Objectives. All Polyethylene Tibial components in Total Knee Arthroplasty have been in use for some years, studies showing equivalent results to Total Knee Arthroplasty (TKA) with metal-backed Tibial components at 10 years have shown no significant difference between the two on radiostereometric analysis and revision rates[1]. Post operative patient outcome data using standard metal-backed Tibial components is widely reported in the literature. This study is looking at patient outcomes following All-polyethylene tibial component TKA. We hypothesize that using standard patient outcome measures, an improvement comparable with that expected for metal-backed tibial component TKA will be shown with All-polyethylene tibial component TKA. Methods. Between August 2006 and August 2008, 229 all-polyethylene tibial component TKA were implanted at the elective orthopedic unit. The choice of implant was entirely dependent on surgeon's preference. Of the 229 patient's, 225 details were available for review, 27 did not wish to take part in the study and 1 patient died a year following surgery of an unrelated illness. The remaining 197 patients agreed to take part in the study. The patient's were contacted either in person or over the telephone and asked to completed questionnaires for standard knee scoring. These included: the Oxford Knee Score (OKS), the WOMAC Score and the SF-12 Score, both pre-operatively and post operatively. Results. All three Scoring systems used showed an overall improvement post-operatively, as would be reasonably be expected. The results for the OKS, WOMAC and SF-12 all showed an improvement comparable with that expected for metal-backed tibial component TKA. Conclusions. Total Knee Arthroplasty using an all-polyethylene tibial component has been shown with these early results to be a reasonable alternative to metal-backed options offering some advantages. [1,2]

Background and Purpose:. Modularity of the tibial component in total knee arthroplasties (TKA) has many surgical benefits. It also reduces inventory related expenses but increases implant cost. The resulting locking mechanism micromotion that leads to non-articular microwear and has been an accepted consequence of modularity. The purpose of this study is to evaluate the risk of revision (all-cause and aseptic) of a monoblock all-polyethylene tibial component compared to a fixed bearing modular tibial construct with the same articular geometry while adjusting for potential confounders in a community based sample of primary TKAs. In addition, younger and older patient specific risk of revision was evaluated. Method:. A retrospective analysis of prospectively collected data from a Total Joint Replacement Registry (TJRR) was conducted. All 27,657 primary TKAs enrolled between 2001 and 2010 performed for any diagnosis with the same implant from a single manufacturer were included in the study. Patient characteristics, as well as surgeon, hospital, procedure, and implant characteristics were compared by the main exposure of interest, i.e. the type of tibial prosthesis (monoblock all-polyethylene vs. metal-backed modular). The main endpoints of the study were all-cause and aseptic revisions only. Descriptive statistics and Cox-regression models were employed. Hazard ratios (HR) and 95% confidence intervals (CI) are provided. Results:. The cohort consisted of 2,306 (8.3%) monoblock all-polyethylene tibial component TKAs and 25,351 (91.7%) modular metal-backed components. No gender, diagnosis or diabetic status differences were noted between the monoblock and modular cohorts. Patients with monoblock tibias were older (71.8 vs. 68.1 yrs, p < 0.001) and had a lower body mass index (30.1 vs. 31.6 kg/m2, p < 0.001). The median follow up time of the cohort was 2.9 years (interquartile range 1.2–5.1 years), during which 22 (0.95%) monoblock arthroplasties and 550 (2.17%) modular arthroplasties were revised. The all-cause revision rate/100 years of follow-up for monoblock and modular cohorts was 0.30 and 0.65, respectively. Their aseptic revision rate/100 of follow-up was 0.18 and 0.35, respectively. In adjusted overall models, the risk of all-cause revision (HR = 0.51, 95% CI 0.33–0.78, p = 0.002) and aseptic revision (HR = 0.59, 95% CI 0.29–1.19, p = 0.139) was lower in the monoblock cohort compared to the modular cohort. In adjusted models of patients 65 years and older, the risk of all-cause revision is 0.59 (95% CI 0.35–0.99, p = 0.045) in the monoblock cohort compared to modular cohort. In adjusted models of patients younger than 65 years old, the risk of all-cause revision (HR = 0.26, 95% CI 0.10–0.72, p = 0.010) and aseptic revision (HR = 0.27, 95% CI 0.11–0.65, p = 0.003) were lower in the monoblock compared to the modular cohort. Conclusion:. For our entire cohort of 27,567 primary fixed bearing TKAs, monoblock all-polyethylene tibial components had a 49% lower risk of revision for all-causes and a 41% lower risk of aseptic revision when compared to modular metal-backed tibial constructs. For patients younger than 65 years old, the all-polyethylene component had a 74% lower risk of all-cause revision and a 73% lower risk of aseptic revisions when compared to modular tibial constructs

Introduction. The precise indications for tibial component metal backing and modularity remain controversial in routine primary total knee arthroplasty. This is particularly true in elderly patients where the perceived benefits of metal backing such as load redistribution and the reduction of polyethylene strain may be clinically less relevant. The cost implications for choosing a metal-backed design over an all-polyethylene design may exceed USD500 per primary knee arthroplasty case. Methods. A prospective randomised clinical trial was carried out at the QEII Health Sciences Centre, Halifax, Nova Scotia, to compare modular metal-backed versus an all-polyethylene tibial component. Outcome measures included clinical range of motion, radiographs, survivorship, Knee Society Clinical Rating System, WOMAC and SF-12. Results. 116 patients requesting primary knee arthroplasty were recruited and randomised between the Smith & Nephew Genesis I non-modular (57) and modular (59) tibial designs between September 1995 and August 1997. At 10 years clinical follow-up, 4 implant revisions or intention-to-revise decisions were recorded in the metal-tray/modular group of which 2 were for aseptic tibial component loosening. 2 implant revisions in the all-polyethylene non-modular group were recorded, neither of which were for tibial component loosening. At 5, 7 and 10 year review; the KSCRS, WOMAC and SF12 scores were similar in both groups. As most patients randomised were over seventy years of age, this impacted significantly on the numbers available for longer term review and data was analysed by comparing pre- and post-operative scores for individual patients. Conclusion. There was no difference in performance between the all-polyethylene tibial component and the metal-backed tibial component. The case for using the all-polyethylene tibia in elderly patients is justified on both clinical efficacy and cost-containment grounds

Background. Total knee arthroplasty (TKA) overall is a very reliable, durable procedure. Biomechanical studies have suggested superior stress distribution in metal-backed tibial trays, however, these results have not been universally observed clinically. Currently, there is a paucity of information examining the survival and outcomes of all-polyethylene tibial components. Methods. We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970–2013). There were 28,224 (88%) metal-backed and 3,715 (12%) all-polyethylene tibial components. The metal-backed and all-polyethylene groups had comparable demographics with respect to sex distribution (57% female for both), mean age (67 vs. 71 years), and mean BMI (31.6 vs. 31.1). Mean follow-up was 7 years (maximum 40 years). Results. The purpose of this investigation was to analyze the outcomes of all-polyethylene compared to metal-backed components in TKA and to determine: (1) is there a difference in overall survival? All-polyethylene tibial components had improved survivorship (P<0.0001) and metal-backed tibias were at increased risk of revision (HR 3.41, P<0.0001); (2) Does body mass index (BMI) or age have an effect on survival of all-polyethylene compared to metal-backed tibial components? All-polyethylene tibias had improved survival (P<0.01) in all age groups except in patients 85 years or greater, where there was no difference (P=0.16). All-polyethylene tibial components had improved survival (P<0.005) for all BMIs except in the morbidly obese (BMI ≥40) where there was no difference (P=0.20); (3) Is there an increased risk of post-operative infection? Metal-backed tibial components were found to have an increased risk of infection (HR 1.60, P=0.003); (4) Is there a difference in the rate of reoperation and post-operative complications? Metal-backed tibial components were found to have an increased risk of reoperation (HR 1.84, P<0.0001). Conclusions. The use of all-polyethylene tibias should be considered for the majority of patients, regardless of age and BMI

Background: Total knee arthroplasty (TKA) overall is a very reliable, durable procedure. Biomechanical studies have suggested superior stress distribution in metal-backed tibial trays, however, these results have not been universally observed clinically. Currently, there is a paucity of information examining the survival and outcomes of all-polyethylene tibial components. Methods: We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970–2013). There were 28,224 (88%) metal-backed and 3,715 (12%) all-polyethylene tibial components. The metal-backed and all-polyethylene groups had comparable demographics with respect to sex distribution (57% female for both) mean age (67 vs. 71 years), and mean BMI (31.6 vs. 31.1). Mean follow-up was 7 years (maximum 40 years). Results: The purpose of this investigation was to analyze the outcomes of all-polyethylene compared to metal backed components in TKA and to determine (1) is there a difference in overall survival? All-polyethylene tibial components had improved survivorship (P<0.0001) and metal backed tibias were at increased risk of revision (HR 3.41, P<0.0001). (2) Does body mass index (BMI) or age have an affect on survival of all-polyethylene compared to metal-backed tibial components? All-polyethylene tibias had improved survival (P<0.01) in all ages groups except in patients 85 years or greater, where there was no difference (P=0.16). All-polyethylene tibial components had improved survival (P<0.005) for all BMI's except in the morbidly obese (BMI ≥40) where there was no difference (P=0.20). (3) Is there an increased risk of post-operative infection? Metal-backed tibial components were found to have an increased risk of infection (HR 1.60, P=0.003). (4) Is there a difference in the rate of reoperation and post-operative complications? Metal-backed tibial components were found to have an increased risk of reoperation (HR 1.84, P<0.0001). Conclusions: The use of all-polyethylene tibias should be considered for the majority of patients, regardless of age and BMI

Background: Total knee arthroplasty (TKA) overall is a very reliable, durable procedure. Biomechanical studies have suggested superior stress distribution in metal-backed tibial trays, however, these results have not been universally observed clinically. Currently there is a paucity of information examining the survival and outcomes of all-polyethylene tibial components. Methods: We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970–2013). There were 28,224 (88%) metal-backed and 3,715 (12%) all-polyethylene tibial components. The metal-backed and all-polyethylene groups had comparable demographics with respect to sex distribution (57% female for both) mean age (67 vs. 71 years), and mean BMI (31.6 vs. 31.1). Mean follow-up was 7 years (maximum 40 years). Results: The purpose of this investigation was to analyze the outcomes of all-polyethylene compared to metal-backed components in TKA and to determine (1) is there a difference in overall survival? All-polyethylene tibial components had improved survivorship (P<0.0001) and metal-backed tibias were at increased risk of revision (HR 3.41, P<0.0001). (2) Does body mass index (BMI) or age have an effect on survival of all-polyethylene compared to metal-backed tibial components? All-polyethylene tibias had improved survival (P<0.01) in all ages groups except in patients 85 years or greater, where there was no difference (P=0.16). All-polyethylene tibial components had improved survival (P<0.005) for all BMI's except in the morbidly obese (BMI ≥40) where there was no difference (P=0.20). (3) Is there an increased risk of post-operative infection? Metal-backed tibial components were found to have an increased risk of infection (HR 1.60, P=0.003). (4) Is there a difference in the rate of reoperation and post-operative complications? Metal-backed tibial components were found to have an increased risk of reoperation (HR 1.84, P<0.0001). Conclusions: The use of all-polyethylene tibias should be considered for the majority of patients, regardless of age and BMI

Background. Total knee arthroplasty (TKA) overall is a very reliable, durable procedure. Biomechanical studies have suggested superior stress distribution in metal-backed tibial trays, however, these results have not been universally observed clinically. Currently, there is a paucity of information examining the survival and outcomes of all-polyethylene tibial components. Methods. We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970–2013). There were 28,224 (88%) metal-backed and 3,715 (12%) all-polyethylene tibial components. The metal-backed and all-polyethylene groups had comparable demographics with respect to sex distribution (57% female for both) mean age (67 vs. 71 years), and mean BMI (31.6 vs. 31.1). Mean follow-up was 7 years (maximum 40 years). Results. The purpose of this investigation was to analyze the outcomes of all-polyethylene compared to metal-backed components in TKA and to determine (1) is there a difference in overall survival? All polyethylene tibial components had improved survivorship (P<0.0001) and metal-backed tibias were at increased risk of revision (HR 3.41, P<0.0001). (2) Does body mass index (BMI) or age have an effect on survival of all-polyethylene compared to metal-backed tibial components? All-polyethylene tibias had improved survival (P<0.01) in all ages groups except in patients 85 years or greater, where there was no difference (P=0.16). All-polyethylene tibial components had improved survival (P<0.005) for all BMI's except in the morbidly obese (BMI ≥40) where there was no difference (P=0.20). (3) Is there an increased risk of post-operative infection? Metal-backed tibial components were found to have an increased risk of infection (HR 1.60, P=0.003). (4) Is there a difference in the rate of reoperation and post-operative complications? Metal-backed tibial components were found to have an increased risk of reoperation (HR 1.84, P<0.0001). Conclusions. The use of all-polyethylene tibias should be considered for the majority of patients, regardless of age and BMI

Introduction. There is a demand for longer lasting arthroplasty implants driving the investigation of novel material combinations. PEEK has shown promise as an arthroplasty bearing material, with potentially relatively bio inert wear debris [1]. When coupled with an all-polyethylene tibial component this combination shows potential as a metal-free knee. In this study, the suitability of PEEK Optima® as an alternative to cobalt chrome for the femoral component of total knee replacements was assessed using experimental knee wear simulation under two kinematic conditions. Methods. Three cobalt chrome and three injection moulded PEEK Optima® (Invibio Biomaterial Solutions, UK) femoral components of similar geometry and surface roughness (mean surface roughness (Ra) ∼0.02µm) were coupled with all-polyethylene GUR1020 (conventional, unsterilised) tibial components in a 6 station ProSim knee simulator (Simulation Solutions, UK). 3 million cycles (MC) of wear simulation were carried out under intermediate kinematics (maximum anterior-posterior (AP) displacement 5mm) followed by 3MC under high kinematics (AP 10mm) [2] with 25% serum as the lubricant. The wear of the tibial component was assessed gravimetrically. At each measurement point, the surface roughness of the femoral components was determined using contacting profilometry and throughout testing, the bulk lubricant temperature was monitored close to the articulating surfaces. Statistical analysis was carried out using ANOVA, with significance at p<0.05. Results. Figure 1 shows the wear rate of the all-polyethylene tibial components. After 3MC of intermediate kinematics, the mean wear rate of UHMWPE articulating against cobalt chrome was 1.0±2.3mm3/MC and against PEEK was similar (p=0.06) 2.5±0.8mm3/MC. Scratches were apparent on the surface of the PEEK implant in the AP direction significantly (p<0.05) increasing mean surface roughness of the PEEK components (Table 1) compared to pre-test values. The surface topography of the cobalt chrome components (Table 2) was similar to pre-test measurements. Increasing AP displacement caused no significant increase in the wear of the tibial inserts against either material. Under intermediate kinematics, the mean bulk lubricant temperature was 28.0±0.7°C for cobalt chrome and significantly higher (p<0.001) for PEEK, 29.5±0.1°C; kinematic conditions had no effect on the lubricant temperature. Conclusions. This study showed a similar wear rate of all-polyethylene tibial components against PEEK and cobalt chrome femoral components of similar initial surface topography and geometry. Wear simulation with a higher AP displacement did not increase the wear of the polyethylene, in contrast to other designs of knee replacements, potentially due to the low conforming geometry of the implant [3]. The linear scratching on the surface of the PEEK implants did not increase the wear rate of the tibial components and the surface did not deteriorate further between 3 and 6 MC. A higher mean lubricant temperature was measured with PEEK femoral components, which was attributed to the higher friction of the PEEK-PE bearing couple. However it is not known whether this is clinically relevant or an artefact of the continuous running of the simulator. PEEK Optima® shows promise as the femoral component in a metal-free knee

While the vast majority of total knee replacements performed throughout the world employ a modular metal-backed tibial tray, and not an all-polyethylene tray, this issue remains controversial. Proposed advantages to a metal-backed tray include: a) decreased bending strains, b) reduces compressive stresses in the cement and cancellous bone beneath the baseplate (especially in asymmetric loading), c) distributes load more evenly across the interface. Proposed advantages of an all-polyethylene tray include: a) cost reduction, b) reduced polyethylene thickness with the same amount of bone resection, c) increased tensile stresses at the interface during eccentric loading. The challenge is at present we don't know the >10-year track record of current generation tibial components. This debate centers on the <60-year-old. This is the most difficult patient in total knee arthroplasty with higher revision rates than an older cohort. It makes sense to use an all-polyethylene tibia if the revision rates turn out to be similar and you don't intend to do a polyethylene exchange in the future. It makes sense to do a modular tray if the results are similar, but there is an intention to do a polyethylene exchange in the future. If either one of these implants choices has a lower cumulative revision rate, then that is the implant of choice at present. However, we need to understand that at present we don't know if the results of current generation all-polyethylene tibial components will indeed be equal to metal-backed components. The most recent data from the Australian registry suggests that in fact all-polyethylene tibial components have a higher failure rate than metal-backed components when looking at the entire class of design. This would be expected to be even more significant in the younger patient

There is no question that excellent long-term results have been demonstrated with all-polyethylene tibial components. Moreover, improvements in polyethylene to increase wear resistance, maintain mechanical strength, and improve oxidative resistance lend even greater credence to the use of an all-polyethylene tibial component. There are several issues of concern. In revision knee replacement for reasons such as patellofemoral problems where the components are otherwise ideal, the arthrotomy performed during the revision usually creates a slight laxity requiring a thicker polyethylene or even a different tibial conformity. With an all-polyethylene tibia, this would require full component revision. It is also true that, even after careful trial reduction, the surgeon occasionally will find that the final construct is slightly lax requiring a thicker final insert. This again is difficult in the situation of all-polyethylene tibia. One of the advantages of an all-polyethylene tibia is to avoid back-sided wear that posed a substantial problem in the past. Most component systems have successfully dealt with a problem of back-sided wear making the advantage of a nonmodular all-polyethylene tibia moot. Finally, in a modular system, the surgeon has the advantage of cementing all components with the tibial trial and then having the ability to remove the trial component, clear the back of the knee and insert the final insert. Lowering health care costs is a laudable and necessary endeavor. We must choose TKR implants to fit patient demand and not overuse or underuse technology and know the true cost of the implants we use

There is no question that excellent long-term results have been demonstrated with all-polyethylene tibial components. Moreover, improvements in polyethylene to increase wear resistance, maintain mechanical strength, and improve oxidative resistance lend even greater credence to the use of an all-polyethylene tibial component. There are several issues of concern. In revision knee replacement for reasons such as patellofemoral problems where the components are otherwise ideal, the arthrotomy performed during the revision usually creates a slight laxity requiring a thicker polyethylene or even a different tibial conformity. With an all-polyethylene tibia, this would require full component revision. It is also true that, even after careful trial reduction, the surgeon occasionally will find that the final construct is slightly lax requiring a thicker final insert. This again is difficult in the situation of all-polyethylene tibia. One of the advantages of an all-polyethylene tibia is to avoid back-side wear that posed a substantial problem in the past. Most component systems have successfully dealt with the problem of back-side wear making the advantage of a nonmodular all-polyethylene tibia moot. Finally, in a modular system, the surgeon has the advantage of cementing all components with the tibial trial and then having the ability to remove the trial component, clear the back of the knee and insert the final insert

Metal-backed tibial components in total knee arthroplasty (TKA) currently dominate the orthopaedic market due to intra-operative flexibility afforded by modularity. Metal-backing was first used in TKA as a method to potentially improve loading distributions over the tibial plateau at the interface between the prosthesis and the supporting cancellous bone. Many studies have compared metal-backed and all-polyethylene tibial components with variable survivorship. We have found decreased clinical survivorship with all-polyethylene Anatomic Graduated Component (AGC) TKA's (Biomet, Inc, Warsaw, Indiana) compared to the non-modular metal-backed design at 10-year follow up, 68% vs 98%, respectively. Loosening or bony collapse beneath the medial plateau accounted for 74% of failures in our AGC all-polyethylene cohort. We hypothesised that all-polyethylene tibial components may lead to increased strains in the proximal tibia with the AGC-TKA design, possibly correlating to osseous overload in the medial compartment and accounting for the increased observed rates of clinical failures in the all-polyethylene group. Finite element studies and our lab studies have shown that metal-backing reduces system stresses in the PMMA bone cement, as well as in the underlying cancellous bone. Overall, in every measurement region with a statistically significant difference in shear strain, higher strain was measured in the all-polyethylene implanted tibiae compared to metal-backed components. Statistically significant increases in strain from 126 μɛ (p=0.0131) to 745 μɛ (p=0.0011) and from 40% (p=0.0010) to 587% (p=0.0054) were seen in the all-polyethylene experimental group. We believe this may correlate with the higher failure rates we have observed in the AGC all-polyethylene cohort compared to the metal-backed cohort from our institution. Other all-poly TKA designs with varied articular congruities may afford improved or equal survivorship to metal backed implants at a reduced cost

Implant selection in TKA remains highly variable. Surgeons consider pre-operative deformity, patient factors such as BMI and bone quality, surgical experience, retention or substitution for the PCL, type of articulation and polyethylene, cost, and fixation with or without cement. We have most frequently implanted the same implant for the majority of patients. This is based on the fact that multiple large series of TKAs have demonstrated that the most durable TKAs have been non-modular metal-backed tibial components, retention of the PCL, with a cemented all-polyethylene patellar component. Polymer wear must be addressed for long-term durability. One method for reducing polyethylene wear is eliminating modularity between a metal-backed tray and the articular bearing surface. This can be done with a metal-backed implant as with the IB-1, AGC, Vanguard Mono-lock, or with elimination of the metal backing via a one piece all-polyethylene tibial component. The all-polyethylene implants appear design and patient sensitive. We observed higher clinical failure rates in a flat-on-flat design. Other authors have observed improved survivorship with coronal dishing of the articular surfaces which centralises osseous stresses. All-polyethylene implants have promise in the future but require proven design and fixation design features

Introduction:. The earliest evidence of particle-induced response is found in the synovium, leading to osteolytic defect. The degree of synovitis can be quantified by magnetic resonance imaging (MRI). This is the first long-term, prospective, matched-pair study using MRI to analyze wear-induced synovitis and osteolysis between rotating-platform posterior-stabilized (RP-PS), fixed-bearing metal-back (FB-MB), and all-polyethylene tibial (APT) designs in active patients with identical femoral components and polyethylene. Methods:. From September 1999 to October 2001, a matched-pair analysis of 24 TKAs (18 patients, 3 groups: 8 RP-PS, 8 FB-MB, and 8 APT) was performed. TKAs were matched for age, sex, body mass index (BMI), and University of California Los Angeles (UCLA) activity scores. All patients underwent MRI using MAVRIC (multi-acquisition variable-resonance image combination) knee protocol designed to reduce metal susceptibility artifact. Images were evaluated for volumetric measure of synovitis and/or osteolysis and presence of fibrous membrane formation at the cement-bone interface. Results:. The mean age was 64 ± 5 years (59–72). The mean follow-up was 11.6 ± 0.7 years (10–13). The mean UCLA score at the time of surgery was 8.5 ± 2.6 (5–10). Reactive synovitis was observed in 6 RP-PS (75%), all 8 FB-MB (100%), and 6 APT (75%) knees. There was a significant difference between the volumetric synovitis in RP-PS (4046 mm3 ± 4502 mm3), and FB-MB knees (24498 mm3 ± 22248 mm3), p < 0.001. Osteolysis with bone loss more than 4 mm was seen in 3 FB-MB, 2 APT, but in none of the RP-PS knees. There was no statistical difference for osteolysis between the three designs. Conclusion:. Based of this study, it appears that particle induced synovitis is evident in all 3 types of bearing surfaces, however, it is significantly less in the RP-PS group. This is in contradiction to the report of retrieval studies

INTRODUCTION. we have previously reported that bone preparation is quite precise and accurate relative to a preoperative plan when using a robotic arm assisted technique for UKA. However, in that same study, we found a large variation between intended and final tibial implant position, presumably occuring during cement curing. In this study, we reviewed a subsequent cohort of patients in which the tibial and femoral components were cemented individually with ongoing evaluation of tibial component position during cement curing. METHODS AND MATERIALS. Group 1 comprised the simultaneous cementing techniquegroup of patients, previously reported on, although their x-rays were re-analyzed. Group 2 consisted of the individual cementing technique cohort. All implants were identical, specifically a flat, inlay all-polyethylene tibial component. Postoperative x-rays from each cohort of patients were evaluated using image analysis software. Statistical evaluation was performed. RESULTS. In Group 1, average bone preparation was 5.13 + 2.70 degrees of varus and 7.40 + 2.59 degrees of posterior slope. Final implant position was 3.56 + 1.93 degrees of varus and 5.19 + 3.37 degrees of slope. The variance from intended position was 2.31 + 1.74 degrees of varus and 3.80 + 2.90 degrees of slope. For Group 2, average bone preparation was 5.26 + 3.70 degrees of varus and 5.49+ 2.39 degrees of posterior slope. Final implant position was 6.58 + 3.40 degrees of varus and 6.11 + 2.39 degrees of slope. The variance from intended position was 1.82 + 1.42 degrees of varus and 1.39 + 1.48 degrees of slope. ANOVA revealed no differences between groups regarding bone prep in the coronal plane, final implant slope, or variation from intended coronal position. However, bone prep in the sagittal plane showed statistically significant more slope for Group 1 (p = 0.03), increased slope in Group 2 (p=0.004), and greater variation from intended sagital position for Group 1. CONCLUSIONS. Independent cementing of implants showed decreased variation in final tibial component position. However, some implants showed up to 6 degrees of malposition from the intended position. We believe this to be a shortcoming of the inlay style of tibial component for UKA, which even cannot be overcome with the precision and accuracy of a robotic arm assistant

Two big problems exist with the all-polyethylene cemented tibial component; the polyethylene and the cement. The polyethylene is too weak and flexible to bear high tibial load, so it deforms and loosens. The interface stresses are too high when two flexible structures are poorly bonded and heavily loaded. Modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-80's for versatility and to facilitate screw fixation for cementless implants. These designs allow exchange of various polyethylene thicknesses, and aids the addition of stems and wedges. Other advantages include the reduction of inventory, and the potential for isolated tibial polyethylene exchanges as a simpler revision procedure. Several studies have documented the high failure rate of isolated polyethylene exchange procedures, because technical problems related to the original components are left uncorrected. However, revision for wear is the simplest revision ever!. Since the late 1980's the phenomena of polyethylene wear and osteolysis has been observed much more frequently when compared with earlier eras. The reasons for this increased prevalence of synovitis, progressive osteolysis, and severe polyethylene wear remain unclear. There is some association with the widespread use of both cementless and cemented modular tibial designs. Improved polyethylene attachment is the answer even if a screw, a wire, or a pin is needed. Do not abandon the module tibia

Two big problems exist with the all-polyethylene cemented tibial component; the polyethylene and the cement. The polyethylene is too weak and flexible to bear tibial load, so it deforms and loosens. The interface stresses are too high when two flexible structures are poorly bonded and heavily loaded. Modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-1980s for versatility and to facilitate screw fixation for cementless implants. These designs allow exchange of various polyethylene thicknesses, and aid the addition of stems and wedges. Other advantages include the reduction of inventory, and the potential for isolated tibial polyethylene exchanges as a simpler revision procedure. Several studies have documented the high failure rate of isolated polyethylene exchange procedures, because technical problems related to the original components are left uncorrected. However, revision for wear is the simplest revision ever!. Since the late 1980s the phenomena of polyethylene wear and osteolysis have been observed much more frequently when compared with earlier eras. The reasons for this increased prevalence of synovitis, progressive osteolysis, and severe polyethylene wear remain unclear. There is some association with the widespread use of both cementless and cemented modular tibial designs. Improved polyethylene attachment is the answer even if a screw, a wire, or a pin is needed. Do not abandon the modular tibia on any patient

Two big problems exist with the all-polyethylene cemented tibial component—the polyethylene and the cement. The polyethylene is too weak and flexible to bear tibial load, so it deforms and loosens. Isoelastic material has never worked, and it never will. The interface stresses are too high when two flexible structures are poorly bonded and heavily loaded. Critical review of the literature fails to make a convincing case for use of cement in TKA. Many studies demonstrate clinical, mechanical, and biological failure when cement is used for fixation. Work by Ryd et al. has shown that initial migration within the first few months diminished rapidly after the first 6 months with virtually no additional movement for years after. They also found that cemented components do not remain rigidly fixed to bone long-term, but loosen enough to move 0.2 to 2.1 mm at the bone-cement interface with provocative testing. Although bone-ingrowth tibial components migrate slightly more initially than cemented ones do, they stabilise and do not sink progressively. Screw fixation adds rigidity, but does not seem to improve results. Rigidity of initial fixation is the most important feature after alignment to ensure pain-free function after arthroplasty, and can be achieved with press-fit techniques in TKA. Several early reports of bone-ingrowth TKA had inferior results because the tibial component had no stem, peg, or screw fixation, leading to implant migration and loosening. An effective stem has been shown to greatly improve tibial component fixation. The cut upper surface of the prepared tibia has areas that are too weak to withstand the forces that are applied to the surface, and failure in compression is likely unless fixation is augmented. An effective stem also reduces the shear and tensile loads at the bone-prosthesis interface. The effectiveness of compression or compaction of the tibial cancellous bone with an appropriately sized tibial metaphyseal stem has been shown, and probably was a major factor in the long-term success of fixation in our series. Clinical results of TKA with osteointegration techniques for fixation of the femoral and tibial components in our series are comparable with the best series reported with cemented fixation. Many recent studies show significant advantages of osteointegration over cement fixation in TKA. Fixation of implants with PMMA pressed into cancellous bone eventually loosens, and fixation of a metal component to bone cement also is tenuous in most cases. Cement is disappearing rapidly from use in total hip, ankle, and shoulder arthroplasty, and soon will be replaced with osteointegration technique in the knee. Perhaps the most appealing aspect of bone-ingrowth TKA is bone preservation. The ease of revisability because of good bone was encouraging in the components that wore, loosened, or became infected in the current series of TKA. These knees are functioning as well as knees with primary TKA. Should these knees develop additional problems, progressive destruction of bone is unlikely to occur, even if repeated revision is necessary