Session X1I - Foot and Ankle
Fixation of Posterior Malleolar Fractures for Syndesmotic Stability
Purpose: Syndesmotic injuries are common in ankle fractures, and traditional syndesmotic fixation is associated with inherent morbidity and often requires a second procedure. When the posterior malleolus is fractured, the posterior syndesmotic ligaments may remain intact and attached to the fragment. We sought to evaluate the incidence of the posterior-inferior tibiofibular ligament (PITFL) rupture in posterior malleolar ankle fractures, and to assess the syndesmotic stability following fixation of the posterior malleolus fragment compared to a syndesmotic screw in a cadaver model.
Methods: 36 consecutive patients who sustained a closed ankle fracture that involved the posterior malleolus were evaluated prospectively using standard radiographic examinations and MRI. This patient cohort was evaluated for incidence of rupture of the PITFL, as assessed by a musculoskeletal MRI radiologist. Twelve matched lower extremity cadaver specimens were used for biomechanical testing. A simulated pronation-external rotation fracture pattern with a posterior malleolar fragment was created. Pairs received fixation of either the posterior malleolus or the syndesmosis using standard techniques, and were tested for rotatory syndesmotic stability.
Results: Of the 36 patients with posterior malleolar fractures, 35 (97%) retained continuity of at least a portion of the PITFL on MRI. In the biomechanical testing portion, one specimen pair was grossly unstable following fixation and was unable to be evaluated. In 3 pairs (60%), the posterior malleolus fixation led to significantly greater stability of the syndesmosis (average, 18% versus 240% of intact rotation, P<0.01). In one pair (20%), the syndesmotic screw was significantly more stable (98% versus 14%, P<0.01), and in one pair (20%), no difference was found.
Conclusions: When the posterior malleolus is fractured as a component of a rotational ankle injury, the PITFL was at least partly intact and attached to the fragment in the vast majority of cases. Reduction and fixation of the posterior malleolus led to greater syndesmotic stability than a syndesmotic screw in more than half of the specimen pairs in this pronation-external rotation cadaveric model fracture.
Significance: Restoration of syndesmotic stability may be achieved by fixation of the posterior malleolus in lieu of a syndesmotic screw. Although further investigation is warranted, these concepts may be useful in eliminating the need for syndesmotic screw fixation in select patients.