Meridith E. Greene

Large diameter femoral heads on highly cross-linked polyethylene: minimum 3-year results.

Contemporary highly cross-linked polyethylenes have become the most widely used alternative bearing surfaces in total hip replacement and may be paired with large diameter femoral heads (> 32 mm) in patients considered to be at high risk for dislocation. We report on a prospective series of 42 patients (45 hips) who had total hip replacement using large diameter cobalt-chrome femoral heads articulating with a highly cross linked polyethylene after a minimum of 3 years followup (mean 3.3 years). At final followup, the final patient cohort showed excellent clinical results with no radiographic failures or episodes of loosening. There was no evidence of pelvic or femoral osteolysis. One patient sustained a dislocation due to a grossly malpositioned acetabular component necessitating early isolated acetabular revision. The average yearly steady state wear rate was −0.06 ± 0.41 mm/year. The results of our short-term prospective series indicated total hip replacement with large femoral heads articulating with a highly cross linked polyethylene showed excellent wear characteristics and clinical results and could be considered in patients at increased risk for dislocation.Level of Evidence: Therapeutic studies, level IV (case series). See Guidelines for Authors for a complete description of levels of evidence.

Minimum 6-year followup of highly cross-linked polyethylene in THA.

To reduce wear rates and particulate debris, highly cross-linked polyethylene has been in use in total hip arthroplasty for 8 years. We designed this followup study to primarily determine the total penetration rate of the femoral head and the steady-state wear rate of cross-linked polyethylene in patients undergoing primary total hip arthroplasty. We retrospectively reviewed data from 182 patients (200 hips) with a minimum 6-year followup (mean, 6.9 years; range, 6-8 years) and an average age of 60.2 years at surgery. The average Harris hip score, University of California-Los Angeles activity score, and WOMAC score were 91.1, 6.3, and 11.3, respectively. Radiographic evaluation showed no evidence of loosening or osteolytic lesions around the cup or stem. No revisions were performed for polyethylene wear or liner fracture. The average steady-state wear rate was −0.002 ± 0.01 mm per year and −0.026 ± 0.13 mm per year for 28-mm and 32-mm head sizes, respectively. We observed no correlation between the total wear rate and femoral head size, brand of polyethylene, age, gender, primary diagnosis, mode of fixation, surgical approach, University of California-Los Angeles activity score, Harris hip score, or WOMAC. Highly cross-linked polyethylene liners are associated with excellent midterm clinical, radiographic, and wear results in this group of patients.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Biologic fixation of total hip implants. Insights gained from a series of canine studies.

Biologic fixation of total hip replacement implants with porous surfaces by means of bone ingrowth became a clinical reality largely through the many experimental studies that were carried out in the 1960s, 1970s, and 1980s. Polymethylmethacrylate bone cement had been the material of choice for implant fixation until then, when it was realized that bone can grow into the porous surfaces of implants if appropriate pore geometries are provided. Porous metals, polymers, and ceramics had been investigated as candidate implants, and porous-coated metal implants were chosen on the basis of the advances in sintering technologies, biocompatibility, and strength considerations (Fig. 1). Consistently obtaining bone growth into functioning total joint replacement components under the conditions of physiologic loading, however, remained a problem. Canine studies were critically important in defining the conditions necessary for consistent bone growth into these devices and thus in the development of porous-surface prostheses for biologic fixation. Our experience with such studies is presented here. Fig. 1 Different types of porous surfaces available for biologic ingrowth. From top to bottom: plasma sprayed surfaces, sintered beaded surfaces with large spheres, sintered beaded surfaces with small spheres, and diffusion-bonded fiber-metal surfaces. The three figures from left to right in each column show representative cross-sections through the porous surfaces. Between 1980 and 1985, more than sixty total hip arthroplasties were performed with use of porous-coated metal components in dogs in order to assess a variety of factors that might influence bone ingrowth. The dog model was chosen because of the large amount of data available on the skeletal renewal dynamics of the dog. In addition, dogs are known to have early development of arthritis of the hip and were thought to provide a good animal model for total hip replacement surgery. The canine acetabulum is also shallower and more dysplastic than the human …

Comparison of femoral head penetration using RSA and the Martell method.

Radiostereometry has high precision and accuracy measuring polyethylene wear in total hip arthroplasty but requires a specialized setup. The Martell method is simpler and can be used on larger populations. The hypothesis that the radiostereometry analysis and the Martell analysis would yield comparable wear data from the same group of patients having total hip arthroplasty was tested. A group of twenty-five total hip arthroplasty patients who had both radiostereometry and standard anterior-posterior pelvic and cross-table lateral radiographs of sufficient quality for analysis were identified. The films were taken at postoperative periods of 6 weeks, 1 year, 2 years, and 5 years. Femoral head penetration was measured by both methods at each time point. The median penetration rates measured by each method decreased over time. Penetration results were affected by method of analysis, time, and dimension, with greater penetration for Martell compared with radiostereometry at each time point, greater penetration with increasing time for each method, and larger three-dimensional magnitude compared with two-dimensional analysis. Level of Evidence: Case series Level IV. See Guidelines for Authors for a complete description of levels of evidence.

Standing versus supine radiographs in RSA evaluation of femoral head penetration.

Evaluation of polyethylene acetabular component wear in total hip arthroplasties commonly is performed using serial radiographs of the hip by measuring the change in the location of the center of the femoral head in relation to the acetabular component. Of the different methods currently used for this purpose, radiostereometric analysis (RSA) is considered the most accurate and precise. In all such radiographic studies, it is assumed the femoral head is seated into the deepest portion of the acetabular component during all radiographic examinations. Although most radiographs used for wear measurements are taken with the patient supine, we questioned whether standing radiographs, with substantial joint load, are better suited for these measurements. We evaluated two groups of patients having total hip arthroplasty who had radiostereometric radiographs taken in supine and standing positions. The average femoral head penetration that occurred between the 6-month and 2-year time interval was measured with radiographs taken in the standing or supine position. We found no difference between the average total femoral head penetration when using supine or standing radiographs.

Age- and health-related quality of life after total hip replacement: Decreasing gains in patients above 70 years of age

Background — While age is a common confounder, its impact on health-related quality of life (HRQoL) after total hip replacement is uncertain. This could be due to improper statistical modeling of age in previous studies, such as treating age as a linear variable or by using age categories. We hypothesized that there is a non-linear association between age and HRQoL. Methods — We selected a nationwide cohort from the Swedish Hip Arthroplasty Register of patients operated with total hip replacements due to primary osteoarthritis between 2008 and 2010. For estimating HRQoL, we used the generic health outcome questionnaire EQ-5D of the EuroQol group that consits or 2 parts: the EQ-5D index and the EQ VAS estimates. Using linear regression, we modeled the EQ-5D index and the EQ VAS against age 1 year after surgery. Instead of using a straight line for age, we applied a method called restricted cubic splines that allows the line to bend in a controlled manner. Confounding was controlled by adjusting for preoperative HRQoL, sex, previous contralateral hip surgery, pain, and Charnley classification. Results — Complete data on 27,245 patients were available for analysis. Both the EQ-5D index and EQ VAS showed a non-linear relationship with age. They were fairly unaffected by age until the patients were in their late sixties, after which age had a negative effect. Interpretation — There is a non-linear relationship between age and HRQoL, with improvement decreasing in the elderly.

Precision of radiostereometric analysis (RSA) of acetabular cup stability and polyethylene wear improved by adding tantalum beads to the liner

Background and purpose — In traditional radiostereometric analysis (RSA), 1 segment defines both the acetabular shell and the polyethylene liner. However, inserting beads into the polyethylene liner permits employment of the shell and liner as 2 separate segments, enabling distinct analysis of the precision of 3 measurement methods in determining femoral head penetration and shell migration. Patients and methods — The UmRSA program was used to analyze the double examinations of 51 hips to determine if there was a difference in using the shell-only segment, the liner-only segment, or the shell + liner segment to measure wear and acetabular cup stability. The standard deviation multiplied by the critical value (from a t distribution) established the precision of each method. Results — Due to the imprecision of the automated edge detection, the shell-only method was least desirable. The shell + liner and liner-only methods had a precision of 0.115 mm and 0.086 mm, respectively, when measuring head penetration. For shell migration, the shell + liner had a precision of 0.108 mm, which was better than the precision of the shell-only method. In both the penetration and migration analyses, the shell + liner condition number was statistically significantly lower and the bead count was significantly higher than for the other methods. Interpretation — Insertion of beads in the polyethylene improves the precision of femoral head penetration and shell migration measurements. A greater dispersion and number of beads when combining the liner with the shell generated more reliable results in both analyses, by engaging a larger portion of the radiograph.

Women in Charnley class C fail to improve in mobility to a higher degree after total hip replacement

Background— The Charnley comorbidity classification organizes patients into 3 classes: (A) 1 hip involved, (B) 2 hips involved, and (C) other severe comorbidities. Although this simple classification is a known predictor of health-related quality of life (HRQoL) after total hip replacement (THR), interactions between Charnley class, sex, and age have not been investigated and there is uncertainty regarding whether A and B should be grouped together. Methods — We selected a nationwide cohort of patients from the Swedish Hip Arthroplasty Register operated with THR due to primary osteoarthritis between 2008 and 2010. For estimation of HRQoL, we used the generic health outcome questionnaire EQ-5D of the EuroQol group. This consists of 2 parts: the EQ-5D index and the EQ VAS estimates. We modeled the EQ-5D index and the EQ VAS against the self-administered Charnley classification. Confounding was controlled for using preoperative HRQoL values, pain, and previous contralateral hip surgery. Results — We found that women in class C had a poorer EQ-5D outcome than men. This effect was mostly due to the fact that women failed to improve in the mobility dimension; only 40% improved, while about 50% of men improved. Age did not interact with Charnley class. We also found that the classification performed best without splitting or aggregating classes. Interpretation — Our results suggests that the self-administered Charnley classification should be used in its full capacity and that it may be interesting to devote special attention to women in Charnley class C.

Three Year RSA Evaluation of Vitamin E Diffused Highly Cross-linked Polyethylene Liners and Cup Stability

Vitamin E diffusion into highly cross-linked polyethylene (E-XLPE) is a method for enhancing oxidative stability of acetabular liners. The purpose of this study was to evaluate in vivo penetration of E-XLPE using radiostereometric analysis (RSA). Eighty-four hips were recruited into a prospective 10-year RSA. This is the first evaluation of the multicenter cohort after 3-years. All patients received E-XLPE liners (E1, Biomet) and porous-titanium coated cups (Regenerex, Biomet). There was no difference (P=0.450) in median femoral head penetration into the E-XLPE liners at 3-years comparing cobalt-chrome heads (-0.028mm; inter-quartile range (IQR) - 0.065 to 0.047) with ceramic heads (-0.043mm, IQR - 0.143to0.042). The 3-year follow-up indicates minimal E-XLPE liner penetration regardless of head material and minimal early cup movement.

Radiostereometric Analysis Study of Tantalum Compared with Titanium Acetabular Cups and Highly Cross-Linked Compared with Conventional Liners in Young Patients Undergoing Total Hip Replacement

BACKGROUND Radiostereometric analysis provides highly precise measurements of component micromotion relative to the bone that is otherwise undetectable by routine radiographs. This study compared, at a minimum of five years following surgery, the micromotion of tantalum and titanium acetabular cups and femoral head penetration in highly cross-linked polyethylene liners and conventional (ultra-high molecular weight polyethylene) liners in active patients who had undergone total hip replacement. METHODS This institutional review board-approved prospective, randomized, blinded study involved forty-six patients. Patients were randomized into one of four cohorts according to both acetabular cup and polyethylene liner. Patients received either a cementless cup with a titanium mesh surface or a tantalum trabecular surface and either a highly cross-linked polyethylene liner or an ultra-high molecular weight polyethylene liner. Radiostereometric analysis examinations and Short Form-36 Physical Component Summary, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), University of California Los Angeles (UCLA) activity, and Harris hip scores were obtained preoperatively, postoperatively, at six months, and annually thereafter. RESULTS All patients had significant improvement (p < 0.05) in Short Form-36 Physical Component Summary, WOMAC, UCLA activity, and Harris hip scores postoperatively. On radiostereometric analysis examination, highly cross-linked polyethylene liners showed significantly less median femoral head penetration at five years (p < 0.05). Steady-state wear rates from one year to five years were 0.04 mm per year for ultra-high molecular weight polyethylene liners and 0.004 mm per year for highly cross-linked polyethylene liners. At the five-year follow-up, the median migration (and standard error) was 0.05 ± 0.20 mm proximally for titanium cups and 0.21 ± 0.05 mm for tantalum cups. CONCLUSIONS In this young population who had undergone total hip replacement, radiostereometric analysis showed significantly less femoral head penetration in the highly cross-linked polyethylene liners compared with that in the conventional ultra-high molecular weight polyethylene liners. Penetration rates were one order of magnitude less in highly cross-linked polyethylene liners compared with ultra-high molecular weight polyethylene liners. There was no significant difference in proximal migration between the tantalum and titanium acetabular cups through the five-year follow-up (p > 0.19).