EVALUATION OF FRACTURE PREDILECTION IN THE CALCANEUS AFTER EXTERNAL FIXATOR PIN REMOVAL

Objectives/Hypothesis: External fixators have been advocated for the t reatment of intra-articular fractures of thr distal tibia, so-called ' 'pilon'' or ''plafond'' fractures. Current recommendations include pla cement of external fixator pins, which vary in diameters up to six mil limeters, in the talus and calcaneus. Removal of a relatively large pi n may create a large defect in the bone, theoretically increasing frac ture predilection with weight bearing. The objective was to compare th e compressive load at failure of intact and formerly instrumented calc anei. It was hypothesized that the pin hole defect would not lead to a clinically significant difference in compressive load at failure. Stu dy Design: A biomechanical evaluation of randomized matched pairs of c adaveric calcanei. Methods: Fresh human calcanei were harvested, embed ded in casting compound, and tested painwise. Among pairs of calcanei, one served as the control, and the other was drilled with a 6.0-mm pi n in the posterior portion. The pin was removed before biomechanical e valuation. Testing was performed in compression under displacement con trol on a hydraulic materials testing system. Results: There was a 22% reduction in compressive load at failure (p = 0.021) of the drilled v ersus intact specimens. Compared with intact calcanei, defect calcanei had a compressive failure load much closer to fords that might be enc ountered with walking and running. Conclusions: The six-millimeter-pin defect is a significant stress riser, and protected, progressive weig ht bearing after pin removal should be recommended.