Shallow knee flexion angle during femoral tunnel creation using modified transtibial technique can reduce femoral graft bending angle in ACL reconstruction

Abstract

Purpose: The purpose of this study was to compare femoral graft bending angle between patients with femoral tunnel reamed at less than 80° of knee flexion and those with 80° and above in anatomical anterior cruciate ligament (ACL) reconstruction using modified transtibial technique.

Methods: Forty-eight patients who underwent ACL reconstruction using bone-patellar-tendon-bone autograft in modified transtibial technique and CT scan at 1 week postoperatively were included in this study. A femoral guidewire insertion into aimed femoral position at the medial wall of the femoral lateral condyle was started at about 75° of knee flexion. When the tip of the guidewire was blown out into femoral posterior wall, the guidewire was inserted again after increasing knee flexion angle. Distance from femoral tunnel exit on the femoral lateral cortex-femoral posterior cortex (Distance-E) was measured on postoperative lateral radiograph. Femoral and tibial tunnel position was measured on 3-D CT images. In addition, femoral graft bending angle was measured on reconstructed 2-D CT images. Patients were divided into two groups depending on whether femoral tunnel was created at less than 80° of knee flexion (group A) or 80° or more (group B).

Results: There were 32 patients in group A and 16 patients in group B, respectively. Average knee flexion angle was 77.2° [standard deviation (SD) 1.6] in group A and 83.6° (SD 2.4) in group B, respectively (p < 0.05). Average Distance-E was 5.1 mm (SD 2.6) in group A and 6.6 mm (SD 3.8) in group B, respectively. There was no significant difference in the femoral and tibial tunnel position between group A and B. Femoral graft bending angle was significantly smaller in group A [average angle: 50.9° (SD 6.6)] than in group B [average angle: 55.0° (SD 6.6)] (p < 0.05).

Conclusions: Anatomical femoral tunnel was able to be created at less than 80° of knee flexion in two-thirds of patients. Shallower flexion angle (less than 80°) provided gentler femoral graft bending angle compared to 80° or more of knee flexion. Therefore, femoral tunnel creation in modified transtibial technique should be started at between 75° and 80° of knee flexion to reduce femoral graft bending angle. Shallow knee flexion angle during femoral tunnel creation using modified transtibial technique can reduce femoral graft bending angle and may lead to better clinical outcomes in ACL reconstruction.

Levels of evidence: Retrospective comparative study, Level III.

Keywords: Anterior cruciate ligament; Bone–patellar tendon–bone autograft; Graft bending angle; Transtibial.