[The relationship between MRI findings and duration of symptoms in transient osteoporosis of the hip].

OBJECTIVES We investigated the relationship between magnetic resonance imaging (MRI) findings and duration of symptoms in patients with transient osteoporosis of the hip (TOH). METHODS The study included nine patients (7 men, 2 women; mean age 45 years; range 31 to 54 years) with TOH, whose symptoms disappeared after conservative treatment. MRI scans of the patients were retrospectively and independently reviewed twice by two radiologists to assess the presence of a subchondral hypointense fracture line, to calculate the area of subchondral fracture, and to classify the extent of bone marrow edema into four groups as A, B, C, and D. Duration of symptoms before and after MRI was recorded and associations between symptom duration and MRI findings were assessed. RESULTS The intraobserver and interobserver correlation coefficients showed an excellent agreement for both radiologists. A subchondral fracture was detected in seven patients; of whom, bone marrow edema corresponded to group B, C, and D in 2, 2, and 3 patients, and the mean fracture areas were 8.5 mm(2), 18.2 mm(2), and 29.7 mm(2), respectively. The mean symptom duration in these patients before MRI was 1.8 months (range 1 to 4 months), and relief of symptoms after MRI took 4, 5, and 6.6 months in groups B, C, and D, respectively. In the presence of a similar extent of bone marrow edema, the occurrence of subchondral fracture and increase in the fracture area were associated with delayed relief of symptoms. Subchondral fracture area was also correlated with the extent of bone marrow edema. Two patients without a subchondral fracture had bone marrow edema of group A and D, and the symptoms disappeared in one month and three months following MRI, respectively. CONCLUSION Our results show that the extent of involvement of the proximal femur may vary in TOH, and that time to clinical improvement may be closely related to the presence and size of subchondral fracture, and the extent of bone marrow edema.