Is premorbid scapulohumeral rhythm restored with anatomic or reverse shoulder arthroplasty for cuff-intact osteoarthritis? An in-vivo dynamic radiography study

TL;DR

This study compares shoulder movement patterns after two types of shoulder replacement surgeries and finds that both improve movement but do not fully restore normal function.

Contribution

The study provides in-vivo dynamic radiography evidence on scapulohumeral rhythm restoration after anatomic and reverse shoulder arthroplasty.

Findings

Both aTSA and rTSA significantly improved scapulohumeral rhythm from preoperative levels.

Postoperative scapulohumeral rhythm was lower in both aTSA and rTSA groups compared to normal controls.

There was no significant difference in scapulohumeral rhythm between aTSA and rTSA postoperatively.

Abstract

Anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) are both treatment options for advanced glenohumeral osteoarthritis with an intact rotator cuff; however, decision making is controversial, especially among younger active patients. Restoring native shoulder kinematics may be an important consideration for implant longevity and ultimate shoulder function, but in-vivo assessment and comparisons have been historically difficult. The purpose of this study was to compare scapulohumeral rhythm (SHR) between aTSA and rTSA when performed for patients with cuff-intact osteoarthritis and compare these with preoperative values and normal controls.

A retrospective analysis was performed on 71 shoulders that underwent arthroplasty for cuff-intact osteoarthritis, aTSA (n = 28) and rTSA (n = 43), who had dynamic digital radiography performed more than 6 months postoperatively and compared these to 32 normal controls. SHR was calculated by dividing the change in glenohumeral abduction (ΔH) by the change in scapular upward elevation (ΔS) using the formula SHR = ΔH/ΔS, across the total range of abduction below 120° and between the 0°-30°, 30°-60°, 60°-90°, and 90°-120° abduction intervals. A paired subgroup analysis was performed on 14 aTSA and 14 rTSA shoulders with both pre- and postoperative dynamic digital radiography. Descriptive statistics were used to summarize data and differences between groups were analyzed using unpaired Student's t-tests for continuous variables, and a paired t-test for subgroup analyses, as well as a Bonferroni correction for multiple statistical tests. Interclass correlation of measurements was used to calculate the inter-rater reliability between the two measurers. All analyses were carried out using R v. 3.6.1. (R Foundation for Statistical Computing, Vienna, Austria). A P value of less than .05 was considered statistically significant.

The aTSA cohort had a similar median rest–120° SHR of 2.00 compared to 1.95 for the rTSA cohort (P = .948), but both were lower than normal controls with a SHR of 2.38 (P < .001). Preoperative vs. postoperative analyses of the aTSA and rTSA cohorts show significant improvements in preoperative to postoperative median rest–120° SHR from 1.36 to 2.10 (P = .0002) and 1.34 to 2.04 (P = .002), respectively. The inter-rater reliability was 0.99.

Patients who underwent aTSA and rTSA for rotator cuff–intact glenohumeral osteoarthritis are associated with lower SHRs than normal asymptomatic patients; however, SHRs significantly improved from preoperative levels. There was no difference between postoperative SHRs for rTSA and aTSA. aTSA and rTSA both partially restore coordination between the glenohumeral and scapulothoracic joints, although not to the extent of normal healthy shoulders.

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