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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.

Wear Debris in Total Joint Replacements.

In vivo degradation of prosthetic implant materials is increasingly recognized as a major factor limiting the durability of total joint arthroplasty. In vivo degradation occurs primarily by means of wear processes that can generate large quantities of particulate debris. This debris can stimulate an adverse local host response leading to periprosthetic bone loss, which can compromise implant fixation and bone stock. The authors review the basic mechanisms of implant degradation and the host response to particulate degradation products, particularly in the context of the pathogenesis of osteolysis. Submicron polyethylene particles (mean size, 0.5 um) are the dominant type of wear particle present in periprosthetic tissues associated with uncemented hip replacements. Polyethylene wear can be minimized by improving the quality of the polyethylene, avoiding use of large-diameter (greater than 28 mm) femoral heads in total hip arthroplasty, and improving the design and fabrication of modular connections, which can be important sources of three-body wear particles. Advances in the understanding of the basic mechanisms of osteolysis are critical to the development of preventive measures that will minimize the clinical impact of this phenomenon.

Use of bisphosphonates to improve the durability of total joint replacements.

Total joint arthroplasty is very effective for improving the quality of life of patients with end-stage arthritis. Despite advances in materials, surgical technique, and rehabilitation regimens, joint replacements are still fraught with complications leading to their premature failure. Aseptic loosening and osteolysis are the primary causes of implant failure. Other reasons include early migration of components leading to instability, lack of ingrowth into implant porosities, and bone loss caused by stress shielding. Pharmaceutical agents used for preventing and managing postmenopausal osteoporosis (eg, bisphosphonates) may in the future play an important role in improving the long-term duration of joint arthroplasties. Early findings indicate that bisphosphonates upregulate bone morphogenetic protein-2 production and stimulate new bone formation. Because of their anabolic effect on osteoblasts, bisphosphonates have the potential to enhance bone ingrowth into implant porosities, prevent bone resorption under adverse conditions, and dramatically extend the long-term durability of joint arthroplasties. The long-term effects of bisphosphonate use on the mechanical properties of bone have not been adequately investigated. Along with improvements in implant design and material properties, bisphosphonates and other pharmaceutical agents may, in the near future, be part of the growing armamentarium that provides more durable joint arthroplasties.

Taking a Closer Look at Osteolysis in TAA Patients

Questions remain regarding potential triggers of bone matrix resorption

Jennie McKee

“Osteolysis is a frustrating condition: it’s what leads to total ankle arthroplasty (TAA) failure even when the surgeon has done everything right,” said Murray J. Penner, MD, FRCSC, of the University of British Columbia, Vancouver Coastal Health Authority, and Providence Health Care in Vancouver, British Columbia.

Wear and Osteolysis in Total Knee Arthroplasty

Wear and osteolysis initiated by polyethyelene wear debris is a major limitation of the long-term success of total knee arthroplasty. Osteolysis generally occurs around the tibial baseplates and femoral and patellar components of total knee replacements. Many factors influence the amount of wear and osteolysis that occurs over time, including patient, implant, and surgical factors.Multiple factors related to the manufacturing of the polyethylene implant influence the extent of wear; therefore, surgeons should be cautious in considering enhanced polyethylenes pending results of further investigations. Ultra-high–molecular-weight polyethylene (UHMWPE) has long been the conventional polymer for use in total knee replacement. Cross-linked UHMWPEs have in fact replaced conventional UHMWPE (gamma sterilized in air or an inert gas) for total hip replacements in the United States. In total knee replacements, however, the reduced fatigue strength of UHMWPE with cross-linking remains a concern. Current material research has focused on improving the fatigue-resistant properties of UHMWPE without the loss of resistance to wear and oxidation.

The Biologic Response to Bearing Materials

Total joint arthroplasty (TJA) is a common and highly successful orthopaedic procedure for which surgeons can use different bearing materials. The materials used for TJA must be both biocompatible to minimize adverse local tissue reactions and robust enough to support weight bearing during common daily activities. Modern bearing materials for TJA are made from metals and their alloys, polymers, and ceramics. The orthopaedic surgeon should be knowledgeable about the biologic response to the different bearing materials used for TJA, as well as the wear by-products generated.

Use of Systemic Pharmaceutical Adjuncts to Enhance Bone Healing After Surgery

Anabolic agents such as parathyroid hormone and anti-catabolic agents such as diphosphonates were originally approved to treat bone disorders, including osteoporosis, Paget disease, and osteogenesis imperfecta. Today, these agents are increasingly being used to enhance bone healing after surgery. Yet despite the reported benefits of these medications in the postoperative period, most orthopaedic surgeons in the United States remain reluctant to use them after total joint arthroplasty, trauma surgery, or spine surgery. This article reviews the most commonly prescribed systemic pharmacologic agents for enhancing bone healing after surgery, with a particular focus on the mechanisms by which these medications work and their potential therapeutic applications, the complications and risks attending their prescription, and contraindications to their use. Prospects and trends in the use of both established and new therapeutic agents for enhancing bone healing are also presented.