Neurovascular anatomy around the knee: Relevance of the dangers of self-drilling external fixator pin tips

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.