SLR - June 2017 - Mohomad M. Al-Sawah

Dynamic Stress Testing Is Unnecessary for Unimalleolar Supination-External Rotation Ankle Fractures with Minimal Fracture Displacement on Lateral Radiographs

Reference: Nortunen S, Leskela HV, Haapasalo H, Flinkkila T, Ohtonen P, Pakarinen H. Dynamic Stress Testing Is Unnecessary for Unimalleolar Supination-External Rotation Ankle Fractures with Minimal Fracture Displacement on Lateral Radiographs. J Bone Joint Surg Am. 2017 Mar 15;99(6): 482–487.

Reviewed By: Mohomad M. Al-Sawah, DPM

Residency Program: Providence-Providence Park Hospital, Southfield, MI  

Podiatric Relevance: Ankle fractures are commonly seen and treated by foot and ankle surgeons. The most common fracture pattern is the SER-type fracture. When evaluating standard radiographs, it is difficult to objectively differentiate stable vs. unstable ankle fractures with regards to isolated lateral malleolar fractures without medial clear space widening or syndesmotic diastasis. External rotation stress or weightbearing/gravity testing typically is performed to identify unstable ankle fractures that would benefit from open reduction and anatomical restoration. There are some downsides to stressing SER ankle fractures, including increased pain for the patient and radiation exposure to the clinician and to the patient. This study aimed to identify factors/objective measures that can be evaluated on standard ankle radiographs to determine which findings influenced ankle stability using external rotation stress radiographs as the reference. The authors hypothesized that ankles with minimally displaced lateral malleolar fractures are stable and do not require further stress testing.

Methods:
The authors screened 308 prospectively collected nonstress radiographs of skeletally mature patients with isolated fibular Lauge-Hansen supination-external rotation ankle fractures. For inclusion, the fracture must show no medial widening or incongruity on standard ankle radiographs. They only included adult patients with typical SER oblique fractures that originated <2 cm above the talar dome. An external rotation stress test was performed by two orthopaedic trauma surgeons. Exclusion criteria included patients who had a pathologic fracture, concomitant fractures that contraindicated external rotation stress or a previous ankle injury. The final group included 286 adults with several measurements recorded on the mortise and lateral ankle radiographs. The ankle mortise was considered unstable when the medial clear space was ‡5 mm and at least 1 mm larger than the superior tibio-talar clear space. The two senior orthopaedic trauma surgeons analyzed all standard mortise and lateral nonstress radiographs in separate sessions and were blinded to each other’s measurements.

Results: The group of 217 patients with stable ankles after external stress test evaluation had a mean medial clear space (and standard deviation) of 3.5 ± 0.6 mm. This group had an average of 1.8 mm posterior fracture diastasis. The group of 69 patients with unstable ankles had a mean medial clear space of 5.7 ± 1.1 mm. This group had an average of 3.3 mm of posterior fracture diastasis. Female sex, a posterior diastasis of <2 mm and only two fracture fragments were independent factors for predicting a stable ankle mortise.

Conclusions: The authors have identified important objective findings for predicting stable SER-type lateral malleolar ankle fractures that would not require further stability testing: A posterior fracture diastasis of less than 2 mm on lateral radiographs and having only two fracture fragments. These findings should assist foot and ankle surgeons when deciding which isolated lateral malleolus fracture should be further stressed based on standard ankle radiographs using the measurements discussed. However, if questioning exact fracture displacement or unable to accurately assess these objective findings, manual or gravity stress test should be performed to rule out instability and to prevent potential pain/detrimental posttraumatic arthritis following SER ankle fractures. 

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