Early Weightbearing After Operatively Treated Ankle Fractures: A Biomechanical Analysis

Background: No consensus exists regarding the timing of weightbearing after surgical fixation of unstable traumatic ankle fractures. We evaluated fracture displacement and timing of displacement with simulated early weightbearing in a cadaveric model. Methods: Twenty-four fresh-frozen lower extremities were assigned to Group 1, bimalleolar ankle fracture (n=6); Group 2, trimalleolar ankle fracture with unfixed small posterior malleolar fracture (n=9); or Group 3, trimalleolar ankle fracture with fixed large posterior malleolar fracture (n=9) and tested with axial compressive load at 3 Hz from 0 to 1000 N for 250 000 cycles to simulate 5 weeks of full weightbearing. Displacement was measured by differential variable reluctance transducer. Results: The average motion at all fracture sites in all groups was significantly less than 1 mm (P < .05). Group 1 displacement of the lateral and medial malleolus fracture was 0.10.1 mm and 0.40.4 mm, respectively. Group 2 displacement of the lateral, medial, and posterior malleolar fracture was 0.6 +/- 0.4 mm, 0.5 +/- 0.4 mm, and 0.5 +/- 0.6 mm, respectively. Group 3 displacement of the lateral, medial, and posterior malleolar fracture was 0.1 +/- 0.1 mm, 0.5 +/- 0.7 mm, and 0.5 +/- 0.4 mm, respectively. The majority of displacement (64.0% to 92.3%) occurred in the first 50 000 cycles. There was no correlation between fracture displacement and bone mineral density. Conclusion: No significant fracture displacement, no hardware failure, and no new fractures occurred in a cadaveric model of early weightbearing in unstable ankle fracture after open reduction and internal fixation. Clinical Relevance: This study supports further investigation of early weightbearing postoperative protocols after fixation of unstable ankle fractures.