CONFORMATION OF THE CROUP

Although the hindlimbs support little more than 40% of the body weight, they supply by far the greater part of the forward impetus in locomotion. This thrust is delivered through the hip and sacroiliac joints, which are intrinsically more stable than the shoulder and scapulothoracic synsarcosis, the corresponding “joints” of the forelimb.

Despite the muscular development, the coxal tuber remains a conspicuous landmark that is palpable in its whole extent and visible in its upper part (Figure 24-1/2). The sacral tuber (Figure 24-1Z2'), difficult to palpate in most animals, rises a little above the level of the adjacent spinous processes. The ischial tuber (Figure 24-1/5) is also not always easy to appreciate, although its location and a general impression of its form may be obtained on deep palpation over the muscles that form the caudal contour of the croup and thigh. If this is done, the slope of the pelvis may be estimated by visualizing the line joining the coxal and ischial projections. In the standard, generally approved conformation, this line forms an angle of about 30° with the horizon; from this it may be inferred that the sacrum is more or less horizontal. When the angle is significantly smaller—and the two tubers come close to sharing the same horizontal plane—the tail appears to be set high. When the angle is significantly greater, the animal is said to be goose-rumped. The croup is short in such animals, and the hamstring muscles are reduced in length and in the leverage they may exert. Although this is clearly disadvantageous, some compensation is obtained from the more stable support the limbs afford the trunk, and many horsemen and horsewomen find a gently sloping croup acceptable in a saddle horse. Undue prominence of the sacral tubers (“hunter’s bumps”) sometimes develops, especially in show jumpers and other horses subjected to similar repeated stress. The deformity is commonly ascribed to subluxation of the sacroiliac joints.

The position of the hip joint cannot be determined directly but may be deduced from its relationship to the greater trochanter of the femur. This protuberance is divided into low cranial and high caudal parts, sepa­rately identifiable on palpation (Figure 24-1Z5,5'). At more distal levels, the third trochanter (prominent only in this species) and the lateral epicondyle are easily dis­tinguished and may be used to reveal the orientation of the femur. This bone is more nearly vertical than is often supposed (see Figure 19-1).