Quantification of the pivot-shift test using a navigation system with non-invasive surface markers

The purpose of this study was to validate the quantitation of the pivot-shift phenomenon by using a navigation system with non-invasive surface markers. Measurements obtained using this system were compared with those obtained using commercial pin-fixed markers. Seventy patients with anterior cruciate ligament (ACL) injuries were assessed under general anaesthesia. Knee kinematics during the pivot-shift test were recorded using an image-free navigation system with a commercial transmitter placed on the thigh and lower leg (surface markers) or those fixed to the femur and the tibia via metal pin fixators (pin-fixed markers). For quantitation of the pivot-shift phenomenon, posterior tibial reduction (PTR) was calculated using the two types of navigation system markers and were then compared. PTRs measured using the two types of markers were also compared with clinical grade of the pivot-shift test, as determined by an examiner. The pivot-shift phenomenon could be identified in all patients on the navigation screen. The PTR measured using surface markers moderately correlated with that measured using pin-fixed markers (rho = 0.524, p < 0.001). There were also moderate correlations between clinical grades and the PTRs measured using either the surface markers (rho = 0.522, p < 0.001) or the pin-fixed markers (rho = 0.645, p < 0.001). The present study demonstrated that PTR, during the pivot-shift test, may be quantified in ACL-injured knees, using a navigation system with surface markers, and that the PTR measured with surface markers moderately correlated both with the PTR obtained using pin-fixed markers and with the clinical grade of the pivot-shift test. A customised method of fixing transmitters with reflective markers to patients' thighs and shins with Velcro straps is non-invasive and could assess and record the knee kinematics, especially the pivot-shift test, in ACL-injured and ACL-reconstructed knees before, during, and after surgery using a navigation system. Case series, Level IV.