Anterior acetabulum of right hip
The hip consists of the two coxal bones. Each coxal bone was developed in a fusion of three bones. The superior ilium fuses with the inferior and anterior pubis and also with the inferior and posterior ischium. The superior border of the ilium is the iliac crest which ends in the anterior superior iliac spine. The pubis contains the symphysis pubis, which is a joint connecting the right and left coxal bones. The acetabulum is a deep fossa (pocket) on the lateral side of each coxal bone where the ilium, pubis and ischium combined. The largest bone in the body is the femur. On its proximal end, the rounded head of the femur articulates with the coxal bone, within the acetabulum. The head narrows distally into the neck. Lateral to the neck is a massive projection called the greater trochanter. Medial and inferior is the lesser trochanter. These trochanter serve as sites for muscle attachments. The hip is a synovial, ball-and-socket type joint formed by the head of the femur and acetabulum of the coxal bone. The acetabulum fits tightly around the head of the femur so that unlike the shoulder, the hip sacrifices a degree of movement for additional stability. The hip joint, like other joints, is made up of specialized structural elements that serve as precisely fitting moving parts. The head of the femur rotates freely within the smooth, concentric surface of the acetabulum. An extremely low friction tissue, hyaline cartilage, lines this joint as well as others in the human body. The friction between two hyaline cartilage surfaces is much less than the best man-made bearing. The hip allows movement in all three planes of motion including flexion-extension, abduction-adduction and medial to lateral rotation. Abduction is movement of the leg away from midline and is limited by the greater trochanter contacting the outer ridge of the acetabulum. Adduction is movement of the leg towards the midline. Medial rotation is seen by rotating the leg inward about a vertical axis. Lateral rotation is a more extensive movement for the hip, and is outward about a vertical axis.
A normal acetabulum "covers" the upper (superior) portion of the head of the femur as well as a partial portion of the front (anterior) and back (posterior) of the femoral head. Acetabular dysplasia is a condition defined by inadequate development of an individual's acetabulum. The resulting acetabulum is shallow and "dish shaped" rather than "cup shaped". The upper portion (roof of the acetabulum is obliquely inclined outward rather than having the normal horizontal orientation. Because of these abnormalities, the superior and usually anterior femoral head are incompletely covered by this dysplastic acetabulum. Individuals with acetabular dysplasia usually develop through childhood and adolescence without symptoms or knowledge of their abnormality. By the age of 30 however the patient typically experiences pain from their hip and they often seek medical evaluation and an X-ray discloses the abnormality (acetabular dysplasia). Other patients may have been treated for hip problems as an infant or child. Acetabular dysplasia is often also associated with abnormalities in the shape of the upper femur which may contribute to the patient's hipsymptoms. Acetabular dysplasia is associated with an abnormally high stress on the outer edge (rim) of the acetabulum which leads to degeneration of the articular cartilage (arthritis). It is also possible for breakdown of the acetabular labrum (rim cartilage of the acetabulum) or a fatigue fracture of the rim of the acetabulum to occur as a result of this rim overload. Any one or a combination of these conditions can cause hip pain sufficient for the patient to seek medical evaluation and treatment. When the diagnosis of acetabular dysplasia is made, the X-ray also usually shows a sign of arthritis which is most commonly an acetabular cyst though increased bone density, a femoral head cyst, osteophytes (bone spurs), and/or cartilage thinning may also be present. If the dysplasia is left uncorrected worsening of the arthritis is predictable and often progresses to a severe status within a few years and sometimes even a few months. For the patient, this means increasing hip pain, progressive loss of hip motion, and worsening functional capabilities. Periacetabular Osteotomy (PAO) is a surgical treatment for acetabular dysplasia that preserves and enhances the patient's own hip joint rather than replacing it with an artificial part. The goal is to alleviate the patient's pain, restore function, and maximize the functional life of their dysplastic hip. Traumatic bilateral hip dislocation is a very rare event. The combination of an anterior and posterior hip dislocation is even more unusual. The most common cause is motor vehicle collisions. The typical mechanism is thought to be due to an unrestrained, front seat occupant of the vehicle striking their knee against the dashboard at the time of a sudden deceleration. Depending on which direction the knee is turned and whether the hip is in abduction or adduction, the resulting dislocation will be either an anterior dislocation or posterior dislocation. Anterior dislocations occur from forced hip abduction impinging the femoral neck or trochanter against the superior portion of the acetabulum forcing the femoral head through the anterior capsule. Acetabular fractures are usually the result of major direct trauma to the pelvis and femur. The acetabulum may be classified into the anterior (iliopubic) column, the posterior (ilioischial) column, and the dome of the acetabulum. Posterior wall fracture is usually the result of posterior hip dislocation.
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