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

Important Factors for Retrograde Nailing Through Total Knee Arthroplasty: A Cadaveric Study

OBJECTIVES

Evaluate how total knee arthroplasty (TKA) implant design, femoral component size, and preoperative knee range of motion affect retrograde femoral nailing.

METHODS

Cadaveric specimens were prepared for TKA with a single radius (SR) or medial pivot (MP) design and tested with cruciate retaining (CR), cruciate substituting (CS), and posterior stabilizing (PS) 9-mm liners. Knee extension identified the minimum flexion required to pass an opening reamer without impinging on TKA components. The angle between the reamer path and the femoral shaft was calculated from lateral fluoroscopic images.

RESULTS

In SR TKA, the average flexion required was 70, 71, and 82 degrees for CR, CS, and PS, respectively. The required flexion in PS was significantly greater (P = 0.03). In MP TKA, the average flexion required was 74, 84, and 123 degrees for CR, CS, and PS, respectively. The required flexion was significantly greater in CS and PS designs (P < 0.0001). Femoral component size did not affect the minimum flexion required. The entry reamer resulted in 9.2 (SR) and 12.5 (MP) degrees of apex anterior deviation.

CONCLUSIONS

When performing retrograde nailing through either of these TKA designs with a 12-mm opening reamer, at least 70 degrees of knee flexion is required to avoid damage to the polyethylene liner or femoral component. PS implants require significantly more flexion with both TKA designs. Femoral component size did not affect the flexion requirement. Approximately a 10-degree deviation exists between the reamer path and femoral shaft.