2015 ISAKOS Biennial Congress ePoster #1410

Obesity Has No Effect on Outcomes Following Robotic-Assisted Unicompartmental Knee Arthroplasty

Johannes F. Plate, MD, PhD, Winston-Salem, NC UNITED STATES
Marco A. Augart, BS, Winston-Salem, NC UNITED STATES
Thorsten M. Seyler, MD, Baltimore, MD UNITED STATES
Daniel N. Bracey, MD, Winston-Salem, NC UNITED STATES
Aneitra Hoggard, BS, Winston-Salem, NC UNITED STATES
Dan Sun, BS, Winston-Salem, NC UNITED STATES
Michael Akbar, MD, Heidelberg GERMANY
Riyaz Hassanali Jinnah, MD, FRCS, Winston-Salem, NC UNITED STATES
Gary G. Poehling, MD, Winston-Salem, NC UNITED STATES

Wake Forest School of Medicine, Winston-Salem, NC, USA

FDA Status Cleared

Summary: Obesity had no influence on the mid-term clinical outcomes, readmission, and revisions rates of patients who underwent medial robotic-assisted UKA; however, obesity was associated with increased hospital resource utilization and narcotic pain medication requirements.




Obesity is described as a classic contra-indication to unicompartmental knee arthroplasty (UKA). In recent years, the indications for UKA have been expanded to include patients with a higher body mass index (BMI); however the impact of BMI on revision rates following UKA remains controversial. The purpose of this study was to assess the influence of obesity on the outcomes of UKA with a robotic-assisted system. The hypothesis was that increased body mass index does not influence the surgical outcomes and hospital resource utilization after robotic-assisted UKA.


The medical center joint registry was analyzed for patients who underwent robotic-assisted UKA and had a minimum follow-up of 24 months. Patients were stratified in weight categories based on the WHO classification system. Patient medical records were assessed for 90-day mortality and readmissions, postoperative complications, and revision rate. Patients’ postoperative opioid pain medication requirements and the number of physical therapy sessions for discharge clearance were recorded. Chi-square analysis was used to assess the influence of BMI on postoperative complications, revision surgeries, and 90-day readmissions. Correlation analysis was used to analyze the influence of BMI on length of surgery and hospitalization. Statistical analysis was performed with alpha 0.05.


There were 746 medial robotic-assisted UKAs (672 patients) with a mean age of 64 years (range, 28-90) and a mean follow-up time of 34.6 months (range, 24-65). Mean overall body mass index (BMI) was 32.1kg/m2 (range, 17.6-56.9); 61% of patients were overweight or obese (BMI 25-34.9 kg/m2) and 27% of patients were severely obese to super obese (BMI >35kg/m2). Patient BMI did not influence the rate of revision surgery to TKA (5.8%) or conversion from InLay to OnLay design (1.8%, p=0.338). The type of prosthesis (InLay/OnLay) regardless of BMI had no influence on revision rate (p=0.069).
There was significant correlation between increasing BMI and higher ASA score (p<0.001), but there was no correlation between Charlson comorbidity index and BMI (p=0.096). Mean length of surgery was 61 minutes (range, 17-152 minutes) without correlation to BMI (p=0.168). Mean length of hospitalization was 40 hours (range, 6-215 hours) without correlation to BMI (p=0.915). BMI did not influence 90-day readmissions (4.4%, p=0.526), but showed significant correlation with higher opioid medication requirements and a higher number of physical therapy session for discharge clearance (p=0.031).


These findings suggest that BMI has no influence on the short to mid-term clinical outcomes and readmission rates of patients who underwent medial robotic-assisted UKA. This finding concurs with previous studies assessing the influence of BMI on conventional UKA, which found no association between BMI and failure rate. The revision rate of the current study is similar to the reported revision rates of national registries. Therefore, the classic contra-indication of a BMI greater than 30kg/m2 may not be justified with the use of robotic-assisted UKA designs. Furthermore, BMI had no effect on length of hospital stay, length of surgery, or 90-day readmission rate. However, increased BMI was associated with increased narcotic pain medication requirements and utilization of physical therapy resources prior to discharge.