Information on knee kinematics during surgery is currently lacking. The aim of this study is to describe intra-operative kinematics evaluations during uni-compartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) by mean of a navigation system. Anatomical and kinematic data were acquired by Kin-Nav navigation system and analysed by a dedicated elaboration software developed at our laboratory. The study was conducted on 20 patients: 10 patients undergoing mini-invasive UKA and 10 patients undergoing posterior-substituting-rotating-platform TKA. In both group of patients the surgeon performed passive knee flexion immediately before and immediately after the prosthetic implant. Pattern and amount of internal/external tibial rotation in function of flexion were computed and significant changes between before and after implant were evaluated adopting Student’s t-test (significant level p=0.05).

UKA implant did not significantly change the pattern of internal/external tibial rotation, nor the total magnitude of tibial rotation (15.75°±7.27°) during range of flexion (10°–110°), compared to pre-operative values (17.87°±7.34°, p=0.25). Magnitude of tibial rotation in TKA group before surgery (8.00°±3.67°) was significantly less compared to UKA patients and did not changed significantly after implant (5.96°±4.88°, p=0.09). Pattern of rotation before and after TKA implant were different between each other and between pattern in UKA patients both before and after implant.

Intra-operative evaluations on tibial rotation during knee flexion confirmed some assumptions on knee implants from post-operative methods and suggest a more extensive use of surgical navigation systems for kinematic studies.

Total knee arthroplasty (TKA) is actually a satisfactory technique to reduce pain and enhance mobility in osteoartritic pathologies (OA) of the knee. However, life of the implant is strictly dependent on restoration of correct knee kinematics, as alteration of motion pattern could led to abnormal wear in prosthetic components and also damage soft tissues. The aim of our study was to evaluate new kinematic tests to be performed during surgery in order to improve the standard intra-operative evaluation of the outcome on the individual case. We used Kin-Nav navigation system to acquire anatomic and kinematic data, which were analysed by a dedicated elaboration software developed at our laboratory. Ten patients undergoing rotating platform cruciate substituting TKA were considered for this study. Immediately before the implant and immediately after component positioning, the surgeon performed 3 complete knee flexion imposing internal tibial rotation (IPROM) and 3 complete knee flexion imposing external tibial rotation (EPROM). Tibial rotation during IPROM and EPROM tests was plotted in function of flexion (in the range 10°–110°). Repeatability of IPROM and EPROM was tested by calculating ICC (Intra-class Correlation Coefficient) between 3 repeated curves. Distance between IPROM curve and EPROM curve was computed at various degree of flexion. Maximum distance obtained during all range of flexion before and after the implant were compared by Student’s t-test (significant level p=0.05).

ICC for repeated motions were 0.99 for IPROM and 0.98 for EPROM. Maximum distance between tibial rotation in IPROM and EPROM was 27.82±6.98 before implant and significantly increased (p=0.001) to 40.09±6.92 after TKA. In one case we observed that the value remained similar before and after implant (from 33.11 to 33.98) while in one case we observed very large increase of rotation (from 30.56 to 50.01).

The proposed kinematic tests were able to quantify the increase of tibial rotation after TKA implant. Future development of the study are encouraging and will include a larger sample and reflections on individual findings.

Aims: This work describes a new intraoperative computer-assisted method for the evaluation of joint kinematics in both total (TKA) and uni-compartmental (UKA) knee arthroplasty. We report schematically the protocol and the preliminary in-vivo results we obtained on 11 patients (9 UKA – 2 TKA).

Methods: The system consists of an optoelectronic localizer, 2 reference arrays and a dedicated acquisition software, that permits the real-time control of limb position and allows the acquisition of joint motions. After a first phase of registration (anatomical landmarks identification) the surgeon executes, both before and after the reconstruction, a series of passive tests: range of motion (PROM) evaluation, varus-valgus (VV) stress at 0°, and VV at 30°. Furthermore the surgeon can acquire also anatomical surfaces (tibial plateaus, femoral condyles, prosthetic components, etc.). The 3D kinematic evaluations and anatomical data are recorded before and after the joint reconstruction. This new methodology has been used during 11 interventions fulfilled at our institute. We compare the PROM results with literature, and we also analyzed the interoperator repeatability in the execution of the tests (3 repetitions performed by a senior surgeon).

Results: The kinematic analysis of the PROM showed that there were no significant differences between per-operative and post-operative in all UKA cases. In the 2 TKR cases internal-external (IE) rotations appeared reduced after the implant, but further data are necessary to have a statistical evidence. The extension was improved both in UKA and TKA. The VV laxity at 0 ° was significantly reduced (p < 0.001), while at 30 ° stayed constant (p = 0.010). In all the TKR cases the evaluation of contact areas between femoral and tibial components showed normal pattern, and in UKA the contacts remain inside the prosthesis areas. Measured kinematic parameters (knee rotations, screw-home mechanism and alignment) were comparable with literature and manual estimation at surgical time.

Conclusions: The proposed protocol optimizes surgical times and minimizes invasiveness. The preliminary results showed that the system is able to quantify new kinematic parameters during intraoperative evaluations, provides data about alignments, gaps, stability and 3D motions of the individual knee and therefore can allow an accurate and real-time estimation of the passive knee function. Moreover the new 3D anatomical and kinematic data can improve the biomechanical understanding of the pathological and prosthetic knees.