Evaluating the stability of external fixators following pelvic injury: A systematic review of biomechanical testing methods

This systematic review aims to identify previously used techniques in biomechanics to assess pelvic instability following pelvic injury, focusing on external fixation constructs. A systematic literature search was conducted to include biomechanical studies and to exclude clinical trials. Of an initial 4666 studies found, 38 met the inclusion criteria. 84 % of the included studies were retrieved from PubMed, Scopus, and Web of Science. The studies analysed 106 postmortem specimens, 154 synthetic bones, and 103 computational models. Most specimens were male (97 % synthetic, 70 % postmortem specimens). Both the type of injury and the classification system employed varied across studies. About 82 % of the injuries assessed were of type C. Two different fixators were tested for FFPII and type A injury, five for type B injury, and fifteen for type C injury. Large variability was observed for external fixation constructs concerning device type and configuration, pin size, and geometry. Biomechanical studies deployed various methods to assess injury displacement, deformation, stiffness, and motion. Thereby, loading protocols differed and inconsistent definitions of failure were determined. Measurement techniques applied in biomechanical test setups included strain gauges, force transducers, and motion tracking techniques. An ideal fixation method should be safe, stable, non-obstructive, and have low complication rates. Although biomechanical testing should ensure that the load applied during testing is representative of a physiological load, a high degree of variability was found in the current literature in both the loading and measurement equipment. The lack of a standardised test design for fixation constructs in pelvic injuries across the studies challenges comparisons between them. When interpreting the results of biomechanical studies, it seems crucial to consider the limitations in cross-study comparability, with implications on their applicability to the clinical setting.