Joint registries suggest a downward trend in the use of uncemented Total Knee Replacements (TKR) since 2003, largely related to reports of early failures of uncemented tibial and patella components. Advancements in uncemented design such as trabecular metal may improve outcomes, but there is a scarcity of high-quality data from randomised trials. 319 patients <75 years of age were randomised to either cemented or uncemented TKR implanted using computer navigation. Patellae were resurfaced in all patients. Patient outcome scores, re-operations and radiographic analysis of radiolucent lines were compared. Two year follow up was available for 287 patients (144 cemented vs 143 uncemented). There was no difference in operative time between groups, 73.7 v 71.1 mins (p= 0.08). There were no statistical differences in outcome scores at 2 years, Oxford knee score 42.5 vs 41.8 (p=0.35), International Knee Society 84.6 vs 84.0 (p=0.76), Forgotten Joint Score 66.7 vs 66.4 (p=0.91). There were two revisions, both for infection one in each group (0.33%). 13 cemented and 8 uncemented knees underwent re-operation, the majority of these being manipulation under anaesthetic (85.7%), with no difference (8.3% vs 5.3%, 95% CI -2.81% to 8.89%, p = 0.31). No difference was found in radiographic analysis at 2 years, 1 lucent line was seen in the cemented group and 3 in the uncemented group (0.67% v 2.09%, 95%CI -4.1% to 1.24%, p = 0.29). We found no difference in clinical or radiographic outcomes between cemented and uncemented TKR including routine patella resurfacing at two years. Early results suggest there is no difference between cemented and uncemented TKR at 2 years with reference to survivorship, patient outcomes and radiological parameters

Due to shorter hospital stays and faster patient rehabilitation Unicompartmental Knee Replacements (UKR) are now considered more cost effective than Total Knee Joint Replacements (TKJR). Obesity however, has long been thought of as a relative contraindication to UKR due to an unproven theoretical concern of early loosening. This study is a retrospective review of patient reported outcome scores and revision rates of all UKR with recorded BMI performed by the Canterbury District Health Board (CDHB) from January 2011 and September 2021. Patient reported outcome scores were taken preoperatively, at 6 months, 1 year, 5 years and 10 years post operatively. These included WOMAC, Oxford, HAAS, UCLA, WHOQOL, normality, pain and patient satisfaction. 873 patients had functional scores recorded at 5 years and 164 patients had scores recorded at 10 years. Further sub-group analysis was performed based on patient BMI of <25, 25–30, 30–35 and >35. Revision data was available for 2377 UKRs performed in Christchurch during this period. Both obese (BMI >30) and non-obese (BMI <30) patients had significantly improved post-operative scores compared to preoperative. Pre-operatively obese patients had significantly lower functional scores except for pain and UCLA. All functional scores were lower in obese patients at 5 years but this did not meet minimum clinical difference. At 10 years, there was significantly lower HAAS, satisfaction and WOMAC scores for obese patients but no difference in Oxford, normality, WHOQOL, UCLA and pain scores. There was no significant difference in the improvement from pre-operative scores between obese and non-obese patients. All cause revision rate for obese patients at 10 years was 0.69 per 100 observed component years compared to 0.76 in non-obese. This was not statistically significant. Our study proves that UKR is an excellent option in obese patients with post-operative improvement in functional scores and 10 year survivorship equivalent to non-obese patients

Abstract. Patient Reported Outcome Measures (PROMs) can be completed using paper and postal services (pPROMS) or via computer, tablet or smartphone (ePROMs). We have investigated whether there are differences in scores depending on the method of PROMs acquisition for the Oxford Knee (OKS) and the EQ-5D scores, at one and two years post operatively. Patient demographics, mode of preferred data collection and pre-and post-operative PROMs for Total Knee Replacements (TKRs) performed between 1st January 2018 and 31st December 2018 were collected. During the study period, 1573 patients underwent TKRs. The average OHS and EQ-5D pre-operatively scores was 19.47 and 0.40 respectively. 71.46% opted to undertake post-operative questionnaires using ePROMs. The remaining 28.54% opted for pPROMS. The one and two-year OHS for ePROMS patients increased to 37.64 and 39.76 while the OHS scores for pPROMS patients were 35.71 and 36.83. At the one and two-year post-operative time intervals, a Mann-Whitney test showed statistical significance between the modes of administration for OHS (P-Value = 0.044 and 0.01 respectively). The one and two-year EQ-5D for ePROMS patients increased to 0.76 and 0.78 while the EQ-5D scores for pPROMS patients were 0.73 and 0.76. The P-Value for Mann-Whitney tests comparing the modes of administration for EQ-5D were 0.04 and 0.07 respectively. There is no agreed mode of PROMs data acquisition for the OKS and EQ-5D Scores. While we have demonstrated an apparent difference in scores depending on the mode of administration, further work is required to establish the influence of potentially confounding factors

Introduction. At a minimum 12 years follow-up the Authors performed a matched paired study between 2 groups: Bi-Unicompartimental (femoro-tibial) versus Total Knee Replacements, both navigated, they hypothesised that Bi-UKR guarantees a clinical score and patient satisfaction at least similar to TKR without differences in survivorship. Materials and Methods. 19 BI-UKR (1999–2003) were included in the study (group A). Every single patients in group A was matched to a computer-assisted TKR implanted in the same period (group B). The clinical outcome was evaluated using the Knee Society Score, the GIUM Score and the WOMAC Arthritis Index. Radiographically the HKA angle and the Frontal Tibial Component angle (FTC) were. Statistical analysis of the results was performed and Kaplan-Meir survival rate was assessed in both the groups. Results. No statistically significant difference was seen for the Knee Society, Functional and GIUM scores between the 2 groups. Statistically significant better WOMAC Function and Stiffness indexes were registered for the Bi-UKR group. All the TKR implants still remained positioned within 4 degrees of an ideal HKA angle of 180° and ideal FTC angle of 90° with a statistically significant better alignment compared to the Bi-UKR group. The Kaplan-Meier survival did not show any statistical significant differences in survivorship. Discussion. At 12 years minimum follow-up there are no significant differences in survivorship and clinical score despite a worse implant alignment WOMAC function and stiffness scores are still statistically better in the Bi-UKR group

Introduction

The input mechanical properties of knee replacement bearing materials, such as elastic modulus and Poisson's ratio, significantly contribute to the accuracy of computational models. They should therefore be determined from independent experimental studies, under similar test conditions to the clinical and experimental conditions, to provide reliability to the models. In most cases, the reported values in the literature for the elastic modulus and Poisson's ratio of the bearing materials have been measured under tensile test conditions, in contrast to the compressive operating conditions of the total knee replacements (TKR). This study experimentally determined the elastic modulus and Poisson's ratio of conventional and moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under compressive test conditions. These material parameters will be inputs to future computational models of TKR.

Introduction

Surface wear of polyethylene is still considered a long-term risk factor for clinical success, particularly as life expectancy and activity levels increase. Computational models have been used extensively for preclinical wear prediction and optimization of total knee replacements (TKR). In most cases, the input wear parameters (wear factors and coefficients) to the computational models have been experimentally measured under average contact stresses to simulate standard activities. These wear studies are not therefore applicable for more adverse conditions that could lead to edge loading and high stress conditions, including higher levels of activities and severe loading conditions. The current study investigated the multidirectional pin-on-plate wear performance of moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under high applied nominal contact stress, to be used as inputs to a computational model investigating adverse high stress conditions.

Total knee replacements (TKR) have been the main choice of treatment for alleviating pain and restoring physical function in advanced degenerative osteoarthritis of the knee. Recently, there has been a rising interest in minimally invasive surgery TKR (MIS-TKR). However, accurate restoration of the knee axis presents a great challenge. Patient-specific-instrumented TKR (PSI-TKR) was thus developed to address the issue. However, the efficacy of this new approach has yet to be determined. The purpose of the current study was thus to measure and compare the 3D kinematics of the MIS-TKR and PSI-TKR in vivo during sit-to-stand using a 3D fluoroscopy technology.

Five patients each with MIS-TKR and PSI-TKR participated in the current study with informed written consent. Each subject performed quiet standing to define their own neutral positions and then sit-to-stand while under the surveillance of a bi-planar fluoroscopy system (ALLURA XPER FD, Philips). For the determination of the 3D TKR kinematics, the computer-aided design (CAD) model of the TKR for each subject was obtained from the manufacturer including femoral and tibial components and the plastic insert. At each image frame, the CAD model was registered to the fluoroscopy image via a validated 2D-to-3D registration method. The CAD model of each prosthesis component was embedded with a coordinate system with the origin at the mid-point of the femoral epicondyles, the z-axis directed to the right, the y-axis directed superiorly, and the x-axis directed anteriorly. From the accurately registered poses of the femoral and tibial components, the angles of the TKR were obtained following a z-x-y cardanic rotation sequence, corresponding to flexion/extension, adduction/abduction and internal/external rotation.

During sit-to-stand the patterns and magnitudes of the translations were similar between the MIS-TKR and PSI-TKR groups, with posterior translations ranging from 10–20 mm and proximal translations from 29–31mm. Differences in mediolateral translations existed between the groups but the magnitudes were too small to be clinically significant. For angular kinematics, both groups showed close-to-zero abduction/adduction, but the PSI-TKR group rotated externally from an internally rotated position (10° of internal rotation) to the neutral position, while the MIS-TKR group maintained at an externally rotated position of less than 5° during the movement.

During sit-to-stand both groups showed similar patterns and magnitudes in the translations but significant differences in the angular kinematics existed between the groups. While the MIS-TKR group maintained at an externally rotated position during the movement, the PSI-TKR group showed external rotations during knee extension, a pattern similar to the screw home mechanism in a normal knee, which may be related to more accurate restoration of the knee axis in the PSI-TKR group. A close-to-normal angular motion may be beneficial for maintaining a normal articular contact pattern, which is helpful for the endurance of the TKR. The current study was the first attempt to quantify the kinematic differences between PSI and non-PSI MIS. Further studies to include more subjects will be needed to confirm the current findings. More detailed analysis of the contact patterns is also needed.

The trabecular metal Monoblock TKR is comprised of a porous tantalum base plate with the polyethylene liner embedded directly in the porous metal. An alternative design, the trabecular metal Modular TKR, allows polyethylene liner insertion into the locking base plate after base plate implantation, but removes the low modulus of elasticity that was inherent in the Monoblock design. The purpose of this study was to compare the fixation of the Monoblock and Modular trabeucular metal base plates in a randomised controlled trial.

Fifty subjects (30 female) were randomly assigned to receive the uncemented trabecular metal Monoblock or uncemented trabecular metal Modular knee replacement. A standard procedure of tantalum marker insertion in the proximal tibial and polyethylene liner was followed with uniplanar radiostereometric analysis (RSA) examinations immediately post-operatively and at 6 week, 3 month, 6 month, and 12 month follow-ups. The study was approved by the Research Ethics Board and all subjects signed an Informed Consent Form.

Twenty-one subjects received Monoblock components and 20 received Modular components. An intra-operative decision to use cemented implants occurred in 5 cases and 4 subjects did not proceed to surgery after enrollment. The clinical precision of implant migration measured as maximum total point motion (MTPM) was 0.13 mm (upper limit of 95% confidence interval of double exams). Implant migration at 12 months was 0.88 ± 0.64 mm (mean and standard deviation; range 0.21 – 2.84 mm) for the Monoblock group and 1.60 ± 1.51 mm (mean and standard deviation; range 0.27 – 6.23 mm) for the Modular group. Group differences in 12 month migration approached clinical significance (p = 0.052, Mann Whitney U-test).

High early implant migration is associated with an increased risk for late aseptic loosening. Although not statistically significant, the mean migration for the Modular component group was nearly twice that of the Monoblock, which places it at the 1.6 mm threshold for “unacceptable” early migration (Pijls et al 2012). This finding is concerning in light of the recent recall of a similar trabecular metal modular knee replacement and adds validity to the use of RSA in the introduction of new or modified implant designs.

Reference: Pijls, B.G., et al., Early migration of tibial components is associated with late revision: a systematic review and meta-analysis of 21,000 knee arthroplasties. Acta Orthop, 2012. 83(6): p. 614–24.

Joint replacement of the hip and knee remain very satisfactory operations. They are, however, expensive. The actual manufacturing of the implant represents only 30% of the final cost, while sales and marketing represent 40%. Recently, the patents on many well established and successful implants have expired. Companies have started producing and distributing implants that purport to replicate existing implants with good long-term results.

The aims of this paper are to assess the legality, the monitoring and cost saving implications of such generic implants. We also assess how this might affect the traditional orthopaedic implant companies.

Cite this article: Bone Joint J 2016;98-B:892–900.

Introduction. Orthopaedic theatres can be noisy. Noise exposure is known to be related to reduced cognition, reduced manual dexterity and increased rates of post-operative wound infection. Up to 50% of orthopaedic theatre staff have features of Noise-Induced Hearing Loss (NIHL) with higher levels in consultants compared to registrars. Exposure to noise levels of 90dB(A) at work for a career of 40 years, equates to a 51% risk of hearing loss. Materials & methods. A Casella CEL-242 meter was positioned in the corner of the theatre tent. Recordings were taken for 17 Total Knee Replacements (TKRs) and 11 Total Hip Replacements (THRs). This meter recorded the decibel level once per second (whereas EU Regulation requires equivalent continuous level measurement). Results. Noise levels reached 105.6dB(A) using a hammer during a TKR and 97.9dB(A) with an oscillating saw. Decibel levels exceeded 90dB(A) in every operation within the sample. Percentages of readings at 80.0dB(A) or above, per case, were calculated to estimate the proportion of our data above the EU regulation Lower Action Level; the maximum was 12.6% and they appeared to be greater in TKRs. Discussion. The small percentage of values at 80.0dB(A) or above indicates that the equivalent continuous decibel level for an average 8 hour day would be below the EU Lower Action Level. It was expected that TKRs would have higher percentages of decibels at 80.0dB(A) or above, given the greater time spent sawing in this procedure. Exposure to levels above 90dB (which occurred in every case) for short time periods is proven to cause irreversible loss of hearing. Minor damage accumulates throughout a career of 40 years, and can result in NIHL. Conclusion. Tools used in orthopaedic theatre produce impulse noises that can cause NIHL. Average daily exposure can be assumed to be acceptable. Further investigation is required

Patient specific instrumentation (PSI) for elective knee replacements in arthritic knees with severe deformities and in revision scenarios is becoming increasingly popular due to the advantage of restoring the limb axes, improved theatre efficiency and outcomes. Currently available systems use CT scan or MRI for pre-operative templating for design considerations with varied accuracy for sizing of implants.

We prospectively evaluated 200 knees in 188 patients with arthritic knees with deformities requiring serial clinical assessment, radiographs and CT scans for PSI templating for TruMatch knee system (DepuySynthes, Leeds, UK). The common indications included severe arthritic deformities, previous limb fractures and in obese limbs with difficult clinical assessment. Surgical procedure was performed on standard lines with the customised cutting blocks.

The ‘lead up’ time between the implant request and the operating date was 5 weeks on an average. We compared the pre op CT images and the best fit post-operative x- rays. The sizing accuracy for femur and tibia was 98.93 % and 95.75% respectively. All blocks fitted the femur and tibia. There were no bail outs, no cutting block breakage, 1 patient had residual deformity of 20 degrees, and 1 patient had late infection. The length of hospital stay, economic viability in terms of theatre turnover, less operating time, cost of sterilisation in comparison to conventional knee replacement surgery with other factors being unchanged was also assessed.

The projected savings was substantial along with improved geometrical restoration of the knee anatomy. We recommend the use of PSI based on CT scan templating in difficult arthritic knees.

The natural knee allows multi-planar freedoms of rotation and translation, while retaining stability in the antero-posterior direction. It allows flexion with roll back, and medial, lateral and central rotation movements. The natural femoral condyles of the knee are spiral, therefore inducing a side to side translatory movement during flexion and extension. Incorporating all these features is vital in successful knee replacement design. The different knee designs currently in use demonstrate different deficiencies in knee function. A study of 150 Posterior Cruciate (PCL) Retaining Total Knee Replacements [1] has shown that in 72% of knees direct impingement of the tibial insert posteriorly against the back of the femur was responsible for blocking further flexion. The mean pre-operative range of flexion was 105° and post-operative was 105.9°. For every 2mm decrease in posterior condylar offset, the maximum flexion was reduced by 12.2°. The major disadvantage of the Posterior Stabilised (PS) Total Knee Replacement is gross anterior to posterior mid-flexion instability [2]. The Medial Rotation Total Knee Replacement is good in mid-flexion but not in high flexion where the femur slides forward on the tibia leading to impingement. The Birmingham Knee Replacement (BKR) is a rotating platform knee design which is stable throughout the range of flexion. In high flexion, the BKR brings the femur to the back of the tibia. The BKR also has spiral femoral condyles, matching the natural kinematics of the knee. The combined static and dynamic effect is 10mm lateral translation of the femur in flexion and vice versa in extension. Results for seventy nine BKRs (in seventy two patients) show the best Oxford Knee Score of 12 at follow up – excluding ten patients whose inferior scores were due to other pathologies. Knee flexion results show a 21° post-operative improvement in range of flexion. On objective independent testing, maximum walking speed is slower for patients with a standard knee replacement (6.5km/h) and the loading through the replaced side does not match the normal side. Comparatively, patients with a BKR have a faster maximum walking speed of 11km/h and the loading closely matches that of the normal knee. Studies based on the National Joint Register PROMs data [2] show that nearly thirty percent of Total Knee Replacement patients are not much better since their operation. A lot of improvement is needed in the design of knee replacements in order to achieve better function for knee replacement patients

Introduction

To meet the demands of younger more active patients more robust pre-clinical wear testing methods are required, in order to simulate a wider range of activities. A new electromechanical simulator (Simulation Solutions, UK) with a greater range of motion, a driven abduction/adduction axis and improved input kinematic following has been developed to meet these requirements, as well as requirements of the relevant international standards. This study investigated the wear of a fixed bearing total knee replacement using this new electromechanical knee simulator, comparing with previous data from a pneumatic simulator.

Introduction. Total knee arthroplasty (TKA) has proven clinical success with reported longterm survivorship of 92% in the elderly population. Concerns regarding increased loosening rates and potential need for multiple revision surgeries in patients younger than 60 years have traditionally discouraged TKA in younger patients. The purpose of this study was to review the longterm clinical and radiographic results of patients under the age of 45 yrs who underwent a total knee replacement. Materials and Methods. A retrospective review of our institutional database was performed between January 1996 and December 2004 The criteria for inclusion in the study were as follows: age 45 years or younger at index arthroplasty, cemented condylar prosthesis, and a minimum follow-up of 9 years. A total of 39 consecutive primary cemented condylar knee arthroplasties in patients with end stage arthritis were performed in 36 patients who were 45 years or younger. The median length of followup was 13.6 years. There were 18 men and 21 women. The mean age was 40.6 years (range, 28–44). There were 23 right, 16 left, and 3 bilateral procedures. The mean body mass index was 31.2 kg/m2. Clinical and radiological evaluations were performed before surgery and at 6 weeks, 3 months, 1 year and every 2 years subsequently. Knee scores were calculated using the Knee Society Clinical Rating Scores (KSCRS), SF-12 and WOMAC scores to assess pre, and post-operative function. Postoperative anteroposterior and lateral views were assessed for femoral and tibial component position, alignment, and presence or progression of radiolucent lines at the bone-cement and prosthesis-cement interfaces. Statistical analysis was performed using the 2-sample test or Wilcoxon rank sum test for comparison of continuous variables. Kaplan-Meier analysis of implant survival was performed with failure defined as femoral component revision due to any cause. Results. There was a statistically significant improvement in clinical outcome measures between pre and post-operative SF-12, WOMAC, and KSCRS validated scoring systems. 41% of patients had previous surgery prior to the TKA with 87% of patients receiving a cruciate sacrificing TKA and 64% of patients receiving a patellar resurfacing. There were 4 revisions in total, 2 patients were revised for pain, 1 for instability and 1 for infection treated with a single stage revision, the average time to revision was 3 years. There were no cases of aseptic loosening with an overall survival of 89.8% at an average follow-up of 13.6 yrs. The Kaplan-Meier estimated survival rate to revision was estimated to be % at 10 years and % at 15 years Radiographic assessment did not reveal any evidence of component migration, malalignment or radiolucencies at final follow up. There was no evidence of progressive radiolucencies noted on zonal analysis around both tibial and femoral components on serial radiographs in any patient. Conclusion. Excellent clinical outcomes are reported for patients 45 years of age or less who have undergone TKA. For the young patient who is not a candidate for other joint conserving or preserving procedures, Total Knee Replacements provide a successful longterm outcome

Tibial and femoral loosening are major causes for implant failure in total knee arthroplasty. Jefferey (1991) reported a significantly lower rate of loosening when varus or valgus was within 3 degrees of mechanical axis in an eight year follow up. Coulle (Dec1999) reported 48% unacceptable alignment in non-navigated knees and Reed (Aug 2002) reported 35% alignments deviating more than 3 degrees from mechanical axis when navigation was not used.

We report our series of 286 navigated knee replacements using the Aesculap Search system (21 cases) and the Aesculap e-motion versions 4.2, 4.3 and 4.4 (265 cases) between April 2003 and December 2012 by the author (A.D) and analysed the correction achieved against the zero mechanical axis. Postoperative measurement of the angles on long length films was done in 23 cases. This matched with the intraoperative corrections achieved as studied using per-operative computer data stored for every case. We continued to use the data stored in the AESCULAP System to correlate the findings in the rest of the cases. The average mechanical axis achieved was 1.3 degrees. All cases had mechanical axes within 3 degrees.

We were thus able to achieve a high level of correction of the mechanical axes predictable to achieve better clinical outcomes.

Introduction. Valgus knees are generally more difficult to get acceptable alignment and balance than the varus knee. Most of these are due to anatomical variations in both the diaphysis of the femur, with low valgus angles (angle between the anatomic and mechanical axis of the femur) and the tibial diaphysis. In addition there are those with dysplastic lateral distal femoral condyle s and low external femoral angles (below 84 degrees). Aim. To assess the clinical results, patient satisfaction and alignment and balance achieved in those with a pre-operative mechanical valgus above 10 degrees. Method. There were 1038 Total Knee Replacements (TKR) performed by one surgeon from 2006 to 2012. 274 (26%) had valgus mechanical alignments pre operatively, and of this group there were 84 (31%) that had mechanical axis (MA) > 9degrees. Long leg X-rays were used to assess pre and post-operative and component alignment. Patients were assessed by means of the Knee Society Score and a satisfaction rating. Results. 64% had a post-operative MA < 4 degrees, 34% were between 4 and 6 and 2% > 6 degrees. 89%, 85% and 100% reported knee satisfaction respectively for these 3 groups. The valgus knees in this series with a pre-operative MA = 9 degrees had a satisfaction rate of 90%. Discussion. Severe valgus knees can be adequately corrected and balanced but need significant release or relative lengthening of the LCL by epicondylar osteotomy. Final alignment did / did not affect outcome or satisfaction. NO DISCLOSURES

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.

Summary Statement

Using current analysis/methodology, new implant technology is unlikely to demonstrate a large enough change in patient function to impact on the cost-effectiveness of the procedure.

As allergic reactions to implant wear are gaining more attention [4], the incorporation of ceramic materials to device design appears to be a promising development. In particular, ceramic femoral components of total knee replacements have been designed to produce less wear under standard [1] and adverse [5] implant conditions.

Whereas the wear reduction effect of ceramics is generally accepted for hip implants, the corresponding effect for knee implants is not proven. Ezzet et al. reported a wear reduction of 42% for standard wear conditions [2] and of 55% for adverse wear conditions [3] when compared to a geometrically identical CoCr femoral component. In contrast to these findings, an analysis of the EndoLab® database has indicated wear rates of ceramic knee implants that are comparable to traditional low wear material couplings (Figure 1), and are within the range of clinically established devices.

The purpose of this study was to directly compare two TKR designs, one fixed bearing and one mobile bearing, each made of traditional CoCr to one made of alumina matrix composite (BIOLOX®delta, CeramTec, Germany) ceramic material. The BPK-S Rotating Platform System (Peter-Brehm, Germany; Figure 2) and the MULTIGEN PLUS fixed bearing (Lima, Italy) were knee simulator wear tested according to ISO 14243-1 (2002). A total of three specimens plus one loaded soak control for each group (four groups in total) was subjected to 5 million standard gait cycles. The anterior-posterior (AP) and internal-external rotational (IE) motion of the implants resulting from the external load application of this force controlled test was recorded continuously. Wear was determined gravimetrically. The surface appearance of contact areas was analyzed by light microscopy and particle analysis was performed according to ISO 18129. For the mobile bearing groups, a mean wear rate of 2.47 mg per million cycles (StdDev. 0.38) was determined for the CoCr implant and of 1.10 mg per million cycles (StdDev. 0.46) for the BIOLOX®deltaimplant (Figure 3). The total AP and IE motion of the two groups did not differ. However, motion during stance phase was considerably higher for the ceramic group, indicating reduced frictional resistance (data not shown).

For the fixed bearing groups, a mean wear rate of 12.01 mg per million cycles (StdDev. 3.28) was determined for the CoCr implant and of 1.78 mg per million cycles (StdDev. 0.40) for the BIOLOX®delta implant.

Based upon the EndoLab® experience the ceramic total knee replacements tested perform as good as the best performing metallic total knee replacements. However it can be concluded that for the two implant systems tested the wear rate is reduced by more than 50% by using ceramic on polyethylene articulation when compared to an identical cobald crome design.

Bilateral simultaneous total knee replacement surgery remains controversial with arguments for and against its use. Doing sequentially staged TKR's is a safer procedure and may have additional benefits as set out below.

If both knees need to be replaced we have often seen that the symptoms of the contralateral knee improve after the one knee is replaced and that patients wait some time before having the opposite knee replaced.