A biomechanical comparison of Kirschner-wire fixation on fracture stability in Salter-Harris type I fractures of the proximal humeral physis in a porcine cadaveric model

Abstract

BackgroundThe physis is the weakest component of immature long bones, and physeal fractures constitute about 30% of fractures in growing dogs. Fractures of the proximal humeral physis typically have a Salter Harris type I or II configuration. These fractures require accurate reduction and adequate stabilization to allow for any potential continued longitudinal bone growth, in conjunction with physeal fracture healing. Conventional internal fixation of these fractures involves insertion of two parallel Kirschner wires, although other methods described include tension band wiring, Rush pinning, and lag screws. However these recommendations are based on anecdotal evidence, and information about the biomechanical stability of physeal fracture repair is sparse. The unique anatomical structure of the epiphyseal-metaphyseal complex makes the gripping of the epiphysis for ex vivo biomechanical testing of physeal fracture repair very challenging. The objective of our study was to biomechanically assess the optimal number (three, two or one) of implanted Kirschner wires in a porcine Salter Harris I proximal humeral physeal fracture model, using motion analysis tracking of peri-fragmental retro-reflective markers while constructs were subjected to a constant axial compression and a sinusoidal torque of +/− 2 Nm at 0.5 Hz for 250 cycles.ResultsThere were significant differences between the three constructs (three, two or one Kirschner wire repair) for gross angular displacement (p < 0.001). The difference between three pins and two pins on toggle was not significant (p = 0.053), but both three-pin and two-pin fixation significantly reduced rotational toggle compared to one-pin fixation. Construct stiffness was not significantly different between any of the pin groups (p > 0.33).ConclusionsMotion analysis tracking using peri-fragmental markers in this porcine model of physeal fracture repair found that the stability at the fracture site of one-pin fixation was significantly less than two-pin and three-pin fixation. Whether there was increased stabilization of these fractures with three-pin fixation compared to two-pin fixation was not conclusive in this porcine model.

Feline Distal Tibial Physeal Fracture Repair Using a Modified Cross-Pin Technique with Four Pins

“…While it is assumed that extra Kirschner wires provide additional moment of inertia and additional points of fixation, the precise biomechanical effect of this remains unproven pending controlled mechanical testing. A biomechanical study using a porcine humeral proximal physeal fracture model under sinusoidal torsional loads failed to demonstrate an increase in stability between two and three Kirschner wire fixation, 23 but the Kirschner wires were placed in a parallel fashion, and biomechanical conclusions when comparing to our technique of four cross-pins cannot be drawn.…”

Salter-Harris Type II Humeral Head Fracture with Kirschner Wire Fixation in a Goat

“…14 Although construct stiffness was not significantly different between any of the pin groups of the study, threepin fixation was elected in this case as it demonstrated increased construct stiffness comparatively to two-and one-pin fixation in the porcine model. 14 In this report, one pin was observed to inadvertently exit the cartilage of the humeral head and was withdrawn immediately until the tip of the pin was below the cartilage surface. Although this may result in an increased risk of developing progressive osteoarthritis and pain, the authors believe this to likely be insignificant in long term; however, further long-term radiography would be required to substantiate this claim.…”

Proximal epiphyseal fracture of humerus in dog: Case report

“…Cabe ressaltar que o método ideal de fixação das fraturas da fise do úmero proximal não está estabelecido. Atualmente, há uma falta de conhecimento comparativo sobre a eficácia biomecânica dos métodos de fixação interna para fraturas da fise do úmero proximal (Ma et al, 2017). Os mesmos autores ainda relatam que vários métodos de fixação são descritos, contudo o grau de estabilidade em relação a fixação interna que permitirá o crescimento ósseo em fraturas de placa de crescimento proximal do úmero em cães é desconhecido.…”