Overview
The femur (os femoris) forms the skeleton of the thigh. It articulates at the hip with the acetabulum and at the stifle (articulatio genus, the anatomical knee) with the tibia and patella. It is wrapped in large muscle masses, so only the greater trochanter and some distal landmarks can be palpated. Unlike cattle and the dog, the horse has a third trochanter.
Proximal end
- Head (caput ossis femoris): hemispherical, with a deep medial notch rather than a simple fovea; the ligament of the femoral head and the accessory ligament, unique to the horse, attach in it.
- Neck (collum ossis femoris): short and poorly defined.
- Greater trochanter (trochanter major): divided into a cranial and a higher caudal part; the latter rises above the head and receives the gluteus medius.
- Lesser trochanter (trochanter minor): medial, insertion of the iliopsoas.
- Third trochanter (trochanter tertius): a prominent crest on the lateral surface, at the junction of the proximal and middle thirds; insertion of the gluteus superficialis.
Shaft and distal end
- Supracondylar fossa (fossa supracondylaris): deep, on the caudal surface; origin of the superficial digital flexor.
- Trochlea (trochlea ossis femoris): the medial ridge is much wider and higher than the lateral and has a proximal thickening, the tubercle of the medial ridge, over which the patella hooks to lock the stifle in the stay apparatus.
- Medial and lateral condyles: caudal articular surfaces in contact with the menisci and tibia; between them, the intercondylar fossa.
- Extensor fossa: between the lateral condyle and the trochlea; origin of the long digital extensor and the peroneus tertius.
Clinical relevance
- Subchondral bone cysts: lesions of the medial femoral condyle in young horses that cause pelvic limb lameness; treated arthroscopically or by injection into the lesion.
- Osteochondrosis of the stifle: mainly affects the lateral trochlear ridge; it causes distension of the femoropatellar joint in foals and young horses.
- Femoral fractures: mainly in foals, from trauma; in the adult the body weight makes repair very difficult.
- Coxofemoral luxation: rare in the horse thanks to the accessory ligament; when it occurs it usually comes with rupture of that ligament or acetabular fractures.