Lateral Drawer Test Assesses Ankle Instability in Weber B Fibula Fractures
Key findings
- This study compared the lateral drawer test, a new test for examining patients with isolated Weber B ankle fractures, to gravity stress view radiographs for evaluating mortise instability
- The lateral drawer test had high sensitivity (83%), specificity (97%), positive predictive value (96%) and negative predictive value (86%)
- The maneuver was well tolerated, resulting in a minimal increase in visual analog scale pain scores
- The lateral drawer test should not be the sole determinant of ankle instability, but can help guide surgical decision-making when coupled with additional stress radiographs
The role of physical examination to evaluate mortise instability in isolated fibula fractures has essentially been abandoned, because prior studies suggest a lack of diagnostic accuracy. Instead, instability is typically assessed radiographically during stress maneuvers or after a period of physiologic loading.
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Now, researchers at Massachusetts General Hospital have proposed the "lateral drawer test." Similar to determining ankle ligament laxity via the anterior drawer test, the test helps determine mortise instability in isolated Weber B ankle fractures.
John Z. Zhao, MD, of the Harvard Combined Orthopaedic Residency Program, Soheil Ashkani-Esfahani, MD, director of the Foot & Ankle Research and Innovation Lab, John Y. Kwon, MD, chief of the Foot & Ankle Service, and colleagues report in Foot & Ankle Orthopaedics that the test can help determine the optimal timing of stress radiographs.
The Test
The lateral drawer test is performed with the patient in a seated position. The examiner stabilizes the leg with one hand while the other hand grips the hindfoot and applies direct lateral stress to the neutrally positioned ankle.
During the stress maneuver, the examiner minimizes inversion or eversion through the tibiotalar and subtalar joints. Placing a thumb over the medial gutter minimizes inversion/eversion and provides a better feel for the translational movement.
In this study, the lateral drawer test was graded as follows:
- Grade 0—No instability/symmetric to contralateral ankle
- Grade I—Translation <5 mm
- Grade II—Translation ≥5 mm
Study Methods
The researchers prospectively studied 62 adults who presented with an acute isolated Weber B ankle fracture within one week of injury. There were 41 females and 21 males, mean age of 49 (range, 21–85). Using a visual analog scale (0–10), patients rated their pain at rest before manipulation and their maximal pain during the maneuver.
For each patient, the team obtained three radiographic views of the non-weight-bearing ankle (anteroposterior, lateral, and mortise) as well as the gravity stress view (GSV), which was used as the "true" test of instability. The examining orthopedic surgeons did not view the radiographs until after performing the lateral drawer test.
Results
30 patients (48%) demonstrated an unstable ankle fracture, defined as medial clear space (MCS) ≥5 mm on the GSV. There was a strong correlation between grade on the lateral drawer test and the extent of MCS widening (ρ=0.82; P<0.005).
Compared with the GSV, the lateral drawer test demonstrated a sensitivity of 83%, specificity of 97%, positive predictive value of 96% and negative predictive value of 86%.
The average pain score was 4.2 before the test and 4.9 after. No patient demonstrated guarding during the examination that precluded the provider from performing the test.
Guidance for Orthopedic Surgeons
The lateral drawer test is so quick to perform, it can be seamlessly integrated into the physical examination. However, even a sensitivity of 83% is too low to be used as the sole determinant for surgical indications.
The lateral drawer test can be regarded as an additional piece of data to help determine the optimal timing of stress radiographs:
- Grade 0 or I—Patients may safely forego additional stress radiographs at the initial clinic visit and may be asked to follow up after one week of weight-bearing, as tolerated. Weight-bearing radiographs may be taken at that later time
- Grade II—Obtain a stress radiograph and evaluate for MCS widening at the initial visit
In this way, the lateral drawer test would decrease the number of patients who need additional radiographs at the initial clinic visit and shorten the waiting time for patients with grossly unstable ankle fractures who may otherwise be told to try a period of weight-bearing.
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