OTA 2005 Posters
Scientific Poster #84 Foot & Ankle
External Rotation Stress Examination of the Normal Ankle
Purpose: The Weber B supination external rotation-type fibular fracture represents a heterogeneous group of injuries in terms of ankle mortise stability. Static radiographic evaluation and clinical examination may fail to identify a concomitant deltoid ligament rupture (ligamentous SE-4) and an unstable ankle mortise. A stress radiograph has been shown to be a sensitive examination for detection of deltoid incompetence in patients with an intact ankle mortise and supination-external rotation fibular fractures. Our purpose was to determine the behavior of the normal ankle during stress examination. We investigated the radiographic alteration of the medial clear space (MCS) during ankle stress examination of uninjured ankles.
Methods: 50 healthy volunteers (22 male, 28 female) were recruited for this prospective, IRB-approved study. Exclusions included a history of a significant ankle sprain, fracture, or surgery. All 50 volunteers had bilateral mortise radiographs. Radiographic stress examination was then performed bilaterally (mortise radiograph with 10° internal rotation of the leg, neutral ankle dorsiflexion, and 8 to 10 lbs external rotation stress). A single radiologic technician performed all of the studies at a standard distance from the leg. A stress positive study was considered to be a MCS >4 mm, with >1 mm difference between the MCS and the superior joint space.
Results: The average MCS measured 2.54 mm. The average MCS in men was 2.73 mm, compared to 2.39 mm in females. The average difference of the MCS between the right and left ankles of the same person was 0.1 mm. With stress examination, the average MCS enlarged to 2.92 mm. The average difference between the stressed and unstressed ankle was 0.38 mm. There were no significant statistical differences from side to side in the same individual (P= 0.16). Males and females exhibited no significant differences in the amount of MCS widening with stress examination (P = 0.70). All 50 participants had a MCS 4 mm on initial films. 49 of the 50 participants had a MCS 4 mm on stress examination. Although the MCS increased an average of 0.38 mm, 98 of 100 ankles still had a MCS 4 mm. Only one patient had a "stress positive ankle" and this was present bilaterally.
Conclusion/Significance: The normal ankle shows considerable side to side similarity of the MCS in both the stressed and unstressed setting. The MCS increased an average of 0.38 mm, 98 of 100 ankles still had a MCS 4 mm. This study lends credence to the hypothesis that widening of the MCS to 4 mm during stress exam of a Weber B supination external rotation ankle fracture represents an incompetent deltoid. Comparison stress examination in an equivocal case may be a benefit.