Session IV - Foot & Ankle

Fri., 10/6/06 Foot & Ankle, Paper #23, 10:47 am

Indications and Interpretation of Stress Radiographs in Weber B Ankle Fractures

Ferras Zeni, MD (a-Henry Ford Hospital); A. Bouffard, MD (*);
M. van Holsbeeck, MD (*); C. Les, DVM, PhD (*); R. Vaidya, MD, FRCSc (*);
Henry Ford Hospital, Detroit, Michigan, USA

Background: Treatment of nondisplaced Weber B ankle fractures depends on overall assessment of ankle stability. In isolated lateral malleolar fractures, stability hinges on the competence of the deep portion of the deltoid ligament. Several methods have been proposed in order to evaluate ankle stability. The purpose of this study is to define the indications for a stress radiograph and establish criteria for a positive stress radiograph.

Methods: We performed a prospective, consecutive study of 27 ankles with isolated Weber B lateral malleolus fractures with a reduced ankle mortise (medial clear space <4 mm). Patients with peripheral neuropathy were excluded. All patients were evaluated clinically. Patients rated their overall tenderness medially and laterally with significant tenderness being defined as greater than minimal pain. Also, the patient's level of pain (visual analog scale) in eight anatomic locations was noted as was the degree of swelling. Ultrasound was performed to evaluate the integrity of the deltoid ligament and was classified as a complete tear, partial tear, or normal. Radiographs were performed of both the fractured and the contralateral ankles. Radiographic evaluation also included bilateral stress radiographs. Measurements included medial clear space (MCS), superior clear space (SCS), stress medial clear space (MCSS), MCSS(fx) B MCS(fx), MCSS(fx) B SCS(fx), and MCSS(fx) B MCS(nl).

Results: Fourteen patients appeared normal on ultrasound examination, eight had partial tears, and five had full thickness tears. There was a consistent anterior to posterior progression of ligamentous injury. Based on the visual analog scale, the difference in the level of tenderness posteromedially between the complete tear (7 ± 1) and the partial tear (1.3 ± 2.4) group was significant (P = .0004). The presence of significant medial pain had a positive predictive value of 75% with regard to deltoid ligament pathology (partial or complete). The lack of medial pain had a negative predictive value of 73% for no tear. All patients with a complete tear had significant pain. The MCSS(fx) in patients with a complete tear, partial tear, and no tear was 6.6 ± 1.7 mm, 4.5 ± 0.4 mm, and 3.9 ± 0.5 mm. Differences between all groups was significant (P = .02). The average MCS stress in the normal ankle was 2.9 mm or 0.5 mm greater than MCS without stress. Using ultrasound as our gold standard for a complete ligament rupture, sensitivity and specificity was 100% for an MCS stress >5.0 mm. Furthermore, the differences between all three groups was statistically significant when looking at MCSS(fx) B MCS(nl) (P <.001).

Conclusion: Stressed MCS in the fractured ankle (MCSS[fx]) >5 mm should be used as an absolute cutoff for ankle instability indicative of complete deep deltoid ligament rupture. We found that tenderness correlates with deltoid ligament damage and can be used to stratify the risk of deltoid ligament involvement. The lack of significant medial tenderness, especially posteromedially, implies the absence of a complete ligament tear and eliminates the need for stress examination. Stress radiographs of the normal ankle are unnecessary.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.
· 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.