Background: Clinical weightbearing provocation tests, like the duck walk test, may be of value in diagnosing or screening for medial meniscal tears. However, evidence of the diagnostic accuracy of the duck walk test is lacking.
Questions/purposes: (1) To determine the sensitivity and specificity of the duck walk test in diagnosing medial meniscal tears. (2) To determine whether tear location, tear cause (traumatic versus degenerative), and ACL insufficiency were associated with differences in the sensitivity and specificity of the test.
Methods: A convenience sample of 136 patients of all ages was retrospectively analyzed by evaluating the outpatient knee clinic appointment list of one orthopaedic surgeon for patients with a broad range of knee injuries who had a prior MRI before (24%) or after (76%) physical examination and had a duck walk test stated in their patient records. Of 230 patients with MRI requested by one orthopaedic surgeon attributable to knee complaints, 136 (59%) fulfilled the inclusion criteria; 70 (52%) patients were male and 66 (49%) were female, with a mean age of 42 (± SD 14) years. The duck walk test was performed in case of suspected meniscal injury, based on mechanism of injury, general joint line pain, and/or mechanical complaints (ie, locking, giving away). The test is performed by squatting and "waddling" before rising and is positive in case of general joint line pain or painful "clicking". Interobserver repeatability was not evaluated, but the test is well defined and leaves little room for difference in interpretation. Diagnostic accuracy measures were evaluated. Since the convenience sample in this study consisted of patients who had a duck walk test and MRI, and a positive result of the duck walk test almost certainly increased the probability that MRI would be ordered in the majority (76%) of the patients, the test properties calculated here-especially sensitivity-should be considered inflated.
Results: The calculated sensitivity of the duck walk test was 71% (95% CI, 59%-81%) and there was low specificity of 39% (95% CI, 27%-52%). We found no difference in sensitivity between medial (67%; 95% CI, 51%-80%) and lateral (76%; 95% CI, 50%-92%; p = 0.492) meniscal tears. With the numbers available, we compared these patients with patients without a history of trauma and with an intact ACL. We found no difference among patients with traumatic tears (79%; 95% CI, 59%-91%; p = 0.253) and in patients with ACL tears (77%; 95% CI, 46%-94%; p = 0.742).
Conclusions: Because of the issue of verification bias, the actual sensitivity of this test in practice is likely much lower than the calculated sensitivity we observed. In addition, the test did not seem to perform better in patients with trauma or ACL insufficiency, nor was it more effective in detecting medial than lateral tears, although the numbers on some of those comparisons were rather small. Based on these results, we conclude that used alone, the duck walk test likely has little value in practice as a screening test. However, it is conceivable that it could be used in combination with other provocative tests for screening purposes. Future studies might consider using it as a means to best identify which patients should undergo MRI for the possibility of a meniscal tear.
Level of evidence: Level III, diagnostic study.