Session VII - Foot / Ankle

Sat., 10/12/13 Foot/Ankle, PAPER #84, 11:09 am OTA 2013

Stress Ankle Radiographs and Predictability of Deep Deltoid Ligament Injury in a Supination–External Rotation Cohort

Patrick C. Schottel, MD; Marschall B. Berkes, MD; Milton T.M. Little, MD;
Matthew R. Garner, MD; Jacqueline Birnbaum, BS; David L. Helfet, MD; Dean G. Lorich, MD;
Hospital for Special Surgery, New York, New York, USA

Background/Purpose: Stress ankle radiographs are commonly performed to determine deltoid ligament integrity in patients with a supination–external rotation (SER) pattern ankle fracture. Recognition of a medial-sided injury in this cohort is important as this fracture pattern is considered unstable and it has been shown that these patients benefit from surgical stabilization. However, there is variability in the literature as to what constitutes a positive stress ankle radiograph and to date only cadaver studies have examined the sensitivity and specificity of differing medial clear space (MCS) measurements. The purpose of our study was to compare the injury and stress radiographs of SER-pattern ankle fractures with or without a deep deltoid ligament injury and determine the predictive ability of the MCS in identifying a deltoid ligament tear.

Methods: All patients with an SER-pattern fibula fracture without a medial malleolus fracture from 2006 to 2012 were identified from the senior surgeon’s prospectively collected ankle fracture database. Only patients with injury ankle radiographs, an external rotation stress radiograph, and an ankle MRI scan within 1 week of the injury were included for analysis. All stress radiographs were performed in the emergency department by an on-call orthopaedic resident. MCS was measured using our institution’s picture archiving and communication system (PACS) and represented the distance from the medial aspect of the talus horizontally to the articular surface of the medial malleolus at the talar dome. This distance was measured and recorded for both the non-stress and stress ankle mortise radiographs. The integrity of the deep deltoid ligament was by two independent and blinded fellowship-trained attending musculoskeletal radiologists based on the ankle MRI.

Results: 52 patients were eligible for analysis. The average patient age was 47.5 years and 53.8% (28 of 52) were male. Of the 52 patients, 50% (26) had no MRI evidence of a deep deltoid ligament rupture and therefore were classified as an SER II or SER III injury. The other 50% (26 of 52) were classified as SER IV equivalent injuries due to MRI evidence of a high-grade deep deltoid ligament tear. SER II/III patients demonstrated an average MCS distance of 4.34 mm during stress radiographs. The SER IV cohort’s average MCS was 5.81 mm when the ankle was stressed. Comparison of the average MCS measurements between the two groups was significantly different (P <0.001). Finally, an absolute MCS on stress radiograph of greater than 5.0 mm had a calculated 65.4% sensitivity and 76.9% specificity for identifying a deep deltoid ligament tear. The corresponding positive and negative predictive values were 73.9% and 69.0%, respectively.

Conclusion: External rotation stress ankle radiographs are a common method for determining deltoid ligament integrity in patients with an SER ankle fracture. We have shown that stress radiographs are able to accurately distinguish between patients with or without a deep deltoid ligament injury based on the extent of MCS widening. We also found that a stress view MCS measurement greater than 5.0 mm had a 65.4% sensitivity and 76.9% specificity for identifying a deep deltoid ligament tear.

Alphabetical Disclosure Listing

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.