Biomedical subjects

Robert H Hopper

Publications and source records attributed to Robert H Hopper.

17 recordsLinked to original sources

PubMed2006

A randomized prospective evaluation of outcomes after total hip arthroplasty using cross-linked marathon and non-cross-linked Enduron polyethylene liners.

Cross-linked liners were introduced with the promise that they would substantially reduce polyethylene wear. In 1999, our institution initiated a prospective study to compare the outcome of total hip arthroplasty patients who were randomized to non-cross-linked Enduron liners with that of total hip arthroplasty patients who were randomized to Marathon polyethylene liners that had been cross-linked with 5 Mrad (50 kGy) of gamma-irradiation and heat-treated to eliminate free radicals. At a mean follow-up of 5.7 years, the clinical outcomes among the Marathon and Enduron liners were similar. However, the mean wear rate was 0.01 +/- 0.07 mm/y for the Marathon group, which represents a 95% reduction compared with the mean wear rate of 0.19 +/- 0.12 mm/y for the Enduron group. In addition, the incidence of osteolysis was lower in the Marathon group.

Adult↗

PubMed2005

The effect of total hip arthroplasty cup design on polyethylene wear rate.

Using 743 total hip arthroplasties that included 6 hemispheric porous-coated cup designs, this study used a multiple linear regression to identify those factors that influenced polyethylene wear rates. Wear rates for each hip were based on serial head penetration measurement made with computer-assisted techniques. Implant factors associated with an increased wear rate included terminal sterilization with a non-cross-linking chemical surface treatment, a 4-mm lateralized liner, a cobalt-chrome femoral head, and a longer shelf life for liners gamma-irradiated in air. After accounting for these implant characteristics and patient factors, wear rates among the 6 cup designs were not significantly different (P = .89). Although polyethylene wear is frequently characterized for specific implant designs, this study demonstrated that there are several common factors that influence polyethylene wear rates.

Acetabulum↗

PubMed2005

Diagnostic features of pelvic osteolysis on computed tomography: the importance of communication pathways.

BACKGROUND: Progressive periacetabular osteolysis following total hip arthroplasty may require revision surgery. The purpose of this study was to use computed tomography scans of hemipelves retrieved at autopsy from patients who had had a total hip arthroplasty, to define the radiographic characteristics that differentiate clinically important osteolytic lesions from osteoarthritic bone cysts. METHODS: We analyzed forty-four hemipelves that had been retrieved at autopsy at a mean of eight years after a total hip arthroplasty with an uncemented acetabular component. Computed tomography images were analyzed to identify the location, volume, and presence of cortical erosion and/or communication pathways with the joint space for all periacetabular bone defects. Lesions that were not present on preoperative or immediate postoperative plain radiographs were defined as new lesions. These new lesions were compared with those that were present on preoperative or immediate postoperative plain radiographs, which were defined as preexisting lesions. RESULTS: Forty-six lesions were identified on computed tomography, and sixteen of them were preexisting lesions. The mean volume of the preexisting lesions was 1.5 +/- 1.5 cm(3), which was significantly smaller than the mean volume of 5.6 +/- 11.4 cm(3) of the thirty new lesions (p = 0.034). Twenty-eight of the thirty new lesions had a clear communication pathway with the joint space, while thirteen of the sixteen preexisting lesions demonstrated no communication pathway. New lesions were significantly more likely to communicate with the joint space than were preexisting lesions (p < 0.001). Cortical erosion was seen in sixteen of the thirty new lesions; none of the sixteen preexisting lesions exhibited cortical erosion (p < 0.001). CONCLUSIONS: The most important difference between osteolytic lesions and preexisting bone defects was the presence of a communication pathway to the joint space. Lesions that did not have an identifiable communication to the joint space were smaller and were not associated with cortical erosion. Lesions with communication to the joint through multiple pathways or through a central dome hole were larger and more likely to be associated with cortical erosion.

Adult↗

PubMed2004

Long-term porous-coated cup survivorship using spikes, screws, and press-fitting for initial fixation.

This study examined the long-term outcome of a single institution's experience with 4,289 primary total hip arthroplasties using hemispheric porous-coated cups. Initial fixation was achieved with spikes (255 AML TriSpike cups), by press-fitting with rim screws (427 Arthropor cups) or by press-fitting the component (83 Harris-Galante, 391 ACS Triloc+, 2,537 Duraloc, and 596 Pinnacle cups). Among 203 revised hips, only 18 cups were found to be loose at the time of revision. Using revision for any reason as an end point, 15-year survivorship was 82.9% +/- 5.6% (95% confidence interval) for spiked components, 71.6% +/- 8.5% for press-fit cups with adjunctive rim screws, and 72.0% +/- 12.6% for press-fit components (P<.001, log rank). Using revision for aseptic loosening as an end point, 15-year survivorship was 94.7% +/- 3.4% for spiked cups, 98.4% +/- 1.9% for press-fit cups with screws and 100% +/- 0.1% for press-fit cups. Despite an increasing incidence of polyethylene wear-related revisions, porous-coated acetabular components have demonstrated excellent long-term fixation.

Acetabulum↗

PubMed2004

Assessing the pattern of femoral head penetration after total hip arthroplasty.

We evaluated temporal changes in wear rates among 205 primary cementless total hip arthroplasties that had minimum 10-year follow-up and at least 6 follow-up x-rays. Using the pelvic anteroposterior x-rays from each hip, two-dimensional head penetration was measured and wear rates were calculated using several techniques. The average wear rate for the study population did not demonstrate evidence of accelerated wear at 10- to 18-year follow-up. As an increasing number of follow-up x-rays were included in the least-squares linear regression used to calculate the wear rate, the 95% confidence interval associated with the wear rate for an individual hip tended to progressively decrease. These results indicate that a constant wear rate is a reasonable assumption for modeling clinical wear data. Although we cannot quantify the effects of polyethylene oxidation, femoral head roughening, debris accumulation, or activity level changes, the combination of these factors is not leading to clinically perceptible accelerated wear at intermediate to long-term follow-up in this heterogeneous population of cups representing our institutional experience.

Adult↗

PubMed2004

Distal ingrowth components.

The literature documents that distal ingrowth fixation provides a reproducible, durable option that can be used in many femoral revision situations. In this review, we describe our use of cylindrical, extensively porous-coated stems to achieve distal fixation. The procedure involves choosing 5 cm to 7 cm of diaphyseal bone and reaming it cylindrically for a porous-coated femoral stem. Surgical implantation is uncomplicated because the femoral diaphysis aligns the component and imparts a reproducible press-fit sensation during impaction. The complications are well documented and can be avoided with adequate exposure, intraoperative radiographs, and surgical experience. Survivorship data based on femoral revisions done at our institution with extensively porous-coated stems show overall excellent results although a relatively poorer outcome is associated with patients whose prerevision cortical damage involves bone more than 10 cm below the lesser trochanter.

Arthroplasty, Replacement, Hip↗

PubMed2004

Database production and maintenance.

The advent of computers and electronic databases have revolutionized the way that clinical research is done. If study inclusion criteria are saved in the database, creating a study population can be accomplished by constructing an electronic query. Prospectively-entered outcome data related to a particular patient population then can be accessed and exported to a statistical software application for analysis. The senior author has more than 2 decades of experience with computer-based clinical outcome databases. In the context of his personal experience, this review offers some insights related to database design and maintenance.

Arthroplasty, Replacement, Hip↗

PubMed2004

The pros and cons of polyethylene sterilization with gamma irradiation.

This retrospective study evaluated the implant, patient and surgical factors associated with polyethylene wear for one type of porous-coated hemispheric total hip arthroplasty cup. Radiographic wear measurements among 567 Duraloc cups (512 patients) revealed that liners sterilized by gamma-irradiation wore 0.085 mm/year less than those that were sterilized by gas-plasma, a noncross-linking chemical surface treatment. The substantially decreased wear rate associated with gamma-irradiation was attributed to sterilization-induced polyethylene cross-linking. Shelf-aging adversely affected liners that were gamma irradiated in air. On average, highly crystalline Hylamer liners showed a 0.064 mm/year increase in wear rates for each year of shelf storage after terminal sterilization with gamma-irradiation in air. Among conventional Enduron liners, the effect of shelf aging after gamma-irradiation in air was more modest, increasing wear rates by 0.014 mm/year for each year of shelf storage. Because Hylamer's wear performance degraded at about five times the rate of Enduron's, the improved wear resistance associated with gamma-irradiation in air would be lost after 1.3 years of shelf aging for Hylamer compared with 6.1 years for Enduron. For every additional year of age at the time of surgery, the wear rate decreased by 0.003 mm/year. Increased body mass index, a preoperative diagnosis of inflammatory arthritis, and a ceramic femoral head also were associated with decreased wear rates.

Aged↗

PubMed2004

Advancement and separation of apex hole eliminators with cementless Duraloc 100 cups. A report of nineteen cases.

BACKGROUND: From 1992 to 1996, we performed 541 cementless total hip arthroplasties using a Duraloc 100 acetabular component with an apex hole eliminator that did not have a positive stop design. During routine follow-up radiographic evaluation, we noted several hips with advanced or separated hole eliminators. This study presents the clinical consequences of this occurrence and its relationship to polyethylene wear and osteolysis. METHODS: A total of 541 hips (358 with a minimum duration of follow-up of five years) were evaluated clinically with use of the method of Merle D'Aubigné and Postel. Anteroposterior pelvic and iliac oblique radiographs were used to evaluate polyethylene wear, osteolysis, hole eliminator position, and component stability. RESULTS: Nineteen hips that had been followed for an average of eighty-nine months showed advancement or complete separation of the hole eliminator on radiographic evaluation. In most hips, advancement of the hole eliminator was visible on only the iliac oblique radiograph. In all but one hip with separation of the hole eliminator, complete plug separation was detectable on both the iliac oblique and anteroposterior pelvic radiographs. No association was found between polyethylene wear and either advancement or separation of the hole eliminator. No osteolysis was visible radiographically in the hips with hole eliminator advancement, but osteolysis was always visible in the hips that had complete separation of the hole eliminator. CONCLUSIONS: The hole eliminator has been redesigned since November 1995 to prevent possible advancement. However, patients with earlier designs should be followed carefully because advancement or separation can be expected in about 5% of the patients who have been followed for a minimum of five years. Despite this complication, which is seen radiographically, all patients were satisfied with the function of the hip. We do not recommend surgery solely to remove or replace the hole eliminator.

Adult↗

PubMed2003

Long-term in vivo wear performance of porous-coated acetabular components sterilized with gamma irradiation in air or ethylene oxide.

This study evaluated the long-term in vivo wear performance of 2 groups of well-functioning cementless acetabular cups sterilized by different methods. The first group included 31 hips that were implanted with AML TriSpike cups (DePuy, Warsaw, IN) sterilized by gamma-irradiation in air. The second group included 28 hips implanted with Arthropor cups (Joint Medical Products, Stamford, CT) that were sterilized with ethylene oxide. Time-dependent variations in the radiographic wear rates were compared within each group. Changes in the wear rates between 4- and 16-year follow-up times for the TriSpike cups were not significant (P=.09), and there was no evidence to suggest a trend toward substantially increasing wear rates with longer follow-up times. Among the Arthropor cups, the wear rates remained relatively constant between 2 and 14 years of follow-up evaluation. Although clinically apparent late increases in radiographic head penetration rates were not evident, we will continue to monitor all patients for evidence of accelerated wear at late follow-up.

Adult↗

PubMed2003

Correlation between early and late wear rates in total hip arthroplasty with application to the performance of marathon cross-linked polyethylene liners.

Laboratory simulations are typically used to assess the performance of new bearing surfaces for total hip arthroplasty. However, the ability of in vitro studies to accurately predict clinical wear performance remains uncertain. Using computer-assisted radiographic measurement techniques, this study found that the average wear rate based on early (2-3 years) clinical follow-up is representative of the average long-term wear rate for a population. Based on early wear data, Marathon polyethylene liners, cross-linked with 5.0 Mrad of gamma irradiation, are wearing at a mean rate of 0.08 mm/yr. This rate is about half that of non-cross-linked polyethylene but represents a more modest wear reduction than in vitro studies have predicted. If 5 to 10-year Marathon wear data corroborate our short-term results, early clinical wear data should be used to validate hip simulator studies.

Aged↗

PubMed2003

Can component and patient factors account for the variance in wear rates among bilateral total hip arthroplasty patients?

The purpose of this study was to indirectly quantify the effect of patient and component factors on polyethylene wear in patients with bilateral hip arthroplasties. Assuming that both hips experience similar levels of activity, the confounding influence of activity on wear can be removed by comparing wear rates within subjects. We studied temporal wear patterns in 21 patients with bilateral hip arthroplasty with a mean follow-up of 102 months. Each patient had matching acetabular cup and femoral head components implanted in both hips. Regression analyses were used to assess the variation in wear rates between the first and second implanted hips. The r(2) value demonstrated that matched components and patient factors accounted for 61% of the variance in wear rates. The remaining 39% of the variance, which is unaccounted for, indicates that factors other than those related to the components and patient also play a role.

Adult↗

PubMed2003

Clinical consequences of stress shielding after porous-coated total hip arthroplasty.

From a series of 223 extensively porous-coated total hip arthroplasties, 208 hips had radiographic followup at a minimum of 2 years, which could be evaluated for radiographic evidence of stress-shielding. These patients had a mean 13.9-year followup (range, 2-18 years). We compared the outcome of 48 total hip arthroplasties that had radiographically evident stress-shielding with 160 total hip arthroplasties that did not have radiographically visible stress-shielding or that had less severe stress-shielding. Stress-shielding was more likely in females, patients with a low cortical index, and patients with larger stems. At the most recent followup, patients with stress-shielding had a lower mean walking score than patients without stress-shielding and less osteolysis. No patients with stress-shielding had femoral loosening, implant fractures, or loss of porous coating. The revision rate was 13% (six hips) among hips with stress-shielding and 21% (33 hips) among hips without stress-shielding. Fifteen-year survivorship was 93% among hips with stress-shielding and 77% among hips without stress-shielding. Stress-shielding did not produce adverse consequences in these extensively porous-coated total hip arthroplasties.

Arthroplasty, Replacement, Hip↗

PubMed2003

Effect of terminal sterilization with gas plasma or gamma radiation on wear of polyethylene liners.

BACKGROUND: Although terminal sterilization with gamma radiation in air promotes cross-linking, which improves wear resistance, it also results in free radicals, which can oxidize and degrade the mechanical properties of polyethylene liners used for total hip arthroplasty. For this reason, non-cross-linked polyethylene components have also been sterilized with chemical surface treatments, such as gas plasma. In this study, we tested the hypothesis that conventional polyethylene liners cross-linked by sterilization with gamma radiation in air had better in vivo wear performance than non-cross-linked liners sterilized with gas plasma. METHODS: We retrospectively reviewed the wear rates in a series of hips treated with a Duraloc 100 cup, a 28-mm femoral head, and an Enduron liner that had been sterilized with either gamma radiation (sixty-one hips followed for a mean of 5.2 years) or gas plasma (sixty-three hips followed for a mean of 3.9 years). The irradiated liners had been stored with access to ambient oxygen for an average of 1.0 year (range, 0.05 to 5.72 years) prior to implantation. Multiple linear regression was used to assess the effect of the sterilization method on the wear rate while accounting for the possible influence of other factors, including liner geometry, femoral head material, patient gender, cup abduction angle, and age at surgery. RESULTS: The polyethylene liners that had been sterilized with gamma radiation in air had a significantly lower wear rate than did the gas-plasma-sterilized liners (0.097 compared with 0.19 mm/yr, p < 0.001). The sterilization method (p < 0.001) and age at surgery (p = 0.001) were the only factors that we analyzed that correlated with the wear rate. CONCLUSIONS: The in vivo wear of conventional polyethylene liners that had been sterilized with gamma radiation in air was, on the average, 50% less than that of non-cross-linked liners sterilized with gas plasma. LEVEL OF EVIDENCE: Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Gamma Rays↗

PubMed2002

The odyssey of porous-coated fixation.

Among all primary total hip arthroplasties (THAs) performed at our institution between 1977 and 1998, we retrospectively reviewed the outcome of 3,314 THAs performed with Anatomic Medullary Locking (AML), Prodigy, and Solution stems (all DePuy, Warsaw, IN). These hips included 460 proximally coated stems and 2,854 extensively coated stems. Survivorship rates for proximally and extensively coated stems were >95% at 15 years, using revision for any reason as an endpoint. Slight differences in thigh pain, stress shielding, and patient satisfaction were not significant. The 2.8% rate of component loosening among proximally coated stems was significantly higher than the 1.1% rate observed with extensively coated stems. Because of the relatively easy, reproducible surgical technique associated with extensively porous-coated stems and the perception of marginally better outcome, we prefer to use extensively porous-coated stems for all primary THAs.

Adult↗

PubMed2002

Fractures of the greater trochanter induced by osteolysis with the anatomic medullary locking prosthesis.

Pathologic fractures of the greater trochanter associated with trochanteric osteolysis are a late complication of total hip arthroplasty that have been described only in case reports. In this study of 208 consecutive total hip arthroplasties with mean 12.2-year radiographic follow-up, we reviewed the incidence, presentation, treatment, and outcome of such fractures. A radiographic review revealed 9 hips (4.3%) with trochanteric fractures resulting from osteolysis, occurring at a mean follow-up of 129 months. Five were diagnosed at the time of their radiographic appearance. Four were treated without operative fixation, using crutches and limited weight bearing for 4 to 6 weeks. Seven fractures healed in situ without major displacement. One resulted in a nonunion of the tip of the greater trochanter, and the radiographic outcome of a recent fracture was unknown. We found that the risk of sustaining a fracture was independent of the size of the osteolytic lesion; however, the risk increased significantly when the lysis eroded the cortical bone of the greater trochanter. In our experience with the extensively porous-coated AML stem (DePuy, a Johnson & Johnson Company, Warsaw, IN), conservative treatment leads to reasonable radiographic and clinical results in cases with limited initial fracture displacement.

Adolescent↗

PubMed2002

Effect of acetabular modularity on polyethylene wear and osteolysis in total hip arthroplasty.

BACKGROUND: Debris from polyethylene wear causes osteolysis. In this study, we examined the effect of acetabular liner modularity on polyethylene wear and osteolysis. METHODS: We compared forty-one hips (thirty-nine patients) treated with a nonmodular, porous-coated acetabular component with a matched group of forty-one hips (forty patients) treated with a modular acetabular component. The groups were matched by patient gender and age, type of polyethylene material, method of polyethylene sterilization, femoral head size and manufacturer, and stem manufacturer. The mean follow-up period was 5.3 years (range, 3.8 to 6.8 years) for the nonmodular group and 5.5 years (range, 3.8 to 8.0 years) for the modular group. Using serial radiographs and a computer-assisted method, we measured two-dimensional head penetration into the polyethylene liner. Temporal head-penetration data and linear regression analysis were used to calculate the true wear rates. RESULTS: The nonmodular acetabular components demonstrated a lower, but not a significantly lower, mean true wear rate than did the modular components (0.11 compared with 0.16 mm/yr, p = 0.22), and they were associated with a significantly lower rate of osteolysis (2% compared with 22%, p = 0.01). In addition, the true wear rates of the nonmodular components were less variable than those of the modular components. The 95% confidence interval for the wear rates of the nonmodular components (0.08 to 0.13 mm/yr) was nearly half that of the modular group (0.11 to 0.20 mm/yr). CONCLUSIONS: The lower and more consistent true wear rates of the nonmodular components could be attributed to the fact that these cups were designed to have greater liner-shell conformity, greater liner thickness, and less liner-shell micromotion than modular components. These design factors could have favorably altered the stress distribution throughout the liner and could have thereby decreased wear. Although nonmodular components may present a partial solution to the problems of wear and osteolysis, they pose a disadvantage when a failed liner in a bone-ingrown acetabular component needs to be revised.

Acetabulum↗