Quantifying and comparing torsional strains after olecranon plating

Purpose: Any torsion experienced at a fracture site will directly translate into shearing forces and has been regarded as detrimental to healing. The purpose of this study was to determine which plating system currently on the market controls torsional forces about comminuted olecranon fractures most effectively. Methods: Five olecranon plates (Acumed, Synthes-SS, Synthes-Ti, ITS/US Implants and Zimmer) were implanted to stabilise a simulated comminuted fracture pattern in 50 fresh-frozen, cadaveric elbows. All specimens were evaluated by dual energy X-ray absorptiometry (DXA) scan to determine bone density. Three-dimensional displacement analysis was conducted to assess fragment motion through physiologic cyclic arcs of motion. The specimens were cycled through progressive physiologic loads (0.18-5.6 kg). Movements of the fragments were statistically compared amongst the different implants using one-way analysis of variance (ANOVA) and Tukey Honestly Significant Difference (HSD) post hoc comparisons with a critical significance level of α = 0.05. Results: DXA bone mineral densities (BMDs) ranged from 0.465 to 0.927, with an average of 0.714. The Acumed, Synthes-SS, Synthes-Ti and Zimmer plates allowed <1° of torsion up to 1.6 kg of load. The differences between these plates at this load were not statistically significant. The ITS/US Implants plate, however, allowed significantly more torsion above loads of 2.6 kg (p = 0.045) compared with all other plates. The ITS/US Implants plate allowed over 2° of torsion at 2.6 kg (p = 0.012), and nearly 3° at 3.6 kg (p = 0.045). The Zimmer plate consistently allowed more torsion than the Acumed plate or either of the Synthes plates, but the differences were not statistically significant. Conclusion: Regardless of which olecranon plate is used, the authors recommend limiting postoperative rehabilitation loads to below 1.6 kg in an effort to minimise the detrimental effects of torsion on healing. If loads over 1.6 kg are anticipated, the authors recommend the use of the Acumed plate or either of the Synthes plates.