Future Bearing Surfaces in Total Hip Arthroplasty

One of the most important issues in the modern total hip arthroplasty (THA) is the bearing surface. Extensive research on bearing surfaces is being conducted to seek an ideal bearing surface for THA. The ideal bearing surface for THA should have superior wear characteristics and should be durable, bio-inert, cost-effective, and easy to implant. However, bearing surfaces that are currently being implemented do not completely fulfill these requirements, especially for young individuals for whom implant longevity is paramount. Even though various new bearing surfaces have been investigated, research is still ongoing, and only short-term results have been reported from clinical trials. Future bearing surfaces can be developed in the following ways: (1) change in design, (2) further improvement of polyethylene, (3) surface modification of the metal, (4) improvement in the ceramic, and (5) use of alternative, new materials. One way to reduce wear and impingement in THA is to make changes in its design by using a large femoral head, a monobloc metal shell with preassembled ceramic liner, dual mobility cups, a combination of different bearing surfaces, etc. Polyethylene has improved over time with the development of highly crosslinked polyethylene. Further improvements can be made by reinforcing it with vitamin E or multiwalled carbon nanotubes and by performing a surface modification with a biomembrane. Surface modifications with titanium nitride or titanium niobium nitride are implemented to try to improve the metal bearings. The advance to the fourth generation ceramics has shown relatively promising results, even in young patients. Nevertheless, further improvement is required to reduce fragility and squeaking. Alternative materials like diamond coatings on surfaces, carbon based composite materials, oxidized zirconium, silicon nitride, and sapphire are being sought. However, long-term studies are necessary to confirm the efficacy of these surfaces after enhancements have been made with regard to fixation technique and implant quality.     

Modern metal-on-metal hip implants

This Technology Overview was prepared using systematic review methodology and summarizes the findings of studies published as of July 15, 2011, on modern metal-on-metal hip implants. Analyses conducted on outcomes by two joint registries indicate that patients who receive metal-on-metal total hip arthroplasty (THA) and hip resurfacing are at greater risk for revision than are patients who receive THA using a different bearing surface combination. Data from these registries also indicate that larger femoral head components have higher revision rates and risk of revision and that older age is associated with increased revision risks of large-head metal-on-metal THA. Several studies noted a correlation between suboptimal hip implant positioning and higher wear rates, local metal debris release, and consequent local tissue reactions to metal debris. In addition, several studies reported elevated serum metal ion concentrations in patients with metal-on-metal hip articulations, although the clinical significance of these elevated ion concentrations remains unknown.     

Ceramic-on-ceramic total hip arthroplasty: A new standard—Affirms

Highly cross-linked polyethylene has emerged as an improvement over conventional polyethylene in terms of wear characteristics and osteolysis in total hip replacement; however, decreased material properties could make it unsuitable for use in high-demand patients. Modern ceramic-on-ceramic bearings display extremely low wear and durability that make them an ideal bearing surface. Unfortunately, certain implant designs have been associated with squeaking, which has discouraged widespread use. Proper implant selection, orientation, and surgical technique can lead to optimal results with ceramic bearings, and substantial mid- to long-term data exists to support their use over other bearing surfaces in total hip replacement.     

Long-term results of cementless anatomic total hip replacement in dysplastic hips

This perspective study analyzes the long-term outcomes of cementless anatomic total hip arthroplasty (THA) in patients with developmental dysplasia of the hip (DDH). Between 1990 and 2004, 100 ABG total hip prosthesis were implanted in 87 patients with DDH. The average follow-up was 9 years (range 4–18 years). The mean Harris Hip Score was 87.13 (SD = 14.6) at the last follow-up. Radiographic analysis showed good results for the stems, while in 38% of the hips we recorded periacetabular bone resorption. Mean linear polyethylene wear was 0.23 mm/year. Ten revisions have been performed, survival rate was 99% for the stems and 90% for the cups. Cementless THA with hemispherical cup and anatomical stem is recommended when possible for patients with DDH although high rates of polyethylene wear and subsequent osteolysis have been the limiting factor in the long-term success of this implant.     

Durability of implant fixation after less-invasive total hip arthroplasty

Less-invasive techniques for total hip arthroplasty (THA) have sparked an increased interest among orthopedic surgeons and patients. There has been concern regarding decreased surgical exposure and compromise in prosthesis durability. We present the first long-term outcome of THA performed via the mini-incision posterior approach to show the durability of implant fixation. We compare the clinical and radiographic findings with previously published findings of authors using the same femoral implant and standard surgical techniques over a similar follow-up period. Ninety implants were followed for 10 to 13 years. Clinical evaluation revealed a Harris Hip Score of 92.3. Radiographic evaluation revealed proximal bone atrophy in 57% and lucent lines in 14% of femurs and 11% of cups. Osteolysis was noted in 10% and was associated with polyethylene wear. There were no cases of aseptic stem loosening. Eight polyethylene inserts were revised for wear. These 10-year minimum follow-up findings are consistently comparable with previously published studies using the same implant and larger surgical approaches followed for a similar period. Mini-incision THA technique did not compromise the long-term clinical and radiographic findings when compared with conventional techniques.     

Unconstrained tripolar implants for primary total hip arthroplasty in patients at risk for dislocation

We performed a retrospective study on 167 primary total hip arthroplasty (THA) procedures in 163 patients at high risk for instability to assess the reliability of unconstrained tripolar implants (press-fit outer metal shell articulating a bipolar polyethylene component) in preventing dislocations. Eighty-four percent of the patients had at least 2 risk factors for dislocation. The mean follow-up length was 40.2 months. No dislocation was observed. Harris hip scores improved significantly. Six hips were revised, and no aseptic loosening of the cup was observed. The tripolar implant was extremely successful in achieving stability. However, because of the current lack of data documenting polyethylene wear at additional bearing, the routine use of tripolar implants in primary THA is discouraged and should be considered at the present time only for selected patients at high risk for dislocation and with limited activities.     

Ceramic-on-polyethylene: The experience of the Ranawat Orthopaedic Center

Traditionally, metal-on-polyethylene has been the gold standard bearing in total hip arthroplasty. Ceramics were introduced as an alternative bearing because of their superior mechanical properties. Our institution has found that ceramic-on-polyethylene has consistently shown lower in vivo wear rates compared to metal-on-polyethylene. The latest generation of ceramic-on-polyethylene, BIOLOX delta-on-highly cross-linked polyethylene, has shown an excellent linear wear rate (0.006 mm/yr), which is much lower than previously found wear rates for cobalt–chrome-on-highly cross-linked polyethylene (0.011 mm/yr). The minimal wear rate of BIOLOX delta-on-highly cross-linked polyethylene provides the potential to increase long-term survivorship and become the new gold standard bearing in THA.     

Long-term survival of McKee-Farrar total hip prostheses

Because of the recent resurgence of interest in metal-on-metal bearing components for total hip arthroplasties, the long-term results of 153 consecutive McKee-Farrar total hip arthroplasties done in 129 patients by one surgeon between 1969 and 1973 were evaluated. A retrospective chart review provided patient demographics (age, gender, weight, primary diagnosis), revision dates, indications, and implant survival data. The average age of the patients at implantation surgery was 61 years (range, 28-85 years) and these patients were observed as many as 28 years. Primary diagnoses included osteoarthritis (49% of implants), rheumatoid arthritis (38%), and other conditions (13%). During the 28 years of followup, five implants were revised for infection and 14 implants were revised for aseptic loosening. Survivorship analysis of the McKee-Farrar prostheses had a 20-year probability of implant survivorship of 84%, and a 28-year implant survivorship of 74%. Excellent long-term results of the McKee-Farrar prosthesis were seen. Given the inherent problems associated with implant wear debris, especially polyethylene wear particles, second generation metal-on-metal bearing implants may offer a viable alternative to current designs. Their excellent long-term survival may infer particular suitability for use in younger patients.     

Ceramic-on-ceramic bearings in total hip arthroplasty: “The future is now”

Total hip arthroplasty (THA) currently provides durable long-term outcomes, but osteolysis secondary to polyethylene wear debris remains a cause of aseptic loosening and revision. Ceramic-on-ceramic bearings surfaces have a long history of successful clinical use. Reported limitations of ceramic bearings are fracture and squeaking, but their incidence has been reduced through the evolution of fourth-generation ceramic compounds and a greater understanding of the role of component positioning, edge loading and resultant noise generation. The optimum bearing surface is one with very low wear rates, a low coefficient of friction, scratch resistance and is biologically inert. It is also one that can safely accommodate larger femoral head sizes to minimize dislocation rates without damaging the taper junction. Such a material already exists with modern ceramics, making them the ideal bearing material for total hip arthroplasty. “The future is now”.     

Clinical applications of oxidized zirconium

Total joint arthroplasty is being performed in younger, more active patients, which necessitates improved implant longevity and enhanced component performance. Over the past decade, there has been an increased focus on alternative bearing materials as a potential solution to these issues. Historically, cobalt-chromium has been the material of choice as a bearing surface for both the femoral component in total knee arthroplasty (TKA) and the femoral head articulation in total hip arthroplasty (THA). In recent years, oxidized zirconium (OxZr) has been introduced as a bearing surface with superior resistance to surface roughening, improved frictional characteristics, and excellent biocompatibility as compared with cobalt-chrome. This article demonstrates the use of OxZr as an alternate bearing in the setting of TKA, THA, and hip hemi-arthroplasty based on its biomaterial properties as it applies to polyethylene and native cartilage surface articulation.     

Long-term outcome of surface replacement with comparison to an age- and time-matched primary total hip arthroplasty cohort

Surface replacement (SR) was introduced as a bone-conserving alternative to total hip arthroplasty (THA) 3 decades ago, then was abandoned due to polyethylene wear, stress shielding, and loosening. Improved bearing surfaces have renewed interest in SR. This study examined long-term SR outcome compared to an age- and time-matched THA cohort. Average age was 47 years at index procedure with 16 years follow-up (range, 5-28). Revision rates were 86% and 40% in SR and THA groups, respectively. However, at 20 years, with an end point of either intact SR or primary THA in the SR group, survivorship was 64% +/- 6% versus 39% +/- 7% unrevised in THA cohort. Contemporary and rapidly changing technology may result in longer-term SR success and improved THA longevity in young patients.     

Preoperative demand matching is a valid indicator of patient activity after total hip arthroplasty

The validity of preoperative demand matching as an indicator of patient activity following total hip arthroplasty (THA) was evaluated by studying 518 patients (mean age, 67 years; range, 26-92 years) who were assigned to 4 categories of decreasing demand: I (high demand), 68 patients (13%); II, 144 patients (28%); III, 281 patients (54%); and IV (low demand), 25 patients (5%). Preoperative Lahey Clinic Demand Category (as defined by age, weight, expected activity, health, and bone stock) was significantly correlated with self-reported, postoperative patient activity (P = .0038, R2 = .2024) and was much more predictive than any individual variable. Because patient activity is related to hip joint bearing surface wear, implant selection and resource allocation could be influenced by using demand matching to identify patients with high postoperative demand who may benefit from improvements in implant technology. Demand matching may also be used to stratify patient activity in long-term outcomes studies of THA.     

How prevalent are implant wear and osteolysis, and how has the scope of osteolysis changed since 2000?

Although the incidence of failures resulting from wear-related osteolysis and associated severe bone defects are expected to diminish with important advances in polyethylene manufacturing and processing, alternative bearing surfaces, implant design, and revision techniques, current failures still reflect concerns regarding earlier ultra-high-molecular-weight polyethylene sterilization and degradation. Clinical experience before the year 2000 included rates of wear and osteolysis from 10% to as high as 70% at 7- to 14-year follow-up. With recent advances, early clinical results are encouraging, demonstrating 50% to 81% decreases in radiographic wear rates. These improvements should eventually reduce the burden of future revision hip and knee surgery. However, the long-term in vivo durability of total hip arthroplasties using these alternative materials and bearing couples has not yet been well established, and considerably fewer clinical data are available for other types of joint arthroplasties, such as total knee arthroplasty.     

Long-Term Follow-Up of Conventional Polyethylene in Total Hip Arthroplasty in Young Patients: Heightened Wear-Related Complications Are Observed at the Beginning of the Third Decade

BackgroundConventional polyethylene (CPE) was used widely in the past as a bearing surface in total hip arthroplasty (THA). As CPE THAs age and the revision burden continues to grow, it is increasingly important to understand the durability and failure mechanisms of this bearing material. Currently, such long-term data remain limited, particularly in younger, more active patients in whom wear issues are of greater concern.MethodsWe retrospectively reviewed 90 hips (77 patients) that underwent primary THA with CPE bearings on cobalt chrome femoral heads at age ≤50 years at 20-year minimum follow-up (mean 21.6 [20-23]). We analyzed polyethylene wear rates, clinical outcomes (modified Harris Hip Score, University of California, Los Angeles Activity Score), and implant survivorship.ResultsWear analysis revealed a median linear wear rate of 0.113 mm/y (95% CI 0.102-0.148) and a median volumetric wear rate of 41.20 mm³/y (95% CI 43.5-61.0). Modified Harris Hip Scores remained 37 points above preoperative baseline (P < .001) and University of California, Los Angeles scores 1.4 points above baseline (P = .018) at 21.6-year mean follow-up. Twenty-nine hips (32.2%) were revised, 20 of which (22.2%) were wear-related at a median of 15.4 years (interquartile range 11.4-19.5). Survivorship free from wear-related revision was 95.6% (95% CI 88.7-98.3), 87.9% (78.6-93.3), 78.1% (49.6-66.5), and 61.1% (41.3-67.0) at 10, 15, 20, and 25 years.ConclusionWear-related issues developed at increasingly high rates after 15 years, suggesting the need for surveillance after this time. The long-term wear and survivorship data of this study may be used as a benchmark when evaluating the performance of contemporary bearings in young, active THA patients.     

Wear testing of a canine hip resurfacing implant that uses highly cross‐linked polyethylene

Hip resurfacing offers advantages for young, active patients afflicted with hip osteoarthritis and may also be a beneficial treatment for adult canines. Conventional hip resurfacing uses metal‐on‐metal bearings to preserve bone stock, but it may be feasible to use metal‐on‐polyethylene bearings to reduce metal wear debris while still preserving bone. This study characterized the short‐term wear behavior of a novel hip resurfacing implant for canines that uses a 1.5 mm thick liner of highly cross‐linked polyethylene in the acetabular component. This implant was tested in an orbital bearing machine that simulated canine gait for 1.1 million cycles. Wear of the liner was evaluated using gravimetric analysis and by measuring wear depth with an optical scanner. The liners had a steady‐state mass wear rate of 0.99 ± 0.17 mg per million cycles and an average wear depth in the central liner region of 0.028 mm. No liners, shells, or femoral heads had any catastrophic failure due to yielding or fracture. These results suggest that the thin liners will not prematurely crack after implantation in canines. This is the first hip resurfacing device developed for canines, and this study is the first to characterize the in vitro wear of highly cross‐linked polyethylene liners in a hip resurfacing implant. The canine implant developed in this study may be an attractive treatment option for canines afflicted with hip osteoarthritis, and since canines are the preferred animal model for human hip replacement, this implant can support the development of metal‐on‐polyethylene hip resurfacing technology for human patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1196–1205, 2018.

     

New alternate bearing surfaces in total hip arthroplasty: A review of the current literature

As indications for total hip arthroplasty (THA) have expanded, the incidence of THA has increased among younger patients, who live longer and tend to place more strain on implants via higher activity levels. This demographical shift accentuates the importance of advancing innovation to ensure implant longevity for younger and more active patients. Future innovation, as it pertains to THA components, is likely to focus on modifying implant designs and tribology in conjunction with identification and application of newer biomaterials. By reviewing the literature for development status of various materials and novel design advancements in THA component outside of the standard highly cross-linked polyethylene, this investigation provided an update on the current and future status of design initiatives as they pertain to THA. Though the highlighted alternative bearing surfaces have shown promising in vitro and limited, yet encouraging clinical data, they lack larger and longer-term clinical trial results. Further research and innovation is warranted to identify the optimal bearing surface to most effectively accommodate for the trend of younger and more active patients undergoing THA. Implant longevity is crucial if the clinical success of THA is to be maintained.     

How have alternative bearings (such as metal-on-metal, highly cross-linked polyethylene, and ceramic-on-ceramic) affected the prevention and treatment of osteolysis?

Osteolysis is a multifactorial process dependent on surgical technique, implant design, patient factors, and material composition. Alternative bearing surfaces, such as highly cross-linked polyethylene, ceramic-on-ceramic, and metal-on-metal articular surfaces, have been introduced in an attempt to reduce wear and osteolysis following total hip arthroplasty. Intermediate-term follow-up data available suggest that the prevalence and severity of osteolysis may be reduced with these materials compared with conventional metal-on-polyethylene bearing surface couples. However, long-term data are presently unavailable; the future performance of these bearings awaits clinical validation.     

Conventional Polyethylene in Total Hip Arthroplasty in Young Patients: Survivorship,Wear Analysis,and Clinical Outcomes Between 15 and 20 Years

Background

Total hip arthroplasty (THA) remains a successful procedure for most patients. However, there is a paucity of information regarding the long-term performance of conventional polyethylene (CPE) bearings in young patients undergoing THA.