Volume 17-1, Spring 2008

Tribology is the study of friction, wear, lubrication mechanisms, and their interrelationships. Biotribiology focuses on understanding diarthrodial joints and has been a branch of tribology since 1973. Since then, biotribology has played a prominent role in the evaluation and development of joint prostheses, contributing to reduced wear and increased longevity. Total joint replacements are now common for arthritic patients and are also used in treating a variety of other orthopaedic conditions. For this reason, a complete understanding of the joint lubrication and microstructure that exists in nature is crucial. A subfield of biotribology, biomimetic tribology, has been formed with this goal in mind. This review covers the basic concepts of tribology, provides a brief historical perspective on joint prostheses, and presents the application of tribology in understanding diarthrodial and prosthetic joints. (Journal of Surgical Orthopaedic Advances 17(1):2–5, 2008) Key words: arthroplasty, hip, joint, knee, lubrication, tribology, wear

Traditional metal-on-polyethylene total hip replacements are prone to wear with secondary osteolysis and aseptic loosening, especially in younger, more active patients. Metal-on-metal represents an alternative bearing surface that offers much lower wear rates with the aim of improving longevity and the use of larger femoral heads that confer increased inherent stability, resulting in fewer patient restrictions and improved patient satisfaction. This article discusses the science and clinical evidence in support of choosing metal-on-metal as a bearing as well as its limitations. (Journal of Surgical Orthopaedic Advances 17(1):6–11, 2008) Key words: hip resurfacing, metal-on-metal, revision surgery, total hip, wear

Bone conservation and preservation, joint stability, and low wear of the large metal-on-metal resurfacing bearings have been convincingly demonstrated in the current literature. The clinical results of 600 MM Hybrid Conserve Plus Resurfacing in 519 patients with an average follow-up of 6.9 years (range, 4.0-10.4 years) have been excellent. The average age was 48.9 years, 74% of the patients were male, and the study included all etiologies of the young with arthritis. The complication rates other than dislocation and fracture of the femoral neck are comparable between resurfacing and conventional total hip replacement. The incidence of femoral neck fracture is low (1.2% worldwide) with less than 0.6% in this series and none occurring in the last 5 years due to proper patient selection and improved surgical technique. Component loosening after metal-on-metal resurfacing has been significantly reduced and acetabular component loosening is uncommon and has not happened in this series. Femoral bone preparation and optimal cementing techniques are paramount to prevention of femoral loosening. Clearance between the cylindrically reamed part of the head and the component varies in different designs, and the surgeon must note the need for different cementing strategies for different recommended clearances. The learning curve of a surgeon undertaking resurfacing can be greatly reduced by observation and hands-on training in specialized centers with surgeons experienced in resurfacing. (Journal of Surgical Orthopaedic Advances 17(1):12–16, 2008) Key words: hip resurfacing current status

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. (Journal of Surgical Orthopaedic Advances 17(1):17–26, 2008) Key words: ceramic, oxinium, polyethylene wear, total knee arthroplasty, zirconium

Polyethylene wear-induced osteolysis is the most significant primary factor limiting the life span of total joint arthroplasty. To reduce ultra-high-molecular-weight polyethylene (UHMWPE) particulate wear debris, highly cross-linked polyethylene (HXPE) bearings have been introduced in total hip arthroplasty (THA). In vitro hip simulator wear studies with HXPE have demonstrated a decrease in volumetric wear at the hip by 42% to 100% when compared with conventional metal-on-polyethylene bearings. Early to intermediate clinical results suggest that the in vivo wear properties of HXPE products are superior to those of conventional UHMWPE. Second-generation HXPE materials that utilize alternate cross-linking and free radical quenching techniques have been developed and propose to further minimize wear and oxidation. (Journal of Surgical Orthopaedic Advances 17(1):27–33, 2008) Key words: highly cross-linked polyethylene, osteolysis, total hip arthroplasty

Wear particles are the most important cause of aseptic loosening of orthopaedic devices. To reduce the amount of particles generated from the conventional metal-on-polyethylene system, alternative bearings have been introduced. However, there are some concerns about so-called ‘‘adverse reactions’’ to these bearing surfaces. Despite an apparent longevity, metal particles and metal ions released from the prosthesis can induce a series of adverse reactions. The purpose of this review is to provide the readers an up-to-date overview of the literature on the biological responses to different bearing surfaces with particular reference to metal-on-metal bearings and the local and systemic effect of metal ions. (Journal of Surgical Orthopaedic Advances 17(1):34–39, 2008) Key words: adverse reactions, bearing surfaces, ceramic-on-ceramic, metal-on-metal

Second-generation metal-on-metal (MOM) bearing couples produce less wear debris than firstgeneration implants due to a better understanding of design parameters coupled with improved manufacturing processes. Wear debris generated by MOM bearings is extremely small compared with that from conventional metal-on-polyethylene bearings and can potentially be larger in number. Reductions in metal wear debris may be achieved by the use of differential hardness (DH) bearings for use with surface or total hip replacement implants. Laboratory testing has demonstrated that DH bearings exhibited less abrasive, adhesive, and surface fatigue damage than previous-generation MOM bearing couples. In addition, recent clinical trials have demonstrated a reduction in metal ion levels in patients who were implanted with a differential hardness bearing system. DH bearings may represent a third generation of hard bearing implants for use in hip replacement surgery that may potentially result in less complications and better success rates. (Journal of Surgical Orthopaedic Advances 17(1):40–44, 2008) Key words: clearance, differential hardness, form, lubrication, metal ions, surface roughness, wear

Today, joint replacements are expected to meet greater demands of younger, more active patients and be in service longer than ever before. To meet these demands and reduce the potential for early failure due to osteolysis, alternate bearings surfaces have been developed to minimize the amount of wear in total hip arthroplasties. Improved wear performance, biocompatibility, scratch resistance, a no ion release property, reduced friction, and wettability are characteristics that make ceramics one of the most significant advances in total hip replacement. The manufacturing process for producing alumina ceramic has improved dramatically in recent years, resulting in favorable outcomes. In spite of this, a number of concerns exist. This article describes the incidence and possible causes of various complications associated with ceramic-on-ceramic bearing surfaces. (Journal of Surgical Orthopaedic Advances 17(1):45–50, 2008) Key words: ceramic fracture, ceramic-on-ceramic bearing, complications, total hip arthroplasty, wear rate

Ceramics have been used as a bearing surface in total hip arthroplasty (THA) for more than 30 years. Properties of this material which make it particularly attractive for this application include its hardness, high compression strength, and excellent wettability. The low incidence of biologically significant particle generation and clinically significant osteolysis with the use of ceramics in THA reflects these properties. However, low fracture toughness and linear elastic behavior demonstrated by ceramic make it prone to breakage under stress. Improvements in the processing of ceramic as well as advances in engineering of head-neck articulations and liner design have led to an overall decrease in the incidence of ceramic fracture and dislocation. This article reviews the science behind the use of ceramics in THA, the clinical results of ceramics in THA, including complications unique to this bearing surface, and future directions for the application of ceramics in THA. (Journal of Surgical Orthopaedic Advances 17(1):51–57, 2008) Key words: alumina, ceramics, total hip arthroplasty

Total hip arthroplasty revision due to osteolysis is of considerable concern to the orthopedic surgeon because revisions make up 25% of all total hip arthroplasties today. These revision rates coupled with improvements in cup fixation highlight a common, yet challenging problem of osteolytic lesions in the presence of well-fixed acetabular components. Two case reports are presented of osteolytic lesions treated with debridement and a calcium sulfate graft without the removal of a well-fixed cup. At 3 years postoperatively, both cases show excellent results and no evidence of component compromise. (Journal of Surgical Orthopaedic Advances 17(1):58–61, 2008) Key words: calcium sulfate, osteolysis, revision hip surgery