BACKGROUND: Morbid obesity has been associated with increased complications after primary total knee arthroplasty (TKA), but previous studies have failed to take factors such as body composition and fat distribution into consideration. The aims of this study were to (1) assess the interobservable and intraobservable reliabilities of measuring anterior knee subcutaneous fat thickness on lateral knee radiographs and (2) determine if these measurements associate with early complications in patients with morbid obesity. METHODS: Using a retrospective case-control analysis, we reviewed 1689 primary TKAs performed in morbidly obese patients at our institution from 1995 to 2012. All patients (n = 58) who required reoperation for wound complication or infection within 90 days were compared to a matched cohort of morbidly obese patients who did not require early reoperation. Distances from patella skin (prepatellar thickness) and tibial tubercle skin (pretubercular thickness) were measured on routine lateral knee radiographs and associated with outcomes. RESULTS: Intraobserver and interobserver reliabilities were excellent for both measurements. Knees in the reoperation group had significantly greater prepatellar (P = .0001) and pretubercular (P = .0006) soft tissue thickness. Prepatellar thickness ≥15 mm and pretubercular thickness ≥25 mm increased the risk of early reoperation by 2.0× (P = .0003) and 1.6× (P = .023), respectively, and were more predictive measurements than body mass index. CONCLUSION: Anterior knee subcutaneous fat thickness can be reproducibly measured on lateral knee radiographs and is associated with a significantly increased risk of early reoperation for wound complications and infection after primary TKA in morbidly obese patients.
BACKGROUND: Morbid obesity has been associated with increased complications after primary total knee arthroplasty (TKA), but previous studies have failed to take factors such as body composition and fat distribution into consideration. The aims of this study were to (1) assess the interobservable and intraobservable reliabilities of measuring anterior knee subcutaneous fat thickness on lateral knee radiographs and (2) determine if these measurements associate with early complications in patients with morbid obesity. METHODS: Using a retrospective case-control analysis, we reviewed 1689 primary TKAs performed in morbidly obesepatients at our institution from 1995 to 2012. All patients (n = 58) who required reoperation for wound complication or infection within 90 days were compared to a matched cohort of morbidly obesepatients who did not require early reoperation. Distances from patella skin (prepatellar thickness) and tibial tubercle skin (pretubercular thickness) were measured on routine lateral knee radiographs and associated with outcomes. RESULTS: Intraobserver and interobserver reliabilities were excellent for both measurements. Knees in the reoperation group had significantly greater prepatellar (P = .0001) and pretubercular (P = .0006) soft tissue thickness. Prepatellar thickness ≥15 mm and pretubercular thickness ≥25 mm increased the risk of early reoperation by 2.0× (P = .0003) and 1.6× (P = .023), respectively, and were more predictive measurements than body mass index. CONCLUSION: Anterior knee subcutaneous fat thickness can be reproducibly measured on lateral knee radiographs and is associated with a significantly increased risk of early reoperation for wound complications and infection after primary TKA in morbidly obesepatients.