The Mark Coventry Award Articular: Contact Estimation in TKA Using In Vivo Kinematics and Finite Element Analysis

In vivo fluoroscopy is a well-known technique to analyze joint kinematics of the replaced knee. With this method, however, the contact areas between femoral and tibial components, fundamental for monitoring wear and validating design concepts, are hard to identify. We developed and tested a novel technique to assess condylar and post-cam contacts in TKA. The technique uses in vivo motion data of the replaced knee from standard fluoroscopy as input for finite element models of the prosthesis components. In these models, tibiofemoral contact patterns at the condyles and post-cam articulations were calculated during various activities. To test for feasibility, the technique was applied to a bicruciate posterior-stabilized prosthesis. Sensitivity of the finite element analysis, validation of the technique, and in vivo tests were performed. To test for potential in the clinical setting, five patients were preliminarily analyzed during chair rising-sitting, stair climbing, and step up-down. For each task and patient, the condylar contact points and contact line rotation were calculated. The results were repeatable and consistent with corresponding calculations from traditional fluoroscopic analysis. Specifically, natural knee kinematics, which shows rolling back and screw home, seemed replicated in all motor tasks. Post-cam contact was observed on both the anterior and posterior faces. Anterior contact is limited to flexion angle close to extension; posterior contact occurs in deeper flexion but is dependent on the motor task. The data suggest the proposed technique provides reliable information to analyze post-cam contacts

Mark Coventry Award: Articular Contact Estimation in TKA Using in vivo Kinematics and FEA

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Three-dimensional implant position and orientation after total knee replacement performed with patient-specific instrumentation systems

Patient-specific instrumentation systems are entering into clinical practice in total knee replacement, but validation tests have yet to determine the accuracy of replicating computer-based plans during surgery. We performed a fluoroscopic analysis to assess the final implant location with respect to the corresponding preoperative plan. Forty-four patients were analyzed after using a patient-specific system based on CT and MRI. Computer aided design implant models and models of the femur and tibia bone portions, as for the preoperative plans, were provided by the manufacturers. Two orthogonal fluoroscopic images of each knee were taken after surgery for pseudo-biplane imaging; 3D component locations with respect to the corresponding bones were estimated by a shape-matching technique. Assuming that the corresponding values at the preoperative plan were equal to zero, discrepancies were taken as an indication of accuracy for the systems. A repeatability test revealed that the technique was reliable within 1 mm and 1°. The maximum discrepancies for all the patients for the femoral component were 5.9 mm in a proximo-distal direction and 4.2° in flexion. Good matching was found between final implantations and preoperative plans with mean discrepancies smaller than 3.1 mm and 1.9°.status: publishe

Three-dimensional implant position and orientation after total knee replacement performed with patient-specific instrumentation systems

Patient-specific instrumentation systems are entering into clinical practice in total knee replacement, but validation tests have yet to determine the accuracy of replicating computer-based plans during surgery. We performed a fluoroscopic analysis to assess the final implant location with respect to the corresponding preoperative plan. Forty-four patients were analyzed after using a patient-specific system based on CT and MRI. Computer aided design implant models and models of the femur and tibia bone portions, as for the preoperative plans, were provided by the manufacturers. Two orthogonal fluoroscopic images of each knee were taken after surgery for pseudo-biplane imaging; 3D component locations with respect to the corresponding bones were estimated by a shape-matching technique. Assuming that the corresponding values at the preoperative plan were equal to zero, discrepancies were taken as an indication of accuracy for the systems. A repeatability test revealed that the technique was reliable within 1 mm and 1\ub0. The maximum discrepancies for all the patients for the femoral component were 5.9 mm in a proximo-distal direction and 4.2\ub0 in flexion. Good matching was found between final implantations and preoperative plans with mean discrepancies smaller than 3.1 mm and 1.9\ub

Cup-To-Neck Contact and Range of Motion after Total Hip Arthroplasty with Large Head Diameters: An Original Three-Dimensional Combined Gait and Videofluoroscopy Analysis

After a total hip arthroplasty, a limited range of motion and lower-limb disability continue to be observed, with these being mainly associated with the implant design and the head-to-neck ratio. Larger diameters of the head bearings were assumed to provide better stability, a larger range of motion, and smaller risks of dislocation and stem-to-liner impingement. However, these claims have never been demonstrated in real patients. The specific aim of this study was to assess, via multi-instrumental analysis, whether the range of motion of a replaced hip is limited by the stem-to-liner contact in patients with large femoral head diameters. Twenty-three patients with a total hip arthroplasty were evaluated at their one-year follow-ups using clinical and instrumental examinations. A combined three-dimensional gait analysis of the full body and videofluoroscopy analysis of the replaced hip were performed during the execution of standard, i.e., daily living, and more demanding motor tasks. The latter were meant to reach the extreme range of motion at the replaced hip site, thus revealing possible stem-to-liner contact. An original technique based on imaging and computer-aided design (CAD) models of the prosthesis components was developed to calculate the stem-to-liner distance. Excellent clinical scores were observed in the study. The gait analysis showed that the range of motion of the replaced hip in the sagittal plane, averaged over all patients, ranged from 28° to 78° in standard activities. In more demanding tasks, single peaks were as high as 110°, 39°, and 60° in the sagittal, frontal, and transverse anatomical planes, respectively. In all motor tasks, the stem-to-liner distances ranged from 8.7 to 13.0 mm on average, with one outlier minimum distance being 2.2 mm. This study shows that, even in demanding motor tasks and with an extreme range of motion, the hip joint replaced with large femoral head diameters did not experience impingement between the prosthesis components

Better joint motion and muscle activity are achieved using kinematic alignment than neutral mechanical alignment in total knee replacement

Introduction: In total knee replacement (TKR), neutral mechanical alignment (NMA) is generally targeted during prosthetic component implantation. An original implantation approach has been recently proposed, referred to as kinematic alignment (KA). This is based on the alignment of the pre-arthritic lower limb undergoing TKR, which is reconstructed using suitable image-based techniques during the surgical planning phase. Particularly, KA is thought to allow better soft-tissue balance [1] and restoration of knee physiological function than NMA. Patient-specific instrumentation (PSI), recently introduced in TKR to execute more accurate and personalized prosthesis component implantation, can be used in the achievement of KA. In detail, KA approach via PSI has the potential to result in more physiological knee motion, including relevant muscle activity, but this has not been demonstrated yet. The aim of this study was to report knee kinematics and electromyography (EMG) for a number lower limb muscles from two TKR patient groups, i.e. operated according to NMA via conventional instrumentation, or according to KA via PSI. Methods: A four-centre randomized study of 144 patients was designed; in each centre, 36 patients affected by primary gonarthrosis were recruited for TKR and implanted with a cruciate-retaining fixed-bearing prosthesis with patella resurfacing (Triathlon\uae by Stryker\uae, Kalamazoo, MI-USA). In our centre 20 patients were implanted so far. 17 of these patients, i.e. 11 operated targeting NMA (group A) via convention instrumentation and 6 targetingKA(group B) via PSI (ShapeMatch\uae by Stryker\uae, Kalamazoo, MI-USA), were assessed clinically using the International Knee Society Scoring (IKSS) System and biomechanically at 6-month follow-up. Knee kinematics during stair-climbing, chair-rising and extension-against-gravity was evaluated by 3D video-fluoroscopy (CAT\uae Medical System, Monterotondo, Italy) synchronized with 4-channel EMG analysis (EMG Mate, Cometa\uae, Milan, Italy) of the main knee ad/abductor and flexor/extensor muscles. Knee motion data were reconstructed to calculate flex/extension (FE), ad/abduction (AA), and internal/external rotation (IE), together with the rotation of tibial base-plate contact-line (CLR), this being the line connecting the medial (MCP) and lateral (LCP) condyle contact points. MCP and LCP antero-posterior translations were also calculated and reported in % of tibial base-plate length. Results: Postoperative knee and functional IKSS scores in group A were 78\ub120 and 80\ub123, worst than in group B, respectively 91\ub112 and 90\ub115. Knee motion patterns were much more consistent over patients in group B than A. In both groups, normal ranges were found for FE, IE and AA, the latter being generally smaller than 3\u25e6. Average IE ranges in the three motor tasks were respectively 8.2\ub13.2\u25e6, 10.1\ub13.9\u25e6 and 7.9\ub14.0\u25e6 in group A, and 6.6\ub14.0\u25e6, 10.5\ub12.5\u25e6 and 11.0\ub13.9\u25e6 in group B. Corresponding MCP translations were 13.8\ub15.6% anterior, 17.0\ub16.6% posterior and 15.4\ub16.9% posterior in group A, and 13.0\ub13.4%, 16.6\ub15.3% and 16.6\ub15.6% all posterior in group B; LCP values were all posterior, i.e. 9.5\ub13.6%, 11.1\ub14.3% and 8.7\ub12.6% in group A, and 10.2\ub12.1%, 13.7\ub18.6% and 14.6\ub19.8% in group B. Relevant CLRs were 8.2\ub13.2\u25e6, 10.2\ub13.7\u25e6 and 8.8\ub15.3\u25e6 in group A, and 7.3\ub13.5\u25e6, 12.6\ub12.6\u25e6 and 12.5\ub14.2\u25e6 in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this being proving more stability in the knee joint after TKA according KA. Discussion: These results reveal that better function occurs usingKAthanNMAin TKR. Though small differences were observed between TKR groups in terms of motion data, the higher data consistency and the less prolonged muscle activations identified using KA support the claim of a more natural soft tissue balance in corresponding knees. More patients are needed to establish the superiority of KA. Reference [1] Eckhoff DG, et al. J Bone Joint Surg Am 2005;87(Suppl. 2):71\u201380