Study points to importance of clinical assessment

A study of lateral ankle ligament abnormalities in persons without symptoms indicates that clinical assessment of ankle instability remains critical to diagnosis, even with widespread use of magnetic resonance imaging (MRI).

The study, presented by Nelson Fong SooHoo, MD, at the 2011 American Orthopaedic Foot & Ankle Society Specialty Day, involved both asymptomatic patients and those with chronic lateral instability (CLI). It found that MRIs frequently show an abnormal-appearing lateral collateral ligament (LCL) complex in asymptomatic patients, many of whom do not recall history of an injury.

Lateral ankle sprains are the most common musculoskeletal injuries in athletes. Most result from inversion injuries and affect the LCL complex, a group of three ligaments (anterior talofibular, calcaneofibular, and posterior talofibular). The sequence of injury is predictable, moving from anterior to posterior. Conservative treatments are generally effective in enabling most patients to return to activity, but chronic instability may develop in a minority of patients.

In functional instability, the ankle gives way, leading to recurrent sprain; mechanical instability involves objective ligament incompetency. Both functional and mechanical instability may co-exist, and when conservative measures fail, lateral ligament reconstruction is indicated.

Abnormalities common in asymptomatic patients
Conventional MRI appearance of LCL complex abnormalities has been described as having high specificity (100 percent, or correctly identifying all instances of LCL complex abnormalities) but low sensitivity (50 percent, or correctly identifying only half of patients without LCL complex abnormalities). Dr. SooHoo noted that incidental LCL complex abnormalities are often encountered, raising questions about their significance in functionally stable ankles. This is particularly true if the patient has nonspecific ankle pain and an otherwise normal-appearing MRI scan or other pathology requiring repair, such as that involving the peroneal tendon or osteochondral injury.

In the study, Dr. SooHoo and colleagues use MRI to evaluate LCL complex abnormalities in an asymptomatic population. They compared the findings with those of patients with CLI who would subsequently undergo LCL reconstruction. They also evaluated the associated peroneal tendon pathology in both groups of patients.

The study group consisted of 14 ankles in 11 asymptomatic volunteers and 5 ankles in 5 patients with CLI who subsequently underwent lateral ligament reconstruction. Musculoskeletal radiologists reviewed the MRI scans to identify ligament abnormalities such as thickening, thinning, morphologic irregularity, tearing, and absence, examined peroneal tendon injury, including tendinosis, tearing, subluxation or dislocation, and superior peroneal retinaculum tear.

Overall, 8 of the 14 asymptomatic ankles (57 percent) demonstrated some type of LCL complex abnormality on MRI and 9 (64 percent) had peroneal tendon abnormality. In the 5 symptomatic ankles, MRI identified 4 with LCL complex abnormality and 1 with peroneal tendon abnormality. The findings are summarized in Table 1.

Among the limitations of the study, Dr. SooHoo said, was the small number of volunteers and patients. “If you wanted to establish a more accurate prevalence, you would need additional participants across a broader age range,” he said. (The range in this study was 29 to 47 years; mean age, 35 years.)

Dr. SooHoo also noted the difficulty in distinguishing remote tears from normal variations on MRIs. Finally, optimal comparison of asymptomatic versus CLI ankles is precluded by several factors including differing MRI modalities (3T magnet vs. 1.5T magnet).

Although this was a small study, Dr. SooHoo noted that it “reinforces the importance of using clinical symptoms to correlate with findings of an abnormal LCL complex on conventional MR imaging.”

Dr. SooHoo’s coauthors for “MR Evaluation of Asymptomatic Lateral Ankle Ligament Instability and Comparitive Findings in Patients with Chronic Lateral Ankle Instability” are David Sandman, MD; Kambiz Motamedi, MD; Benjamin Levine, MD; C. J. Gottsegen, MD; and Seeger Leanne, MD.

Disclosure information: None of the authors reported any conflicts.

Terry Stanton is senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

• Lateral ankle sprains resulting from inversion injuries can affect the lateral collateral ligament (LCL) complex and lead to chronic instability.
• A review of MRI scans of a small number of patients with and without symptoms of ankle injury found LCL abnormalities in more than half (57 percent) of asymptomatic patients.
• Limitations include small study size, age range of patients, and differing MRI modalities.
• Correlating clinical symptoms to MRI findings is important in planning treatment.