The articular capsule of the hip is of exceptional strength. It is attached above to the entire circumference of the acetabulum, and below to the neck of the femur in such a way that while the whole of the anterior and inferior aspects of the neck lies within its attachment, only the inner half of the posterior and superior aspects is intra-capsular. The capsule is augmented by several accessory bands, the most important of which is the _ilio-femoral or [inverted Y]-shaped ligament_ of Bigelow, which passes from the anterior inferior iliac spine to the anterior inter-trochanteric line, its fasciculi being specially thick towards the upper and lower ends of this ridge. The medial limb of this ligament limits extension of the thigh, while the lateral limits eversion and adduction. The weakest part of the capsular ligament lies opposite the lower and back part of the joint.
The hip-joint is surrounded by muscles which contribute to its strength, the most important from the surgical point of view being the obturator internus, which plays an important part in certain dislocations, and the ilio-psoas, which influences the attitude of the limb in various lesions in this region.
Except in thin subjects, the constituent elements of the hip-joint cannot be palpated through the skin. A line drawn vertically downwards from the middle of Poupart's ligament passes over the centre of the joint, which in adults lies on the same level as the tip of the great trochanter. In children it is somewhat higher.
For purposes of clinical diagnosis it is necessary to locate certain bony prominences, the most important being--(1) The _anterior superior iliac spine_, which is most readily recognised by running the fingers along Poupart's ligament towards it. (2) The _ischial tuberosity_, which in the extended position of the limb is overlapped by the lower margin of the gluteus maximus muscle, and is therefore not easily located with precision. By flexing the limb and making pressure from below upwards in the gluteal fold, the smooth, rounded prominence can usually be detected. (3) The quadrilateral _great trochanter_ is readily recognised on the lateral aspect of the hip. Its highest point or _tip_ can best be felt by pressing over the gluteal muscles from above downwards.