Purpose: The growing trend of morbidly obese (BMI 40+) patients requiring a total joint replacement is becoming major concern in total knee Arthroplasty (TKA). The purpose of this study was to investigate the affects that BMI may have on implant longevity and clinical patient outcome using historical patient data.

Method: A consecutive cohort of 3083 TKA’s in 2048 patients since 1995 (minimum 2 years follow-up) were evaluated. Pre-operative scores, latest scores, and change in clinical outcome scores (KSCRS, SF12, WOMAC) were analyzed using ANOVA and Kaplan-Meier (K-M) survivorship was determined.

Results: K-M cumulative survival at 10 years by BMI group was 0.951±0.033 for Normal and Underweight (< 25, n=277), 0.944±0.024 for Overweight (25–29.9, n=915), 0.882±0.032 for Obese (30–39.9, n=1460) and 0.843±0.076 for Morbidly Obese (40+, n=352). Cumulative revision rates were 1.8% for Normal and Underweight, 1.9% for Overweight, 2.9% for Obese and 2.8% for Morbidly Obese. All pre-operative clinical scores were significantly different between the Morbidly Obese and all other BMI groups (p< 0.05), with the non-morbidly obese having higher scores in all cases. Significant difference was found in the change in WOMAC domain scores and the KSCRS knee score (p< 0.05) between the morbidly obese group and all other BMI groups, with the morbidly obese having the greatest improvement in all domains.

Conclusion: The morbidly obese patient cohort (BMI > 40) undergoing TKA demonstrated the most significant improvement in clinical outcome scores; however also had the lowest cumulative 10 year survivorship. This risk/benefit information is important in pre-operative discussions with this challenging, and increasingly prevalent, patient population.