It is a lot to take in and process that the practice of orthopedic surgery has an inaccurate perspective on the anatomy of the hip. And that the surgeries for femoroacetabular impingement (FAI), developmental dysplasia (DDH), and osteoarthritis of the hip are often based on fallacious imaging studies and erroneous diagnoses.
Yet, that is the place we must start if we are to come to the higher understanding that common degenerative disorders of the hip are preventable and best treated by non-surgical means.
In chronic hip disorders, where is the pain and where, exactly, is the disease located? Patients most often experience pain deep in the groin, which radiates around the hip to the lower back. Surgeons insist the disease is usually focused on the anterior-superior aspect of the labrum and bony acetabulum, while 19th century orthopedists verified that it is almost always located in the soft tissues surrounding the joint.
Working with this conundrum gives valuable insights into the true cause of chronic hip disease, and why surgical treatments so often lead to disastrous long-term outcomes.
First we must agree that when standing with a wide-radius lumbar curvature, the pelvis does not exist in the ‘anterior pelvic plane’ of the classic orthopedic paradigm. Rather, in this position the pubic bones are underneath the body like straps of a saddle, and the anterior superior iliac spine is located just above the crease where the abdominal wall meets the thigh. A comparison of the chimpanzee and the human skeleton illustrates this point (Figure 1).
When the pelvis is fully ‘nutated’, or rotated forward, the arched acetabular roof is perfectly symmetrical from front to back (Figure 2). Just behind the human acetabulum sits the ischial tuberosity (sit bone), which along with the acetabulum, forms the most massive area of the bony pelvis.
This orientation of the arched roof of the hip joint occurs in all other mammals (Figure 3 – cow acetabulum). If the pelvis were not in this position, gravity would cause the acetabular roof to form a shape other than a symmetrical half circle. And indeed, this is what happens when the body is held in chronic ‘counternutation’, with the tailbone tucked under and the pelvis rotated slightly backward.
The forces of gravity cause re-modeling of bone at what is now the anterior-superior aspect of the acetabulum. In a pelvis that is rotated backward, the load-bearing roof of the joint has moved to the front of the acetabulum. Counternutation of the pelvis causes the femoral head to be held slightly up and out of its socket. Over time, the acetabulum becomes oblong in shape (Figure 4) and its fibrocartilage labrum hypertrophies, or expands, which is the body’s attempt to give better coverage to the joint.
This condition is diagnosed as ‘dysplasia’, for which the highly morbid peri-acetabular osteotomy is often indicated. Imaging studies may show the femoral head being held slightly up and out of its socket, yet most surgeons are completely unaware that the heads move down and medially (toward each other) when the patient climbs off the radiology table and stands upright. If the femoral head is still located slightly up and out of the joint, shortened and contracted ligaments are holding it there.
Similar radiographic illusions are used to diagnose FAI. Countless surgeries have been performed for ‘pincer’ FAI based on AP radiographs such as Figure 5. The bony protrusion (circled) seen in this x-ray has no correlation with the actual architecture of the acetabular roof. The two-dimensional radiograph, taken at an angle that looks up into the pelvis, projects the acetabular wall laterally, when in fact it is rotated down and medially in the standing body. Pincer impingement, as described by Reinhold Ganz, is a figment of the collective imagination of orthopedic hip surgeons.
Humans have a choice whether to sit, stand, and move with the arched acetabular roof forming either a symmetrical half circle, or a lopsided oval. Contemporary hip surgeries attempt to address the symptoms and not the cause of chronic hip pain.