SLR - December 2018 - Stephanie Petrofski

Assessment of Ankle Mortise Instability after Isolated Supination-External Rotation Lateral Malleolar Fractures

Reference: Jeong BO, Kim TY, Baek JH, Song SH, Park JS. Assessment of Ankle Mortise Instability after Isolated Supination-External Rotation Lateral Malleolar Fractures. J Bone Joint Surg Am. 2018;100(18):1557–1562.

Scientific Literature Review

Reviewed By: Stephanie Petrofski, DPM
Residency Program: The Jewish Hospital, Cincinnati, OH

Podiatric Relevance: Ankle fractures are a common injury seen and treated by foot and ankle surgeons. In isolated supination-external rotation type lateral malleolar fractures, detecting deltoid integrity is of the utmost importance in determining whether the fracture is considered stable or unstable. It has been shown that stable fractures can be treated nonoperatively with good results, whereas unstable fractures often have better outcomes when surgically managed. When there is no clear radiographic evidence of medial clear space widening, the external rotation stress test has been recognized and widely accepted as the most reliable indicator of deltoid instability. However, recently, the gravity stress test has gained more popularity as the surgeon is not exposed to radiation, there is a lower probability of human error in interpretation and the patient is subjected to less pain. Currently, few studies have compared the accuracy of diagnostic methods, such as clinical examination, the gravity stress test and magnetic resonance imaging (MRI) with that of the ER stress test for the diagnosis of ankle mortise instability or deep deltoid ligament incompetence, and fewer studies have described associations between the results of the various methods. The purpose of the present study was to analyze the diagnostic accuracy and utility of clinical findings, the gravity stress test and MRI, in comparison with the ER stress test, to diagnose ankle mortise instability in patients with an isolated SER-type lateral malleolar fracture.

Methods: A level II prospective study was performed on 37 skeletally mature patients over 16 years of age who had a unilateral Lauge-Hansen SER-type isolated lateral malleolar fracture and did not demonstrate medial widening or ankle joint incongruity on standard ankle radiographs. The external rotation stress test was done according to previously published guidelines and used as a reference to compare the sensitivity, specificity, likelihood ratio (LR) and posttest probability of ankle instability when using clinical exam findings, gravity stress test and MRI findings for diagnosing ankle mortise instability after an isolated SER lateral malleolar fracture.

Results: Using ER stress testing as a reference, the prevalence of ankle mortise instability in the study population of 39 patients was 57 percent. No significant association was found between the clinical findings and the ER stress test results. The only significant association between MRI and ER stress test results was the presence of tears in the deep and/or superficial deltoid ligaments on MRI. There was also a significant association between the ER stress test and the gravity stress test as well. Taken together, it was found that none of the three variables were sufficient to diagnose medial ankle incompetence alone; however, when more than one factor was positive, the probability of the ER stress test also being positive increased.

Conclusions: Although the gravity stress test was considered reliable in diagnosing ankle mortise instability, the study findings indicated that when used alone, it does not qualify as a replacement for the ER stress test. However, when used in combination with clinical findings or MRI findings, its diagnostic value was almost equivalent to that of the ER stress test. 

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