Radiographically Occult Navicular Stress Fracture Diagnosed with Point of Care Ultrasound (POCUS): A Case Report

Case Diagnosis: 21 year-old female D1 distance athlete with insidious midfoot pain diagnosed with navicular stress fracture on ultrasound.

Case Description or Program Description: The patient presented with a two week history of right foot arch pain exacerbated by running. She reported a gradual onset of pain without known mechanism of injury or inciting event. Her pain was located at the medial longitudinal arch posteriorly, along the tibialis posterior tendon, and the navicular. Physical exam was notable for tenderness to palpation at the right medial longitudinal arch, the tibialis posterior tendon near the navicular bone, and at the navicular tuberosity. Ultrasound of the navicular was notable for significant cortical elevation, thickening of the region superficial to the cortex, increased power doppler flow deep to the cortex, and sonopalpation tenderness.

Setting: Military sports medicine clinic.

Assessment/Results: Radiographs were negative for fracture or stress injury. MRI noted osseous edema at the medial navicular with possible incomplete stress fracture. Follow-up CT and MRI were positive for navicular bone stress injury.

Discussion (relevance): Stress fractures account for 0.7% to 20% of all sports medicine clinic injuries. Navicular stress fractures are particularly notable because of their difficulty to diagnose in the early stages and high risk of nonunion. Plain radiographs can be normal for several weeks before callus or fracture lines appear. This can lead to a delayed diagnosis and possible complications, including bone remodeling, non-union injuries, and loss of function. MRI is the standard of care for detecting bone stress injuries, a non-invasive method with good sensitivity but high cost and poor accessibility in some areas. When in resource limited environments, such as certain deployable settings, POCUS can play a vital role in the early detection of stress fractures and prevention to significant disability.

Conclusions: POCUS has valuable utility in the early diagnosis of bone stress injuries, especially in environments without advanced imaging.