A. Seth Greenwald

Bone-graft Substitutes: Facts, Fictions, and Applications

It is estimated that more than 500,000 bone-grafting procedures are performed annually in the United States, with approximately half of these procedures related to spine fusion. These numbers easily double on a global basis and indicate a shortage in the availability of musculoskeletal donor tissue traditionally used in these reconstructions (Fig. 1). Fig. 1: United States trends in musculoskeletal tissue donors. Source: United Network for Organ Sharing and the Musculoskeletal Transplant Foundation. This reality has stimulated a proliferation of corporate interest in supplying what is seen as a growing market in bone-substitute materials (Fig. 2). These graft alternatives are subjected to varying degrees of regulatory scrutiny, and thus their true safety and effectiveness in patients may not be known prior to their use by orthopaedic surgeons. It is thus important to gain insight into this emerging class of bone-substitute alternatives. Fig. 2: United States sales of bone graft and bone substitutes. Source: Orthopedic Network News, industry estimates. The biology of bone grafts and their substitutes is appreciated from an understanding of the bone formation processes of osteogenesis, osteoinduction, and osteoconduction. Graft osteogenesis: The cellular elements within a donor graft, which survive transplantation and synthesize new bone at the recipient site. Graft osteoinduction: New bone realized through the active recruitment of host mesenchymal stem cells from the surrounding tissue, which differentiate into bone-forming osteoblasts. This process is facilitated by the presence of growth factors within the graft, principally bone morphogenetic proteins (BMPs). Graft osteoconduction: The facilitation of blood-vessel incursion and new-bone formation into a defined passive trellis structure. All bone graft and bone-graft-substitute materials can be described through these processes. Fresh autogenous cancellous and, to a lesser degree, cortical bone are benchmark graft materials that allograft and bone substitutes attempt to match in in vivo performance. They incorporate all of the above properties, are …

Antibiotic-Loaded Bone Cement for Infection Prophylaxis in Total Joint Replacement

Use of antibiotic-loaded bone cement for prophylaxis against infection is not indicated for patients not at high risk for infection who are undergoing routine primary or revision joint replacement with cement. The mechanical and elution properties of commercially available premixed antibiotic-loaded bone-cement products are superior to those of hand-mixed preparations. Use of commercially available antibiotic-loaded bone-cement products has been cleared by the United States Food and Drug Administration only for use in the second stage of a two-stage total joint revision following removal of the original prosthesis and elimination of active periprosthetic infection. Use of antibiotic-loaded bone cement for prophylaxis against infection in the second stage of a two-stage total joint revision involves low doses of antibiotics. Active infection cannot be treated with commercially available antibiotic-loaded bone cement as such treatment requires higher doses of antibiotics.

Mobile-bearing knee replacement: concepts and results.

In summary, if TKRs are to be performed in patients who are younger and more active than those who had the initial procedures in the 1970s and 1980s, better wear performance is imperative for long-term durability, especially if surgeons continue to consider the versatility associated with modular knee-replacement systems to be a necessity. At least with some designs, including the Oxford knee and the LCS knee, the results after a minimum follow-up of 10 years are comparable with the best results after arthroplasty with fixed-bearing designs in terms of wear, loosening, and osteolysis (Table 7). As with fixed-bearing designs, there are additional challenges in terms of optimizing bearing-surface conformity and improving kinematics. Improvements in future designs of mobile-bearing total knee replacements should include better control of bearing mobility patterns to reduce the prevalence of the abnormal kinematic motions that have been observed in fluoroscopic evaluations.

Soft-tissue balancing of the hip: the role of femoral offset restoration.

Inadequate soft-tissue balancing is a major yet often underemphasized cause of failure for primary and revision total hip arthroplasty. Accordingly, contemporary cemented and cementless hip prostheses have been designed with consideration of this issue, and this has substantially increased the long-term survival of total hip replacements. Therefore, it is important for orthopaedic surgeons to be familiar with the rationale, biomechanical principles, and clinical implications associated with soft-tissue balancing of the hip as well as strategies to avoid inadequate soft-tissue balancing and systematic techniques to restore adequate soft-tissue tensioning during total hip arthroplasty.

Clinical Performance of Highly Cross-Linked Polyethylenes in Total Hip Arthroplasty

Aseptic loosening secondary to wear-debris-induced osteolysis has been identified as the leading cause of late failure of total hip arthroplasty. Highly cross-linked polyethylene acetabular liners were developed as one approach to reducing this wear. Preclinical laboratory wear testing showed a number of cross-linked polyethylenes to have dramatically less wear than the polyethylene that had been in use for several decades. After the initial bedding-in phase (one to two years), the percent reductions in the wear rate, as indicated by the amount of penetration of the head into the socket evident on serial radiographs, have been comparable with what was predicted from preclinical hip-simulator testing of the highly cross-linked polyethylenes. To our knowledge, there have been no reports of clinically relevant osteolysis that was clearly attributable to wear of a highly cross-linked polyethylene acetabular liner. However, the clinical performance of these materials should be closely monitored with long-term follow-up.

Uncemented rotating-platform total knee replacement: a five to twelve-year follow-up study.

BACKGROUND Mobile-bearing knee designs represent an alternative to conventional fixed-bearing total knee arthroplasty. We present the results of a prospective, intermediate-term clinical follow-up study of the bicruciate ligament-sacrificing porous-coated Low Contact Stress rotating-platform total knee design. METHODS Between February 1984 and January 1994, 528 uncemented primary knee replacements were performed in 421 patients. All patellae were resurfaced with use of the Low Contact Stress rotating patellar component. The average age of the patients at the time of the index procedure was sixty-nine years. The study group included 261 women and 160 men. Patients were evaluated at three months, six months, and yearly thereafter with use of the 100-point New Jersey Orthopaedic Hospital knee-scoring system. In addition, a radiographic analysis of the tibial, femoral, and patellar components was performed at each interval. RESULTS There were twenty-nine failures that resulted in revision. The Kaplan-Meier estimate of implant survival at twelve years was 89.5% (95% confidence interval, 83.4% to 95.6%). The total clinical scores improved significantly compared with the preoperative scores for the first twelve months postoperatively and then plateaued. Three hundred and twenty-one knees had adequate radiographic follow-up (average, 8.1 years; range, five to twelve years). Zonal radiographic analysis revealed ninety-three instances of radiolucent lines (eighty-two of which measured <1 mm in width), with the greatest number of radiolucent lines (thirty-nine) being located around the tibial tray stem. None of these lines were deemed to be progressive, and no knee with a radiolucent line that measured >2 mm was revised because of failure. CONCLUSIONS This first-generation uncemented, mobile-bearing, bicruciate ligament-sacrificing knee replacement was associated with a good survival rate and demonstrated clinical efficacy during the five to twelve-year follow-up interval. .

The Effects of Shelf Life on Clinical Outcome for Gamma Sterilized Polyethylene Tibial Components

Tibial component shelf life was examined as a contributory factor of the in vivo failure of gamma sterilized prosthetic knee replacements. One hundred eighty-eight Synatomic total knee replacements sterilized by gamma irradiation in air were implanted by one surgeon into 147 patients between May 1985 and December 1994. Of these, 135 knees in 105 patients with a mean followup of 5.8 years (range, 2.1-11.3 years) were included in the study. The mean shelf life of the implants was 3.6 years (range, 0.1-10.7 years). Clinical failure for this study was defined as component retrieval resulting from polyethylene degradation. The knee components were divided into three different groups determined by their shelf storage durations of 0 to 4 years (Group 1, 93 components), between 4 and 8 years (Group 2, 21 components), or greater than 8 to 11 years (Group 3, 21 components). Six prostheses were revised because of polyethylene degradation after a mean implantation time of 2.5 years (range, 1.1-3.8 years). The mean shelf life of these six prostheses was 8.4 years (range, 5.8-9.6 years). Five years after implantation, prostheses that had shelf lives of less than 4 years had a 100% survival rate. Those that had shelf lives of 4 to 8 years before implantation had an 88.6% survival rate, and those prostheses that had shelf lives greater than 8 to 11 years had a 79.2% survival rate.

Polymer Insert Stress in Total Knee Designs During High-Flexion Activities: A Finite Element Study

T he success of total knee arthroplasty has contributed to its widening application to younger, more active patient populations whose daily regimen includes more demanding high-flexion activities. Worldwide expansion to patient populations in the Middle East and Asia, where the attainment of high degrees of knee joint flexion is often a cultural requirement, has been steadily increasing in recent years. The present study reveals the contact areas and stresses that are associated with polymer insert abrasion. Finite-element models were created of four total knee designs during the most highly loaded portions of three different high-flexion activities, and the results suggest their efficacy in clinical use. Three mobile-bearing designs (including the Dual Bearing Knee [Finsbury Orthopaedics, Surrey, United Kingdom], e.motion [Aesculap, Tuttlingen, Germany], and P.F.C. Sigma RPF [DePuy, a Johnson and Johnson Company, Warsaw, Indiana] devices) and one fixed-bearing design (the Legacy LPS-Flex Fixed Bearing device [Zimmer, Warsaw, Indiana]) were evaluated. The latter two designs are currently available for clinical use in the United States. A three-dimensional, finite element model was created for each total knee design by measuring the articular surfaces of implantable quality parts with use of a laser profilometer. Maximum joint loads and the angles of knee flexion at which they occurred were determined through a meta-analysis of the literature for three high-flexion activities: ascending stairs1 …

Alternative Bearing Surfaces: The Good, the Bad, and the Ugly

This article discusses current bearing-surface alternatives for long-term total hip articulations involving metal-polyethylene, ceramic-polyethylene, metal-metal, and ceramic-ceramic couples. The enduring success of the low-friction arthroplasty advanced by Sir John Charnley as a solution for painful hip problems can be appreciated by the fact that, in 1999, more than 270,000 hip arthroplasties were performed in the United States. Over the last three decades, patient profiles have changed substantially, resulting in demands for a greater service life of ultra-high molecular weight polyethylene hip components. Material failure, often leading to an osteolytic response, is increasingly associated with younger, more active patients. In this context, the low-friction solution has become a problem, limiting in vivo system longevity (Figs. 1 and 2). Fig. 1: A marked osteolytic response in a fifty-year-old patient. Fig. 2: Corresponding intracellular polyethylene debris viewed under polarized light. Previous attempts to improve the performance of ultra-high molecular weight polyethylene have included carbon-fiber reinforcement (Poly-2) and, more recently, polymer reprocessing to enhance mechanical properties (Hylamer). The former was withdrawn from the market because of excessive inflammatory response, whereas the latter has been linked to debris-induced osteolytic responses in early reports. Laboratory simulation has demonstrated that the resistance of ultra-high molecular weight polyethylene to wear is improved with increased cross-linking of the carbon-hydrogen polymer chains. A number of thermal and chemical processing solutions have been described. One such approach involves component storage at elevated temperatures in an oxygen-depleted environment. This is done following irradiation and encourages kinetic recombination of the carbon-hydrogen free radicals created by the radiation process. Other techniques deliver increased radiation doses to the component material followed by remelting to quench free radicals. While this results in dramatic wear reduction in laboratory simulations (Fig. 3), it also changes the amorphous and crystalline regions of the polymer, affecting mechanical properties and potentially reducing fatigue strength. …

Basic Orthopaedic Biomechanics and Mechano-Biology. 3rd ed.

Van C. Mow and Rik Huiskes, editors. Philadelphia: Lippincott Williams and Wilkins; 2005. 720 pages.