SLR - March 2015 - Jacqueline Donovan

Stability Assessment of the Ankle Mortise in Supination-External Rotation-Type Ankle Fractures: Lack of Additional Diagnostic Value of MRI

Reference: Nortunen S, Lepojärvi S, Savola O, Niinimäki J, Ohtonen P, Flinkkilä T, Lantto I, Kortekangas T, Pakarinen H. Stability Assessment of the Ankle Mortise in Supination-External Rotation-Type Ankle Fractures: Lack of Additional Diagnostic Value of MRI. J Bone Joint Surg Am. 2014 Nov 19;96(22):1855-62.

Scientific Literature Review

Reviewed By: Jacqueline Donovan, DPM
Residency Program: Grant Medical Center
 
Podiatric Relevance:  This prospective diagnostic study assessed the efficacy of MRI in the application of SER type ankle fractures. The stability of the ankle mortise is one of the most important factors in determining between non-operative and operative treatment of ankle fractures. The goal of the study was to assess the utility of MRI of the deltoid ligament for evaluation of the stability of the ankle mortise in SER type ankle fractures.  The hypothesis was that the deep deltoid ligament is only substantially injured in unstable ankle fractures.

Methods: Inclusion criteria consisted of all patients with a unilateral Lauge-Hansen SER-type ankle fracture with no medial widening or incongruity on standard ankle radiographs from March 2012 to April 2013. Of the eighty-seven patients who were screened for inclusion in the study, twenty-six could not be included. The final study included sixty-one patients with an isolated SER-type lateral malleolar fracture with no widening of the medial clear space or incongruity on radiographs. In the manual external-rotation stress test the tibia was stabilized with one hand and internally rotated 10 to 15 degrees for a true mortise view, the ankle was turned to neutral flexion and an external rotation force was applied to the forefoot. An ankle mortise radiograph was taken and the medial tibiotalar clear space was measured as the distance between the lateral border of the medial malleolus and the medial border of the talus at the level of the talar dome.  The manual external rotation stress test was considered positive if the medial clear space was greater than or equal to 5 mm. Each patient underwent a 3.0-T Magnetom Skyra MRI at an average of 9 ± 6 days post injury.  

Results: Thirty-one (51 percent) of the patients had a positive external rotation stress test and thirty (49 percent) of the patients had a negative external rotation stress test. The medial clear space was greater than or equal to 5 mm in twenty-eight patients and less than 5 mm in thirty-three patients. The anterior deep deltoid ligament was edematous in twenty-three patients, partially torn in thirty-three patients and completely torn in five patients. The posterior deep deltoid was edematous in twenty-four patients, partially torn in thirty-five patients and completely torn in two patients. None of the patients exhibited an uninjured deep deltoid ligament according to the MRI. The two patients with a total tear of the deep deltoid had a medial clear space of 7 and 11 mm. The medial clear space averaged 5.0 ± 1.1mm in the forty-five patients with a partial tear. The medial clear space averaged 4.6 ± 1.3mm in the fourteen patients with an edematous deep deltoid ligament injury observed by MRI.  

Conclusions: The use of a MRI when choosing between operative and non-operative treatment of a SER-type ankle fracture is of no additional value. It is not recommended to order MR imaging in choosing between operative and non-operative treatment of an SER-type ankle fractures. The conclusion from the above information is that MR imaging provides no additional information to the provider while evaluation ankle instability in an acute injury.  

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