gms | German Medical Science

Objectives: Quantification of the anterior and rotational laxity of the knee allows recognizing an anterior cruciate ligament (ACL) insufficiency. The GNRB system 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. 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.

Methods: 40 patients were included (25 men and 15 women) with a mean age of 28 years. All patients were operated on with an arthroscopic-assisted ACL reconstruction with either bone-patellar-bone or semi-tendinosus autograft.

The anterior knee translation was assessed before the operation with the GNRB system by application of a calibrated postero-anterior force of 250 N at 25° of knee flexion. The anterior knee translation was measured intra-operatively before ACL reconstruction with the navigation system with application of a non-calibrated, manually applied, maximal postero-anterior force. The rotational knee motion was measured intra-operatively before ACL reconstruction with the navigation system with application of a non-calibrated, manually applied, maximal internal and external torque. The measurements of the anterior translation by the GNRB system and the navigation system were compared by appropriate statistical tests at a 0.05 level of signficance.

Results and Conclusion: 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. The systematic bias may have a significant influence on the operative technique, especially by surgeons who use a patient-specific reconstruction with different techniques according to the severity of the laxity. Furthermore, the pre-operative measurement of the anterior tibial translation may not predict the abnormal rotational motion of the knee, and cannot support the choice for an extra-articular graft augmentation to enhance the intra-articular graft reconstruction prior to the operating room.