Coronal Alignment Patterns in Primary Anterior Cruciate Ligament Tears: The Influence of Tibial Dominance on Both Varus and Valgus Alignment

Background: While the effect of increased posterior tibial slope on the anterior cruciate ligament (ACL)-deficient knee is increasingly recognized, the specific patterns of coronal alignment and their effects on concomitant knee abnormalities remain relatively underappreciated. Purpose/Hypothesis: The purpose of this study was to evaluate overall coronal-plane alignment in patients with primary ACL tears, identifying individual mechanical femoral and tibial angles, and whether secondary concomitant injuries associated with ACL tears were related to overall or individual mechanical femoral and tibial alignment. Our null hypothesis was that there would be no differences in the tibial or femoral influence among the coronal alignment groups. Study Design: Case series; Level of evidence, 4. Methods: The preoperative coronal alignment of patients undergoing primary ACL reconstructions were assessed retrospectively between June 2019 and July 2024. Patients were categorized into neutral, varus, and valgus groups based on their long-limb coronal mechanical axis. Coronal measurements were obtained, including the mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA), to determine individual alignment of the femur and the tibia. The neutral mLDFA and mMPTA were defined by a range within 1 standard deviation from the mean mLDFA and mMPTA values of the neutral group. Varus and valgus alignment were assessed, including if the variation originated from the tibia, the femur, or both. Comparisons to posterior tibial slope, sex, and concomitant injuries were analyzed. Results: The study consisted of 250 patients (116 female). The mean mLDFA was 86.3 degrees +/- 1.7 degrees, and the mean mMPTA was 87.3 degrees +/- 2.2 degrees. The mean mechanical hip-knee-ankle angle and joint line convergence angle were 179.9 degrees +/- 2.9 degrees and 1.3 degrees +/- 1.0 degrees, respectively. On the basis of the mechanical axis, 113 patients were classified as having neutral alignment, 77 as having varus alignment, and 60 as having valgus alignment. The mMPTA was the primary cause of overall alignment in both the varus (54.5%) and valgus (65.0%) groups. Female patients had a significantly higher mMPTA than male patients (88.1 degrees vs 86.7 degrees, respectively), indicating less overall tibial varus alignment (P < .001), and there were significantly more female patients in the valgus group (P < .001). Concomitant meniscal, chondral, and ligament injuries displayed no significant associations between each coronal alignment group. Conclusion: The present study found that overall varus and valgus alignment were influenced more often by the tibia, or the mMPTA, than by the femur, especially for valgus alignment. Additionally, female patients exhibited significantly more overall valgus alignment than male patients, with the tibia being the primary determinant of valgus alignment. Finally, coronal alignment did not influence concomitant meniscal, chondral, or ligament injuries.