SONOGRAPHY OF THE ANTERIOR CRUCIATE LIGAM ENT - POTENTIAL AND LIMITATIONS

We carried out sonography of the femoral origin of the anterior crucia te ligament in the dorsal cross section with a 7.5-MHz linear scanner in 25 test subjects with healthy knee joints. A physiological differen ce between the sides in the size of the hypoechoic region of the origi n could be defined on the basis of the measurements obtained in both k nee joints. Values outside a reference range which could be evluated f rom this difference were rated as pathological in terms of an anterior cruciate ligament rupture. The reliability of this method in definiti vely diagnosing an anterior cruciate ligament rupture was analysed sta tistically as compared to the golden standard of arthroscopy on 65 pat ients by means of the two-by-two frequency table test. The femoral ori gin of the cruciate ligament in 25 test subjects had a median width of 3.1 mm (range 1.7-5.8 mm) on the right and 3.4 mm (range 1.7-4.4 mm) on the left. The median difference between the sides is 0.4 mm (range 0-1.8 mm). If the 3rd to the 97th percentile is selected as the refere nce range, our data show a physiological difference between the sides of 0-1.5 mm. The median age of the 65 patients was 31 years (range 14- 74 years). Two thirds of all patients were men. A rupture of the anter ior cruciate ligament was diagnosed sonographically in 19 patients. Th e result was confirmed arthroscopically in 15 patients. In 4 patients, there was a false positive sonographic finding. Forty-six patients di d not fulfil the sonographic criteria of a rupture of the anterior cru ciate ligament. Of these, 38 showed an intact anterior cruciate ligame nt on arthroscopy. Eight patients had a false-negative sonographic fin ding. The corresponding statistical analysis showed sensitivity of 65% , specificity of 90% and precision of 79%. Accordingly, the diagnostic reliability of knee joint sonography in diagnosing a rupture of the a nterior cruciate ligament appears to be unsatisfactory, since old rupt ures, above all, cannot be imaged with certainty (sensitivity 65%). On the other hand, a positive sonographic finding points with relative c ertainty to a rupture of the anterior cruciate ligament even before th e operation (precision 79%). Histological analysis of the cruciate lig ament preparations obtained intraoperatively showed that in particular the fresh anterior cruciate ligament rupture can be imaged sonographi cally. Retrospectively, knowledge of the history is thus crucial for i nterpretation of the sonographic image. After acute trauma to the knee , a side difference in the femoral region of origin of the anterior cr uciate ligament of more than 1.5 mm, as revealed sonographically, is a certain indication that the anterior cruciate ligament is ruptured. W hen there is a positive sonographic finding, ligament strain, synovial bleeding and partial ruptures of the anterior cruciate ligament as we ll as plica ruptures must be considered as possible diagnoses.