A biomechanical evaluation of rotator cuff footprint contact mechanics after rotator cuff repair with and without the augmentation of a subacromial balloon.

Background: It was the objective of this study to evaluate the contact area and pressure between a repaired rotator cuff tendon and bone for several different rotator cuff repair techniques, with and without a subacromial balloon spacer. It was hypothesized that the contact area and pressure at the rotator cuff footprint would increase with a subacromial balloon spacer following all repair techniques evaluated.

Methods: Ten cadaveric shoulders were mounted onto a biomechanical shoulder simulator. A full-thickness 2-cm rotator cuff tendon tear was simulated, and repaired using single-row, double-row, and transosseous equivalent (TOE) techniques. Each repair was assessed without and with subacromial balloon augmentation (InSpace System; Stryker). The balloon spacers were evaluated with 60%, 80%, 100%, and 120% of their recommended final fill volume. The orientation of the balloon was also examined by inserting it through lateral and posterior shoulder portals. A thin pressure sensor film (Model 4201; Tekscan Inc.) was securely fixed to the rotator cuff footprint at the location of the tendon tear prior to testing and was used to evaluate contact area and pressure between the repaired tendon and bone for each variable assessed.

Results: Without balloon augmentation, the greatest contact area and pressure were observed with the TOE technique, followed by double-row and single-row methods (P < .001). Subacromial balloon augmentation only significantly (P = .003) increased contact area for the single-row technique. Among the 3 techniques, balloon augmentation did not significantly increase contact pressure (all P ≥ .136). Balloon spacer orientation was found to significantly influence contact area (P = .007), whereas the spacer orientation (P = .059) and fill volume (P = .197) did not significantly influence contact pressure. Optimal contact area and pressure at the supraspinatus footprint were observed when using a TOE repair technique with a balloon spacer inserted through a lateral portal with a fill volume below that of the recommended fill volume.

Discussion: Subacromial balloon augmentation following rotator cuff repair significantly enhances the contact area between the repaired tendon and bone when used with a single-row repair technique. Balloon augmentation, however, did not significantly increase rotator cuff footprint pressure or contact in a double-row or TOE repair techniques. Insertion of the spacer through a lateral portal with a fill volume less than or equal to that of the recommended final fill volume was found to result in the most optimal contact area and pressure between the repaired tendon and bone.