Mobile-bearing Knee Prosthesis Research Articles

No clinical difference at mid-term follow-up between TiN-coated versus uncoated cemented mobile-bearing total knee arthroplasty: a matched cohort study

Nitride-based ceramic coating was introduced into surgical implants to improve hardness, reduce abrasion, and decrease the risk of metal-induced adverse reactions, especially for patients with suspected or identified metal hypersensitivity. The study aimed to evaluate the effectiveness and safety of a titanium nitride (TiN) coated prosthesis with a mobile bearing design. This was a retrospective matched-cohort study from a single center, comparing clinical outcomes between patients receiving either a TiN-coated versus an uncoated cobalt-chromium-molybdenum (CoCrMo) prostheses for primary total knee replacement. Seventeen patients received the TiN prosthesis between 2015 and 2019. These were matched 1:2 with patients receiving uncoated mobile-bearing knee prostheses with the same design manufacturer. Fourteen patients in the TiN group had complete 5-year follow-up data and were compared with 34 patients from the CoCrMo group. The Knee Society Score was 170.6±28.0 (Function subscore 83.7±17.5 and Knee subscore 86.9±13.8) in the TiN group and 180.7±49.4 (Function subscore 87.5±14.3 and Knee subscore 93.2±9.6) in CoCrMo group, with no statistically significant difference (p=0.19). One patient underwent a revision for instability requiring the removal of the implant in the TiN group and none in the CoCrMo group. The survival rates were 92.9% (CI95% 77.3-100.0) and 100.0% in the TiN group and CoCrMo group respectively (p=1.0). TiN-coated TKA with mobile bearing resulted in satisfactory clinical outcomes, and a low revision rate, and there was no complication related to the coated implant. The use of TiN-coated prostheses in case of confirmed or suspected metal allergy provides satisfactory short-term clinic outcomes.

Result of posteromedial capsule and superficial medial collateral ligament release on gap and alignment in total knee arthroplasty in varusknee deformity by computer assisted surgery measurement: a retrospective stud

Soft tissue release and gap balancing in total knee arthroplasty (TKA) are important issue and lack of conclusive result. We performed posteromedial capsule (PMC) and superficial medial collateral ligament (sMCL) release by preservation of anterior attachment of pes anserine. Gaps and alignment were recorded by computer assisted surgery measurement.Results:T: The mean correction of varus deformity after PMC release and sMCL release were 4.88 ± 2.82° and 3.39 ± 1.7 respectively with the mean FC after PMC and sMCL release correction of 5.57 ± 3.5 and 1.34 ± 2.9° respectively. The mean medial gap changes on full extension after PMC and sMCL release was 1.83 ± 1.39 and 1.67 ± 1.04 mm. respectively with the mean medial gaps at 90 degree flexion after PMC and sMCL release changes of 0.73 ± 0.9 and 5.14 ± 2.11 mm. respectively. The mean lateral gap changes on extension after PMC and sMCL release were -1.3 ± 1.83 and -1.1 ± 1.6 mm. respectively with the mean lateral gaps at 90 degree flexion after PMC and sMCL release changes of -0.19 ± 1.03 and 0.06 ± 1.75 mm. here were 21 patients (16 female and 5 male) with mean age of 68 (48-78) years. The mean body mass index was 28.49 (20.70 – 39.95) kg/m2. The mean preoperative hip-knee-ankle angle was varus 8.12 (3.5-16.0) degrees with mean flexion contracture of 11.3 (3.5-16.0) degrees. Sixteen knees were implanted with Fixed bearing knee prosthesis and five knees were implanted with Mobile bearing knee prosthesis (Table.1). We performed PMC release in all patients, and combined PMC and sMCL release in fourteen patients. The mean correction of varus deformity after PM release and sMCL release were 4.88 ± 2.82 and 3.39 ± 1.7 degrees respectively. While the mean correction of flexion contracture after PMC release and sMCL release were 5.57 ± 3.5 and 1.34 ± 2.9 degrees respectively (Fig.8). The mean medial gaps change on extension after PMC and sMCL release were 1.83 ± 1.39 and 1.67 ± 1.04 mm. respectively. The mean medial gaps change at 90 degree flexion after PMC and sMCL release were 0.73 ± 0.9 and 5.14 ± 2.11 mm. respectively (Fig.9). The mean lateral gaps change on extension after PMC and sMCL release were 1.3 ± 1.83 and -1.1 ± 1.6 mm. respectively. The mean lateral gaps change at 90 degree flexion after PMC and sMCL release were -0.19 ± 1.03 and 0.06 ± 1.75 mm. (Fig.9). There is no instability of knee after PMC and sMCL release.Materials and Methods:Twenty one patient had been operated on. TKA with computer assisted surgery was performed using PMC and sMCL release by preservation of anterior attachment of pes anserine. Alignment, medial and lateral gaps were measured by computer assisted surgery. The mean age was 68 (48-78) years with the mean preoperative hip-kneeankle angle of 8.12 (3.5-16.0) degrees and the mean flexion contracture (FC) of 11.3 (3.516.0) degrees.Conclusion:We believe that sMCL release with preservation of anterior attachment of pes anserinus in total knee arthroplasty has additional effect on varus knee correction after PMC release without creation of knee instability.

Short term results of low contact stress total knee arthroplasty: Original article

Introduction: Conventional fixed-bearing knee prostheses have been proved to be clinically successful in elderly individuals with low activity levels. Polyethylene wear and loosening remain important problems with current fixed-bearing knee prostheses. In mobile-bearing knee prosthesis rotation of polyethylene insert is allowed and the contact area of the articular surface can be greatly increased and there can be a consequent reduction in contact stresses, and decreased polyethylene wear and there is decreased constraint forces at the bone and tibial prosthesis interface leading to decreased loosening. The objective of this study were to assess the clinical outcome of the procedure, to assess the complication rate of bearing dislocation associated with mobile bearing prosthesis, to compare our results with those of other similar studies and to compare the results of the study with those of fixed bearing prosthesis done earlier in our institute.Materials and Methods: This prospective study involved 30 total knee arthroplasties which were performed on 20 patients using Low Contact Stress (LCS) prosthesis. The patients were assessed pre-operatively and pos-operatively clinically and radiologicallyat each visit and also using the Knee Society Rating System. The Depuy (Johnson & Johnson) LCS total knee arthroplasty was used in this study.Results: Total of 30 total knee arthroplasties were performed using low contact stress prosthesis in 20 patients. The mean post-operative knee society knee and function scores in the present study were 89.2 (range, 73-97) and 87 (range, 75-100), at mean follow-up period of 16 months. Our study has shown excellent results in 26 knees and good results in 4 knees. Conclusion: LCS prosthesis TKR showed excellent clinical outcome with excellent improvement in the pain relief scores, this study was comparable with other studies and those of studies on total knee replacement with fixed bearing prosthesis performed earlier in the same institute.

Clinical Outcome of Medial Pivot Compared With Press-Fit Condylar Sigma Cruciate-Retaining Mobile-Bearing Total Knee Arthroplasty

BackgroundThe purpose of this study was to compare the long-term clinical results, radiographic results, range of knee motion, patient satisfaction, and the survival rate of Medial-Pivot posterior cruciate-substituting, knee prosthesis and a press-fit condylar (PFC) Sigma cruciate-retaining mobile-bearing knee prosthesis in the same patients. MethodsOne hundred eighty-two patients received Medial-Pivot knee prosthesis in one knee and a PFC Sigma knee prosthesis in the contralateral knee. The minimum duration of follow-up was 11 years (range, 11-12.6 years). ResultsThe knees with a Medial-Pivot knee prosthesis had significantly worse results than those with a PFC Sigma knee prosthesis at the final follow-up with regard to the mean postoperative Knee Society knee scores (90 compared with 95 points), Western Ontario and McMaster Universities Osteoarthritis Index score (25 compared with 18 points), and range of knee motion (117° compared with 128°). Patients were more satisfied with PFC Sigma knee prosthesis (93%) than with Medial-Pivot knee prosthesis (75%). Complication rates were significantly higher in the Medial-Pivot knee group (26%) than those in the PFC Sigma knee group (6.5%). Radiographic results and survival rates (99% compared with 99.5%) were similar between the 2 groups. ConclusionAlthough the long-term fixation and survival rate of both Medial-Pivot and PFC Sigma prostheses were similar, we observed a worse knee score, worse range of knee motion, and patient satisfaction was less in the Medial-Pivot knee group than in the PFC Sigma knee group. Furthermore, complication rate was also higher in the Medial-Pivot knee group than the other group.

Does low-constraint mobile bearing knee prosthesis give satisfactory results for severe coronal deformities? A five to twelve year follow up study.

Severe varus and valgus knee deformities traditionally are replaced with constrained implants, with a number of disadvantages. We present our results in this challenging group using a low constraint deep-dish mobile bearing implant design. One hundred fifty-four patients (170 arthroplasties) who underwent primary TKA using a deep-dish, mobile bearing posterior-stabilized implant for severe varus (HKA < 170°) or valgus (HKA > 190°) deformity between 2004 and 2009 were evaluated at a mean of 6.6years post-operatively (minimum of 5years). Alignment improved from a pre-operative mean (±SD) varus deformity of 167.4° (±2.6°) and a mean (±SD) valgus deformity of 194.1° (±4.0°) to an overall mean (±SD) post-operative mechanical alignment of 178.6° (±3.2°). Twenty-three patients had post-operative varus alignment, five patients had post-operative valgus alignment and 134 knees were in neutral alignment (within 3° spread). Clinical scores at final follow-up were excellent (IKS score 93.8 (±7.4) and function score 82.4 (±20.2)). Three patients were re-operated upon: one deep infection, one periprosthetic fracture and one revision at 144months for aseptic loosening of the femoral component. No patient was revised for instability or implant failure. The survival rate at fiveyears was 99.4% and at tenyears 98.6%. Satisfactory outcomes can be achieved in patients with substantial varus or valgus deformities using low constraint deep-dish mobile bearing implant, standard approach and appropriate soft tissue releases.

Retrospective 5-Year Analysis of Revision Rate and Functional Outcome of TKA With and Without Patella Implant.

The aim of this study was to compare a patient cohort after total knee arthroplasty (TKA) in terms of the revision rate and the functional outcome, with and without patella resurfacing. Sixty-six patients (71 TKAs) were implanted with the mobile-bearing knee prosthesis system e.motion UC (Aesculap AG, Tuttlingen, Germany). These patients were divided into 2 groups, 1 of which received primary patella resurfacing (PPR; 51 TKAs) and 1 of which did not (non-PPR; 20 TKAs), with an average follow-up of 65.6 months (±6.9). The cohort was recorded consecutively. The evaluation was performed using the Knee Society Score and selected questions relating to the Knee Injury and Osteoarthritis Outcome Score, as well as with radiographs. Results showed that PPR was no better than non-PPR in terms of functional outcome. Two knees (10%) were revised in the non-PPR group, and 1 knee (1.96%) in the PPR group (not significant). In this cohort, 100% of implants, including the 5 TKAs of patients who did not attend the follow-up examination, had neither explanted nor loosened at the time of follow-up examination. The authors concluded that the revision rate for PPR is slightly lower, and this avoids the need for secondary patella resurfacing. The risk for complications is low, and the functional outcome is comparable. [Orthopedics. 2016; 39(3):S31-S35.].

NexGen® LPS mobile bearing total knee arthroplasty: 10-year results.

Mobile bearing (MB) knee prostheses were designed to improve the performances of the total knee arthroplasties (TKA). The clinical superiority of MB prosthesis compared to its fixed bearing counterpart has remained elusive. This study prospectively evaluates the cumulative survivorship, clinical, radiographic results, and complications of a large series of MB TKAs in relation to patient age, sex, severity of arthritis, and patellar resurfacing. This study evaluates the 5- to 10-year cumulative survival rate of the NexGen(®) LPS MB. Between 2000 and 2005, we performed a consecutive series of 332 MB, posterior-stabilized TKA in 249 patients (mean age 71.2 years, SD 6.9). The implants were clinically evaluated with the Hospital Special Surgery Knee Score (HSS-KS) and radiographically with the Knee Society Roentgenographic Evaluation System (KS-RES). The mean follow-up was 76.3 months (minimum 5 years). The HSS-KS improved from 55 pre-operatively to 86 at the end of follow-up. According to the KS-RES, the implants were anatomically aligned and progressive radiolucent lines appeared in four knees (1.2 %). The patella was selectively resurfaced in 162 of 332 knees. Patients with the patella resurfaced had better clinical results compared to those not resurfaced, but there was no difference in terms of survival. The cumulative survival rate was 98.4 % at 10 years (Kaplan-Meier's analysis). This MB implant provided reliable and durable clinical results with a survivorship of over 98 % at 10 years, in unselected patients regardless of age, sex, severity of disease, and patellar treatment.

Dynamic finite element analysis of mobile bearing type knee prosthesis under deep flexional motion.

The primary objective of this study is to distinguish between mobile bearing and fixed bearing posterior stabilized knee prostheses in the mechanics performance using the finite element simulation. Quantifying the relative mechanics attributes and survivorship between the mobile bearing and the fixed bearing prosthesis remains in investigation among researchers. In the present study, 3-dimensional computational model of a clinically used mobile bearing PS type knee prosthesis was utilized to develop a finite element and dynamic simulation model. Combination of displacement and force driven knee motion was adapted to simulate a flexion motion from 0° to 135° with neutral, 10°, and 20° internal tibial rotation to represent deep knee bending. Introduction of the secondary moving articulation in the mobile bearing knee prosthesis has been found to maintain relatively low shear stress during deep knee motion with tibial rotation.

Mobile-Bearing Total Knee Arthroplasty: A Full Traumatic Rotation of 180°

From February 2008 to September 2012 we implanted 204 mobile-bearing knee prostheses in 192 patients. All the prostheses were cemented (both femoral and tibial components), and the patella was not replaced. Only one early complication of the implants (1/204 = 0.004%) occurred after a traumatic event as a full 180° rotation of the mobile-bearing polyethylene insert. A 78-year-old woman presented with swelling and severe pain at her right knee. This traumatic event was the only case among our mobile-bearing insert patients. The failed polyethylene inserts were retrieved and studied using a scanning electron microscope (SEM, ZEISS EVO 50 EP, Cambridge, UK) operating at 20 kV. Scratching and pitting were found on the UHMWPE insert perpendicular to the machining tracks for the concave surface. SEM micrographs of the insert showed burnishing on the concave surfaces and longitudinal scratches were clearly detectable and well-marked on the analyzed surfaces. A traumatic, fully rotating, polyethylene insert is rare and our case is the first report describing a traumatic event with a complete 180 degree rotation mobile-bearing in a total knee prosthesis. In the literature few reports discuss clinical outcomes after total knee arthroplasty in patients with Parkinson's disease and they cite mixed results. However, some authors suggest that posterior-stabilized and cruciate-retaining TKA should work well while others prefer cruciate-retaining, condylar constrained kinetics, or hinged devices. Although we did not implant a posterior-stabilized mobile-bearing total knee prosthesis or a constrained prosthesis, we obtained good clinical and radiological results at the 2-year followup.

180° rotatory dislocation of the rotating platform of a posterior-stabilized mobile-bearing knee prosthesis; possible complication after closed reduction of a posterior dislocation – a case report –

Dislocation of the rotating platform is a significant early complication of mobile-bearing total knee arthroplasty. The authors report an unusual case of acute 180° rotatory dislocation of the rotating platform after closed reduction of a posterior dislocation of a posterior-stabilized mobile-bearing total knee prosthesis. A 71-year-old male with knee osteoarthritis underwent TKRA using a posterior-stabilized mobile-bearing prosthesis. Posterior dislocation of the prosthesis occurred at 5weeks postoperatively, and closed reduction of the posterior dislocation resulted in complete 180° rotatory dislocation of the rotating platform. The patient was treated by open exploration and polyethylene exchange for a larger component. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee prosthesis can occur given valgus laxity and causes a 90° spin-out of the polyethylene insert, and that closed reduction attempts may contribute to complete 180° rotatory dislocation of the rotating platform. Special attention should be given to both AP and lateral views to ensure that the platform is truly reduced and not rotated by 180°. Plain digital radiography, which enhances the density of polyethylene, or arthrography is helpful for diagnosing this complication.

Demonstration of a New Technique Using Radioisotope Tracers to Measure the Backside Wear Rate on Tibial Inserts

Local backside wear measurements on ultra-high molecular weight polyethylene (UHMWPE) tibial inserts in LCS mobile bearing knee prostheses have been performed using a new radioisotope tracing technique. The radioisotope tracers 97Ru and 101mRh were synthesized via a fusion evaporation reaction and recoil-implanted into cylindrical plugs of UHMWPE. The labelled plugs were carefully fitted into tibial inserts at two relevant locations. With bovine serum acting as a lubricant, the tibial inserts were then worn in vitro for 500,000 and 780,000 cycles, respectively, in a pneumatic knee motion simulator. Results reflect the non-linear change of wear during the wear-in phase and its evolution to a long-term steady-state rate. This new technique shows potential for extracting localized wear rates across the backside of a tibial insert in order to develop a comprehensive backside wear model.

A meta-analysis of the fixed-bearing and mobile-bearing prostheses in total knee arthroplasty

We asked whether the mobile-bearing knee prostheses could offer clinical and radiographic advantages over the fixed-bearing knee prostheses. We conducted a systematic review and meta-analysis to evaluate the validity of this theory. We searched PubMed, EMBASE, Ovid and the Cochrane Central Register of Controlled Trials from January 1979 to June 2010 for randomized controlled studies comparing the effect of fixed- and mobile-bearing prostheses in TKA. We assessed the methodological quality of the studies and abstracted the relevant data independently. 15 studies involving 1,950 knees were identified in this analysis. No statistically significant difference was present in terms of KSS, patient preference, radiolucent line around implant and prosthesis-related complications as compared to the fixed- and mobile-bearing knee design. Theoretically, mobile-bearing implant design could improve clinical and radiographic outcomes as being compared to fixed-bearing implant design, but the anticipated effectiveness has not been implemented in the current clinical practice at mid-term follow up.

Wear of a Mobile Bearing Uni-Compartmental Knee Replacement Prosthesis: A Comparison of In Vitro and In Vivo Wear Rates

Abstract Wear induced osteolysis is cited as the primary cause of aseptic loosening in knee replacements. It has been postulated that mobile bearing (MB) knee prostheses reduce wear as they allow lower contact stress through high congruency between components while maintaining a wide range of joint motion. In vitro wear simulations are preclinical tests for predicting the performance of new designs of partial and total knee replacements. This study investigates the wear of a leading design of MB uni-compartmental knee replacement (UKR) by quantifying the in vitro wear rate and linear penetration of the polyethylene meniscal bearing. Three medial and three lateral MB UKRs (Uniglide, Corin, Ltd., U.K.) were tested in a three station wear simulator using force control as defined in ISO 14243-1. Volumetric wear was determined gravimetrically every half million cycles (MC) up to 10 MC. Maximum linear penetration wear was measured after 10 MC. Volumetric wear rates of 1.65±0.28 mm3/MC (mean±SD) and 1.66±0.31 mm3/MC were recorded for the medial and lateral bearings, respectively, and the wear of all bearings was linear. Previous simulator studies have reported mean wear rates of 3.8 to 10.4 mm3/MC for MB UKRs. Maximum linear penetration wear rates of 0.013±0.001 mm/MC and 0.012±0.001 mm/MC were recorded for the medial and lateral bearings, respectively, after 10 MC. This was in agreement with that reported for well functioning MB UKRs through in vivo measurement (0.01 mm/year) and compared favourably to that reported for fixed bearing designs (0.15 mm/year). The results of this study show that in vitro measurements correlate well to in vivo measurements of wear. This indicates that the current in vitro methodology for the simulation of wear in MB UKRs is a valid tool for preclinical assessment of MB UKR prostheses.

Mid-Term Survivorship Results for a Rotating-Platform Knee Prosthesis

Interest in mobile-bearing knee prostheses is increasing in the US market. We studied results at 2 to 5 years with a mobile-bearing system that includes a cobalt-chrome tibial tray and femoral component with a polyethylene cruciate-retaining tibial component insert that allows rotation around a central axis and can be used with cruciate-retaining or posterior-stabilized femoral components. The inserts used in this study were cruciate retaining and did not include the posterior-stabilized design. The goal of this study was to demonstrate the function and safety of this prosthesis along with the lack of spinout, which is a major concern in the mobile-bearing knee. Four hundred thirty-five knees constituted the study cohort and underwent survivorship analysis and complication reporting. Routine clinic evaluations included pre- and postoperative radiographs and Knee Society knee and function scores at 6 and 12 weeks and every 2 years. The most recent follow-up data within 2 to 5 years was included for the study along with survey data. Flexion at most recent follow-up averaged 125°. Knee Society score at most recent visit averaged 88 of 100. Knee Society function score averaged 83 of 100. Radiographic results were available for 226 knees, with 97.3% assessed as normal and 6 with these issues: patella stress fracture (3), aseptic tibial loosening (1), patellar osteolysis (1), and patella aseptic loosening (1). In comparison with the fixed-bearing knee equivalent, this mobile-bearing knee demonstrated at least equivalent results in terms of survivorship, function, and patient satisfaction in the short- and mid-term.

Osteolysis in Well-functioning Fixed- and Mobile-bearing TKAs in Younger Patients

Periprosthetic osteolysis is an increasingly prevalent complication of TKA. To reduce the polyethylene wear and periprosthetic osteolysis, particularly in young patients, the design of the contemporary fixed-bearing TKAs has been modified and mobile-bearing TKAs have been introduced. We asked whether the prevalence of osteolysis would be less in well-functioning mobile-bearing TKAs than in well-functioning contemporary fixed-bearing TKAs in young patients. We compared 488 patients (894 knees) who received fixed-bearing knee prostheses with 445 patients (816 knees) who received mobile-bearing knee prostheses. There were 187 men and 301 women (mean age, 58.6 years; range, 33-65 years) in the fixed-bearing group and 167 men and 278 women (mean age, 55.7 years; range, 33-65 years) in the mobile-bearing group. The mean followup was 12.6 years (range, 10-17 years) in the fixed-bearing group and 12.9 years (range, 10-17 years) in the mobile-bearing group. The incidence of osteolysis was 1.6% (14 of 894 knees) in the fixed-bearing group and 2.2% (18 of 816 knees) in the mobile-bearing group at the final review. The mean postoperative Knee Society knee and function scores were 92.9 points and 83.5 points, respectively, in the fixed-bearing group and 90.7 points and 83.8 points, respectively, in the mobile-bearing group. The revision rates were 3.7% (33 of 894 knees) in the fixed-bearing group and 2.7% (22 of 816 knees) in the mobile-bearing group. We found the incidence of osteolysis, rate of revision, and implant survivorship were similar between fixed-bearing and mobile-bearing TKAs in younger patients.

Is there any superiority in the clinical outcome of mobile-bearing knee prosthesis designs compared to fixed-bearing total knee prosthesis designs in the treatment of osteoarthritis of the knee joint?

To substantiate the validity and relevance of the mobile-bearing knee prosthesis design compared to the fixed-bearing design, concerning the clinical outcome, this review was conducted. Articles published in 6 major orthopaedic journals were screened. Only randomized controlled trials, which investigate the clinical outcome, were included. The clinical outcome parameters of each study were analysed. Despite the numerous quantities of publications in orthopaedic literature, we could conclude, that only a few of them are randomized controlled trials. Although better kinematics of mobile-bearing knee prosthesis designs compared to fixed-bearing knee prosthesis designs are reported, no superiority of one of the bearing designs concerning clinical outcome could be revealed. Because no superiority of one of the designs concerning revision rate, survival and outcome can be found, the cheaper one should be the one to be recommended. For this reason, we advise that further research, comparing the costs and cost-benefit of mobile-bearing compared to fixed-bearing knee prosthesis designs, should be performed.

Mid-term results with a highly congruous mobile-bearing knee prosthesis

Two hundred and six consecutive total knee arthroplasties were performed in 180 patients with a highly congruous mobile-bearing knee prosthesis. At mean follow-up of 78 months (range: 60-102 months), the outcomes of 181 knees in 158 patients were evaluated using the American Knee Society's Knee and Functional scoring system and Radiological scoring system. Mean values for Knee and Function scores were 92.6 and 81.1, respectively versus 51.8 and 43.4 preoperatively; mean flexion range was 113.6 degrees versus 110.8 degrees preoperatively. There were no cases of bearing dislocation and no radiological signs of loosening or osteolysis. Secondary patella resurfacing was done in 7 of 52 knees in which the patella was not primarily resurfaced. Arthroplasty survival with revision for aseptic loosening as the endpoint was 100% (95% CI: 97.7-100) at 5 years and at 8 years (95% CI: 87.2-100); with revision of the arthroplasty for any reason including one revision for infection as the endpoint, survival was 99.5% (95% CI: 96.9-100) at 5 years and at 8 years (95% CI: 86.9-100). The overall results were satisfactory and compared with those of other mobile-bearing knee prostheses featuring full or partial congruence. No significant differences were noted for range of motion, knee scores and function scores between two subsets of knees that received a bearing allowing only rotation or rotation and 5 mm anteroposterior translation. Longer follow-up is needed to evaluate possible benefits of high congruence and of specific modes of bearing mobility with respect to wear and bony fixation.

Clinical and radiological results of high flex total knee arthroplasty: a 5 year follow-up

In a prospective randomized study, we compared the results after implantation of the mobile bearing high flex TKA with a fixed bearing posterior stabilized TKA in 60 patients (30 patients each group). We evaluated the hospital for special surgery-score (HSS) and different radiological parameters preoperatively, as well as 3 months, 3 and 5 years postoperatively. Three months postoperatively, the high flex group showed better results in scores for pain, ROM (122.5 degrees vs. 107.33 degrees), as well as in the overall HSS (87.21 vs. 82.68 points). Three and 5 years postoperatively, there were no differences between both the groups in all scores, but the HSS is still increasing. The theoretical advantages of the mobile bearing knee prostheses were reflected in the clinical results, only partly and temporarily.

The Self-Aligning knee prosthesis: clinical and radiological outcome and survival analysis at 5-year follow up

The purpose of this study is to evaluate the clinical and radiological results and the survival of the SAL II mobile bearing knee prosthesis at 5-year follow up. Between February 1995 and March 1998 a total of 246 SAL II total knee arthroplasties were performed in 232 patients. The mean follow up was 5.0 years. Thirteen revisions had been carried out (5%). The mean total Knee Society Score increased from 88 preoperatively to 153 and 155 at 1 and 5 years follow up, respectively. The mean flexion angles were 106 degrees and 107 degrees pre- and postoperatively. None of the prostheses showed radiological loosening. No dislocations or subluxations of inserts were seen. The Kaplan-Meier cumulative survival is 95% for revision for any reason at 5.0 years, with a worst case scenario of 91%. The survival for aseptic loosening is 99%. The results of SAL II after a minimum follow up of 5 years are favourable and comparable with fixed bearing and other mobile bearing designs in terms of Knee Society Score and survival. Noteworthy are the good radiological results of this device which showed a good fixation of the prosthesis at 5 years.

Limited rotation of the mobile-bearing in a rotating platform total knee prosthesis

The hypothesis of this study was that the polyethylene bearing in a rotating platform total knee prosthesis shows axial rotation during a step-up motion, thereby facilitating the theoretical advantages of mobile-bearing knee prostheses. We examined 10 patients with rheumatoid arthritis who had a rotating platform total knee arthroplasty (NexGen LPS mobile, Zimmer Inc. Warsaw, USA). Fluoroscopic data was collected during a step-up motion six months postoperatively. A 3D–2D model fitting technique was used to reconstruct the in vivo 3D kinematics. The femoral component showed more axial rotation than the polyethylene mobile-bearing insert compared to the tibia during extension. In eight knees, the femoral component rotated internally with respect to the tibia during extension. In the other two knees the femoral component rotated externally with respect to the tibia. In all 10 patients, the femur showed more axial rotation than the mobile-bearing insert indicating the femoral component was sliding on the polyethylene of the rotating platform during the step-up motion. Possible explanations are a too limited conformity between femoral component and insert, the anterior located pivot location of the investigated rotating platform design, polyethylene on metal impingement and fibrous tissue formation between the mobile-bearing insert and the tibial plateau.