HISTORY: 20 year old NCAA Div. 3 female swimmer who was recently diagnosed with Hashimoto’s thyroiditis and placed on Levothyroxine 50mcg, about one month prior to presentation with no other significant PMH. She was running on the treadmill when she developed pain over the lateral right ankle. This was her only third time training on a treadmill, she typically does not run. She denied any trauma or falling while on the treadmill. She immediately stopped running, thinking the pain would subside, however it did not. She reported to the athletic trainer at her college. Her monthly menses that had not changed in frequency or intensity. PHYSICAL EXAMINATION: Well developed, well nourished, in NAD, slight limp. Thyroid: slight enlarged, no nodules. Skin: not dry Hair: not falling out CV: RRR, no murmurs, rubs. MSK: demonstrated normal strength, intact gross sensation of the foot and ankle, with TTP over the distal fibula, no deformity, minimal swelling of distal fibular. Her fibular rock test was negative. Her ATFL, CFL, and PTFL were all intact. Distal sensation was intact. Single leg heel raise was painful but could perform. DIFFERENTIAL DIAGNOSIS: 1) Lateral Ankle Sprain 2) Distal Tibia or Fibula occult or pathologic fracture 3) Tarsal Tunnel syndrome 4) Gout/ Pseudogout 5) Peroneal Tendon subluxations vs. tear 6) Degenerative Joint Disease 7) Osteochondral Lesion of Talus 8) Distal Fibular Stress Fracture 9) Popliteal Artery Entrapment 10) Exertional Compartment Syndrome TEST AND RESULTS: X-rays demonstrated a non-displaced transverse fracture of the distal fibula just proximal to level of the mortise. CBC: WNL, Chem 7: WNL. Following labs were ordered: PTH, TSH, estrogen, CBC and vitamin D levels. FINAL WORKING DIAGNOSIS: Non-traumatic Distal Fibular fracture in a swimmer TREATMENT AND OUTCOMES: She was placed in Short leg cast and made non-weight-bearing for 6 weeks. She progressed and did well. Lab work that was ordered was never acquired. She ended up transferring to a college in Colorado. Phone follow up was done. She has returned to swimming without issue. She no longer runs.