Transient Osteoporosis of the Hip

The transient osteoporosis of the hip joint is the temporary loss of bone density in the head of the femur. The condition is often self-limiting and is different from both age-related osteoporosis and avascular necrosis of the hip joint.

The transient osteoporosis of the hip joint may cause disabling pain in the hip region that may cause the patient to limp. The management is nonsurgical but it is important to rule out other serious bone diseases such as avascular necrosis that may require early surgery.

The bones in the human body are living tissues that require a constant supply of nutrients and oxygen to maintain function. The bones consist of a bony matrix that is mineralized with calcium and phosphate to provide strength. The bone cells are involved in the constant turnover of the mineralization to maintain the structure and strength of the bone.

The hip joint is formed by the head of the femur that rotates in the socket formed by the acetabulum. The ends of the ball and the socket are covered with a glistening white tissue known as the articular cartilage. The articular cartilage allows the smooth rotation of the joint. The hip joint is unique due to its limited blood supply.

Transient Osteoporosis of the Hip joint – Causes and Risks

The exact cause of transient osteoporosis of the hip joint is unknown but it has been hypothesized to be caused by temporary disruption of the blood supply of the head of the femur. The loss of blood supply may be caused by blockage of the veins of the head of the femur. The veins take the blood away from the head of the femur after the nutrients are extracted from the arteries.

The blockage of the veins may create a back pressure that may lead to swelling in the head of the femur. The swelling may further reduce the blood supply to the head of the femur. The density of the head of the femur reduces leading to specific signs in radiological studies. The reduction in the bone density (osteolysis and osteoporosis) may decline further over the months and slowly recover in about 12 months.

The transient osteoporosis of the hip occurs most often in middle-aged men and pregnant females in the last 3 months of their pregnancy.

Symptoms

Patients with transient osteoporosis of the hip joint often complain of hip pain located over the groin region. The pain may be located on the side of the hip or even in the buttock besides the groin. Patients report worsening of the pain on weight-bearing activities such as walking, navigating stairs, or standing.

The hip pain may significantly worsen to the point where the patient may start limping. The limping occurs as the patient tries to spend less time on the painful hip while walking. The patient may also have painful movements, especially when doing those movements by themself (active movements). As the head of the femur gets considerably weaker, any high-impact activity may potentially lead to a fracture of the bone.

Diagnosis

The diagnosis of transient osteoporosis of the hip joint is a diagnosis of exclusion after all other possible diseases have been ruled out. The physician performs an extensive physical examination to look for tenderness (points of pain) and the hip range of motion. The physician may request radiological studies in the form of an X-ray.

The initial X-rays of the hip joint may be normal and only later X-rays may show a decrease in density of the hip joint. The joint space is always maintained (normal) in transient osteoporosis of the hip joint.

The physician may also order a CT scan that shows a higher resolution of the bony structures in the hip joint. MRI may show the early changes associated with transient osteoporosis of the hip. The MRI scan of the hip joint may show bone edema and the loss of density. A nuclear bone scan similarly is able to pick up the changes associated with transient osteoporosis earlier as compared to other modalities.

The radiological studies may be withheld in a pregnant female although an MRI is considered safe in pregnancy. However, any imaging study in a pregnant female is only done after consultation with their obstetrician and their primary care provider.

Management

The treatment of transient osteoporosis of the hip joint is nonsurgical. The management involves the use of pain medication such as nonsteroidal anti-inflammatory drugs like ibuprofen or naproxen, partial weight-bearing, and avoidance of any high impact activity. The patients may be advised to use a cane to offload the joint. Physical therapy is aimed to maintain the strength and flexibility of the muscles around the hip while not bearing weight.

Prognosis and Differential Diagnosis

The patients report a complete resolution from their symptoms in one to one and a half years. There is no residual deformity of disease that may cause long-term disability.

Transient osteoporosis may be confused with generalized age-related osteoporosis that affects all the bones of the body and not just the head of the femur. The patients suffering from osteoporosis are usually post-menopausal females or patients with metabolic bone disorders.

Transient osteoporosis may also be mistaken with another bone disease called avascular necrosis (AVN). In AVN of the hip joint, there is bone death of the head of the femur secondary to disruption of the blood supply. The exact cause is unknown in AVN but patients with a history of corticosteroid use or alcohol abuse are more susceptible to having AVN.

Any injury to the hip that may disrupt the blood supply may also cause AVN. Compared to transient osteoporosis, AVN of the hip generally affects both the hip joints. AVN of the hip joint is a progressive disorder that may require early surgical intervention compared to transient osteoporosis that is managed nonsurgically.