JAAOS

JAAOS, Volume 16, No. suppl 1


Are there biological markers of wear?

Potential systemic markers of implant wear include products of the wear process (particles and ions) and mediators of the inflammatory reaction that can be induced by wear. Ions from polymers used in arthroplasty are not specific, but high metal ion levels may help identify patients with unexpectedly high wear of metal-on-metal implants. The kinetics of ion production, transport, and excretion are complex, however, so it is currently difficult to interpret the significance of mild elevations in metal ions. Indices of bone turnover (eg, collagen fragments) and mediators involved in the inflammatory reaction to particles (eg, osteoprotegerin, RANKL, interleukins) may be associated with osteolysis, but systemic disorders (eg, osteoarthritis) and the use of medications that influence bone remodeling limit the predictive value of these analytes with respect to the consequences of implant wear. Using genomic and proteomic methods to measure multiple analytes offers promise, but the challenge is to identify markers specifically associated with wear that are not elevated by other conditions that often coexist in this patient population.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Biological Markers|Foreign-Body Reaction|Hip Prosthesis|Humans|Immunologic Factors|Metals|Osteolysis|Prosthesis Design|Prosthesis Failure|Stress

    • Mechanical

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How are wear-related problems diagnosed and what forms of surveillance are necessary?

Prospective, randomized clinical wear studies have shown significant wear reduction when highly cross-linked, e-beamed, melted polyethylene was compared with conventional polyethylene sterilized by gamma irradiation in air. More complete assessment of wear-induced osteolysis in the general total hip arthroplasty patient population must rely on registries with follow-up of large populations of patients through radiographic evaluation of wear-related factors, such as suboptimal placement of the implant components, osteolytic defects, and aseptic loosening. Follow-up radiographs should be obtained in the early postoperative period and at 1, 5, and 10 years postoperatively, and then every 1 to 5 years, thereafter depending on radiographic findings of osteolysis and its progression. When pathologic findings are present, further examinations, such as oblique Judet views and magnetic resonance imaging (MRI) with artifact minimization should be considered to provide a better determination of the extent of the osteolysis. Because conventional radiographs underestimate the prevalence and extent of osteolysis in many instances, diagnosis and surveillance should be performed with radiographic edge detection, spiral computed tomography (CT), MRI, radiostereometric analysis, and quantitation of wear and osteolysis, including bone and soft-tissue lesions. Helical CT has demonstrated excellent specificity in identifying and quantifying the extent of osteolysis. MRI can more accurately localize both osseous and soft-tissue particulate disease, and detect granuloma and compression on adjacent nerves and vessels.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Equipment Failure Analysis|Humans|Joint Prosthesis|Magnetic Resonance Imaging|Osteolysis|Polyethylene|Prosthesis Design|Prosthesis Failure|Randomized Controlled Trials as Topic|Stress

    • Mechanical|Tomography

    • Spiral Computed

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How do alternative bearing surfaces influence wear behavior?

Metal, ceramic, and polyethylene liners represent contemporary bearing choices for total joint replacement. Each has limitations in terms of design, sensitivity to manufacturing, and surgical placement. With polyethylene, larger femoral heads represent a design restriction and a potential wear issue. One side benefit is that polyethylene does not click, squeak, or create stripe wear. The attraction of hard-on-hard bearings (metal-on-metal, ceramic-on-ceramic) is that their typically ultra-low wear alleviates concerns with large femoral head designs. However, hard-on-hard bearings produce stripe wear due to the effects of the rigid liner edge. Slight subluxation (microseparation) during swing phase of gait can result in stripe wear on the ball and liner rim. In addition, high levels of implant wear with vertically placed cups can be anticipated. Currently, only alumina-on-alumina bearings can claim virtually no biologic risk. Thus, the role of laboratory studies is to isolate relevant aspects of performance by cup design and to predict the risk-benefit ratios in patients requiring total hip replacement.

    • Keywords:
    • Aluminum|Biocompatible Materials|Ceramics|Equipment Failure Analysis|Friction|Hip Prosthesis|Humans|Materials Testing|Metals|Polyethylene|Prosthesis Design|Prosthesis Failure|Stress

    • Mechanical|Surface Properties

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How do material properties influence wear and fracture mechanisms?

The wear and fracture mechanisms of ultra-high-molecular-weight polyethylene (UHMWPE) hip and knee implant components are of great interest. The material properties of UHMWPE are affected by ionizing radiation as used for sterilization and cross-linking. Cross-linking with high-dose irradiation has been shown to improve the wear resistance of UHMWPE. However, cross-linking leads to a loss in properties such as ductility and resistance to fatigue crack propagation. Highly cross-linked UHMWPE may be more susceptible than conventional UHMWPE to fracture under severe clinical conditions (eg, impingement). Contemporary hip and knee simulator studies provide good information with which new UHMWPE formulations can be screened for clinical wear performance. However, comparable methodologies are lacking for screening UHMWPEs for fracture resistance. Mechanical tests as well as computational material and structural models should be developed to evaluate the combined effect of material and geometry (structure) on fracture resistance under clinically relevant loading conditions.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Equipment Failure Analysis|Humans|Joint Prosthesis|Materials Testing|Polyethylenes|Prosthesis Design|Prosthesis Failure|Radiation

    • Ionizing|Sterilization|Stress

    • Mechanical|Surface Properties

    • Subspecialty:
    • Trauma

    • Basic Science

How has the biologic reaction to wear particles changed with newer bearing surfaces?

Orthopaedic surgeons have new tools that address the problem of aseptic loosening and osteolysis, and these tools are now in widespread clinical use. Hard-on-hard bearing couples as well as metal-on-highly cross-linked polyethylene bearing couples have lower volumetric wear rates and represent promising solutions to reduce the prevalence of osteolysis and aseptic loosening in total joint arthroplasty. Volumetric wear rates alone, however, do not completely predict the osteolytic potential that is also a function of particle composition, size, morphology, and a number of other particle characteristics. Host factors, including differing innate reactivities to wear products and adaptive immune responses, remain important but incompletely defined. Although the toxicologic significance of local and systemic elevations in metal ions has not been definitively established, monitoring patients with metal-on-metal bearings with serum metal ion levels can be useful to determine the state of the bearing. Furthermore, optimization of these bearing systems to further diminish wear and corrosion would be highly desirable.

    • Keywords:
    • Adaptation

    • Physiological|Arthroplasty

    • Replacement|Biocompatible Materials|Foreign-Body Reaction|Humans|Joint Prosthesis|Osteolysis|Particle Size|Polyethylenes|Prosthesis Design|Prosthesis Failure|Surface Properties

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

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.

    • Keywords:
    • Biocompatible Materials|Ceramics|Equipment Failure Analysis|Hip Prosthesis|Humans|Materials Testing|Metals|Osteolysis|Polyethylene|Prosthesis Design|Prosthesis Failure|Stress

    • Mechanical|Surface Properties

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How have new designs and new types of joint replacement influenced wear behavior?

As the principles of joint arthroplasty become increasingly refined and more widely established, new designs are being developed that require careful evaluation for their propensity to generate wear debris in vivo. In the past several years, new designs intended to improve clinical performance have emerged in both total knee replacement and total spinal disk replacement. Advances in these types of implants have the potential for major clinical impact in the coming decade, due to the large number of patients seeking treatment of knee arthritis as well as back pain, neck pain, and radiculopathy.

    • Keywords:
    • Arthroplasty

    • Replacement|Chromium Alloys|Equipment Failure Analysis|Humans|Intervertebral Disk|Joint Prosthesis|Knee Joint|Materials Testing|Polyethylene|Prosthesis Design|Prosthesis Failure|Stainless Steel|Surface Properties|Titanium

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How have new sterilization techniques and new forms of polyethylene influenced wear in total joint replacement?

Polyethylene has undergone many changes over the past several decades, including changes in consolidation processes, resin types, sterilization methods, packaging, and the extent of cross-linking. We believe that new sterilization techniques and forms of polyethylene have generally improved wear performance. Polyethylene sterilized without the use of radiation has been shown to have relatively high rates of wear in vivo. Ram-extruded polyethylene sterilized via gamma irradiation in air has been the most commonly used bearing material in the past several decades. Recently, components molded and gamma-sterilized without oxygen as well as highly cross-linked material have found increased clinical use. Exposure of polyethylene to radiation, either to sterilize it or to intentionally cross-link it, has been shown to improve the wear performance of the material. Newer second-generation methods of cross-linking polyethylene include the use of vitamin E, which quenches free radicals and demonstrates promise in providing low wear and desirable mechanical properties.

    • Keywords:
    • Arthroplasty

    • Replacement|Biocompatible Materials|Electrons|Equipment Failure Analysis|Gamma Rays|Humans|Joint Prosthesis|Materials Testing|Polyethylene|Prosthesis Design|Prosthesis Failure|Sterilization

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

How have wear testing and joint simulator studies helped to discriminate among materials and designs?

Historically, hip joint simulators most often have been used to model wear of a bearing surface against a bearing surface. These simulators have provided highly accurate predictions of the in vivo wear of a broad spectrum of bearing materials, including cross-linked polyethylenes, metal-on-metal, ceramic-on-ceramic, and others in development. In recent years, more severe conditions have been successfully modeled, including jogging, stair climbing, ball-cup micro separation, third-body abrasion, and neck-socket impingement. These tests have served to identify improved materials and to eliminate some with inadequate wear resistance prior to their clinical use. Simulation of the knee joint is inherently more complex than it is for the hip. It is more difficult to compare the results of laboratory tests with actual clinical performance, due to the lack of accurate in vivo measures of wear. Nevertheless, knee simulators, based on force control or motion control, have successfully reproduced the type of surface damage that occurs in vivo (eg, burnishing, scratching, pitting) as well as the size and shapes of the resultant wear particles. Knee simulators have been used to compare molded versus machined polyethylene components, highly cross-linked polyethylenes, fixed versus mobile bearings, and oxidized zirconia and other materials, under optimal conditions as well as more severe wear modes, such as malalignment, higher loading and activity levels, and third-body roughening.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Biomechanics|Computer Simulation|Equipment Failure Analysis|Hip Prosthesis|Humans|Knee Prosthesis|Materials Testing|Prosthesis Design|Prosthesis Failure|Stress

    • Mechanical

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

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.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Device Removal|Equipment Failure Analysis|Humans|Joint Prosthesis|Osteolysis|Polyethylene|Prevalence|Prosthesis Design|Prosthesis Failure|Reoperation

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

Orthopaedic joint devices: the FDA's short answers to your questions.

This article briefly describes the US Food and Drug Administration regulatory process for medical devices, focusing on orthopaedic joint device examples. The mission of the Center for Devices and Radiological Health is to promote and protect the health of the public by ensuring that the medical devices that reach US consumers are safe and effective for their intended function. A question and answer section is included as a reference guide for the orthopaedic community to broadly address some common issues related to orthopaedic device constructs, such as hybridization of joint systems, labeling claims, modifications to ultra-high-molecular-weight polyethylene sought by manufacturers to minimize wear and osteolysis, combination products, and the responsibilities of an orthopaedic surgeon. The FDA relies on accurate scientific evidence and regulatory science to determine the safety and effectiveness of orthopaedic joint devices.

    • Keywords:
    • Device Approval|Government Regulation|Humans|Joint Prosthesis|Legislation

    • Medical|Orthopedic Equipment|Product Labeling|Prosthesis Design|United States|United States Food and Drug Administration

    • Subspecialty:
    • Adult Reconstruction

    • Clinical Practice Improvement

    • Basic Science

What are the guidelines for the surgical and nonsurgical treatment of periprosthetic osteolysis?

Periprosthetic osteolysis is most often diagnosed by plain radiographs. Because these radiographs routinely underestimate the extent of the lesion, three-dimensional imaging should be used early in the evaluation process to confirm the presenting extent of disease. If the osteolytic process is asymptomatic, scheduled regular follow-up should be instituted until the lesion can be confirmed to be stable or until the decision is made to proceed with surgery. Nonsurgical management with pharmacologic agents has not proved to be effective. If surgery is contemplated, a three-dimensional evaluation with magnetic resonance imaging or helical computed tomography can assist in preoperative planning. Surgical intervention requires complete débridement of the lesional membrane and removal of the wear-generator--with or without component removal and with or without bone grafting, depending on the individual circumstances. A standardized follow-up evaluation mechanism for all patients should be a part of total joint arthroplasty management.

    • Keywords:
    • Acetabulum|Arthroplasty

    • Replacement|Biocompatible Materials|Clinical Protocols|Debridement|Humans|Joint Prosthesis|Osteolysis|Practice Guidelines as Topic|Prosthesis Design|Prosthesis Failure|Reoperation

    • Subspecialty:
    • Adult Reconstruction

What are the local and systemic biologic reactions and mediators to wear debris, and what host factors determine or modulate the biologic response to wear particles?

New clinical and basic science data on the cellular and molecular mechanisms by which wear particles stimulate the host inflammatory response have provided deeper insight into the pathophysiology of periprosthetic bone loss. Interactions among wear particles, macrophages, osteoblasts, bone marrow-derived mesenchymal stem cells, fibroblasts, endothelial cells, and T cells contribute to the production of pro-inflammatory and pro-osteoclastogenic cytokines such as TNF-alpha, RANKL, M-SCF, PGE2, IL-1, IL-6, and IL-8. These cytokines not only promote osteoclastogenesis but interfere with osteogenesis led by osteoprogenitor cells. Recent studies indicate that genetic variations in TNF-alpha, IL-1, and FRZB can result in subtle changes in gene function, giving rise to altered susceptibility or severity for periprosthetic inflammation and bone loss. Continuing research on the biologic effects and mechanisms of action of wear particles will provide a rational basis for the development of novel and effective ways of diagnosis, prevention, and treatment of periprosthetic inflammatory bone loss.

    • Keywords:
    • Basic Helix-Loop-Helix Transcription Factors|Biocompatible Materials|Bone Resorption|Dinoprostone|Endothelial Cells|Fibroblasts|Foreign-Body Reaction|Humans|Interleukin-1|Interleukin-6|Interleukin-8|Joint Prosthesis|Macrophage Colony-Stimulating Factor|Osteoclasts|Osteogenesis|Prosthesis Failure|RANK Ligand|Stem Cells|T-Lymphocytes|Tumor Necrosis Factor-alpha

    • Subspecialty:
    • Basic Science

What design factors influence wear behavior at the bearing surfaces in total joint replacements?

Bearing surface wear in total joint replacements arises from local stresses that exceed the mechanical strength of the articulating materials. Because both the tensile/compressive principal stresses and maximum shear stress near the bearing surface increase when contact stresses increase, minimizing contact stresses has been a central design goal, especially in total knees. Wear rates increase with factors such as increased sliding distance in metal-on-polyethylene bearings, or suboptimal fluid film lubrication in the case of hard-on-hard total hip implants. These factors in turn depend directly on implant design. Advanced preclinical assessment technologies such as laboratory physical simulators and finite element analyses have provided means by which the dependence of wear rate on mechanical design factors can be quantified. However, untoward complexities occurring in vivo, such as impingement or third-body challenge, can appreciably compromise wear performance even for implants that are well-designed in terms of bearing surface stress minimization.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Compressive Strength|Equipment Failure Analysis|Humans|Joint Prosthesis|Materials Testing|Metals|Polyethylene|Prosthesis Design|Prosthesis Failure|Shear Strength|Stress

    • Mechanical|Surface Properties|Tensile Strength

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

What experimental approaches (eg, in vivo, in vitro, tissue retrieval) are effective in investigating the biologic effects of particles?

Understanding the complex cellular and tissue mechanisms and interactions resulting in periprosthetic osteolysis requires a number of experimental approaches, each of which has its own set of advantages and limitations. In vitro models allow for the isolation of individual cell populations and have furthered our understanding of particle-cell interactions; however, they are limited because they do not mimic the complex tissue environment in which multiple cell interactions occur. In vivo animal models investigate the tissue interactions associated with periprosthetic osteolysis, but the choice of species and whether the implant system is subjected to mechanical load or to unloaded conditions are critical in assessing whether these models can be extrapolated to the clinical condition. Rigid analysis of retrieved tissue from clinical cases of osteolysis offers a different approach to studying the biologic process of osteolysis, but it is limited in that the tissue analyzed represents the end-stage of this process and, thus, may not reflect this process adequately.

    • Keywords:
    • Animals|Arthroplasty

    • Replacement|Biocompatible Materials|Disease Models

    • Animal|Humans|Joint Prosthesis|Osteolysis|Prosthesis Failure|Research Design|Stress

    • Mechanical

    • Subspecialty:
    • Basic Science

What is the outcome of treatment for osteolysis?

Periprosthetic osteolysis secondary to wear-induced particle generation is a common long-term complication of hip and knee replacement and frequently results in the need for revision surgery. Management of significant bone defects remains a surgical challenge. Surgical intervention must address the wear particle generator (usually, but not always, the bearing surface), the osteolytic defects, and implant-related issues, primarily fixation and alignment. Indications for surgical intervention in the absence of loosening and pain are not well established. In general, patient age and activity level, the location and size of the osteolytic defect, and the clinical record of the implant system will dictate treatment choices.

    • Keywords:
    • Arthroplasty

    • Replacement

    • Hip|Arthroplasty

    • Knee|Humans|Joint Prosthesis|Osteolysis|Prosthesis Design|Prosthesis Failure|Reoperation|Treatment Outcome

    • Subspecialty:
    • Trauma

    • Adult Reconstruction

What other biologic and mechanical factors might contribute to osteolysis?

An overwhelming consensus exists that wear particles are the primary driving force in aseptic loosening of orthopaedic implants. Nonetheless, considerable evidence has emerged demonstrating that various other factors can modulate the biologic activity of orthopaedic wear particles. Two of the most studied modulating factors are bacterial endotoxins and implant motion.

    • Keywords:
    • Anti-Bacterial Agents|Arthroplasty

    • Replacement|Equipment Failure Analysis|Humans|Joint Prosthesis|Lipopolysaccharides|Macrophages|Osteolysis|Polyethylene|Prosthesis Design|Prosthesis Failure|Stress

    • Mechanical

    • Subspecialty:
    • Basic Science

What patient and surgical factors contribute to implant wear and osteolysis in total joint arthroplasty?

Total joint arthroplasty has been a successful operation for decades. Our current patients are younger and more active than those in the past. They place higher demands on themselves and have expectations commensurate with their lifestyles. Time-limited longevity with the large number of anticipated total joint replacement procedures and their potential burden to health care is a growing concern. In the past two decades, implant wear and osteolysis have been identified as major causes for the failure of otherwise well-functioning implants. Osteolysis can be divided into several categories: patient-specific, implant-specific, and the result of surgical factors. Although these categories are interrelated and not mutually exclusive, they enable us to build a framework in which to further advance our understanding of osteolysis and apply this information in a clinically relevant manner.

    • Keywords:
    • Arthroplasty

    • Replacement|Equipment Failure Analysis|Humans|Joint Prosthesis|Life Style|Osteolysis|Prosthesis Design|Prosthesis Failure|Reoperation|Risk Factors|Stress

    • Mechanical|Surface Properties

    • Subspecialty:
    • Adult Reconstruction

    • Basic Science

What potential biologic treatments are available for osteolysis?

The host response to wear debris particles constitutes a major component of periprosthetic osteolysis and aseptic loosening. Thus, biologic interventions represent a logical approach to prevent this complication of total joint replacement. Several major obstacles must be overcome before a therapeutic intervention can emerge, most notably the development of a safe and effective drug, as well as the development of a quantitative outcome measure that can prove efficacy in a relatively small multicenter trial of patients with established osteolysis. Research is needed in several areas, including whether a threshold phenomenon exists for osteolytic progression, whether anabolic agents administered postoperatively can significantly increase osteointegration of the implant and reduce the potential for aseptic loosening, and whether RANKL antagonists can inhibit the progression of periprosthetic osteolysis. Imaging advancements and an osteolysis registry would significantly enhance the potential for a successful clinical trial.

    • Keywords:
    • Anabolic Agents|Anti-Inflammatory Agents

    • Non-Steroidal|Arthroplasty

    • Replacement|Diphosphonates|Humans|Immunologic Factors|Interleukin-1|Joint Prosthesis|Osteolysis|Prosthesis Failure|RANK Ligand|Tumor Necrosis Factors

    • Subspecialty:
    • Clinical Practice Improvement

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