Biomechanical analysis of the pectoralis major tendon and comparison of techniques for tendo-osseous repair.

BACKGROUND: Various described surgical techniques exist for the repair of pectoralis major ruptures at the tendo-osseous junction. It is unclear how these techniques restore the native properties of the pectoralis major tendon because its biomechanical properties have not been described.

HYPOTHESIS: All repairs will have lower initial biomechanical profiles than the native attachment, and transosseous sutures will demonstrate improved initial biomechanical performance compared with anchors or buttons.

STUDY DESIGN: Controlled laboratory study.

METHODS: Twenty-four fresh-frozen cadaveric shoulders were randomized to 4 equal groups, including 3 experimental repair groups and 1 control group of intact pectoralis major tendons. The characteristics of the native anatomic footprint were recorded, and the experimental groups underwent pectoralis detachment, followed by subsequent repair. The restoration of the anatomic footprint was recorded. All specimens were tested with cyclic loading and load-to-failure protocols with load, displacement, and optical marker data simultaneously collected.

RESULTS: Under cyclic loading, the intact specimens demonstrated a significantly higher secant stiffness (74.8 ± 1.6 N/mm) than the repair groups (endosteal Pec Button [PB], 46.2 ± 6.4 N/mm; suture anchor [SA], 45.9 ± 8.7 N/mm; transosseous [TO], 44.2 ± 5.5 N/mm). Measured as a percentage change, the PB and SA groups showed a significantly higher initial excursion than the intact group (PB, 24.0% ± 11.7%; SA, 17.5% ± 6.9%; intact, 2.2% ± 1.0%), and the PB group demonstrated a significantly higher cyclic elongation than the intact group (PB, 7.5% ± 2.9%; intact, 1.5% ± 1.5%). Under load-to-failure testing, the intact group showed a significantly greater maximum load (1454.8 ± 795.7 N) and linear stiffness (221.0 ± 111.7 N/mm) than the 3 repair groups (PB, 353.5 ± 88.3 N and 63.5 ± 6.9 N/mm; SA, 292.0 ± 73.3 N and 77.0 ± 7.8 N/mm; TO, 359.2 ± 110.4 N and 64.5 ± 14.1 N/mm, respectively). All repair constructs failed via suture pulling through the tendon.

CONCLUSION: The biomechanical characteristics of the transosseous repair, suture anchors, or Pec Button repair were inferior to those of the native pectoralis tendon. There was no significant difference in any of the biomechanical outcomes among the repair groups. Further refinement and evaluation of suture technique and configuration in pectoralis major repair should be considered.

CLINICAL RELEVANCE: Transosseous repair, suture anchors, and endosteal Pec Buttons appear to confer similar biomechanical integrity for pectoralis major repair. Restricting early activities to thresholds below the identified failure loads seems prudent until soft tissue healing to bone is reliably achieved.