Retrograde femoral nail placement: Quantifying the limits of knee flexion and extension

Background The purpose of this study was to identify the optimal degree of knee flexion to prevent intra-articular injury during retrograde femoral nail placement. Methods 10-mm retrograde femoral nails were inserted through a medial parapatellar approach into 12 cadaver knees to determine the safe range of flexion to allow reaming and nail passage without injury to the patella or tibia. Approximately one-third of the lengths of the nails were left protruding from the intercondylar notch, and the knees were ranged in flexion until contact was made with the patella and then into extension until contact was made with the proximal tibia. The angle at which contact first occurred was measured clinically and radiographically. A safe range for portal placement was determined. Results Nail placement without impingement on the patella or proximal tibia, as measured radiographically, was from a mean of 34° (range 27-42°) to 52°(range 45-56°) of flexion. The arc of safety, defined as the difference between the angle of the knee at initial contact of the nail and patella and the angle of the knee at initial contact of the nail and tibial plateau, was a mean of 17°(range 11-21°). Clinical measurements with a goniometer reflected a similarly acceptable range from approximately 35-60°. Conclusions Retrograde femoral nailing can lead to damage of the intraarticular surfaces of the knee. To mitigate this risk, use of a lateral radiograph with knee flexion angles ranging from 34-52° may aid in accurate portal creation and nail placement.