The angular appearance of the hindquarters of cattle is due in part to the robust formation of the pelvic girdle, much of which is outlined below the skin, and in part to the weak development of the muscles of the croup.
The sacral tuber is palpable to the side of the lumbosacral space even though it fails to reach the height of the sacral crest. (Its occasional elevation above the crest prompts suspicion of sacroiliac dislocation.) This tuber is joined to the much more prominent coxal tuber (“hook bone”) by the iliac crest, which is only thinly—and incompletely—covered by the gluteus medius (Figures 31-1 and 31-2).
The triangular ischial tuber (“pin bone”) is raised considerably above the pelvic floor and projects largely or wholly above the vulva. Its subcutaneous dorsal angle is joined by the sacrotuberous ligament; because the edge of this ligament is not covered by muscle, it is readily palpable (Figure 31-3/1').The line connecting coxal and ischial tubers reveals the slope of the pelvis. An angle larger than usual is associated with a more upright pelvic inlet; a smaller angle (flattened rump) requires the femur to be carried more vertically, which is a conformation thought to predispose to concussive trauma of the hip joint. Neither inspection nor palpation directly reveals the position of this joint, which must be deduced by reference to the palpable greater trochanter; this is situated lateral and slightly caudal to the femoral head, below the intertu- beral line (Figure 31-3/2). The disturbance of this relationship suggests fracture of the neck or dislocation of the head of the femur. Dislocation may occur in several directions and is thought to be facilitated by the relative weakness or occasional absence of the sole intraarticular ligament (ligamentum capitis). Most commonly the trochanter is displaced dorsocranially to project above the intertuberal line. This joint is nominally a ball-and- socket joint, but the extension of the femoral articular surface onto the semicylindrical neck makes it evident that flexion and extension must be the principal movements. However, the degree of outward rotation of the thigh that accompanies flexion ensures that the stifle is carried free of the abdomen.
The cavity of the joint may be reached if a needle is inserted directly in front of the trochanter and is advanced medially and slightly crani- ally. The deep location and contractions of the muscle pierced en route make the procedure difficult to accomplish successfully.The most striking features of the regional muscles are the relative weakness of the gluteal group and the absence of vertebral origins of the semitendinosus and semimembranosus. The gluteus superficialis is wholly incorporated within the biceps to form the combination sometimes known as gluteobiceps. The gluteus medius possesses a well-defined deep division (gluteus accessorius) with its own insertion tendon that enjoys the protection of a synovial bursa where it passes lateral to the greater trochanter. This bursa is occasionally inflamed. The biceps fills the caudolateral part of the thigh and has a wide insertion spread between the fascia lata, patella, lateral patellar ligament, and, via the crural fascia, the tibia and calcaneus. A large bicipital bursa intervenes between the lateral epicondyle of the femur and the part of the insertion proceeding to the patellar ligament. The bursa, which may communicate with the stifle joint cavity is sometimes the site of a painful inflammation, most often encountered in cattle required to rest on bare concrete. The insertions of the semitendinosus and semimembranosus and the actions of the group follow the usual pattern.
The adductor muscles of the medial thigh, the deep group about the hip joint, and the quadriceps femoris require no special notice. The tensor fasciae latae at the cranial margin of the thigh is a guide to the location of the subiliac lymph node.