Obesity Does Not Compromise Outcomes of Robotic-assisted UKA

    A study from Wake Forest School of Medicine found no correlation between increasing BMI and outcomes or resource utilization following unicompartmental knee arthroplasty. The exceptions: opioid pain medication use and physical therapy sessions.

    Researchers from Wake Forest School of Medicine, Winston-Salem, North Carolina, have found that obesity does not have an adverse effect on outcomes in robotic-assisted unicompartmental knee arthroplasty (UKA).

    The study was presented at the 2015 ISAKOS Biennial Congress in Lyon France.

    In the past, orthopaedic surgeons had generally shied away from performing UKA in patients with a higher body mass index (BMI). But as the technique for UKA has improved, and complication rates have been reduced, surgeons have been more willing to expand the indications for UKA to include patients with a higher BMI.

    The goal of the study from Wake Forest was to evaluate the impact of BMI on outcomes of UKA with a robotic-assisted system. The researchers used their medical center’s joint registry to examine data on 746 medial robotic-assisted UKAs (672 patients) with a mean follow-up of 34.6 months (range, 24-65).

    Patients had a mean age of 64 years (range, 28-90) and a mean BMI of 32.1kg/m2 (range, 17.6-56.9). Most patients – 88% – were overweight:

    • 61% were overweight or obese (BMI 25-34.9 kg/m2)
    • 27% were severely to super obese (BMI >35kg/m2)

    The researchers hypothesized that BMI would not influence outcomes or hospital resource utilization.

    They were right on the first count: BMI had no effect on revision to total knee arthroplasty or conversion from an inlay to an onlay prosthesis design. The researchers found a significant correlation between increasing BMI and higher ASA score (P<0.001), but no correlation between Charlson comorbidity index and BMI (P=0.096).

    They were also partly right on the second count: BMI did not correlate with mean length of surgery (61 minutes; range, 17-152, P=0.168), mean length of hospitalization (40 hours; range, 6-215 hours; P-0.915), or 90-day readmission rate following the procedure (4.4%, p=0.526).

    But increasing BMI did correlate with 2 factors related to the hospitalization for UKA: higher opioid medication requirements and higher number of physical therapy sessions before the patient could be cleared for discharge (P=0.031).

    The researchers noted that their revision rate – 5.8% – is in line with revision rates reported for conventional UKA (4.7% to 6.5%) by national registries in Australia, New Zealand, Sweden, Norway, and the United Kingdom.

    They believe that based on their results, “the classic contraindication of a BMI greater than 30kg/m2 may not be justified with the use of robotic-assisted UKA designs.”


    Plate JF, Augart, MA, Seyler TM, et al. Obesity Has No Effect on Outcomes Following Robotic-Assisted Unicompartmental Knee Arthroplasty(ePoster 1410). Presented at the 2015 ISAKOS Biennial Congress, June 7-11, 2015, Lyon France.