THU439 Baby's Coming, Break A Leg! A Case Of Transient Osteoporosis Of The Hip

Disclosure: A. Khan: None. A. Syeda: None. H.B. Aftab: None. Introduction: Pregnancy-associated osteoporosis (PAO) is a rare condition presenting as fragility fractures usually in the latter part of pregnancy or immediate postpartum period. Vertebral fractures are more commonly reported but femoral fractures have also been described in the literature as a distinct entity: transient osteoporosis of the hip (TOH). We present a case of bilateral (B/L) femoral fractures in a woman during pregnancy and in the postpartum period. Case: A 31-year-old, gravida 1 female developed left leg pain at 26 weeks of gestation. The pain radiated from her left lower back to her left knee. It was severe in intensity resulting in her walking with crutches. Subsequent MRI of the left hip showed subchondral insufficiency fracture of the femoral head with prominent bone marrow edema extending from the head into the femoral neck. She was managed conservatively with non-weight bearing status and oral analgesics. She had an uncomplicated vaginal delivery at 39 weeks of gestation. During the first postpartum week she developed right hip pain. MRI of right hip revealed nondisplaced right femoral head subchondral insufficiency fracture with associated effusion and synovitis. She recovered within the next 3 months with resolution of her pain with conservative management. Other than limited calcium intake in childhood, there were no other identifiable risk factors for osteoporosis. Bone density scan revealed normal Z-scores at the lumbar spine and non-dominant wrist. The hips were not evaluated. Workup for secondary causes of osteoporosis was unremarkable including normal serum calcium, PTH, phosphorus, magnesium, SPEP, tissue transglutaminase antibodies, estradiol, LH, FSH, prolactin levels. However, 24-hour urine calcium level was low at 11 (35-250) mg/24hr. Elevated levels of bone specific alkaline phosphatase and urine N-telopeptide (NTX) were noted at 19.9 (5.3-19.5) mcg/L and 110 (4-64) nM BCE/mM creatinine, respectively. Patient was continued on vitamin D and calcium supplements. She breastfed for the initial 2 months but was advised to stop. At her most recent follow up visit 4 months postpartum patient was doing well. Discussion: TOH is a rare entity, and presentation as B/L femoral fractures is exceedingly rare. During pregnancy and lactation, the skeletal system undergoes bone loss to compensate for the calcium demand of the fetal skeletal system. In TOH, venous stasis from the gravid uterus resulting in bone marrow edema is the proposed mechanism in addition to pregnancy associated bone loss. In our patient, a low 24-hr urine calcium could suggest low calcium intake which could have contributed to the fracture as well. While recurrence of PAO has been described, no recurrence of TOH has been reported in subsequent pregnancies. Our case highlights the importance of keeping this rare entity on the differential in pregnant women presenting with back or hip pain. Presentation: Thursday, June 15, 2023