Periacetabular osteolysis in association with well-fixed cementless components was first recognised as a serious clinical problem in the early 1990s. By the mid-1990s, revision surgery for pelvic osteolysis secondary to polyethylene wear was the most common revision hip procedure performed. As a result, new bearing surfaces were introduced in hopes of reducing wear volume and thus reducing pelvic osteolysis. These included highly crosslinked polyethylene, ceramic-on-ceramic and metal-on-metal bearing surfaces. Metal-on-metal has for the most part been eliminated in conventional hip replacement because of the concerns centered around adverse local tissue reactions. Both highly crosslinked polyethylene and ceramic-on-ceramic bearings have been successful in limiting wear and all but eliminating clinically significant osteolysis. Multiple reports on highly crosslinked polyethylene have documented wear rates below the lysis threshold. No reports of revision for wear have been reported despite twenty years of in-vivo use. Of import to the surgeons, all manufacturers commonly used in North America have performed well. In addition, highly crosslinked polyethylene has been relatively insensitive to head size allowing the use of 36mm femoral heads routinely. Similar reports are noted with ceramic-on-ceramic bearings. However, highly crosslinked has dominated the North American market because it is a relatively forgiving bearing surface and comes at a lower cost. Currently, there is a trend towards the use of ceramic femoral heads – not because of wear concerns, but concerns related to taper corrosion and large cobalt-chrome femoral heads

Key Points:. Historically, 22.25, 26, 28, or 32 mm metal femoral heads were used in primary total hip arthroplasty, but innovations in materials now permit head sizes 36 mm or larger. Stability and wear of primary total hip arthroplasty are related to the diameter and material of the femoral head. Larger diameter femoral heads are associated with increased joint stability through increases in arc range of motion and excursion distance prior to dislocation. Fixation of the acetabular component may be related to the size of the femoral head, with increased frictional torque associated with large diameter heads and certain polyethylene. Linear wear of highly crosslinked polyethylenes seems unrelated to femoral head diameter, but larger heads have been reported to have higher volumetric wear. Mechanically assisted crevice corrosion at the connection between the modular femoral head and neck may be associated with the femoral head size and material. Cobalt chromium alloy, alumina ceramic composite, or oxidised zirconium femoral heads on highly crosslinked polyethylene are the most commonly used bearing surfaces, but each may have unique risks and benefits. Conclusions. At present, there is a wave of enthusiasm for the routine use of “large” (32, 36 mm, or larger) femoral heads with highly crosslinked polyethylene for the vast majority of patients having a primary THA. It may be reasonable to consider the “graduated femoral head-outer acetabular diameter system”, using 28 mm femoral heads with “smaller” acetabular components (<50 mm), 32 mm femoral heads with acetabular components 50 – 56 mm outer diameter, and 36 mm or larger femoral heads with acetabular components 58 mm or larger in diameter, to minimise both the risk of dislocation and the frictional torque. Although the linear wear of highly crosslinked polyethylene appears to be independent of head size, the reported increase in volumetric wear with large femoral heads and highly crosslinked polyethylene requires further study, and should temper the use of femoral heads 36 mm or larger in younger and more active patients. With its long and successful history, it is difficult to recommend the complete abandonment of the cobalt chromium alloy femoral head in all patients having a primary THA. Alumina ceramic or oxidised zirconium heads may be considered for younger, heavier, and more active patients, who seem to have the highest risk of trunnion corrosion. Surgeons and patients should be aware of the unique possible complications of these two newer femoral head materials

Wear of the tibial polyethylene liner of total knee arthroplasty (TKA) is complex and multifactorial. The issues involved include those of implant design and locking mechanism, surgical-technical variability, and patient weight and activity level. However, tibial polyethylene fabrication, including bar stock, amount of irradiation, quenching of free radicals, and sterilization may also be factors in the long-term survival of TKA. Highly crosslinked polyethylene is now widely used in total hip arthroplasty, but its value and use in TKA is a subject of great controversy. In making a decision to use these products, the surgeon should consider multiple sources of evidence: in-vitro wear testing; clinical cohort studies; randomised controlled trials; registry survival data; and retrieval analyses. The two questions to be asked are: is there a value or benefit in the use of these new polyethylenes, and what are the risks involved with the use of these products?. Laboratory testing, generally to 5 million cycles, has shown a significant decrease in tibial polyethylene wear of several products, with both cruciate-retaining and substituting designs, and under adverse conditions. Retrospective cohort studies and RCTs comparing conventional and highly crosslinked polyethylene have shown little difference between the two products at mean follow-up times of 5 years. One registry study showed no difference in the rate of revision at short-term follow-up, but the Australian Joint Replacement Registry in 2014 did report a decreased rate of revision for loosening and osteolysis in “young patients” with one particular tibial polyethylene. The risks of the use of highly crosslinked polyethylene include fracture (the tibial liner, PS post, and patella pegs), and particle size-reactivity. However, these risks appear to be quite low. Retrieval data shows lower damage scores with certain polyethylenes, and variable changes in the oxidation score. At present, the data does not support the widespread or routine use of highly crosslinked or antioxidant polyethylene in TKA. However, consideration should be given for use of certain products in young and active patients. Longer-term follow-up will ultimately determine the role of highly crosslinked polyethylene in TKA

Only a little over a decade ago the vast majority of primary total hip replacements performed in North America, and indeed globally, employed a conventional polyethylene insert, either in a modular version or in a cemented application. Beginning in the early 2000's there was an explosion in technology and options available for the bearing choice in total hip arthroplasty. Highly crosslinked polyethylene was introduced in 1998, and within a few short years the vast majority of polyethylene inserts performed in North America were manufactured from this material. Globally there was a mixed picture with variable market penetration. Surgeons had seen historically poor results with attempts at “improving” polyethylene in the past and many were hesitant to use this new technology. Many randomised clinical trials have been performed and all have shown to a greater or lesser degree, that indeed the highly crosslinked polyethylene insert has undergone less linear and volumetric wear than its more conventional counterpart. The challenge, however, is as we approached mid-term results, orthopaedic manufacturers began altering the polyethylene to improve wear and improve mechanical strength. Therefore while ten-year and greater data will ultimately be published, the actual polyethylene in use at that time will be a different material. Additionally while wear rates are undoubtedly lower, we are still waiting for long-term results of actual osteolytic lesion development and the effect that highly crosslinked polyethylene will have on this clinical scenario. That being said, with over a decade of clinical experience, unquestionably highly crosslinked polyethylene has truly been a revolution in design, essentially eliminating polyethylene wear as an early failure mode. During this same decade metal-on-metal implants had seen a significant resurgence in use. Metal-on-metal implants had in-vitro advantages with very low wear rates. They allowed the use of large metal heads and articulations, thereby improving range of motion and stability. Concerns always existed regarding the production of metal ions and the potential for metal hypersensitivity, as well as possible systemic effects. Metal hypersensitivity remains a diagnosis of exclusion with no definitive diagnostic tests to either screen for it, or diagnose it, if suspected. Over the past few years metal-on-metal implant use has dropped significantly, to the point now in 2013, where the only remaining application is resurfacing implants in the younger male patient. Ceramic-on-ceramic bearings enjoy the lowest wear rates of all currently available hip articulations. Historically there has been concern regarding fracturing of both the inserts and the heads, although current generation ceramic-on-ceramic bearings have a much lower reported fracture rate. The phenomenon of a squeaking articulation remains a concern for both patient and surgeon. Conflicting reports exist on whether this is related to implant malposition or is a function of the bearing itself. As with other bearings, improvements in technology continue to evolve and newer ceramics have recently been introduced and are in clinical practice. The future will continue to see the evolution of the articulation in total hip arthroplasty. Patients are undergoing total hip replacements at younger ages and clearly have higher demands than seen historically. That being said, two factors will have a major influence on future developments. The tremendous clinical success of highly crosslinked polyethylene should have us all question the need for significant changes in bearing material and the current environment following the multiple issues with metal-on-metal is one of evolutionary, rather than revolutionary, design and introduction

The selection of an acetabular component for primary hip arthroplasty has narrowed significantly over the past 10 years. Although monoblock components demonstrated excellent long-term success the difficulty with insertion and failure to fully appreciate full coaptation of contact with the acetabular floor has led to almost complete elimination of its utilization. Modular acetabular components usually with titanium shells and highly crosslinked polyethylene are by far the most utilised today. This is particularly true with mid-term results demonstrating excellent wear rates and extremely low failure rates and the concern of possible mechanical failure of highly crosslinked polyethylene not being a clinical problem. Ceramic liners are also used but problems with squeaking articulations and liner chipping have made highly crosslinked polyethylene the preferred liner material. Metal-on-metal except in surface replacement arthroplasty is rarely used in primary hip arthroplasty. With instability in total hip replacement still being a significant and the leading cause of revision hip replacement the dual mobility articulation has emerged as an increasingly used acetabular component. This is composed of either a monoblock cobalt chrome socket articulating with a large polyethylene liner into which the femoral head is constrained. The polyethylene liner becomes essentially a larger femoral head articulation and hip stability is significantly improved. A modular dual mobility can also be utilised with a titanium shell and a cobalt chrome liner inserted into the shell and then a dual mobility articulation. In a recent series of 182 dual mobility cups, all monoblock ADM, in high risk patients undergoing primary total hip replacement there was 1 interprosthetic dislocation which occurred during reduction of a dislocation. Average follow up was 4.4 years with a range of 2–6.6 years

Contemporary polyethylene liners for total hip replacements were introduced in the late 1990's to address osteolysis associated with wear of conventional polyethylene. Every major device manufacturer introduced an “enhanced polyethylene”. In the ensuing decade plus, every major arthroplasty meeting had presentations and debates about the wear resistance and mechanical properties of these new polymers. The results have been remarkable and now with 17 to 18 years of use in patients, we have yet to see clinically significant osteolysis in our patients regardless age or activity level. The results can be summarised as follows: All currently commercially available highly crosslinked polyethylenes produced by major device companies have demonstrated a reduction in wear and osteolysis. At the 2016 Closed Meeting of The Hip Society, none of the surgeons attending had seen a clinically significant case of osteolysis associated with highly crosslinked polyethylene. Registry data demonstrates the superiority of the highly crosslinked materials over conventional polyethylenes. Historical concerns over a reduction in mechanical properties have not been borne out in clinical studies. Although highly crosslinked polyethylene liner fractures have been reported, they are rare and probably related to specific designs or surgical technique issues. It is important to remember that there were rare cases of fracture of conventional polyethylene as well. With currently reported wear rates of the enhanced polyethylenes, polyethylene thickness is unlikely to be a factor in long-term durability with well-designed sockets. Bench data has demonstrated that polyethylene thickness is not a risk factor for wear or fracture if well supported by the metal shell. Thin unsupported polyethylene is at risk for fracture. Although the new anti-oxidant polyethylenes (eg. Vitamin E) have performed well in wear studies, there is no clinically available evidence to support their use based on enhanced fracture toughness

Only a little over a decade ago the vast majority of primary total hip replacements performed in North America, and indeed globally, employed a conventional polyethylene insert, either in a modular version or in a cemented application. Beginning in the early 2000's there was an explosion in technology and options available for the bearing choice in total hip arthroplasty. Highly crosslinked polyethylene was introduced in 1998, and within a few short years the vast majority of polyethylene inserts performed in North America were manufactured from this material. Globally there was a mixed picture with variable market penetration. Surgeons had seen historically poor results with attempts at “improving” polyethylene in the past and many were hesitant to use this new technology. Many randomised clinical trials have been performed and all have shown to a greater or lesser degree, that indeed the highly crosslinked polyethylene insert has undergone less linear and volumetric wear than its more conventional counterpart. This replicates well the hip simulator data. The challenge, however, is as we approached mid-term results, orthopaedic manufacturers began altering the polyethylene to improve wear and improve mechanical strength. Therefore while 10-year and greater data will ultimately be published, the actual polyethylene in use at that time will be a different material. Additionally, while wear rates are undoubtedly lower, we are still waiting for long-term results of actual osteolytic lesion development and the effect that highly cross-linked polyethylene will have on this clinical scenario. That being said, with over a decade of clinical experience, unquestionably highly crosslinked polyethylene has truly been a revolution in design, essentially eliminating polyethylene wear as an early failure mode. The question still remains as to the best material for the femoral ball. Essentially two options exist – cobalt chrome and ceramic (Delta). There are theoretically advantages to ceramic heads; however they come at a cost premium: 1.) To date there have been no published reports that demonstrate any improved clinical outcomes with the use of ceramic heads. In fact, the Australian registry demonstrates that the cumulative revision rate is lowest with CoCr heads (at 10 years, 4.3% with CoCr on XLPE and 4.6% with ceramic on XLPE). 2.) Costs continue to be significantly higher for ceramic heads. A price premium of 2–4× higher cost for ceramic over CoCr heads exists in most global markets. 3.) Trunion issues. An emerging concern is corrosion at the head neck junction in THA. Ceramic heads should theoretically have a lower incidence of taper corrosion. To date this is unproven, as is the actual incidence of this as a significant clinical problem

INTRODUCTION. Wear and polyethylene damage have been implicated in up to 22% of revision surgeries after unicompartmental knee replacement. Two major design rationales to reduce this rate involve either geometry and/or material strategies. Geometric options involve highly congruent mobile bearings with large contact areas; or moderately conforming fixed bearings to prevent bearing dislocation and reduce back-side wear, while material changes involve use of highly crosslinked polyethylene. This study was designed to determine if a highly crosslinked fixed-bearing design would increase wear resistance. METHODS. Gravimetric wear rates were measured for two unicompartmental implant designs: Oxford unicompartmental (Biomet) and Triathlon X3 PKR (Stryker) on a knee wear simulator (AMTI) using the ISO-recommended standard. The Oxford design had a highly conforming mobile bearing of compression molded Polyethylene (Arcom). The Triathlon PKR had a moderately conforming fixed bearing of sequentially crosslinked Polyethylene (X3). A finite element model of the AMTI wear simulation was constructed to replicate experimental conditions and to compute wear. This approach was validated using experimental results from previous studies. The wear coefficient obtained previously for radiation-sterilized low crosslinked polyethylene was used to predict wear in Oxford components. The wear coefficient obtained for highly crosslinked polyethylene was used to predict wear in Triathlon X3 PKR components. To study the effect design and polyethylene crosslinking, wear rates were computed for each design using both wear coefficients. RESULTS. Wear rates were significantly lower (69%) for the Triathlon fixed-bearing design compared to the Oxford mobile-bearing design (Fig 1, p<0.01). The FEA model predicted 46% of wear occurring at the back side of the mobile bearing (Fig 2). When wear was computed for the Triathlon PKR design using the wear coefficients used for the low crosslinked polyethylene, wear rates increased to 13.9 mg/million cycles. DISCUSSION. We used a combined experimental and computational approach to quantify factors contributing to polyethylene wear after unicompartmental knee arthroplasty. To isolate the effect of crosslinking level and mobile-bearing design, we computed wear rates for both designs using the same wear coefficient obtained for low crosslinked polyethylene. Wear rates in the low crosslinked Triathlon PKR insert increased by more than 160% relative to those in the highly crosslinked Triathlon X3 PKR. The finite element method facilitates computation of relative back-side to front-side wear, which is challenging to obtain experimentally. The back-side wear Oxford mobile bearing was 46% of total wear. Major factors contributing to the difference in wear were back-side wear (46%) and increased crosslinking (63%) with the combined effect having an additive effect. Our FEA-predicted wear penetration rates (0.024 mm/million cycles) also compare well to in vivo studies, which reported penetration rates of 0.022 mm/year for Oxford bearings. A validated computer model is extremely valuable for efficient evaluation of wear performance and design development. In summary, increasing conformity to increase contact area and reduce contact stress may not be the sole predictor of wear performance. A highly crosslinked polyethylene insert in a fixed-bearing design may provide the high wear performance of a mobile-bearing design without the increased risk for bearing dislocation

Introduction. The first highly crosslinked and melted polyethylene acetabular component for use in total hip arthroplasty was implanted in 1998 and femoral heads larger than 32mm in diameter introduced 2004. The purpose of this study was to re-assemble a previous multi-center patient cohort in order to evaluate the radiographic and wear analysis of patients receiving this form of highly crosslinked polyethylene articulating against large diameter femoral heads at a minimum of 10 years follow-up. Methods. Two centers contributed patients to this ongoing clinical study. Inclusion criteria for patients was: primary THR; femoral heads greater than 32mm; minimum 10 year follow-up. 69 hips have been enrolled with an average follow-up of 11.2 years (10–15), 32 females (50%). Wear analysis was performed using the Martell Hip Analysis software. Radiographic grading was performed on the longest follow-up AP hip films. The extent of radiolucency in each zone greater than 0.5mm in thickness was recorded along with the presence of sclerotic lines and osteolysis. Results. Wear analysis: Using the average of the slopes of the individual regression lines, the wear rate was 0.004±0.094mm/yr. Using the early to latest film method, the wear rate was 0.035±0.076mm/yr. Radiographic analysis: Acetabular side: the greatest incidence of radiolucency occurred in zone 1 at 27%; sclerotic lines had a less than 2% incidence in any of the 3 zones; there was no identified osteolysis. Femoral side: the highest incidence of radiolucencies was in zones 1 and 3, 7% and 4%; sclerotic lines were rare in any zone, maximum in zone 3, 4%; there was no identified osteolysis. Conclusion. The wear of this form of irradiated and melted highly crosslinked polyethylene remained at levels lower than the detection limit of the software at minimum 10 year follow-up and there was no identified osteolysis

Introduction. The first highly crosslinked and melted polyethylene acetabular component for use in total hip arthroplasty was implanted in 1998. Numerous publications have reported reduced wear rates and a reduction in particle induced peri-prosthetic osteolysis at short to mid-term follow-up. The purpose of this study was to re-assemble a previous multi-center patient cohort in order to evaluate the radiographic and wear analysis of patients receiving this form of highly crosslinked polyethylene articulating against 32mm femoral heads or less at a minimum of 13 years follow-up. Methods. Inclusion criteria for patients was a primary THR with femoral heads 32mm or less and a minimum 13 year follow-up. 139 hips have been enrolled with an average follow-up of 13.7 years (13–16), 80 females (57%). Wear analysis was performed using the Martell Hip Analysis software. Radiographic grading was performed on the longest follow-up AP hip films. The extent of radiolucency in each zone greater than 0.5mm in thickness was recorded along with the presence of sclerotic lines and osteolysis. Results. Wear analysis: Using the average of the slopes of the individual regression lines, the wear rate was 0.006±0.033mm/yr. Using the early to latest film method, the wear rate was 0.003±0.056mm/yr. Radiographic analysis: Acetabular side: the greatest incidence of radiolucency occurred in zone 1 at 21%; sclerotic lines had a less than 2% incidence in any of the 3 zones; there was no identified osteolysis. Femoral side: the incidence of radiolucencies was limited to zone 1, 2%; sclerotic lines were rare in any zone, maximum in zone 3, 4%; there was no identified osteolysis. Conclusion. The wear of this form of irradiated and melted highly crosslinked polyethylene remained at levels lower than the detection limit of the software at minimum 13 year follow-up and there was no identified osteolysis

A standard is defined as something established by authority, custom, or general consent. Clearly that does not exist for ceramic on ceramic total hip replacement. A better question is: Is there any indication for a ceramic on ceramic total hip. The answer to that question should when possible be based on clinical outcome data including the value added (or not) with this more expansive technology. Ceramic on ceramic has been popularised based on its low wear. Is this clinically relevant? Probably not, based on currently available data. Both metal on highly crosslinked polyethylene and ceramic on highly crosslinked polyethylene have very low clinically documented wear rates with excellent outcomes in multiple studies. In addition, ceramic on ceramic bearings are more sensitive to implant position. Whereas polyethylene may tolerated edge loading and impingement, ceramic bearings are less likely to do so. Dislocation remains one of if not the top reason for early revision. Even with newer ceramics, there are still less options to fine tune hip stability with ceramic on ceramic bearing surfaces. When looking at the overall, risk of revision, Bozic et al concluded that hard bearings provided no benefit in terms of risk reduction of revision. Considering their higher cost, they questioned the use of these products especially in the 65 and older age group. Looking at the Australian Registry, the cumulative percent revision for ceramic-ceramic THA was 5.7% at 11 years compared to 5.1% for metal on crosslinked poly. The hazard ratio (adjusted for age and gender) was 1.09 in favor of ceramic on poly and the difference was highly significant (p=0.012). When one take into account the increased cost of ceramic on ceramic bearings, it is hard to make a case for ceramic on ceramic bearings. Any use of ceramic on ceramic bearings would have to be based on the hypothesis that in the long run in young active patients they may provide an advantage. This is a hypothesis with no data to support it currently

Increased femoral head size reduces the rate of dislocation after total hip arthroplasty (THA). With the introduction of highly crosslinked polyethylene (HXLPE) liners in THA there has been a trend towards using larger size femoral heads in relatively smaller cup sizes, theoretically increasing the risk of liner fracture, wear, or aseptic loosening. Short to medium follow-up studies have not demonstrated a negative effect of using thinner HXLPE liners. However, there is concern that these thinner liners may prematurely fail in the long-term, especially in those with thinner liners. The aim of this study was to evaluate the long-term survival and revision rates of HXLPE liners in primary THA, as well as the effect of liner thickness on these outcomes. We hypothesized that there would be no significant differences between the different liner thicknesses. We performed a retrospective database analysis from a single center of all primary total hip replacements using HXLPE liners from 2010 and earlier, including all femoral head sizes. All procedures were performed by fellowship trained arthroplasty surgeons. Patient characteristics, implant details including liner thickness, death, and revisions (all causes) were recorded. Patients were grouped for analysis for each millimeter of PE thickness (e.g. 4.0-4.9mm, 5.0-5.9mm). Kaplan-Meier survival estimates were estimated with all-cause and aseptic revisions as the endpoints. A total of 2354 patients (2584 hips) were included (mean age 64.3 years, min-max 19-96). Mean BMI was 29.0 and 47.6% was female. Mean follow-up was 13.2 years (range 11.0-18.8). Liner thickness varied from 4.9 to 12.7 mm. Seven patients had a liner thickness <5.0mm and 859 had a liner thickness of <6.0mm. Head sizes were 28mm (n=85, 3.3%), 32mm (n=1214, 47.0%), 36mm (n=1176, 45.5%), and 40mm (n=109, 4.2%), and 98.4% were metal heads. There were 101 revisions, and in 78 of these cases the liner was revised. Reason for revision was instability/dislocation (n=34), pseudotumor/aseptic lymphocyte-dominant vasculitis associated lesion (n=18), fracture (n=17), early loosening (n=11), infection (n=7), aseptic loosening (n=4), and other (n=10). When grouped by liner thickness, there were no significant differences between the groups when looking at all-cause revision (p=0.112) or aseptic revision (p=0.116). In our cohort, there were no significant differences in all-cause or aseptic revisions between any of the liner thickness groups at long-term follow-up. Our results indicate that using thinner HXPE liners to maximize femoral head size in THA does not lead to increased complications or liner failures at medium to long term follow-up. As such, orthopedic surgeons can consider the use of larger heads at the cost of liner thickness a safe practice to reduce the risk of dislocation after THA when using HXLPE liners

With the introduction of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA), orthopaedic surgeons have moved towards using larger femoral heads at the cost of thinner liners to decrease the risk of instability. Several short and mid-term studies have shown minimal liner wear with the use HXLPE liners, but the safety of using thinner HXPLE liners to maximize femoral head size remains uncertain and concerns that this may lead to premature failure exist. Our objective was to analyze the outcomes for primary THA done with HXLPE liners in patients who have a 36-mm head or larger and a cup of 52-mm or smaller, with a minimum of 10-year follow-up. Additionally, linear and volumetric wear rates of the HXLPE were evaluated in those with a minimum of seven-year follow-up. We hypothesized that there would be minimal wear and good clinical outcome. Between 2000 and 2010, we retrospectively identified 55 patients that underwent a primary THA performed in a high-volume single tertiary referral center using HXLPE liners with 36-mm or larger heads in cups with an outer diameter of or 52-mm or smaller. Patient characteristics, implant details including liner thickness, death, complications, and all cause revisions were recorded. Patients that had a minimum radiographic follow-up of seven years were assessed radiographically for linear and volumetric wear. Wear was calculated using ROMAN, a validated open-source software by two independent researchers on anteroposterior X-rays of the pelvis. A total of 55 patients were identified and included, with a mean age of 74.8 (range 38.67 - 95.9) years and a mean BMI of 28.98 (range 18.87 - 63-68). Fifty-one (94.4%) of patients were female. Twenty-six (47.7%) patients died during the follow-up period. Three patients were revised, none for liner wear, fracture or dissociation. Twenty-two patients had a radiographic follow-up of minimum seven years (mean 9.9 years, min-max 7.5 –13.7) and were included in the long-term radiographic analysis. Liner thickness was 5.5 mm at 45 degrees in all cases but one, who had a liner thickness of 4.7mm, and all patients had a cobalt-chrome head. Cup sizes were 52mm (n=15, 68%) and 50mm (n=7, 32%). Mean linear liner wear was 0.0470 mm/year (range 0 - 0.2628 mm) and mean volumetric wear was 127.69 mm3/year (range 0 - 721.23 mm3/year). Using HXLPE liners with 36-mm heads or bigger in 52-mm cups or smaller is safe, with low rates of linear and volumetric wear in the mid to long-term follow-up. Patients did not require revision surgery for liner complications, including liner fracture, dissociation, or wear. Our results suggest that the advantages of using larger heads should outweigh the potential risks of using thin HXLPE liners

Introduction:. Although commonly used, the clinical performance of highly crosslinked polyethylene in total knee arthroplasty (TKA) remains unknown and concerns exist regarding fatigue resistance and oxidation, particularly in posterior-stabilized (PS) designs. The purpose of this study is to compare highly crosslinked and conventional polyethylene in a PS TKA design at a minimum of 5-years. Methods:. A prospective cohort study of 114 consecutive TKAs in 83 patients was performed as a subset of a multi-center prospective study. All TKAs utilized an identical PS design. Conventional polyethylene inserts were used in 50 knees and second-generation highly cross-linked polythethylene inserts were implanted in 64 TKAs. All patients were followed with clinical outcome measures (Short-Form 36, Knee Society Scores, WOMAC and LEAS) and radiographically for a minimum of 5 years. Results:. The mean age of the highly cross-linked polyethylene group was 4 years less than the conventional group (p = 0.03). There was no difference in BMI (p = 0.3) or preoperative outcome measures between groups with numbers available. Seven patients died or were lost to follow up and one underwent revision for infection at 3 months postoperatively. 103 TKAs obtained minimum 5-year follow up. Mean Knee Society Scores were 12 points higher (p = 0.01) and 14 points higher (p = 0.005) in the physical function subset of the SF-36 in the highly cross-liked polyethylene group. There was no difference in the other outcome measures with the numbers available. There was no radiographic osteolysis or mechanical failures related to the tibial polyethylene in either group. Conclusion:. Mechanical failure or radiographic osteolysis was not observed with either conventional or highly cross-linked polyethylene in this PS TKA design at mid-term follow up. To our knowledge, this is the first minimum 5-year follow-up of highly cross-linked polyethylene in a posterior-stabilized design. While the results support comparative safety, longer-term follow-up is warranted to determine if wear resistance and mechanical properties of highly crosslinked polyethylene are maintained. Significance: Concerns regarding early fatigue failure and mechanical complications related to the PS post-cam articulation of highly-crosslinked polyethylene in TKR were not substantiated at a minimum of 5 years clinical followup in this prospective cohort study. Highly cross-linked polyethylene demonstrated clinical equivalency compared to conventional polyethylene, even when used in a younger and presumably more active patient group

Introduction:. Microseparation has resulted in more than ten-fold increase in ceramic-on-ceramic and metal-on-metal bearing wear, and even fracture in a zirconia head [1–4]. However, despite the greater microseparation reported clinically for metal-on-polyethylene wear, less is known about its potential detrimental effects for this bearing couple. This study was therefore designed to simulate the effects of micromotion using finite element analysis and to validate computational predictions with experimental wear testing. Methods:. Experimental wear rates for low and highly crosslinked polyethylene hip liners were obtained from a previously reported conventional hip wear simulator study [5]. A finite element model of the wear simulation for this design was constructed to replicate experimental conditions and to compute the wear coefficients that matched the experimental wear rates. We have previous described out this method of validation for knee wear simulation studies [6,7]. This wear coefficient was used to predict wear in a Dual-Mobility hip component (Fig 1). Dual mobility total hip arthroplasty components, Restoration ADM (Fig 1), with highly crosslinked acetabular liners were experimentally tested: the control group was subjected to wear testing using the ISO 14242-1 waveform on a hip wear simulator. The microseparation group was subjected to a nominal 0.8 mm lateral microseparation during the swing phase by engaging lateral force springs and reducing the swing phase vertical force. Results:. The wear coefficients that matched experimental wear rates for the low and highly crosslinked polyethylene liners were 4.57×10. −10. and 5.89×10. −11. mm. 3. N. −1. mm. −1. , respectively. Introducing microseparation in the conventional hip increased the wear rate by 15.59 mm. 3. /million cycles in the low crosslinked liner and by 1.12 mm. 3. /million cycles in the highly crosslinked liner (Fig 2). Discussion:. Microseparation did increase predicted wear rates for the low crosslinked polyethylene liner and supports the hypothesis that microseparation can adversely affect the wear of hip arthroplasty. However, the predicted and experimental increase for the dual mobility highly crosslinked liners due to microseparation was low (3.3 mm. 3. and 2.9 mm. 3. /million cycles, respectively) and below the threshold for clinical relevance. The small increase in wear rate in our study supports the high wear tolerance to wear of a dual-mobility sequentially crosslinked polyethylene liner

The challenges faced by hip surgeons have changed over the last decade. Historically, fixation, polyethylene wear, osteolysis, loosening and failure to osseointegrate dominated the discussions at hip surgery meetings. With the introduction of highly crosslinked polyethylene, wear and osteolysis are currently not significant issues. Improved surgical technique has resulted in a high rate of osseointegration and once fixed, loosening of cementless components is rare. In this session, we will focus on issues that orthopaedic surgeons performing hip surgery routinely face including bearing couples in the young active patient, implant choices in the dysplastic hip and osteoporotic femur, evaluation and management of the unstable hip and differential diagnosis of the painful THR

Management of symptomatic osteonecrosis of the hip includes either some type of head preservation procedure or a total hip arthroplasty (THA). In general, once there is collapse of the femoral head, femoral head preservation procedures have limited success. There are a number of different femoral head preservation procedures that are presently performed and there is no consensus regarding which one is most effective. These procedures involve a core decompression with some type of vascularised or nonvascularised grafting of the femoral head. Core decompression with bone grafting of the femoral head with stem cells harvested from the iliac crest and vascularised fibula grafts are the two most popular femoral head preservation procedures. Once the femoral head has collapsed then a THA should be performed when the patient has significant disability. In the past, total hip arthroplasty in osteonecrosis patients was not considered a highly successful procedure because it was performed in younger patients (most patients are younger than fifty years of age) and longevity was limited by wear and osteolysis. The advent of reliable cementless acetabular and femoral fixation and alternative bearing surfaces (i.e. highly crosslinked polyethylene liners) has been associated with improved outcomes and enhanced longevity. THA is considered the procedure of choice even for young patients (less than 30 years old) with collapse of the femoral head and significant pain and disability

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

The challenges faced by hip surgeons have changed over the last decade. Historically, fixation, polyethylene wear, osteolysis, loosening and failure to osseointegrate dominated the discussions at hip surgery meetings. With the introduction of highly crosslinked polyethylene, wear and osteolysis are currently not significant issues. Improved surgical technique has resulted in a high rate of osseointegration and once fixed, loosening of cementless components is rare. In this section, we will focus on issues that orthopaedic surgeons performing hip surgery routinely face including bearing couples in the young active patient, implant choices in the dysplastic hip and osteoporotic femur, evaluation and management of the unstable hip and differential diagnosis of the painful THR

Total knee replacements are being more commonly performed in active younger and obese patients. Fifteen-year survivorship studies demonstrate that cemented total knee replacements have excellent survivorship, with reports of 85 to 97%. Cemented knee arthroplasties are doomed to failure due to loss of cement-bone interlock over time. Inferior survivorship occurs in younger patients and obese patients who would be expected to place increased stress on the bone-cement interfaces. Roentgen stereophotogrammetric analysis (RSA) studies have indicated that cementless fixation should perform better than cemented fixation. However, cementless fixation for total knee replacement has not gained widespread utilization due to the plethora of poor results reported in early series. The poor initial results with cementless total knee replacement have occurred due to poor implant designs such as cobalt chrome porous interfaces, poor initial tibial component stability, lack of continuous porous coating, poor polyethylene, and use of metal-backed patellae. I have used cementless fixation for total knee replacements for young, active, and heavy patients since 1986 when durability over 20 years is desirable. My series of over 1,300 cementless TKAs represents about 20% of the 6,500 total knees I have performed from 1986 to 2017. I have seen initial failures in my series due to the use of metal-backed patellae with thin polyethylene, older generation polyethylene, and use of screws with the tibial components which provide access to the metaphyseal bone for polyethylene wear debris. Overall implant fixation failures were still significantly low due to the use of a highly porous titanium surface on both the tibial and femoral components. With the advent of utilizing implants with continuous porous surfaces and highly crosslinked polyethylene, and elimination of use of metal-backed patellae and tibial screws, I have only had one revision due to aseptic loosening or osteolysis in the last 1,071 cases performed since 2002. Almost 50% of total knees are now performed on patients under the age of 65. A 55-year-old patient has a 30 year life expectancy. Modern total knee replacement design has made biological fixation predictable for young and heavy patients. Because it is a biological interface, it should respond better than cement to the increased stresses that will be applied over many years by our younger, more active and heavier total knee population