The lesser trochanter femur is a bony bump on the lateral side of the proximal surface of the body of the femur. It is the site for insertion of the gluteus superficialis muscle.
The femur is the longest bone in the leg and is the only one that articulates directly with the pelvis. It has a large round head at its proximal end, which articulates with the acetabulum of the hip socket in the pelvis. The femur has a medial and a lateral condyle at its distal end that articulate with the meniscal cartilages of the knee joint. Between the femoral condyles is an intercondylar fossa where the cruciate ligaments (cranial and caudal) attach.
A common problem with the femur is called osteochondrosis. This is a condition in which the articular cartilage becomes separated from the underlying bone. This can lead to pain and swelling in the area of the trochlea. It can also affect the femoral head, causing it to shift cranio-medially. The trochlea can also be displaced laterally by force applied to the hind limb.
Luxation of the hip can be caused by trauma, a fall from a height or by excessive stretching of the muscle groups in the hind limb during exercise. In these cases the femoral head is usually shifted cranio-medially and the greater trochanter appears prominent. It may be palpable externally and crepitus can be felt on manipulation.
Other causes of luxation of the hip include over-exercising the horse and incorrect shoeing. The femur is normally a very strong bone that has few fractures, but it can break in very unusual circumstances.
Fractures of the lesser trochanter can be very painful and can impair function and athletic performance. Fortunately, they are relatively rare in horses and usually heal spontaneously.
When a horse is injured, it is important to take a careful history and exam and make sure the diagnosis is correct. X-rays and ultrasound can be used to help in diagnosing the injury. The fracture can be quite painful and the horse will likely be lame for a while, but they will eventually recover.
A study published in the Journal of the American Veterinary Medical Association reported on eight horses that were treated for third trochanter fractures. All but one of the horses returned to full athletic potential. One of the horses that did not return to full activity had a secondary condition, but the other seven all recovered from their injuries without complications.
When a horse has a fracture of the lesser trochanter, the fetlock will appear shorter and the hip joint may be displaced cranio-medially. It is important to be able to differentiate this from other injuries of the hip so that treatment can begin promptly. This will help prevent the fetlock from becoming locked and immobile, which could be a very serious problem in a sport horse. The horse can be put into a cast or splint for protection. The horse should be kept under close observation for any signs of recurrent fractures or lameness.