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