Radiostereometric Analysis Research Articles

Inducible displacement of cementless total knee arthroplasty components with conventional and weight-bearing CT-based radiostereometric analysis.

Aseptic loosening remains one of the top causes of revision surgery of total knee arthroplasty (TKA). Radiostereometric analysis (RSA) is used in research to measure implant migration, however limitations prevent its clinical use. New methods have allowed the same measurements as RSA to be performed with computed tomography (CT) scanners (CT-RSA). The objective of this study is to determine inducible displacement measurements from weight-bearing computed tomography (WBCT) and conventional RSA to assess implant stability. Participants (n = 17) completed RSA exams in the supine and standing position, and WBCT exams in the seated (leg extended) and standing position. Double examinations were performed in the seated (WBCT) or supine (RSA) positions. Inducible displacements were measured with model-based RSA (MBRSA) for RSA exams, and a novel CT-RSA software, V3MA, for WBCT exams. Precision of each technique was calculated between double examinations. Precision data for tibial component total translations and rotations were 0.05 mm and 0.118°, respectively with WBCT-RSA, and were 0.108 mm and 0.269°, respectively with MBRSA. MTPM precision was 0.141 mm with WBCT-RSA and was 0.168 mm with MBRSA. Inducible displacement MTPM of the tibial component was 0.244 ± 0.220 mm with WBCT-RSA and 0.662 ± 0.257 mm with MBRSA. Inducible displacement measurements with MBRSA were significantly different from WBCT-RSA for tibial component anterior tilt (p = 0.0002). WBCT-RSA demonstrated comparable precision to MBRSA, and both techniques measured inducible displacements consistent with stable components. Clinical Significance: As the availability of WBCT increases, its use as an alternative to MBRSA is supported to measure the instantaneous fixation of implant components.

The Effect of Low-Dose CT Protocols on Shoulder Model-Based Tracking accuracy Using Biplane Videoradiography.

Model-based tracking is being increasingly used to quantify shoulder kinematics and typically employs computed tomography (CT) to create the 3D bone volumes, which adds to the total radiation exposure. Lower-dose CT protocols may be possible given the contrast between bone and the surrounding soft tissues. The purpose of this study was to describe the dose-accuracy tradeoff between low-dose CT scans and the kinematic tracking accuracy of the humerus, scapula, and clavicle when tracked using an intensity-based registration algorithm. Three fresh-frozen cadavers consisting of the torso and bilateral shoulders were tested. The CT protocols investigated included a full-dose protocol and 4 experimental low-dose protocols that modulated x-raytube current and peak voltage. Bead-based tracking (i.e., radiostereometric analysis) served as the reference standard to which model-based tracking results were compared. Accuracy was described in terms of both segmental (humerus, scapula, and clavicle) and joint (glenohumeral, acromioclavicular) kinematics using root-mean-square (RMSE), bias, precision, and worst-case errors. The low-dose CT scans resulted in an average dose reduction of 70.6-92.8%. RMSEs tended to increase as CT dose decreased with average glenohumeral errors increasing from 0.5° and 0.6 mm to 0.6° and 0.6 mm between the highest and lowest-dose protocols, and average acromioclavicular errors increasing from 0.6° and 0.8 mm to 0.7° and 0.9 mm. However, the difference in joint kinematic errors between the highest and lowest-dose CT scanning protocols was generally small (≤0.3°, ≤ 0.1 mm). It is possible to substantially reduce the CT dose associated with shoulder motion analysis using biplane videoradiography without significantly impacting data fidelity.

Elbow Kinematics With Increasing Radial Head Arthroplasty Overlengthening Evaluated With Dynamic Radiostereometric Analysis

Elbow Kinematics With Increasing Radial Head Arthroplasty Overlengthening Evaluated With Dynamic Radiostereometric Analysis

Accuracy and precision of Volumetric Matching Micromotion Analysis (V3MA) is similar to RSA for tibial component migration in TKA.

Radiostereometric analysis (RSA) is the current gold standard to determine implant migration, but it requires bone markers and special equipment. Therefore, we developed VoluMetric Matching Micromotion Analysis (V3MA), a software program for Computed Tomography-based radiostereometric analysis (CT-RSA). This study aimed to determine the accuracy and precision of V3MA in vitro compared to RSA and provide a clinical proof of concept. The accuracy (RMSE (Root Mean Squared Error)) and precision (SD (standard deviation)) of V3MA were compared to RSA. A tibial component was placed in 21 different positions within a cadaveric bone to assess accuracy. For precision,a total of 20 repeated zero-migration examinations from 4 cadaveric bones with cemented tibial components were performed. In 6 total knee arthroplasty (TKA) patients 1 to 5 year migration was measured with V3MA and RSA. V3MA accuracy ranged between 0.02 and 0.09 mm for translations and was 0.01° for internal-external rotations. For RSA, the accuracy ranged between 0.03 and 0.09 mm for translations and was 0.09° for internal-external rotations. V3MA precision ranged between 0.01 and 0.06 mm for translations and 0.02 to 0.07° for rotations. RSA precision ranged between 0.00 and 0.06 mm for translations and 0.04 to 0.25° for rotations. V3MA was successful in 6 clinical cases and no systematic bias was present. In conclusion, the accuracy and precision of V3MA were similar to RSA. Therefore, V3MA is a promising alternative to RSA in migration measurements of tibial components in TKA.

Evaluation of conventional and CT-based radiostereometric analysis for inducible displacement measurements after total hip arthroplasty.

Though radiostereometric analysis (RSA) is the gold standard for migration tracking, computed tomography-based RSA (CT-RSA) does not require marker beads and is available for clinical adoption. This study investigated CT-RSA in comparison to RSA for assessing hip implant stability with inducible displacement (ID) examinations. Patients (n = 48) from a previous study returned to be re-examined for femoral stem stability with CT-RSA and RSA imaging. Implant migration since patients last follow-up was calculated as a measure of stability. ID was assessed between alternated leg rotation scans for CT-RSA and between supine and weight-bearing scans for RSA. Measurements from ID and double examinations were compared between CT-RSA and RSA. All stems were well-fixed with migration <0.2 mm/year. ID measurements were lower with CT-RSA than RSA for distal translation (mean difference = 0.122 mm, p < 0.0001), total translation (mean difference = 0.158 mm, p < 0.0001), and total rotation (mean difference = 0.449°, p < 0.0001). The ID and double exam were significantly different for total translation and total rotation for CT-RSA, and significantly different for medial, distal, and total translation, and total rotation for RSA. Precision ranged from 0.049 to 0.130 mm in translation and 0.061° to 0.220° in rotation for CT-RSA, and from 0.108 to 0.269 mm in translation and 0.151° to 0.670° in rotation for RSA. ID measurements from both CT-RSA and RSA were minimal, consistent for a cohort with well-fixed stems. CT-RSA demonstrated superior precision in all axes compared to RSA. Clinical Significance: Future work should explore the use of CT-RSA in patients with suspected loosening as a potential diagnostic tool.

Glenohumeral joint kinematics during apprehension-relocation test in patients with anterior shoulder instability and glenoid bone loss.

This study aimed to quantify the shoulder kinematics during an apprehension-relocation test in patients with anterior shoulder instability (ASI) and glenoid bone loss using the radiostereometric analysis (RSA) method. Kinematics were compared with the patient's contralateral healthy shoulder. A total of 20 patients with ASI and > 10% glenoid bone loss and a healthy contralateral shoulder were included. RSA imaging of the patient's shoulders was performed during a repeated apprehension-relocation test. Bone volume models were generated from CT scans, marked with anatomical coordinate systems, and aligned with the digitally reconstructed bone projections on the RSA images. The glenohumeral joint (GHJ) kinematics were evaluated in the anteroposterior and superoinferior direction of: the humeral head centre location relative to the glenoid centre; and the humeral head contact point location on the glenoid. During the apprehension test, the centre of the humeral head was 1.0 mm (95% CI 0.0 to 2.0) more inferior on the glenoid for the ASI shoulder compared with the healthy shoulder. Furthermore, the contact point of the ASI shoulder was 1.4 mm (95% CI 0.3 to 2.5) more anterior and 2.0 mm (95% CI 0.8 to 3.1) more inferior on the glenoid compared with the healthy shoulder. The contact point of the ASI shoulder was 1.2 mm (95% CI 0.2 to 2.6) more anterior during the apprehension test compared to the relocation test. The humeral head centre was located more inferior, and the GHJ contact point was located both more anterior and inferior during the apprehension test for the ASI shoulders than the healthy shoulders. Furthermore, the contact point displacement between the apprehension and relocation test revealed increased joint laxity for the ASI shoulder than the healthy shoulders. These results contribute to existing knowledge that ASI shoulders with glenoid bone loss may also suffer from inferior shoulder instability.

Elbow kinematics with increased lengthening of a radial head arthroplasty evaluated with dynamic radiostereometric analysis.

The aim of this study was to evaluate the kinematics of the elbow following increasing length of the radius with implantation of radial head arthroplasties (RHAs) using dynamic radiostereometry (dRSA). Eight human donor arms were examined by dRSA during motor-controlled flexion and extension of the elbow with the forearm in an unloaded neutral position, and in pronation and supination with and without a 10 N valgus or varus load, respectively. The elbows were examined before and after RHA with stem lengths of anatomical size, + 2 mm, and + 4 mm. The ligaments were maintained intact by using a step-cut lateral humeral epicondylar osteotomy, allowing the RHAs to be repeatedly exchanged. Bone models were obtained from CT scans, and specialized software was used to match these models with the dRSA recordings. The flexion kinematics of the elbow were described using anatomical coordinate systems to define translations and rotations with six degrees of freedom. The greatest kinematic changes in the elbows were seen with the longest, + 4 mm, implant, which imposed a mean joint distraction of 2.8 mm in the radiohumeral joint and of 1.1 mm in the ulnohumeral joint, an increased mean varus angle of up to 2.4° for both the radius and the ulna, a mean shift of the radius of 2.0 mm in the ulnar direction, and a mean shift of the ulna of 1.0 mm posteriorly. The kinematics of the elbow deviated increasingly from those of the native joint with a 2 mm to a 4 mm lengthening of the radius. This confirms the importance of restoring the natural length of the radius when undertaking RHA.

Polyethylene wear and cup migration of cemented total hip arthroplasty with femoral heads made of oxidized zirconium, steel, or cobalt chromium: a 10-year secondary analysis from a randomized trial using radiostereometry.

We aimed to evaluate polyethylene (PE) wear, cup migration, and clinical outcome over 10 years in total hip arthroplasties (THA) using different articulations. This is a secondary analysis of 150 patients randomized into 5 groups, using different articulations: Charnley/Charnley Ogee for steel and conventional polyethylene (CPE), or Spectron EF/Reflection with either CPE or highly cross linked polyethylene (XLPE) cups, paired with heads made of either cobalt-chromium (CoCr) or oxidized zirconium (OxZr). All cups were cemented. Patients underwent repeated radiostereometric analysis (RSA) measurements for up to 10 years to assess wear and migration. Clinical outcome was assessed using Harris Hip Score (HHS). After 10 years, the XLPE cups demonstrated low wear rates: 0.08 mm (95% confidence interval [CI] -0.11 to 0.26 mm) with CoCr heads and 0.06 mm (CI -0.14 to 0.26 mm) with OxZr heads, with a mean difference of 0.01 mm (CI -0.26 to 0.29 mm). In contrast, CPE cups exhibited significantly more wear: 1.35 mm (CI 1.16 to 1.55 mm) with CoCr heads and 1.68 mm (CI 1.44 to 1.92 mm) with OxZr heads, with a mean difference of 0.33 mm (CI 0.02 to 0.64 mm). The Charnley/Ogee group (CPE) showed PE wear of 0.34 mm (CI 0.12 to 0.56 mm). The CPE groups with OxZr and CoCr heads had 0.67 mm (CI 0.38 to 0.96 mm) and 0.35 mm (CI 0.09 to 0.61 mm) greater proximal migration respectively than the corresponding XLPE groups. HHS was similar across all groups. We found no significant advantage of OxZr over CoCr heads in reducing wear or migration. XLPE demonstrated a major reduction in wear as well as a reduction in cup migration compared with CPE. Charnley performed better than the other CPE cups in terms of PE wear and cup migration. No differences in clinical outcome were found.

6-year follow-up on migration outcomes: a randomised clinical trial of cemented vitamin E-stabilised highly crosslinked versus standard polyethylene cup in total hip arthroplasty.

In a previous study we have shown that a cemented vitamin E-doped highly cross-linked polyethylene (VEPE) compared to a conventional polyethylene cup in total hip arthroplasty (THA) has a slightly higher proximal migration but significantly lower wear rates up to 2 years after surgery. In this follow-up study we investigated the same cohort at 6 years. This was a double-blinded, non-inferiority, randomised controlled trial on patients with osteoarthritis, with a mean age of 66 years. Patients were randomly assigned to receive either the conventional polyethylene cup or the VEPE cup in a 1:1 ratio. The primary endpoint was proximal implant migration of the cup measured with radiostereometric analysis (RSA). Secondary endpoints included wear rate of the cup and patient-reported outcome measurements (PROM). At the 6-year follow-up, 25 patients (11 controls, 14 VEPE) were available for RSA measurements, and we found no statistically significant difference in proximal migration between the VEPE and control groups. The wear rate was significantly lower in the VEPE group compared to controls, 0.03 mm/year and 0.07 mm/year, respectively with a mean difference 0.04 mm, (95% CI, 0.02-0.06 mm). There were no cup revisions and no difference in PROM between the groups. Based on our 6-year results, the VEPE group exhibited no statistical or clinically relevant difference compared to the control group, and the wear rate was significantly lower in the VEPE group. The use of a cemented vitamin E-doped highly cross-linked cup is a good option in total hip arthroplasty.

Measuring total hip arthroplasty liner wear using the EOS Imaging System: experimental and clinical results.

The low-dose EOS Imaging System is an emerging tool for 3-dimensional measurements in orthopedics. The clinical feasibility for measuring total hip arthroplasty (THA) liner wear has not yet been investigated. We aimed to evaluate the feasibility of using EOS to measure THA liner wear by examining the experimental accuracy using a THA phantom and clinical precision of patients with THA, considering a clinically relevant precision at the 95% repeatability limit to be 0.2 mm. An experimental THA phantom with movable stem and a fixed cup with a plastic liner was constructed to simulate progressive 3D liner wear. Series of 11 pairs of radiographs with 50 μm femoral movement in between were obtained for each 3D axis in EOS. 30 patients with a THA were scanned twice using EOS to assess precision. Model-based radiostereometric analysis (RSA) was used for wear measurement. The mean difference (true minus simulated wear) with standard deviation (SD) and 95% limits of agreement for experimental THA wear were 0.005 (0.037) and [-0.069 to 0.079] mm for the vertical (y) axis. The mean (SD) and 95% repeatability limit for precision for clinical measurement were -0.029 (0.105) and 0.218 mm. Experimental THA liner wear using EOS was within clinically relevant tolerances and without bias. The clinical precision was just outside our defined clinically relevant precision. Compared with conventional RSA, EOS is less accurate and precise but may still be of value for certain clinical applications, provided larger sample size or longer follow-up are available.

Tibial Baseplate Migration Is Not Associated with Change in Patient-Reported Outcome Measures and Clinical Scores After TKA: A Secondary Analysis of 5 Radiostereometric Analysis Studies with 10-Year Follow-up.

Radiostereometric analysis (RSA) provides highly accurate data about the migration of a total knee arthroplasty (TKA) component. However, patient-reported outcome measures (PROMs) reflect the patients' perspective of their functional status, pain, and overall health after TKA. The aim of this study was to evaluate the association between tibial implant migration and change in postoperative PROMs and clinical scores, using data pooled from long-term follow-up RSA studies. Individual implant migration data were collected from 5 randomized RSA studies, including a total of 300 patients with 6 distinct TKA implant designs (all Stryker). Tibial implant migration (maximum total point motion [MTPM]) was evaluated with RSA at 3 months, 1 year, and 2, 5, 7, and 10 years postoperatively. The Knee Society Score (KSS)-Knee and KSS-Function and Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales were collected in all studies at the same follow-up times. Linear mixed-effects models, with adjustment for TKA implant design and patient characteristics, were used to analyze the data. The 3-month follow-up visit was used as the baseline to assess the association between implant migration and PROMs across the 10-year follow-up. No association between tibial implant migration and change in KSS-Knee (p = 0.384), KSS-Function (p = 0.737), KOOS-Symptoms (p = 0.398), KOOS-Pain (p = 0.699), KOOS-Activities of Daily Living (p = 0.205), KOOS-Sport and Recreation (p = 0.702), or KOOS-Quality of Life (p = 0.368) was found across the entire follow-up. Similar results were found when using the 2-year follow-up as the baseline, after which both cemented and uncemented implants are expected to have stabilized. Tibial baseplate migration was not associated with postoperative worsening in PROMs or clinical scores in patients who underwent TKA. These findings suggest that implant migration, as measured with RSA, measures a different parameter (i.e., implant-bone fixation) than PROMs (i.e., patient perception) and clinical scores. Therefore, to assess the performance and safety of TKA implant designs, RSA and PROMs cannot be used interchangeably during the postoperative follow-up of patients and evaluation of the fixation of knee implants. Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

If the Patient-Reported Outcome Measures After Total Knee Arthroplasty Are Good, Do Any Other Measurements Really Matter?: Commentary on an article by Thies J.N. van der Lelij, MD, et al.: "Tibial Baseplate Migration Is Not Associated with Change in Patient-Reported Outcome Measures and Clinical Scores After Total Knee Arthroplasty. A Secondary Analysis of 5 Radiostereometric Analysis Studies with 10-Year Follow-up".

If the Patient-Reported Outcome Measures After Total Knee Arthroplasty Are Good, Do Any Other Measurements Really Matter?: Commentary on an article by Thies J.N. van der Lelij, MD, et al.: "Tibial Baseplate Migration Is Not Associated with Change in Patient-Reported Outcome Measures and Clinical Scores After Total Knee Arthroplasty. A Secondary Analysis of 5 Radiostereometric Analysis Studies with 10-Year Follow-up".

Greater Postoperative Biceps Tendon Migration Following Biceps Tenodesis Correlates with Lower Patient Reported Outcomes Scores

To assess the relationship between tendon migration, as measured by radiostereometric analysis (RSA), and patient-reported outcome measures (PROMs) following biceps tenodesis (BT); to determine the likelihood of achieving clinically significant outcomes (CSOs) following BT; and to identify factors that impact CSO achievement. Patients undergoing arthroscopic suprapectoral or open subpectoral BT at a single, high-volume academic medical center were prospectively enrolled. A tantalum bead sutured to the tenodesis construct was utilized as a radio-opaque marker. Biceps tendon migration was measured on calibrated radiographs at 12 weeks postoperatively. PROMs (Constant-Murley score [Constant], Single Assessment Numeric Evaluation [SANE], and Patient-Reported Outcomes Measurement Information Systemic-Upper Extremity [PROMIS-UE]) were collected preoperatively and at ≥2 years follow-up. Of 115 patients enrolled, 94 (82%) patients were included (median age=52 years and BMI=31.4 kg/m2). At a mean follow-up of 2.9 years, median Constant, SANE, and PROMIS-UE were 33 (interquartile range [IQR]=26-35), 90 (IQR=80-99), and 47 (IQR=42-58), respectively. Median tantalum bead migration was 6.5 mm (IQR 1.8-13.8). There was a significant correlation between migration and Constant (r2 = 0.222, beta= -0.554, 95% CI -1.027- [-0.081], P=0.022), SANE (r2 = 0.238, beta= -0.198, 95% CI -0.337 - [-0.058], P=0.006) and PROMIS-UE (r2 = 0.233, beta= -0.406, 95% CI -0.707 - [-0.104], P=0.009). In univariable analysis, higher BMI was associated with achievement of substantial clinical benefit (SCB, unadj-OR=1.078, 95%CI 1.007-1.161, P=0.038). Greater bead migration was negatively associated with achievement of minimal clinically important difference (MCID, unadj-OR=0.969, 95% CI 0.943-0.993, P=0.014) and patient acceptable symptomatic state (PASS, unadj-OR 0.965, 95% CI 0.937-0.989, P=0.008) on all 3 instruments. A 1 cm-increase in tenodesed biceps tendon migration was associated with a decrease in Constant, SANE, and PROMIS-UE of 6, 2, and 4 points, respectively, at a mean of 2.9 years after surgery. Most patients achieved clinically significant outcomes (CSOs) for these PROMs by latest follow-up, and greater biceps tendon construct migration was negatively associated with the likelihood of CSO achievement. IV, retrospective case series.

COMPARISON OF THE CT-BASED MICROMOTION ANALYSIS METHOD VERSUS MARKER-BASED RADIOSTEREOMETRIC ANALYSIS IN MEASURING FEMORAL STEM MIGRATION

Early micromotion of hip implants measured with radiostereometric analysis (RSA) is a predictor for late aseptic loosening. Computed Tomography Radiostereometric Analysis (CT-RSA) can be used to determine implant micro-movements using low-dose CT scans. CT-RSA enables a non-invasive measurement of implants. We evaluated the precision of CT-RSA in measuring early stem migration. Standard marker-based RSA was used as reference. We hypothesised that CT-RSA can be used as an alternative to RSA in assessing implant micromotions.We included 31 patients undergoing Total Hip Arthroplasty (THA). Distal femoral stem migration at 1 year was measured with both RSA and CT-RSA. Comparison of the two methods was performed with paired-analysis and Bland-Altman plots. Furthermore, the inter- and intraobserver reliability of the CT-RSA method was evaluated.No statistical difference was found between RSA and CTMA measurements. The Bland-Altman plots showed good agreement between marker-based RSA and CT-RSA. The intra- and interobserver reliability of the CT-RSA method was found to be excellent (≥0.992).CT-RSA is comparable to marker-based RSA in measuring distal femoral stem migration. CTMA can be used as an alternative method to detect early implant migration.

Comparison of 5-year cup and stem migration between ceramic-on-ceramic and ceramic-on-polyethylene bearing in press-fit total hip arthroplasty: a randomised controlled trial using radiostereometric analysis.

The inelasticity of ceramic bearings might affect primary stability and migration of implants in press-fit total hip arthroplasty (THA). This randomised controlled trial compares migration patterns of the uncemented Delta-TT cup and H-MAX S stem between ceramic and polyethylene liners, up to 5 years follow-up. Patients receiving primary press-fit THA were randomly allocated to a ceramic (n = 28) or polyethylene (n = 25) liner. Migration was measured using model-based radiostereometric analysis (RSA) at baseline and 1.5, 3, 6, 12, 24 and 60 months postoperatively and compared between groups using mixed models statistical analysis. The focus of this study is on the 2- to 5-year migration of the Delta-TT cup and migration during complete follow-up of the H-MAX S stem up to 5-years. At 5-year follow-up, mean (95% CI) proximal cup translation was 0.56 (0.37-0.74) mm in ceramic and 0.58 (0.25-0.90) mm in polyethylene (p = 0.729). The mean change in adduction was 1.05° (0.27-1.82°) in ceramic and 0.78° (-0.16-1.71°) in polyethylene. Mixed modelling showed that all between-group effects were ⩽0.20 mm for translation and ⩽0.22° for rotation at 5 years postoperatively (p ⩾ 0.23). Mean cup migration between 2 and 5 years was limited (all parameters <0.17 mm and <0.30°). At 5-year follow-up, mean stem subsidence was 2.09 mm (0.89-3.29 mm) in ceramic and 2.55 (0.97-4.12) mm in polyethylene. The mean change in internal rotation was 3.69° (1.98-5.40°) in ceramic and 4.01° (2.20-5.81°) in polyethylene. Most stem migration occurred up to 1.5 months, stabilising afterwards. All between-group effects were ⩽0.75 mm for translations and ⩽1.41° for rotations (p ⩾ 0.26). 5-year migration patterns of press-fit cups and stems were similar between ceramic and polyethylene liners. The Delta-TT cup and H-MAX S stem showed secondary stabilisation and remained stable up to 5 years in both groups, which is promising for long-term survival with both liner types. ClinicalTrials.gov (NCT03093038).

Glenoid wear and migration pattern of a humeral head resurfacing implant: a prospective study using radio stereometric analysis

Background and purposeThe humeral head resurfacing arthroplasty (HHR) is normally used as a hemi shoulder arthroplasty and has been in use for the treatment of Gleno-Humeral osteoarthritis of the shoulder (OA) for more than 30 years. Some studies, however, shows that anatomical total shoulder arthroplasty provides better improvement in function than a HHR for patients with OA. Reasons for this may be a progressive glenoid wear (GW) or loosening of the HHR. We therefore wanted to investigate the migration pattern (MP) of the HHR and also GW by using Radio Stereometric Analysis (RSA). Patients and methods21 patients (21 shoulders) with OA and a mean age of 64 years were enrolled in the study. They all received the Copeland humeral resurfacing head and were followed for 2 years with RSA. We evaluated the clinical outcome at 2 years with Western Ontario Osteoarthritis of the Shoulder (WOOS), EuroQol 5 dimension 3L (EQ-5D) and Constant Shoulder Score (CSS). In addition, we assessed data on WOOS and revisions until 5 years follow-up by using the local clinic data within the Swedish Shoulder Arthroplasty Register. ResultsAfter an initial migration at two months the implants were stable in relation to the humerus with no statistically significant difference between the 2 months and the 2 years value (p=0.23). The GW continued to increase during the study period with an initial migration of mean 2.3 mm and at 2 years 3.5 mm with a statistically difference between the 6 months and 2 years value (p=0.046). The WOOS, EQ-5D and CSS were all improved at 2 years compared to the preoperative values. We found a weak correlation between GW at 2 years and the WOOS score at 2 and 5 years, but these did not reach statistical significance. There were 4 revisions within 5 years after the primary operation, all due to pain. ConclusionThe marker-free RSA can be used in clinical studies for assessing migration in HHR implants and was also for the first time used to measure GW. The Copeland HHR seems to obtain a secure fixation in the humerus but shows continuous GW up to two years.

Five-year migration of uncemented femoral components in total knee arthroplasty with either highly cross-linked or conventional polyethylene inserts: a blinded randomized controlled trial using radiostereometric analysis.

The aim of this study was to compare the migration of the femoral component, five years postoperatively, between patients with a highly cross-linked polyethylene (HXLPE) insert and those with a conventional polyethylene (PE) insert in an uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary aims included clinical outcomes and patient-reported outcome measures (PROMs). We have previously reported the migration and outcome of the tibial components in these patients. A double-blinded randomized controlled trial was conducted including 96 TKAs. The migration of the femoral component was measured with radiostereometry (RSA) at three and six months and one, two, and five years postoperatively. PROMs were collected preoperatively and at all periods of follow-up. There was no clinically relevant difference in terms of migration of the femoral component or PROMs between the HXLPE and PE groups. The mean difference in migration (maximum total point motion), five years postopeatively, was 0.04 mm (95% CI -0.06 to 0.16) in favour of the PE group. There was no clinically relevant difference in migration of the femoral component, for up to five years between the two groups. These findings will help to establish a benchmark for future studies on migration of femoral components in TKA.

Model-based Roentgen Stereophotogrammetric Analysis (RSA) of polyethylene implants

Model-based Roentgen Stereophotogrammetric Analysis (RSA) is able to measure the migration of metallic prostheses with submillimeter accuracy through contour-detection and 3D surface model matching techniques. However, contour-detection is only possible if the prosthesis is clearly visible in the radiograph; consequently Model-based RSA cannot be directly used for polymeric materials due to their limited X-ray attenuation; this is especially clinically relevant for all-polyethylene implants. In this study the radiopacity of unicompartmental Ultra-High Molecular Weight Polyethylene (UHMWPE) knee bearings was increased by diffusing an oil-based contrast agent into the surface to create three different levels of surface radiopacity. Model-based RSA was performed on the bearings alone, the bearings alongside a metallic component held in position using a phantom, the bearings cemented into a Sawbone tibia, and the bearings at different distances from the femoral component. For each condition the precision and accuracy of zero motion of Model-based RSA were assessed. The radiopaque bearings could be located in the stereo-radiographs using Model-based RSA an accuracy comparable to metallic parts for translational movements (0.03 mm to 0.50 mm). For rotational movements, the accuracy was lower (0.1∘ to 3.0∘). The measurement accuracy was compared for all the radiopacity levels and no significant difference was found (p=0.08). This study demonstrates that contrast enhanced radiopaque polyethylene can be used for Model-based RSA studies and has equivalent translational measurement precision to metallic parts in the superior-inferior direction.

Radial head arthroplasty diameter impact on elbow kinematics evaluated by dynamic radiostereometric analysis.

Radial head arthroplasty (RHA) reestablishes elbow stability after complex radial head fracture, but complication rates are high, possibly due to inappropriate implant sizing. Knowledge of impact of radial head implant diameter on elbow kinematics is limited and warranted. This study evaluated elbow kinematics of different radial head implant diameters after RHA using dynamic radiostereometric analysis (dRSA). Eight human donor arms were examined with dRSA during elbow flexion with the forearm in unloaded neutral position, and in supinated- and pronated position without and with 10N either varus or valgus load, respectively. Elbow kinematics were examined before and after RHA with head diameters of anatomical size, -2 mm (undersized), and +2 mm (oversized). The ligaments were kept intact by use of step-cut humerus osteotomy for repeated RHA exchange. Bone models were obtained from CT, and by AutoRSA software bone models were matched with dRSA recordings. The elbow kinematics were described using anatomical coordinate systems. Compared to the native radial head during elbow flexion, the anatomical sized RHA shifted 2.0 mm in ulnar direction during unloaded pronated forearm position. The undersized RHA shifted 1.5 mm in posterior direction and 2.1 mm in ulnar direction during unloaded pronated forearm position and increased the varus angle by 2.4° during supinated loaded forearm position. The oversized RHA shifted 1.6 mm in radial direction during loaded supinated forearm position. The anatomically sized RHA should be preferred as it maintained native elbow kinematics the best. The kinematic changes with oversized and undersized RHA diameters were small, suggesting forgiveness for the RHA diameter size. Level III.

Stable polyethylene inlay fixation and low polyethylene wear rate in fixed-bearing total knee arthroplasty at five to six years' follow-up.

Micromotion of the polyethylene (PE) inlay may contribute to backside PE wear in addition to articulate wear of total knee arthroplasty (TKA). Using radiostereometric analysis (RSA) with tantalum beads in the PE inlay, we evaluated PE micromotion and its relationship to PE wear. A total of 23 patients with a mean age of 83 years (77 to 91), were available from a RSA study on cemented TKA with Maxim tibial components (Zimmer Biomet). PE inlay migration, PE wear, tibial component migration, and the anatomical knee axis were evaluated on weightbearing stereoradiographs. PE inlay wear was measured as the deepest penetration of the femoral component into the PE inlay. At mean six years' follow-up, the PE wear rate was 0.08 mm/year (95% confidence interval 0.06 to 0.09 mm/year). PE inlay external rotation was below the precision limit and did not influence PE wear. Varus knee alignment did not influence PE wear (p = 0.874), but increased tibial component total translation (p = 0.041). The PE inlay was well fixed and there was no relationship between PE stability and PE wear. The PE wear rate was low and similar in the medial and lateral compartments. Varus knee alignment did not influence PE wear.