Biomechanical and Clinical Benefits of Pmma Augmentation of Post-Traumatic Void by Plating of Unstable Proximal Humeral Fractures

To investigate the biomechanical properties of locking-plate fixation and augmentation with PMMA cement placed in the posttraumatic void formed in humeral head and to assess its clinical application in the treatment of unstable proximal humeral fractures (PHFx). Biomechanical stability was investigated at three-fragment PHFx in 8 pairs of fresh-frozen humerus with a mean donor age of 76 and a range of 66–92, divided into 2 groups and fixed with a locking plate with identical screw position and configuration. Augmentation by 6 mL PMMA cement in plastic-phase placed in the posttraumatic void of the humeral head was performed in one of the groups. At the clinical outcomes of 120 patients with plated PHFx, assigned to groups of 63 cases with no augmentation, 28 with bonegraft augmentation and 29 with cement augmentation, were assessed in this study. DASH, CS, pain scores and range of motion were analyzed at 3, 6 and 12 months. Statistical analysis was performed with factors for treatment and age groups, Neer fracture types and follow-up periods, and with the consideration of age as a covariate. The biomechanical testing revealed that varus deformity, secondary dislocation, screw's cut-out and bending of the screws passing through the posttraumatic void from its distal row were statistically significantly less in the augmentation group with 2000, 4000, 6000, 8000 and 10000 cycles, p < 0.01. The number of cycles to reach 2 mm of fracture dislocation in the medial aspect of the humeral head was statistically significantly higher in the augmentation group, p = 0.02. The clinical results showed DASH and CS improved following cement augmentation at three and six months compared to bone grafting, being significant when correcting for age as a covariate (p ≤ 0.007). Established worsened values at a higher age for non-augmented and grafted patients (p ≤ 0.044), this was not the case for cement augmented patients (p ≥ 0.128). Augmentation with PMMA cement placed in the formed posttraumatic void of the humeral head during fixation of PHFx with a locking plate significantly increases stability against varus deformity and reduces the risk of biomechanical complications associated with osteosynthesis. From a clinical perspective treatment of metaphyseal defects with PMMA cement augmentation in elderly patients with complex PHFx, demonstrate equivalent short-term results to 6 months compared to augmentation with bone graft or no augmentation—despite the patient group being older and with a higher rate of more severe fracture patterns.