Evaluation of fracture predilection in the calcaneus after external fixator pin removal

Objectives/Hypothesis: External fixators have been advocated for the treatment of intra-articular fractures of the distal tibia, so-called "pilon" or "plafond" fractures. Current recommendations include placement of external fixator pins, which vary in diameters up to six millimeters, in the talus and calcaneus. Removal of a relatively large pin may create a large defect in the bone, theoretically increasing fracture predilection with weight bearing. The objective was to compare the compressive load at failure of intact and formerly instrumented calcanei. It was hypothesized that the pin hole defect would not lead to a clinically significant difference in compressive load at failure. Study Design: A biomechanical evaluation of randomized matched pairs of cadaveric calcanei. Methods: Fresh human calcanei were harvested, embedded in casting compound, and tested pairwise. Among pairs of cal-canei, one served as the control, and the other was drilled with a 6.0-mm pin in the posterior portion. The pin was removed before biomechanical evaluation. Testing was performed in compression under displacement control on a hydraulic materials testing system. Results: There was a 22% reduction in compressive load at failure (p = 0.021) of the drilled versus intact specimens. Compared with intact calcanei, defect calcanei had a compressive failure load much closer to forces that might be encountered with walking and running. Conclusions: The six-millimeter-pin defect is a significant stress riser, and protected, progressive weight bearing after pin removal should be recommended.