Biomechanical strength and failure mechanism of different tubercula refixation methods within the framework of an arthroplasty for shoulder fracture.

BACKGROUND: Tuberosity repair in shoulder fracture prosthesis implantation still remains a challenge often leading to poor functional outcomes, despite a variety of materials and suggested suture patterns. We aimed to evaluate, which forces currently used suture and cerclage materials withstand and to assess whether they are useful with regard to stability of reconstruction of tuberosities and which failure modes they display.

MATERIAL AND METHODS: Using sheep infraspinatus tendons with attached tuberosities three different suture materials (suture 1: Ethibond size 2; suture 2: Orthocord size 2; suture 3: Fiberwire size 5) and a 0.8mm titanium cerclage wire were investigated. For each suture material as well as the cerclage wire 6 tests were carried out. A material testing machine was used to perform cyclic loading tests (20mm/min, Fmin =50N, Fmax =100N, respectively after 50 cycles: Fmax +50N until failure). Outcome measures and thus comparison criteria were the maximum holding force, number of cycles reached, total elongation of the system (tendon and suture) and qualitative appraisal and documentation of the mechanism of failure.

RESULTS: Overall average maximum forces between the fixation materials differed significantly (P=0.003), especially suture 3 (braided polyethylene coating, non-resorbable polyfile UHMW core) displayed superior results in comparison to the cerclage wire (P=0.016). Although, primary elongation of the cerclage technique was significantly lower compared to the suture materials (P=0.002). All tests showed a high initial lengthening and caused incision-like defects in the bone or tendon and led to failure and huge displacement of the tuberosities.

DISCUSSION: Currently used suture and cerclage materials have a limited usefulness for refixation of tuberosities due to an increased risk of obstruction for bony consolidation.

LEVEL OF EVIDENCE: Basic science, Biomechanics.