Scapulothoracic orientation has a significant influence on the clinical outcome after reverse total shoulder arthroplasty.

ABSTRACT

BACKGROUND: Computer simulation has indicated a significant effect of scapulothoracic orientation and posture on range of motion (ROM) after reverse total shoulder arthroplasty (RTSA). We analyzed this putative effect on the clinical and radiologic outcome post-RTSA. METHODS: We retrospectively assessed 2-year follow-up data of RTSA patients treated at our clinic between 2008 and 2019. Patients were categorized into posture types A, B, and C based on an established method using scapular internal rotation on preoperative cross-sectional imaging. We compared differences in clinical ROM, pain, Subjective Shoulder Value, Constant Score, Shoulder Pain and Disability Index (SPADI), quality of life (EuroQol-5 Dimensions-5 Level utility index), and radiologic outcomes between posture types using linear regression analyses. RESULTS: Of 681 included patients, 225 had type A posture, 326 type B, and 130 type C. Baseline group characteristics were comparable, although the type C group had a higher proportion of females (60% [A], 64% [B], 80% [C]) with lower abduction strength (0.7 kg [A], 0.6 kg [B], 0.3 kg [C]) and a slightly higher proportion with a Grammont design RTSA (41% [A], 48% [B], 54% [C]). There were significant adjusted differences in mean (±standard deviation) active flexion (A 137° ± 21°; B 136° ± 20°; C 131° ± 19°) and passive flexion (A 140° ± 19°; B 138° ± 19°; C 134° ± 18°), active (A 127° ± 26°; B 125° ± 26°; C 117° ± 27°) and passive abduction (A 129° ± 24°; B 128° ± 25°; C 121° ± 25°), SPADI (A 81 ± 18; B 79 ± 20; C 73 ± 23), and pain (A 1.2 ± 1.7; B 1.6 ± 2.2; C 1.8 ± 2.4) between posture types at 2 years (P ≤ .035). A higher distalization shoulder angle was associated with better abduction in type C patients (P = .016). Type C patients showed a trend toward a higher complication rate (3.9% vs. 1.1% [A], 3.2% [B]) (P = .067). CONCLUSIONS: Type C posture influences the 2-year clinical outcome of RTSA patients in terms of worse flexion, abduction, SPADI, and pain. Scapulothoracic orientation and posture should be considered during the patient selection process, preoperative planning, and implantation of an RTSA.