Safe Zones and Trajectory of Femoral Pin Placement in Robotic Total Knee Arthroplasty

BACKGROUND: Robotic-assisted total knee arthroplasty may result in array pin-related complications. Lack of knowledge on ideal pin placement results in varied insertion sites and trajectory, with unknown risks to surrounding neurovascular structures. METHODS: This study included 10 lower-extremity magnetic resonance images. Images were subdivided into 6 zones of study. Zones consisted of a correlating axial image with femoral pin placement replicated by drawing a line angled 45° from the anterior to posterior reference in the anteromedial to posterolateral femoral quadrants. The distances from the pin paths to the neurovascular structures were measured. RESULTS: Zone 2C demonstrated femoral pin trajectory an average of 14 mm from the femoral artery/vein. In Zone 2B, proximity increased to an average of 30 mm to the femoral artery and 29 mm to the femoral vein. At Zone 1A, the popliteal artery and vein were on average 22 mm from the femoral pin, while the common peroneal nerve was an average of 21 mm. Placing pins in Zone 1A poses a high risk of injury to the genicular arteries. Women demonstrated greater proximity to neurovascular structures than men in 66% of the sites (P < .05). CONCLUSIONS: This classification system for safe zones and trajectory of femoral pin placement in robotic-assisted total knee arthroplasty demonstrates that proximally, the profunda femoris and femoral artery/vein are at risk of injury, while distally, the genicular arteries, common peroneal nerve, and popliteal artery/vein are at risk. Caution should be exercised if femoral pins are inserted with an angle less than 45°, especially in women.