Clinical Issues Summary (2008)

Total hip and knee arthroplasty are among the most successful operations in orthopaedic surgery in patients with disabling arthritis. Although the percentage of hip and knee revision cases has not changed in recent years, the absolute number of these difficult cases has increased because of the greater number of primary arthroplasties currently being performed. Wear-associated periprosthetic osteolysis is a “silent disease” that can progress without symptoms until catastrophic structural failure or mechanical loosening of the implant occurs. Specific welldescribed patient, surgical, implant design, and material-related factors are associated with increased wear and osteolysis. In particular, young, active, heavy patients are at increased risk for wear. Therefore, emphasis should be placed on routine patient follow-up, perhaps every 3 to 5 years after the initial year of implantation for stable prostheses without osteolysis or other known problems. Furthermore, patient education tools should be developed that focus on the lack of early symptoms of osteolysis and the risk of delaying treatment until failure occurs. Clinical research directed at the clinical and economic impact of earlier diagnosis of osteolysis under specific follow-up protocols is warranted. Modification of the current ICD-9 codes to subcategorize modes of failure will also help delineate which revisions can be attributed to wear-related osteolysis. To ascertain the long-term prevalence of wearrelated osteolysis, the orthopaedic community in the United States should support the creation of a national joint registry and should encourage collaboration with industry to assist in tracking pertinent material and design changes that have been instituted. Diagnosis and surveillance of wear-induced osteolysis include measurements of wear to assess the extent of the generation of wear debris and imaging methods to assess the extent, location, and progression of the periprosthetic osteolysis process. To this end, methods such as radiographic edge detection, spiral computed tomography, magnetic resonance imaging, as well as radiographic stereometric analysis (in selected patient cohorts), and quantitation of wear and osteolysis (including bone and soft-tissue lesions) are necessary. In particular, the use of computed tomography and magnetic resonance imaging in diagnosing the extent of osteolysis should be extended to large cohorts to examine the efficacy of these diagnostic tools and to establish guidelines for their clinical use in the evaluation of new hip and knee replacement designs. There is an ongoing need for techniques to measure wear in total knee arthroplasty cases. With regard to treatment, ongoing surveillance may be appropriate for very small, nonprogressive osteolytic lesions in noncritical areas. However, surgical management of progressive wear-associated osteolytic lesions is indicated, as pharmacologic treatments have not been successful. Standardized methods to measure the extent of wear and osteolysis and to assess the outcome of bone grafting and other treatments are being developed. Surgical intervention must address the wearparticle generator, the osteolytic defects, and implant-related issues such as fixation and alignment. Patient age and activity level, the location and size of the osteolytic defects, and the clinical record of the implant system should be considered. Surgical treatment must be individualized. Such treatment varies, from débridement with changing worn bearing surfaces with or without bone grafting of osteolytic lesions, to more extensive procedures that replace the entire prosthesis and restore structural bone loss. Simpler, less extensive procedures should be considered when the implants have a good track record and exhibit satisfactory alignment and when highquality replacement parts are readily available. Better devices for extracting malfunctioning prostheses are available to limit bone loss. Prospective standardized multicenter trials using defined treatment protocols are required to improve the level of evidence of revision procedures. Second-generation cementless implants have shown excellent durability of fixation up to 15 to 20 years. Early clinical success with very low rates of wear and osteolysis has been shown with all three couples of alternative bearings for hip replacement (metal-on-metal, highly cross-linked polyethylene, ceramic-on-ceramic). However, the data are based on short-term follow-up. Because of the minimal amount of wear present, there is a need for the development of monitoring techniques for hard bearings and for the knee. The expectation from these early observational data is that wear and the resulting loosening and aggressive bone loss will not be observed on long-term follow-up. All three bearing couples are very sensitive to surgical technique and, specifically, to proper acetabular positioning. This is at the root of the early complications that have been reported: fracture of the implant (cross-linked polyethylene); squeaking and impingement wear (ceramicon-ceramic bearings); and runaway wear, osteolysis, and immune system -related complications (metalon-metal bearings). These problems may be complicated by the use of minimally invasive techniques that do not afford adequate visualization, particularly in the hands of the less experienced surgeon. There is a need to establish the relative indications and contraindications for the choice of one bearing couple over another. There are no definitive guidelines to help the practicing surgeon other than those provided by commercial interests because no system has shown clear superiority over the others. Less information is available concerning the use of highly cross-linked polyethylene in the knee, where the experience is shorter term and the mechanical environment is more demanding. Thus, prospective, randomized, multicenter long-term studies comparing the different available bearings are needed, particularly in young and active patient populations. Furthermore, a national arthroplasty registry will be of unique value to establish effectiveness of the different bearings among the general population.