Abstract
Introduction
The use of a surgical navigation system has been demonstrated to allow to intraoperatively analyze knee kinematics during total knee arthroplasty (TKA), thus providing the surgeon with a quantitative and reproducible estimation of the knee functional behaviour. Recently severak authors used the computer assisted surgery (CAS) for kinematic evaluations during TKA, in particular to evaluate the achievement of a correct joint biomechanics after the prosthesis implantation. The major concern related to CAS is that the movements are usually passively performed, thence without a real active task performed by the subject. Starting from the hypothesis that the passive kinematics may properly describe the biomechanic behaviour of the knee, the main goal of this work was to intra-operatively compare the active kinematics of the limb, analysing a flexion movement actively performed by the patient, and the passive kinematics, manually performed by the surgeon.
Methods
The anatomical and kinematic acquisitions were performed on 31 patients TKA using a commercial navigation system (BLU-IGS, Orthokey, USA). All the surgeries were performed under local anesthesia, which specifically allowed to acquire the passive and active kinematics including three flexion movements. Both in pre- and post-implant conditions, internal-external (IE) rotations and anterior-posterior (AP) translations were estimated to track any changes in the kinematic pattern.
Results
The IE rotations showed no statistical difference (n.s.) for all the condition under study, in particular no differences existed between the active and the passive kinematics (Figure 1). Similarly, the AP translations (Figure 2) did not show any statistical difference (n.s.) both between active and passive flexion movement, and between pre- and post- implant conditions (n.s.).
Conclusions
The use of a navigation system in TKA has beed identified to be extremely useful not only to assist the operator in providing a proper surgical procedure, but also in performing an accurate estimation of the joint kinematics. The performed analysis of the active flexion movement compared to the passive one, demonstrated that the absence of the active muscle contraction did not affect the knee kinematics estimation. The analysis of knee kinematics with CAS could be considered therefore comparable to other techniques which allow to analyse the dynamic control performed by the subject during active tasks, such as fluoroscopy or gait analysis.
