912 - Hip Pain in the Third Trimester: A Case of Transient Osteoporosis of Pregnancy

A 31 year-old G1P000 female at 35 weeks gestation presented to the Sports Medicine clinic for one month history of severe, progressive right hip pain and inability to bear weight on the affected extremity. Her pain began after she had outstretched her leg assisting someone at work. Afterwards, she had decreased range of motion with limited mobility requiring a wheelchair for ambulation. Physical examination revealed limited right hip range of motion, positive Stinchfield, FABER, FADIR, Scour tests and tenderness to palpation over the right greater trochanter. Magnetic Resonance Imaging (MRI) of the right hip confirmed an acute subchondral insufficiency fracture of the right femoral head with extensive associated bone marrow edema. She was managed conservatively with a strict six-weeks period of non-weight bearing of the right lower extremity, acetaminophen as needed for analgesia, and empiric vitamin D and calcium supplementation.

Discussions:

Transient osteoporosis of the hip in pregnancy should be considered a key differential diagnosis for third-trimester patients presenting with acute, debilitating hip pain. It’s a rare, transitory disorder that is thought to be idiopathic, though several pathophysiologic mechanisms have been proposed. These include vascular disturbances, neurogenic factors, hormonal changes, and altered calcium metabolism, particularly in the third trimester when fetal calcium demand peaks. Incidence and prevalence data have not been well established secondary to its rare nature and being under diagnosed. The development of a subchondral insufficiency stress fracture in this patient highlights a severe potential complication stemming from the profound, localized bone density loss characteristic of this condition.

Conclusions: This case emphasizes the importance of maintaining a high index of suspicion for transient osteoporosis of pregnancy in third trimester patients with debilitating hip pain. Prompt intervention with protected weight-bearing can alleviate symptoms and prevent progression to severe complications such as insufficiency fractures.