Background: The treatment of ankle fractures often depends on the integrity of the deltoid ligament. Diagnosis of a deltoid ligament tear depends on the measurement of the medial clear space. We sought to evaluate the impact of ankle plantar flexion on the medial clear space.
Methods: Mortise radiographs were made for twenty-five healthy volunteers, with the ankle in four positions of plantar flexion (0°, 15°, 30°, and 45°). Four observers measured the medial clear space and the superior clear space on each radiograph. The mean medial clear space at 0° was defined as the control, and the deviation of the medial clear space from the control value was calculated at 15°, 30°, and 45° of plantar flexion. The ratio of the medial clear space to the superior clear space was determined on all radiographs, and ratios that were false-positive for a deltoid ligament injury were identified.
Results: Fourteen male and eleven female volunteers were evaluated. The average increase in the medial clear space when ankle plantar flexion was increased from 0° to 45° was 0.38 mm (95% confidence interval, 0.18 to 0.58 mm). This increase was significant (p = 0.005). The average increase in the medial clear space was 0.04 mm when ankle plantar flexion was increased from 0° to 15° and 0.22 mm when it was increased from 0° to 30°. Neither of these changes was significant (p = 0.99 and 0.20). The prevalence of false-positive findings of deltoid injury based on the ratio of the medial clear space to the superior clear space increased as ankle plantar flexion increased, but this increase did not reach significance in our study group (p = 0.18).
Conclusions: Plantar flexion of the ankle produces changes in radiographic measurements of the medial clear space. The potential for false-positive findings of deltoid disruption increases with increasing ankle plantar flexion.
Clinical Relevance: This study highlights the importance of the ankle being in a neutral position when radiographs are made to measure the medial clear space to assist in the decision of whether to perform nonoperative or operative treatment.
Investigation performed at the Department of Orthopaedic Surgery, Naval Medical Center San Diego, San Diego, California
Disclaimer: The views expressed in this article are those of the authors and do not reflect the official policy of the Department of the Navy, the Department of Defense, or the United States Government.
Read in part at the Annual Meetings of the Orthopaedic Trauma Association, Denver, Colorado, October 15-18, 2008; Society of Military Orthopaedic Surgeons, Las Vegas, Nevada, December 8-13, 2008; and American Academy of Orthopaedic Surgeons, Las Vegas, Nevada, February 25-28, 2009.
Disclosure: 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.
- Copyright © 2010 by The Journal of Bone and Joint Surgery, Incorporated
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