Transient Hip Osteoporosis: What Happens Over Time?

In this article, orthopedic surgeons from Israel report on the natural history of transient hip osteoporosis. Natural history refers to what happens in the disease process and in the bone over time. Osteoporosis is a decrease in bone density potentially leading to weak and brittle bones. Transient means it’s temporary. The condition resolves or gets better over time.

Transient osteoporosis of the hip is rare but not unknown. There are certain groups of people affected most often. These include middle-aged men (ages 30-60) and pregnant women (during the third trimester). This doesn’t mean other people can’t develop this problem. Cases of transient osteoporosis of the hip have been reported in teenagers and women who aren’t pregnant. Such cases are very rare.

How would you know if you had this problem? First, symptoms of sudden hip and groin pain develop that get worse and cause the person to limp. The pain is severe enough to send the patient to the doctor. But X-rays and blood work are normal. The painful symptoms last several weeks to several months. The changes in bone go away gradually, usually within a year’s time.

MRIs are really needed to make the diagnosis. The authors of this study found that out by following a group of 37 men and women with this condition. The patients ranged in ages from 21 to 75 years old. None of the women in this study were pregnant. Although the left hip is affected most often during pregnancy, in this group of nonpregnant individuals, there was an equal distribution between right and left hips. A few of the men went on to develop transient osteoporosis of the other hip.

The investigators took X-rays and MRIs periodically throughout the course of treatment. Imaging studies were repeated during follow-up that extended over a period of years (up to nine years). X-rays did not show any evidence of osteoporosis or other changes to identify the problem. Bone scans suggested osteonecrosis (death of bone) in the head of the femur (thigh bone).

The key finding in MRIs was the presence of crescent lines. These are low-signal lines in the subchondral bone. Subchondral refers to the first layer of bone just under the joint cartilage. MRIs also showed fluid called bone edema. The authors caution that bone edema can be present with stress fractures and bone tumors. So the presence of bone edema doesn’t necessarily confirm that the patient has transient osteoporosis.

Special bone scans for osteoporosis called DEXA were done on 25 of the patients. DEXA stands for dual-energy X-ray absorptiometry. A more up-to-date abbreviation for that term is DXA. DXA provides a bone density measurement that can be compared to the expected norm. A small number of patients had severe enough osteoporosis to warrant treatment with medication. No real reason could be found for the problem. They did all have calcium-deficient diets.

Given the fact that transient osteoporosis of the hip goes away over time, it is considered a benign condition. MRIs are able to differentiate between transient osteoporosis and osteonecrosis. Treatment is very different for these two conditions, so making the distinction is helpful and important.

Conservative care is the standard for transient osteoporosis. Non weight-bearing with crutches is advised until the diagnosis is confirmed and stress fracture is ruled out. Once it’s clear that the condition is transient osteoporosis, then the patient can be progressed to walking with crutches while putting weight on the leg as tolerated by the individual patient. Swimming is encouraged and advised.

MRIs taken at six-week intervals showed a decrease in bone edema even as the patients reported reduced pain and improved function. Everyone in the study got better and the condition resolved on its own. The authors note that anyone with signs of osteoporosis that doesn’t go away with time must be followed carefully and treated more aggressively than when transient osteoporosis is the only problem. In such cases, DXA scans and lab work to look for an endocrine problem are advised.