Radiostereometric Analysis Radiographs Research Articles

What is the Long-term Wear of a 5-Mrad Highly Crosslinked Polyethylene Liner? A 14-year RSA Study.

Lower doses of irradiation (≤ 5 Mrad) during the manufacture of highly crosslinked polyethylene acetabular liners may result in less crosslinking and an increased wear rate. Radiostereometric analysis (RSA) studies have found that wear of more highly irradiated highly crosslinked polyethylene liners (7 to 10 Mrad) decreases at longer-term follow-up compared with earlier reports of the same cohorts. Although wear of 5-Mrad irradiated liners appears to increase at midterm follow-up, it is unclear whether that remains true at longer follow-up. We asked: (1) In patients who underwent THA with a 5-Mrad highly crosslinked polyethylene liner, what is the wear rate evaluated with RSA during the first 14 years? (2) Does the wear rate decrease after 6 years in situ? This is a brief follow-up of prior RSA studies performed at 2 and 6 years. We prospectively reviewed the longer-term wear rate in 13 patients who underwent primary THAs with the same design of a 5-MRad irradiated crosslinked acetabular liner and a 28-mm cobalt-chromium articulation. Of the initial 30 patients who were enrolled, 13 (43%) were available at the 14-year timepoint; nine patients had died, 1 patient had withdrawn, 1 had an intraoperative fracture, 3 patients were too infirm to have radiographs, 2 had no baseline RSA radiographs, and 1 had poor-quality RSA images. Tantalum markers were inserted during surgery, and all patients had RSA radiographic examinations at 1 week, 6 months, and 1, 2, 6, and 14 years postoperatively. The mean ± standard deviation proximal, 2D, and 3D wear rates calculated between 1 year and 14 years were 0.019 ± 0.013 mm, 0.022 ± 0.015 mm, and 0.025 ± 0.019 mm per year, respectively. No patient had proximal 2D or 3D wear rates exceeding 0.06 mm per year. An increasing wear rate over time was measured for proximal and 2D wear rates between 6 and 14 years (0.024 and 0.030 mm per year) compared with that between 1 and 6 years (0.008 and 0.010 mm per year; p = 0.03). The proximal, 2D, and 3D wear of a highly crosslinked polyethylene liner produced using 5-Mrad radiation remains low in the longer-term. With the small numbers available in a long-term RSA study such as this, we confirmed that the wear rate did not decrease at longer-term follow-up, unlike previous RSA studies of more highly irradiated highly crosslinked polyethylene liners. Nevertheless, the wear rate remains very low and below the threshold typically associated with the development of osteolysis (0.1 mm/year of wear). This should provide assurance to orthopaedic surgeons monitoring patients with this 5-Mrad irradiated liner in situ, while providing useful information to manufacturers of future highly crosslinked polyethylene liners. Level IV therapeutic study.

Large articulations do not increase wear rates of thin second-generation highly cross-linked polyethylene liners at ten years.

Radiostereometric analysis (RSA) is the most accurate radiological method to measure in vivo wear of highly cross-linked polyethylene (XLPE) acetabular components. We have previously reported very low wear rates for a sequentially irradiated and annealed X3 XLPE liner (Stryker Orthopaedics, USA) when used in conjunction with a 32 mm femoral heads at ten-year follow-up. Only two studies have reported the long-term wear rate of X3 liners used in conjunction with larger heads using plain radiographs which have poor sensitivity. The aim of this study was to measure the ten-year wear of thin X3 XLPE liners against larger 36 or 40 mm articulations with RSA. We prospectively reviewed 19 patients who underwent primary cementless THA with the XLPE acetabular liner (X3) and a 36 or 40 mm femoral head with a resultant liner thickness of at least 5.8 mm. RSA radiographs at one week, six months, and one, two, five, and ten years postoperatively and femoral head penetration within the acetabular component were measured with UmRSA software. Of the initial 19 patients, 12 were available at the ten-year time point. The median proximal, 2D, and 3D wear rates calculated between one and ten years were all less than 0.005 mm/year, with no patient recording a proximal wear rate of more than 0.021 mm/year. Importantly, there was no increase in the wear rate between five and ten years. The very low wear rate of X3 XLPE liners with larger articulations remains encouraging for the future clinical performance of this material.

2-Year Radiostereometric Analysis Evaluation of a Short, Proximally Coated, Triple-Taper Blade Femoral Stem Versus a Quadrangular-Taper Stem With Reinforced Proximal Body: A Randomized Controlled Trial

BackgroundCementless stem designs with proximal metaphyseal fixation aim to achieve better load distribution, reduce stress shielding, and improve primary stability. The purpose of this prospective, randomized controlled trial was to evaluate the 2-year migration and clinical outcomes of two cementless femoral stems. MethodsA total of 60 participants undergoing primary total hip arthroplasty for any cause were randomly allocated to receiving either a proximally coated, short blade stem or a quadrangular-taper stem with a reinforced proximal body. Radiostereometric analysis radiographs were performed postoperatively and at 6 weeks, 6 months, 1 year and 2 years. The Harris Hip Score, Oxford Hip Score and the EuroQol five-dimension were also collected. ResultsAt two years, the median subsidence of the short-blade stem was 0.097 millimeters (mm) [Interquartile range (IQR) −0.67 to 0.08)] versus 0.086 mm(IQR, −0.29 to 0.005, P = .683); medial translation 0.023 mm (IQR 0.08 to 0.12) versus 0.029 mm(IQR −0.07 to 0.10, P = .907); anterior translation 0.035 mm (IQR −0.23 to 0.33) versus 0.07 mm (IQR −0.13 to 0.08, P = .268). At 24 months postoperatively, there were no stem revisions and Patient-Reported Outcome Measures (PROMs) were comparable between groups. ConclusionBoth cementless stems exhibited a predictable migration pattern and achieved initial stability. There was no difference in migration across the three Cartesian axes at any time point. Clinical outcomes and PROMs were also comparable. Biological fixation of both implants evidenced by the radiostereometric analysis and excellent PROMs are likely to translate to longer-term stability, which would need to be corroborated by longer-term outcome studies.

Highly Crosslinked Polyethylene Liners Have Negligible Wear at 10 Years: A Radiostereometric Analysis Study.

The introduction of crosslinked ultra-high molecular weight polyethylene (XLPE) acetabular liners has been very successful, with decreased wear and reduction in the rates of revision hip arthroplasties. XLPE is the preferred articulation for most surgeons; however, there are concerns about the long-term performance of XLPE liners created with different manufacturing processes, which may lead to time-dependent failure, including accelerated wear, after several years. (1) What is the amount and rate of wear during the first 10 years using radiostereometric analysis (RSA) measurements of patients who had THAs that included a second-generation XLPE bearing? (2) Does the rate of wear change after 5 years in situ? This is a brief follow-up of a previous RSA study. In that study, we prospectively enrolled 21 patients with osteoarthritis who underwent primary cementless THA with an XLPE acetabular liner (three cycles of 3Mrad annealed) and 32-mm articulation. That group represented 44% of the 48 THAs performed by the surgeon at the hospital where RSA was available; 16 had cemented hips, leaving 32 who were invited to participate in this study. Of those, 11 lived rurally and declined to participate, leaving 21 patients who were included in the initial study. Since then, three patients died, one developed dementia and could not participate, and one had revision THA for reasons other than wear, leaving 16 patients available for analysis at 10 years. Tantalum markers were inserted during surgery, and all patients had RSA radiographs taken at 1 week, 6 months, and 1, 2, 5, and 10 years postoperatively. Femoral head penetration into the acetabular component was measured with RSA, including bedding-in during the first year and annual wear thereafter. The median medial, proximal, anterior, two-dimensional (2D), and three-dimensional (3D) wear rates between 1 and 10 years were -0.001, 0.004, -0.012, 0.000, and 0.002 mm/year, respectively. No patient in this cohort had a proximal or 2D wear rate greater than 0.025 mm/year. The median proximal wear rate between 5 and 10 years (0.002 mm/year) was not greater than wear at 1 to 5 years (0.004 mm/year). Femoral head penetration in this second-generation XLPE liner remained very low at 10 years and accelerated wear after 5 years in situ did not occur. Concerns about late-onset wear from oxidation of irradiated-annealed XLPE were not observed. The low level of wear remains encouraging for the future clinical performance of this material. Level II, therapeutic study.

Stable glenoid component of reverse total shoulder arthroplasty at 2 years as measured with model-based radiostereometric analysis (RSA)

Background and purpose — Reverse total shoulder arthroplasty (TSA) is used for treating cuff arthropathy, displaced proximal humeral fractures (PHF), and in revision shoulder surgery, despite sparse evidence on long-term results. We assessed stability of the glenoid component in reverse TSA, using model-based RSA. Patients and methods — 20 patients (mean age 76 years, 17 female), operated on with reverse TSA at Oslo University Hospital, in 2015–2017 were included. Indications for surgeries were PHFs, malunion, cuff arthropathy, and chronic shoulder dislocation. RSA markers were placed in the scapular neck, the coracoid, and the acromion. RSA radiographs were conducted postoperatively, at 3 months, 1 year, and 2 years. RSA analysis was performed using RSAcore with Reversed Engineering (RE) modality, with clinical precision < 0.25 mm for all translations (x, y, z) and < 0.7° for rotations (x, z). Scapular “notching” was assessed in conventional radiographs. Results — 1 patient was excluded due to revision surgery. More than half of the patients displayed measurable migration at 2 years: 6 patients with linear translations below 1 mm and 8 patients who showed rotational migration. Except for one outlier, the measured rotations were below 2°. The migration pattern suggested implant stability at 2 years. 10 patients showed radiolographic signs of “notching”, and the mean Oxford Shoulder Score (OSS) at 2 years was 29 points (15–36 points). Interpretation — Stability analysis of the glenoid component of reversed total shoulder arthroplasty using reversed engineering (RE) model-based RSA indicated component stability at 2 years.

Long-term migration of a cementless stem with different bioactive coatings. Data from a “prime” RSA study: lessons learned

Background and purpose — Little is known about the long-term migration pattern of cementless stems in total hip arthroplasty (THA). Furthermore, the role of bioactive coatings in fixation, and thus migration, remains uncertain. Hydroxyapatite (HA) is the most commonly used bioactive coating. However, delamination of the coating might induce loosening. Alternatively, fluorapatite (FA) has proved to be more thermostable than HA, thereby potentially increasing longevity. We assessed the long-term migration of cementless stems with different coatings using radiostereometric analysis (RSA), thereby establishing a reference for acceptable migration. Patients and methods — 61 THAs in 53 patients were randomized to receive either a HA, FA, or uncoated Mallory-Head Porous stem during the years 1992 to 1994. Primary outcome was stem migration measured using RSA and secondary outcome was the Harris Hip Score (HHS). Evaluation took place preoperatively and postoperatively on the second day, at 6, 12, 25 and 52 weeks, and annually thereafter. At the 25-year follow-up, 12 patients (17 THAs) had died and 1 patient (1 THA) was lost to follow-up. Due to the high number of missing second-day postoperative RSA radiographs, the 1-year postoperative RSA radiograph was used as baseline for the comparative analyses. Results — Mean follow-up was 17 years (SD 6.6). All stems showed initial rapid migration with median subsidence of 0.2 mm (–0.1 to 0.6) and median retroversion of 0.9° (–3.2 to 2) at 12 months, followed by stable migration reaching a plateau phase. No stem was revised, albeit 1 stem showed continuous subsidence up to 1.5 mm. Comparing the different coatings, we could not find a statistically significant difference in overall 25-year migration (p-values > 0.05). Median subsidence at 15-year follow-up was for HA –0.1 mm (–0.4 to 0.2), for FA 0 mm (–0.1 to 0.2), and for uncoated stems 0.2 mm (–0.1 to 0.5). Median internal rotation at 15-year follow-up was for HA not available, for FA 1.1° (–0.5 to 2.6), and for uncoated stems 0° (–0.5 to 0.4). HHS were also comparable (p-values > 0.05), with at 15-year follow-up for HA 85 points (41–99), for FA 76 points (61–90), and for uncoated stems 79 points (74–90). Interpretation — The long-term migration pattern of cementless stems using different bioactive coatings has not previously been described. No beneficial effect, or side effect at long-term follow-up of bioactive coatings, was found. The provided migration data can be used in future research to establish thresholds for acceptable migration patterns cementless stem designs.

Effective radiation dose in radiostereometric analysis of the hip

Background and purpose — Radiostereometric analysis (RSA) is the gold standard to study micromotion of joint replacements. RSA requires the acquisition of additional radiographs increasing the radiation dose of patients included in RSA studies. It is important to keep this dose as low as possible. Effective radiation dose (ED) measurements of RSA radiographs for different joints were done by Teeuwisse et al. some years ago using conventional radiology (CR); for total hip arthroplasty (THA), Teeuwisse et al. reported an ED of 0.150 milliSievert (mSv). With the modern digital radiography (DR) roentgen technique the ED is expected to be less.Material and methods — In this phantom study, simulating a standard patient, the ED for hip RSA radiographs is determined using DR under a variety of different roentgen techniques. The quality of the RSA radiographs was assessed for feasibility in migration analysis using a (semi-)automatic RSA analysis technique in RSA software.Results — A roentgen technique of 90 kV and 12.5 mAs with additional 0.2 copper (Cu) + 1 mm aluminum (Al) external tube filters results in an ED of 0.043 mSv and radiographs suitable for analysis in RSA software.Interpretation — The accumulated ED for a standard patient in a 2-year clinical hip RSA study with 5 follow-up moments and a double acquisition is below the acceptable threshold of 1.0 mSv provided by the EU radiation guideline for studies increasing knowledge for general health.

Accuracy of EBRA-cup measurements after reconstruction of severe acetabular defects at revision THR.

Radiostereometric analysis (RSA) is the most accurate method of measuring component migration using radiographs but is restricted to use in prospective studies. Ein-Bild-Roentgen-analyze (EBRA)-Cup can be used retrospectively, but its accuracy to measure component migration following revision is unknown. This study aimed to determine the accuracy of EBRA-Cup measurements of uncemented acetabular component migration after revision total hip replacement (THR). The secondary aim was to compare the number of cases identified using EBRA-Cup and RSA as having proximally migrated above and below 1 mm at 2 years postoperatively. EBRA-Cup measurements were performed on plain antero-posterior pelvic radiographs taken at the same time as RSA radiographs in a prospective cohort of 53 hips undergoing acetabular revision. At 2 years, the mean difference between the RSA and EBRA-Cup measurements for 17 components used to treat pelvic discontinuity was 0.90 mm, significantly greater than the mean difference of 0.28 mm for 36 components without discontinuity (P = .0001). The mean difference between the RSA and EBRA-Cup measurements at 2 years for hips that were reconstructed with an acetabular component alone, 0.28 mm, was significantly lower than hips that were reconstructed with an acetabular component in combination with an augment and/or cage, 0.74 mm (P = .0005). In conclusion, EBRA-Cup can accurately measure migration of uncemented acetabular components used at revision THR. The presence of pelvic discontinuity, and addition of augments and cages, significantly influenced the accuracy of EBRA-Cup measurements. EBRA-Cup and RSA had good agreement on classification of components that migrated proximally above or below 1 mm at 2 years, with 100% sensitivity, and 87% specificity.

Long-term migration characteristics of the Corail hydroxyapatite-coated femoral stem: a 14-year radiostereometric analysis follow-up study.

The magnitude and pattern of acceptable long-term migration of cementless femoral stems are not well understood. The Corail hydroxyapatite-coated cementless stem is a clinically successful and commonly used femoral stem with a long-term migration pattern not previously described in the literature. The aim of this study was to assess the long-term migration of the Corail hydroxyapatite-coated cementless stem using radiostereometric analysis (RSA) at 14-year follow-up, thereby establishing a benchmark acceptable long-term migration pattern for hydroxyapatite-coated cementless prostheses. A prospective cohort of 29 patients (30 hips) undergoing primary total hip arthroplasty for primary hip osteoarthritis were enrolled into a study to characterise the migration of the Corail cementless stem. A total of 13 patients (4 males, 9 females) with mean age 82 (range 68-92) underwent repeat RSA radiographs at minimum 10years post-operation (mean 13.9years, range 13.3-14.4). Subsidence of the stem was measured and compared to prior measurements taken at 6months and 1, 2, and 6years. None of the 13 patients have been revised. The migration at 6months, 1year, 2years, and 6years has been previously recorded. At mean 14-year follow-up, the cohort mean subsidence of the cementless stem was 0.70mm (range - 0.06 to 3.61mm). For each stem followed up at 6months and 14years, the mean subsidence over this period was 0.05mm (range - 0.14 to 0.57mm). There is no significant difference in mean subsidence at 6months and 14years (p = 0.43). The long-term pattern of the subsidence of the Corail femoral stem has not previously been described. Subsidence occurs within the first 6months, after which there is persistent stabilisation of the implant to 14years. This study provides a description of a long-term acceptable migration pattern to which new hydroxyapatite-coated cementless prostheses may be compared. II.

Mechanical Stability of the Prodisc-C Vivo Cervical Disc Arthroplasty: A Preliminary, Observational Study Using Radiostereometric Analysis.

Study Design:Prospective cohort study.Objective:To investigate the primary stability of the Prodisc-C Vivo cervical disc arthroplasty with regard to the adjacent cervical vertebrae using radiostereometric analysis (RSA), and to monitor its clinical performance.Methods:Sixteen patients with degenerative cervical disc disease were included. RSA radiographs were obtained at the first postoperative day, at 6 weeks, 3 months, and 6 months postoperatively. Migration (translation [mm]) of the superior and inferior implant components were measured with model-based RSA, expressed along the 3 orthogonal axes, and calculated as total translation. Clinical outcomes were Neck Disability Index, numeric rating scales for neck and arm pain, Likert-type scales for satisfaction, and adverse events. Range of motion was reported as C2-C7 flexion-extension mobility (ROM).Results:At final follow-up, no significant increase over time in median total translation was found. One inferior and 3 superior components subsided but were asymptomatic. ROM remained stable and clinical outcomes improved over time. Although 3 patients were unsatisfied and 3 adverse events occurred, this was not related to translation of the components.Conclusions:On a group level, both components of the Prodisc-C Vivo cervical disc arthroplasty remained stable over time and below the clinical threshold of 1 mm. Individual outliers for translation were not clinically relevant and probably related to settling of the components into the vertebral endplates. RSA allowed us to perform a preliminary but accurate study on the micromotion of a new cervical disc replacement in a small sample size, without putting large numbers of patients at risk.

No effect of additional screw fixation of a cementless, all-polyethylene press-fit socket on migration, wear, and clinical outcome

Background and purpose — Additional screw fixation of the all-polyethylene press-fit RM cup (Mathys) has no additional value for migration, in the first 2 years after surgery. However, the medium-term and long-term effects of screw fixation remain unclear. We therefore evaluated the influence of screw fixation on migration, wear, and clinical outcome at 6.5 years using radiostereometric analysis (RSA).Patients and methods — This study involved prolonged follow-up from a previous randomized controlled trial (RCT). We analyzed RSA radiographs taken at baseline and at 1-, 2-, and 6.5-year follow-up. Cup migration and wear were assessed using model-based RSA software. Wear was calculated as translation of the femoral head model in relation to the cup model. Total translation, rotation, and wear were calculated mathematically from results of the orthogonal components.Results — 27 patients (15 with screw fixation and 12 without) were available for follow-up at 6.5 (5.6–7.2) years. Total translation (0.50 mm vs. 0.56 mm) and rotation (1.01 degrees vs. 1.33 degrees) of the cup was low, and was not significantly different between the 2 groups. Wear increased over time, and was similar between the 2 groups (0.58 mm vs. 0.53 mm). Wear rate (0.08 mm/year vs. 0.09 mm/year) and clinical outcomes were also similar.Interpretation — Our results indicate that additional screw fixation of all-polyethylene press-fit RM cups has no additional value regarding medium-term migration and clinical outcome. The wear rate was low in both groups.

Five-Year Experience of Vitamin E–Diffused Highly Cross-Linked Polyethylene Wear in Total Hip Arthroplasty Assessed by Radiostereometric Analysis

BackgroundVitamin E–diffused highly cross-linked polyethylene (VEPE) was developed to reduce oxidation without compromising mechanical strength. The purpose of this study was to evaluate VEPE in vivo using radiostereometric analysis (RSA) and patient-reported outcome measures (PROMs). MethodsFifty-one hips were enrolled. Each patient received a VEPE liner, a porous titanium shell, and an uncemented stem with a 32-mm cobalt–chrome femoral head. Tantalum beads were inserted into the VEPE to measure femoral head penetration using RSA. RSA radiographs and PROMs were obtained preoperatively immediately after surgery, 6 months, 1, 2, 3, and 5 years after surgery. ResultsForty-seven hips returned at 3 years, and 42 hip at 5 years. The mean ± standard error of the mean proximal head penetration into the polyethylene was 0.06 ± 0.01 at 5 years. The amount of head penetration did not change significantly with increasing time in vivo. The mean ± standard error of the mean Harris Hip Score was 58 ± 2 preoperatively, which improved significantly to 93 ± 2 at 5 years (P < .001). ConclusionThe head penetration into VEPE liners was low compared with non-VEPE at 5 years. After settling of the liners in the early period, no significant head penetration occurred from 2- to 5-year follow-up. All PROMs improved significantly from preoperative to postoperative and remained very favorable at 5 years. This study documents the longest-term evaluation of in vivo wear performance of VEPE.

Low Wear of a Second-generation Highly Crosslinked Polyethylene Liner: A 5-year Radiostereometric Analysis Study

A sequentially irradiated and annealed, second-generation highly crosslinked polyethylene (XLPE) liner was introduced clinically in 2005 to reduce in vivo oxidation. This liner design has also been shown to reduce wear in vitro when compared with conventional and first-generation crosslinked liners. To date, there is only one study reporting an in vivo wear rate of this liner at 5 years' followup. However, that study used measurements made from plain radiographs, which have limited sensitivity, particularly when monitoring very low amounts of wear. What is the amount and direction of wear at 5 years using radiostereometric analysis (RSA) in patients who had THAs that included second-generation XLPE? We prospectively reviewed 21 patients who underwent primary cementless THA with the same design of XLPE acetabular liner and 32-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographs at 1 week, 6 months, and 1, 2, and 5 years postoperatively. Femoral head penetration within the acetabular component was measured with UmRSA(®) software. One patient died and two had incomplete radiographs leaving 18 radiographic series for analysis. The mean amounts of proximal, two-dimensional, and three-dimensional head penetration between 1 week and 5 years were 0.018, 0.071, and 0.149 mm, respectively. The mean proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 5 years were all less than 0.001 mm/year with no patient recording a wear rate of more than 0.040 mm/year. The head penetration of a second-generation XLPE liner remained low at 5 years and the wear rate calculated after the first year was low in all directions. This low level of wear remains encouraging for the future clinical performance of this material.

Stable fixation of an osseointegated implant system for above-the-knee amputees

Background and purpose Rehabilitation of patients with transfemoral amputations is particularly difficult due to problems in using standard socket prostheses. We wanted to assess long-term fixation of the osseointegrated implant system (OPRA) using radiostereometric analysis (RSA) and periprosthetic bone remodeling.Methods 51 patients with transfemoral amputations (55 implants) were enrolled in an RSA study. RSA and plain radiographs were scheduled at 6 months and at 1, 2, 5, 7, and 10 years after surgery. RSA films were analyzed using UmRSA software. Plain radiographs were graded for bone resorption, cancellization, cortical thinning, and trabecular streaming or buttressing in specifically defined zones around the implant.Results At 5 years, the median (SE) migration of the implant was –0.02 (0.06) mm distally. The rotational movement was 0.42 (0.32) degrees around the longitudinal axis. There was no statistically significant difference in median rotation or migration at any follow-up time. Cancellization of the cortex (plain radiographic grading) appeared in at least 1 zone in over half of the patients at 2 years. However, the prevalence of cancellization had decreased by the 5-year follow-up.Interpretation The RSA analysis for the OPRA system indicated stable fixation of the implant. The periprosthetic bone remodeling showed similarities with changes seen around uncemented hip stems. The OPRA system is a new and promising approach for addressing the challenges faced by patients with transfemoral amputations.

Implant Migration after Early Weightbearing in Cementless Hip Replacement

Twenty-nine patients (five women and 24 men) with an average age of 47 years (range, 24-59 years) had 37 total hip arthroplasties using a hydroxyapatite-coated double-wedge press-fit femoral component. All patients had a Type A bone quality. Patients were either mobilized with weightbearing as tolerated or toe-touch weightbearing for 6 weeks postoperatively. After 6 weeks all patients were advanced to weightbearing as tolerated. Radiostereometric analysis radiographs were taken at 3 days, 6 weeks, and 6 months postoperatively to measure migration of the femoral component. Radiostereometric analysis revealed no difference in stem migration between the two groups as defined by maximal total point migration. There was a difference in the vertical (proximal-distal) migration within the first 6 weeks between groups (0.81 mm versus 0.13 mm), but not afterwards (0.17 mm versus 0.18 mm). Continuous migration after 6 weeks was observed in three patients from each group. There was no loosening in either group within a 2-year followup. Weightbearing as tolerated is recommended for young patients with excellent bone quality after cementless total hip arthroplasty with a double-wedge press-fit femoral component. Diagnostic study, Level I (testing of previously developed diagnostic criteria in series of consecutive patients--with previously applied reference gold standard). See the Guidelines for Authors for a complete description of levels of evidence.