Scorpio NRG Research Articles

Morphology characters of resected femoral and tibial surface in chinese population: intraoperative anthropometric study in patients at a tertiary hospital

BackgroundsMismatch between knee surface and prosthesis components is related to postoperative complications. Morphological differences between ethnicity and gender may affect prosthesis coverage. The purpose of this study is to describe morphological characters of resected knee surface (distal femur, proximal tibia) in the Chinese population, analyze the influence of gender and other demographical factors, and validate the effect of ethnic difference by calculating the coverage of Western-designed knee prostheses on Chinese knee surface.MethodsIntraoperative anthropometries were performed during total knee arthroplasty performed by one single team. After screening out severe deformities and bone defects, data were separated via prosthesis system. Multiple linear regression and partial correlation analysis of morphological parameters on age, gender, height, weight were used to find out independent factors influencing morphology. Based on the 5 mm-tolerance in the prosthesis, simulation on scatter plots was brought out to calculate the prosthesis coverage to the resected bone surface.ResultsA total of 865 cases of total knee arthroplasty were involved in this study. Though gender differences were found in all knee morphological parameters regardless of the type of prosthesis, significant association was only found between gender and mediolateral width of femoral surface after adjusting demographical factors (p < 0.001). The two included prosthesis systems, Genesis-II and Scorpio NRG covered most cases in at least one dimension. Males had lower complete coverage and higher no coverage rate on femurs. Asymmetry prostheses had higher lateral coverage on tibiae.ConclusionsBased on our analysis, the only confirmed demographical factor in knee morphology is gender on femoral mediolateral length. Wider femoral prostheses for males may improve results of gender-specific prostheses. The overall fitness between Western-designed prostheses and Chinese knee surface is appliable, but the ratio of complete coverage is low. Further modification of prostheses systems can aim at the number of sizes and geometrical shapes.

Effects of Denervation on the Mid-term Results of Knee Joint Functions after Non-resurfaced Total Knee Arthroplasty

Objective: Total knee arthroplasty (TKA) has become an effective treatment modality for end-stage osteoarthritis and rheumatoid arthritis. Postoperative problems such as anterior knee pain affect postoperative patient satisfaction. Patellar denervation has been proposed as a technique to relieve pain, but its efficacy remains controversial. This study evaluated the mid- and long-term effects of patellar denervation on postoperative knee joint functions, hoping to provide better guidance for clinical practice. Methods: This study is a prospective randomized controlled double-blind study. 58 patients undergoing bilateral non-resurfaced total knee arthroplasty were included and randomized into two groups. Both groups underwent total knee arthroplasty while patellar denervation was performed only on the experimental group. Information regarding whether if patellar denervation was performed were withheld from all patients and outcome assessors. All surgeries were performed by the same high-level professional physician, and the post-stable knee prosthesis system (PS Scorpio NRG PS, Stryker) was used during the surgeries. The knee joint functions were evaluated by professional assessors before and after surgery. The evaluation indicators mainly include KSS scoring, Western Ontario and McMaster Universities (WOMAC) scoring and Visual Analogue Scale (VAS), FJS scoring, etc. The follow-up period was 3 years and 5 years after surgery. Results: The experimental group had better KSS and FJS scores than the control group, the difference was statistically significant. There was no significant inter-group difference in WOMAC and VAS scores. Conclusion: The patellar denervation in TKA patients has positive effects on the mid- and long-term recovery of knee joint functions, and the postoperative satisfaction is better.

Resurfacing versus not-resurfacing the patella in one-stage bilateral total knee arthroplasty: a prospective randomized clinical trial

PurposeResurfacing the patella in one-stage bilateral total knee arthroplasty (TKA) remains debatable. This study aimed to assess the mid-term outcomes of patients after one-stage bilateral TKA performed with and without patellar resurfacing, respectively, with at least five years of follow-up.MethodsSixty-six patients (132 knees) scheduled for first-ever one-stage bilateral TKA due to osteoarthritis received patellar resurfacing and retention, respectively, on one knee and the other, randomly selected. All patients received Scorpio NRG knee prostheses and were evaluated by radiology (anteroposterior, lateral, and axial views) pre-operatively and yearly post-operatively, for at least five years. Knee Society Score and Feller Score values were measured. Anterior knee pain, patellar clunk, and patient satisfaction were assessed.ResultsOne patient died within five years of operation and four were lost to follow-up. One patient developed severe dementia and could not be constructively questioned. Therefore, 60 patients (120 knees) were finally analyzed. There were significantly improved Knee Society and Feller scores (P < 0.001) in the resurfacing group compared with the non-resurfacing group post-operatively. Anterior knee pain and patellar clunk rates were lower on the resurfaced side compared with the non-resurfaced side (P < 0.001). Meanwhile, 47% and only 7% patients preferred the resurfaced and non-resurfaced sides, respectively, at final follow-up. No revision was performed for patellofemoral complications, and no significant differences were found between the two groups in radiographic outcomes.ConclusionsUsing the Scorpio NRG knee prosthesis, patellar resurfacing is superior to non-resurfacing in patients with osteoarthritis observed for ≥ five years.Registration trials numberNCT03600922Key Points• Findings Patellar resurfacing is superior to non-resurfacing in osteoarthritis (OA) patients undergoing total knee arthroplasty (TKA) with the Scorpio NRG knee prosthesis.• Implications Patellar resurfacing should be performed in OA patients during TKA.• Caution Several prosthesis types should be assessed in the same study setting, and multicenter studies are required before generalizability of the present findings.

Long-term results of total knee arthroplasty with single-radius versus multi-radius posterior-stabilized prostheses

BackgroundSingle-radius (SR) prostheses and multi-radius (MR) prostheses have different theoretical advantages; however, there has been a paucity of evaluations comparing the two. This study was designed to compare the 10-year clinical, radiological, and survival outcomes of SR and MR posterior-stabilized prostheses in total knee arthroplasty (TKA).MethodsIn this retrospective cohort study, 220 consecutive patients undergoing TKA between October 2006 and October 2007 were divided into the SR group (106 patients, Stryker Scorpio NRG) and the MR group (114 patients, DePuy Sigma PFC), with a minimum follow-up of 10 years. Clinical, functional, and radiological outcomes, as well as satisfaction rates and survival results, were evaluated.ResultsHospital for Special Surgery and Short Form-12 health survey scores were all significantly improved in both groups at the final follow-up (P < 0.05), but the groups did not differ. The SR group had significantly less anterior knee pain (AKP) and painless crepitation (P < 0.05). Radiological results in terms of radiolucent lines and component position angle showed no differences between groups. The Kaplan-Meier survival curve estimates at 10 years were not significantly different between the groups (P = 0.4172).ConclusionBoth SR and MR posterior-stabilized prostheses can lead to satisfactory outcomes. The SR prosthesis design gave less anterior knee pain than did the MR prostheses. Two prostheses showed no differences in terms of clinical scales, radiological results, satisfaction rates, and survival results at a long-term follow-up. More accurate measurements are required.

Comparative study of existing knee prosthesis with anthropometry of Indian patients and other races, a computer tomography 3D reconstruction-based study

Background: Appropriate component sizing plays an important role in determining the functional outcome following total knee arthroplasty. Comparative studies of different populations have shown significant differences in the anthropometric parameters of knees in different race groups which negates the possibility of using a single sized implant system across different ethnic groups. This study evaluates the dimensions of femoral and tibial articular surfaces of Indian patients and compares the parameters with other ethnic groups and correlates the dimensions with five different commercially available knee systems.Material & Methods: Computerized tomography (CT) scans of contralateral normal knees of patients who underwent the scan for various ailments of the knee were retrieved retrospectively from the hospital database and 3D reconstruction of the images was done. Mediolateral dimensions (fML,tML), Anteroposterior dimensions (fAP, tAP) and aspect ratio (fML/fAP, tML/tAP) of the femur and tibia respectively were calculated and compared with the dimensions of different ethnic groups as well as the femoral and tibial components of five different knee prosthesis systems. ResultsThe average fML in the study group was less than that of Caucasian knees but was marginally larger than other ethnic groups. The fAP, tML and tAP was found to be smaller than all other ethnic groups but a larger femoral aspect ratio was reported than other ethnic groups. Among the implant systems, only NexGen LPS and Scorpio NRG implant femoral components closely matched the femoral dimensions in the study group whereas all implant systems showed significant mismatch with tibial component dimensions when compared to the study populations. ConclusionThis study concludes that the dimensions of Indian knees are different from other ethnic groups and the use of commercially available knee Implants designed based on measurements in Caucasian populations can lead to significant mismatch between implant and resected bone surfaces.

Contraintes de contact articulaire fémorotibial dans les prothèses totales de genou à plateau fixe

BackgroundRotational allowance at the tibiofemoral joint would be required during deep flexion. However, the amount of flexion and rotation has not been investigated in modern total knee arthroplasty (TKA) designs. The present study aimed to determine the contact stress in five posterior-stabilized fixed-bearing TKA designs. HypothesisWe hypothesized that the contact area and stresses at the tibiofemoral articular surfaces vary according to the type of implant design and tested condition. Materials and methodsThe contact area and mean and peak contact stresses at the tibiofemoral articular surfaces were determined when a compressive load of 1200N was applied to a NexGen LPS Flex, Scorpio NRG, Genesis II, PFC Sigma, and Foundation implant. Measurements were performed at 0° and 45° flexion with 0°, 5°, 10°, and 15° rotation, and at 90° and 135° flexion with 0, 5°, 10°, 15°, and 20° rotation. ResultsThe LPS Flex showed that the femoral component could not achieve 20° rotation at 135° flexion. The Scorpio NRG showed less than 20MPa of contact stress at all conditions. The Genesis II showed higher contact stress than 20MPa at 135° flexion with 20° rotation. The PFC Sigma showed that the femoral component could not achieve >10° rotation at any flexion angle. The Foundation showed more than 20MPa of contact stress at 90° flexion with 20° rotation and at 135° flexion with 10°, 15°, and 20° rotation. DiscussionSurgeons should be more aware of the variable contact conditions of the tibiofemoral articular surfaces in individual TKA designs. Level of evidenceLevel IV, basic science study.

Variable tibiofemoral articular contact stress in fixed-bearing total knee arthroplasties.

Rotational allowance at the tibiofemoral joint would be required during deep flexion. However, the amount of flexion and rotation has not been investigated in modern total knee arthroplasty (TKA) designs. The present study aimed to determine the contact stress in five posterior-stabilized fixed-bearing TKA designs. We hypothesized that the contact area and stresses at the tibiofemoral articular surfaces vary according to the type of implant design and tested condition. The contact area and mean and peak contact stresses at the tibiofemoral articular surfaces were determined when a compressive load of 1200N was applied to a NexGen LPS Flex, Scorpio NRG, Genesis II, PFC Sigma, and Foundation implant. Measurements were performed at 0° and 45° flexion with 0°, 5°, 10°, and 15° rotation, and at 90° and 135° flexion with 0, 5°, 10°, 15°, and 20° rotation. The LPS Flex showed that the femoral component could not achieve 20° rotation at 135° flexion. The Scorpio NRG showed less than 20MPa of contact stress at all conditions. The GenesisII showed higher contact stress than 20MPa at 135° flexion with 20° rotation. The PFC Sigma showed that the femoral component could not achieve >10° rotation at any flexion angle. The Foundation showed more than 20MPa of contact stress at 90° flexion with 20° rotation and at 135° flexion with 10°, 15°, and 20° rotation. Surgeons should be more aware of the variable contact conditions of the tibiofemoral articular surfaces in individual TKA designs. Level IV, basic science study.

Total and intercondylar notch bone resection in posterior stabilized knee arthroplasty: analysis of five manufacturer designs

The study aimed to volumetrically measure and compare the bone amount removed through the intercondylar femoral notch and the total bone amount removed through five different brands of implant design in order to provide orthopaedic surgeons with opinions in respect of implant selection. Ten implants from five different total knee arthroplasty implant manufacturers, namely Nex-Gen Legacy, Genesis 2 PS, Vanguard, Sigma PS and Scorpio NRG PS, were applied to a total of 50 sawbone models. Equal or the closest sizes of each brand on the anteroposterior plane were selected, and cuts were made following the standard technique. The removed bone pieces were measured in terms of volume and length in three planes, and were statistically analysed. The comparison made by excluding femoral notch cuts did not produce any statistically significant difference between the amounts of bone removed. The following data were volumetrically obtained from the intercondylar femoral notch cut: Vanguard (3.6±0.4cm3), Nex-Gen (3.7±0.5cm3), Sigma (5.7±0.4cm3), Genesis 2 (6.3±0.3cm3) and Scorpio NRG (6.7±0.7cm3). There was no statistical difference between Genesis 2 and Scorpio NRG (n.s.), or between Nex-Gen and Vanguard (n.s.). The smallest volumetric value measured in the removed intercondylar femoral notch cut was obtained using Vanguard. There are significant differences between implant designs in terms of preserving bone stock, and a large proportion of the difference arises from the intercondylar femoral notch cut.

In vivo kinematic analysis of posterior-stabilized total knee arthroplasty for the valgus knee operated by the gap-balancing technique.

Most in vivo kinematic studies of total knee arthroplasty (TKA) report on the varus knee. The objective of the present study was to evaluate in vivo kinematics of a posterior-stabilized fixed-bearing TKA operated on a valgus knee during knee bending in weight-bearing (WB) and non-weight-bearing (NWB). A total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis and that were operated on using the gap balancing technique were evaluated. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimensional to 3-dimensional registration technique. The average flexion angle was 111.3°±7.5° in WB and 114.9° ± 8.4° in NWB. The femoral component demonstrated a mean external rotation of 5.9° ± 5.8° in WB and 7.4° ± 5.2° in NWB. In WB and NWB, the femoral component showed a medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion. The medial condyle moved similarly in the WB condition and in the NWB condition. The lateral condyle moved posteriorly at a slightly earlier angle during the WB condition than during the NWB condition. We conclude that similar kinematics after TKA can be obtained with the gap balancing technique for the preoperative valgus deformity when compared to the kinematics of a normal knee, even though the magnitude of external rotation was small. IV.

Design and kinematics in total knee arthroplasty

Posterior stabilised (PS) total knee arthroplasty (TKA) design development that focused on restoring normal knee kinematics was followed by the introduction of reason-guided motion designs. Although all PS fixed-bearing knee designs were thought to have similar kinematics, reports show they have differing incidences and magnitudes of posterior femoral rollback and axial rotation. In this retrospective comparative study between two guided-motion total knee systems, we hypothesised that kinematic pattern has an influence on clinical and functional outcomes. This study represents the continuation of a previously reported clinical and kinematics analysis. We retrospectively reviewed 347 patients treated with two different TKA designs: Scorpio NRG (Stryker Orthopedics) and Journey Bi-Cruciate Stabilised (BCS) knee system (Smith & Nephew). Two hundred and eighty-one patients were assessed clinically. Patients were divided into groups according to implanted TKA. Clinical evaluation with the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire was performed. Fifteen Scorpio NRG and 16 Journey BCS patients underwent video fluoroscopy during stair climbing, chair rising/sitting and step up/down at sixmonths of follow-up. At an average 29months of clinical follow-up, patients with Journey BCS TKAs reported better clinical results. Stiffness was more frequently reported in the Journey group (5.2% vs 1.2%), whereas anterior knee pain was observed in the Scorpio NRG group (1.9%) only. Both prosthetic models reported different posterior translation of the medial and lateral contact points (CP) in all analysed motor tasks during knee flexion (BCS 10-18mm; NRG Scorpio 2-3mm). Both designs produced progressive external rotation of the femoral component relative to the tibia during flexion. Journey BCS showed statistically significant better KOOS results. The higher posterior femoral rollback observed in the kinematic assessment of this design, associated with a better patellofemoral design, may be the reason for better clinical outcome. The reported cases of stiffness and anterolateral joint pain could be attributed to excessive medial and lateral tibiofemoral posterior translation. The NRG group demonstrated good axial rotation, but this was not coupled with physiological kinematic patterns. Patellofemoral pain can be explained by a less friendly femoral-groove design. TKA clinical-functional outcome and complications were highly influenced by the bearing geometry and kinematic pattern of prosthetic designs.

Comparison of Two Year Follow-Up Results in High Flexion Total Knee Arthroplasty with Lospa and Scorpio NRG

Purpose: The purpose of this study is to evaluate the clinical and radiologic results after high flexion Lospa (Corentec Inc.) and Scorpio NRG (Stryker Inc.) total knee arthroplasty. Materials and Methods: We prospectively compared 205 knees in 128 patients who underwent arthroplasty using Lospa (group A) and 164 knees in 102 patients who underwent arthroplasty using Scorpio NRG (group B) from September 2010 to March 2012 at Department of Orthopaedic Surgery, Sun General Hospital (Daejeon, Korea). Mean follow-up period was 23 months in group A and 24 months in group B. The radiologic analysis included the change of mechanical axis deviation and femoro-tibial angle, implant position (α, β, γ, δ), and patellar tilt. The clinical results were evaluated according to hospital for special surgery (HSS), knee society score (KSS), and range of motion. Results: Mechanical axis deviations were change in varus from 34.8 mm to 2.6 mm (p=0.02) in group A, and change in varus from 34.3 mm to 3.1 mm (p=0.04) in group B; no statistically significant difference was observed between them (p=0.13). Femoro-tibial angles were varus 4.3 to valgus 6.6 (p=0.02) in group A, and varus 4.4 to valgus 6.5 (p=0.03) in group B; no significant difference was observed between them (p=0.25). No significant difference in implant position was observed between the two groups (p=0.25 in α, p=0.17 in β, p=0.12 in γ, p=0.17 in δ). Mean HSS improved from 48.5 to 93.6 (p=0.02) in group A, and from 41.4 to 94.4 (p=0.01) in group B. Conclusion: Lospa total knee arthroplasty showed excellent early radiologic, clinical results and no statistically significant difference in the results was observed between Lospa and Scorpio NRG.

Lateral approach is advantageous in total knee arthroplasty for valgus deformed knee

IntroductionFor the total knee arthroplasty in valgus deformed knee, superiority of the medial or lateral approach is still controversial. We compared the short-term result of two approach groups.Materials and methodsForty-seven knees in rheumatoid arthritis with valgus deformity from 6° to 24° were randomly divided into two group; medial approach (24 knees) and lateral approach (24 knees). We used Scorpio NRG PS for all knees. Median postoperative periods were 43 months in both groups. We compared the surgical time, and alignment on standing radiograph, range of motion (ROM) pre/postoperatively, and degrees of soft-tissue release procedure, and lateral laxity measured by stress radiograph immediately after operation and at final follow-up.ResultPre/postoperative alignment, surgical time, lateral laxity, and preoperative ROM had no significant in two groups; however, postoperative flexion was superior in lateral approach group 123.8°, 109° in medial approach group. All cases required iliotibial band (ITB) release at Gerdy’s tubercle, 83 % ITB at joint level, 21 % lateral collateral ligament (LCL), 17 % popliteus tendon (PT) in medial approach group, and 88 % ITB at Gerdy’s tubercle, 46 % ITB at joint level, 13 % LCL, 4 % PT in lateral approach group.DiscussionIn the valgus knee, lateral structures are tight. Lateral approach can directly adjust the tight structure, and also less vascular compromise to the patella than medial approach with lateral patellar release. Less invasiveness to the quadriceps muscle in lateral approach could result into better range of motion after the surgery.

Scorpio NRG TKAにおける大腿骨外旋ガイドの精度について

【目的】当科ではScorpio NRG TKAの大腿骨回旋アライメント決定に際し，measured resection法では既存のガイド（3度外旋ガイド）を，gap control法ではJDK-miniのガイドを用いている．今回，術者の設定外旋角通りに後顆の骨切りが行えているか調査し，ガイドの精度について検討した．【対象と方法】対象は内側型変形性膝関節症の診断で両側同時TKAを行った25例50膝で，片側をgap control法で対側をmeasured resection法で行った．術前後のCTにてCTAを計測し，設定した大腿骨外旋骨切り角と，実際の骨切り角である術中外旋骨切り角を調査し，その再現性とばらつきを両群間で検討した．【結果】設定外旋骨切り角と術中外旋骨切り角との差に有意差は認めなかったが，設定外旋骨切り角と術中外旋骨切り角の差の絶対値はMeasured群3.0±1.1度に対してGap群1.2±0.4度と有意差を認めた．【考察】3度外旋ガイドは設置しやすい利点はあるが精度が劣ると考えられた．

The Correlation of Postoperative Femoral Component Rotation Angle and Patella Tilt Angle with Clinical Results in Total Knee Arthroplasty

Purpose: The aim of this study was to analyze the correlation of postoperative femoral component rotation angle and patella tilt angle with clinical results for total knee arthroplasty. Materials and Methods: Ninety-six cases in 48 patients who underwent total knee arthroplasty between March 2002 and February 2010 were enrolled. Femoral component rotation angle (FRA) and patella tilt angle (PTA) were measured with postoperative computed tomography. Clinical results were evaluated using American Knee Society knee score & function score and Feller's patella score. We analyzed the correlation of FRA and PTA with clinical outcomes. We also compared clinical results between the PFC Ⓡ Sigma group and the Scorpio Ⓡ group, and the patello-femoral symptom group and a symptom-free group. Results: The mean FRA was 1.40 o of internal rotation. The patellar tilt angle was 3.79 o of lateral tilt. The mean knee score was 90.5, the function score was 77.4, and the patella score was 23.9. There was a significant difference between FRA and knee scores (p=0.031, r=−0.284). There were no significant differences between FRA and function score or patella score. The correlation of PTA and clinical results was not significant. The mean FRA was 2.00 o of internal rotation in the PFC Ⓡ Sigma group, and it was significantly different than for the Scorpio NRG Ⓡ group which had 0.81 o of internal rotation; but there were no significant differences between the two groups in clinical results. The patello-femoral symptom group deviated more from the mean FRA than did the symptom-free group. Conclusion: Internal rotation of the femoral component is correlated with poor clinical results after total knee arthroplasty. The correlation of patella tilt angle and clinical results was not significant.

Contact Stress at the Anterior Aspect of the Tibial Post in Posterior-Stabilized Total Knee Replacement

Retrieval studies have demonstrated polyethylene wear and deformation of the anterior aspect of the tibial post of posterior-stabilized total knee replacements. We are not aware of any study that has analyzed the effects of the design of the femoral notch and the anterior aspect of the tibial post of posterior-stabilized total knee replacements on contact area, stress, and location. The purpose of the present study was to determine the levels of contact stress generated in three posterior-stabilized total knee replacement designs when the femoral intercondylar notch impinges on the anterior aspect of the tibial post. The contact area, mean and peak contact stresses, and contact location at the anterior aspect of the tibial post were determined when a posterior force of 100 N was applied to a NexGen LPS Flex, Genesis II, and Scorpio NRG total knee replacement. Measurements were performed at -15 degrees, -10 degrees, -5 degrees, 0 degrees, and 5 degrees of flexion of the femoral component both in neutral and with 5 degrees of rotation of the tibial component. Each measurement was sequentially performed five times, and the data were compared within and between the designs with use of analysis of variance and a post-hoc Scheffé F test. The NexGen LPS Flex exhibited two contact areas on the medial and lateral corners of the anterior aspect of the post, whereas both the Genesis II and Scorpio NRG exhibited a single horizontal band. The NexGen LPS Flex showed the largest total contact area of the three designs at -15 degrees, -10 degrees, and 5 degrees of flexion. The NexGen LPS showed the lowest mean contact stress at -15 degrees and 5 degrees but showed the highest peak contact stress at -5 degrees and 0 degrees. The Scorpio NRG showed the highest mean contact stress under all conditions and showed the highest peak contact stress at -15 degrees, -10 degrees, and 5 degrees. With 5 degrees of rotation of the tibial component, peak contact stress increased, relative to neutral, 1.2 to twofold (depending on the flexion angle) in the Genesis II design. The mean and peak contact stresses were variable for all three designs and the test conditions, approaching and in some cases exceeding the compressive yield stress for polyethylene. The geometry of the metal femoral notch and polyethylene tibial post in the axial and sagittal planes significantly affected contact area, mean and peak stresses, and contact location at the anterior aspect of the tibial post.

Photoelastic Measurements of Polymer Insert Stress in the Knee Prostheses Designed for High/Deep Flexion

This paper presents the experimental results of photoelasticity for determining the magnitude and distribution of stresses on the polyethylene insert of the knee prostheses designed for high/deep knee flexion. The prostheses used in our experiment were a conventional posterior stabiliser knee, Scorpio NRG (Non-Restricted Geometry, Stryker Co., USA) and CFK (Complete Flexion Knee, Japan Medical Material Co., Japan), which we have developed to enable the patient to make a complete knee flexion (i.e. seiza in Japanese). Prior to the photoelastic experiment, we had introduced the forces exerted on the knee joint during ascending from deep knee flexion. Here we took squatting as an example of deep knee flexion instead of seiza because ascending from seiza contains complex modalities. The introduced data in terms of knee angles and joint forces were applied to the photoelastic models. The results demonstrated that after the knee angle became larger than 90°, the shear stresses on the post and cam of NRG were higher than those on the ball and socket of CFK. We conclude that the design and the configuration of CFK is acceptable at deep knee flexion from a load-bearing viewpoint.

Contact Stress Analysis of the Conforming Post-Cam Mechanism in Posterior-Stabilized Total Knee Arthroplasty

The present study evaluated the effects of extent of conformity of post-cam design on contact area and stress at post-cam mechanism using 4 different posterior-stabilized prostheses. TRAC and Alpina with full-conformed post-cams exhibited the largest contact area at 90° and 120°. PFC sigma RPF with partial conformed post-cam had the largest contact area at 150°. Scorpio NRG with less conformed post-cam had smaller contact area than the others. Lifting of femoral component decreased contact area and increased contact stress of TRAC and Alpina. Recent modifications of post-cam design have increased contact area, contributing to lower contact stress. None of these prostheses exhibited constant low contact stress throughout flexion. Further modifications of post-cam mechanism are necessary to provide lower contact stress throughout deep knee flexion.

Photoelastic Measurements of Polymer Insert Stress in the Knee Prostheses Designed for High/Deep Flexion

This paper presents the experimental results of photoelasticity for determining the magnitude and distribution of stresses on the polyethylene insert of the knee prostheses designed for high/deep knee flexion. The prostheses used in our experiment were a conventional posterior stabiliser knee, Scorpio NRG (Non‐Restricted Geometry, Stryker Co., USA) and CFK (Complete Flexion Knee, Japan Medical Material Co., Japan), which we have developed to enable the patient to make a complete knee flexion (i.e. seiza in Japanese). Prior to the photoelastic experiment, we had introduced the forces exerted on the knee joint during ascending from deep knee flexion. Here we took squatting as an example of deep knee flexion instead of seiza because ascending from seiza contains complex modalities. The introduced data in terms of knee angles and joint forces were applied to the photoelastic models. The results demonstrated that after the knee angle became larger than 90°, the shear stresses on the post and cam of NRG were higher than those on the ball and socket of CFK. We conclude that the design and the configuration of CFK is acceptable at deep knee flexion from a load‐bearing viewpoint.