We appreciate Drs. Carney and Kuhn's interest in our article (1). We maintain our conclusion that gravity stress views are equivalent to the manual stress radiograph for determining deltoid ligament injury in association with an isolated fibular fracture. In order to further clarify this, we reviewed radiographs up to October 2007 from the initial study endpoint. There were an additional 8 supination external rotation type II (SER II) fractures and 19 SER IV fractures with adequate radiographs. Medial clear space measurements were again made using the same PACS system. These results were then added to the previously published results.

The average medial clear space for SER II injuries was 3.93mm (SD=0.68) while SER IV was 6.48mm (SD=2.23) (p<0.000001). A post hoc power analysis was performed and showed that these results were adequately powered. No patient treated as an SER II with nonoperative management showed any widening of the medial clear space during follow-up. We have used this protocol successfully at our teaching institution for 3 years. We have found it easy to administer and reliable in correctly diagnosing stable or unstable SER type fractures.

We understand the point that Drs. Carney and Kuhn bring up, and hope that this additional data adequately answers their questions. We appreciate other colleagues critically evaluating our study and results as this dialogue furthers the understanding of this topic. Moreover, a continual peer review ensures that the “science” behind the study is appropriate and valid.

Reference:

1. Gill JB, Risko T, Raducan V, Griimes JS, Schutt RC. Comparison of manual and gravity stress radiographs for the evaluation of supination-external rotation fibular fractures. J Bone Joint Surg Am. 2007;89:994-999.

To The Editor:

We would like to applaud the investigators in their attempt to better clarify how to determine ankle stability in the presence of an isolated lateral malleolar fracture with the use of gravity stress radiographs. They conclude that the gravity stress radiograph is equivalent to the manual stress radiograph for determining deltoid ligament injury in association with an isolated fibular fracture. However, with closer examination of their statistical results we believe this conclusion to be uncertain. The authors were only able to find a 0.74 mm average increase in medial clear space (4.26 mm to 5.00 mm) when comparing the SER II to SER IV patients using gravity stress radiographs. It is stated within the article that the p value for this difference is <_0.05. this="this" is="is" a="a" small="small" increase="increase" in="in" medial="medial" clear="clear" space="space" and="and" while="while" the="the" stated="stated" p="p" value="value" implies="implies" significance="significance" we="we" would="would" submit="submit" that="that" _0.74="_0.74" mm="mm" average="average" not="not" clinically="clinically" significant.="significant." one="one" expect="expect" larger="larger" between="between" an="an" ser="ser" ii="ii" injury="injury" iv="iv" if="if" incompetent="incompetent" deltoid="deltoid" ligament="ligament" being="being" adequately="adequately" evaluated.="evaluated." /> The conclusion the authors propose is further in doubt when considering the reported standard deviation for the SER IV gravity stress group. The standard deviation for the SER IV gravity stress group was 1 mm which is larger than the average increase in medial clear space (0.74 mm) found between the SER II and SER IV groups using gravity stress radiographs. This is a curious finding when considering the authors implication that the study holds adequate power. In fact, when performing a post hoc power analysis for the gravity stress test medial clear space changes using the authors stated alpha of 0.05 and beta 0.10 with an increase from the average of 4.26 mm in the SER II group to 5.00 mm in the SER IV groups it is evident that the study is underpowered. Therefore, it needs to be stated clearly that there is a significant chance for Type II error in this study and the strong conclusions stated are in question.

The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.