Unicortical button fixation provides higher strength compared with transosseous repair for subscapularis tendon in total shoulder arthroplasty

Phob Ganokroj; Alexander R Garcia; Justin F M Hollenbeck; Ryan J Whalen; Justin R Brown; Amelia Drumm; Trevor J McBride; Sunikom Suppauksorn; Toufic R Jildeh; Matthew T Provencher

doi:10.1016/j.jse.2024.07.019

Unicortical button fixation provides higher strength compared with transosseous repair for subscapularis tendon in total shoulder arthroplasty

J Shoulder Elbow Surg. 2024 Aug 31:S1058-2746(24)00611-6. doi: 10.1016/j.jse.2024.07.019. Online ahead of print.

Affiliations

¹ The Steadman Philippon Research Institute, Vail, CO, USA; Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
² The Steadman Philippon Research Institute, Vail, CO, USA.
³ The Steadman Philippon Research Institute, Vail, CO, USA; Department of Orthopaedic Surgery, Brooke Army Medical Center, Fort Sam Houston, TX, USA.
⁴ Institute of Orthopaedics, Lerdsin General Hospital, Bangkok, Thailand.
⁵ The Steadman Philippon Research Institute, Vail, CO, USA; Department of Orthopaedic Surgery, Michigan State University, East Lansing, MI, USA.
⁶ The Steadman Philippon Research Institute, Vail, CO, USA; The Steadman Clinic, Vail, CO, USA. Electronic address: mprovencher@thesteadmanclinic.com.

PMID: 39218347
DOI: 10.1016/j.jse.2024.07.019

Abstract

Background: Subscapularis tendon (SSc) dysfunction after total shoulder arthroplasty (TSA) results in poor functional outcomes. There have been numerous SSc repair constructs tested biomechanically and clinically; however, none has been demonstrated as superior. Newer techniques and implants have emerged but have not been fully tested.

Hypothesis: We hypothesized that the unicortical button (UB) fixation would provide significantly improved restoration of the anatomic footprint and biomechanical properties compared with transosseous (TO) repair of the SSc.

Methods: A digital footprint of SSc humeral insertion was obtained in 6 pairs of fresh-frozen cadaveric shoulders using a 3-dimensional digitizer. A complete SSc tear was created, and each pair of shoulders was randomized to either SSc repair with UB or TO repair. Each specimen underwent a cyclic loading protocol, followed by pull to failure. The failure load, elongation at failure, gapping failure, number of cycles until failure, the load at key gapping points (1 mm, 3 mm, 5 mm, and 10 mm), and the failure mode were recorded using high-resolution video recording. Three-dimensional surfaces of the insertion footprint and repair site were obtained, and surface areas were calculated using a custom MATLAB script and laser scanner. Paired t tests were conducted to compare differences between the 2 repair groups.

Results: Failure load was significantly higher in the UB group (382.4 N ± 56.5 N) than in the TO group (253.6 N ± 103.4 N, P = .005). TO repair provided higher gapping at failure (28.8 mm ± 8.2 mm) than UB repair (10.4 mm ± 6.8 mm, P = .0017). UB repair had significantly higher load at the 1-mm, 5-mm, and 10-mm gapping than TO repair, with P = .042, P = .033, and P = .0076, respectively. There were no significant differences in elongation failure, the difference in footprint area from native to repair states, or the percentage of the restored footprint area between the groups (P = .26, P = .18, and P = .21, respectively).

Conclusions: The UB fixation showed a significantly lower gap at failure, higher failure load and number of cycles until failure, and higher gap loads than the traditional TO repair for SSc. Although more clinical research is necessary, the UB fixation that uses cortical bone presents promising results.

Keywords: Subscapularis tendon; anatomic total shoulder arthroplasty; repair; subscapularis management; transosseous repair; unicortical button fixation.