Transient osteoporosis: Not just the hip to worry about

Abstract

Transient osteoporosis (TO) is a clinical syndrome characterized by joint pain and the presence of bone marrow edema on magnetic resonance imaging (MRI), both of which spontaneously resolve over time. Transient osteoporosis most commonly affects the hip, but also may involve other lower extremity sites. TO likely represents a disorder that may be monoarticular or "migratory" with involvement of two or more lower extremity sites sequentially affected over a number of months. We report on two cases of transient osteoporosis, one involving the knee and one involving the hip, demonstrating the utility of serial bone mineral density measurements at both sites. Additionally, we are able to report on the microarchitectural changes seen at the distal femur on ultra-high resolution (7 T) MRI. Case #1 describes a recurrence of transient osteoporosis of the hip three years after a similar presentation at the contralateral hip and highlights the findings of rapidly changing bone mineral density in this clinical syndrome. In contrast to the spine, hip and forearm, peripheral bone density measurements at the knee are rarely reported and to our knowledge Case #2 represents the first report of transient osteoporosis of the knee demonstrating bone density findings similar to that seen in the hip. We postulate that transient osteoporosis of the knee is part of a clinical spectrum most commonly seen in the hip and one that is marked by lower extremity joint pain, bone marrow edema on MRI and transient decreases in bone mineral density all of which spontaneously resolve without sequelae.

Keywords: Bone marrow edema; High resolution 7 T MRI; Transient osteoporosis; Transient osteoporosis of the hip; Transient osteoporosis of the knee.

Fig. 1

A: Left femoral neck BMD of 0.783 g/cm² and a T-score of − 2.1; B: Normal right femoral neck bone density of 1.111 and a T score of + 0.

Fig. 2

A and B: Repeat BMD testing at 3 months revealing normal left and right femoral neck bone density.

Fig. 3

MRI of right hip revealing diffuse bone marrow edema.

Fig. 4

Repeat BMD when patient presented with right hip pain. A: Normal left femoral neck BMD. B: Right femoral neck BMD of 0.836 g/cm² with a T score of − 1.8.

Fig. 5

MRI of the left knee revealing marked bone marrow edema and focal subchondral fracture in the weight-bearing region of the lateral femoral condyle.

Fig. 6

A: High resolution 7 T MRI revealing deterioration of bone microarchitecture in the affected left knee (boxes) compared to the unaffected right knee; B: Higher power view of microarchitectural changes affecting distal femur.

Fig. 7

A and B: Bone density of left distal femur showing regional osteopenia with marked improvement of BMD at one year follow up.