In Vivo Performance of Moderately Crosslinked, Thermally Treated Polyethylene in a Prospective Randomized Controlled Primary Total Knee Arthroplasty Trial.

Cross-linked bearings have been developed for use in total knee arthroplasty that exhibit improved wear properties, but at the expense of a decrease in mechanical strength of the cross-linked material. Adoption has been slow due to fears of mechanical failure secondary to this alteration in mechanical properties. This prospective, randomized study compared mid-term survivorship, clinical and radiographic results of a conventional polyethylene (GVF) to a cross-linked polyethylene (XLK) in total knee prostheses of the same design. At minimum 5-year follow-up there was no difference in survivorship, clinical performance or radiographic findings between the groups. There were no revisions for polyethylene wear, osteolysis or tibial insert dissociation. Most importantly, there were no revisions for mechanical failure or fracture of the polyethylene bearing in either group.

The relationships between femoral cortex geometry and tissue mechanical properties.

Bone tissue and geometry are constantly modified through modeling and remodeling at the periosteal, endosteal and intracortical envelopes. Results from several studies indicate that femoral bone geometry is a predictor of whole bone strength (e.g. femoral neck strength), however, it is not known whether there is a relationship between bone structural and material properties. Bone geometry can be determined from parameters based on plane X-ray radiogrammetry which are used to evaluate femoral bone quality for implant success. If there is a relationship between these parameters and tissue mechanical properties, this would have implications in the interpretation of such parameters for assessment of fracture risk and in further understanding of bone biology. Following measurement of radiogrammetric parameters from antero-posterior and medio-lateral X-rays (cortical thickness, bone diameter, bone area, moment of inertia, cortical index, Singh index), human femurs were machined into standard test specimens for assessment of tensile fracture toughness (GIc) of the tissue. Results indicated that tensile fracture toughness generally increased with increasing bone size. We also found that fracture toughness of the tissue was significantly related to radiogrammetric indices and that some of these indices explained a greater variability in toughness than porosity, age or gender.

Minimum 5-year results of modular metal-on-metal total hip arthroplasty.

This study reports minimum 5-year results of 95 hips implanted with a Pinnacle (DePuy, Warsaw, Ind) modular metal-on-metal acetabular prosthesis. Clinical scores such as the Harris Hip and Western Ontario and McMaster Universities Arthritis Index revealed excellent clinical outcomes at mean 6-year follow-up. With the use of large-diameter femoral heads, dislocation was rare, occurring in only 1 hip. Moreover, no acetabular and only 3 femoral osteolytic lesions were detected. Kaplan-Meier survivorship at 7 years after arthroplasty was 97.8% for the total hip arthroplasty construct and 100% for the acetabular shell. No unexplained pain or other complication attributable to wear debris or the metal-on-metal articulation was observed. These findings indicate that total hip arthroplasty with this specific modular metal-on-metal bearing performed well in a high-demand population at midterm follow-up.

Prevalence and clinical relevance of radiographic signs of impingement in metal-on-metal hybrid hip resurfacing.

BACKGROUND: Implant-related impingement has been reported following metal-on-metal hip resurfacing, and reactive osseous patterns associated with implant-bone impingement have been identified. The purpose of this study was to determine the prevalence and clinical implications of radiographic signs of femoral neck-acetabular cup impingement following metal-on-metal hip resurfacing. METHODS: Serial anteroposterior and lateral radiographs made five to 12.9 years postoperatively were available for ninety-one of the first 100 metal-on-metal hip resurfacing procedures (in eighty-nine patients) performed by the senior author. These radiographs were reviewed by a single independent observer, who was blinded to the clinical results. Radiographic signs of impingement were assessed and were correlated with clinical outcomes. RESULTS: Twenty hips (in eighteen patients) had at least one of two reactive osseous signs: a solitary exostosis (six hips, 7%) and an erosive "divot-type" deformity (twenty hips, 22%). Each radiographic sign occurred predominantly at the superior aspect of the femoral neck just distal to the femoral component. None of the patients with such an impingement sign reported any symptoms or discomfort during examination of the range of hip motion. These patients had a greater mean postoperative University of California Los Angeles activity score and a greater mean range of hip motion than the patients without an impingement sign. Based on the numbers available, there was no association between component size, abduction angle and anteversion angle of the socket, femoral stem-femoral shaft angle, or femoral component-femoral neck ratio and the occurrence of repetitive impingement signs on radiographs. CONCLUSIONS: The reactive osseous features identified in this study should facilitate the radiographic assessment of impingement in other patients following hip resurfacing arthroplasty. Longer-term follow-up is needed to determine whether radiographic signs of impingement are of prognostic consequence.

Clinical and radiographic results of metal-on-metal hip resurfacing with a minimum ten-year follow-up.

BACKGROUND: There was a need for information about the long-term performance of the modern generation of hip resurfacing implants. A retrospective review of the first 100 hips that had implantation of one resurfacing design and had been followed for a minimum of ten years was performed. METHODS: Between 1996 and 1998, 100 CONSERVE PLUS hip resurfacing devices were implanted by a single surgeon in eighty-nine patients. The mean age of the patients was 49.1 years, and fifty-nine patients were male. Primary osteoarthritis was the etiology for sixty-four hips. All patients were assessed clinically and radiographically. RESULTS: The mean duration of follow-up was 11.7 years (range, 10.8 to 12.9 years). Two patients were lost to follow-up, and five patients died of causes unrelated to the surgery. Eleven hips had conversion to total hip arthroplasty because of loosening of the femoral component (eight), a femoral neck fracture (one), recurrent subluxation (one), and late infection (one). The Kaplan-Meier survivorship was 88.5% at ten years. None of the resurfacing arthroplasties failed in the twenty-eight hips that had a femoral component of >46 mm and no femoral head cystic or necrotic defects of >1 cm. Five hips had narrowing of the femoral neck, three had radiolucent zones interpreted as osteolysis, and twenty had signs of neck-socket impingement. Five hips had radiolucencies around the metaphyseal stem (two partial and three complete) that had been stable for 7.8 to 10.2 years. The mean scores on the University of California at Los Angeles (UCLA) system at the time of the latest follow-up were 9.5 points for pain, 9.3 points for walking, 8.9 points for function, and 6.8 points for activity; the mean scores on the physical and mental components of the Short Form-12 (SF-12) were 47.3 and 50.5 points, respectively; and the mean Harris hip score was 90 points. CONCLUSIONS: The results of the present series constitute a reference point to which subsequent series should be compared. These ten-year results in a group of young patients are satisfactory, and the low rate of osteolysis is encouraging, but longer follow-up is required for comparison with conventional total hip arthroplasty.

Midterm results of all-polyethylene tibial components in primary total knee arthroplasty.

Our goal was to determine the 7-year survivorship of a total knee arthroplasty system with all-polyethylene tibial components. From June 1996 to December 1997, 129 consecutive patients (177 knees) (>/=70 years old) underwent such primary arthroplasty at 2 centers in the United States. The 88 patients (120 knees) with 7 years or more of follow-up were evaluated radiographically and functionally. Average results included: Knee Society Score, 93.7 points (SD, 8.1); Knee Society function score, 68.9 points (SD, 27.6); range of motion, 119 degrees (SD, 10.9); osteolysis, 0%; stress shielding, 6.6%; progressive radiolucencies, 2.5%; Kaplan-Meier survivorship (revision), 99.4% (95% confidence intervals, 98.2%-100.0%). At midterm follow-up, an all-polyethylene tibial component proved to be an excellent surgical option for total knee arthroplasty in an elderly patient population.

Midterm results with the PFC Sigma total knee arthroplasty system.

We prospectively studied 207 consecutive patients (284 knees) undergoing total knee arthroplasty (June 1996 to December 1997) with a cemented tricompartmental Sigma PFC (DePuy Orthopaedics, Warsaw, Ind) total knee arthroplasty via a standard procedure (median follow-up, 87 months). Cruciate-retaining (272 knees, 96%) and cruciate-substituting (12, 4%) implants were used. There was one revision secondary to a ligament disruption after a fall. No implants were radiographically loose or at risk for loosening. Radiolucencies (none>2 mm or progressive) were shown on anteroposterior (7% of medial tibias) and lateral (17% of posterior femora) radiographs. Knee Society pain scores improved significantly (preoperative median, 20 points; postoperative median, 50 points [P<.001]). The PFC Sigma Knee system has excellent midterm durability.

Sterilization and wear-related failure in first- and second-generation press-fit condylar total knee arthroplasty.

UNLABELLED: We compared the incidence of wear-related failures between two large cohorts of patients undergoing total knee arthroplasty implanted with identical modular tibial trays and polyethylene inserts sterilized by different methods. A total of 1183 second-generation press-fit condylar prostheses having inserts packaged and sterilized in an oxygen-free environment were assessed at a minimum 5-year followup (mean, 7.0 years). Wear-related failure was defined as (1) osteolysis greater than 100 mm2 or (2) revision of the implant resulting from osteolysis, polyethylene wear, chronic synovitis, and/or effusion. Wear-related survivorship was calculated using Kaplan-Meier survival analysis. Results were compared with our previously published study of 1287 first-generation press-fit condylar modular knees having inserts sterilized by gamma irradiation in air at 5-year minimum followup (mean, 7.8 years). The wear-related failure rate for the second-generation design was 1.1% and 10-year survivorship was 97.0% compared with 8.3% failure and 87.7% 10-year survival for the first-generation design. For second-generation components, patient age was the only variable correlated with wear-related failure. For first-generation components sterilized in air, several variables were correlated to wear-related failure with shelf age of the polyethylene insert being the most important factor. These data emphasize the dramatic effect improvements in polyethylene manufacturing, specifically sterilization methods, can have on implant survivorship. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Metal-on-metal hybrid surface arthroplasty. Surgical Technique.

BACKGROUND: Following the reintroduction of metal-on-metal articulating surfaces for total hip arthroplasty in Europe in 1988, we developed a surface arthroplasty prosthetic system using a metal-on-metal articulation. The present study describes the clinical and radiographic results of the first 400 hips treated with metal-on-metal hybrid surface arthroplasties at an average follow-up of three and a half years. METHODS: Between November 1996 and November 2000, 400 metal-on-metal hybrid surface arthroplasties were performed in 355 patients. All femoral head components were cemented, but only fifty-nine of the short metaphyseal stems were cemented. The patients had an average age of forty-eight years, 73% were men, and 66% had a diagnosis of osteoarthritis. Clinical and radiographic follow-up was performed at three months postoperatively and yearly thereafter. RESULTS: The majority of the patients returned to a high level of activity, including sports, and 54% had activity scores of >7 on the University of California at Los Angeles activity assessment system. Kaplan-Meier survivorship curves demonstrated that the rate of survival of the components at four years was 94.4%. For patients with a surface arthroplasty risk index score of >3, the rate of survival of the components at four years was 89% compared with a rate of 97% for those with a score of

Radiographic evaluation of a monoblock acetabular component: a multicenter study with 2- to 5-year results.

Serial radiographs of a porous tantalum monoblock acetabular cup design were evaluated for cup stability and signs of successful osteointegration. Of 574 primary consecutive total hip replacements in 542 patients performed by 9 surgeons at 7 hospitals, 414 cases were available for minimum 2-year follow-up. Follow-up averaged 33 months and ranged from 24 to 58 months. Postoperative radiographs revealed acetabular gaps in 100 zones in 80 (19%) hips: 29 in zone I, 67 in zone II, and 4 in zone III. At last follow-up, 84 (84%) of the zones with gaps completely filled in, and all 4- and 5-mm gaps filled in. There was no progression of any postoperative gap, no evidence of continuous periacetabular interface radiolucencies, no evidence of lysis, and no revisions for loosening. Although these short-term results are encouraging, further follow-up will be required to assess whether the monoblock design and the low modulus of elasticity of porous tantalum will reduce the incidence of periacetabular stress shielding and occurrence of osteolysis.

Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study.

BACKGROUND: Following the reintroduction of metal-on-metal articulating surfaces for total hip arthroplasty in Europe in 1988, we developed a surface arthroplasty prosthetic system using a metal-on-metal articulation. The present study describes the clinical and radiographic results of the first 400 hips treated with metal-on-metal hybrid surface arthroplasties at an average follow-up of three and a half years. METHODS: Between November 1996 and November 2000, 400 metal-on-metal hybrid surface arthroplasties were performed in 355 patients. All femoral head components were cemented, but only fifty-nine of the short metaphyseal stems were cemented. The patients had an average age of forty-eight years, 73% were men, and 66% had a diagnosis of osteoarthritis. Clinical and radiographic follow-up were performed at three months postoperatively and yearly thereafter. RESULTS: The majority of the patients returned to a high level of activity, including sports, and 54% had activity scores of >7 on the University of California at Los Angeles activity assessment system. Kaplan-Meier survivorship curves demonstrated that the rate of survival of the components at four years was 94.4%. For patients with a surface arthroplasty risk index score of >3, the rate of survival of the components at four years was 89% compared with a rate of 97% for those with a score of

Long-term radiographic changes in cemented total hip arthroplasty with six designs of femoral components.

Measurements were made from annual follow-up radiographs, obtained over 27.6 years, of 860 cemented total hip arthroplasties implanted by one surgeon. Femoral components were made of stainless steel or titanium alloy, were non-modular, and were all fixed with cement, and acetabular cups were all-polyethylene and were fixed with cement. Radiographic outcome was correlated with the shape and material of the femoral component. Specifically, throughout the follow-up, stems made of titanium alloy were at greater risk of developing bone-cement radiolucent lines than those made of stainless steel, the difference ranging from approximately 10-50 percent at 2-10 years of follow-up. Similarly, titanium alloy stems were at greater risk of developing endosteal scalloping, indicating osteolytic lesions. Among the stainless steel Charnley cobra and straight-narrow Charnley stems, none developed cement fracture, only one became radiographically loose and one developed endosteal scalloping. The differences in the risk of developing radiolucent lines, cement fracture and progressive loosening among these stems were correlated with the relative rigidity of the femoral stems, and were generally consistent with the predictions made heretofore using finite element models, although differences in stem surface finish and femoral ball size and material could have also influenced the results.

Time-dependent circumferential deformation of cortical bone upon internal radial loading.

Short and long duration tests were conducted on hollow femoral bone cylinders to study the circumferential (hoop) creep response of cortical bone subjected to an intramedullary radial load. It was hypothesized that there is a stress threshold above which nonlinear creep effects dominate the mechanical response and below which the response is primarily determined by linear viscoelastic material properties. The results indicate that a hoop stress threshold exists for cortical bone, where creep strain, creep strain rate and residual strain exhibited linear behavior at low hoop stress and nonlinear behavior above the hoop stress threshold. A power-law relationship was used to describe creep strain as a function of hoop stress and time and damage morphology was assessed.