Influence of knee flexion and femoral cross-pin insertion angle on posterolateral structures of the knee and lateral fixation lengths during ACL reconstruction

Some studies have investigated knee flexion angle on the sagittal plane and insertion angle of the cross-pin on the coronal plane to evaluate proper femoral fixation. They evaluated the possibilities of injury to the posterolateral (PL) and neurovascular structures using several methods. The purposes of this study were to evaluate (1) the influence of knee flexion and femoral cross-pin insertion angles on knee PL structures and (2) the lateral fixation length of the cross-pin. Ten fresh cadaveric knees with no previous surgeries around the knee were used. Transtibial femoral tunnels (1:30 or 10:30 o'clock position) were made at three different knee flexion angles (70A degrees, 90A degrees, and 110A degrees). Two cross-pin guidewires (superior and inferior pins) were drilled at three different insertion angles [downward 30A degrees, 0A degrees (parallel to floor line), and upward 30A degrees] for each knee flexion position. The distances from the insertion point of the two cross-pins to the lateral collateral ligament (LCL) and popliteus tendon (PT), and the distance from the lateral wall of the femoral tunnel to the lateral cortex of the femoral condyle were measured. No significant differences were observed in the superior and inferior pin depths (p = 0.56 and 0.39). The distances from the superior pin to the LCL and from the inferior pin to the LCL were significantly shorter in all knee flexions with 0A degrees and an upward 30A degrees insertion angle than with 70A degrees and 90A degrees knee flexion with a downward 30A degrees insertion angle, respectively (superior pin: p = 0.02 and 0.03; inferior pin: p = 0.03 and 0.03). No significant difference was observed in the distance between the superior pin and inferior pins and the PT (p = 0.25). The cross-pin was inserted close to the LCL and PT, and a downward 30A degrees angle was the safest insertion angle. Lateral fixation length was sufficient for the cross-pin fixation in the 10:30- or 1:30-positioned femoral tunnel.