Georgios Digas

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.

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.

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 xray 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.

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.

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.

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.

New polymer materials in total hip arthroplasty: Evaluation with radiostereometry, bone densitometry, radiography and clinical parameters

Aims: To evaluate the outcome of different types of polyethylene, bone cements and one design of uncemented fixation with porous and ceramic coating using radiostereometry, bone densitometry, conventional radiography and clinical parameters. Materials and methods: Study 1: 201 patients were extracted from 5 prospective randomised studies to evaluate femoral head penetration at two years with radiostereometry in four basic designs, cemented Lubinus and Reflection cups, uncemented Trilogy and Reflection cups. Studies II and III. 60 patients (61 hips) were randomised to receive either highly cross-linked or conventional all PE cups. 32 patients with bilateral arthrosis received hybrid THA with highly crosslinked PE on one side and conventional on the contra lateral side. Femoral head penetration and the migration of the cups were evaluated with radiostereometry in the supine and standing positions. DEXA and conventional radiography were used to evaluate the bone mineral density and radiolucencies around the cemented acetabular component. Studies IV and V: 90 patients (97 and 96 hips respectively) were stratified depended on age, gender, diagnosis and preoperative BMD to create 3 main groups of socket fixation. In the first group fluoride containing cement was used, in the second group Palacos cum Gentamicin and in the third hybrid THA with porous coated HA/TCP cup. In the hybrid group the fixation of the femoral component was again randomised to either of the two cements. The results on femoral and acetabular sides are presented separately in studies IV and V, respectively. Results: Study I: Cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates compared with gamma-sterilized polyethylene. Regression analysis showed that the type of sterilization, age and weight was the most important factors affecting the penetration rate. Studies II and III: In the cemented study the proximal penetration was lower in the study group independent of position at 3 years, while in the hybrid study the penetration was lower in the study group only in the supine position at 2 years. The migration of the cup did not differ between the plastics in both studies. At 2 years the periprosthetic radiolucency and BMD did not differ significantly between the 2 types of PE used in the cemented study. Study IV: The subsidence of the stem did not differ between the groups, but the periprosthetic BMD decreased more in fluoride cement group at 2 years. Conventional radiography revealed higher progression of radiolucent lines in the Palacos group, but only in one region. Study V: The proximal migration of the cup was almost similar in all three groups. The three dimensional migration was increased in patients with osteoporosis. Postoperative radiolucent lines tended to disappear with use of porous coating covered with HA/TCP. Conclusions : Study I: EtO sterilized polyethylene increased the femoral head penetration. Age and weight were also important predictors of the penetration rate. Studies II and III. The highly cross-linked polyethylene decreased the penetration rate mainly after one year probably reflecting less wear. The different mechanical properties of the two types of PE studied did not affect the early fixation of the cemented cup. Study IV: There were no obvious advantage of addition of fluoride to acrylic bone cement when used to fixate the femoral component. Study V: Use of fluoride containing cement or uncemented fixation did not improve the early stability of the socket compared to Palacos with Gentamicin.

Influence of design variations on early migration of a cemented stem in THA.

The clinical results of using different cemented stems in total hip arthroplasty may vary because of shape, surface finish, and choice of metal alloy. Less is known about the influence of size and offset using one and the same design. Data from 140 patients (140 hips) of a cohort constituting 197 patients (231 hips) implanted with cemented Spectron Primary stems were extracted from patients studied in four randomized studies primarily designed for other purposes. Stem size (1, 2, 3, or larger), normal/extra offset, neck length and true offset (horizontal length between the stem and head center of the inserted modular implant) were recorded in millimeters. The radiographic appearance of the cementing was graded on the immediate postoperative radiograph according to Barrack. The patients were examined with radiostereometric analysis of stem migration for a 2-year followup period. Stem Size 1 (the smallest) showed an insignificant increase in subsidence compared with the bigger sizes. Using stepwise linear regression analysis, the quality of the cementing (Barrack C2) was the only parameter that had any certain influence of the subsidence at 2 years. Stem size 2 tended to show minimum valgus alignment and sizes 1 and 3 and bigger showed minimum varus tilting. Our findings suggest that placement of the stem with the tip against the posterior cortex (C2) and stem size influence the primary fixation in different ways. This effect is small, however, indicating that further confirmation with longer followup is necessary. Level of Evidence: Therapeutic Level II-1 (prospective cohort study). See the Guidelines for Authors for a complete description of levels of evidence.

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

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.

Risedronate does not enhance fixation or BMD in revision cups: randomised study with three years follow-up

Background Bisphosphonates may improve implant fixation by inhibition of bone resorption and stimulation of osteoblasts by up regulation of BMP-2. However, there are few clinical studies in this area. Questions/purpose Does treatment with oral bisphosphonates improve implant fixation and bone remodelling around the acetabular component after revision arthroplasty with or without use of morselised allograft? Patients and methods Fifty-three patients received university pharmacy blinded medication for three months: 5 mg risedronate or placebo one dosage and 1 g calcium carbonate and 800IE cholecalciferol per day. Forty-one patients were operated upon with revision of the cup. The revisions were performed with an uncemented (Trilogy, Zimmer, Warsaw, USA) or a cemented (Ogee, Depuy Int, England) cup. Radiostereometric analysis was obtained within one week after the operation, at three and six months, and after one, two and three years to study cup migration. Bone mineral density was measured postoperatively, at six months, one and two years, using DEXA. The presence and extension of radiolucent lines and graft remodelling were studied on conventional radiography. Results The risendronate group revealed less anterior-posterior rotation at 6 months. We found no significant differences in migration at three years, change in bone mineral density, or graft remodelling and radiolucent lines formation between groups. Conclusions We could not demonstrate any beneficial effects of oral administration of risedronate on the fixation, bone mineral density or bone remodelling of revision cups using various amount of bone graft.