Obesity Severity and Stiffness After Total Knee Arthroplasty Revisited: A Contemporary Analysis of Patients Requiring...

Obesity has historically been associated with worse outcomes following total knee arthroplasty (TKA), and concerns regarding postoperative stiffness and poor response to manipulation under anesthesia (MUA) have contributed to body mass index-based restrictions on surgical eligibility. Contemporary optimization and rehabilitation protocols may have mitigated these risks. This study evaluated the association between obesity severity and postoperative stiffness requiring MUA and post-MUA range of motion outcomes in a large modern obese cohort.

We retrospectively reviewed primary elective TKAs performed in patients who had a body mass index ≥ 30 at a single high-volume tertiary center between 2016 and 2022. Patients were categorized by World Health Organization obesity class. The primary outcome was stiffness requiring MUA. The secondary outcomes included repeat MUA, subsequent procedures for stiffness, maximum flexion, and post-MUA success, defined as achievement of ≥ 90 degrees of flexion without revision. Comparisons across obesity classes used Chi-square and nonparametric testing.

Among 12,237 TKAs, MUA was performed in 396 cases (3.2%) and did not differ across obesity classes (P = 0.132). Pairwise analysis showed a lower MUA rate in class III versus class II obesity (P = 0.018). Among 239 patients included in post-MUA analyses, overall success was 90.8%, including 93.1% in class III, and did not differ by obesity class (P = 0.896). Rates of repeat MUA, arthroscopic intervention, and revision for stiffness were similarly low across classes. The maximum postoperative flexion showed a modest, nonsignificant decrease with increasing obesity class (P = 0.145).

In this contemporary obese TKA cohort, increasing obesity severity was not associated with higher MUA rates, inferior post-MUA range of motion, or increased need for subsequent stiffness-related procedures. These findings suggest that increasing obesity severity is not associated with higher rates of postoperative stiffness or inferior outcomes following MUA and that concern for stiffness alone should not serve as a categorical barrier to TKA or MUA when clinically indicated.