- Under arthroscopic stress examination in a cadaveric model, disruption of the deltoid ligament appeared to destabilize the syndesmosis in the coronal plane when associated with disruption of at least two syndesmotic ligaments
- These findings occurred equally when the diastasis was measured in the anterior and posterior third of the distal tibiofibular articulation
- Injuries involving just the DL and anterior-inferior tibiofibular ligament did not meet the study definition of syndesmotic instability, but nonoperative treatment may be advisable
- Clinicians should suspect syndesmotic instability in patients with syndesmotic injuries who also demonstrate medial ankle ligamentous involvement
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The deltoid ligament (DL) has a key role in stabilizing the medial ankle joint, but it's unknown whether it helps stabilize the syndesmosis. This is important to investigate because up to half of patients who have tears or other injuries to the DL have associated syndesmotic injuries.
Massachusetts General Hospital Chief of the Foot & Ankle Center Christopher W. DiGiovanni, MD, and Daniel Guss, MD, MBA, foot and ankle orthopedic surgeon, and colleagues report in Foot and Ankle International that injury to the DL can contribute to instability of the syndesmosis. Unlike previous research that relied on x-rays and intraoperative fluoroscopy, this study used arthroscopy to detect more pronounced syndesmotic instability.
As part of the study, the researchers examined eight cadaveric specimens (mean age, 49 years; all males). All specimens underwent ligamentous transection in the same sequence: first the DL, then the anterior–inferior tibiofibular ligament (AITFL), interosseous ligament (IOL) and posterior–inferior tibiofibular ligament (PITFL). The fibula was kept intact to simulate purely ligamentous injury or operative fixation of a fibular fracture.
In the intact ligamentous state, as well as after each stage of ligament transection, the researchers measured coronal plane tibiofibular diastasis at both the anterior and posterior third of the incisura. Measurements at each stage of ligament transection were then repeated during a lateral hook test (applied via a force gauge). The researchers compared the results to the stress measurements of the intact syndesmosis.
In the anterior third of the incisura, there was no significant difference in tibiofibular diastasis in the intact state versus the diastasis measured after transection of the DL alone, or after transection of the AITFL and the DL. However, anterior third diastasis did increase significantly after further injury (transection of the IOL, then transection of the PITFL).
In the posterior third of the incisura, findings were analogous to those measured in the anterior third.
The researchers note that combined disruption of the DL and AITFL can be difficult to evaluate on x-ray, because an unstable syndesmosis may not present with tibiofibular widening. In this study, the increased distal tibiofibular diastasis in combined DL and AITFL injuries averaged only 0.7 mm, falling outside the study definition of syndesmotic instability.
Such injuries can have clinical consequences, though, the researchers comment. They speculate that combined DL and AITFL injuries can be treated with a period of immobilization, as recommended in previous studies.
The authors conclude that clinicians should have a heightened index of suspicion for syndesmotic instability when evaluating patients with syndesmotic injuries who also demonstrate medial ankle ligamentous involvement.
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