Is ultrasound diagnosis reliable in acute extensor tendon injuries of the knee?

Ruptures of the patellar and quadriceps tendon are rare injuries requiring immediate repair to re-establish knee extensor continuity and allow early motion. Ultrasound is extensively used as a diagnostic tool before surgery on acute traumatic tears of the patellar tendon and quadriceps tendons. The aim of our study was to evaluate the role of sonography in diagnosing quadriceps and patellar tendon rupture and in differentiating partial from complete tears. We conducted a retrospective review of 51 consecutive patients who had a surgical intervention for suspected acute quadriceps and patellar tendon rupture over a 5-year period. Intra-operative findings were compared with pre-operative clinical examination. Radiographs, ultrasound and MRI reports were reviewed. On clinical examination, 22 patients had a suspected patellar tendon rupture and 29 patients had a suspected quadriceps tendon rupture. Diagnosis was confirmed by clinical examination and plain radiographs alone in 13 patients, with additional ultrasound performed in 24 patients and MRI scan performed in 14 patients. There were 8 false positives out of 24 [33.3%] in the ultrasound proven group and 1 false positive out of 13 [7.69%] in the clinical examination and radiographs only group. MRI was 100% accurate. We conclude that ultrasonography is not a reliable method in establishing the diagnosis of acute injuries to the extensor mechanism of the knee, particularly the quadriceps tendon ruptures in the obese and the very muscular patients. If there is clinical ambiguity, MRI scan is a better investigation tool before undertaking surgical treatment.