short caudal phase of the stride at the walk. Cases of osteochondrosis within the coxofemoral joint or of subchondral bone cysts within the coxofemoral joint are rare but have been reported. Osteochondrosis can lead to secondary osteoarthritis. However, arthroscopic removal of osteochondral fragments, if done early, can mitigate the development of degenerative joint disease.
In foals, septic arthritis of the coxofemoral joint is observed occasionally as a consequence of hematogenous spread. Septic arthritis can lead to the development of osteoarthritis due to the damaging effects of infection on cartilage and synovial membranes.
For established osteoarthritis, treatment is usually supportive, consisting of NSAIDs, intra-articular corticosteroids, or other supportive care. In cases of septic arthritis, treatment should consist of surgical debridement and lavage in conjunction with local and systemic antimicrobials.
In cases of osteoarthritis, the prognosis for soundness is poor. Foals can be treated successfully for septic arthritis; in adult horses, however, successful treatment is unlikely unless the condition is diagnosed quickly and treated aggressively. The prognosis is guarded to poor in all cases of hip arthritis in horses; lameness is progressive, atrophy ensues, and quality of life deteriorates.
Key Points
Lameness arising from the coxofemoral joint can be challenging to diagnose and is associated with a guarded to poor prognosis.
Incomplete pelvic fractures, when detected early, have an excellent prognosis for return to athletic function with appropriate rest.
Complete fractures of the body of the pelvis are generally catastrophic injuries in horses.
For More Information
Barrett EL, Talbot AM, Driver AJ, Barr FJ, Barr AR. A technique for pelvic radiography in the standing horse. Equine Vet J. 2006;38(3):266-270. doi:10.2746/042516406776866435.
Geburek F, Rötting AK, Stadler PM, Comparison of the diagnostic value of ultrasonography and standing radiography for pelvic–femoral disorders in horses. Vet Surg. 2009;38(3):310-317. doi:10.1111/j.1532-950X.2009.00508.x
Also see pet health content regarding disorders of the hip in horses.
