Outside-In vs. Anteromedial Portal Drilling During Primary ACL Reconstruction: Comparison at Two Years

Anteromedial (AM) and outside-in (OI) are two commonly used techniques for drilling the femoral tunnel during anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to compare clinical and radiographic outcomes of patients undergoing primary ACLR using either AM or OI femoral drilling with minimum two year follow-up.

Overall, 138 prospectively enrolled patients undergoing primary ACLR underwent AM or OI femoral drilling. Patients were categorized by femoral drilling technique and were evaluated pre-operatively as well as at six weeks and two years post-operatively. Outcomes scores were collected at each visit using SF-36 PCS and MCS components, KOOS, and the Knee Activity Rating Scale. Complications, including graft failure, stiffness requiring manipulation under anesthesia, and revision surgery were also collected.

Overall, 47 (34.1%) patients underwent AM femoral drilling and 91 (65.9%) patients underwent OI femoral drilling. Univariate analysis revealed no difference in pre-operative outcomes with the exception of the AM group having higher KOOS Knee Pain (p=0.023) and WOMAC Pain (p=0.036) scores. Postoperatively, OI femoral tunnels had a higher radiographic coronal angle (68.8°±8.6° vs 51.4°±11.3°; p<0.001) and knee extension (1.2°±2.7 vs 2.9°±4.0°; p=0.010). There were no differences in knee flexion, complications, or graft failure. Postoperatively, the AM group had higher KOOS ADL and WOMAC Functional (85 vs. 79 ,p=0.030) scores at the six week mark, although these differences did not meet the minimal clinically importance difference1. Graft failure at two years were similar in the AM and OI groups (8.5% vs. 6.6%, p=0.735). Multivariate analysis showed no clinical outcome differences between AM and OI techniques.

ACL reconstruction using the AM technique yielded lower radiographic coronal tunnel angle and slightly decreased knee extension. The theoretical risk of graft failure secondary to higher coronal angle of the graft as it passes around a sharper femoral tunnel aperture was not observed. Additionally, differences in pre-operative KOOS Knee pain existed but these differences were not significant postoperatively. We conclude no clinically relevant differences by two years in patients undergoing primary ACL reconstruction using either AM or OI femoral drilling techniques. Level of Evidence: Level II Prospective Comparative Study.