Abstract
Introduction:
Reverse total shoulder arthroplasty (RTSA) has become instrumental in relieving pain and returning function to patients with end-stage rotator cuff disease. A distalized and medialized center of rotation in addition to a semi-constrained implant design allows the deltoid to substitute for the non-functioning rotator cuff. The purpose of this study was to examine the relationship between specific deltoid and rotator cuff muscle parameters and functional outcomes following RTSA.
Methods:
Patients undergoing RTSA by a single surgeon were enrolled in a prospective, IRB approved RTSA outcomes registry. Inclusion criteria were diagnosis of cuff tear arthropathy or massive rotator cuff tear, a minimum 2-year follow-up, and a preoperative shoulder MRI. We excluded patients undergoing revision arthroplasty, fracture, and a history of previous open shoulder surgery. For the 28 patients meeting our criteria, the cross-sectional area (CSA) of the anterior, middle, and posterior deltoid were measured on an axial MRI (Figure 1). Fatty infiltration (FI) of the deltoid, supraspinatus (SS), infraspinatus (IS), teres minor, and subscapularis were assessed on sagittal T1-MRI quantitatively via image processing and qualitatively on the 5-point Fuchs scale by a fellowship-trained musculoskeletal radiologist. Outcome measures included active forward elevation (aFE), active external rotation (aER), active internal rotation (aIR), strength in abduction, Constant-Murley score (CMS), Subjective Shoulder Value (SSV), Visual Analogue Scale (VAS) pain, and American Shoulder and Elbow Surgeons (ASES) total and ASES activities of daily living (ADL) scores as assessed by a trained, clinical research nurse. Correlation of deltoid CSA and FI with outcomes measures was analyzed with a Spearman rank correlation coefficient (ρ) with significance at P < .05.
Results:
The correlations between preoperative deltoid size and quantitative deltoid FI to postoperative function are shown in Table 1. The total deltoid CSA showed the most significant, positive correlations with outcome measures. The anterior deltoid CSA showed the strongest correlation to postoperative strength in abduction. Quantitative FI of the deltoid was negatively associated with several outcome measures (Table 1). Quantitative FI of the SS and IS demonstrated a significant negative correlation with aER (ρ = −.732, P = .039 and ρ = −.790, P = .004, respectively). The grade of FI, as assessed using the Fuchs scale, did not correlate to any clinical outcome data.
Discussion and Conclusion:
Preoperative deltoid size and FI of the deltoid and the rotator cuff muscles correlate to 2-year functional outcomes following RTSA. The anterior, posterior, and total CSA of the deltoid had significant, positive associations with several outcome measures, whereas FI of the deltoid, SS, and IS had significant, negative associations, particularly with humeral rotation. In the future, optimization of deltoid and rotator cuff muscle function preoperatively may improve functional outcomes in RTSA.
