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J Am Acad Orthop Surg, Vol 16, No suppl_1, July 2008, S7-S13.
© 2008 the American Academy of Orthopaedic Surgeons
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What patient and surgical factors contribute to implant wear and osteolysis in total joint arthroplasty?

Audrey K. Tsao, MD, Lynne C. Jones, PhD and David G. Lewallen, MD

Dr. Tsao is in private practice, Sun City West, AZ. Dr. Jones is Associate Professor, Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, MD. Dr. Lewallen is Professor of Orthopedic Surgery, Mayo Clinic College of Medicine, and Chair, Division of Adult Reconstructive Surgery, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN.

*The Implant Wear Symposium 2007 Clinical Work Group included John J. Callaghan, MD, John M. Cuckler, MD, Jorge O. Galante, MD, DMSc, Alejandro González Della Valle, MD, Stuart B. Goodman, MD, PhD, James I. Huddleston, MD, Lynne C. Jones, PhD, David G. Lewallen, MD, Henrik Malchau, MD, PhD, William Maloney, MD, Amanda Marshall, MD, Wayne Paprosky, MD, Hollis G. Potter, MD, Michael D. Ries, MD, Aaron Rosenberg, MD, Thomas P. Sculco, MD, Bernard N. Stulberg, MD, Audrey K. Tsao, MD, and Timothy Wright, PhD.

Dr. Tsao or a member of her immediate family has received miscellaneous nonincome support, commercially derived honoraria, or other nonresearch-related funding from Zimmer, holds stock or stock options in Implex, and is a consultant or employee of Zimmer. Dr. Lewallen or a member of his immediate family has received royalties from Zimmer; serves as a consultant to or is an employee of Orthosonics, Zimmer, and Bristol-Myers Squib; and has received research or institutional support from DePuy, Stryker, and Zimmer. Neither Dr. Jones nor a member of her immediate family has received anything of value or owns stock in a commercial company or institution related directly or indirectly to the subject of this article.


   Abstract
Top
 Abstract
Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
 Future Directions for Research
 Figures
 Tables
 References
 
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.

Wear and osteolysis following total joint arthroplasty occur as a result of a complex interaction of variables. These variables include patient-specific characteristics (eg, weight, activity level) that affect the magnitude and direction of loads across the joint as well as joint kinematics;1-4 implant design and material factors that control how the implant components respond to the mechanical burden placed upon them.5-7 Equally important are surgical factors (eg, component position, orientation) that can also affect joint loads and kinematics. When surgical technique is optimized, the ideal implant position is realized and the best possible wear performance of the total joint arthroplasty can be achieved. However, when malpositioned, damaged, or misassembled, a specific prosthesis may experience greatly increased wear. Osteolysis can occur as a response to periprosthetic particulate debris that results from and is dependent on material type as well as particle size, shape, and amount.8-12 The multiple factors influencing clinical wear performance of hip and knee arthroplasty can be separated into patient-specific, implant-specific, and surgical factors that contribute to wear directly or indirectly.


   Patient-specific Factors
Top
 Abstract
 Patient-specific Factors
Implant-specific Factors
 Surgical Factors
 Future Directions for Research
 Figures
 Tables
 References
 
Patient-specific factors that affect joint loading or wear following hip and knee arthroplasty are listed in Table 1.12-15 Activity level gauged with pedometer measurements can vary as much as 45-fold between individuals following arthroplasty.16 Patients with active lifestyles often return to recreational activities that markedly increase joint-loading conditions (eg, running, jumping, pivoting, stair climbing).17 Increased body weight can be associated with increased magnitude of force and altered kinematics, although the detrimental effects of excessive weight can be counterbalanced by decreased activity levels and loading cycles that accompany a sedentary lifestyle.18,19 In general, any patient-specific factors that increase the magnitude of joint load per step or the number of loading cycles per year will have an adverse effect on wear performance and can thus increase the rate and severity of associated osteolysis.2,3,18,20


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  		Table 1  Patient-specific Factors Affecting Joint Wear
 
Selected preoperative diagnoses such as posttraumatic arthritis and osteonecrosis have been associated with higher prosthesis failure rates when compared with osteoarthritis. These increased rates of aseptic loosening, wear, and osteolysis are probably a consequence of the higher activity level and younger age of these patients.21 Because of relatively high rates of knee osteoarthritis many years following meniscal and anterior cruciate ligament injuries due to sports participation, these injuries lead to altered kinematics that can affect the onset and progression of arthritis (and hence the need for arthroplasty). The recent increase in young females with anterior cruciate ligament injuries resulting from sports participation will likely yield higher arthroplasty rates at younger ages in the cohort of female individuals currently aged 15 to 30 years, even when they are treated with surgical repair. This will increase the already predominantly female population of arthroplasty patients. Recent anthropometric data on differences between sexes and races indicate that patients who perform activities such as deep flexion for kneeling, load implants beyond current design characteristics and risk increasing wear and associated osteolysis.8,22-29

The shifting demographics in the United States will lead to increased numbers of younger individuals undergoing arthroplasty.21,30,31 This shift, coupled with the expansion of indications for total joint arthroplasty to include more active patients, will result in increased risk of implant wear compared with the older, lighter, and less active arthroplasty populations of years past. Currently, many patients have higher expectations of hip and knee arthroplasty, exacerbated by media reports and direct-to-consumer marketing efforts by manufacturers, hospitals, and surgeons. Moreover, many patients are motivated to remain physically active after surgery, with some resuming participation in high-impact and competitive sports. This substantial shift in the type of patients seeking arthroplasty will have a potential adverse effect on wear performance. Additionally, this makes comparison to historical data on wear performance in older, more sedentary arthroplasty patients and to earlier outcome studies difficult and may not provide accurate predictions for surgeons and their patients. In fact, surgeons are increasingly encountering patients seeking arthroplasty who are highly active and clinically symptomatic. These patients do not want to return to normal activity in a disabled state but expect to maintain their prior high activity level. This represents a major change in the patient population undergoing total joint arthroplasty compared to prior decades. Coupled with demographic trends, this will result in a dramatic, nonlinear increase in the number of primary and revision arthroplasty procedures performed in the United States (Figures 1 and 2).


Figure 1
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  		Figure 1 Estimated population growth in the United States, 1995 to 2010.

 

Figure 2
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  		Figure 2 A, The projected number of primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) procedures in the United States from 2005 to 2030. B, The projected number of revision THA and TKA procedures in the United States from 2005 to 2030. (Reproduced with permission from Kurtz S, Ong K, Lau E, Mowat F, Halpern M: Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89:780-785.)

 

   Implant-specific Factors
Top
 Abstract
 Patient-specific Factors
 Implant-specific Factors
Surgical Factors
 Future Directions for Research
 Figures
 Tables
 References
 
Implant-specific factors that affect wear performance of both hip and knee arthroplasties are summarized in Table 2. In total hip arthroplasty, bearing options include metal or ceramic-on–compression-molded or highly cross-linked polyethylene, ceramic-on-ceramic, and metal-on-metal articulations. Improvements in wear resistance with all of these articulations compared with prior conventional ultra-high–molecular-weight polyethylene (UHMWPE) sterilized by gamma irradiation in air are supported at least by midterm (5-year follow-up) clinical data; long-term data currently are unavailable. Unlike total hip replacement, the primary choice of materials for the bearing surfaces in total knee arthroplasty has been limited to metal-on-polyethylene. Material issues have focused on the type of metal and surface characteristics, the type of UHMWPE, modularity (and associated backside wear), and the type of implant fixation. Studies have shown that wear and delamination are influenced by sterilization method, resin type, and manufacturing method.32-35 Cross-linking has been shown to decrease wear in laboratory simulations, but alterations in mechanical properties in first-generation highly cross-linked polyethylene may adversely impact resistance to breakage, fatigue cracking, and the performance of locking mechanisms.5,36 This is especially true in poorly positioned implants and those experiencing excessive edge loading. Implant design may contribute to kinematic conditions that accelerate wear debris generation. Backside wear has been demonstrated in both modular metal-backed acetabular and tibial components.37 Several other design factors can influence wear of tibial knee components; these include modularity, UHMWPE insert thickness, locking mechanism, presence of screw holes, inclusion of a mobile or rotating platform, and whether the posterior cruciate ligament is retained.38,39 All of these factors can influence contact stresses experienced by the UHMWPE insert and, thus, the wear of these components.40-42 Furthermore, a stable implant interface, regardless of type of fixation, can limit access of wear particles to the host bone, providing no gaps exist between the prosthesis and bone interface. Surgeon education, awareness, and selection of implants intraoperatively have a direct bearing on patient outcome.33


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  		Table 2  Implant-specific Factors Affecting Joint Wear
 

   Surgical Factors
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 Abstract
 Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
Future Directions for Research
 Figures
 Tables
 References
 
Surgical factors that affect the wear performance of hip and knee arthroplasty are listed in Table 3. Surgical factors have also been shown to play a role in wear mechanisms. Surgical technique affects the thicknesses of bone resection, implant sizing, alignment of each component, articulation and impingement with the opposing implant, and soft-tissue balance.22,43-46 All of these factors can influence the articulation of the components and the contact stresses experienced by the bearing materials.43 Errors of surgical technique such as component malalignment and malrotation can dominate any advantages of improved design or material wear resistance, increasing the chances of focal loading and increased wear.47-49 Acetabular component malpositioning can lead to impingement, which in turn can increase the wear of both the UHMWPE bearing surface as well as the modular interface within the metallic shell. Even careful attention to technique by high-volume, experienced arthroplasty surgeons cannot always prevent variability in knee implant kinematics, as revealed by fluoroscopic studies of joint motion, that could result in accelerated wear.21,30,50


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  		Table 3  Surgical Factors Affecting Joint Wear
 
Concerns have emerged that the newer, less invasive surgical approaches may diminish exposure and visualization and produce a new surgeon learning curve. This may increase the difficulties experienced in both hip and knee surgery in achieving optimal implant position and placement and avoiding iatrogenic implant surface damage. Regardless of exposure, iatrogenic third-body particulate–induced wear may be increased by suboptimal cementing technique, residual bone chips, or debris generated from instruments and implant insertion.

Evaluating surgical technique by studying implant position has been limited by two-dimensional radiographs, although computed tomography studies have been used to assess component rotation and occult osteolysis in selected problem cases. Computer-assisted surgical methods are evolving as a means of reliably achieving accurate soft-tissue balance and proper implant and limb alignment with fewer outliers. Eventually, computerized instrumentation systems may provide surgeons with meaningful kinematic data intraoperatively, which would be expected to lead to improved joint function and reduce wear. However, no clinical improvement in implant survivorship or patient outcomes has been demonstrated thus far with computer-assisted methods, with the possible exception of lower dislocation rates.19,51,52

Larger diameters of femoral heads in total hip arthroplasties have been correlated with increased volumetric wear of conventional UHMWPE, while greater linear wear rates have been observed with smaller femoral head diameters. With the introduction of highly cross-linked polyethylenes and other alternative bearings, larger hip arthroplasty head sizes can be used without adversely affecting wear. Thus, head sizes ≥32-mm diameter are becoming more routine in the United States, except in those cases in which a small acetabular component is necessary. This shift has been prompted by hip-wear simulator experiments showing wear to be minimally affected by changes in head size up to 40 mm and showing newer, highly cross-linked polyethylene materials to be effective at insert thicknesses down to a few millimeters. Short-term clinical studies using highly cross-linked UHMWPE acetabular components have indeed shown reduced wear consistent with laboratory wear simulator data.36,53-57

In total knee arthroplasty, the complex interaction of the tibiofemoral and patellofemoral bearing surfaces requires precise coronal, sagittal, transverse, and rotational alignment.48 Balancing the extensor mechanism to avoid patellar subluxation, tilt, excessive thickness, and/or patella baja or alta avoids increased contact stresses from impingement or maltracking. The complex kinematics of tibiofemoral motion can induce increased contact and subsurface stresses on the UHMWPE tibial insert due to subtle differences in mismatched component sizing, tibial spine or femoral cam impingement in posterior cruciate ligament–sacrificing designs, or increased shear stresses or impingement with imbalanced soft tissues.


   Future Directions for Research
Top
 Abstract
 Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
 Future Directions for Research
Figures
 Tables
 References
 
Although the new materials available for hip and knee arthroplasty offer the promise of reduced wear, the population presenting for surgery has never been more challenging from an implant wear perspective. The balance between patient demand and concerns for wear and fixation has historically pushed the envelope for implant design, materials, and surgical technique. Future clinical studies will define the success of these efforts.


   Figures
Top
 Abstract
 Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
 Future Directions for Research
 Figures
Tables
 References
 


   Tables
Top
 Abstract
 Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
 Future Directions for Research
 Figures
 Tables
References
 


   References
Top
 Abstract
 Patient-specific Factors
 Implant-specific Factors
 Surgical Factors
 Future Directions for Research
 Figures
 Tables
 References
 

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