Highly crosslinked polyethylene does not reduce aseptic loosening in cemented THA 10-year findings of a randomized study.

BACKGROUND: Polyethylene (PE) wear particles are believed to cause aseptic loosening and thereby impair function in hip arthroplasty. Highly crosslinked polyethylene (XLPE) has low short- and medium-term wear rates. However, the long-term wear characteristics are unknown and it is unclear whether reduced wear particle burden improves function and survival of cemented hip arthroplasty. QUESTIONS/PURPOSES: We asked whether XLPE wear rates remain low up to 10 years and whether this leads to improved implant fixation, periprosthetic bone quality, and clinical function compared to conventional PE. METHODS: We randomized 60 patients (61 hips) to receive either PE or XLPE cemented cups combined with a cemented stem. At 10 years postoperatively, 51 patients (52 hips) were evaluated for polyethylene wear and component migration estimation by radiostereometry, for radiolucent lines, bone densitometry, and Harris hip and pain scores. Revisions were recorded. RESULTS: XLPE cups had a lower mean three-dimensional wear rate between 2 and 10 years compared to conventional PE hips: 0.005 mm/year versus 0.056 mm/year. We found no differences in cup migration, bone mineral density, radiolucencies, functional scores, and revision rate. There was a trend toward improved stem fixation in the XLPE group. The overall stem failure rate was comparably high, without influencing wear rate in XLPE hips. CONCLUSIONS: XLPE displayed a low wear rate up to 10 years when used in cemented THA, but we found no clear benefits in any other parameters. Further research is needed to determine whether cemented THA designs with XLPE are less prone to stem loosening. LEVEL OF EVIDENCE: Level I, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Fixation and bone remodeling around a low-modulus stem seven-year follow-up of a randomized study with use of radiostereometry and dual-energy x-ray absorptiometer.

Thirty-eight patients (40 hips) randomly received either an uncemented fully porous-coated composite stem (Epoch; Zimmer, Warsaw, Ind) or an uncemented proximally porous-coated solid stem (Anatomic; Zimmer). Patients were followed up for 7 years using radiostereometry, dual-energy x-ray absorptiometry, conventional radiography, the Harris Hip Score, and a pain questionnaire. Both stem designs achieved excellent outcome for fixation (stem subsidence and stem rotations close to zero) and clinical outcome, without any difference between the 2 groups (P > .12). Median wear rates were low despite use of conventionally gamma-sterilized polyethylene. No stem was radiographically loose on the postoperative radiographs. The low-modulus composite stem had positive effects on early proximal bone remodeling in Gruen regions 1, 2, 6, and 7 (P < .04). However, at 7 years, this bone-sparing effect persisted in only the calcar region (Gruen region 7).

Randomized comparison between 3 surface treatments of a single anteverted stem design: 84 hips followed for 5 years.

Eighty patients (84 hips) randomly received an anteverted cobalt-chromium stem (Lubinus SP2; Waldemar Link, Hamburg, Germany) with matte, polymethyl methacrylate-coated, or polished surface (uncollared). Radiostereometry was used to study migration and wear; and the bone mineral density was studied with dual-energy x-ray absorptiometry at 6 months, 1 year, 2 years, and 5 years. The polished stems had subsided 0.1 to 0.2 mm more at 6 months and 0.3 to 0.4 mm more at 5 years than the matte and precoated versions (P < .0001) and subsided mainly inside the cement mantle. The rotations of the stem and the migration and wear of the cemented cup did not differ between the 3 groups. After 1 and 2 years, the polished stems had lost significantly less bone mineral in Gruen zones 1, 2, 6, and 7 (P = .004 to .03); but this difference had disappeared after 5 years. The period of improved bone remodeling around the polished version coincided with the early period of increased subsidence, suggesting that stem motions inside the mantle resulted in a favorable loading of the proximal femur. Our observations suggest that alternative shapes could be possible on future polished femoral stem designs.

Bioactive cement or ceramic/porous coating vs. conventional cement to obtain early stability of the acetabular cup. Randomised study of 96 hips followed with radiostereometry.

Ninety patients (96 hips) scheduled for THA were stratified to fixation of the acetabular component in three main groups of about equal size. Fluoride cement, porous coated press-fit cup with ceramic coating or Palacos cum Gentamicin cement were used. All patients received Spectron EF stem. The migration of the cups and the femoral head penetration into the socket were measured with radiostereometric analysis. At 2 years the choice of fixation did not influence the migration or rotation of the cup. Patients with compromised bone quality showed increased three-dimensional (3D or total) migration. Proximal and 3D penetration rates were increased in cemented compared with the uncemented cups (p<0.001), which probably not could be related to the choice of fixation. Appearance of radiolucent lines was almost equal in the two cemented groups. Uncemented cups had less radiolucent lines at 2 years. Fluoride containing cement or uncemented fixation did not improve the early postoperative stability of the socket.

Evaluation of a femoral stem with reduced stiffness. A randomized study with use of radiostereometry and bone densitometry.

BACKGROUND: Femoral stems with reduced stiffness were introduced in total hip arthroplasty to facilitate proximal load transfer and thereby reduce periprosthetic bone loss. Poor fixation and unacceptably high revision rates turned out to be a major problem with these prostheses. The purpose of the present study was to evaluate the early performance of a low-modulus stem (one that is less stiff) with the potential to address the problem of fixation by the use of a surface coating. The coating consisted of a titanium porous mesh proximally covered with a mixture of hydroxyapatite and tricalcium phosphate. METHODS: Thirty-nine men and twenty-six women (sixty-eight hips) with noninflammatory arthritis were studied. The patients were randomized to receive either a porous-coated composite stem with reduced stiffness (Epoch) or a stiff stem with a porous coating (Anatomic). Both stems were inserted without cement, had a ceramic coating on the proximal two-thirds, and were supplied with tantalum beads. At the time of the operation, tantalum markers were also placed into the proximal part of the femur. The patients were followed for up to two years after the operation and were evaluated with use of repeated radiostereometric measurements, measurements of bone-mineral density, conventional radiography, and Harris hip scores. RESULTS: Both stems showed optimum fixation with median subsidence and stem rotations that were close to zero. Repeated measurements of bone-mineral density revealed early loss of bone mineral in all Gruen regions in both treatment groups. The loss of bone mineral around the Epoch stems was significantly reduced at two years in Gruen regions 1, 2, 6, and 7 (p < 0.0005 to 0.04). Measurements on postoperative radiographs showed no difference in stem positioning or fill, but the Epoch stems had significantly more endocortical contact on both the anteroposterior (p < 0.0005) and the lateral radiograph (p = 0.02). At two years postoperatively, the Epoch stems had fewer sclerotic lines surrounding the stem (p = 0.002) and less sclerosis at the tip of the prosthesis (p = 0.001) compared with the Anatomic stems. The clinical results in terms of the Harris hip score, which was determined in all hips, and pain or discomfort, which was evaluated in thirty-seven hips treated at the same hospital, were not found to be different, with the numbers available. CONCLUSIONS: Contrary to previous studies of other designs with reduced stiffness, the Epoch stem achieved excellent primary fixation. Despite this rigid fixation, the proximal loss of bone-mineral density was less than that associated with the stem with a stiffer design. These results should encourage additional long-term studies with a larger patient population.

5-year experience of highly cross-linked polyethylene in cemented and uncemented sockets: two randomized studies using radiostereometric analysis.

BACKGROUND: Laboratory tests and early clinical studies have shown that highly cross-linked polyethylene (PE) markedly improves wear resistance compared to conventional PE. We evaluated this type of PE in two randomized clinical studies using radiostereometric analysis (RSA). The 2- and 3-year follow-up of these studies have already been reported. We found a lower penetration rate for the highly cross-linked PE than for conventional PE. We now report the outcome after 5 years. PATIENTS AND METHODS: 60 patients (61 hips) with a median age of 55 years were randomized to receive either highly cross-linked PE (Durasul) or conventional cemented all-polyethylene sockets of the same design. 55 patients (56 hips) were followed for 5 years. In the second study, 32 patients (64 hips) with a median age of 48 years and with bilateral primary or secondary osteoarthritis of the hip had hybrid total hip arthroplasty with liners made of highly cross-linked PE (Longevity) on one side and conventional PE on the other. 23 patients in this study have passed the 5-year follow-up. RESULTS: Bedding-in and creep for the Durasul all-PE was reached by 2 years, and by 1 year for the Longevity liners. In both control groups with conventional PE, this was reached by 6 months. The steady-state wear rate was close to zero in the two study groups and 0.06 mm/year for the conventional PE in the two control groups. INTERPRETATION: We found that use of highly crosslinked PE instead of conventional PE reduced the wear by more than 95%, which supports continued use of this type of PE in young, active patients.

Different loss of BMD using uncemented press-fit and whole polyethylene cups fixed with cement: repeated DXA studies in 96 hips randomized to 3 types of fixation.

BACKGROUND: In cemented THA, aseptic loosening of the cup is more common than loosening of the stem, while periprosthetic osteolysis of the socket resulting in difficult reconstruction problems has emerged as the most significant problem with cementless cup fixation. PATIENTS AND METHODS: 90 patients (96 hips) scheduled for THA were stratified in three groups according to the method of fixation of the acetabular component: acrylic bone cement with fluoride (Cemex-F), porous-coated press-fit cup with ceramic coating (Trilogy, uncemented) and acrylic cement with gentamicin (Palacos). All patients received the Spectron EF stem. Acetabular bone mineral density was measured with dual-energy X-ray absorptiometry (DXA) 1 week postoperatively, and after 12 and 24 months. The periprosthetic BMD was evaluated in 5 ROIs positioned around the acetabular component. RESULTS: In the uncemented sockets, the BMD had decreased proximally and medially to the cup after 2 years. The difference was significant in the proximal region as compared to the control group (Palacos). No difference was noted between the 2 groups with cemented components after 2 years. Stepwise linear regression analysis showed that loss of periprosthetic BMD in the proximal high-pressure region after 2 years increased with higher postoperative BMD and when the uncemented design had been used. INTERPRETATION: Contrary to previous studies of cemented stems, the use of fluoride cement did not influence the periprosthetic BMD 2 years after the examination. Increased loss of BMD with use of uncemented press-fit cups in the region in which osteolytic lesions are commonly found suggests that stress shielding may initiate the development of this complication. Longer follow-up will, however, be necessary to substantiate this hypothesis.

Addition of fluoride to acrylic bone cement does not improve fixation of a total hip arthroplasty stem.

UNLABELLED: Improved fixation to bone is vital for improving the long term success of cemented implants. Addition of fluoride to acrylic bone cement may be one way to improve the quality of the bone cement interface and thereby reduce the risk of loosening. Ninety patients (97 hips) with a median age of 70 years (range, 31-81 years) scheduled for total hip arthroplasty were randomized to receive a stem fixed with fluoride-containing acrylic bone cement or conventional acrylic bone cement. Fixation and bone remodeling around the femoral component was studied with radiostereometry and dual-energy xray absorptiometry up to 5 years after the operation in 73 patients (77 hips). Radiostereometric evaluation at 5 years revealed no differences in stem migration (subsidence/lift-off) or rotations. The stem subsidence inside the mantle was similar in the two groups. At 5 years the study group had lost more bone mineral in Gruen regions 5 and 7 than the controls. The Harris hip and pain score did not differ. Use of fluoride containing bone cement did not improve the stem fixation compared with a conventional cement used up to 5 years, but resulted in more pronounced loss of bone mineral density in the medial cortex. LEVEL OF EVIDENCE: Therapeutic Level I. 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.

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

UNLABELLED: 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.

Fluoride-containing acrylic bone cement in total hip arthroplasty. Randomized evaluation of 97 stems using radiostereometry and dual-energy x-ray absorptiometry.

Ninety patients (97 hips) scheduled for total hip arthroplasty were stratified to fixation of the femoral component using fluoride-containing cement or Palacos with gentamicin. Whole polyethylene Reflection and press-fit Trilogy cups were used. All patients received Spectron EF stem. The micromotions of the stem were measured with radiostereometric analysis and the periprosthetic bone mineral density with automatic and manual dual-energy x-ray absorptiometry (DEXA) analysis. At 2 years, the choice of cement did not influence the subsidence or rotations of the stem. The DEXA analysis revealed more loss of periprosthetic bone mineral density in fluoride cement group. We speculate that forming of fluorapatite crystals, toxic effects of the fluoride, or lower radiopacity of the fluoride cement might explain this finding. According to our study with 2-year of follow-up, there is no obvious advantage of addition of fluoride to acrylic bone cement when used to fixate the femoral component in total hip arthroplasty.

Increase in early polyethylene wear after sterilization with ethylene oxide: radiostereometric analyses of 201 total hips.

We evaluated polyethylene wear by measuring femoral head penetration in 201 THA (median age 62 (31-81) years, 117 women) extracted from 5 randomized studies aimed to assess various fixation principles. There were 30 cemented all-polyethylene Lubinus cups sterilized by gamma irradiation in a reduced oxygen environment, 65 porous-coated Trilogy cups with liners gamma-sterilized in inert gas. Moreover, 37 cemented cups were sterilized with ethylene oxide (Reflection all-poly) and 69 porous-coated cups had liners sterilized in ethylene oxide (Reflection). 28 mm femoral heads were used in all cups. The patients were followed with repeated radiostereometric measurements (RSA) up to 2 years. The activity level of the patients was evaluated by a questionnaire. After 2 years, cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates, as compared with gamma-sterilized polyethylene. The penetration did not differ between the gamma-irradiated designs. Using stepwise linear regression analysis, we found that the type of sterilization, age and weight were the most important predictors and that they determined the direction of the proximal penetration rate. Activity score, male gender and proximal migration of the cup had little effect. The accelerated wear observed with the EtO-sterilized polyethylene causes concerns about long-term problems and especially in younger patients.

Highly cross-linked polyethylene in cemented THA: randomized study of 61 hips.

Highly cross-linked polyethylene (PE) has been introduced as an alternative bearing material in total hip arthroplasty (THA) because of high wear resistance in laboratory tests but the clinical experience of this material is limited. We evaluated a highly cross-linked PE (warm irradiated adiabatic melting, absorbed dose, 95 kGy) in a randomized study of cemented THAs. Cups of the same design but made of conventionally gamma irradiated PE (absorbed dose, 25-40 kGy) constituted the control group. Sixty-one hips (30 women, 30 men) with a median age of 55 years (range, 35-70 years) were included. All patients received a Spectron stem with 28-mm CoCr head. Radiostereometric examinations with the patient supine or standing were done at regular intervals. Wear was measured with the patient in the supine position from the first postoperative week, whereas examinations done with the patient standing were initiated 3 months after the operation. Dual x-ray absorptiometry and conventional radiography were used to evaluate the bone mineral density and the radiolucencies around the acetabular component. Fifty-two patients (53 hips; 25 highly cross-linked, 28 control) have been followed up for 2 years. At the 2-year followup, the highly cross-linked cups showed 50% reduction of proximal wear compared with the control group, when the patients were studied standing. When evaluated supine, the difference in proximal wear did not reach significance. The migration of the socket, the relative changes of periprosthetic bone mineral density, and the progression of radiolucencies between the immediately postoperative followup and 2-year followup did not differ. Highly cross-linked PE showed increase resistance to wear. Different mechanical properties of the two types of PE studied did not alter the performance of the cup in terms of fixation, periprosthetic bone loss, and radiographic appearance. However, the followup is short and these results are preliminary.

The Otto Aufranc Award. Highly cross-linked polyethylene in total hip arthroplasty: randomized evaluation of penetration rate in cemented and uncemented sockets using radiostereometric analysis.

The annual wear rate in polyethylene articulations should be 0.1 mm or less to avoid future osteolysis. Highly cross-linked polyethylene shows an 80 to 90% wear reduction in hip simulator testing, but the clinical documentation of this new polyethylene is still inadequate. We evaluated the highly cross-linked polyethylene in two prospective randomized clinical studies. Thirty-two patients (12 men, 20 women; 64 hips) with a median age of 48 years (range, 29-70 years) with bilateral primary or secondary arthrosis of the hip had hybrid total hip arthroplasty with liners made of highly cross-linked polyethylene on one side and conventional polyethylene on the other. Twenty-seven patients in this study have passed 2 years followup. A further group, comprised of 60 patients (61 hips) with a median age of 55 years (range, 35-70 years), was randomized to receive either highly cross-linked polyethylene or conventional cemented all-polyethylene of the same design. Forty-nine of these 60 patients have been observed for 3 years. In both studies all patients received Spectron stems with 28-mm Co-Cr heads. Radiostereometric examinations with the patient supine or standing were done at regular intervals. Wear was measured in the supine position from the first postoperative week, whereas standing examinations were initiated 3 months after the operation. The penetration rate almost was identical in the study and control groups at 6 months after the operation. Thereafter, the penetration rate leveled out in the two groups with highly cross-linked polyethylene. At 2 years the highly cross-linked polyethylene liner showed 62% lower proximal penetration and 31% lower total (three-dimensional) penetration when the patients were examined in supine position. The highly crosslinked all-polyethylene cemented cups showed lower proximal penetration in both positions. The better wear performance of highly cross-linked polyethylene could increase the implant longevity. Longer followup is needed to evaluate if this new material is associated with less occurrence of osteolysis.