Forefoot Pain In Young Female Runner With Relative Energy Deficiency In Sport

HISTORY: 19 y.o. female runner with history of right third metatarsal stress fracture a year ago presented for second opinion on recurrent right forefoot pain. Medical history notable for iron deficiency anemia, one year of amenorrhea, gluten and lactose free diet. Four months prior, patient was completing return to run progression after stress fracture when she lost her balance while riding bicycle, slamming foot hard on concrete. Pain persisted, manifesting as dull ache worse at night and with walking, better with rest and ibuprofen. PHYSICAL EXAMINATION: BMI 18.2 kg/m2, 8th percentile for age. Bilateral pes cavus, for which she wears custom foot orthotics. Focal tenderness to palpation at right distal second metatarsal from both dorsal and plantar aspects. No pain with metatarsal squeeze. Otherwise range of motion and strength normal. DIFFERENTIAL DIAGNOSIS: 1. Second metatarsal bone stress injury2. Interdigital neuroma3. Plantar plate tear TEST AND RESULTS:- Labs notable for low estradiol with low normal FSH (hypothalamic amenorrhea); low T3 with low normal TSH & free T4 (sick euthyroid)- DXA with BMD Z-score of -1.7 in lumbar spine- MRI obtained soon after symptom onset showed bone marrow edema of second metatarsal head, with corresponding decreased T1 signal, interpreted as grade 3 stress reaction by radiology, orthopedic, and primary care sports medicine physicians- Radiograph at time of our evaluation showed flattening of second metatarsal head with sclerosis, consistent with Freiberg infraction FINAL WORKING DIAGNOSIS: Avascular necrosis of second metatarsal TREATMENT AND OUTCOMES: 1. Initial management for BSI in context of REDs. Continued nonweightbearing status for total of 8 weeks, with goal to avoid collapse or degeneration of metatarsal head and need for surgery.2. Shockwave previously reported for osteonecrosis to promote bone revascularization. Patient was treated with high energy electromagnetic focused shockwave (3000 shocks titrated to 0.40 mJ) for 5 sessions performed weekly.3. After 8 weeks, repeat MRI showed interval decrease in subchondral edema of second metatarsal head with decreased conspicuity of fracture line; no evidence of subarticular collapse. Weightbearing was gradually advanced. She returned to unrestricted running without return of pain.