Shoulder motion decreases as body mass increases in patients with asymptomatic shoulders

BACKGROUND: Higher complication rates are reported after shoulder arthroplasty in obese patients. Understanding the effect of body mass index (BMI) on range of motion (ROM) in asymptomatic shoulders may be useful in evaluating clinical outcomes for patients of varying BMIs presenting with shoulder pathology. The purpose of this study is to investigate patient characteristics, in particular BMI, that may affect ROM outcomes after shoulder arthroplasty. METHODS: Individuals aged 18 years or older (mean 57.21 ± 16.27 years) were recruited with asymptomatic shoulder presentation and without history of shoulder injury. A total of 224 shoulders were grouped into 4 BMI categories, and ROM was measured with a goniometer. Analysis was performed between patient demographics and ROM. RESULTS: Analyzed continuously, BMI negatively correlated with ROM for internal rotation (IR; r = −0.511, P < .01), forward elevation (FE; r = −0.418, P < .01), and external rotation (ER; r = −0.328, P < .01). ROM analyzed by BMI category revealed a dose effect of BMI vs ROM. Obese patients demonstrated a significant decrease in IR whereas morbidly obese patients had significant decreases for all ranges: IR (r = −0.469, P < .01), FE (r = −0.452, P < .01), and ER (r = –0.33, P < .01). Normal- and overweight patients revealed no significant correlations with ROM. CONCLUSION: As BMI is negatively correlated with ROM of the asymptomatic shoulder, patients with higher BMIs may be predisposed to diminished outcomes postoperatively. These baseline correlations will allow surgeons to make postoperative expectations and anticipate poorer outcomes of shoulder ROM in obese patients.