Introduction: With external fixation of the femur and tibia, iatrogenic injury to neurovasculature from self-drilling tips of fixation pins is an important consideration in pin placement. Precise knowledge of the neurovascular anatomy in the distal femur and proximal tibia is important to limit potential pin misplacement. Method: Six pin placement sites on six cadaveric legs were used in accordance with current placement techniques. After pin placement, the soft tissue around each pin was dissected and the distances between the pin tips and the surrounding neurovasculature were measured. Results: The resultant data allow for a description of safe and unsafe corridors which can be used for external fixator pin placement. Safe sagittal insertion into the distal femur should consist of two pins: (1) 90 mm ± proximal from the proximal pole of the patella and 3 mm ± medially, (2) 55 mm ± proximal from the proximal pole of the patella and 2 mm ± laterally. Safe coronal insertion into the distal femur should consist of two pins: (1) 30 mm ± proximal to the lateral epicondyle, (2) 100 mm ± proximal to the lateral epicondyle. Safe proximal tibial pin placement should consist of two pins and be placed at an oblique angle: (1) 20 mm ± distal to the tibial tuberosity and 2 mm ± medially, (2) 55 mm ± distal to the tibial tuberosity and 2 mm ± medially. Discussion: This study forms an investigation into the safe areas for placement of external fixator pins, within the distal femur and proximal tibia, specifically, detailing the best practice for pin placement in relation to the tips of the external fixation pins.

A 74-year-old woman presented with sudden onset pain and swelling in her right wrist. Plain radiographs showed a pathological fracture through a lytic lesion. The patient had a past medical history of melanoma on her right thigh, which had been excised two years previously. She was referred to the bone cancer unit to undergo a series of investigations that included a magnetic resonance imaging scan, bone scintigraphy and a computed tomography-guided biopsy. Collectively, all investigations revealed a solitary bone metastasis from her previous melanoma in the right distal radius. The patient was treated symptomatically and underwent internal fixation with cement augmentation for symptom control. With the incidence of melanoma increasing, this case demonstrates the importance of being vigilant of unusual presentations.