Introduction: Concerns of backside wear have made the use of the all polyethylene tibial component a viable choice in primary total knee arthroplasty. This study compares the results of two groups, one with a modular tibial component and one with an all polyethylene tibial component. Materials: Between 1986 and 1995, 670 patients underwent total knee arthroplasty using one design with a PCL retaining prosthesis. 500 patients in this group were implanted with a modular tibial component and 170 an all polyethylene tibial tray. The groups were comparable in sex and age (74.1 years for the metal trays and 75.8 years for the all polyethylene components.). The average follow up is 83.9 months for the metal tray group and 74.8 months for the all poly tibial group. The arthroplasties were evaluated annually using the Knee Society guidelines. Results: The postoperative Knee Society Score were 74.5 (metal) and 73.9 (all polyethylene). Joint specific scores for the all polyethylene were slightly higher at 89.9 compared to 88.5 for the metal tray group. Revision rates were 1.8% (3 cases in the polyethylene group) and .8% for the metal group (8 cases). The 3 revisions in the all polyethylene group were for late infections while 5 of the 8 in the metal group demonstrated polyethylene wear/osteolysis. Discussion and conclusions: The clinical results of the all polyethylene group are equal the modular tibial tray group. Because of the excellent radiographic results and non-existent mechanical failure rate to date, the all polyethylene group also provides an opportunity to reduce wear debris with subsequent osteolysis

All polyethylene tibial components (APT) for total knee joint replacement have been recently reintroduced due to their past success and cost savings with respect to knee designs with a metal backed tibial tray (MBT). However, isolated cases of collapse of the medial bone in APT designs have been observed by the authors prompting this investigation. The objective of this study was to investigate the stress/strain distribution within the cancellous bone for the APT and MBT systems, particularly looking at the effects of coverage of the tray over the proximal tibia in each design. A three-dimensional finite element model of the proximal tibia implanted with a tibia tray was generated. An elliptical cylindrical tibia tray with a peg was modeled as being perfectly bonded to a PMMA layer on the superior surface of the cancellous and cortical bone. Gap size between the edge of the tray and outer of the cancellous bone, was introduced in the medial direction. Load was applied on the superior surface of the tibial insert in the medial side. Two lift-off loading cases were used, a low load of 800N (1 body-weight) and a high load of 3200N (4 x BW), both on the medial side. Permanent plastic deformation and collapse was allowed only in the cancellous bone, while all other materials were modeled elastically. Under low load conditions within the elastic limit, introducing a gap between the tray and the cortical bone produced a stress/strain intensity in the cancellous bone beneath the edge of the tray. The strain in the cancellous bone within the APT design was generally 3 times greater than the MBT design, however, peak strain values were similar at the edge of the tray. Whilst the strain increased with the introduction of a gap the resulting strain was not sensitive to the gap size for both designs. Under high load conditions, permanent plastic deformation and bone collapse were observed in the cancellous bone at the edge of the tibial tray in both designs where a gap was introduced. The maximum strain in the cancellous bone was found to be more sensitive to the gap size for the APT design than the MBT design. This can be contributed to the difference in the load transfer through the cancellous bone in the two designs. The MBT design with the more rigid tibial tray transfered higher load through the outer cortical bone than the APT design. The less rigid APT design resulted in progressive collapse of the cancellous bone beneath the tray. Particularly significant was the volume of highly stressed cancellous bone which was 4 times greater in the APT design compared to the MBT design. The results suggest that coverage may be a more important parameter for the APT design than the MBT design. The APT design may, therefore, be more suited to patients with better bone quality

Unicompartmental knee replacements (UKRs) have inconsistent and variable survivorships reported in the literature. It has been suggested that many are revised for ongoing pain with no other mode of failure identified. Using a medial UKR with an all-polyethylene non-congruent tibial component from 2004–7, we noted a revision rate of 9/98 cases (9.2%) at a mean of 39 months. Subchondral sclerosis was noted under the tibial component in 3/9 revisions with well fixed implants, and the aim of this study was to investigate this as a mode of failure. 89 UKRs in 77 patients were investigated radiographically (at mean 50 months) and with SF-12 and Oxford Knee scores at mean follow up 55 months. Subjectively 23/89 cases (25%) had sclerosis under the tibial component. We describe a method of quantifying this sclerosis as a greyscale ratio (GSR), which was significantly correlated with presence/absence of sclerosis (p<0.001). Significant predictors of elevated GSR (increasing sclerosis) were female sex (p<0.001) and elevated BMI (P=0.010) on both univariate and multivariate analysis. In turn, elevated GSR was significantly associated with poorer improvement in OKS (p<0.05) at the time of final follow up. We hypothesise that this sclerosis results from repetitive microfracture and adaptive remodelling in the proximal tibia due to increased strain. Finite element analysis is required to investigate this further, but we suggest caution should be employed when considering all polyethylene UKR implants in older women and in those with BMI >35

The aim was to evaluate the polyethylene wear in an uncemented all polyethylene titanium coated acetabular cup a minimium of ten years post-operatively, and to determine the effect of supine “stress” radiographs on 3-dimensional polyethylene wear, compared with “non-stress” radiographs. Twenty seven hips in twenty five patients were examined, and standard and stress radiographs were performed. All radiographs were analysed using Polywear 5 auto, to measure 2d, 3d, and volumetric wear. Wear measurements were performed three times to minimise error. Radiographs were analysed for osteolysis. There were 12 males and 13 females. Eighteen patients had a diagnosis of osteoarthritis.20 patients had a ceramic head and 7 a metal head. There was no association between wear rates and age, weight, diagnosis, Harris hip score or femoral head type. There was no acetabular osteolysis. The average linear wear was 0.11 +/− 0.08 mm/yr. The stress radiographs did not influence the 2D or 3D wear measurements. This sudy shows a similar wear rate to most published series. The stress radiographs did not influence the wear measurements. The absence of osteolysis is of interest as other uncemented cups have significant osteolysis at ten years

The review of the first 325 Exeter Universal hips reported good long term survivorship despite the majority of cups being metal backed. We have reviewed the long term performance of the concentric all-polyethylene Exeter cups used with the Universal Exeter stem.

Clinical and radiographic outcomes of 263 consecutive primary hip arthroplasties in 242 patients with mean age 66 years (range, 18 to 89) were reviewed. 118 cases subsequently died none of whom underwent a revision. Eighteen hips have been revised; thirteen for aseptic cup loosening, three for recurrent dislocation and two for deep infection. Three patients (four hips) were lost to follow-up. The minimum follow-up of the remaining 123 hips was 10 years (mean 13.3 years, range 10–17). Radiographs demonstrated 4 (4%) of the remaining acetabular prostheses were loose. The Kaplan Meier survivorship at 14.5 years with endpoint revision for all causes is 91.5% (95% CI 86.6 to 96.2%). With endpoint revision for aseptic cup loosening, survivorship is 93.3% (CI 88.8 to 97.8%).

This series included a number of complex cases requiring bone blocks and/or chip autograft for acetabular deficiencies. The concentric all polythene Exeter cup and Exeter stem has excellent long term results particularly when factoring in the complexity of cases in this series.

The review of the first 325 Exeter Universal hips reported good long term survivorship despite the majority of cups being metal backed. We have reviewed the long term performance of the concentric all-polyethylene Exeter cups used with the Universal Exeter stem.

Clinical and radiographic outcomes of 263 consecutive primary hip arthroplasties in 242 patients with mean age 66 years (range, 18 to 89) were reviewed. 118 cases subsequently died none of whom underwent a revision. Eighteen hips have been revised; thirteen for aseptic cup loosening, three for recurrent dislocation and two for deep infection. Three patients (four hips) were lost to follow-up. The minimum follow-up of the remaining 123 hips was 10 years (mean 13.3 years, range 10–17). Radiographs demonstrated 6 (6%) of the remaining acetabular prostheses were loose. The Kaplan Meier survivorship at 14.5 years with endpoint revision for all causes is 91.5% (95% CI 86.6 to 96.2%). With endpoint revision for aseptic cup loosening, survivorship is 93.3% (CI 88.8 to 97.8%).

This series included a number of complex cases requiring bone blocks and/or chip autograft for acetabular deficiencies. The concentric all polythene Exeter cup and Exeter stem has excellent long term results particularly when factoring in the complexity of cases in this series.

Purpose

The aim of the present study was to look at survivorship and patient satisfaction of a fixed bearing unicompartmental knee arthroplasty with an all-polyethylene tibial component.

The aim of this study was to measure polyethylene wear in uncemented metal-backed cups and compare it with cemented ultra-high molecular weight (UHMW) polyethylene cups in a controlled double-blind study.

The study group was made up of 91 patients aged 50 to 70 years undergoing THR for unilateral OA of the hip between February 1995 and July 2002. The male to female ratio was 40:60. In all patients, a cemented stem and 28-mm ceramic head was inserted, using a third-generation cementing technique and UHMW polyethylene. Patients were randomly allocated to receive either a cemented or uncemented acetabular cup. Eight patients were lost to follow-up.

Cemented cups were used in 28 patients (mean age 64 years). The mean thickness of the polyethylene was 9.6 mm (7.5 to 12.5). The mean liner thickness in the metal-backed cups was 8.9 mm (7 to 12.2). In measuring wear, baseline 3-month postoperative radiographs were compared with the most recent follow-up radiographs and Martell software was used.

The polyethylene in metal-backed cups had a mean wear rate of 0.49 mm at 4.7 years, with a mean annual wear rate of 0.12 mm. The cemented polyethylene cups had a mean wear rate of 0.45 mm at 5.3 years, with a mean annual wear rate of 0.11 mm.

The study is ongoing. Currently we conclude that there is no significant difference in the annual wear rate of polyethylene in uncemented metal-backed cups and cemented cups.

BACKGROUND

During revision hip arthroplasty, removal of a well-fixed, ingrown metal acetabular component may not be possible. Therefore, a new polyethylene liner can be cemented into the existing shell via the cement locking mechanism. We report the indications, technique, and results of cementing an acetabular liner into a well-fixed cementless acetabular shell.

We compared the rate of revision of two classes of primary anatomic shoulder arthroplasty, stemmed (aTSA) and stemless (sTSA) undertaken with cemented all polyethylene glenoid components. A large national arthroplasty registry identified two cohort groups for comparison, aTSA and sTSA between 1. st. January 2011 and 31. st. December 2020. A sub-analysis from 1 January 2017 captured additional patient demographics. The cumulative percentage revision (CPR) was determined using Kaplan-Meier estimates of survivorship and hazard ratios (HR) from Cox proportional hazard models adjusted for age and gender. Of the 7,533 aTSA procedures, the CPR at 8 years was 5.3% and for 2,567 sTSA procedures was 4.0%. There was no difference in the risk of revision between study groups (p=0.128). There was an increased risk of revision for aTSA and sTSA undertaken with humeral head sizes <44mm (p=0.006 and p=0.002 respectively). Low mean surgeon volume (MSV) (<10 cases per annum) was a revision risk for aTSA (p=0.033) but not sTSA (p=0.926). For primary diagnosis osteoarthritis since 2017, low MSV was associated with an increased revision risk for aTSA vs sTSA in the first year (p=0.048). Conversely, low MSV was associated with a decreased revision risk for sTSA in the first 6 months (p<0.001). Predominantly aTSA was revised for loosening (28.8%) and sTSA for instability/dislocation (40.6%). Revision risk of aTSA and sTSA was associated with humeral head size and mean surgeon volume but not patient characteristics. Inexperienced shoulder arthroplasty surgeons experience lower early revision rates with sTSA in the setting of osteoarthritis. Revision of aTSA and sTSA occurred for differing reasons

Total knee replacement (TKA) is one of the most successful procedures in orthopaedic surgery. Although originally limited to more elderly and less active individuals, the inclusion criteria for TKA have changed, with ever younger, more active and heavier patients receiving TKA. This broadening of indications coincided with the widespread adoption of modular cemented and cementless TKA systems in the 1980's, and soon thereafter wear debris related osteolysis and associated prosthetic loosening became major modes of failure for TKA implants of all designs. Initially, tibial components were cemented all polyethylene monoblock constructs. Subsequent long-term follow-up studies of some of these implant designs have demonstrated excellent durability in survivorship studies out to twenty years. While aseptic loosening of these all polyethylene tibial components was a leading cause of failure in these implants, major polyethylene wear-related osteolysis around well-fixed implants was rarely (if ever) observed. Cemented metal-backed nonmodular tibial components were first introduced to allow for improved tibial load distribution and protection of the underlying (often osteoporotic) bone. Eventually, modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-80s mainly to facilitate screw fixation for cementless implants. These designs also provided intraoperative versatility by allowing interchange of various polyethylene thicknesses, and also aided the addition of stems and wedges. Modular vs. All Polyethylene Tibial Components in Primary TKA: Kremers et al. reviewed 10,601 adult (>18 years) patients with 14,524 condylar type primary TKA procedures performed at our institution between 1/1/1988 and 12/31/2005 and examined factors effecting outcome. The mean age was 68.7 years and 55% were female. Over an average 9 years follow-up, a total of 865 revisions, including 252 tibia revisions were performed, corresponding to overall survival of 89% (Confidence intervals (CI): 88%, 90%) at 15 years. In comparison to metal modular designs, risk of tibial revision was significantly lower with all polyethylene tibias (HR 0.3, 95% CI: 0.2, 0.5). With any revision as the endpoint, there were no significant differences across the 18 designs examined. Similarly, there were no significant differences across the 18 designs when we considered revisions for aseptic loosening, wear, osteolysis. Among patient characteristics, male gender, younger age, higher BMI were all significantly associated with higher risk of revisions (p<0.008). In a more recent review from our institution of over 11, 600 primary TKA procedures, Houdek et al. again showed that all polyethylene tibial components had superior survivorship vs. metal backed designs, with a lower risk of revision for loosening, osteolysis or component fracture. Furthermore, results for all polyethylene designs were better for all BMI subgroups except for those <25 BMI where there was no difference. All polyethylene results were also better for all age groups except for those under age <55 where there again was no difference. Finally, in a recently published meta-analysis of 28 articles containing data on 95,847 primary TKA procedures, all polyethylene tibial components were associated with a lower risk of revision and adverse outcomes. The available current data support the use of all polyethylene tibial designs in TKA in all patients regardless of age and BMI. In all patients, (not just older individuals) use of an all polyethylene tibial component is an attractive and more cost effective alternative, and is associated with the better survivorship and lower risk of revision than seen with modular metal backed tibial components

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

Two stage exchange has been the gold standard in North America for the treatment of infected knee replacements. The choice of static vs. articulated spacers has been debated for a number of years. At our institution our choice of spacer for 2 stage exchanges is an articulated spacer. This allows motion between stages which facilitates recovery, and makes the second stage technically easier. In a study from our institution we followed 115 infected TKAs treated with the PROSTALAC articulated spacer for 5–9 years. Success for eradication of infection was 88%. With a repeat 2 stage, overall infection control was 98%. In addition, we compared functional outcomes to a group of aseptic knee revisions and found no difference in functional outcomes with standard quality of life outcome scores. While the articulated spacer was our treatment of choice in 2 stage exchange around 2012, the company that manufactured the PROSTALAC knee components ceased to manufacture them. At that time, based on the work of 2 previous studies (Hofmann, Lee), we continued to use articulated spacers. However, this was now the so-called Hofmann technique with a new standard femoral component with an all polyethylene tibia. The only difference from a standard knee revision was no stems and the utilization of high dose antibiotics. We also followed the principles from Europe of one stage exchange, such as wide debridement and soaking in dilute betadine for 15 minutes. More recently as of Sept 2015 we have used an all polyethylene tibia with a keel. The hope being that this will give a more stable tibia than previous and perhaps make a second stage unnecessary. Our first case was September 2015. The intention was not to do a second stage if the infection was eradicated and the patient had good pain relief and function. To date we have implanted 28 of these and in 80% of cases we have not had to do a second stage revision. Further study will reveal where this inadvertent one stage fits in our practi

The purpose of this investigation is to assess the rate of wear the effect once the “bedding in period”/ poly creep had been eliminated. Creep is the visco-elastic deformation that polyethylene exhibits in the first 6–12 weeks. We also assessed the wear pattern of four different bearing couples in total hip arthroplasty (THA): cobalt-chrome (CoCr) versus oxidized zirconium (OxZir) femoral heads with ultra-high molecular weight polyethylene (UHMWPE) versus highly-crosslinked polyethylene (XLPE) acetabular liners. This was a randomized control study involving 92 patients undergoing THA. They were randomized to one of four bearing couples: (1) CoCr/UHMWPE (n= 23), (2) OxZir/UHMWPE (n=21), (3) CoCr/XLPE (n=24), (4) OxZir/XLPE (n=24). Patients underwent a posterior approach from one of three surgeons involved in the study. All patients received a porous-coated cementless acetabular shell and a cylindrical proximally coated stem with 28 mm femoral heads. Each patient was reviewed clinically and radiographically at six weeks, three and 12 months, two, five and 10 years after surgery. Standardized anteroposterior and lateral radiographs were taken. All polyethylene wear was measured by an independent blinded reviewer. Linear and volumetric wear rates were measured on radiographs using a validated computer software (Polyware Rev. 5). Creep was defined as the wear at 6 or 12 weeks, depending on if there was a more than 10% difference between both measurements. If a greater than 10% difference occurred than the later period's wear would be defined as creep. 72 hips were included in analysis after exclusion of seven revisions, three deaths and 10 losses to follow-up. The annual linear wear rates (in mm/y) at 10 years were (1) 0.249, (2) 0.250, (3) 0.074 and (4) 0.050. After adjusting for creep these rates become were (1) 0.181, (2) 0.142, (3) 0.040 and (4) 0.023. There is statistical differences between raw and adjusted linear wear rates for all bearing couples. The percentage of the radiographically measured wear at 10 years due to creep is (1) 30% (2) 44%, (3) 58.5% and (4) 51.5% with significant differences in couples with XLPE versus those with UHMWPE. There was no significant correlation between age, gender, cup size, tilt, planar anteversion and the linear or volumetric wear rates. The linear wear rate of both UHMWPE and XLPE are even lower thxdsxzan previously described when creep is factored out. XLPE has again demonstrated far superior linear wear rates at 10 years than UHMWPE. There were no significant differences in wear rate at 10 years between CoCr and OxZir, this may be due to an underpowered study. XLPE exhibits proportionally more creep than UHMWPE within the first 6–12 weeks and accounts for more of the total wear at 10 years as measured radiographically at the end period

Aims

The aims of this study were to identify and evaluate the current literature examining the prognostic factors which are associated with failure of total elbow arthroplasty (TEA).

In an effort to address the relatively high rate of glenoid component lucent lines, loosening and failure, tantalum/trabecular metal glenoid implant fixation has evolved as it has in hip and knee arthroplasty. Trabecular metal-anchored glenoid implants used in a consecutive patient case series have demonstrated a lower failure rate than traditional all polyethylene cemented glenoids. Although the radiographs of some patients demonstrated small focal areas of lucency, none have become loose, and only two have actually demonstrated glenoid component failure due to a fracture 6 years after the index procedure. One with glenoid loosening was due to polyethylene wear from a massive cuff tear occurring 8 years after the index procedure. Most patients experienced significant improvements in shoulder range of motion and reduction in pain. Trabecular metal-anchored glenoids when carefully implanted do not produce excessive failure rates, but rather result in functional improvements while decreasing operative time

Introduction. We have investigated middle-term clinical results of total hip arthroplasty (THA) cemented socket with improved technique using hydroxyapatite (HA) granules. IBBC (interfacial bioactive bone cement method, Oonishi) (1) is an excellent technique for augmenting cement-bone fixation in the long term. However, the technique is difficult and there are concerns over some points, such as bleeding control, disturbance of cement intrusion to anchoring holes by granules, difficulty of the uniform granular dispersion to the acetabular bone. To improve the original technique, we have modified IBBC (M-IBBC), and investigated the middle-term clinical results and radiographic changes. Materials and Methods. K-MAX HS-3 THA (Kyocera, Japan), with tapered cemented stem with small collar and all polyethylene cemented socket, was used for THA implants (Fig.1). Basically the third generation cementing technique was used for THA using bone cement. The socket fixation was performed with bone cement (Endurance, DePuy) and HA granules (Ca10(PO4)6(OH)2, Boneceram P; G-2, 0.3–0.6mm in size, Olympus, Japan) (Fig.2). In original IBBC technique, HA granules were dispersed on reamed acetabulum before cementing. In M-IBBC technique, HA granules were attached to bone cement on plastic plate, then inserted to reamed acetabulum and pressurized (Fig.3). 112 hip joints (95 cases) were operated between June 2010 and March 2014, and followed. The average follow-up period was 6.5 years, and average age at operation was 66.5 years. The clinical results were evaluated by Japan Orthopaedic Association Hip Score (JOA score), and X-p findings were evaluated using antero-posterior radiographs. The locations of radiolucent lines were identified according to the zones described by Delee and Charnley for acetabular components, and Zone 1 was divided into two parts, outer Zone 1a and inner Zone 1b. Results and Discussion. Revision was not performed. JOA score improved from 47 to 88. Socket and stem loosening was not observed. X-p findings of sockets demonstrated radiolucent line in Zone 1a/1b/2/3 in 0.9/0/0/0% immediately after the operation, 6.3/1.8/0/0.9% at 2 years postoperatively. After 2 years there was no progressive change, however, improvement of radiolucent line in Zone 1a was observed in two cases after 3 years postoperatively. Accordingly, at 5 years radiolucent line in Zone 1a/1b was observed in 4.4/1.8%. Oonish has reported excellent clinical results of THA with IBBC (1). To easily perform IBBC, we have modified the technique, improving the problems of IBBC. In this study, radiolucent line was observed at the margin of the socket in a small number of cases, and there was no progressive change. In addition, improvement of radiolucent line was observed in M-IBBC in this study, which was not observed in conventional cementing technique. Conclusions. It is demonstrated that M-IBBC provides stable socket cement fixation for THA. The interesting finding in M-IBBC cases was the improvement of radiolucent line, suggesting osteoconductive property of hydroxyapatite granules at the interface after the operations. The promising long-term clinical results of M-IBBC method, were expected. For any figures or tables, please contact the authors directly

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 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

Total knee replacement is one of the most successful procedures in orthopaedic surgery. Although originally limited to more elderly and less active individuals, the inclusion criteria have changed, with ever younger, more active and heavier patients receiving TKA. Currently, wear debris related osteolysis and associated prosthetic loosening are major modes of failure for TKA implants of all designs. Initially, tibial components were cemented all polyethylene monoblock constructs. Subsequent long-term follow-up studies of these implants have demonstrated excellent durability in survivorship studies out to twenty years. Aseptic loosening of the tibial component was one of the main causes of failure in these implants. Polyethylene wear with osteolysis around well fixed implants was rarely (if ever) observed. Cemented metal-backed nonmodular tibial components were subsequently introduced to allow for improved tibial load distribution and to protect osteoporotic bone. Long-term studies have established that many one-piece nonmodular tibial components have maintained excellent durability. Eventually, modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-80s mainly to facilitate screw fixation for cementless implants. These designs also provided intraoperative versatility by allowing interchange of various polyethylene thicknesses, and also aided the addition of stems and wedges. Since the late 1980's, 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, but there is no question that it was associated with the widespread use of both cementless and cemented modular tibial designs. Mayo Data: Modular versus All Polyethylene Tibial Components in Primary TKA. The study population included 10,601 adult (>18 years) patients with 14,524 primary TKA procedures performed at our institution between 1/1/1988 and 12/31/2005. Mean age was 68.7 years and 55% were female. Overall revision rates and revisions for loosening, wear/osteolysis were compared across different designs using Cox proportional hazards regression models adjusting for age, sex, calendar year and body mass index (BMI). Over an average 9 years follow-up, a total of 865 revisions, including 252 tibia revisions were performed, corresponding to overall survival of 89% (Confidence intervals (CI): 88%, 90%) at 15 years. In comparison to metal modular designs, risk of tibial revision was significantly lower with all-poly tibias (HR 0.3, 95% CI: 0.2, 0.5). Overall, posterior cruciate-retaining (CR) designs performed better than the posterior-stabilised (PS) designs (p=0.002). With any revision as the endpoint, there were no significant differences across the 18 designs examined. Similarly, there were no significant differences across the 18 designs when we considered revisions for aseptic loosening, wear, osteolysis. Among patient characteristics, male gender, younger age, higher BMI were all significantly associated with higher risk of revisions (p<0.008). Summary: Available data support the use of nonmodular tibial designs in TKA in order to prevent or reduce the chance of backside wear, third body particles from resulting metallic debris and associated polyethylene induced osteolysis. In all patients, (not just older individuals) use of an all polyethylene tibial component is an attractive and more cost effective alternative, and is associated with the best survivorship and lowest risk of revision

Aims. The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated. Methods. Three different grades of polyethylene were compared in this study; conventional ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE). In addition, tibial baseplates with a fixed-bearing and a mobile-bearing insert were evaluated to understand differences in the contact properties. The inserts were implanted in neutral alignment and with a 10° internal malrotation. The contact stress, von Mises stress, and equivalent plastic strain (PEEQ) on the tibial posts were extracted for comparison. Results. The stress and strain on the tibial post for the three polyethylenes greatly increased when the insert was placed in malrotation, showing a 38% to 56% increase in von Mises stress and a 335% to 434% increase in PEEQ. The VEPE insert had the lowest PEEQ among the three materials. The mobile-bearing design exhibited a lower increase in stress and strain around the tibial posts than the fixed-bearing design. Conclusion. Using VEPE for the tibial component potentially eliminates the risk of material permanent deformation. The mobile-bearing insert can help to avoid a dramatic increase in plastic strain around the tibial post in cases of malrotation. The mobility allows the pressure to be distributed on the tibial post and demonstrated lower stresses with all three polyethylenes simulated. Cite this article: Bone Joint Res 2020;9(11):768–777