Extramedullary Tibial Guide Alignment Is Not Affected by Excess Lower Limb Fat Distribution in Total Knee Arthroplasty

Background The goal of this study is to investigate whether excess lower limb fat distribution affects tibial guide alignment in conventional total knee arthroplasty (TKA) with extramedullary guides. A thicker soft tissue envelope may affect the accuracy of extramedullary cutting guide placement and subsequent instrumentation. Previous studies have used body mass index (BMI) to stratify patients, a poor proxy of lower limb fat distribution, which may explain conflicting results reported on this topic to date. This study overcomes this issue by using a novel, radiographic anthropometric index to assess lower limb fat distribution. Methodology This is a single-surgeon, single-implant, single-centre retrospective series of 102 consecutive primary TKAs. The suprapatellar fat index (SPFI) and BMI were recorded for all patients, and postoperative tibial component alignment measurements were calculated. Secondary outcome measures included femoral component alignment, femorotibial alignment, length of hospital stay, tourniquet time, blood loss, and complications/reoperations. Results In this study, 102 patients (average age of 69) had an average BMI of 30.8 kg/m(2) (19.2-45.5 kg/m(2)) and an average SPFI of 0.26 (0.09-0.57). Multiple regression analysis demonstrated that increasing leg fat distribution did not affect tibial component alignment in the coronal or sagittal plane. Conclusions Excess lower limb fat distribution, simply measured using the SPFI , does not have a significant effect on tibial component positioning when extramedullary guides are used in conventional TKA.