Hip pain

Introduction
In the Asian community, unlike the Western community where hip replacement ideas were formulated for a generally heavy-set people who developed osteoarthritis of the hip, primary osteoarthritis of the hip is uncommon. In general the more common causes of hip pain in Asia are developmental dysplasia of the hip and avascular necrosis of the hip. Increasingly however, as knowledge of these conditions becomes widespread with intervention and prevention being instituted earlier a condition known as femora-acetabular impingement has become apparent in this community.

Standard workup
A good physical examination is required in all patients and is critical to understanding the functional loss in such patients. In all significant hip disease, internal rotation of the hip is usually limited. An xray is done and usually gives a good indication of all forms of disease except early avascular necrosis. For this an MRI with arthrogram (where the hip is injected with a dye) is used. This gives an idea not only of the presence of avascular necrosis, but also of cartilage loss and acetabular labral injuries.

Causes of hip pain 
(Note: All cases shown here have been operated on by A/Prof Saminathan Suresh Nathan and are not permitted to be reproduced for any publication without prior written consent)

1. Avascular necrosis
Avascular necrosis is a very common cause of hip pain in this part of the world. The diagnosis describes a condition in which the blood supply to the head and neck if reduced and the head of the femur dies. In the early stages if the disease it may be possible to surgically bring the blood supply back tot he hip but in later stages a hip replacement is inevitable. The condition can be part of rheumatic diseases like systemic lupus erythematosus (SLE), heavy alcohol consumption or among deep-sea divers. The most common cause, however, is due to the use of steroid medications either in Western medicine prescriptions or in traditional folk preparations (Figure 1a).


Figure 1. In the Asian community the more common causes of hip arthritis is that due to avascular necrosis (a) where cavities form in the head due to bone death (arrowed) and developmental dysplasia where the head becomes uncovered (arrowed) due to a shallow acetabulum.

2. Developmental dysplasia
In this condition the acetabulum becomes shallow and the hip, by being poorly contained does not develop well resulting in osteoarthritis at a later stage. Severe forms usually present at birth but more subtle forms present in middle age (Figure 1b).


Figure 2. Increasingly femoro-acetabular impingement is being recognized as a cause of pain and predisposition to arthritis. The example shown here is the cam type where a bump forms on the head (arrowed). If young enough these sorts of patients may benefit from having these bumps removed instead of hip replacement surgery.

3. Femoro-acetabular impingement
This is a controversial condition that has become increasingly recognized over the last decade. Whether it is essentially a normal variant, part of dysplasia as a spectrum or a primary condition is a question of some debate. It exists in 3 forms - the pincer variant (where the edges of the acetabulum hug the head tightly, the cam form with a mis-shapened head and the combined form. In the past such conditions would be dismissed as normal variants but it is presently believed to be a significant cause of arthritis. In the early stages this condition may be amenable to surgical correction but in the later stages hip replacement gives the best results (Figure 2).

4. Osteoarthritis
Primary hip osteoarthritis is an uncommon condition among Asians. It may be due to some injury or abnormality in the past like femoro-acetabular impingement. It is characterized by decreased cartilage (loss of joint space), hard bone formation (subchondral sclerosis), cavities (cysts), bony spikes (osteophytes) and angular deformities (varus, valgus, subluxation). The condition is termed primary when no cause can be found or secondary to some other insult in the past (Figure 3a).


Figure 3. In the Asian community primary osteoarthritis of the hip is rare (a). Rheumatic diseases can be responsible for some of the worse examples of hip arthritis (b).

5. Inflammatory arthritis
This can be auto-immune (rheumatoid arthritis, SLE) or metabolic (gout) and is characterised by erosion of the joint (Figure 3b).

6. Secondary arthritis and other causes
Previous trauma, infection or congenital deformities (developmental dysplasia) or pediatric malformations (slipped capital femoral epiphysis and Perthe's disease) can all result in secondary arthritis in the adult. Disease in the spine and knee can sometimes be felt or referred to the knee (Figure 4).
 


Figure 4. The really bizarre case of arthritis shown here is of Charcot arthropathy where the patient has no feeling in the hip due to syphyllis. These patients indavertantly traumatize their hips (arrowed) without knowing it is as they have reduced pain sensation.

Conclusion
With increasingly better imaging a small group of individuals are being diagnosed with a decidedly Western form of hip disease. This condition was probably already prevalent in the community before but did not have an appropriate solution for care. Presently however, we are increasing our understanding of femoro-acetabular impingement offering repairs and osteoplasties at earlier stages and hip replacements in the older patients. This enables such patients to continue their active lifestyles.