Intraarticular calcaneal fractures: biomechanical analysis of two fixation constructs

The aim of this biomechanical study was to investigate the fixation stability of a small low-profile 2.7 mm variable-angle locking anterolateral calcaneal plate supplemented with two additional independent cortex screws versus a traditional small 3.5 mm locking calcaneal plate in a standardized Sanders IIc fracture model.

Sixteen fracture models cocomposed of three polymer blocks (fragments) each and simulating Sanders IIc intra‑articular calcaneal fractures were assigned to two groups. Group 1 (control) received a small 3.5 mm locking calcaneal plate, while Group 2 received a small 2.7 mm variable‑angle locking anterolateral calcaneal plate with two additional independent cortex screws. All constructs were instrumented using prefabricated pilot holes and standardized screw configurations. Biomechanical testing was conducted implementing a 3‑point-bending setup and progressively increasing cyclic loading to failure. Angular interfragmentary movements were quantified via motion tracking along with cycles to clinically relevant failure.

Initial stiffness (N/mm) in Group 1 (65.2 ± 34.7) was significantly lower versus Group 2 (232.5 ± 48.6), p = 0.020. Although angular interfragmentary movements around the anteroposterior axis were significantly greater in Group 1 versus Group 2 (p < 0.001), Group 1 demonstrated significantly smaller angular interfragmentary movements around the mediolateral axis for the central-to-posterior and anterior-to-posterior fragment pairs (p ≤ 0.004), while no significant difference between the groups was identified with regard to the central-to-anterior fragment pair (p ≥ 0.377). Cycles and loads (N) to clinically relevant failure in Group 1 (3635 ± 176 and 92.7 ± 3.5) were significantly lower versus Group 2 (17433 ± 628 and 368.7 ± 12.6), p < 0.001. Failure mode in Group 1 involved plate deformation, whereas Group 2 failed through breakage or bending of the independent cortex screws.

Biomechanically, fixation implementing a small low-profile 2.7 mm variable-angle locking anterolateral calcaneal plate supplemented with two additional independent cortex screws demonstrated stability comparable to, and in certain respects superior to that achieved with a small 3.5 mm locking calcaneal plate in a standardized Sanders IIc fracture model. However, the findings of this laboratory study do not establish an isolated benefit of the 2.7 mm plate itself, nor do they demonstrate clinical superiority or support alterations to postoperative weight-bearing protocols.