Biomechanical evaluation of cable and suture cerclages for tuberosity reattachment in a 4-part proximal humeral fracture model treated with reverse shoulder arthroplasty

• Published in: Journal of shoulder and elbow surgery 2018-10, Vol.27 (10), p.1816-1823
• Main Authors: Knierzinger, Dominik, Heinrichs, Christian H., Hengg, Clemens, Konschake, Marko, Kralinger, Franz, Schmoelz, Werner
• Format: Article
• Language: English
• Subjects: Aged; Arthroplasty, Replacement, Shoulder; Biomechanical Phenomena; Cadaver; Epiphyses; Female; Fracture Fixation, Internal - methods; Humans; in vitro investigation; Male; Materials Testing; Middle Aged; proximal humeral fracture; reverse total shoulder arthroplasty; Shoulder Fractures - surgery; suture; Sutures; Titanium; titanium alloy cable; Tuberosity reattachment
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2018.04.003

Sufficient tuberosity fixation in proximal humeral fractures treated with shoulder arthroplasty is essential to gain a good clinical outcome. This biomechanical study evaluated the strength of the reattached tuberosities in reverse total shoulder arthroplasty fixed with cables or with sutures in a cerclage-like technique. Considering the mechanical advantages of flexible titanium alloy cables compared with conventional sutures for cerclage-like fixations, we hypothesized that titanium alloy cables would achieve higher fixation strengths of the tuberosities compared with heavy nonabsorbable sutures. A 4-part fracture was created on 8-paired proximal human humeri. The tuberosities were reduced anatomically and fixed by 2 heavy nonabsorbable sutures (suture group) or by two 1-mm titanium alloy cables (cable group) in a cerclage-like technique around the neck of the prosthesis. The humeri were placed in a custom-made test setup enabling internal and external rotation. Cyclic loading with a stepwise increasing load magnitude was applied with a material testing machine, starting with 1 Nm and increasing the load by 0.25 Nm after each 100th cycle until failure of the fixation occurred (>15° rotation of the tuberosities). Any motion of the tuberosities was measured with a 3-dimensional ultrasound motion analysis system. Overall, the cable group reached 1414 ± 372 cycles, and the suture group reached 1257 ± 230 cycles until the fixations failed (P = .313). The suture group showed a significantly higher rotation of the lesser tuberosity relative to the humerus shaft axis after 200, 400, and 600 cycles compared with the cable group (P = .018-.043). Tuberosities reattached with cable cerclages showed higher fixation strength and therefore less rotation compared with suture cerclages in a 4-part proximal humeral fracture model treated with reverse total shoulder arthroplasty. Whether this higher fixation strength results in higher bony ingrowth rates of the tuberosities and thus leads to a better clinical outcome needs to be investigated in further clinical studies.