Aims. To establish our early clinical results of a new total knee arthroplasty (TKA) tibial component introduced in 2013 and compare it to other designs in use at our hospital during the same period. Methods. This is a retrospective study of 166 (154 patients) consecutive cemented, fixed bearing, posterior-stabilized (PS) TKAs (ATTUNE) at one hospital performed by five surgeons. These were compared with a reference cohort of 511 knees (470 patients) of other designs (seven manufacturers) performed at the same hospital by the same surgeons. There were no significant differences in age, sex, BMI, or follow-up times between the two cohorts. The primary outcome was revision performed or pending. Results. In total, 19 (11.5%) ATTUNE study TKAs have been revised at a mean 30.3 months (SD 15), and loosening of the tibial component was seen in 17 of these (90%). Revision is pending in 12 (7%) knees. There was no difference between the 31 knees revised or with revision pending and the remaining 135 study knees in terms of patient characteristics, type of bone cement (p = 0.988), or individual surgeon (p = 0.550). In the reference cohort, there were significantly fewer knees revised (n = 13, 2.6%) and with revision pending (n = 8, 1.5%) (both p < 0.001), and only two had loosening of the tibial component as the reason for revision. Conclusion. This new TKA design had an unexpectedly high early rate of revision compared with our reference cohort of TKAs. Debonding of the tibial component was the most common reason for failure. Additional longer-term follow-up studies of this specific component and techniques for implantation are warranted. The version of the ATTUNE tibial component implanted in this study has undergone modifications by the manufacturer. Cite this article: Bone Joint J 2021;103-B(6 Supple A):137–144

Summary Statement. Wear of total knee replacement (TKR) is a clinical concern. This study demonstrated low-conformity moderately cross-linked-polyethylene fixed bearing TKRs showed lower volumetric wear than conventional-polyethylene curved fixed bearing TKRs highlighting potential improvement in TKR performance through design and material selection. Introduction. Wear of total knee replacement (TKR) continues to be a significant factor in the clinical performance of the implants. Historically, failure due to delamination and fatigue directed implant design towards more conforming implants to reduce contact stress. However, the new generations of more oxidatively-stable polyethylene have improved the long-term mechanical properties of the material, and therefore allowed more flexibility in the bearing design. The purpose of this study was to investigate the effect of insert conformity and material on the wear performance of a fixed bearing total knee replacement through experimental simulation. Methods. The wear of TKR bearings were investigated using a physiological six station Prosim knee wear simulator (Simulator Solutions, UK). Six samples of each test configuration (Sigma CR fixed bearing knees (DePuy Synthes, UK) were studied, and compared with previously reported data, tested under identical conditions (1, 2). The central axis of the implant was offset from the aligned axes of applied load and tibial rotation to replicate a right knee. High kinematics, under anterior-posterior displacement control was used for this study (3). The lubricant was 25% (v/v) calf serum supplemented with 0.03% (v/v) sodium azide solution in deionised water, as an antibacterial agent, and was changed approximately every 0.33Mc. Wear was assessed gravimetrically and moisture uptake accounted for using unloaded soak controls. Results. The wear rates for the moderately cross-linked inserts (XLK) were significantly lower than the conventional polyethylene (GVF) for all geometries (ANOVA, p<0.05). There was a significant reduction in wear rate as the insert geometry became less conforming for both materials (ANOVA, p<0.05). The wear scars areas were comparable in size and shape between materials, within a geometry group. The size of the wear scar changed with conformity, with the curved inserts showing the largest scars in both anterior-posterior and medial-lateral dimensions, and the flat inserts showing the smallest wear scars. Discussion/Conclusion. The introduction of a moderately cross-linked polyethylene insert was shown to significantly reduce the wear of a fixed bearing total knee replacement compared with a conventional material. There was a trend for reducing wear rate with reducing conformity for both materials, suggesting that reduced conformity results in higher contact pressures and reduced contact area, leading to a reduced surface for wear to occur. Both material and conformity were shown to have a significant impact on the wear of a fixed bearing TKR, and therefore provide opportunity for enhancing wear performance through material and design selection

Purpose of the study. Assessing medium term outcome of medial Uni compartmental replacement and whether there is a difference in outcome between mobile and fixed bearing variants of the same prosthesis. Methods. Knee outcome was assessed in 150 patients (81 male, 69 females, mean age 67.0±10.4yrs) undergoing medial UKR knee (Uniglide, Corin Medical, UK) using either fixed or mobile bearing prosthesis between 2002-2007. All operations were performed by members of the Bristol knee group. All patients were scored using the American Knee Score (AKS), Oxford Knee Score (OKS), and WOMAC pre-operatively and at 2-year follow up. The mobile group (n=93) comprised 43 males and 50 females, aged 62.8±8.9yrs. The fixed bearing group (n=57) comprised 38 males and 19 females, aged 74±8.8yrs. Results. Pre-operative measures of AKS, OKS, and WOMAC did not significantly differ between mobile and fixed bearing groups (p>0.05) with scores in the range of 111-113 out of 175, 19.6 out of 48, and 36.7-37.5 out 60, in the AKS, OKS, and WOMAC respectively. Two-year follow up scores for AKS, OKS, and WOMAC demonstrated a significant (p<0.0001) improvement in function with scores ranging from 167-171, 33.1-34.5, and 23.3-24.8 points respectively. No significant difference was observed at 2-year follow up between mobile or fixed bearing groups (p>0.05). Discussion. Two-year follow up outcome scores demonstrated a significant improvement in patient function for both fixed and mobile bearing prostheses compared with pre-operative scores, with no differences in outcome observed between mobile or fixed bearing devices

Aim: This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Methods: Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implementation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured. Results: Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1′500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration (500 ± 287 με), and the fixed bearing configuration (500 ± 286 μ ε). In response to 10° internal rotation, this strain increased to 782 ± 371 μ ε and 1000 ± 389 μ ε for the mobile and fixed tibial component, respectively. In response to 10° external rotation, minimal principal strain decreased to 421 ± 233 μ ε for the mobile bearing, but increased to 632 ± 293 μ ε for the fixed bearing. These differences between mobile and fixed bearing scenarios were statistically highly significant. Conclusion: For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia as the fixed bearing tibial component. The difference in strain levels may be of importance to understand bone remodeling and osseointegration

Introduction Movement between the polyethylene insert and the metal tibial tray in modular fixed bearing total knee arthroplasty (TKA) due to a poor locking mechanism is said to occur. The resulting “backside wear” is proposed as one cause of osteolysis and subsequent loosening. In vitro analysis has revealed movements between the poly and the tibial tray both in non-implanted designs as well as in implants extracted during revisions and at autopsy. Scratch marks on the surfaces at the tray-poly interface have been found indicating rotatory movements between the components. The purpose of this study was to determine in vivo the existence and magnitude of movements between the poly and the tibial tray in modular metal-backed TKA. Methods Ten patients (median age 71) operated with the NextGen modular fixed bearing TKA due to gonarthrosis were analyzed. This TKA has lipped edges around the entire periphery of the implant to capture and secure the poly insert. The metal tray of the tibial component was equipped with five tantalum markers, and the polyethylene insert with six markers. Radiostereometric (RSA) investigation was performed within one week post-op, and at 12 months. Change in position of the poly insert in relation to the metal tray between the post-op and the 12 months investigations was analyzed as rotations about, and translations along the cardinal axis of the knee. The Insert motion index according to Engh et al (2001) was calculated. Results Between the surgery and 12 months post-operatively there was a median external rotation of the poly in relation to the metal tray of 0.4 (range: 0.09 to 0.73). Median insert motion index was 0.36 mm (range 0.2 mm to 0.6 mm). Subsidence and lift-off of the polyethylene were very small and below the detection limit of RSA (< 0.08 mm). Conclusions This study shows for the first time that movements do occur in vivo between the polyethylene insert and the metal tray in modular fixed bearing TKA, even in designs with a full peripheral capture mechanism. The movements occur in the plane of the metal tray (i.e. external rotation, medial-lateral and anteroposterior translation), but no movements are detected in directions out of this plane (proximal-distal translation). The magnitudes of these translations are equivalent to those found in in vitro studies of explanted components. This study thus questions the efficacy of the locking mechanism in modular fixed bearing TKA. In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source

This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implantation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured. Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1,500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration(500 ± 287m;e;), and the fixed bearing configuration (500 ± 286m;e;). In response to 10° internal rotation, this strain increased to 782 ± 371m;e; and 1000± 389m;e; for the mobile and fixed tibial component, respectively. In 10° external rotation, minimal principal strain decreased to 421 ± 233m;e; for the mobile bearing, but increased to 632 ± 293m;e; for the fixed bearing. These differences between mobile and fixed bearing scenarios were highly statistically significant. For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia than the fixed bearing tibial component. The difference in strain levels may be of importance for bone remodeling and osseointegration

The purpose of this study was to compare the clinical and radiological results of the PFC flex mobile bearing design with those of the LPS flex fixed bearing design in high-flex total knee arthroplasty. Between January 2005 and November 2006, forty-six patients who received PFC flex mobile bearing prosthesis in one knee and LPS flex fixed bearing prosthesis in the contralateral knee followed up for a minimum 2 years were evaluated. Clinical results were assessed using the ROM, HSS score, the Knee rating systems of the knee society, WOMAC score and SF-36. Radiological results were evaluated tibio-femoral angle and loosening or osteolysis of components. We subdivided preoperative less 90 degree and more 90 degree in each group. Mean ROM range of last follow up was increased to 131.1 degree in LPS group and 130.1 degree in PFC group. But there was no significant difference between the two groups. HSS score, knee pain and function score, WOMAC score, SF-36 score didn’t differ significantly between two groups. But descending stairs, rising from sitting, bending to the floor more improved significantly in LPS group. T-F angle was changed from preoperative 8.2 degree varus to a postoperative 4.8 degree valgus. No knee had aseptic loosening or osteolysis. Postoperative ROM was increase significantly in both groups. We found no significant differences between the two groups with regard to clinical and radiological parameters excepts descending stairs, rising from sitting, bending to the floor in WOMAC score. There was no aseptic loosening or osteolysis but needed long term observation about these concerns

Introduction and Aims: Fixed bearing and mobile bearing knee designs are currently used in clinical practice with little evidence based research available to determine superiority of one system. The purpose of this study was to compare the results between a cruciate retaining mobile bearing and two cruciate retaining fixed bearing total knee prostheses. Method: We performed a prospective, randomised, blinded clinical trial to compare a mobile bearing to two standard fixed-bearing implants. We evaluated the short- and long-term outcomes of the SAL. ®. (Sulzer) mobile bearing versus the AMK. ®. (Depuy) and Genesis II. ®. (Smith & Nephew) fixed bearing, total knee joint replacements. Ninety patients were randomised to receive one of the three prostheses. Patients were evaluated pre-operatively, at three, 12 months and annually thereafter. Patient demographics, radiographs, and multiple outcome measures (WOMAC, SF-12 and the Knee Society Clinical Rating System) were evaluated. A single observer was used to measure range of motion scores. Results and Discussion: No patients were lost to follow-up. One patient was withdrawn due to dementia before three months, one patient died prior to the two-year follow-up, and one patient was revised for infection at six months, leaving 87 patients at an average follow-up of 3.37 years (range 2.91–4.44 years). There were no significant differences in any outcome measures or radiographic findings. There were no differences in KSCRS at two years (SAL – 167, AMK – 158, GenesisII – 166 ). There were no differences in WOMAC scores or SF-12 survey scores. There were no differences in knee flexion at two years (SAL – 117. °. , AMK – 115. °. , GenesisII – 118. °. ). Therefore, no differences in multiple outcome measures were seen between a cruciate retaining mobile bearing and two cruciate retaining fixed bearing total knee prostheses. Conclusion: In this prospective randomised clinical trial no differences could be seen between a mobile bearing and two fixed bearing designs at a minimum of two years follow-up. Long-term evaluation will be required to comment on differences in polyethylene wear and implant longevity

Abstract. Introduction. Medial fix bearing unicompartmental knee replacement (UKR) designs are consider safe and effective implants with many registries data and big cohort series showing excellent survivorship and clinical outcome comparable to that reported for the most expensive and surgically challenging medial UKR mobile bearing designs. However, whether all polyethylene tibial components (all-poly) provided comparable results to metal-backed modular components during medial fix bearing UKR remains unclear. There have been previous suggestions that all-poly tibia UKR implants might show unacceptable higher rates of early failure due to tibial component early loosening especially in high body max index (BMI) patients. This study aims to find out the short and long-term survival rate of all-poly tibia UKR and its relationship with implant thickness and patient demographics including sex, age, ASA and BMI. Material and Methods. we present the results of a series of 388 medial fixed bearing all-polly tibia UKR done in our institution by a single surgeon between 2007–2019. Results. We found out excellent implant survival with this all-poly tibia UKR design with 5 years survival rate: 96.42%, 7 years survival rate: 95.33%, and 10 years survival rate: 91.87%. Only 1.28% had early revision within 2 years. Conclusion. Fixed bearing medial all-poly tibia UKR shows excellent survivor rate at 2, 5, 7 and 10 years follow up and the survival rate is not related with sex, age, BMI, ASA grade or implant thickness. Contrary to the popular belief, we found out that only 1.71% of all implants was revised due to implant loosening

Purpose of Study: Fixed bearing unicompartmental knee replacement (UKR) has become popular since several series have now shown good 10 year survivorship and excellent function. However little is known about survival during the second decade. Method: From the Bristol database of over 4000 knee replacements 203 St. Georg Sled UKR’s which had already survived 10 years were identified. The mean age at surgery was 67 years (48–85), with 64% being female. This cohort has been further reviewed at an average of 14.8 years (10–30) from surgery to determine survivorship and function. Results: Survivorship during the second decade was 87.5%. 58 patients (69 knees) had died with implant in situ and only 2 after revision. A further 15 UKR’s have been revised at an average of 13 years post op; 7 for progression of disease in the opposite compartment, 4 for tibial loosening, 3 for polyethylene wear, 2 for femoral component fracture and 2 for infection. 99 knees were followed for 15 years, 21 knees for 20 years and four for 25 or more years. The average Bristol knee score of the surviving knees fell from 86 to 79 during the second decade, largely as a result of aging. A previous study of the St Georg. Fixed bearing UKR showed an 89% 10 year survivorship and this is now extended to 82% at 15 years and 76.5% at 20 years. Conclusion: Satisfactory survival of fixed bearing UKR can be achieved in the second decade suggesting that the indications for mobile bearings require careful definition since there is a higher incidence of complications in many people’s hands

BACKGROUND:. Implant wear continues to be a limitation of total knee replacement (TKR). Wear simulator studies are a valuable screening tool in new implant development. The purpose of this study was to determine the ability of micro-CT to prospectively measure wear in TKR implants during a wear simulator trial. METHODS:. Three identical cruciate-retaining, fixed bearing cobalt-chromium-molybdenum (CoCrMo) on conventional EtO-sterilized polyethylene TKA implants underwent wear simulator testing up to 3.2 million cycles using gait inputs; loaded-soaks were used to correct for fluid absorption. The implants were weighed and scanned with micro-CT (at 50 micron resolution) before and after testing. The gravimetric mass was converted to volume based on the density of polyethylene. Volume change due to wear was calculated from both the gravimetric and micro-CT methods. The pre- and post-wear test micro-CT geometries were co-registered and the deviations between the two were measured. RESULTS:. The mean wear volume was 90.8 ± 12.2 mm. 3. measured gravimetrically and 66.4 ± 13.3 mm. 3. measured by micro-CT (p = 0.002). While underestimating wear volume compared to gravimetric analysis, micro-CT demonstrated strong correlation (r. 2. = 0.99, slope difference from zero p < 0.0001). No subsurface changes such as cracks were noted in the micro-CT images. Maximum penetration (from wear and creep) was 0.77 ± 0.20 mm medially and 0.41 ± 0.06 mm laterally. Deformation up to 0.180 mm was noted on each side of the inserts after wear testing. Discussion:. Micro-CT underestimation of wear volume compared to gravimetric analysis is consistent with previous reports of micro-CT use. The discrepancy could be caused by a scaling error in the micro-CT volume reconstruction, or an error in the fluid uptake correction for gravimetric analysis. Micro-CT had a strong correlation with gravimetric analysis, and also enables analysis of the implant subsurface, and measurements of penetration and surface deformation. The wear volume was consistent with other fixed bearing TKR couples made from CoCrMo and conventional non-irradiated polyethylene

The outcome and survivorship of osteotomy for medial compartment osteoarthritis are closely correlated to the changes in the weight bearing axis. Questions remain over the optimal correction when undertaking medial unicompartmental knee replacement (UKR). Prospective data was collected on 50 patients (30F:20M) undergoing fixed bearing medial UKR which included pre-operative and 12 month Oxford Knee Scores and pre and post-operative weight-bearing long-leg radiographs. The weight bearing axis was measured from the centre of the femoral head to the mid-point of the talus. The point at which this axis crossed the tibial plateau was expressed as a percentage of the width of that plateau - 0 (medial cortex) to 100% (lateral cortex). Regression method and correlation coefficients were used to assess the relationship between the response and variables. A significant correlation was seen between the 12 month score and the change in axis, which was maintained when the pre-operative score was adjusted for (p = 0.043 and 0.046 respectively). Larger changes in scores were seen with larger changes in axis (p = 0.046) when the pre-operative axis was adjusted for. Higher BMIs reported worse scores at 12 months (p = 0.022) and a smaller overall change in score one year post-operatively (p = 0.037). This significance was improved when the pre-operative scores were adjusted (p = 0.017 and 0.017 respectively). Proximity of correction of axis to the assumed contralateral normal was weakly correlated (p = 0.049) to the 12 month score, especially when BMI was corrected for. These results suggest that the weight bearing axis and BMI do play a significant role in early patient outcomes following fixed bearing unicompartmental knee replacement

Background: The osteolysis in revision total knee arthroplasty was observed. The purpose of this study was to compare the prevalence and characteristics of osteolysis recognized in revision total knee arthroplasties between the failed mobile bearing and fixed bearing knees. Methods: Eighty revision total knee arthroplasties were done between 1995 and 1998. The primary prosthesis that failed included thirty-four mobile bearing (Low Contact Stress) knees and forty-six fixed bearing knees of vary prostheses. At the time of revision surgery, all the interfaces between bone and prosthesis or cement were routinely checked and recorded for evidence of osteolytic resorption of bone. Preoperative radiographs were assessed independently by two authors for evidence of focal or severe periprosthetic osteolysis. The presence of the lesion was recorded. The demographic data included age and body weight was reviewed. The interval between the primary and revision surgery was recorded. The revision technique was reviewed. A statistical technique of chi-square test was applied in this study. Results: Osteolysis was recognized in sixteen of thirty-four mobile bearing knees (47 per cent) with thirteen knees involved distal femur and in six of forty- six fixed bearing knees (13 per cent) with four knees involved distal femur. The incidence of osteolysis was statistically significant difference between the mobile bearing and fixed bearing knees (p< 0.05). An overall 28 per cent (twenty-two knees) incidence of osteolysis was identified intraoperatively. The overall incidence of osteolysis in distal femur was 21 per cent (seventeen knees). The average time interval from the primary surgery to revision was 108 months. All the knees were affected by osteoarthritis. The most common site of osteolytic bone resorption was the posterior femoral condyle. Conclusions: Comparing to the fixed bearing knees, the mobile bearing (Low Contact Stress) knees were at increased risk for osteolysis in our series. Osteolysis occurred predominantly on the femoral side, especially adjacent to the prostheses in posterior condyle. Radiographic evaluation of osteolysis in distal femur is unreliable

Introduction. Wear debris induced osteolysis and loosening continue to be causes of clinical failure in total knee replacement (TKR). Laboratory simulation aims to predict the wear of TKR bearings under specific loading and motion conditions. However, the conditions applied may have significant influence on the study outcomes (1). The aim of this study was to examine the influence of femoral setup and kinematic inputs on the wear of a conventional polyethylene fixed bearing TKR through experimental and computational models. Methods. Six right Sigma CR fixed bearing TKRs (DePuy Synthes, Leeds, UK) with curved polyethylene inserts (GVF, GUR1020 UHMWPE) were tested in Prosim knee simulator (Simulator Solutions, UK). The femoral bearing was set up with the centre of rotation (CoR) on either on the distal radius of the implant (Distal CoR), as indicated by the device design, or according to the ISO specification (ISO CoR; ISO14243-3). The tests were conducted under ‘High Kinematics’ (2). It was necessary to reverse the direction of the anterior-posterior displacement for the tests conducted with the ISO centre of rotation to maintain the contact region within the insert surface (Reverse High Kinematics). Tests were conducted for three million cycles, lubricated with 25% bovine serum, with wear assessed gravimetrically. The computational wear model for the TKR was based on the contact area and an independent experimentally determined non-dimensional wear coefficient, previously validated against the experimental data (3). Results. Good agreement was found between our computational and experimental models (Figure 1). The effect of femoral setup (and adjusted input kinematics) was shown to be significant (ANOVA, p < 0.05), with lower wear under the ISO CoR conditions. The reduction in wear was approximately 49% compared with the Distal CoR. A comparison of the final wear scar area showed the scars to be smaller and located more anteriorly under the ISO CoR/Reverse High Kinematic conditions, compared with the distal CoR study (Figure 2). Discussion. The femoral setup was shown to have a significant impact on the computational and experimental wear rates, with the ISO CoR condition having approximately half the wear of the Distal CoR. It appears that through changing the centre of rotation (and subsequently the anterior-posterior direction) the relative motion and contact mechanics at the articulating surface are altered (1). This study highlights the significant influence test setup conditions may have on the wear of a. It is proposed that there is a need to examine TKR bearings under a broad range of conditions, rather than one study condition to fully assess wear performance

We report the short term follow up of nineteen consecutive PFC sigma unicompartmental knee replacements carried out in our institution with minimum one year follow up. The PFC Sigma medial unicompartmental knee replacement is a fixed bearing, cemented unicompartmenal knee replacement. There are currently no published reports of follow up for the PFC Sigma medial unicompartmental knee replacement. Nineteen patients (nineteen knees) underwent PFC sigma medial unicompartmental knee arthroplasty. The pre-operative diagnosis was osteoarthritis in eighteen patients and osteonecrosis in one patient. There were ten males and nine females with a mean age of sixty four years. All patients had clinical and radiological review at one year. All operations were carried out by the two senior authors (BPR and BL). The mean length of admission was 2.7 days (Range 2–5). There have been no infective or thromboembolic complications to date. The mean oxford scores improved from 41 (Range 26–52) pre-operatively to 18 (15–27) at one year follow-up. The mean range of motion improved from 115 degrees of flexion preoperatively to 125 degrees. All radiographs were satisfactory at one year follow up with no evidence of loosening. We report the promising early results of a new medial unicompartmental knee replacement with at least one year follow up. No early complications or infections were identified in our cohort of patients

Purpose. Prospective randomized intervention trial to determine whether patients undergoing rotating platform total knee arthroplasty have better clinical outcomes at two years when compared to patients receiving fixed bearing total knee arthroplasty as measured by the WOMAC, SF-36 and Knee Society (KSS) scores. Method. 67 consecutive patients (33 males and 34 females; average age 66 years) were randomized into either receiving a DePuy Sigma rotating platform (RP) total knee arthroplasty (29 patients) or a DePuy Sigma fixed bearing (FB) total knee arthroplasty (38 patients). Inclusion criteria included patients between the ages of 45–75 undergoing single-sided total knee arthoplasty for clinically significant osteoarthritic degeneration. Pain, disability and well-being were assessed using the WOMAC, KSS, and SF-36 preoperatively and at 6 months, 1 year and 2 years post-operatively. In addition, intraoperative measures were collected. Pre-operative radiographs were analyzed using the Kellgren and Lawrence Score, modified Scotts Scoring and mechanical axis. Post-operative radiographs were collected at 1 and 2 years and analyzed to identify evidence of prosthetic loosening, implant positioning and limb alignment. Results. The two groups were well-matched following randomization (age, BMI, side) and had no significant differences in intraoperative measures (operative time, estimated blood loss). There were no differences in the groups with respect to their preoperative radiographs. The average female patient was younger compared to their male cohorts (mean female = 63; mean male 68 p=0.005). The post-operative radiographs did not reveal any differences between RP and FB groups when comparing sagittal alignment of femoral and tibial components, patellar tilt and patellar location. With respect to clinical outcomes, both groups reported statistically significant improvements in KSS, WOMAC and SF-36 scores. There were no differences in their pre- and post-operative SF-36 mental component scores. The 1 year WOMAC function score was significantly higher (worse outcome) in the FB group (mean = 18) compared to the RP group (mean 7.8) (p < 0.01). Two year KSS scores were significantly higher (better outcome) in the FB group (mean = 95.7) compared to the RP group (mean = 85.9) (p < 0.05). Conclusion. Both rotating platform and fixed bearing total knee arthroplasty result in clinical improvement over pre-operative function, but has no effect on the mental component of the SF-36. The current study suggests that there is not a clear benefit in selecting either a rotating platform or a fixed bearing total knee system; rather both implants result in improved function. Interestingly, when comparing the results of the WOMAC and KSS, although both measure functional outcomes, when applied to the same population demonstrate differing sensitivity

Introduction: In vivo fluoroscopic studies have shown considerable differences in kinematics between different designs of knee prostheses and compared to the natural knee. Most noticeably, lift off of the femoral condyles from the tibial insert has been observed in many patients (. Dennis et al, 2003. ). The aim of this study was to simulate lateral femoral condylar lift off in vitro and to compare the wear of fixed bearing knee prostheses with and without lift off. Materials and Methods: 12 PFC Sigma cruciate retaining fixed bearing knees (DePuy, Leeds, UK) were tested. The 10 mm thick inserts were manufactured from GUR1020 UHMWPE and gamma irradiated in a vacuum. The inserts snap fitted into titanium alloy tibial trays, and articulated against Co-Cr-Mo alloy femoral components. The testing was carried out on six station simulators (Prosim, Manchester, UK). Femoral axis loading (maximum 2.6 kN) and the flex-ion-extension profile (0–58°) were adopted from ISO 14243 (1999). The internal/external rotation was ± 5° and anterior/ posterior displacement 0–5 mm. Six of the knees were tested under these standard conditions for 4 million cycles. A further six knees were tested under these conditions with the addition of lateral femoral condylar lift off, for 5 million cycles. The lift off was achieved by introducing an adduction moment to the tibial carriage, producing a separation of approximately 1 mm during the swing phase of the simulator cycle. The simulator was run at 1 Hz and the lubricant used was 25% newborn calf serum. Wear was determined gravimetrically, using unloaded soak controls to adjust for moisture uptake. Statistical analysis was performed using Students t-test (p < 0.05). Results: Under the standard kinematic conditions the mean wear rate with 95% confidence limits was 8.8 ± 4.8 mm3/million cycles. When femoral condylar lift off was simulated the mean wear rate increased to 16.2 ± 2.9 mm3/million cycles, which was statistically significantly higher (p < 0.01). The wear patterns on the femoral articulating surface of all the inserts showed more burnishing wear on the medial condyle than the lateral. However, in the simulation of lift off the medial condyle was even more aggressively worn with evidence of adhesion and surface defects. Discussion: The presence of lateral femoral condylar lift off resulted in a higher wear rate on the medial compartment of the PFC Sigma fixed bearing knee. This could be due to elevated contact stresses as the lateral lift off produced uneven loading of the bearing. Further, additional medial/lateral sliding of the medial condyle whilst it remained in contact may have accelerated the wear by cross shearing of the polyethylene in the medial/lateral direction. This direction is weakened when the polyethylene is preferentially molecularly orientated by sliding in the flexion-extension axis. The implications of condylar lift off include premature wear of the polyethylene and possible component loosening

Purpose of Study: Fixed bearing unicompartmental knee replacement (UKR) has become popular since several series have shown good 10 year survivorship and excellent function. However little is known about survival during the second decade. Method: From the Bristol database of over 4000 knee replacements 203 St. George Sled UKR’s which had already survived 10 years were identified. The mean age at surgery was 67 years (48–85), with 64% being female. This cohort has been further reviewed at an average of 14.8 years (10–30) from surgery to determine survivor-ship and function. Results: Survivorship during the second decade was 87.5%. 58 patients (69 knees) had deceased with implant in situ, only 2 after revision. A further 15 UKR’s have been revised at an average of 13 years post op; 7 for progression of disease, 4 for tibial loosening, 3 for polyethylene wear, 2 for femoral component fracture and 2 for infection. 99 knees were followed for 15 years and 21 knees for 20 years. The average Bristol knee score of the surviving knees fell from 86 to 79 during the second decade. A previous study showed an 89% 10 year survivor-ship and this is now extended to 82% at 15 years and 76.5% at 20 years. Conclusion: Satisfactory survival of fixed bearing UKR can be achieved in the second decade suggesting that the indications for mobile bearings require careful definition since there is a higher incidence of complications in many people’s hands

Introduction and Aims A randomised controlled trial (RCT) and a multi-centre unilateral cohort study were performed as part of the stepwise introduction of a new mobile bearing knee. The aim was to ensure that outcome for the new device was at least as good as that for an established fixed bearing device. This paper presents three year follow up of the published one year results. Instability and prevalence of “clicking” from the joint were examined in detail. Method 1. A multi-centre RCT of patients undergoing bilateral knee replacement compared functional outcome between two different prostheses, the new mobile bearing device (TMK) and an established fixed bearing device (AGC). 2. A separate multi-centre cohort of 166 patients who had undergone a unilateral mobile bearing procedure at least six months previously was used to assess complication rate and corroborate any findings from the bilateral trial. Outcome measures included Oxford Knee Scores, American Knee Society ratings and complication rate. Results The bilateral trial revealed no significant differences in outcome between the two devices. Revision rate for all (199) mobile bearing knees was less than 2%. The mean Oxford Knee Score for outcome for all mobile bearing knees was 37.1 ± 10.1. About 7% of patients reported instability. Clicking was more common in the TMK (48%) than in the AGC (30%) and was reported as a problem in 16% of TMK’s in the cohort study. However, clicking was unrelated to outcome score in both studies. Conclusion At three years, the mobile bearing device was as good as the fixed bearing device. There was a relatively high prevalence of “clicking” in the TMK but the cause remains unclear. Furthermore, the symptom was not associated with poor functional outcome. The bilateral RCT and cohort study allows assessment of function and potential problems. It provides rigourous scientific justification for the introduction and early assessment of new implants

Introduction. Total knee arthroplasty (TKA) is a well-established procedure associated with excellent clinical results. We have previously reported that intraoperative knee kinematics correlate with the clinical outcome in mobile bearing TKA. In addition, the intraoperative knee kinematics pattern does not correlate with the degree of preoperative knee deformity in mobile bearing TKA. However, the relationship among preoperative knee deformity, intraoperative kinematics and clinical outcome in fixed bearing TKA has been unknown. The purpose of this study is to compare the relationship among preoperative knee deformity, knee kinematics after fixed bearing TKA and the clinical outcome including the subjective outcomes evaluated by the new knee society score (KSS). Materials and Methods. A cross-sectional survey of thirty-five consecutive medial osteoarthritis patients who had a primary TKA using a CT-based navigation system was conducted. All knees had a Kellgren-Lawrence grade of 4 in the medial compartment and underwent a primary posterior stabilized TKA (Genesis II, Smith&Nephew) between May 2010 and October 2012. In all cases, a computed tomography-guided navigation system (Brain LAB, Heimstetten, Germany) was used. All surgery was performed by the subvastus approach and modified gap technique. Intraoperative knee kinematics was measured using the navigation system after implantation and closure of the retinaculum and soft tissue except for the skin. Subjects were divided into two groups based on intraoperative kinematic patterns: a medial pivot group (M group, n=19)(Figure 1) and a non-medial pivot group (N group, n=16)(Figure 2). Subjective outcomes with the new KSS and clinical outcomes were evaluated. Statistical analysis to compare the two groups was made using unpaired a Student t test. Result. Regarding the postoperative clinical result (knee flexion angle, knee extension angle, mechanical FTA,% mechanical axis), there were no significant differences between the two groups. Although there were also no significant differences in KSS evaluation between the two groups, there was a tendency for M group to be superior to N group in current knee symptom (M group: 17.3±5.6, N group: 12.9±8.2, p = 0.07) and functional activities (M group: 55.1±21.5, N group: 42.7±22.6, p = 0.10). Regarding preoperative examination, varus knee deformity (mechanical FTA and% mechanical axis) in N group was significantly more severe than that of M group (p=0.04, p=0.04, respectively). Discussion. Over half of patients (54%) could achieve medial pivot kinematics in fixed bearing TKA with the possibility to improve a subjective clinical result. Although we previously could not detect any relationship between preoperative varus knee deformity and intraoperative kinematics in mobile bearing TKA, the preoperative varus knee deformity in the non-medial pivot group was significantly severer than that of the medial pivot group in fixed type TKA. Our results indicate that if a TKA is done to a severe varus knee deformity the postoperative knee kinematics tend to result in a non-medial pivot pattern. In conclusion, because it tends to result in a non-medial pivot pattern, extra care needs to be taken to avoid postoperative abnormal knee kinematics in the performance of a fixed type TKA to a severe varus knee deformity

Introduction: Mobile bearing TKRs may allow some axial rotation and also compensate for a slight tibiofemoral rotational mismatch. This is thought to provide better kinematics and a more natural patellar movement. This theoretical advantage has not been verified in clinical studies for the tibiofemoral kinematics. However, little is known about the patellofemoral kinematics of mobile bearing TKRs. The aim was to compare patellar kinematics among the anatomic knee, fixed bearing TKR and mobile bearing TKR. Methods: Optical computer navigation marker arrays (Brainlab) were attached to the femur, tibia and patella of 9 whole lower extremities (5 fresh cadavers). The trial components of a fixed bearing posterior stabilised TKR (FB) (Sigma PFC, Depuy) were implanted using a tibia first technique. Then the tibia component was changed to a posterior stabilised mobile bearing tibia component (MB) (Sigma RP Stabilised). The patellae were not resurfaced. The knees were moved through a cycle of flexion and extension on a CPM machine. Medial/lateral shift and tilt was measured relative to the patella position in the natural knee at full extension always with soft tissue closure. The path of the trochlea and patellar groove of the femoral component was registered. Values are expressed as mean+/−one standard deviation. Statistical analysis: two tailed paired Student’s T-test. Results: M/L shift: There was a tendency for the patella to track 2mm more laterally throughout the flexion range with a FB or MB TKR compared to the natural knee, but this did not reach significance. Tilt: The patella in the natural knee tilted progressively laterally from extension to flexion, plateauing at 50° of flexion (20°: 1.9+/−2.7°, 40°: 5.6+/−5.4°, 60°: 6.2+/−6.4°, 80°:6.5+/−7.3°, 90°: 6.4+/−7.7°). With a FB or MB TKR the patellae also tilted laterally up to 50 degree of flexion, but then started to tilt back medially, reaching the neutral position again at 90°. The patellae of the FB and MB TKRs were significantly more medially tilted at 50° to 90° of flexion compared to the natural knee. But there was no difference between the FB and MB TKRs. (Fixed bearing: 20°: 2.5+/−7.2° p=0.30, 40°: 3.7°+/−6.5° p=0.15, 60°: 3.1+/−5.8° p=0.02, 80°:1.2+/−6.5° p=0.001, 90°: 0.3+/−7.2° p=0.001, Mobile bearing: 20°: 0.3+/−5.5° p=0.27, 40°: 3.6+/−5.2° p=0.08, 60°: 2.1°+/−5.8 p=0.01, 80°: 0.2+/−6.8 p=0.003, 90°: −0.6+/−7.3 p=0.002; vs. natural). Trochlea position: The centre of the patellar groove of the femur component was more lateral than the trochlea by 2–5mm, it also extended 10mm further proximally. Conclusion: There are kinematic differences in patellar tracking between the natural and a FB/MB TKR. This may be due to a slightly different position of the patellar groove. The patellar kinematics of the MB TKR is not more natural compared to the FB TKR

The Profix knee replacement arthroplasty manufactured by Smith and Nephew has been in use for the past five years however there are few published outcome data for this prosthesis. The purpose of this study was to provide clinical outcome data for a cohort of patients with a Profix TKR at a minimum 3 years follow up. There were 65 joint replacements in 58 patients all performed by or under the direct supervision of one of two senior consultant Orthopaedic surgeons. There were 34 right and 31 left knees replaced in 31 male and 27 female patients. Mean age of the patients was 69 years (51–84 years) and mean body mass 89Kg (45–140Kg). The femoral component was uncemented in 49 knees and cemented in 16 knees. The tibial component was cemented in all 65 cases. There were 53 mobile bearing polyethylene inserts and 12 fixed bearing knees. The patella was resurfaced primarily in 32 cases. Using the Oxford Knee score, the mean knee score was 20.7 (Range 12–42) where a perfect score is 12 and the worst possible score 60. Mean clinical range of movement was 111 degrees (Range 90–130 degrees). Of the 65 joints, 13 have required or are awaiting some form of re-operation. These included 3 for patellae that were not resurfaced at the index arthroplasty, 6 for secondary insertion or revision of mobile bearing locking-screws and one femoral revision for failure of on-growth of an uncemented femoral component. The finding of loosening of the mobile bearing locking screw in three well functioning knees highlights the importance of Xray follow-up of patients even if their knee scores are entirely satisfactory. Overall, the clinical results of this prosthesis are satisfactory, however these data would support routine patellar resurfacing and use of the cemented fixed bearing option for the Profix arthroplasty

Between 1995 and 1998, eighty revision total knee arthroplasties were done for the primary reason of advanced polyethylene wear. The primary arthroplasties prosthesis that failed included thirty-four mobile bearing knees and forty-six fixed bearing knees. In thirty-four Low Contact Stress (LCS) mobile bearing knees, osteolysis was identified intraoperatively in sixteen knees (forty-seven per cent). There were varying of fixation methods included nine cemented, four cementless and three hybrids. In forty-six fixed bearing knees, osteolysis was identified intraoperatively in six knees (thirteen per cent). The fixation methods of prostheses included two cemented and four cementless. The incidence of osteolysis was statistically significant difference between the mobile bearing and fixed bearing knees (p< 0.02). Both scattering electron microscope (SEM) and light scattering analysis were used to examine the UHMWPE wear debris collected from tissue sample. The particle size analyzed by light-scattering is coincident with the measurement by SEM. The major type of wear debris extracted from failed knee prostheses is granular shape. There are more granular wear debris appear in the mobile bearing knees than in the fixed bearing knees. The particle size of UHMWPE wear debris with osteolysis was significantly smaller than that without osteolysis. The high rate of osteolytic lesions in mobile bearing knee (LCS) is well illustrated in our result that a lot of fine UHMWPE wear debris generated in the Low Contact Stress knee. The result also illustrates that there is no relationship between fixation methods and the third body wear that associate with osteolysis

Introduction. Unidirectional mobile bearing knees (RP) were developed to optimise the tibio-femoral articulation in an effort to enhance function and reduce polyethylene wear. The self aligning bearing should also benefit the patello-femoral joint further improving outcome. This study was designed to assess whether these potential benefits are realised in the clinical setting. Methods. A total of 352 patients undergoing a PS PFC Sigma TKR were randomly allocated to receive either a Mobile Bearing (176 knees) or a Fixed Bearing (176 knees) tibial tray. Within each group a further randomisation for patella resurfacing versus retention was included. All knees were scored using standard tools (Oxford, AKSS, Patella Score) by independent nurse specialists. At 5 year review there had been 38 deaths (19 in each group), 5 revisions (4 fixed, 1 RP), 7 late patella resurfacings (4 fixed, 3 RP) and a small number of other patients had withdrawn, leaving 142 fixed bearing knees and 144 mobile bearing knees for evaluation. Results. The rotating platform TKR design had no impact on range of motion, Oxford Knee Score and American Knee Society knee and function scores when compared to its fixed bearing equivalent at minimum 5 year follow-up. Patella resurfacing, however, resulted in a greater improvement in knee function score from pre-op when compared to patella retention (25.5 vs 15.5, p=0.0015), with subsequent significant benefits seen in the SF-12 Physical and Total Scores (p=0.0004 and p=0.017 respectively). 5 year survivorship curves with revision for any cause as the endpoint were similar for both groups (fixed 96.2%, mobile 97.6%). This survivorship rises to 100% for both designs when considering aseptic loosening alone. Conclusion. There was no difference in performance between the fixed and RP groups. Patella resurfacing offered advantages over patella retention with this design and we would recommend its routine use

Introduction. Unidirectional mobile bearing knees (RP) were developed to optimise the tibio-femoral articulation in an effort to enhance function and reduce polyethylene wear. The self-aligning bearing should also benefit the patello-femoral joint further improving outcome. This study was designed to assess whether these potential benefits are realised in the clinical setting. Methods. A total of 352 patients undergoing a PS PFC Sigma TKR were randomly allocated to receive either a Mobile Bearing (176 knees) or a Fixed Bearing (176 knees) tibial tray. Within each group a further randomisation for patella resurfacing versus retention was included. All knees were scored using standard outcome tools (Oxford, AKSS, Patella Score) by independent nurse specialists. Results. At 5 year review there had been 38 deaths (19 in each group), 5 revisions (4 fixed, 1 RP), 7 late patella resurfacings (4 fixed, 3 RP) and a small number of other patients had withdrawn, leaving 142 fixed bearing knees and 144 mobile bearing knees for evaluation. The rotating platform TKR design had no impact on range of motion, Oxford Knee Score and American Knee Society knee and function scores when compared to its fixed bearing equivalent at minimum 5 year follow-up. Patella resurfacing, however, resulted in a greater improvement in knee function score from pre-op when compared to patella retention (25.5 vs 15.5, p=0.0015), with subsequent significant benefits seen in the SF-12 Physical and Total Scores (p=0.0004 and p=0.017 respectively). 5 year survivorship curves with revision for any cause as the endpoint were similar for both groups (fixed 96.2%, mobile 97.6%). This survivorship rises to 100% for both designs when considering aseptic loosening alone. Conclusion. There was no difference in performance between the fixed and RP groups. Patella resurfacing offered advantages over patella retention with this design and we would recommend its routine use

Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR. Aim: To test the hypothesis that the sagittal plane kinematics (and cruciate mechanism) of a fixed bearing medial UKR deteriorate over time (short to long term). A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (> 9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA

Purpose: There are numerous papers from specialist arthroplasty centres outlining results of total knee arthroplasties but little information from outside these major centres. We carried out a review of a fixed bearing total condylar knee replacement used in Dunedin by a variety of surgeons for over 10 years. Method: All patients who received a Duracon/PCA fixed bearing total knee replacement between 1992 and 1996 were assessed clinically, fluoroscopically and completed an SF12, WOMAC and IKSS questionnaire. Results: At a mean 9.7 (8–12) years follow up, 126 (69.6%) patients were available for review and 46 (25%) were deceased. The average age was 72 years (52–88) and the primary diagnosis was osteoarthritis in 95% of the cases. There were 34% Charnley Grade A, 37% Grade B and 29% Grade C respectively. The average IKS Knee score was 72 (23–97) and the functional score was 68 (0–100) with 74% experiencing none or only mild pain. The SF12 assessment revealed a mean physical score of 55 (14–99). Ninety per cent of patients were satisfied with their knee and 89% would have the operation again if required. There was one operative death (PE), one deep infection, 3 PE’s, 3 DVT’s and 5 superficial infections. An MUA was required in 9 cases. Eight knees were revised. Using ‘all revisions’ as an end point. The survival rate was 95.3% at 10 years. Conclusion: These results suggest that knee replacements carried out outside specialist arthroplasty centres perform very well with a survival rate of the implant of 95% at 10 years

Background. Wear and fatigue damage to polyethylene components remain major factors leading to complications after total knee and unicompartmental arthroplasty. A number of wear simulations have been reported using mechanical test equipment as well as computer models. Computational models of knee wear have generally not replicated experimental wear under diverse conditions. This is partly because of the complexity of quantifying the effect of cross-shear at the articular interface and partly because the results of pin-on-disk experiments cannot be extrapolated to total knee arthroplasty wear. Our premise is that diverse experimental knee wear simulation studies are needed to generate validated computational models. We combined five experimental wear simulation studies to develop and validate a finite-element model that accurately predicted polyethylene wear in high and low crosslinked polyethylene, mobile and fixed bearing, and unicompartmental (UKA) and tricompartmental knee arthroplasty (TKA). Methods. Low crosslinked polyethylene (PE). A finite element analysis (FEA) of two different experimental wear simulations involving TKA components of low crosslinked polyethylene inserts, with two different loading patterns and knee kinematics conducted in an AMTI knee wear simulator: a low intensity and a high intensity. Wear coefficients incorporating contact pressure, sliding distance, and cross-shear were generated by inverse FEA using the experimentally measured volume of wear loss as the target outcome measure. The FE models and wear coefficients were validated by predicting wear in a mobile bearing UKA design. Highly crosslinked polyethylene (XLPE). Two FEA models were constructed involving TKA and UKA XLPE inserts with different loading patterns and knee kinematics conducted in an AMTI knee wear simulator. Wear coefficients were generated by inverse FEA. Results. Predicted wear rates were within 5% of experimental wear rates during validation tests. Unicompartmental mobile bearing back-side wear accounted for 46% of the total wear in the mobile bearing. Wear during the swing phase was 38% to 44% of total wear. Discussion & Conclusions. Crosslinking polyethylene primarily decreased (by nearly 10-fold) the wear generated by cross-shear. This result can be explained by the reduced propensity of crosslinked polyethylene molecules to orient in the dominant direction of sliding. A highly crosslinked fixed-bearing polyethylene insert can provide high wear performance without the increased risk for mobile bearing dislocation. Finite element analysis can be a robust and efficient method for predicting experimental wear. The value of this model is in rapidly conducting screening studies for design development, assessing the effect of varying patient activity, and assessing newer biomaterials. This FEA model was experimentally validated but requires clinical validation

Purpose: As part of the step-wise introduction of a meniscal-bearing total knee replacement (Oxford TMK) we needed to know, before proceeding to longer term studies, whether its early clinical results were at least as good as those of an established fixed bearing device (AGC). Material and Methods: With ethical approval, patients requiring bilateral knee replacement for osteoarthritis consented to have the operations under one anaesthetic using one of each prosthesis; to accept random choice of knee; and to remain ignorant which side was which. American Knee Society Scores, Oxford Knee Scores, ROM and pain scores were to be recorded preoperatively and at one year. By January 2001, 40 patients had reached one year and data is available for 36. Results: Preoperatively there was no difference between the two knees. One patient died in the peri-operative period. Results at one year (TMK first): AKSS(Knee) 91.6 / 84.1 (p=0.003), OKS 39.8 / 37.6 (p=0.006), ROM 104 / 104 (p=0.364), Pain (AKSS) 47.3 / 41.7 (p=0.01), Pain (OKS) 3.5 / 2.9 (p=0.006). Conclusion: The TMK performed as well as the AGC. Its AKSS, OKS and pain scores were significantly better. We believe this controlled, blinded trial is the first to have compared the function of a new knee prosthesis with a standard implant before marketing; and the first to have demonstrated a significant clinical advantage for a meniscal-bearing over a fixed bearing TKR. The comparison of bilateral implants in the same patient can reveal significant differences while putting at risk many fewer subjects than would be needed for a classical twocohort RCT

Purpose: In this ongoing trial we are analysing the performance of both a fixed bearing total knee replacement and a mobile bearing total knee replacement using gait analysis and a patient-based questionnaire. We aim to find out if there is a difference in the functional performance of the two types of prosthesis. Method: Patients are taken from the in-patient waiting list of three consultants and introduced to the trial if deemed suitable. Each patient is analysed once pre-operatively and on three occasions post-operatively (6 weeks, 3 months and 1 year) at the university gait analysis laboratory. At each visit various anthropological measurements are recorded and the patient fills in an “Activities of Daily Living” questionnaire. After calibration and measurement of the passive range of motion of both knees each patient has their gait analysed over a series of six walks using a standard 5 camera system with skin marker clusters, the kinematic data from this is supplemented with force-plate recordings and video analysis of each set of walks. Data is recorded for both of the patient’s knees. The staff in the gait analysis laboratory are blinded as to which prosthesis has been used for each patient in an effort to eliminate bias. We present our methodology and some preliminary results

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 20 subjects (20 knees), 10 knees implanted with NexGen Legacy flex with mobile bearing PS TKA, and 10 knees implanted with NexGen Legacy flex 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. 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 BM and FB. The kinematic pathway pattern was externally rotated due to a lateral pivot pattern in both MB and FB. In four subjects, more than 12°axial rotation was observed in knees implanted with FB TKA which allows only 12°axial rotation. The data in this study demonstrates that there was no significant difference in kinematics of weight bearing deep knee bending motion. The advantage of MB is allowance of axial rotation which restricted until 12 °in FB NexGen Legacy flex PS TKA

Introduction and Aims: The study was designed to compare the early results, prospectively, of the fixed-bearing Zimmer NexGen cruciate retaining (CR) and the Zimmer NexGen mobile-bearing knee (MBK) knee arthroplasty. The study was designed to determine whether differences exist in the clinical outcomes between patients receiving different types of bearings. Method: Patients were randomly assigned to receiving either fixed or mobile bearings. Patients were blinded but not assessors to the type of arthroplasty. The study commenced in June 2000. By November 2002, 69 and 70 patients had been recruited into the CR and MBK groups respectively. Consultants were present in 92% of operations and the rest were performed by a senior registrar. The major indication was osteoarthritis (64 CR: 65 MBK). The surgical approach was medial parapatellar in 65 CR and 63 MBK the rest were subvastus, patella resurfacing was not routinely employed. Pre-operative, intra-operative and post-operative data was collated. Results: The body mass index was 32 ± 7 CR and 32 ± 6 MBK. The average age was 67 ± 8 CR and 67 ± 8 MBK. Pain in the contralateral knee was present in 79.7% CR and 74.3% MBK group. Minimum post-operative follow-up was one year. There was no significant difference in the pre-operative and post-operative fixed flexion contracture, 4.3 ± 5.4 to 1.0 ± 2.9 CR and 6.2 ± 6.9 to 0.9 ± 2.8. The mean flexion pre-operatively and post-operatively between the two groups was not significantly different 108 ± 19 to 105 ± 16 CR and 107 ± 15 to 102 ± 13. Patello-femoral joint symptoms diminished from 67% to 12% CR and from 69% to 21% in the MBK group. The dependence on walking aids diminished from 50.7% to 16.7% CR and 51.4% to 26.9% MBK. At one year, nine percent and 21% were dissatisfied in the CR and MBK groups respectively. In the CR group, two revisions had been performed, one for infection and the other for arthrolysis and poly exchange. Two revisions had been carried out in the MBK group, one for extreme ‘clunking’ and the other for arthrolysis with poly exchange. Conclusions: The one-year results suggest that the levels of dissatisfaction and patello-femoral problems are significantly greater in the mobile bearing group as opposed the fixed bearing. The early results would not encourage the use of the mobile bearings. We await the long-term results as regards survivorship of the bearings

Purpose. Total knee arthroplasty (TKA) is the preferred treatment for those with end stage osteoarthritis (OA) and severe functional limitations. With the demographic transition in society, TKA is being offered to a younger patient population. Younger patients are generally more active requiring an increased range of motion, and place greater physiological demands on the prosthesis than typical older patients. The mobile bearing (MB) total knee prosthesis has theoretically been designed to meet these demands. We conducted a meta-analysis and systematic review of randomized controlled trials comparing outcomes of MB and fixed bearing (FB) TKA. Method. After testing for publication bias and heterogeneity, the data were aggregated by fixed effects modelling. Our searches identified 14 studies for reporting our primary outcome of Knee Society Scores (KSS). We also pooled data for post-operative range of motion (ROM) and Hospital for Special Surgery scores (HSS). Results. The standard difference in mean outcome scores for KSS and HSS demonstrated no difference between groups (p = 0.902, and p = 0.426 respectively). Similarly, the pooled data for ROM showed no difference between groups (p = 0.265). Conclusion. The results of our systematic review and meta-analysis of the literature indicate that there are no significant differences between MB and FB TKA in the outcome measures of KSS, ROM or HSS at final follow up. Only 3 of 12 studies found any benefit of MB knees in terms of patient reported pain. There were no differences found between FB and MB regarding patellar instability or stair climbing ability. Implant longevity remains the only outcome measure in which MB implants may provide an advantage

Clinical experience has shown the needs for high flexion. The aim of this study was to evaluate the clinical and radiological results of a fixed bearing high flexion posterior stabilized (PS) total knee arthroplasty (TKA). Between July 2001 and December 2005, 422 TKAs in 288 patients were performed with high flexion PS prosthesis and 378 knees of 258 patients had been followed up for 2 to 6.5 years (mean: 3 years 11 months). We evaluated range of motion (ROM), Knee rating system of the Hospital for Special Surgery (HSS) and Knee Society (KS) score, and radiological results. The mean flexion improved from 110.1 degrees to 126.7 degrees at the latest follow-up. 333 knees (88 %) showed more than 120 degrees of flexion, 105 knees (28 %) more than 140 degrees of flexion. The mean KS clinical score improved from 39 to 93 points (p< 0.01) and KS function score, from 40 to 85.4 points (p< 0.01). The mean HSS score improved from 41.2 to 86.3 points (p< 0.01). In 28 knees, radiolucent line of 1–2 mm in width was observed at zone 1 without symptoms. Aseptic loosening in 4 knees, Mid-flexion instability in 2 knees, superficial infection in 3 knees and deep infection in 3 knees were observed. Total knee arthroplasty with high flexion PS prosthesis showed good ROM and satisfactory early clinical results. Complication rate was similar to those of other series. Close observation and serial radiological evaluation are needed for long term results

Summary. We report a large study of 331 patients at two years post operation who were prospectively randomised to receive either a rotating platform or a fixed bearing knee replacement of an otherwise identical design. Introduction. The mobile bearing total knee replacement was developed as there are theoretical benefits in that it may allow a better range of motion, better patella tracking and lower wear rates. This study was designed to see if these potential advantages are borne out in practice when using a cruciate retaining design. Methods. 331 patients undergoing TKR surgery were randomised to receive either a fixed bearing (170 patients) or a mobile bearing (161 patients). The femoral implant design was identical in the two groups. The tibial polyethylene bearing was either fixed in the metallic tibial tray (FB) or of rotating platform design (RP). All patients were assessed pre-operatively and at two years post-operatively using standard tools (Oxford, AKSS, Patellar Score) by independent nurse specialists. Results. The groups who received the FB and the RP implants have been assessed and their pre-operative to two year outcomes analysed with regard to the improvement in the range of motion (9.1 v. 10.2 degrees), Oxford Knee Score (-19.2 v. -17.6) and American Knee Society Knee and Function scores (51.3 v. 49.5 and 25.3 v. 23.6) at two years follow up. Conclusion. This large study shows that there is no statistical difference between a FB and a RP cruciate retaining TKR at two years post operation

Introduction: Total knee arthroplasty (TKA) has become a successful clinical treatment for patients in regard to relief of pain, correction of deformity and restoration of function with promising long term behaviour [Pradhan et al. 2006]. In TKA the generation of polyethylene wear debris is mainly affected by the factors design of the articulating bearing, contact stresses, kinematics, implant material and surface finish [McEwen et al. 2005]. The objective of our study was to evaluate the in vitro wear behaviour of fixed bearing knee designs in comprehension to the contact mechanics and resultant kinematics for different degrees of congruency. Material and Methods: Wear simulator testing on 12 TKA devices has been performed according to ISO 14243-1 under load control. The knee replacements were tested in the fixed bearing configurations LC, CR and DD with different degrees of tibio-femoral congruency. For gravimetric wear assessment the protocol described in ISO 14243-2 has been used, followed by a kinematic analysis of the single test stations. The articulating contact and subsurface stresses have been investigated in a finite element analysis. Results: The contact areas are increasing from Search® Evolution LC (144 mm2) to Columbus® CR (235 mm2) and Columbus® DD (279 mm2), whereas the peak surface contact stresses are decreasing from Search® Evolution LC (34.4 MPa) to Columbus® CR (20.9 MPa) and Columbus® DD (18.1 MPa). The estimated amount of wear has decreased from Search® Evolution LC (21.4 mg/million cycles) to Columbus® CR (8.9 mg/million cycles) and Columbus® DD (2.2 mg/million cycles). The wear rates between the knee design configurations differ substantially and statistically analysis demonstrates a significant difference (p< 0.01) between the test groups in correlation with congruency. Conclusion: The present study demonstrates the influence of different bearing types on contact stresses, abrasive wear and kinematics for three different degrees of tibio-femoral congruency under elimination of production, material and sterilization parameters. Corresponding author: Dr.-Ing. Thomas M. Grupp. Research and Development: e-mail: . thomas.grupp@aesculap.de

Introduction There are only a limited number of long term studies of total knee arthroplasty but none with a minimum 15 year survivorship of a modular fixed bearing posterior cruciate-retaining prosthesis. Methods We present a consecutive series of 139 total knee arthroplasties (109 patients, average age 67 years), using a non-conforming posterior cruciate-retaining prosthesis, followed for a minimum of 15 years (range, 15.0 to 16.9 years). The patella was resurfaced with an all-polyethylene component in 83% of knees. The tibial component was always cemented, while a porous coated femoral component was used in 84% of knees. Fortyfive patients (59 knees) were followed-up for a minimum of 15 years, 57 (70 knees) had died, five patients (8 knees) were too ill to assess, two patients (two knees) were considered lost to follow-up. Results In this series there were five re-operations, four of which were for polyethylene insert wear. At two of these, the patella was exchanged for early surface wear and one patella was resurfaced for the first time. There was one loose cemented femoral component after more than 15 years. The survival without revision or need for revision for any reason was 99% at 10 years and 95.6% (worst case scenario of 94.2%) at 15 years. The mean Knee Society Score and Function Score at 15 year follow-up was 96 and 78 respectively. The total incidence of radiolucent lines was 13%, with two percent around the femur, 11% around the tibia and zero percent around the patella. None of these lines were of any clinical relevance. There was no evidence of progressive radiolucent lines or component loosening, and one case of zone four femoral osteolysis. Conclusions This single-surgeon series with a minimum 15 year follow-up, and excellent clinical, radiological and survivorship results provides a benchmark upon which other long term studies of modular fixed bearing posterior cruciate retaining total knee arthroplasty can be compared. In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source

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: The aim of this study was to compare the clinical, radiological and functional outcome results of the Scorpio PS TKA prosthesis with either a mobile (MB) or fixed bearing (FB) Pe insert. We hypothesized that the MB group would perform better over time in clinical and functional outcome as well as showing a reduction in anterior knee pain occurrence. Methods: In a prospective, randomised, single centre, multi surgeon clinical study, a total of 100 patients were enrolled equally divided between MB and FB groups. A standard surgical protocol was used for implanting the Scorpio knee prosthesis with either an MB or FB insert. Post-op rehabilitation was standardized and unrelated to insert type. Patients were assessed pre-op and after 3–6-12–24 months post-op. RAND-36 and Knee Society Score (KSS), were assessed as well as pain measurement during functional testing (chair rise and stair climb) using Visual Analogue Scale (VAS) scale. X-rays were assessed for implant positioning, migration, radiolucent lines and patella tilt (using a Skyline view in 30–60 and 90 degrees). Results: Both tests groups showed a statistical significant decrease of VAS pain score over time (p < 0.01). No significant differences were seen between both groups at any time point. results did show the MB group to have less pain the first postoperative year in both chair rise test and stair climb test tests. No statistically significant differences were found in total range of motion between the two groups. Repeated measures tests showed a significant improvement over time for both groups for KSS and most RAND 35 subscores. There were no significant differences between groups at any given follow up moment. Within 8 out of 9 RAND 36 subdivisions showed the MB group to score non significantly better the first postoperative year. After one year the differences disappeared. Radiology showed stable implants with no progressive radiolucent lines in all patients. No significant differences in patellar tilting were found. Discussion: Our hypothesis, that the MB prostheses would provide a better ROM and less anterior knee pain, was not confirmed by the results. In our study the MB group showed less decrease in ROM immediately postop. This phenomenon was also seen by Harrington et al. The MB prosthesis regained its ROM after surgery earlier than the FB implants. This difference could potentially be attributed to the implant design and its kinematics. This advantage did not persist and the FB group slowly leveled. In conclusion, our study does not show any clear advantages in terms of function, pain, ROM, general health, radiological evaluation, KSS and RAND 36 of MB compared with FB TKA at a follow-up of 2 years

To evaluate prospectively the mid-term results of the Zimmer Unicondylar Knee arthoplasty (UKA).

Between 2005 and 2012, 187 unicompartmental knee arthroplasties (UKA) were performed by a single surgeon using a fixed-bearing prosthesis (Zimmer). 37 cases were excluded as either were lost to follow-up or had less than six months follow-up. The study included 150 UKAs. Deformity, if present, was correctable. Patellofemoral joint (PFJ) disease was not considered as an absolute contraindication. The average patient age at the time of surgery was 66 years (range 42–88 years); 78 of which were male. Mean follow-up time was 3.6 years (range 7–81 months). Mean Body Mass Index (BMI) was 29 (range 21–41). Clinical and conventional radiological evaluations were carried out at six months, one, two and five years postoperatively.

147 cases were medial compartment replacement and three were lateral. 86 patients had grade III OA and 64 had grade IV (Kellgren and Lawrence). 113 patients had an element of PFJ disease. The mean Knee Society knee and function scores had an improvement from 55 and 54 points pre-operatively to 95 and 94 points respectively at time of most recent evaluation. The average flexion improved from 116 degrees pre-operatively to 127 degrees. Two cases were revised, one due to progression of osteoarthritis in the lateral compartment of the knee and the other was due to arthrofibrosis.

The Zimmer unicompartmental knee arthroplasty provided excellent pain relief and restoration of function in carefully selected patients. However, long-term studies are necessary to investigate the survival rate for this prothesis.

Background: Mobile-bearing knee replacements have some theoretical advantages over fixed-bearing devices. However, very few randomized controlled clinical trials have been published to date, and studies showed little clinical and subjective advantages for the mobile-bearing using traditional systems of scoring. The choice of the ideal outcome measure to assess total joint replacement remains a complex issue. However, gait analysis provides objective and quantifying evidences of treatment evaluation. Significant methodological advances are currently made in gait analysis laboratories and ambulatory gait devices are now available. The goal of this study was to provide gait parameters as a new objective method to assess total knee arthroplasty outcome between patients with fixed- and mobile-bearing, using an ambulatory device with minimal sensor configuration.

This randomized controlled double-blind study included to date 14 patients: the gait signatures of four patients with mobile-bearing were compared to the gait signatures of nine patients with fixed-bearing pre-operatively and post-operatively at 6 weeks, 3 months and 6 months. Each participant was asked to perform two walking trials of 30m long at his/her preferred speed and to complete a EQ-5D questionnaire, a WOMAC and Knee Society Score (KSS). Lower limbs rotations were measured by four miniature angular rate sensors mounted respectively, on each shank and thigh.

A new method for a portable system for gait analysis has been developed with very encouraging results regarding the objective outcome of total knee arthroplasty using mobile- and fixed-bearings.

Conventional fixed-bearing (FB) knee prostheses have been proved clinically successful. Rotating platform, mobile-bearing (MB) total knee replacements (TKR) have been developed to improve knee kinematics, lower contact stresses on the polyethylene tibial component, minimize constraint, and allow implant self-alignment. The purpose of this study was to characterize and compare the functional outcome of FB- and MB- TKR during gait and deep knee bends, using a motion analysis system. Two groups of five patients with a unilateral FB TKR (PFC) or MB TKR (LCS) underwent a gait analysis study. The normal contralateral limb was used as a control to compare data in the stance phase of gait. Demographic, clinical, and radiographic data were equivalent in the 2 groups. Both MB and FB TKRs gave good functional results in spite of different design rationales. No statistically significant difference was demonstrated between the two groups. However, gait and knee function after TKR was abnormal even though the patients were asymptomatic. A flexional pattern for flex-ion-extension moments at the knee during level walking was present in both types of TKR. Differences in rotational moments between the two groups were observed, with a higher internal rotational moment in the PFC group (PFC, 0.14 Nm/kg; LCS, 0.09 Nm/kg; p=0.094). A stressful weightbearing activity, such as deep knee bends, amplified the functional differences between the different prosthetic designs, indicating that knee kinematics are activity-dependent. Kinetic and kinematic differences noted between the 2 groups reflect different patterns of joint surface motion and loading, with postulated effects on long term failure of the implants through wear, mechanical failure, and loosening. Gait analysis using external skin markers has a limited role in the characterization of the joint surface motion of the prosthetic knee during ambulatory activities because of errors and assumptions inherent in the technique. However, it provides scope for the study of kinetic parameters acting on different knee prostheses during gait.

Introduction

Mobile-bearing TKRs allow some axial rotation and may provide a more natural patellar movement. The aim was to compare patellar kinematics among the normal knee, fixed-bearing and mobile-bearing TKR.

Background: Mobile-bearing knee replacements have some theoretical advantages over fixed-bearing devices. However, very few randomized controlled clinical trials have been published to date, and studies showed little clinical and subjective advantages for the mobile-bearing using traditional systems of scoring.

The choice of the ideal outcome measure to assess total joint replacement remains a complex issue. However, gait analysis provides objective and quantifying evidences of treatment evaluation. Significant methodological advances are currently made in gait analysis laboratories and ambulatory gait devices are now available.

The goal of this study was to provide gait parameters as a new objective method to assess total knee arthroplasty outcome between patients with fixed- and mobile-bearing, using an ambulatory device with minimal sensor configuration.

Methods: This randomized controlled double-blind study included to date 31 patients: the gait signatures of 12 patients with mobile-bearing were compared to the gait signatures of 19 patients with fixed-bearing pre-operatively and post-operatively at 6 weeks, 3 months and 6 months. Each participant was asked to perform two walking trials of 30m long at his/her preferred speed and to complete a EQ-5D questionnaire, a WOMAC and Knee Society Score (KSS). Lower limbs rotations were measured by four miniature angular rate sensors mounted respectively, on each shank and thigh.

Results: Better relative differences between pre-operative and post-operative 3 months and 6 months KSS (122% vs 34% at 3 months, 138% vs 36% at 6 months) and KSS function (154% vs 8% at 3 months, 183% vs 42% at 6 months) scores were observed for the fixed-bearing compared to the mobile-bearing. The same better improvements for fixed-bearing were also found with the range of knee angles (Affected side: 31% vs −5% at 3 months, 47% vs 5% at 6 months), (Unaffected side: 16% vs 5% at 3 months, 15% vs 6% at 6 months) and peak swing speeds of shank (Affected side: 18% vs −2% at 3 months, 30% vs 4% at 6 months), (Unaffected side: 8% vs −3% at 3 months, 7% vs 4% at 6 months).

Conclusions: A new method for a portable system for gait analysis has been developed with very encouraging results regarding the objective outcome of total knee arthroplasty using mobile- and fixed-bearings.

Introduction

There is conflicting evidence about the merits of using mobile bearings at total knee replacement (TKR), partly because most randomised controlled trials (RCTs) have not been adequately powered.

Introduction: Unicondylar knee arthroplasty (UKA) has seen a resurgence in the past decade. Perpetuation of this trend can only be supported through prospective demonstration of efficacy with validated outcomes measures.

Materials & Methods: Thirty-three consecutive cemented medial Miller-Galante UKA’s (Zimmer, Warsaw, IN) were performed in 32 patients (7 males/25 females; mean age of 67 ± 9 years). Average weight, height, and body mass index (BMI) of the patient population was 189 ± 31 lbs (Range, 145–293), 65 ± 4 in (range, 60–75), and 33 ± 5 BMI (range, 25–43), respectively. Average polyethylene thickness (as labelled) for this cohort was 8.3mm (range, 8–12mm). Outcomes were prospectively assessed via the SF-12, WOMAC, and Knee Society Score (KSS). No patients were lost to follow-up. Kaplan-Meier survivorship and Student’s t-test were performed using GraphPad Prism 4 software (GraphPad Software Inc., San Diego, CA).

Results: Minimum follow-up was 39 months with a mean follow up period of 49 (range, 39–59) months. One knee was converted at 6 months at another institution to a TKA. Kaplan-Meier survivorship analysis reported 97% survivorship at 59 months (95% CI). Of the 32 knees remaining, mean preoperative KSS and WOMAC pain scores improved significantly from 52 ± 7 (range, 37–67) to 89 ± 9 (range, 67–100) (p< 0.0001) and from 40 ± 22 (range, 0–80) to 93 ± 14 (range, 35–100) (p< 0.0001), respectively. Additionally, average SF-12 Physical Component scores significantly increased from 30 ± 7 (range, 18–51) at baseline to 49 ± 10 (range, 28–59) at time of follow-up (p< 0.0001). Overall stiffness and physical function assessed via the WOMAC index also exhibited statistically significant improvement, bettering from mean baseline scores of 54 ± 24 (range, 0–100) and 52 ± 19 (range, 25–87) to 84 ± 19 (range, 50–100, p< 0.0001) and 88 ± 15 (range, 44–100, p< 0.0001), respectively. No significant cement/bone interface radiolucencies were found upon thorough radiographic review at 3 years post UKA.

Discussion & Conclusion: The significant improvements observed in knee function & stiffness, and decreases in pain at a mean of 4 years after medial UKA are encouraging. Coinciding results from the physical component of the SF-12 assessment indicate reassurance of physical improvements regarding patient lifestyle. 97% survivorship in the short term would be discouraging if not for the specific circumstances of the sole conversion to TKA. This specific patient went against the advice of the operative surgeon and solicited services at an outside institution in conversion to a TKA despite markedly improved function (Pre-op/3 month post-op WOMAC and KSS of 30/75 and 60/91). Clinical and radiographic follow-up will continue in order to assess the long-term efficacy of medial UKA with the Miller-Galante prosthesis using strict patient selection criteria.

There is conflicting evidence about the merits of mobile bearings in total knee replacement, partly because most randomised controlled trials (RCTs) have not been adequately powered. We report the results of a multicentre RCT of mobile versus fixed bearings. This was part of the knee arthroplasty trial (KAT), where 539 patients were randomly allocated to mobile or fixed bearings and analysed on an intention-to-treat basis. The primary outcome measure was the Oxford Knee Score (OKS) plus secondary measures including Short Form-12, EuroQol EQ-5D, costs, cost-effectiveness and need for further surgery. There was no significant difference between the groups pre-operatively: mean OKS was 17.18 (. sd. 7.60) in the mobile-bearing group and 16.49 (. sd. 7.40) in the fixed-bearing group. At five years mean OKS was 33.19 (. sd. 16.68) and 33.65 (. sd. 9.68), respectively. There was no significant difference between trial groups in OKS at five years (-1.12 (95% confidence interval -2.77 to 0.52) or any of the other outcome measures. Furthermore, there was no significant difference in the proportion of patients with knee-related re-operations or in total costs. In this appropriately powered RCT, over the first five years after total knee replacement functional outcomes, re-operation rates and healthcare costs appear to be the same irrespective of whether a mobile or fixed bearing is used. Cite this article: Bone Joint J 2013;95-B:486–92

Introduction. Backside wear of polyethylene (PE) inlays in fixed-bearing total knee replacement (TKR) generates high number of wear debris, but is poorly studied in modern plants with improved locking mechanisms. Aim of study. Retrieval analysis of PE inlays from contemporary fixed bearing TKRs - to evaluate the relationship between backside wear and liner locking mechanism and material type and roughness of the tibial tray. Methods. MATERIAL. We included five types of implants, revised after min. 12 months (14–71): three models with a peripheral locking rim and two models with a dove-tail locking mechanism. Altogether this study included 15 inlays were removed from TKRs with CoCr alloy tray with a roughened surface and a peripheral locking lip liner (Stryker Triathlon, Ra 5,61 µm), 9 from CoCr trays with peripheral locking lip and untreated surface (Aesculap Search, Ra 0,81 µm), 13 from Ti alloy trays with peripheral locking lip and untreated surface (DePuy PFC Sigma 0,61 µm), 11 from Ti alloy trays with untreated surface and dovetail locking mechanism (Zimmer NexGen, 0,34 µm), and 9 from iplants with a Ti alloy tibial tray with mirror polished surface and dovetail locking mechanism (Smitn&Nephew Genesis II, 0,11 µm). METHODS. Wear of bearing surface and back side of retrieved inlays was examined in 10 sectors under a light microscope. Seven modes of wear were analysed and quantified according to the Hood scale: surface deformation, pitting, embedded third bodies, pitting, scratching, burnishing (polishing), abrasion and delamination. Damage of inlays caused by backside wear was also evaluated using scanning electron microscopy (SEM). Roughness of tibial tray was evaluated using a contact profilometer. Results. We found no differences between wear scores on the articulating surface in all group, they did not correlate with backside wear scores in all groups as well. Compared to all other groups, backside wear scores were significantly higher in implants with untreated Ti alloy tibial tray (P<0,001 Wilcoxon test). Lowest wear rates were found in implants from both Ti and CoCr alloys and peripheral locking rim. Interestingly there was no difference between wear of implants with polished and untreated surface (Fig. 1). SEM analysis demonstrated different wear modes in implants with dovetail mechanism and peripheral rim. The first group demonstrated signs of gross rotational instability, with severe abrasion with an arch-shaped pattern and delaminated PE (Fig 2). In one design we observed severe extrusion of PE into screw holes of the tibial tray. Inlays from trays with peripheral rim presented two types of wear: flattening of machining marks or protrusion of the material caused by the rough surface (Fig 3). Conclusions. This study demonstrates that backside wear is still a problem in modern TKR. Our findings suggest that it is predominantly affected by type of locking mechanism (with peripheral rim performing better), to a lesser extent by surface roughness of the tibial component, while material type does not seem to play an important role. This study was funded by a grant from the National Science Centre nr 2012/05/D/NZ5/01840. To view tables/figures, please contact authors directly

Aims

This study reports updates the previously published two-year clinical, functional, and radiological results of a group of patients who underwent transfibular total ankle arthroplasty (TAA), with follow-up extended to a minimum of five years.