Subacromial Balloon Spacer Implantation for Massive Irreparable Rotator Cuff Tears Is Associated With Restoration of the Acromiohumeral Interval and Glenohumeral Center of Pressure: A Systematic Review and Meta-Analysis of Controlled Laboratory Studies

Background: Biodegradable subacromial balloon spacers (SBSs) have become increasingly used for the treatment of massive irreparable rotator cuff tears given their theorized clinical benefits; however, the relationship between biomechanical functions of the balloon spacer and clinical benefits remains unclear. Purpose: To perform a systematic review and meta-analysis of controlled laboratory studies investigating the use of SBSs for massive irreparable rotator cuff tears. Study Design: Systematic review and meta-analysis; Level of evidence, 4. Methods: PubMed, OVID/Medline, and Cochrane databases were queried in July 2022 for biomechanical data pertaining to SBS implantation in cadaveric models of irreparable rotator cuff tears. Random-effects meta-analysis of continuous outcomes using the DerSimonian-Laird method was performed to estimate pooled-treatment effect sizes between the irreparable rotator cuff tear state and the state in which an SBS was implanted. Data reported variably or in formats not amenable to analysis were presented descriptively. Results: Five studies involving 44 cadaveric specimens were included. At 0 degrees of shoulder abduction, SBS implantation resulted in a mean inferior humeral head translation of 4.80 mm (95% CI, 3.20-6.40; P < .001) relative to the irreparable rotator cuff tear state. This decreased to 4.39 mm and 4.35 mm at 30 degrees and 60 degrees of abduction, respectively. At 0 degrees of abduction, implantation of an SBS was associated with a 5.01-mm (95% CI, 3.56-6.46, P < .001) anterior translation of the glenohumeral center of contact pressure relative to the irreparable tear state. This translation changed to 5.11 mm and 5.49 mm at 30 degrees and 60 degrees of abduction. In 2 studies, SBS implantation restored the glenohumeral contact pressure to that of the intact state and significantly reduced subacromial pressure distribution over a rotator cuff repair state. In 1 study, a high balloon fill volume (40 mL) resulted in a significant 10.3 +/- 1.4-mm more anterior humeral head position relative to the intact cuff state. Conclusion: SBS implantation in cadaveric models of irreparable rotator cuff tears results in significant improvements in humeral head position at 0 degrees, 30 degrees, and 60 degrees of shoulder abduction. Balloon spacers may also improve glenohumeral and subacromial contact pressures, although insufficient evidence currently exists to corroborate these findings. High balloon fill volumes (40 mL) may confer supraphysiologic anteroinferior translation of the humeral head.