Bony increased-offset reverse shoulder arthroplasty vs. metal augments in reverse shoulder arthroplasty: a prospective, randomized clinical trial with 2-year follow-up.

BACKGROUND: Reverse shoulder arthroplasty (RSA) is rapidly being adopted as the standard procedure for a growing number of shoulder pathologies. Lateralization of the glenoid component is known to reduce the incidence of scapular notching and possibly improve postoperative range of motion. A number of methods are used for glenoid component lateralization, including bony increased-offset reverse shoulder arthroplasty (BIO-RSA) and porous metal-augmented baseplates. Presently, there exists little comparative literature on bone vs. metal lateralization. Therefore, the purpose of this study was to compare BIO-RSA to metal-augmented glenoid baseplates by assessing clinical outcomes and baseplate migration using model-based radiostereometric analysis. METHODS: A power analysis indicated 40 patients would be required for this radiostereometric study. Therefore, 41 shoulders were prospectively randomized to receive either glenoid bone grafting (BIO-RSA) or a porous metal-augmented wedge-shaped titanium baseplate for primary reverse shoulder arthroplasty. At the time of primary surgery, all patients also underwent implantation of 8 tantalum marker beads in the glenoid and coracoid. Following surgery, participants were imaged using a calibrated, stereo radiographic technique. Radiographs were acquired at 6 weeks (baseline), 3 months, 6 months, 1 year, and 2 years postoperatively. Migration of the prosthesis was compared between bone and metal lateralization groups at each time point using a mixed effects model with Bonferroni test for multiple comparisons. Outcome measures were acquired preoperatively and 2 years postoperatively. RESULTS: No significant differences were observed along any translation or rotation axis at any time point for either glenoid fixation group (P ≥ .175). Mean total glenoid component translation (± standard deviation) 2 years postoperatively was 0.4 ± 0.2 mm and 0.5 ± 0.3 mm for BIO-RSA and metal-augmented baseplates, respectively (P = .784). No significant differences were observed between groups in active range of motion; pain; American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score; Simple Shoulder Test score; Disabilities of the Arm, Shoulder, and Hand score; Constant Shoulder score; or Subjective Shoulder Value (P ≥ .117), with the exception of increased active external rotation in the BIO-RSA cohort (P = .036). CONCLUSION: This randomized clinical trial assessed reverse shoulder arthroplasty glenoid component migration using model-based radiostereometric analysis. At 2-year follow-up, our results indicate both BIO-RSA and porous metal wedge augmented baseplates provide stable initial fixation, which is maintained at 2 years' follow-up, with no substantial differences in clinical outcomes.

Are short press-fit stems comparable to standard-length cemented stems in reverse shoulder arthroplasty? A prospective, randomized clinical trial.

BACKGROUND: The literature comparing humeral implants in reverse shoulder arthroplasty is sparse. With minimal supporting literature, there has been a trend away from standard-length cemented humeral implants to press-fit stems and, recently, to shorter-stem implants. It is known that early implant migration, within the first 2 years postoperatively, is predictive of later implant loosening and possible revision surgery. Therefore, the purpose of this study was to compare clinical outcomes and implant migration between cemented standard-length humeral stems and press-fit short stems using model-based radiostereometric analysis. METHODS: After a power analysis, 41 shoulders were prospectively randomized to receive either a cemented standard-length or press-fit short humeral stem for primary reverse shoulder arthroplasty between July 2017 and June 2019. Following surgery, participants were imaged with stereo radiographs acquired at 6 weeks (baseline), 3 months, 6 months, 1 year, and 2 years. Migration of the humeral stem at each time point was compared with baseline, with differences in migration between cohorts assessed using a mixed-effects model with the Bonferroni test for multiple comparisons. Patient-reported outcome measures (Subjective Shoulder Value; American Shoulder and Elbow Surgeons shoulder score; Simple Shoulder Test score; Disabilities of the Arm, Shoulder and Hand score; and Constant score) were also compared. RESULTS: At 6 months (P = .025), 1 year (P = .004), and 2 years (P = .001) postoperatively, press-fit short stems migrated significantly more than cemented stems along the superior-inferior translation axis; in addition, they showed greater total translation at 2 years (P = .003). Mean total translation (± standard deviation) at 2 years was 0.4 ± 0.2 mm and 1.0 ± 1.1 mm for the cemented and press-fit cohorts, respectively. Mean migration between the 1- and 2-year time points was minimal for both stem fixation groups along all axes (<0.1 mm and 0.6°). There was no difference in active range of motion, pain, or validated outcome measures between the cohorts at 2 years (P ≥ .170). CONCLUSION: This randomized clinical trial shows that press-fit short humeral stems subside substantially more than standard-length cemented stems but ultimately achieve stability from 1 year through 2 years. Conversely, no significant differences were observed in clinical outcomes between cohorts.

The Effects of Resection Technique on Implant Migration in Single Radius Posterior-Stabilized Total Knee Replacement.

The purpose of the present study was to measure the effects of gap balancing and resection techniques on migration of a single total knee replacement implant design. A total of 23 patients (24 knees) were recruited on referral to either a surgeon performing gap balancing or a surgeon performing measured resection and followed prospectively. All patients received a fixed bearing, posterior stabilized total knee replacement implant of a single radius femoral component design with cement fixation, and all aspects of care outside of resection technique were identical. Patients underwent radiostereometric analysis (RSA) at 2 weeks (baseline), 6 weeks, 3 months, 6 months, 1 year, and 2 years. Migration of the tibial and femoral components was compared between groups. Tibial component migration was greater at 2 years in the gap balancing group (mean difference = 0.336 mm, p = 0.036), but there was no difference at 1 year. One measured resection and three gap balancing tibial components demonstrated continuous migration > 0.2 mm between years 1 and 2. There was no difference in femoral component migration. Small differences in tibial component migration were found between the gap balancing and measured resection techniques. However, comparing the migration to established predictive thresholds for long-term loosening risk, implants performed with both techniques were found to have equally low revision risk.

Validation of In Vivo Linear and Volumetric Wear Measurement for Reverse Total Shoulder Arthroplasty Using Model-Based Radiostereometric Analysis.

Presently, polyethylene wear measurement of reverse total shoulder arthroplasty (rTSA) is restricted to in vitro, in silico, and retrieval analysis, with no method for the quantification of in vivo wear of well-functioning implants. The purpose of this study was to validate the use of model-based radiostereometric analysis (MBRSA) as a measurement tool for in vivo rTSA wear using a phantom setup. Six additively manufactured polyethylene inserts were fabricated, one unworn control and five to represent known wear patterns, and individually fit within the rTSA components. Each insert was imaged using standard radiostereometric techniques and analyzed using MBRSA. From the position and orientation estimation provided by MBRSA, a micro-computed tomography model of the control insert was virtually placed within the metaphyseal tray. The apparent intersection of the glenosphere into the insert was recorded as wear. This method enables wear measurements with a linear precision of 0.21 mm and a bias of 0.36 ± 0.13 mm, and a volumetric precision of 49.3 mm3 , with a bias of 48.9 ± 24.3 mm3 . This technique allows for the in vivo measurement of polyethylene wear without the requirement of marker beads or baseline radiographs, expanding the potential for in vivo wear measurements to larger populations and retrospective analysis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1620-1627, 2019.

Radiostereometric Analysis Permits In Vivo Measurement of Very Small Levels of Wear in TKA.

BACKGROUND: Revision of TKA as a result of polyethylene wear is decreasing, but long-term wear performance of polyethylene is still a topic of interest to surgeons and device manufacturers seeking to improve longevity. Measuring wear of modern, wear-resistant implants has been described using radiostereometric analysis (RSA). Performing in vivo measurements would establish whether implant retrieval studies are representative of wear in well-performing knees. QUESTIONS/PURPOSES: For a single knee implant system, we sought to determine (1) the linear wear rate using RSA; (2) the association between demographic factors and wear rate; and (3) the association between limb alignment and wear rate. METHODS: A total of 49 patients with a minimum followup of 10 years (median, 12 years; range, 10-20 years) were retrospectively selected. During the examined period, 4082 TKAs were performed of which 2085 were the implant examined in this study. There were 71 of these patients who met the criteria including an available full-leg radiograph postoperatively, and 34 of these patients returned for examination along with 15 additional from a separate RSA study that also met the criteria. All patients received a posterior-stabilized, cobalt-chromium-on-conventional polyethylene total knee implant from a single implant system, which was the most commonly used at our institution at the time. Patients underwent standing RSA examinations from 0° to 120° of flexion at a single time point without the use of marker beads. Linear wear rates (including creep) were measured based on intersections between the femoral component and tibial insert models. Associations between wear and patient age at surgery, sex, height, weight, body mass index, tibial insert size, and limb alignment were examined. RESULTS: Using the maximum linear wear rate from any flexion angle, the lateral rate was 0.047 mm/year (interquartile range [IQR], 0.034-0.066 mm/year) and the medial rate was 0.052 mm/year (IQR, 0.040-0.069 mm/year). Using the median of the linear wear rates across all flexion angles, the lateral rate was 0.027 mm/year (IQR, 0.017-0.046 mm/year) and the medial rate was 0.038 mm/year (IQR, 0.022-0.054 mm/year). This rate for males was 0.049 mm/year medially (IQR, 0.042-0.077 mm/year) and 0.032 mm/year laterally (IQR, 0.026-0.059 mm/year), and for females was 0.027 mm/year medially (0.016-0.039 mm/year) and 0.020 mm/year laterally (IQR, 0.013-0.032 mm/year). The wear rate for males was greater medially (difference = 0.022 mm/year, p < 0.001) and laterally (difference = 0.012 mm/year, p = 0.008). There were associations between greater wear and increasing height (ρ = 0.48, p < 0.001 medially and ρ = 0.30, p = 0.04 laterally), decreasing body mass index (ρ = -0.31, p = 0.03 medially), and greater implant size (ρ = 0.34, p = 0.02 medially). Increasingly varus leg alignment was associated with greater medial wear (ρ = 0.33, p = 0.02). CONCLUSIONS: Greater wear rates were associated with demographic factors and leg alignment. Further RSA wear studies of other modern implant systems would provide complementary information to retrieval studies and valuable data on wear resistance. CLINICAL RELEVANCE: Good wear resistance was demonstrated by well-performing implants in patients at long-term followup with wear magnitudes in agreement with reported values from retrieval studies.

Additively manufactured implant components for imaging validation studies.

Radiographic imaging is the current standard for evaluating postoperative joint replacements. Prior to application, such imaging methods need to be validated to determine the lower limits of performance under ideal conditions, using either a phantom or cadaver setup. Conventionally manufactured orthopedic implants for use in such studies are not always accessible and may be cost-prohibitive to purchase. We propose the use of additively manufactured implants as a cheaper, more accessible alternative for use in radiographic imaging validation studies. Bias and repeatability were compared between conventionally manufactured and additively manufactured reverse total shoulder implant sets under a standard model-based radiostereometric analysis phantom study environment. Measurements were compared using the humeral stem or glenosphere model relative to reference bone beads, and the humeral stem relative to the glenosphere model to measure implant relative displacement. Compared to the conventionally manufactured implants, the additively manufactured implants had less bias along the internal-external rotation axis (p < 0.001), but greater bias along the abduction-adduction and flexion-extension rotation axes (p = 0.005, 0.011). Additively manufactured implants had greater repeatability along the internal-external rotation axis (p < 0.001), but worse repeatability along the medial-lateral translation axis (p = 0.001) and the abduction-adduction rotation axis (p < 0.001). Differences were on the orders of 0.01 mm and 0.5°. For the purpose of validating two-dimensional-three-dimensional radiographic imaging techniques of orthopedic implants, additively manufactured implants can be used in place of conventionally manufactured implants, assuming they are fabricated to the manufacturer's specifications. Observed differences were within the errors of the measurement technique and not clinically meaningful.

Radiostereometric analysis using clinical radiographic views: Validation with model-based radiostereometric analysis for the knee.

Radiostereometric analysis is a sophisticated radiographic technique with high measurement accuracy. In order to improve the accessibility of radiostereometric analysis for clinical use, a modified radiostereometric analysis procedure has been previously proposed that enables clinical radiographic views to be used for radiostereometric analysis. It has been successfully validated for its application to the hip wear study with the conventional bead-based radiostereometric analysis environment using computed radiography. In this study, we describe the implementation and validation of this technique for the knee study with the model-based radiostereometric analysis environment using digital radiography. A knee-joint phantom with 6 degrees of freedom was examined, and the bias and repeatability/reproducibility of the modified radiostereometric analysis approach were investigated following the newly updated ASTM recommendations. The bias parameters (mean ± 95% confidence interval) ranged from 0.008 ± 0.003 mm to 0.027 ± 0.006 mm for translation and from 0.014° ± 0.007° to 0.040° ± 0.020° for rotation. The repeatability standard deviation ranged from 0.004 to 0.020 mm for translation and from 0.005° to 0.015° for rotation. The 95% repeatability limit ranged from 0.011 to 0.055 mm for translation and from 0.014° to 0.041° for rotation. The reproducibility standard deviation ranged from 0.004 to 0.023 mm for translation and from 0.006° to 0.040° for rotation. The 95% reproducibility limit ranged from 0.012 to 0.063 mm for translation and from 0.016° to 0.112° for rotation. The modified procedure allows routine clinical radiographs to be used for radiostereometric analysis, which provides the possibility of adding quantitative measurements to current patient registries.

Predictive accuracy of RSA migration thresholds for cemented total hip arthroplasty stem designs.

INTRODUCTION: Radiostereometric analysis (RSA) migration thresholds for cemented total hip stems have been established beyond which an unacceptably high risk of revision is likely to occur. These thresholds are subsidence >0.23 mm or >1.2 mm after 2 years. The purpose of this study was to retrospectively examine after long-term follow-up the predictive accuracy of the two thresholds. METHODS: Data from two previous prospective RSA trials with 2 year follow-up for which minimum 10 year survivorship data was available were used. Thirty-six patients received a Spectron stem, 17 patients received an Exeter stem, and 17 patients received a CPCS stem. Subsidence after 2 years was compared to the migration thresholds, and long-term survivorship and clinical outcome scores were obtained. RESULTS: At 2 years, the Spectron stem subsided 0.046 ± 0.160 mm, the Exeter stem subsided 1.218 ± 0.320 mm, and the CPCS stem subsided 0.681 ± 0.246 mm ( p < 0.0001). The Spectron stem passed both thresholds, the Exeter stem failed both thresholds, and the CPCS stem passed 1 and failed 1 threshold. At 10 years, survivorship exceeded 90% for all stems. CONCLUSION: All stems demonstrated strong 10 year survivorship and equivalent clinical outcome scores, but this success would not have been equally predicted across RSA migration thresholds. Although RSA is a useful predictive tool, care should be taken in applying migration thresholds only to those stem designs they are indicated for, with the threshold of 1.2 mm of subsidence at 2 years being most broadly applicable.

Radiostereometric analysis using clinical radiographic views: Development of a universal calibration object.

Radiostereometric analysis (RSA) is a highly accurate technique used to provide three-dimensional (3D) measurements of orthopaedic implant migration for clinical research applications, yet its implementation in routine clinical examinations has been limited. Previous studies have introduced a modified RSA procedure that separates the calibration examinations from the patient examinations, allowing routine clinical radiographs to be analyzed using RSA. However, in order to calibrate the wide range of clinical views, a new calibration object is required. In this study, a universal, isotropic calibration object was designed to calibrate any pair of radiographic views used in the clinic for RSA. A numerical simulation technique was used to design the calibration object, followed by a phantom validation test of a prototype to verify the performance of the novel object, and to compare the measurement reliability to the conventional calibration cage. The 3D bias for the modified calibration method using the new calibration object was 0.032 ±â€¯0.006 mm, the 3D repeatability standard deviation was 0.015 mm, and the 3D repeatability limit was 0.042 mm. Although statistical differences were present between the universal calibration object and the conventional cage, the differences were considered to be not clinically meaningful. The 3D bias and repeatability values obtained using the universal calibration object were well under the threshold acceptable for RSA, therefore it was successfully validated. The universal calibration object will help further the adoption of RSA into a more routine practice, providing the opportunity to generate quantitative databases on joint replacement performance.

Validation of radiostereometric analysis in six degrees of freedom for use with reverse total shoulder arthroplasty.

A phantom study was conducted to determine bias in motion and bias at zero motion of radiostereometric analysis (RSA) for evaluating implant relative displacement in reverse total shoulder arthroplasty (RTSA). A Sawbones shoulder phantom was fitted with a RTSA implant set and 13 tantalum markers. The model was fixed to a manual micrometer, providing controlled movements though fifteen known increments in translation and twelve increments in rotation (0.02-5.00 mm and 0.1-6.0°), along each translation and rotation axis. Movement between the glenoid and humerus was assessed using beads vs. beads (B/B), model vs. beads (M/B), and model vs. model (M/M) measurement methods in a model-based RSA environment. Bias in motion and bias at zero motion were defined as the difference between measured and accepted reference values, and the difference between double examinations with a theoretical displacement of zero, respectively. Bias in motion ranged from 0.054 ±â€¯0.010 to 0.129 ±â€¯0.014 mm and 0.076 ±â€¯0.025 to 0.126 ±â€¯0.025° (B/B), 0.023 ±â€¯0.009 to 0.126 ±â€¯0.016 mm and 0.111 ±â€¯0.033 to 0.794 ±â€¯0.251° (M/B), and 0.029 ±â€¯0.010 to 0.135 ±â€¯0.030 mm and 0.243 ±â€¯0.088 to 0.384 ±â€¯0.153° (M/M). Bias at zero motion ranged from 0.120 to 0.156 mm and 0.075 to 0.206° (B/B), 0.074 to 0.149 mm and 0.067 to 1.953° (M/B), and 0.069 to 0.259 mm and 0.284 to 1.273° (M/M). This is the first RSA for RTSA study, with results comparable to those validating the use of RSA for hip and knee arthroplasties (accepted as 0.05-0.50 mm and 0.15-1.15°), justifying the potential use of RSA as a tool for measuring implant displacement in the shoulder.

Change in Acetabular Cup Orientation From Supine to Standing Position and Its Effect on Wear of Highly Crosslinked Polyethylene.

BACKGROUND: The purpose of this study is to measure acetabular cup position and wear of the highly crosslinked polyethylene liner in the supine and standing position for patients at a minimum of 10 years after the operation. METHODS: A total of 38 patients were recruited at a mean of 12.5 years after the operation. All patients received a single acetabular cup design with a highly crosslinked liner and a 28-mm cobalt-chromium femoral head. Patients underwent supine and standing radiostereometric examinations in which the X-ray sources and detectors were positioned to obtain an anterior-posterior and cross-table lateral radiograph. Acetabular cup position and the three-dimensional wear rate were measured from the radiographs, and outcome scores were recorded for each patient. RESULTS: Anteversion significantly increased (P < .0001) a mean of 12° from supine (15.1° ± 10.4°) to standing (27.2° ± 10.5°) position. Inclination also significantly increased (P = .001) a mean of 2° from supine (44.4° ± 6.8°) to standing (46.3° ± 7.7°) position. There was no difference (P = .093) in wear rate between supine (0.067 ± 0.070 mm/y) and standing (0.073 ± 0.074 mm/y) positions. There were no correlations between cup orientation and wear rate in either position. CONCLUSION: Highly crosslinked polyethylene is a forgiving bearing material. Although adherence to the traditional acetabular position target zone is recommended, ensuring hip stability and consideration of the patient's functional position are also important objectives to consider for the acetabular position.

Contact Kinematics Correlates to Tibial Component Migration Following Single Radius Posterior Stabilized Knee Replacement.

BACKGROUND: Contact kinematics between total knee arthroplasty components is thought to affect implant migration; however, the interaction between kinematics and tibial component migration has not been thoroughly examined in a modern implant system. METHODS: A total of 24 knees from 23 patients undergoing total knee arthroplasty with a single radius, posterior stabilized implant were examined. Patients underwent radiostereometric analysis at 2 and 6 weeks, 3 and 6 months, and 1 and 2 years to measure migration of the tibial component in all planes. At 1 year, patients also had standing radiostereometric analysis examinations acquired in 0°, 20°, 40°, and 60° of flexion, and the location of contact and magnitude of any condylar liftoff was measured for each flexion angle. Regression analysis was performed between kinematic variables and migration at 1 year. RESULTS: The average magnitude of maximum total point motion across all patients was 0.671 ± 0.270 mm at 1 year and 0.608 ± 0.359 mm at 2 years (P = .327). Four implants demonstrated continuous migration of >0.2 mm between the first and second year of implantation. There were correlations between the location of contact and tibial component anterior-posterior tilt, varus-valgus tilt, and anterior-posterior translation. The patients with continuous migration demonstrated atypical kinematics and condylar liftoff in some instances. CONCLUSION: Kinematics can influence tibial component migration, likely through alterations of force transmission. Abnormal kinematics may play a role in long-term implant loosening.

Varus tibial alignment is associated with greater tibial baseplate migration at 10 years following total knee arthroplasty.

PURPOSE: To examine implant migration and articular behavior of primary total knee arthroplasty (TKA) at 10 years after index surgery and correlate to implant alignment. METHODS: Thirty-five patients underwent a cemented posterior stabilized total knee arthroplasty with a surgical objective of neutral alignment and were enrolled in a long-term radiostereometric analysis (RSA) study. At 10 years after surgery, patients were analyzed for implant migration using RSA as well as radiographic assessment of articular behavior at four positions of knee flexion. Implant position and alignment was measured on full-length radiographs. Patient demographics and reported outcomes were also collected. RESULTS: No difference between patient demographics or patient-reported outcomes were found. When categorized into neutral and varus groupings, no difference in migration was present. If alignment was considered as a continuous variable, there was no correlation between overall leg alignment and migration, however, migration increased with an increasing varus tibial alignment. Although contact location did not differ between neutral and varus groups through a range of motion, condylar liftoff was much more common in the varus group, of which all were lateral liftoff. CONCLUSIONS: Increased tibial varus results in increased implant migration. Overall varus limb alignment is correlated with isolated lateral compartment liftoff, and liftoff occurs more commonly than in neutral aligned knees. The increased migration and liftoff raise concerns about the longevity of malaligned total knee replacements. If a goal of overall varus limb alignment is desired for TKA, the tibia should remain neutral. LEVEL OF EVIDENCE: Level III.

Thirteen-year wear rate comparison of highly crosslinked and conventional polyethylene in total hip arthroplasty: long-term follow-up of a prospective randomized controlled trial.

BACKGROUND: The purpose of this study was to report the radiographic wear rates from a previous randomized controlled trial of first-generation highly crosslinked versus conventional polyethylene in total hip arthroplasty (THA) at a minimum of 13 years' follow-up. METHODS: Patients returned for radiographic imaging and radiostereometric analysis (RSA). Radiographs were reviewed for the presence of osteolysis or component loosening. Femoral head penetration (which includes both wear and creep) was measured using RSA. We compared Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), 12-Item Short Form Health Survey (SF-12) and Harris Hip Scores (HHS) with preoperative values. RESULTS: There was 1 revision in each group. There was no difference in WOMAC, SF-12, or HHS outcome scores between the highly crosslinked and conventional polyethylene groups (all p ≥ 0.13). Wear rate was lower with crosslinked polyethylene than conventional polyethylene (0.04 ± 0.02 mm/year v. 0.08 ± 0.03 mm/year, p = 0.007). CONCLUSION: First-generation crosslinked polyethylene demonstrates greater wear resistance than conventional polyethylene after 13 years of implantation. Crosslinked polyethylene continues to outperform conventional polyethylene into the second decade of implantation.

CONTEXTE: Le but de cette étude était de faire rapport sur les taux d'usure à la radiographie dans la foulée d'un essai randomisé et contrôlé antérieur sur un polyéthylène hautement réticulé de première génération c. classique pour la prothèse totale de la hanche (PTH) après un minimum de 13 ans de suivi. MÉTHODES: Les patients se sont de nouveau présentés pour subir des radiographies et une analyse radiostéréométrique (ARS). On a vérifié à la radiographie la présence d'ostéolyse ou de descellement. La pénétration de la tête fémorale (qui inclut l'usure et le fluage) a été mesurée par ARS. Nous avons comparé l'indice WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index), le questionnaire SF-12 (questionnaire sur la qualité de vie en lien avec la santé en 12 points) et le score HHS (score de Harris pour la hanche) aux valeurs préopératoires. RÉSULTATS: Il y a eu 1 révision dans chaque groupe. On n'a noté aucune différence pour ce qui est des scores WOMAC, SF-12 ou HHS entre les groupes ayant reçu la prothèse de polyéthylène hautement réticulée c. classique (tous p ≥ 0,13). Le taux d'usure a été moindre avec le polyéthylène réticulé qu'avec le polyéthylène classique (0,04 ± 0,02 mm/an c. 0,08 ± 0,03 mm/an, p = 0,007). CONCLUSION: Le polyéthylène réticulé de première génération résiste mieux à l'usure que le polyéthylène classique 13 ans après l'implantation. Le polyéthylène réticulé continue de surclasser le polyéthylène classique au-delà des 10 premières années suivant l'implantation.

Contact Kinematic Differences Between Gap Balanced vs Measured Resection Techniques for Single Radius Posterior-Stabilized Total Knee Arthroplasty.

BACKGROUND: Measured resection (MR) and gap balancing (GB) are common surgical techniques for total knee arthroplasty (TKA). Controversy has arisen as each conceptually differs in how the knee is balanced through bone and soft tissue management. The objective of the present study was to compare both the frequency of condylar liftoff and the location of femorotibial contact from extension through midflexion between patients undergoing GB or MR TKA. METHODS: A total of 24 knees (23 patients) were randomly assigned at referral to either a surgeon performing MR or GB TKA with the same single radius, posterior-stabilized implant (12 per cohort). At 1-year postoperation, patients underwent biplanar radiographic imaging at 0°, 20°, 40°, and 60° of flexion. Condylar liftoff, contact location, and magnitude of excursion on each condyle were measured. Preoperative and postoperative clinical outcome scores were also collected. RESULTS: There was no difference (P = .41) in the frequency of liftoff between cohorts. The MR cohort had more posterior contact on the medial condyle (P < .01) and more anterior contact on the lateral condyle (P < .01) throughout flexion. Motion patterns were similar between cohorts, with similar medial (P = .48) and lateral (P = .44) excursion, which was equal in magnitude between condyles for both MR (P = .48) and GB (P = .73). There was no difference in clinical outcome scores between groups. CONCLUSION: For this particular implant system, GB and MR appear to produce similar kinematic and patient-reported outcome results.

Effect of Acetabular Position on Polyethylene Liner Wear Measured Using Simultaneous Biplanar Acquisition.

BACKGROUND: Studies that have previously examined the relationship between acetabular component inclination angle and polyethylene wear have shown increased wear of conventional polyethylene with high inclination angles. To date, there are no long-term in vivo studies examining the correlation between cup position and polyethylene wear with highly crosslinked polyethylene. METHODS: An institutional arthroplasty database was used to identify patients who had metal-on-highly crosslinked polyethylene primary total hip arthroplasty using the same component design with a minimum follow-up of 10 years. A modified radiostereometric analysis examination setup was utilized, recreating standard anteroposterior and cross-table lateral examinations in a single stereo radiostereometric analysis acquisition. The same radiographs were used to measure inclination angle and anteversion. RESULTS: A total of 43 hips were included for analysis in this study. Average follow-up was 12.3 ± 1.2 years. The average linear wear rate was calculated to be 0.066 ± 0.066 mm/y. Inclination angle was not correlated with polyethylene wear rate (P = .82). Anteversion was also not correlated with polyethylene wear rate (P = .11). CONCLUSION: At long-term follow-up of >10 years, highly crosslinked polyethylene has a very low wear rate. This excellent tribology is independent of acetabular position. The low wear rate highlights the excellent results of metal on highly crosslinked polyethylene, and supports its use in total hip arthroplasty.

Investigation of imaging magnification in radiostereometric analysis.

Radiostereometric analysis is a highly accurate imaging technique. A recent advance in radiostereometric analysis is the use of flat panel digital radiography, which provides the opportunity for quick analysis using radiostereometric analysis. However, such a setup is expensive. Using large cassettes for small joints could minimize the cost. In this article, we investigated the influence of cassette size for small joint examinations with a biplanar radiostereometric analysis setup. Our results indicated that there is no significant difference in the precision when using large cassettes over small cassettes, whether or not imaging magnification is applied.

Marker-based technique for visualizing radiolucent implant components in radiographic imaging.

Radiography is the predominant imaging modality used for the in-vivo analysis of orthopaedic implants. A major disadvantage of radiography is that the articulating joint components that are composed of radiolucent polyethylene cannot be directly visualized. Current strategies attempt to circumvent this limitation by estimating component positions and simplifying the joint system, however, these approaches lead to a number of associated errors. Thus, this study provides a method to enable the visualization of the polyethylene component of total knee replacements in radiographic images. This was achieved through the repeatable insertion of markers and accompanying registration process, which were evaluated in this study for reproducibility and accuracy. An insertion guide was developed to insert tantalum beads into polyethylene tibial surface liners. The bead-inserted liners were micro-CT scanned to obtain 3D surface geometries. An in-vivo mimicking phantom RSA experiment was then used to test the 3D to 2D registration process. The guide positioned the beads consistently to ±0.21 mm. The 3D to 2D registration demonstrated a repeatability of -0.014 ± 0.008 mm. Registration of different bead-inserted tibial liners to the phantom revealed an average error of 0.026 ± 0.047 mm for this visualization method. This visualization approach provides greatly improved registration and inter-component measurements than current alternative strategies. This process is suitable for a number of other joints and would greatly benefit procedures that analyze component interactions and implant performance over time. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2017-2022, 2017.

Radiostereometric analysis using clinical radiographic views: Validation measuring total hip replacement wear.

Radiostereometric analysis (RSA) is a stereo X-ray technique used in clinical research studies to evaluate micro-motion and wear of orthopaedic implants within bone. While highly accurate and precise, its adoption has been limited due to technical requirements such as the need for implanted marker beads and radiograph view angles determined by a calibration cage. We propose a new technique that separates the calibration procedure from the patient examination, enabling clinical radiograph views to be used for RSA measurements. The concept of a reference plate was adapted to establish the link between calibration procedure and patient examination procedure for cassette radiography, which may not be necessary for digital radiography. A hip wear phantom was used to validate this technique by comparing the error and repeatability of the novel procedure with that of conventional RSA. Femoral head penetration was measured versus the acetabular cup (head/cup) and marker beads in the acetabular liner (head/liner). Conventional RSA had lower inferior-superior average error (p = 0.03 for head/cup) while the modified RSA had lower anterior-posterior average error (p = 0.01). Average error was greater but not significantly so for the medial-lateral (p = 0.06) and 3D (p = 0.97) measurements. The head/liner method had lower average errors (p < 0.0001) for both procedures, but did not affect repeatability, which was similar between techniques. The novel procedure's average error and repeatability was therefore, similar to conventional RSA. This new technique could be applied to any joint with two clinical radiograph view angles pending further validation in subjects. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1521-1528, 2016.

Quantification of mouse in vivo whole-body vibration amplitude from motion-blur using x-ray imaging.

Musculoskeletal effects of whole-body vibration on animals and humans have become an intensely studied topic recently, due to the potential of applying this method as a non-pharmacological therapy for strengthening bones. It is relatively easy to quantify the transmission of whole-body mechanical vibration through the human skeletal system using accelerometers. However, this is not the case for small-animal pre-clinical studies because currently available accelerometers have a large mass, relative to the mass of the animals, which causes the accelerometers themselves to affect the way vibration is transmitted. Additionally, live animals do not typically remain motionless for long periods, unless they are anesthetized, and they are required to maintain a static standing posture during these studies. These challenges provide the motivation for the development of a method to quantify vibrational transmission in small animals. We present a novel imaging technique to quantify whole-body vibration transmission in small animals using 280 µm diameter tungsten carbide beads implanted into the hind limbs of mice. Employing time-exposure digital x-ray imaging, vibrational amplitude is quantified based on the blurring of the implanted beads caused by the vibrational motion. Our in vivo results have shown this technique is capable of measuring vibration amplitudes as small as 0.1 mm, with precision as small as ±10 µm, allowing us to distinguish differences in the transmitted vibration at different locations on the hindlimbs of mice.