Body Fat Percentage But Not BMI Was Related to Clinical Function in Patients With Adhesive Capsulitis After Manipulation Under Anesthesia

BACKGROUND: Adhesive capsulitis can substantially impair shoulder function, and manipulation under anesthesia is commonly used for patients with persistent symptoms, yet outcomes vary widely. Previous research has suggested that obesity, commonly assessed through BMI, influences recovery in musculoskeletal conditions. However, BMI does not differentiate between fat and lean mass, which may be more relevant to tissue healing and functional recovery. QUESTIONS/PURPOSES: (1) Does body fat percentage, rather than BMI, predict clinical outcomes after manipulation under anesthesia for adhesive capsulitis? (2) Do patients with different body fat percentage levels experience distinct postoperative clinical outcomes? (3) Are common metabolic comorbidities independent predictors of poor surgical recovery in this population? METHODS: Between December 2022 and December 2023, we treated 280 patients with adhesive capsulitis. Of these, 28% (78 of 280) of patients experienced satisfactory outcomes after nonsurgical treatment, 2% (6 of 280) of patients had concurrent shoulder disorders, and 4% (10 of 280) of patients lacked detailed clinical evaluations. The remaining 66% (186 of 280) of patients underwent manipulation under anesthesia and were the focus of this prospective, observational study. Among these patients, we excluded 0.5% (1 of 186) who received an additional nerve block treatment, 3% (5 of 186) who were transitioned to arthroscopic release, and 2% (4 of 186) who developed surgical complications. Additionally, 4% (7 of 186) of patients were excluded because they did not meet the minimum follow-up duration of 6 months, and 2% (3 of 186) of patients withdrew consent. Thus, 166 patients who underwent manipulation under anesthesia for refractory unilateral adhesive capsulitis at a tertiary care hospital were included in the final analysis. The mean age of the study population was 54 ± 8 years, 27% (44 of 166) of patients were male, and 26% (43 of 166) had left-sided involvement. Regarding comorbidities, 22% (36 of 166) of patients had diabetes, 24% (40 of 166) had hypertension, 23% (38 of 166) had hyperlipidemia, and 13% (22 of 166) had thyroid disorders. Preoperative body fat percentage was measured using bioelectrical impedance analysis 1 day before manipulation under anesthesia, and patients were categorized into sex-stratified body fat percentage groups. In addition to standard demographic and anthropometric assessments, patients were asked preoperatively whether they had a history of diabetes, hypertension, hyperlipidemia, or thyroid disorders. Venous blood samples were also collected after overnight fasting to assess fasting blood glucose, glycated hemoglobin (HbA1c), triglycerides, total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) levels. Functional outcomes were assessed at baseline and 6 months postoperatively, including passive ROM, the Constant-Murley score, Oxford shoulder score (OSS), and VAS for pain. Log-binomial regression was used to compare the predictive value of body fat percentage versus BMI on achieving excellent functional recovery (a Constant-Murley score more than 90). One-way ANOVA with post hoc tests were applied to examine differences in functional outcomes across body fat percentage categories. Additional log-binomial regression and multivariate linear regression models were constructed to evaluate the independent effects of metabolic comorbidities (including diabetes, hyperlipidemia, HbA1c, LDL) on recovery outcomes. RESULTS: After adjusting for other metabolic factors, including diabetes, hyperlipidemia, hypertension, and thyroid disease, we found that body fat percentage, but not BMI, predicted excellent recovery (a Constant-Murley score more than 90): Patients with low and healthy body fat percentages showed higher likelihoods of good outcomes compared with those with an obesity-level body fat percentage (relative risk [RR] 8 [95% confidence interval (CI) 2 to 38] and 14 [95% CI 3 to 64], respectively, with obesity defined as the reference with an RR of 1; p < 0.001). At 6 months after manipulation under anesthesia, female patients with low, healthy, and overweight body fat percentages demonstrated better forward elevation compared with those with an obesity-level body fat percentage (low- versus obesity-level percentages, mean difference 15° [95% CI 9° to 22°]; p < 0.001; healthy versus obesity, mean difference 15° [95% CI 9° to 20°]; p < 0.001; overweight versus obesity, mean difference 8° [95% CI 2° to 14°]; p = 0.004). Male patients showed similar differences with ROM. In addition, female patients with low and healthy body fat percentages demonstrated better Constant-Murley scores compared with those with an obesity-level body fat percentage (low- versus obesity-level percentages, mean difference 8 [95% CI 4 to 12]; p < 0.001; healthy versus obesity, mean difference 10 [95% CI 6 to 14]; p < 0.001; healthy versus overweight, mean difference 6 [95% CI 3 to 9]; p < 0.001). Female patients with low body fat percentages showed elevated pain during activity compared with obesity (low- versus obesity-level percentages, mean difference 1.2 on a 10-point VAS [95% CI 0.4 to 2.0]; p = 0.001). Furthermore, the presence of diabetes and hyperlipidemia were independently associated with a reduced likelihood of excellent recovery (no diabetes versus diabetes, RR 5 [95% CI 2 to 15]; p = 0.004; no hyperlipidemia versus hyperlipidemia, 6 [95% CI 2 to 17]; p < 0.001). After controlling for demographic factors (including sex, age, and duration of symptoms) and major metabolic comorbidities (including diabetes, hypertension, hyperlipidemia, and thyroid disease), we further examined which specific metabolic biomarkers were associated with postoperative ROM. Higher body fat percentage (B = -0.36 [95% CI -0.51 to -0.20]), HbA1c (B = -0.96 [95% CI -1.39 to -0.52]), triglycerides (B = -0.82 [95% CI -1.27 to -0.36]), and low-density lipoprotein (B = -0.93 [95% CI -1.62 to -0.25]) were each associated with lower forward elevation ROM at 6 months. Similarly, higher body fat percentage (B = -0.33 [95% CI -0.65 to -0.003]), HbA1c (B = -1.09 [95% CI -1.53 to -0.65]), and triglycerides (B = -0.78 [95% CI -1.25 to -0.31]) were each associated with lower Constant-Murley score at 6 months. CONCLUSION: In our study, body fat percentage was a more relevant indicator than BMI for postoperative functional recovery after manipulation under anesthesia. Tailored rehabilitation strategies, which prioritize pain management for patients with low body fat percentages and mobility restoration for groups with high body fat percentages, may help reduce the risk of poor clinical function. A comprehensive preoperative assessment that includes a body composition analysis and metabolic profiling may enhance risk stratification and guide personalized rehabilitation strategies. LEVEL OF EVIDENCE: Level II, therapeutic study.