Role of the posterior deep deltoid ligament in ankle fracture stability: A biomechanical cadaver study

ARTICLE HIGHLIGHTS

Research background

Ankle fractures are common injuries, with supination external-rotation (SER) type injuries being the most common sub-group. Operative intervention in the form of open reduction and internal fixation (ORIF) should be reserved for patients with unstable fractures. There is debate within the literature as to which ankle fractures should be fixed and why, with some of this controversy relating to the degree of deltoid ligament injury required to create such instability and necessitate operative intervention.

Research motivation

We feel that many SER type ankle fractures are stable injuries which can be treated non-operatively. Reducing the incidence of unnecessary operations will reduce potential morbidity for patients and reduce healthcare costs. Through the authors’ previous experience in cadaveric dissection, it was felt the posterior portion of the deep deltoid ligament was usually thick and strong, which may afford an ankle fracture stability. We created our protocol to investigate the anatomical basis for ankle fracture instability.

Research objectives

To identify the anatomical basis for instability in SER type ankle fractures.

Research methods

A bespoke jig was created to load a thawed cadaveric ankle specimen both with axial load and rotational torque. The 8 sepecimens were loaded both axially and with external rotation during each stage of a SER type ankle fracture, with AP radiographs recorded at each stage. The radiographs were investigated for evidence of ankle fracture instability in terms of talar shift and talar tilt. A detailed description of the study method is included in the research paper. To our knowledge, our study design is unique answering a question which has never previously been anss in a cadaveric basic science study.

Research results

We determined no evidence of radiological instability in any specimen with an intact posterior deep deltoid ligament. Only on disruption of the posterior deep deltoid ligament instability possible under our test conditions.

Research conclusions

Only ankle fractures with a damaged posterior deep deltoid ligament should require operative intervention. With an intact posterior deep deltoid ligament, the ankle can be held in a neutral position, with the ligament reducing the talus within the ankle mortise.

Research perspectives

Clinical studies to investigate the functional outcomes between SER injuries treated operatively and non-operatively may provide further evidence to support the non-operative treatment of ankle fractures with an intact deep deltoid ligament. Further clinical studies are also needed to investigate the functional outcomes of patients following a SER-IVb type injury. It is unclear whether subtle rotational instability may continue following fibular ORIF. Our cadaveric study suggests rotational instability can occur following ORIF of the fibular in these injuries due to the disrupted posterior deep deltoid ligament. It is unknown whether this remains in vivo after appropriate immobilisation in a plaster cast. If instability remains, further investigation into the role of deltoid ligament repair is needed.