Subcutaneous Fat Thickness as a Risk Factor for Return to OR in Total Knee Arthroplasties

BACKGROUND: Total knee arthroplasty (TKA) is an increasingly common procedure performed in the United States. Post-operative complications after TKA, such as unplanned returns to the operating room for an infection or implant failure, can result in high morbidity for patients. Presently, several patient factors are used to identify higher risk patients prior to surgery, such as body mass index (BMI), although these have limitations. However, the amount of subcutaneous tissue at the surgical site affords an objective evaluation of the degree of surgical exposure required at the time of the operation. Increased amounts of subcutaneous tissue may lead to a prolonged dissection, which may increase rates of infection, which could result in unplanned returns to the OR. The aim of this study is to determine whether subcutaneous fat thickness as measured on pre-operative radiographs is a risk factor for return to OR for TKAs. METHODS: This is an IRB-approved, retrospective review of a series of 596 total knee arthroplasties at two hospitals in a large urban setting over a 2-year period (2010-2011). Pre-operative AP knee radiographs were reviewed and measurements were taken using the same imaging software. A medial knee adipose tissue (MKAT) score was calculated using the ratio of the total width of the distal femoral metaphysis perpendicular to the anatomic axis and the width of the medial adipose tissue along the same plane. Additional variables recorded included gender, ethnicity, diagnosis, laterality, pre-operative BMI, date of last follow-up, return to OR, revision, and deceased status. RESULTS: 596 patients were included in the analysis, of which 24 patients (4%) had an unplanned return to the OR within 3 months of the index operation. In this group, the average pre-op BMI was 32.9 and the average MKAT score was 0.46. The MKAT score was not significantly associated with return to OR (p = 0.15). Age and BMI were the only variables that were significantly associated with return to OR (p = 0.01 and 0.005). CONCLUSIONS: MKAT scores on pre-operative AP knee radiographs are not significantly associated with increased return to OR after primary TKA. The limitations of this study include its retrospective nature and small study population. Although we did not find a statistically significant difference between the two groups, this data is useful in that it can assist with surgical decision making. This data suggests that patients with increased subcutaneous tissue about the knee are not at increased risk of return to the OR after primary TKA.