Purpose: The increasing number of ACL reconstructions has led to the introduction of new techniques irrespective of the fact optimal tunnel angle placement has yet to be established. Improper tunnel angle placement is associated with a variety of complications including graft failure. The purpose of this retrospective study was to compare the reliability of tibial tunnel angles produced by two experienced surgeons using a free hand method or mechanical guide (HowellTM 65° Tibial Guide).

Method: Tibial tunnel angles in the coronal and sagittal planes were determined from anteroposterior and lateral radiographs, respectively, taken at 2 to 6 months postoperatively. Fifty-two sets of digital radiographs were analyzed (free hand = 28, mechanical = 24) with the knee in full extension 100 cm from the beam source. Tunnel angle measurements were calculated using NIH ImageJ software. Each angle was measured by two investigators on three separate occasions with minimum 7 days between each analysis.

Results: There was a significant difference (p< 0.05) in tibial tunnel angle placement between the mechanical guide (64.76 ± 5.88) and free hand (61.11 ± 5.04) group in the coronal plane. No significant difference in tibial tunnel placement in the sagittal plane was detected (mechanical guide =73.63 ± 7.69, free hand = 73.51 ± 6.68). Intra-rater and Inter-rater reliability for measurements in the sagittal (ICC = 0.809; 0.733) and coronal (ICC = 0.69; 0.812) plane ranged from high (> 0.75) to moderate (0.75–0.40), respectively.

Conclusion: Tibial tunnel angles in the coronal plane produced with a mechanical guide are more accurate than those drilled free hand when the intended angle of placement is 65°. The method used to measure tibial angles in this study was reliable within and between investigators. Further research will be conducted to investigate the correlation between tunnel angle placement and patient outcome measures.