Diagnostic value of intraoperative tap test for acute deltoid ligament injury

Deltoid ligament injuries appear with isolated or even no displacement of the lateral malleolus fracture which could easily lead to misdiagnosis, which frequently brings about ankle medial instability and talus shift that eventually lead to the occurrence of ankle osteoarthritis. This study is aimed to investigate the value of the tap test for assessing the integrity of the deltoid ligament intraoperatively.

Ninety-two patients with malleolar fractures and possible acute deltoid ligament injury treated in our hospital from March 2013 to May 2016 were enrolled in this prospective study. The gravity stress test and tap test were performed preoperatively by three physicians independently before and after fixation of the fibula. The sensitivity, specificity, positive and negative predictive values, and false-positive and false-negative rates of both tests were determined based on medial malleolus exploration for the integrity of the deltoid ligament. The inter-observer consistency was also analyzed.

Forty seven (51.1%) versus fifty two (56.5%) of the 92 patients tested positive for deltoid ligament injury according to the preoperative gravity stress test or the subsequent tap test. Forty-eight cases (52.2%) were confirmed during surgery. The sensitivity of gravity stress test was lower than that of tap test (95.8% vs 100%), and specificity of gravity stress test was the same as tap test (97.7% vs 97.7%). Between gravity stress test and tap test, the positive and negative predictive values were 97.9% vs 92.3% and 95.6% vs 100%, and the false-positive and false-negative rates were 2.3% vs 9.09% and 4.2% vs 0%, respectively. Between the two tests results, the percentage of inter-observer agreement was > 90% (kappa coefficient > 0.80).

The tap test has the advantages of high sensitivity, simple operation, and less radiation exposure, suggesting that it is of high diagnostic value for assessing the integrity of the acute deltoid ligament.