Displacement of the sustentacular fragment in intra-articular calcaneal fractures.

Background: The sustentacular fragment in displaced intra-articular calcaneal fractures has historically been portrayed as a "constant fragment," bound to the talus by the interosseous and deltoid ligament complex. Operative treatment typically occurs through a lateral approach, with the remaining calcaneus being reconstructed back to the sustentaculum. We hypothesized that the sustentacular fragment in displaced intra-articular calcaneal fractures does not maintain its relationship to the talus. The purpose of this study was to characterize the frequency, magnitude, and mode of displacement of the sustentacular fragment.

Methods: Computed tomographic (CT) scans of eighty-eight patients with 100 displaced intra-articular calcaneal fractures admitted to our level-I trauma center over a five-year period were retrospectively reviewed. Basic patient demographics and mechanisms of injury were recorded. CT scans were graded according to the Sanders classification, and associated injuries were noted. Angulation and translation of the sustentacular fragment as well as gapping and intra-articular fractures of the middle facet were examined. Angulation exceeding 10° and translation of more than 3 mm were considered diagnostic of displacement.

Results: Overall, the sustentacular fragment was displaced in forty-two of the 100 fractures. Twenty-five of one hundred calcanei had sustentacular fragment angulation of >10°, twenty-four had sustentacular translation >3 mm, twenty had fracture diastasis of the middle facet, and twenty-one had a displaced intra-articular fracture of the calcaneal middle facet. Fractures involving greater than 50% of the posterior facet (consistent with Sanders Type-B and Type-C fracture lines) demonstrated a significant increase in relative risk of angulation and translation of the sustentacular fragment as well as gapping and intra-articular fractures of the middle facet. Three-part or four-part fractures also showed a significant association with overall displacement of the sustentaculum.

Conclusions: This study is the first to our knowledge to quantify in a detailed manner the displacement of the sustentacular fragment as occurring with calcaneal fractures. This displacement disproves the "constant" theory of the sustentacular fragment, and it may alter the quality of the fracture reduction and affect patient outcome. An alternative surgical approach may be indicated for the treatment of certain calcaneal fracture patterns with sustentacular displacement.

Level Of Evidence: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.