This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Tuberculosis of the hip probably begins in the neighborhood of the epiphyseal line of the femur and involves the joint secondarily. The epiphysis of the head begins above near the edge of the articular cartilage and runs obliquely across upward and inward. It is thus entirely within the capsule and when pus forms it first perforates the articular cartilage and enters the joint and then perforates the capsule to point externally. There are three favorite places of exit, viz.: (1) on the posterior surface of the neck between the branches of the ischiofemoral ligament; (2) on the lower anterior surface beneath the iliopsoas tendon, between the pubofemoral and iliofemoral ligaments, through the bursa found here which may communicate with the joint; and (3) at the cotyloid notch.
Fig. 525. - Early stage of coxalgia, showing the affected left limb abducted, thus lowering the pelvis on that side; slightly flexed, thus obliterating the glu-teofemoral fold, and slightly everted.
The head and neck of the femur and also the acetabulum become carious. Pus may find an exit at other places besides those mentioned. It may perforate the acetabulum and show above Poupart's ligament at its outer side, or may break through the upper posterior portion of the capsule. Not often does it break through between the branches of the iliofemoral ligament. When it does break through anteriorly it points in Scarpa's triangle, commonly to the inside of the vessels; when it breaks through posteriorly it descends beneath the fascia lata and points on the posterior or outer portion of the thigh.
The normal angle which the head and neck make with the femoral shaft may vary according to Humphry (Jour. Anat: and Phys., xxiii, 236) from 110 to 140 degrees. Sometimes as a result of injury or disease the neck makes a more acute angle than normal, coming off at an angle of 90 degrees or less. This is called coxa vara (Fig. 526). In some cases it is due to a bending of the neck caused by softening of the bone, as in rachitic affections, or to fracture. The limb is shortened, the trochanter raised above the Roser-Nelaton line, and abduction and flexion are restricted. To rectify it Whitman's operation of wedge-shaped resection is done. A wedge of bone with a base of 2 cm. (3/4 in.), apex inward, is removed at a point opposite the lesser trochanter. The femur is then placed in abduction and the bone allowed to heal. When the limb is brought down the angle of the head and neck will be much increased and the deformity and disability will have been removed.
The term coxa valga has been applied to the opposite condition, when the neck is nearly parallel with the shaft; it is rarer and of less importance than is coxa vara. Orthopaedists regard 135 degrees as the normal limit of the angle between the neck and shaft of the femur, but Humphry placed it at 140 degrees.
Fig. 526. - Normal angle of the head and neck to the shaft of the femur with the alteration in position in coxa valga and coxa vara shown by dotted lines.