Experimental production of extra- and intra-articular fractures of the os calcis.

Although studies have been conducted in the past to duplicate traumatic fractures of the os calcis, biomechanical force data as a function of extra- and intra-articular fractures are not available. Consequently, in this study, a dynamic single impact model was used to provide such information. Using intact human cadaver lower extremities, impact loading was applied to the plantar surface of the foot using a mini-sled pendulum equipment. The proximal tibia was fixed in polymethylmethacrylate. Following impact, pathology to the os calcis was classified into intact (no injury; 14 cases), and extra-articular (6 cases) and intra-articular (6 cases) fractures. Peak dynamic forces were used to conduct statistical analysis. Mean forces for the intact and (both) fracture groups were 4144 N (standard error, SE: 689) and 7802 N (SE: 597). Mean forces for the extra- and intra-articular fracture groups were 7445 N (SE: 711) and 8159 N (SE: 1006). The peak force influenced injury outcome (ANOVA, p<0.005). Differences in the forces were found between intact and injured specimens (p<0.01); intact specimens and specimens with extra-articular pathology (p<0.001); intact specimens and specimens with intra-articular pathology (p<0.005). The present experimental protocol, which successfully reproduced clinically relevant os calcis pathology, can be extended to accommodate other variables such as the simulation of Achilles tendon force, the inclusion of other angles of force application, and the application of the impact force to limited regions of the plantar force of the foot in order to study other injury mechanisms.