Sumesh M. Zingde

In Vivo Determination of Cam-Post Engagement in Fixed and Mobile-bearing TKA

BackgroundKinematics vary, sometimes in important ways, among the different types of total knee arthroplasty (TKA) designs, yet differences between the in vivo mechanisms of cam-post engagement in rotating-platform posterior-stabilized (PS) TKA, bicruciate-stabilized TKA, and fixed-bearing PS TKA designs remain largely uncharacterized.Questions/purposesThe objective of this study was to determine the cam-post mechanism interaction for subjects implanted with three different TKA designs.MethodsIn vivo, analysis was conducted for patients implanted with nine rotating-platform PS TKAs, five knees with a fixed-bearing PS TKA, and 10 knees with a bicruciate-stabilized TKA while performing a deep knee bend. Three-dimensional kinematics of the implant components were determined by analysis of fluoroscopic images during flexion. The distances between the interacting surfaces were measured throughout flexion and instances and locations of contact were identified.ResultsSeven of the 10 bicruciate-stabilized knees analyzed had the femoral component engaged with the anterior aspect of the tibial post at full extension. Posterior cam-post engagement occurred at 34° for the bicruciate-stabilized (range, 17°–68°), 93° for the fixed-bearing PS (range, 88°–100°), and at 97° (range, 90°–104°) for rotating-platform PS TKA. In bicruciate-stabilized and fixed-bearing PS knees, the contact initially occurred on the medial aspect of the posterior surface of the tibial post and then moved centrally and superiorly with increasing flexion. For rotating-platform PS TKA, it was located centrally on the posterior surface of the post at all times.ConclusionsThis study suggests that mobility of the polyethylene might play an important role in ensuring central cam-post interaction in PS TKA. The polyethylene insert rotates axially in accordance with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the fixed-bearing PS TKAs analyzed in this study.Clinical RelevanceWe speculate that this centralized symmetrical contact between the cam and posterior surface of the post could be beneficial clinically in terms of reducing wear of the posterior surface and particularly at the medial extremes of it.Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

3D in vivo femoro-tibial kinematics of tri-condylar total knee arthroplasty during kneeling activities

BACKGROUND Kneeling position can serve as an important posture, providing stability and balance from a standing position to sitting on the floor or vice-versa. The purpose of the current study was to determine the kinematics during kneeling activities after subjects were implanted with a tri-condylar total knee arthroplasty. MATERIALS AND METHODS Kinematics was evaluated in 54 knees using fluoroscopy and a three-dimensional model fitting approach. RESULTS The average knee flexion at before contact status, at complete contact and at maximum flexion was 98.1±9.0°, 107.2±6.7°, and 139.6±12.3°, respectively. On average, there was no gross anterior displacement from before contact status to complete contact. Only slight posterior rollback motion of both condyles from complete contact to maximum flexion was observed. Three of 39 (7.7%) knees experienced anterior movement of both condyles more than 2mm from before contact status to complete contact. Reverse rotation pattern from before contact status to complete contact and then normal rotation pattern from complete contact to maximum flexion were observed. Condylar lift-off greater than 1.0 mm was observed in 45 knees (83.3%). CONCLUSION The presence of the ball-and-socket joint articulation provides sufficient antero-posterior stability in these designs to enable the patients to kneel safely without the incidence of any dislocation. CLINICAL RELEVANCE This study suggests a safe implant design for kneeling.

Can Post-Cam Function Be Replaced by Addition of a Third Condyle in PS TKA?

The purpose of the study was to analyze the effectiveness of an additional ball and socket articulation in implanted knees and whether it can replicate post-cam function. Fifteen knees implanted with a cruciate substituting (CS) polyethylene without a post and ten knees implanted with a posterior stabilized (PS) polyethylene with a post were analyzed using 3D model fitting approach. Two types of designs showed similar posterior translation and similar axial rotation. Most of the contact points at the ball and socket joint stayed within the socket height for the PS group. This study indicates that the ball and socket joint is able to function as a replacement of the post-cam mechanism, which might serve as a new way to achieve posterior stability.

Femoral condylar contact points start and remain posterior in high flexing patients.

This study compares kinematic patterns of 136 patients following total knee arthroplasty with high post-operative knee flexion (HighFlex) versus kinematics of 114 patients with limited knee flexion (LowFlex) using a blocked stratified random sampling study design to reduce confounding and bias. The kinematics was collected using fluoroscopy and 2D to 3D registration for a weight-bearing deep knee bend activity. Both the lateral and the medial condylar contact positions for the HighFlex subjects were significantly more posterior than the LowFlex subjects at full extension and remained that way at all flexion angles. The amount translation of the contact points, axial orientation angle and axial rotation were found to be similar for the two groups. Lift-off was significantly higher in the LowFlex indicating mid-flexion instability.

In vivo kinematic effects of ball and socket third condyle as a post-cam mechanism in tri-condylar knee implants

BACKGROUND Tri-condylar implants containing a ball and socket third condyle as a post-cam mechanism were developed to accommodate a lifestyle requiring frequent deep flexion activities. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during a deep knee bend activity, and to confirm the contact status of the ball and socket joint. METHODS Seventeen knees implanted with tri-condylar implants were analyzed using a 3D to 2D registration approach. A distance of less than 1mm denoted ball and socket contact. Medial and lateral contact positions and axial rotation were compared before and after contact. Moreover, the contact position at the third condyle and the center of the ball joint were analyzed. RESULTS After the third condyle contact, posterior translation of the medial and lateral contact positions increased considerably. Meanwhile, the angular rotation remained still. The center of the third condyle did not move after contact, and the contact position at the third condyle remained low. CONCLUSIONS The third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation, which was proved to work properly as a posterior stabilizing post-cam mechanism.

Kinematic Difference Between Various Geometric Centers and Contact Points for Tri-Condylar Bi-Surface Knee System

The purpose of the study was to analyze the motion of contact points (CPs), lowest points (LPs), and component facet centers of tri-condylar implants. In vivo knee kinematics was assessed for 43 knees implanted with a multi-radii femoral component during deep knee bend activity, using a model fitting approach. Both LPs had the similar positions to the corresponding geometric centers of the femoral component, and the LP and geometric center angles represented the same component rotation angle defined by Grood and Suntay. Antero-posterior translation of both CPs was significantly overestimated, compared to LPs, and the CP angle showed significant differences from other rotation angles. In conclusion LPs seemed better to evaluate kinematics than CPs because polyethylene congruity had considerable effects on CP analysis.