Objectives: To investigate the biomechanical properties of a lateral locked plate alone or in combination with a supplemental medial plate or an intramedullary nail (IMN). Methods: Intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C) were simulated with a standardized model in 28 synthetic femora and divided into 4 groups. Group I was instrumented with a 4.5-mm lateral locked distal femoral plate alone, group II with a lateral locked plate plus a low-profile precontoured 3.5-mm medial distal tibial plate, group III with a lateral locked plate plus a medial 3.5-mm reconstruction plate, and group IV with a lateral locked plate plus a retrograde IMN. Specimens were then axially loaded and cycled to failure or runout. Outcomes of interest were baseline stiffness, survivability, and cycles to failure. Results: Groups III and IV have a significantly higher baseline stiffness (P < 0.001) when compared with groups I and II. Furthermore, groups III and IV had a higher max load to failure (P < 0.01) when compared with groups I and II. The survivability in groups III and IV was 71% and 100%, respectively, while no specimens in group I or II survived maximum loading. There was no significant difference between group III and IV regarding stiffness, survivability, and cycles to failure. Conclusion: When considering fixation for intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C), we found that supplementation of a lateral locked plate with a medial plate or an IMN to be biomechanically superior to lateral locked plating alone regarding stiffness, survivability, and cycles to failure. A low-profile precontoured plate did not add significantly to the construct stiffness in this study.
A small amount of articular incongruity without a step-off can be tolerated by the subtalar joint, in contrast to articular incongruity with a step-off present.
Category: Hindfoot Introduction/Purpose: Subtalar arthritis is a common consequence following calcaneal fracture, and its development is related to the severity of the fracture at the posterior facet. Previous calcaneus fracture models have demonstrated altered contact characteristics when a step-off is created in the posterior facet articular surface. A biomechanical model involving a fracture gap without step-off through the posterior facet has not been developed. In this study, a primary calcaneal fracture line is created to simulate fracture gap displacement without step-off, and to evaluate the resulting contact pressure changes across the posterior facet. Methods: The contact characteristics (peak pressure, area of contact, and centroid of pressure) of the posterior facet of the subtalar joint in six cadaveric below the knee specimens were determined. Contact pressures were measured using Tekscan pressure sensors in five foot positions (neutral, dorsiflexion, plantarflexion, inversion, and eversion) with an axial load of 50% of the cadaveric total body weight. Contact pressures were first determined in the intact foot in all positions in a modified MTS frame. A calcaneal osteotomy was made using a 1 mm osteotome from the posteromedial tuberosity to the anterolateral facet, exiting the facet to simulate a Sanders IIA fracture. The contact characteristics were measured before and after the osteotomy. The simulated fracture was fixed with two 6.4 mm steel dowels. The contact characteristics were then determined with the posterior facet anatomically reduced followed by an incremental increase in fracture gap displacement of 1, 2, and 4 mm. Results: In the intact foot, there was no significant difference in the peak pressures among the five foot positions (p=0.33). The area of contact was significantly less with the foot in inversion compared with neutral (p=0.002), dorsiflexion (p=0.010) or eversion (p=0.033). Peak pressure on the medial fragment (Table 1A) was significantly less with a 4 mm gap compared to a 1 mm gap (p=0.026), a 2 mm gap (p=0.031) or reduced (p=0.030). On the lateral fragment (Table 1B), the peak pressure was significantly increased with a 4 mm gap compared to a 1 mm gap (p=0.026) or a 2 mm gap (p=0.011). Measurements of the contact area and location of the pressure centroids did not show a significant difference on post-hoc testing. Conclusion: The forces across the posterior facet of the subtalar joint were significantly altered after a simulated calcaneal fracture involving gap displacement without step-off. A posterior facet gap of 2 mm did not significantly alter the contact characteristics of the subtalar joint in this study. Significant differences in peak pressure were demonstrated between 4 mm and 2 mm of gap displacement. The peak pressures with 4 mm of gap displacement were significantly increased on the lateral fragment of the posterior facet and decreased on the medial fragment. Changes in posterior facet contact characteristics have not been previously characterized for...
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