Using hip measures to avoid misdiagnosing early rapid onset osteoarthritis for osteonecrosis.

In the early phases, subchondral insufficiency fractures and rapidly destructive osteoarthritis of the hip are often mistaken for osteonecrosis of the hip. Three hip measures were used comparing combined subchondral insufficiency fractures and rapidly destructive 18 osteoarthritis patients to 18 osteonecrosis patients. Due to the rarity of these conditions there was no statistical power. Initial diagnoses for the osteoarthritis patients were recorded. The osteoarthritis group had significantly higher means for Tönnis angle (P < 0.001), lateral center edge angle (P = 0.006), and acetabular extrusion index (P = 0.014). Only 7 of the 18 patients were initially diagnosed without reservation as subchondral insufficiency fracture or rapidly destructive osteoarthritis. Using hip measures will reduce the misdiagnosis of rapid onset osteoarthritis of the hip for osteonecrosis.