Abstract
Quantification of the anterior and rotational laxity of the knee allows recognising an anterior cruciate ligament (ACL) insufficiency and assessing the severity of the lesion. The new GNRB system has demonstrated an improved accuracy and precision in the assessment of the anterior laxity. However, it is not known if this pre-operative measurement is a good predictor of the intra-operative measurement of the knee laxity, especially in the rotational plane. We tested the following hypotheses: 1) the pre-operative anterior knee laxity measured with the GNRB system is predictive for the intra-operative measurement of the anterior knee laxity by a navigation system, and 2) the pre-operative anterior knee laxity measured with the GNRB system is predictive for the intra-operative measurement of the rotational knee laxity by a navigation system,
40 patients operated on for ACL reconstruction were included. The anterior knee translation was assessed before the operation with the GNRB system with a force of 250 N at 25° of knee flexion. The anterior knee translation and the internal-external range of rotation was measured intra-operatively before and after ACL reconstruction with the navigation system. The correlation between 1) the measurements of the anterior laxity by the GNRB system and the navigation system, and 2) the measurements of the anterior translation by the GNRB system and the rotational knee motion measured by the navigation system, were assessed.
There was a significant difference between the measurements of the mean knee anterior laxity by the GNRB system (9.1 ± 2.9 mm) and by the navigation system (11.3 ± 4.0 mm) (p<0.001). There was no significant correlation between the two techniques (R2 = 0.01). However, a satisfactory agreement between the two techniques was observed (R2 = 0.03), with a systematic bias of −3.3 mm for GNRB measurements in comparison to navigated measurements. There was neither significant correlation nor satisfactory agreement between the two techniques when predicting the rotational motion of the knee.
When used prior to ACL reconstruction, the GNRB system underestimates the anterior laxity of the knee that will be measured during the reconstruction by a navigation system, and does not predict the amount of rotational laxity. It is difficult to predict accurately the anterior and rotational knee laxity by pre-operative measurements.
