Our aim was to investigate whether it is possible to predict post-operative kinematics (Post-Ope) from intra-operative kinematics (Intra-Ope) after total knee arthroplasty. Our study were performed for 11 patients (14 knees) who underwent primary PS TKA using CT-based navigation system between Sept.2012 and Sept.2014. The mean subject age was 71.5 ± 5.5 years at the time of surgery. Intra-Ope was measured using the navigation system after implantation during passive full extension and flexion imposed by the surgeon. Under fluoroscopic surveillance, each patient was asked to perform sequential deep knee flexion under both non-weight bearing (NWB) and weight bearing (WB) conditions from full extension to maximum flexion. To estimate the spatial position and orientation, we used a 2- to 3- dimensional (2D3D) registration technique. Intra-Ope and Post-Ope had a common coordinate axis for bones. Evaluations were range of motion (ROM), external rotation angles (ER). The level of statistical significant difference was set at 0.05. Mean ROM in Intra-Ope(130°± 7.9°) was statistically larger than both NWB(121.1°±10.5°) and WB(124.0°±14.7°). No Statistically significant difference was found in the mean ER from 10° to 120° among Intra-Ope (11.2°± 8.5°) and NWB(7.1°±6.0°) and WB(5.3°±3.2°). It is suggested that we could predict Post-Ope from Intra-Ope by considering the increase of the range of motion due to the muscle relaxation condition and the amount of change in the ER.

Bi-cruciate stabilized (BCS) TKA is the prosthesis that aims to substitute bi-cruciate ligament with post-cam engagement. We estimated to describe the in vivo kinematics during deep knee bending in BCS and Cruciate retaining (CR) TKA with the same articular geometry. We analyzed 26 knees who agreed to the current investigation under institutional review board approval. 17 knees were implanted with BCS (Journey ∥BCS, Smith & Nephew. Memphis, US) and 9 knees with CR (Journey∥CR). Each patient was asked to perform deep knee bending under weight-bearing condition. To estimate the spatial position and orientation of the TKA, 2D/3D registration technique with single fluoroscopy was used. We evaluated anteroposterior (AP) translation of the nearest point from femoral component to tibial axial plane for medial and lateral sides, femoral external rotation relative to tibial component and post-cam engagement in BCS. Measurement results were analyzed using Wilcoxon test. Values of P<0.05 were considered statistically significant. Medial AP translation indicated 11.7±5.1% posterior movement in BCS and 4.0±6.6% anterior movement in CR from minimum flexion to 130°. Lateral AP translation indicated 28.9±11.4% posterior movement in BCS and 18.3±6.2% posterior movement in CR from minimum flexion to 130°. Femoral external rotation were observed in both group and the amount of rotation were 5.2°±4.5° in BCS and 8.2°±4.0° in CR. Anterior post-cam engagement was not observed in all cases (76.5%). But medial AP translation in BCS was anteriorly in shallow flexion angles compared to CR. It suggested that anterior post-cam engagement couldn't work in valid.

Introduction

The deformity in osteoarthritis (OA) of the knee has been evaluated mainly in the frontal plane two dimensional X-ray using femorotibial angle. Although the presence of underlying rotational deformity in the varus knee and coexisting hip abnormality in the valgus knee have been suggested, three dimensional (3D) deformities in the varus and valgus knee were still unknown. We evaluated the 3D deformities of the varus and valgus knee using 3D bone models.

Introduction

Posterior cruciate ligament (PCL) preservation in total knee arthroplasty (TKA) is adovocated on the grounds that it provides better restoration of knee joint kinematics as opposed to PCL sacrifice. Mobile-bearing (MB) total knee prostheses have been in the market for a long time, but the PFC-Sigma Rotating Platform (RP) prosthesis (DePuy Orthopaedics, Inc, Warsaw, Ind) has been introduced in the market since 2000. Since, little is known about the in vivo kinematics of MB prostheses especially with cruciate retaining (CR). The objective of this study is to investigate the in vivo kinematics of MB RP-CR total knee arthroplasty during weight-bearing deep knee bending motion.

Background

Mobile-bearing (MB) total knee prostheses have been developed to achieve lower contact stress and higher conformity compared to fixed-bearing total knee prostheses. However, little is known about the in vivo kinematics of MB prostheses especially the motion of the polyethylene insert (PE) during various daily performances. And the in vivo motion of the PE during stairs up and down has not been clarified. The objective of this study is to clarify the in vivo motion of MB total knee arthroplasty including the PE during stairs up and down.

Mobile-bearing (MB) total knee prostheses have been developed to achieve lower contact stress and higher conformity than fixed-bearing total knee prostheses. However, little is known about the in vivo kinematics of MB prostheses especially about the motion of polyethylene insert (PE). And the in vivo motion of PE during squat motion has not been clarified. The objective of this study is to clarify the in vivo motion of MB total knee arthroplasty including PE during squat motion. Patients and methods: We investigated the in vivo knee kinematics of 11 knees (10 patients) implanted with PFC-Sigma RPF (DePuy). Under fluoroscopic surveillance, each patient did a wight-bearing deep knee bending motion. And motion between each component was analyzed using two-to three-dimensional registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components, and PE (implanted with four tantalum beads intra-operatively) from single-view fluoroscopic images. We evaluated the range of motion between the femoral and tibial components, axial rotation between the femoral component and PE, the femoral and tibial component, and the PE and tibial component, and AP translation of the nearest point between the femoral and tibial component and between the femoral component and PE.

Results: The mean range of hyper-extension was 2.1° and the mean range of flexion of 121.2°. The femoral component relative to the tibial component demonstrated 10.4° external rotation for 0–120 degrees flexion. The tibial component rotated 10.2° externally relative to the PE and the femoral component minimally rotated relative to the PE within ± 5 degrees. In upright standing position, the femoral component already rotated externally relative to the tibial component in 6.3°, and the PE also rotated on average 6.4° externally on the tibial tray. Typically the femoral component relative to the tibial component exhibited a central pivot pattern external rotation from extension to 80° knee flexion. Subsequently from 80 to 120°, bilateral condyles moved backward. In a similar fashion, the femoral component relative to the PE exhibited a central pivot pattern external rotation from extension to 70° knee flexion and subsequently bicondylar rollback from 70 to 120° knee flexion.

Discussion and Conclusion: In this study, we evaluated the in vivo motion of PE during squat motion. About this total knee prosthesis, the mobile-bearing mechanism which advantages over fixed-bearing prosthesis to reduce contact stress and keep high comformity might work well, and arc of range of motion was maintained. Furthermore, in upright standing position, the femoral component and tibial component already rotated externally relative to the PE in almost equal measure. This indicated that, self-aligning mechanism, another characteristic of the MB prosthesis might also work well.

Recently mobile-bearing total knee arthroplasty (TKA) has become more popular. However, the advantages of mobile bearing (MB) PS TKA still remain unclear especially from a kinematic point of view. The objective of this study was to investigate the difference and advantage in kinematics of mobile baring PS TKA compared with fixed bearing (FB) PS TKA.

Femorotibial nearest positions for 19 subjects (20 knees), 10 knees implanted with NexGen Legacy flex (Zimmer, Warsaw, IN)with mobile bearing PS TKA, and 10 knees implanted with NexGen Legacy flex (Zimmer, Warsaw, IN)with fixed bearing PS TKA were analyzed using the sagittal plane fluoroscopic images. All the knees were implanted by a single surgeon. All the subjects performed weight bearing deep knee bending motion. We evaluated range of motion, axial rotation of the femoral component, AP translation of medial and lateral sides.

The average range of motion between femoral component and tibial component was 119°±18° in MB and 122°±10 ° in FB. The axial rotation of the femoral component was 11.8°±6.2° in MB and 11.8°±4.9° in FB. There was no significant difference both in range of motion and axial rotation between MB and FB. The AP translation of MB and FB showed same patterns. They were rollback in early flexion, the lateral pivot pattern (the medial condyle moved forward significantly compared with the lesser amount of AP translation for the lateral condyle) at mid flexion, and bicondylar rollback at deep flexion. The rollback in early flexion was 3.4mm in MB and 1.8mm in FB at medial side, 4.2mm in MB and 4.8mm in FB at lateral side. There was no significant difference. The lateral pivot pattern, which moved anteriorly, was 7.8mm in MB and 7.0mm in FB at medial side, 3.0mm in MB and 2.4mm in FB at lateral side. There was no significant difference. The bicondylar rollback at deep flexion was 6.4mm in MB and 7.7mm in FB at medial side, 6.9mm in MB and 4.8mm in FB at lateral side. In four subjects, more than 12°axial rotation was observed in knees implanted with FB TKA which allows only 12°axial rotation.

The results in this study demonstrate that there was no significant difference in kinematics of weight bearing deep knee bending motion between MB and FB. The advantage of MB is allowance of axial rotation which restricted until 12° in FB NexGen Legacy flex PS TKA.

Introduction: Recently several retrieval reports of PS TKA have demonstrated that the wear and deformation can occur on the anterior tibial post and the hyperextension of femorotibial components was a pivotal factor in the mechanism of anterior tibial post impingement. The objective of this study was to investigate the in vivo mechanism of anterior tibial post impingement during gait in PS TKAs.

Methods: Twenty knees with PS TKAs implanted by single surgeon were assessed in this study. The Review Board Committee of the author’s institution approved this study and informed consent was obtained from all patients. In this study ten knees implanted with Scorpio NRG PS (Stryker Orthopedics, Mahwah, NJ) and ten knees implanted with NexGen Legacy-flex fixed (Zimmer, Warsaw, IN) were examined. Each patient was asked to perform treadmill gait under fluoroscopic surveillance in the sagittal plane. Treadmill gait speed was 0.5–1.0 m/s at Patients selected comfortable speed. Patients were explicitly encouraged to fully extend their knees at heel-strike and to avoid a shuffling gait pattern. Patients used light-touch hand-support to maintain the foot position on the treadmill. In vivo 3D poses of the knee prostheses were computed using a two- to three-dimensional (2D/3D) registration technique, which uses CAD models to reproduce spatial postures of the femoral and tibial components from calibrated single-view fluoroscopic images. We evaluated range of motion and the anterior-posterior (AP) translations between femoral and tibial inserts. The anterior tibial post impingement was determined when the proximity between tibial post and femoral cam is within the 0.5mm threshold.

Results: The maximum flexion during gait was 41.9° (25°–56°) in NRG and 42.3° (23°–59°) in Legacy-flex. The minimum flexion during gait was 1.5° (−9.2° − 8.4°) in NRG and 1.8° (−13.0° − 17.0°) in Legacy-flex. The AP translations of the medial and lateral contact points in stance phase were significantly larger in Legacy-flex compared with NRG (medial ; p=0.02,lateral ; p=0.007, Mann-Whitney’s U test). Anterior tibial post impingement was recognized in four knees implanted with Legacy-flex, and in two of three knees, the knee was not hyper extended. On the other hand, no impingement was recognized in knee implanted with NRG.

Discussion: In this study, the anterior tibial post impingement occurred not only in hyper extended knee but also in slightly flexed knee in Legacy-flex. One of the reasons why the anterior tibial post impingement was recognized in Legacy-flex was the large amount of the AP translation in stance phase. Posterior translation in stance phase may be one pivotal factor in the mechanism of the anterior tibial post impingement.

Background: Mobile-bearing (MB) total knee prostheses have been developed to achieve lower contact stress and higher conformity than fixed-bearing total knee prostheses. However, little is known about the in vivo kinematics of MB prostheses especially about the motion of polyethylene insert (PE). And the in vivo motion of PE during deep knee bending under weight-bearing conditions has not been clarified. The objective of this study is to clarify the in vivo motion of MB total knee arthroplasty including PE during weight-bearing deep knee bend motion.

Patients and methods: We investigated the in vivo knee kinematics of 9 knees (9 patients) implanted with PFC-Sigma RPF (DePuy). Under fluoroscopic surveillance, each patient did a wight-bearing deep knee bending motion. And motion between each component was analyzed using two- to three-dimensional registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components, and PE (implanted with four tantalum beads intra-operatively) from single-view fluoroscopic images. We evaluated the range of motion between the femoral and tibial components, axial rotation between the femoral component and PE, the femoral and tibial component, and the PE and tibial component, and AP translation of the nearest point between the femoral and tibial component and between the femoral component and PE.

Results: The mean range of hyper-extension was 2.1° and the mean range of flexion of 121.2°. The femoral component relative to the tibial component demonstrated 13.0° external rotation for 0–120 degrees flexion. The tibial component rotated 12.1° externally relative to the PE and the femoral component minimally rotated relative to the PE within ± 5 degrees. In upright standing position, the femoral component already rotated externally relative to the tibial component in 7.8°, and the PE also rotated on average 8.2° externally on the tibial tray. Typically the femoral component relative to the tibial component exhibited a central pivot pattern external rotation from extension to 80° knee flexion. Subsequently from 80 to 120°, bilateral condyles moved backward. In a similar fashion, the femoral component relative to the PE exhibited a central pivot pattern external rotation from extension to 70° knee flexion and subsequently bicondylar rollback from 70 to 120° knee flexion.

Discussion and conclusion: In this study, we evaluated the in vivo motion of PE during deep knee bend motion under weight-bearing condition. About this total knee prosthesis, the mobile-bearing mechanism which advantages over fixed-bearing prosthesis to reduce contact stress and keep high comformity might work well, and arc of range of motion was maintained. Furthermore, in upright standing position, the femoral component and tibial component already rotated externally relative to the PE in almost equal measure. This indicated that, self-aligning mechanism, another characteristic of the MB prosthesis might also work well.