Diagnosis of knee instability using sonography

Objective. A sonographic method has been developed to diagnose knee joint instabilities and to gain exactly quantifiable and reproducible measurements. Design. Based on biomechanical considerations, a new positioning device to analyse knee instabilities sonographically has been developed and tested in in vivo studies. Background. Common instrumental testing techniques are difficult to reproduce and show a lack of reliability. Method. Using sonography the cortical line of the femur and tibia are observed. At the same time a translation of these two partners at the knee joint is provoked in a defined position using the special holding device and under a defined amount of stress. Using this method 142 healthy people, placed in different age groups, were tested to establish standard values for the physiological knee joint translation. A prearthroscopic stability analysis was performed on 101 patients. Results. This study proves that the special device developed, together with the technique used, provides reliable and exact measurements for knee instability in different translation directions. In healthy subjects the lateral compartment always showed a larger translation than the medial compartment. A gradual increase in translation was determined in the age groups over 30 years. A significant difference of 0.0001 was shown between knee stability and instabilities. Moreover, a further differentiation between partial and total ACL ruptures and chronic instabilities was determined. This provides an important advantage not offered by usual instrumental testing techniques. Conclusions. The ability to diagnose even a very low extent of instability and to differentiate between different kinds of instabilities enables exact controls to be carried out for both conservative and operative treatment.