Effect of nonweight bearing on tibial bone density measured by QCT in patients with hip surgery.

Tibial bone mineral density (BMD) was measured in 11 patients who had undergone hip joint surgery, including 10 women (22-61 years old; mean +/- SD = 42.6+/-10.3) and 1 man (61 years old). Four patients received total hip replacement (THR), while the others underwent rotational acetabular osteotomy (RAO). In one case, the start of rehabilitation was delayed until 4 months after the surgery because of infection at the surgical site. Nine patients underwent hip surgery for osteoarthritis and 2 patients for avascular necrosis. These 2 patients had a history of medication with corticosteroid. BMD of the tibia on the surgically treated side was measured by a peripheral quantitative CT (pQCT) system, which provided three different BMD values of trabecular BMD in the distal portion, total BMD in the distal portion, and total BMD in the diaphysis. The measurements were obtained preoperatively, and at several time points postoperatively, at 2, 4, 6, and 8 weeks and 3, 4, 5, 8, 12, 18, and 24 months after surgery. Brief periods of nonweightbearing lead to significant bone loss, and 1-1.5 years was required to recover to the baseline BMD. Accelerated bone loss was seen in patients in the perimenopausal state, with prolonged bed rest, and in patients receiving corticosteroid. Both trabecular and cortical components were influenced by nonweightbearing and restoration of weightbearing. The decrease in the cortical region occurs after the decrease in the trabecular and endosteal regions.