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.

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.

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.

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.

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.

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.

A randomized trial comparing acetabular component fixation of two porous ingrowth surfaces using RSA.

Several new porous ingrowth surfaces for acetabular component fixation have recently been developed. The purpose of this study was to compare the in vivo fixation achieved by two different porosity ingrowth surfaces using radiostereometric analysis (RSA). Sixty-two patients undergoing primary total hip arthroplasty (THA) were randomized to receive a cementless acetabular component with either a 61% high porosity asymmetric titanium porous surface (StikTite, Smith and Nephew, TN, USA) or a 45% low porosity sintered bead porous surface (Roughcoat, Smith and Nephew, TN, USA). RSA and clinical follow-up examinations were done post-operatively, 6-weeks, 3-months, 6-months, 1-year and 2-years. Both the high porosity StikTite and lower porosity Roughcoat surfaces provided excellent biologic fixation.

Measurement of joint kinematics using a conventional clinical single-perspective flat-panel radiography system.

PURPOSE: The ability to accurately measure joint kinematics is an important tool in studying both normal joint function and pathologies associated with injury and disease. The purpose of this study is to evaluate the efficacy, accuracy, precision, and clinical safety of measuring 3D joint motion using a conventional flat-panel radiography system prior to its application in an in vivo study. METHODS: An automated, image-based tracking algorithm was implemented to measure the three-dimensional pose of a sparse object from a two-dimensional radiographic projection. The algorithm was tested to determine its efficiency and failure rate, defined as the number of image frames where automated tracking failed, or required user intervention. The accuracy and precision of measuring three-dimensional motion were assessed using a robotic controlled, tibiofemoral knee phantom programmed to mimic a subject with a total knee replacement performing a stair ascent activity. Accuracy was assessed by comparing the measurements of the single-plane radiographic tracking technique to those of an optical tracking system, and quantified by the measurement discrepancy between the two systems using the Bland-Altman technique. Precision was assessed through a series of repeated measurements of the tibiofemoral kinematics, and was quantified using the across-trial deviations of the repeated kinematic measurements. The safety of the imaging procedure was assessed by measuring the effective dose of ionizing radiation associated with the x-ray exposures, and analyzing its relative risk to a human subject. RESULTS: The automated tracking algorithm displayed a failure rate of 2% and achieved an average computational throughput of 8 image frames/s. Mean differences between the radiographic and optical measurements for translations and rotations were less than 0.08 mm and 0.07° in-plane, and 0.24 mm and 0.6° out-of-plane. The repeatability of kinematics measurements performed using the radiographic tracking technique was better than ±0.09 mm and 0.12° in-plane, and ±0.70 mm and ±0.07° out-of-plane. The effective dose associated with the imaging protocol used was 15 µSv for 10 s of radiographic cine acquisition. CONCLUSIONS: This study demonstrates the ability to accurately measure knee-joint kinematics using a single-plane radiographic measurement technique. The measurement technique can be easily implemented at most clinical centers equipped with a modern-day radiographic x-ray system. The dose of ionizing radiation associated with the image acquisition represents a minimal risk to any subjects undergoing the examination.

In vitro quantification of wear in tibial inserts using microcomputed tomography.

BACKGROUND: Wear of polyethylene tibial inserts can decrease the longevity of total knee arthroplasty. Wear is currently assessed using laboratory methods that may not permit backside wear measurements or do not quantify surface deviation. QUESTIONS/PURPOSES: We developed and validated a technique to quantify polyethylene wear in tibial inserts using microcomputed tomography (micro-CT), a nondestructive high-resolution imaging technique that provides detailed images of surface geometry in addition to volumetric measurements. METHODS: Six unworn and six wear-simulated polyethylene tibial inserts were evaluated. Each insert was scanned three times using micro-CT at a resolution of 50 µm. The insert surface was reconstructed for each scan and the insert volume was calculated. Gravimetric analysis was performed for all inserts, and the micro-CT and gravimetric volumes were compared to determine accuracy. We created three-dimensional surface deviation maps. RESULTS: Micro-CT generated high-quality three-dimensional renderings of the insert surface geometry. Between-scan precision was 0.07%; we observed no difference between micro-CT and gravimetric volume measurements. CONCLUSIONS: Micro-CT can provide precise and accurate volumetric measurements in addition to quantifiable three-dimensional surface deviation maps for the entire insert surface. The technique has the potential to evaluate wear in wear simulator trials and retrieval studies. CLINICAL RELEVANCE: This micro-CT technique combines the benefits of volumetric and surface scanning methods to quantify wear across all surfaces of polyethylene components with a single tool. When applied in wear simulator and retrieval studies, these measurements can be used to evaluate and predict the wear properties of the components.

Technique to quantify subsurface cracks in retrieved polyethylene components using micro-CT.

No current method to study delamination and subsurface cracking in polyethylene joint replacement components provides accurate, nondestructive, and quantitative measurements. A technique to study damage both at and below the surface could be of great benefit. We report the development of a micro-CT technique to nondestructively examine and quantify subsurface cracking in retrieved polyethylene tibial inserts. Five severely delaminated inserts and two never-implanted inserts were obtained from our institution's implant retrieval library and scanned with micro-CT. The insert subsurface was examined for cracks, and their location and widths were measured using a digital line tool. Subsurface cracks were readily apparent only in the images of the delaminated inserts. Cracks ran horizontally, just below the articular and back-side surfaces, and vertically at the center and lateral edges of the inserts and at the tibial post. Cracks ranged from 0.12 to 6.01 mm below the surface, with widths of 0.06-0.97 mm. Micro-CT can nondestructively visualize and quantify subsurface cracks. This is an enhancement to its previously reported use to quantify surface deviations from wear. Micro-CT is well suited for longitudinal pin-on-disk and wear simulator trials, in addition to studies of retrieved components.

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.

Error analysis of marker-based object localization using a single-plane XRII.

The role of imaging and image guidance is increasing in surgery and therapy, including treatment planning and follow-up. Fluoroscopy is used for two-dimensional (2D) guidance or localization; however, many procedures would benefit from three-dimensional (3D) guidance or localization. Three-dimensional computed tomography (CT) using a C-arm mounted x-ray image intensifier (XRII) can provide high-quality 3D images; however, patient dose and the required acquisition time restrict the number of 3D images that can be obtained. C-arm based 3D CT is therefore limited in applications for x-ray based image guidance or dynamic evaluations. 2D-3D model-based registration, using a single-plane 2D digital radiographic system, does allow for rapid 3D localization. It is our goal to investigate-over a clinically practical range-the impact of x-ray exposure on the resulting range of 3D localization precision. In this paper it is assumed that the tracked instrument incorporates a rigidly attached 3D object with a known configuration of markers. A 2D image is obtained by a digital fluoroscopic x-ray system and corrected for XRII distortions (+/- 0.035 mm) and mechanical C-arm shift (+/- 0.080 mm). A least-square projection-Procrustes analysis is then used to calculate the 3D position using the measured 2D marker locations. The effect of x-ray exposure on the precision of 2D marker localization and on 3D object localization was investigated using numerical simulations and x-ray experiments. The results show a nearly linear relationship between 2D marker localization precision and the 3D localization precision. However, a significant amplification of error, nonuniformly distributed among the three major axes, occurs, and that is demonstrated. To obtain a 3D localization error of less than +/- 1.0 mm for an object with 20 mm marker spacing, the 2D localization precision must be better than +/- 0.07 mm. This requirement was met for all investigated nominal x-ray exposures at 28 cm FOV, and for all but the lowest two at 40 cm FOV. However, even for those two nominal exposures, the expected 3D localization error is less than +/- 1.2 mm. The tracking precision was +/- 0.65 mm for the out-of-plane translations, +/- 0.05 mm for in-plane translations, and +/- 0.05 degrees for the rotations. The root mean square (RMS) difference between the true and projection-Procrustes calculated location was 1.07 mm. It is believed these results show the potential of this technique for dynamic evaluations or real-time image guidance using a single x-ray source and XRII detector.

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.

Development of an RSA calibration system with improved accuracy and precision.

In this study, a new radiostereometric analysis (RSA) calibration cage was developed with the aim of improving the accuracy and precision of RSA. This development consisted of three steps: a numerical simulation technique was first used to design the new cage; a synthetic imaging method was then implemented to predict the performance of the designed cage before it was actually fabricated; and an experimental phantom test was finally conducted to verify the actual performance of the new cage and compare with two currently widely used cages. Accuracy was calculated as the 95% prediction intervals from regression analyses between the measured and actual displacements, and precision was defined as the standard deviation of repeated measurements. The final experimental phantom tests showed that the accuracy and precision of the new calibration cage were improved by about 40% over an existing biplanar cage and by about 70% compared to a uniplanar cage design. This new cage can be used with any skeletal joints, in either static or kinematic examination, which is helpful for the standardization of the RSA application.

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.

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.

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.