Greater Valgus Alignment in Pediatric and Adolescent Patients with a Primary ACL Tear Compared with Healthy Controls

BACKGROUND: Coronal plane angular deformity remains under-investigated in the context of pediatric anterior cruciate ligament (ACL) tears. We hypothesized that baseline coronal alignment in pediatric and adolescent patients with a first-time ACL injury would differ from that in a matched healthy comparison population of patients without knee pathology. METHODS: Patients ≤18 years of age who underwent primary ACL reconstruction and had preoperative lower-extremity hip-to-ankle alignment radiographs (cases) and individuals without lower-extremity conditions that would influence alignment (controls) were matched 1:1 on the basis of age (±1 year) and sex. Coronal plane parameters included the hip-knee-ankle angle (HKA), mechanical axis deviation (MAD), mechanical lateral distal femoral angle (mLDFA), and medial proximal tibial angle (MPTA). Decision stump analyses were used to identify clinically relevant alignment threshold values. RESULTS: A total of 200 patients were included in the analysis (100 per group). The mean age was 12.7 ± 2.1 years in the ACL group (58% White/Caucasian, 50% female) and 13.1 ± 2.4 years in the control group (49% White/Caucasian, 50% female). Compared with controls, patients with an ACL tear demonstrated increased valgus alignment across all 4 parameters: MAD (-4.1 ± 7.8 versus -0.3 ± 7.6 mm; p < 0.001), HKA (-1.4° ± 2.6° versus -0.5° ± 2.3°; p = 0.006), mLDFA (85.3° ± 1.9° versus 86.1° ± 1.7°; p = 0.004), and MPTA (88.0° ± 1.8° versus 87.2° ± 1.9°; p = 0.004). Conditional logistic regression demonstrated increased odds of an ACL tear associated with each 1-unit increase in valgus alignment, as measured by MAD (inverse odds ratio [OR]: 1.06; 95% confidence interval [CI]: 1.02 to 1.10; p = 0.003), HKA (inverse OR: 1.14; 95% CI: 1.02 to 1.27; p = 0.022), mLDFA (inverse OR: 1.27; 95% CI: 1.08 to 1.50; p = 0.005), and MPTA (OR: 1.28; 95% CI: 1.07 to 1.53; p = 0.006). In the decision stump analysis of HKA, a value of -0.5° demonstrated that 60% of participants with ≥0.5° of valgus alignment had an ACL tear compared with 38% of patients with neutral alignment, varus alignment, or <0.5° of valgus alignment. CONCLUSIONS: Pediatric and adolescent patients with an ACL tear demonstrated greater valgus alignment than age- and sex-matched controls, with each 1° increase in HKA valgus alignment increasing the odds of an ACL tear by 14%. Routine preoperative assessment is necessary as coronal plane deformity is modifiable through concomitant implant-mediated guided growth in skeletally immature patients. The inclusion of coronal plane alignment parameters in ACL-related investigations is warranted to elucidate their contribution to injury risk and surgical outcomes. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.