Knee flexion angle is more important than guidewire type in preventing posterior femoral cortex blowout: a cadaveric...

This study compared femoral intraosseous "tunnel" length and distance from the posterior femoral cortex (PFC) when straight and flexible guidewires were drilled through an accessory anteromedial portal at 90° and 120° knee flexion. We had 2 study hypotheses: (1) 120° knee flexion would create longer femoral intraosseous tunnels than 90° knee flexion regardless of guidewire type and (2) 120° knee flexion would display a more consistent PFC blowout safety margin than 90° knee flexion regardless of guidewire type.

Straight and flexible guidewires were drilled at 90° and 120° flexion in 8 cadaveric knees. Guidewire intraosseous length and distance from the PFC were measured at both knee flexion angles. Two-way analysis of variance (guidewire type, knee flexion angle) and a Fisher exact test were used to compare group differences.

Guidewire exit points at 120° knee flexion were located farther from the PFC than at 90° knee flexion regardless of whether flexible guidewires (19.0 ± 5.3 mm v 12.6 ± 3.3 mm) or straight guidewires (12.9 ± 4.5 mm v 5.0 ± 3.3 mm) were used (P < .0001). Straight guidewires drilled at 90° knee flexion were within 3 mm of the PFC in 4 of 8 specimens (50%) compared with 0 of 8 at 120° knee flexion (P = .038). Intraosseous guidewire length was greater at 120° knee flexion regardless of whether straight or flexible guidewires were used (P = .04).

Flexible guidewires and a 120° knee flexion angle both decrease the likelihood of PFC blowout. A 120° knee flexion angle is more important to femoral tunnel length than guidewire type. Use of 120° knee flexion even when drilling flexible guidewires increases the safety margin needed to prevent PFC blowout.

When knee flexion is limited, curved guides and flexible guidewires can help reduce PFC blowout risk and achieve longer tunnels.