Mechanical Testing and Computational Modeling of Scapula Fracture Implants: A Review

This is the first review of mechanical testing or computational modeling articles that analyzed the biomechanical influence of parametrically changing scapula fracture implant (SFI) variables to optimize or characterize performance. PubMed and Embase were explored for articles using inclusion and exclusion criteria: (i) SFI articles that permutated implant variables were included, but articles using only one SFI configuration were excluded; (ii) SFIs comprising of plates (with screws), non-plate isolated "lag" screws, or cerclage wires were included, but anchors/sutures, bone cements, bone grafts, or soft-tissue grafts were excluded; (iii) scapula fractures were included, but adjacent injuries of the clavicle, humerus, labrum/capsule, ligaments/tendons, or muscles were excluded; (iv) cadaveric, synthetic, or computer-generated scapulas were included, but other anatomic sites or biomaterials were excluded; (v) published on any date in any language. The 16 eligible articles considered different scapula regions (i.e., acromion/spine, body, neck), SFI variables (i.e., plate geometry, plate hole type, plate position, plate number, screw angle), and engineering outcome metrics: (i) interfragmentary displacement (i.e., chance of callus growth); (ii) stresses in bones, plates, or screws (i.e., risk of failure); (iii) stresses in the bone under the plate (i.e., risk of bone "stress shielding"); (iv) the number of loading cycles to failure (i.e., fatigue life); (v) overall stiffness (i.e., physical flexibility); or (vi) failure strength (i.e., peak load achieved). This review advises future work for implant variables, bone characteristics, and study protocols, while suggesting SFI configurations with maximum mechanical stability.