Session II - Foot and Ankle

Competence of the Deltoid Ligament in Bimalleolar Ankle Fractures after Medial Malleolar Fixation In-Vivo

Paul Tornetta, III, MD, Boston University Medical Center, Boston, MA

Purpose: Many authors have demonstrated that a medial-sided ankle injury must be present to allow for talar subluxation even in the face of lateral injury. Likewise, cadaveric studies using sectioning techniques have supported the concept that in bimalleolar ankle fractures, fixation of the medial malleolus restores medial support. However, these cadaveric studies may be misleading, as the technique of sectioning insures that the deltoid ligament remains intact. In the clinical setting, there is no information available regarding the status of the deltoid ligament in conjunction with medial malleolar fractures. The purpose of this study was to assess, in vivo, the competence of the deltoid ligament following fixation of the medial malleolus in bimalleolar ankle fractures.

Methods: Twenty-eight consecutive patients with bimalleolar ankle fractures were entered into a prospective study. The average age of the patients was 36 years (18-68). There were 21 SE, 4 PA, and 3 PE injuries by the Lauge-Hansen scheme (OTA classification: [19] 44-B2, [2] 44-B3, [5] OTA 44-C1.2, and [2] 44-C2.2 fractures). All of these fractures were indicated for ORIF on the basis of instability. In each case, the medial malleolus was reduced anatomically and fixed with lag screws as the first stage of the procedure. This was performed without stripping the deltoid attachment to the medial fragment. After the medial malleolus was fixed, a stress radiograph of the ankle was taken with the foot externally rotated. Regardless of the findings of the stress view, the lateral side of the ankle was fixed anatomically using standard techniques and the ankle placed in a cast. Evaluation of the radiographs included: talar shift upon presentation, height and width of the medial malleolar fragment on the preoperative radiograph, superior and medial joint space on the stress view and the postoperative radiograph, and talar subluxation on the stress view and postoperative radiograph. All data were entered prospectively. The stress view was considered positive if the medial joint space was > 4 mm and at least 1 mm greater than the superior joint space, or if there was any talar shift. The positive and negative stress view groups were compared using the data points listed above.

Results: One medial malleolar fracture in a 64 year old woman displaced 2 mm when stressed, and after re-tightening of the screws reduced the fragment, the stress view was not repeated. Of the 27 remaining stress views, 7 (26 %) were positive, indicating deltoid incompetence in conjunction with the medial malleolar fracture. The other 20 fractures had a stable mortise after medial only fixation. In comparing the fractures with positive stress views with those having negative stress views, there were statistical differences in the following variables: medial malleolar height and width, medial joint space on the stress view, and talar shift on the stress view (table). There were no other differences between the groups in age, fracture type, or measured data points. All patients had an anatomic mortise at the completion of the operative procedure.

Discussion: In contradistinction to the assumptions made in cadaveric sectioning studies, the deltoid ligament may be injured in conjunction with a medial malleolar fracture. In this series, the rate of deltoid incompetence was 27 %. The size of the medial malleolar fragment was the most important variable in predicting deltoid competence. The deltoid was competent in all fractures in which the medial malleolar fragment was greater than 2.8 mm wide on the lateral radiograph and incompetent if it was less than 1.7 mm wide. Thus, it may be that the entire medial support of the ankle is injured in all cases, but the injury is a combination of bony and ligamentous disruption. This study further demonstrates that there is an important difference between in vitro cadaveric studies and the true in vivo clinical situation. This study provides the first step in supporting the concept of medial-only fixation for bimalleolar fractures in selected cases. If the stress view reveals a stable mortise, particularly if there is a large medial malleolar fragment, the use of medial-only fixation may be a viable option. However, this technique cannot be justified solely on the basis of this study.

Conclusion: The deltoid ligament was incompetent in 27 % of bimalleolar fractures after medial fixation. The size of the medial malleolar fragment was significantly smaller in the stress (+) group. Injury to the medial side of the ankle appears to be a spectrum of bony and ligamentous disruption. The findings of this study clarify the in vivo injury pattern on the medial side of the ankle and help to define in which cases medial-only fixation may be a viable option.