Extramedullary Guide Alignment Is not Affected by Obesity in Primary Total Knee Arthroplasty

Coronal alignment of the tibial implant correlates with survivorship of total knee arthroplasty (TKA), especially in obese patients. The purpose of this study was to determine if obesity affects coronal plane alignment of the tibial component when utilizing standard extramedullary tibial guide instrumentation during primary TKA. A retrospective review from June 2017 to February 2018 identified 142 patients (162 primary TKAs). There were 88 patients (100 knees) with body mass index (BMI) < 35 kg/m² and 54 patients (62 knees) with BMI ≥ 35.0 kg/m². The cohorts did not differ in age (p = 0.37), gender (p = 0.61), or Charlson's comorbidity index (p = 0.54). Four independent reviewers measured the angle between the base of the tibial component and the mechanical axis of the tibia on the anteroposterior view of long-leg film at first postoperative clinic visit. Outliers were defined as patients with greater than 5 degrees of varus or valgus alignment (n = 0). Reoperations and complications were recorded to 90 days postoperatively. There was no significant difference in mean tibial coronal alignment between the two groups (control alignment 90.8 ± 1.2 degree versus obese alignment 90.8 ± 1.2 degree, p = 0.91). There was no difference in varus versus valgus alignment (p = 0.19). There was no difference in the number of outliers (two in each group, p = 0.73). There was no difference in rate of reoperation (p = 1.0) or complication (p = 0.51). Obesity did not affect coronal plane alignment of the tibial component when using an extramedullary guide during primary TKA in our population.