Precision of CT-based micromotion analysis is comparable to radiostereometry for early migration measurements in cemented acetabular cups

The full radiostereometric analysis migration pattern of tibial components is associated with aseptic loosening : introducing MTPMemax (MTPM estimated maximum)

Aims

Thresholds for acceptable amounts of migration tibial components measured with radiostereometric analysis (RSA) are limited to specific follow-up moments and do not use the full migration pattern. The Michaelis-Menten (MM) model, a non-linear model from biochemistry, could potentially be used to model the entire migration pattern. The purpose of this study was therefore to determine if MM models can be fitted to RSA migration data of tibial components, and if these fitted model parameters can be used for early detection of tibial components at high risk for aseptic loosening.

Methods

Migration patterns of tibial component maximum total point motion (MTPM) over six months, one year, and two years, as well as revision rates for aseptic loosening from previously published systematic reviews, were used. Fitted MM models gave the estimated maximal MTPM (MTPMemax) and a constant (K), which is the time in months at which half the MTPMemax is reached for tibial component designs. To assess model fit, intraclass correlation coefficients (ICCs) were calculated for the modelled MTPMemax and reported five-year MTPM values. The estimated MTPMemax and K-values were plotted against their corresponding five-year revision rate for aseptic loosening.

Results

For six-month, one-year, and two-year migration patterns, the ICC was 0.81, 0.83, and 0.91, respectively, suggesting excellent agreement between calculated MTPMemax values and the known five-year MTPM values. MTPMemax up to 1.3 mm was considered to be safe based on association with aseptic loosening revision rate, while MTPMemax of more than 1.3 mm was unsafe. The K-value could not be used as a predictor for safe versus unsafe implants.

Conclusion

MTPMemax values may be used for early detection of tibial components at high risk for aseptic loosening, possibly offering improvements over the older threshold system.

CT-based Implant Motion Analysis for diagnosing loosening of megaprostheses : validation in a clinical setting

Aims

Megaprostheses are commonly used in patients with primary bone tumours or metastases. The identification of loosening of megaprostheses in these patients using conventional radiography can be difficult. The use of CT-based Implant Motion Analysis (IMA) has been shown to identify loosening of conventional hip prostheses with great accuracy. The aim of this study was to investigate the accuracy of its use in the identification of loosening of the components of megaprostheses.

Methods

This was a retrospective, observational study in which we analyzed its efficacy for the investigation of loosening in 12 patients who underwent 13 IMA examinations, and compared the results with subsequent perioperative findings.

Results

A total of ten IMA examinations in nine patients were positive, and loosening was subsequently verified at operation in eight patients. The positive predictive value of the method was 90% and the negative predictive value was 100%. The sensitivity was 100% and the specificity was 75%.

Conclusion

We recommend the use of this method in the investigation and diagnosis of patients with a megaprosthesis with symptoms suggestive of loosening, and in the preoperative planning of revision surgery.

Effect of head size, head material, and radiation dose on the repeatability of CT-RSA measurements of femoral head penetration

BACKGROUND

The risk of early revision of total hip arthroplasty (THA) for polyethylene wear is now low, but there remains a need to perform wear measurements in patients for clinical surveillance. The gold standard of wear measurements has been radiostereometric analysis (RSA), which has limited availability. The use of computed tomography (CT) to perform THA wear measurement was described a decade ago and found to have acceptable accuracy and precision, but high radiation dose was a concern. Additionally, the use of larger femoral head sizes and ceramic femoral heads has risen in the past decade. The objectives of the study were to determine the effect of femoral head size, femoral head material, and lowered radiation dose on femoral head penetration measurement repeatability.

METHODS

A cadaveric hip was implanted with a cementless THA implant system. CT scans were acquired at a conventional radiation dose and at a reduced dose and repeated for a 32 mm and 36 mm cobalt-chromium femoral heads and a 32 mm ceramic femoral head. Apparent translation of the femoral head versus the acetabular cup was measured between the repeated scans using a CT-RSA software, where deviations from zero indicated measurement precision.

RESULTS

The mean and standard deviation of translations in all planes was <0.200 mm. There was no effect for 3D translation of increasing cobalt-chromium head size (p = 0.2252). Cobalt-chromium heads had superior repeatability compared to ceramic heads at reduced dose (p = 0.022), but not at conventional dose (p = 0.1265). Further, superior repeatability was achieved with the reduced dose scan for the cobalt-chromium head (p = 0.0058), however there was no difference between doses for the ceramic head (p = 0.8148).

DISCUSSION

CT-based wear measurement repeatability is excellent and consistent with prior literature even when implementing a larger femoral head, a ceramic femoral head, or reducing radiation dose to 25% of a conventional clinical scan.

The accuracy and precision of CT-RSA in arthroplasty: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

 Computed tomography-based radiostereometric analysis (CT-RSA) is an alternative to conventional radiostereometric analysis (RSA) in measuring implant migration, circumventing the need for operative insertion of tantalum markers. The accuracy and precision of different CT-RSA techniques in various joints are still unclear, and the effective radiation dose (ED) of CT-RSA is usually higher than RSA. In this systematic literature review, we aimed to provide an overview of the accuracy, precision, clinical precision, and ED of CT-RSA techniques.

METHODS

 We performed a systematic search in PubMed, Cochrane, and Embase databases. Main search items were "arthroplasty" AND "migration" AND "computed tomography." We included full-text English papers, using CT for migration analysis (CT-RSA) in human, animal, or synthetic models with arthroplasties, reporting accuracy and/or precision. Eligible studies were screened and reviewed by 2 authors independently. Main outcomes were accuracy, precision, and clinical precision of CT-RSA in 6 degrees of freedom. Secondary outcome was the mean ED. A meta-analysis on (clinical) precision of CT-RSA was performed.

RESULTS

 23 studies were included involving 163 patients, 20 human cadaveric, 3 porcine cadaveric, and 7 synthetic models. 6 different CT-RSA techniques were used to study 6 different joint components in cervical disc replacement and shoulder, hip, and knee arthroplasty. CT-RSA accuracy ranged between 0.02 and 0.71 mm and 0.03° and 1.00°. CT-RSA precision ranged between 0.00 and 0.47 mm and 0.00° and 1.09°. Mean precision was 0.15 mm (95% confidence interval [CI] 0.05-0.25) in the acetabulum, 0.13 mm (CI 0.00-0.28) and 0.24° (CI 0.00-0.51) in the proximal femur, and 0.04 mm (CI 0.00-0.08) and 0.07° (CI 0.00-0.15) in the proximal tibia. CT-RSA clinical precision ranged between 0.03 and 1.36 mm and 0.06° and 2.25°. Mean clinical precision was 0.13 mm (CI 0.11-0.16) and 0.26° (CI 0.20-0.32) in the acetabulum. The mean ED of CT-RSA ranged between 0.02 and 5.80 mSv.

CONCLUSION

 CT-RSA shows comparable accuracy and precision to standard RSA. CT-RSA seems to be a promising alternative to RSA.

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.

Precision of computer tomography based RSA on femoral implants in total knee arthroplasty: A porcine cadaver study

BACKGROUND

Radiostereometric analysis is the gold standard for assessing migration of orthopaedic implants. The novel CT-based radiostereometric analysis yields high precision of evaluation of tibial implants. We analyzed the precision of CT-based radiostereometric analysis on femoral implants in knee arthroplasty at different dose levels, and compared it to previously published results on tibial implants and the available literature on precision of radiostereometric analysis.

METHODS

We performed a total knee arthroplasty on a porcine cadaver knee. In the subsequent 7 CT scans, we analyzed the precision of the CT-based radiostereometric analysis method in 21 samples at two different effective doses (standard and low dose), and compared this to literature on radiostereometric analysis.

FINDINGS

CT-based radiostereometric analysis of maximum total point motion of femoral and tibial components showed a precision difference of (mean, 95 % confidence interval) 0.18 mm (0.13 to 0.22), P < 0.001. For femoral implants (mean, 95 % confidence interval, standard deviation) we found precisions of 0.25 mm (0.21-0.29, 0.1) and 0.29 (0.25-0.32, 0.08) mm for the standard and low dose protocols respectively. Variability ratios of tibia versus femur and standard versus low dose femur (95 % confidence interval) were 18.3 (7.4-45.1) and 0.7 (0.3-1.7) with respective P-values of <0.001 and 0.40.

INTERPRETATION

CT-based radiostereometric analysis on femoral implants in total knee arthroplasty is feasible and has a lower, yet still acceptable, precision compared to CT-based radiostereometric analysis on tibial implants in a porcine cadaver. However, confirmation in clinical studies is warranted.

CT-based migration analysis of a tibial component compared to radiostereometric analysis : one-year results of a prospective single-group implant safety study

Aims

Radiostereometric analysis (RSA) is considered the gold standard for in vivo migration analysis, but CT-based alternatives show comparable results in the shoulder and hip. We have previously validated a CT-based migration analysis method (CTMA) in a knee phantom compared to RSA. In this study, we validated the method in patients undergoing total knee arthroplasty (TKA). Our primary outcome measure was the difference in maximum total point motion (MTPM) between the differing methods.

Methods

A total of 31 patients were prospectively studied having undergone an uncemented medial pivot knee TKA. Migrations were measured up to 12 months with marker-based and model-based RSA, and CT-RSA.

Results

Mean precision data for MTPM were 0.27 mm (SD 0.09) for marker-based RSA, 0.37 mm (SD 0.26) for model-based RSA, and 0.25 mm (SD 0.11) for CTMA. CTMA was as precise as both RSA methods (p = 0.845 and p = 0.156). At three months, MTPM showed a mean of 0.66 mm (95% CI 0.52 to 0.81) for marker-based RSA, 0.79 (95% CI 0.64 to 0.94) for model-based RSA, and 0.59 (95% CI 0.47 to 0.72) for CTMA. There was no difference between CTMA and marker-based RSA (p = 0.400), but CTMA showed lower migration than model-based RSA (p = 0.019). At 12 months, MTPM was 1.03 (95% CI 0.79 to 1.26) for marker-based RSA, 1.02 (95% CI 0.79 to 1.25) for model-based RSA, and 0.71 (95% CI 0.48 to 0.94) for CTMA. MTPM for CTMA was lower than both RSA methods (p < 0.001). Differences between migration increased between the methods from three to 12 months. Mean effective radiation doses per examination were 0.016 mSv (RSA) and 0.069 mSv (CT). Imaging time for performing RSA radiographs was 17 minutes 26 seconds (SD 7 mins 9 sec) and 4 minutes 24 seconds (SD 2 mins 3 sec) for CT.

Conclusion

No difference in precision was found between CTMA and marker- or model-based RSA, but CTMA shows lower migration values of the tibial component at 12 months. CTMA can be used with low effective radiation doses, and CT image acquisition is faster to perform than RSA methods and may be suitable for use in ordinary clinical settings.

Comparison of the CT-based micromotion analysis method versus marker-based RSA in measuring femoral head translation and evaluation of its intra- and interobserver reliability: a prospective agreement diagnostic study on 27 patients up to 1 year

BACKGROUND AND PURPOSE

 Computed tomography radiostereometric analysis (CT-RSA) assesses implant micromovements using low-dose CT scans. We aimed to investigate whether CT-RSA is comparable to marker-based radiostereometric analysis (RSA) measuring early femoral head migration in cemented stems. We hypothesized that CT-RSA is comparable to marker-based RSA in evaluating femoral head subsidence.

METHODS

 We prospectively included 31 patients undergoing cemented total hip arthroplasty (THA), of which 27 were eligible for the analysis. Femoral head migration at 1 year was measured with marker-based RSA and CT-RSA. Comparison was performed using paired analysis and Bland-Altman plots, and the intra- and interobserver reliability of CT-RSA was assessed Results: The median (interquartile range [IQR]) translation on the Y-axis measured with marker-based RSA was -0.86 mm (-1.10 to -0.37) and -0.83 mm (-1.11 to -0.48) for CT-RSA (i.e. subsidence), with a median difference of -0.03 mm (95% confidence interval [CI] -0.08 to 0.18). The minimal important difference in translation was set to 0.2 mm. This value was excluded from the CI of the differences. No statistical difference was found between marker-based RSA and CT-RSA regarding assessment of subsidence of the femoral head. The Bland-Altman plots showed good agreement between the 2 methods in measuring subsidence of the femoral head. The intra- and interobserver reliability of the CT-RSA method was excellent with intraclass correlation coefficient (ICC) = 1 (0.99-1) and ICC = 0.99 (0.99-1), respectively.

CONCLUSION

 We showed that CT-RSA was comparable to marker-based RSA in measuring femoral head subsidence. Moreover, the intra- and interobserver reliability of the CT-RSA method was excellent, suggesting that the method is assessor independent.

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.

Bone remodeling after revision total hip arthroplasty for large acetabular defects

Large acetabular bone defects are challenging in hip revision surgery. Clinical assessment is crucial to evaluate modern technologies in surgical reconstruction. We aimed to better understand the bone remodeling that occurs following acetabular reconstruction. Our objectives were: (1) To characterize changes in the shape of the pelvis by studying sequential computed tomography (CT) scans collected immediately and 1-year postoperatively and (2) to identify which part of the pelvis is most susceptible to remodeling. We used the CT scans taken at two timepoints, of 24 patients with acetabular bone defects classified as Paprosky IIIB, treated with three-dimensional (3D)-printed custom-made acetabular implants. Segmented 3D models of the bony pelvis were co-registered using three different techniques. A global co-registration of the full pelvis was conducted, followed by the co-registration of the innominate bone and then ilium only, on the ipsilateral reconstructed side. The relative movements of the ilium, ischium, and pubis were analyzed from visual inspection and using co-registration metrics (root mean square error and intersection over union). No bone remodeling was found in 14/24 patients (58%). The co-registration of the innominate bone indicated bone remodeling in five cases (21%), while the remaining five cases (21%) presented remodeling in the global co-registration but not the innominate bone co-registration, suggestive of changes occurring at the sacroiliac joint. Changes in the pelvic shape were greatest at the pubis and ischium. Bone remodeling may occur in complex cases of Paprosky type IIIB defects, after acetabular reconstruction (occurrence of 21%, 5/24 cases). Surgeons and engineers should consider this when monitoring implant migration.

Computational modeling of revision total hip arthroplasty involving acetabular defects: A systematic review

Revision total hip arthroplasty (rTHA) involving acetabular defects is a complex procedure associated with lower rates of success than primary THA. Computational modeling has played a key role in surgical planning and prediction of postoperative outcomes following primary THA, but modeling applications in rTHA for acetabular defects remain poorly understood. This study aimed to systematically review the use of computational modeling in acetabular defect classification, implant selection and placement, implant design, and postoperative joint functional performance evaluation following rTHA involving acetabular defects. The databases of Web of Science, Scopus, Medline, Embase, Global Health and Central were searched. Fifty-three relevant articles met the inclusion criteria, and their quality were evaluated using a modified Downs and Black evaluation criteria framework. Manual image segmentation from computed tomography scans, which is time consuming, remains the primary method used to generate 3D models of hip bone; however, statistical shape models, once developed, can be used to estimate pre-defect anatomy rapidly. Finite element modeling, which has been used to estimate bone stresses and strains, and implant micromotion postoperatively, has played a key role in custom and off-the-shelf implant design, mitigation of stress shielding, and prediction of bone remodeling and implant stability. However, model validation is challenging and requires rigorous evaluation and comparison with respect to mid- to long-term clinical outcomes. Development of fast, accurate methods to model acetabular defects, including statistical shape models and artificial neural networks, may ultimately improve uptake of and expand applications in modeling and simulation of rTHA for the research setting and clinic.

Evaluation of Cervical Vertebral Motion and Foraminal Changes During the Spurling Test Using Zero Echo Time Magnetic Resonance Imaging and Computed Tomography-Based Micromotion Analysis

STUDY DESIGN

Clinical experimental diagnostic study.

OBJECTIVE

The objective of the study was to investigate cervical spine dynamics including changes in the cervical foramina in patients experiencing intermittent arm radiculopathy.

BACKGROUND

Cervical foraminal stenosis is a frequent cause of radicular arm pain. The Spurling test, while specific, lacks the precision to identify symptomatic nerve roots. The relationship among vertebral motion, foraminal changes, and radiculopathy during a Spurling test remains underexplored.

PATIENTS AND METHODS

Ten patients with positive Spurling tests and magnetic resonance imaging (MRI) confirmed 1 or 2-level cervical foraminal stenosis were scanned using the Dynamic MRI Compression System enabling a simulated Spurling test inside the MRI gantry of a 3T MRI scanner with a dedicated neck coil. First, a relaxed image acquisition was undertaken, followed by slowly applying the Spurling test until the patient reported aggravation of radiculopathy or discomfort, where the next image series was taken. Zero echo time MRI was employed to obtain computed tomography (CT)-like images. The images were thereafter analyzed using the Sectra® CT-based Micromotion Analysis software for motion analysis.

RESULTS

The C4/C5 level exhibited the most significant movements both in translation and rotation, with less movements observed in C5 to C6 and C6 to C7 levels. No uniform pattern emerged that differentiated suspected stenotic levels from nonsuspected levels. Despite relatively small vertebral movements, 9/10 of patients reported arm pain during provocation, indicating extremely narrow margins of tolerance.

CONCLUSION

This study demonstrates the utility of zero echo time MRI and CT-based Micromotion Analysis in detecting subtle yet clinically relevant vertebral motions influencing the foramina in the cervical spine during the Spurling maneuver. These findings could lead to a better understanding and potentially improved diagnostic strategies for cervical foraminal stenosis, although further research with a larger cohort is necessary to confirm these results.

Comparison between model-based RSA and an AI-based CT-RSA: an accuracy study of 30 patients

BACKGROUND AND PURPOSE

Radiostereometry (RSA) is the current gold standard for evaluating early implant migration. CT-based migration analysis is a promising method, with fewer handling requirements compared with RSA and no need for implanted bone-markers. We aimed to evaluate agreement between a new artificial intelligence (AI)-based CT-RSA and model-based RSA (MBRSA) in measuring migration of cup and stem in total hip arthroplasty (THA).

PATIENTS AND METHODS

30 patients with THA for primary osteoarthritis (OA) were included. RSA examinations were performed on the first postoperative day, and at 2 weeks, 3 months, 1, 2, and 5 years after surgery. A low-dose CT scan was done at 2 weeks and 5 years. The agreement between the migration results obtained from MBRSA and AI-based CT-RSA was assessed using Bland-Altman plots.

RESULTS

Stem migration (y-translation) between 2 weeks and 5 years, for the primary outcome measure, was -0.18 (95% confidence interval [CI] -0.31 to -0.05) mm with MBRSA and -0.36 (CI -0.53 to -0.19) mm with AI-based CT-RSA. Corresponding proximal migration of the cup (y-translation) was 0.06 (CI 0.02-0.09) mm and 0.02 (CI -0.01 to 0.05) mm, respectively. The mean difference for all stem and cup comparisons was within the range of MBRSA precision. The AI-based CT-RSA showed no intra- or interobserver variability.

CONCLUSION

We found good agreement between the AI-based CT-RSA and MBRSA in measuring postoperative implant migration. AI-based CT-RSA ensures user independence and delivers consistent results.

Load-induced deformation of the tibia and its effect on implant loosening detection

CT imaging under external valgus and varus loading conditions and consecutive image analysis can be used to detect tibial implant loosening after total knee arthroplasty. However, the applied load causes the tibia to deform, which could result in an overestimation of implant displacement. This research evaluates the extent of tibia deformation and its effect on measuring implant displacement. Ten cadaver specimen with TKA were CT-scanned under valgus/varus loading (20 Nm), first implanted without bone cement fixation (mimicking a loose implant) and subsequently with bone cement fixation (mimicking a fixed implant). By means of image analysis, three relative displacements were assessed: (1) between the proximal and distal tibia (measure of deformation), (2) between the implant and the whole tibia (including potential deformation effect) and (3) between the implant and the proximal tibia (reduced deformation effect). Relative displacements were quantified in terms of translations along, and rotations about the axes of a local coordinate system. As a measure of deformation, the proximal tibia moved relative to the distal tibia by, on average 1.27 mm (± 0.50 mm) and 0.64° (± 0.25°). Deformation caused an overestimation of implant displacement in the cemented implant. The implant displaced with respect to the whole tibia by 0.45 mm (± 0.22 mm) and 0.79° (± 0.38°). Relative to the proximal tibia, the implant moved by 0.23 mm (± 0.10 mm) and 0.62° (± 0.34°). The differentiation between loose and fixed implants improved when tibia deformation was compensated for by using the proximal tibia rather than the whole tibia.

CT-Based Micromotion Analysis After Locking Plate Fixation of AO Type C Distal Radius Fractures

Background

Volar locking plate fixation (VLPF) is the most common method for operative fixation of distal radius fractures (DRF). The dorsal ulnar corner (DUC) can be difficult to stabilize as the fragment is small and not exposed when using the volar approach. The purpose of this study was to study fracture fragment migration after VLPF of AO type C DRF, using a volume registration technique of paired CT scans with special focus on the DUC fragment.

Materials and Methods

This pilot study included ten patients with AO type C DRF, all operated with VLPF. The primary outcome was radiographic outcome. Postoperative and 1-year scans were compared and analyzed. Fragment migration was assessed with CT-based micromotion analysis (CTMA), a software technique used for volume registration of paired CT scans.

Results

All plates were stable over time. Two patients showed signs of screw movement (0.2-0.35 mm and 0.35- > 1 mm respectively). Postoperative reduction was maintained, and there was no fragment migration at the 1-year follow-up except for one case with increased dorsal tilt. The DUC fragment was found in 8/10 cases, fixated in 7/8 cases, and not dislocated in any case at the 1-year follow-up.

Conclusion

The CTMA results indicate that variable-angle VLPF after AO type C DRF can yield and maintain a highly stable reduction of the fracture fragments. The DUC fragment remained stable regardless of the number of screws through the fragment. CT volume registration can be a valuable tool in the detailed assessment of fracture fragment migration following volar plate fixation of DRFs.

Dose reduction does not impact the precision of CT-based RSA in tibial implants: a diagnostic accuracy study on precision in a porcine cadaver

BACKGROUND AND PURPOSE

Radiostereometric analysis (RSA) is the gold standard for evaluation of migration of implants. CT-RSA has been shown to have precision at the level of RSA in hip, shoulder, and knee joint replacements. We aimed to assess the impact of dose reduction on precision of CT-RSA on tibial implants, comparing it with previously published data on precision of standard dose CT-RSA on tibial implants.

MATERIAL AND METHODS

We performed a total knee arthroplasty on a porcine knee cadaver, and subsequent CT-RSA with low effective doses (0.02 mSv). We compared the results with previously published CT-RSA data with standard (0.08 mSv) dose. The primary outcome variable was the difference in precision of the maximum total translation (MTT). Secondary variables included ratios of variances and standard deviations, and precision of peripheral point translations, center-of-mass translations, and rotations. A difference of more than 0.1 mm in precision was defined as clinically relevant. Our hypothesis was that precisions of low and standard CT-RSA doses were equal.

RESULTS

Low dose (mean 0.07, 95% confidence interval [CI] 0.06-0.08) and standard dose CT-RSA (0.08, CI 0.07-0.09) achieve similar precision, with difference in precision of MTT of 0.01, CI 0.00-0.02 mm. The F-statistic (0.99, CI 0.63-1.55) and sdtest (1.05, CI 0.43-2.58) also supported this.

CONCLUSION

We conclude that the precision of low dose CT-RSA for tibial implants on a porcine cadaver is equal to standard dose CT-RSA. However, these findings should be confirmed in clinical trials.

Computed tomography micromotion analysis in the follow-up of patients with surgically treated pelvic fractures: a prospective clinical study

PURPOSE

High-energy pelvic fractures are complex injuries often requiring surgical treatment. Different radiological methods exist to evaluate the reduction and healing process postoperatively but with certain limitations. The aim of this study was to evaluate Computed Tomography Micromotion Analysis (CTMA) in a clinical setting for follow-up of surgically treated pelvic fracture patients.

METHODS

10 patients surgically treated for a pelvic fracture were included and prospectively followed with Computed Tomography (CT) at 0, 6, 12 and 52 weeks postoperatively. CTMA was used to measure postoperative translation and rotation of the pelvic fracture during the 52 weeks follow-up. Clinical outcomes were collected through the questionnaires EQ-5D index score and Majeed score.

RESULTS

10 patients were included with mean age (± SD, min-max) 52 (16, 31-80) years and 70% (n = 7) were males. The median (IQR, min-max) global translation from 0 to 52 weeks was 6.0 (4.6, 1.4-12.6) millimeters and median global rotation was 2.6 (2.4, 0.7-4.7) degrees. The general trend was a larger translation between 0 and 6 weeks postoperatively compared to 6-12 and 12-52 weeks. For the clinical outcomes, the general trend was that all patients started from high scores which decreased in the first postoperative follow-up and recovered to different extent during the study period.

CONCLUSION

CTMA was successfully used in the follow-up of surgically treated pelvic fracture patients. Movement in the pelvic fractures after surgical fixation was largest between 0 and 6 weeks.

CT-based migration analysis is more precise than radiostereometric analysis for tibial implants: a phantom study on a porcine cadaver

BACKGROUND AND PURPOSE

Radiostereometric analysis (RSA) is the gold standard for migration analysis, but computed tomography analysis methods (CTRSA) have shown comparable results in other joints. We attempted to validate precision for CT compared with RSA for a tibial implant.

MATERIAL AND METHODS

RSA and CT were performed on a porcine knee with a tibial implant. Marker-based RSA, model-based RSA (MBRSA), and CT scans from 2 different manufacturers were compared. CT analysis was performed by 2 raters for reliability evaluation.

RESULTS

21 double examinations for precision measurements for RSA and CT-based Micromotion Analysis (CTMA) were analysed. Mean (95% confidence interval) precision data for maximum total point motion (MTPM) using marker-based RSA was 0.45 (0.19-0.70) and 0.58 (0.20-0.96) using MBRSA (F-statistic 0.44 [95% CI 0.18-1.1], p = 0.07). Precision data for total translation (TT) for CTMA was 0.08 (0.03-0.12) for the GE scanner and 0.11 (0.04-0.19) for the Siemens scanner (F-statistic 0.37 [0.15-0.91], p = 0.03). When comparing the aforementioned precision for both RSA methods with both CTMA analyses, CTMA was more precise (p < 0.001). The same pattern was seen for other translations and migrations. Mean effective radiation doses were 0.005 mSv (RSA) (0.0048-0.0050) and 0.08 mSv (CT) (0.078-0.080) (p < 0.001). Intra- and interrater reliability were 0.79 (0.75-0.82) and 0.77 (0.72-0.82), respectively.

CONCLUSION

CTMA is more precise than RSA for migration analysis of a tibial implant, has overall good intra- and interrater reliability but higher effective radiation doses in a porcine cadaver.

Low dose CT-based spatial analysis (CTSA) to measure implant migration after ceramic hip resurfacing arthroplasty (HRA): A phantom study

Implant migration is a predictor of arthroplasty survivorship. It is crucial to monitor the migration of novel hip prostheses within premarket clinical investigations. RSA is the gold standard method, but requires calibrated radiographs using specialised equipment. A commercial computed tomography micromotion analysis solution is a promising alternative but is not yet available for use with monobloc ceramic implants. This study aimed to develop and validate a CT-based spatial analysis (CTSA) method for use with ceramic implants. A phantom study was undertaken to assess accuracy and precision. A ceramic hip resurfacing arthroplasty (HRA) and 20 tantalum beads were implanted into a synthetic hip model and mounted onto a 6-degree of freedom motion stage. The hip was repeatedly scanned with a low dose CT protocol, with imposed micromovements. Data were interrogated using a semiautomated technique. The effective radiation dose for each scan was estimated to be 0.25 mSv. For the head implant, precision ranged between 0.11 and 0.28 mm for translations and 0.34°-0.42° for rotations. For the cup implant, precision ranged between 0.08 and 0.11 mm and 0.19° and 0.42°. For the head, accuracy ranged between 0.04 and 0.18 mm for translations and 0.28°-0.46° for rotations. For the cup, accuracy ranged between 0.04 and 0.08 mm and 0.17° and 0.43°. This in vitro study demonstrates that low dose CTSA of a ceramic HRA is similar in accuracy to RSA. CT is ubiquitous, and this method may be an alternative to RSA to measure prosthesis migration.

How Do Classic (Static) RSA and Patient Motion Artifacts Affect the Assessment of Migration of a TKA Tibial Component? An In Vitro Study

BACKGROUND

Classic (static) Roentgen stereophotogrammetric analysis (RSA) is the current gold standard to assess, in vivo, the migration of total joint arthroplasty components. To prevent potential patient motion artifacts during the acquisition of paired radiostereometric images, images must be taken by simultaneously firing both X-ray tubes. However, the influence of nonsynchronized RSA paired images or patient motion artifacts on the precision of RSA and the assessment of implant migration is not well understood.

QUESTIONS/PURPOSES

We assessed (1) the effect of possible patient motion on the precision of RSA and (2) apparent differences in implant migration among axes (in-plane and out-of-plane translations and in-plane and out-of-plane rotations) of possible motion artifacts.

METHODS

Radiographs of two tibial knee arthroplasty components, each fixed in two bone-implant models as a customized phantom, were taken in a uniplanar measurement setup. We evaluated both model-based (implant models from reversed engineering) and marker-based (additional attached implant markers) RSA approaches. Between the simulated reference and follow-up examinations, we used one of the bone-implant models to simulate patient motion and the other to simulate no patient motion in parallel. Two defined protocols were followed for each of the bone-implant models: no-motion and simulated motion protocols. RSA image pairs were analyzed using a model-based RSA software package (MBRSA 4.1, RSA core ). Precision was calculated through repeat examinations, and migration of the two components was assessed for comparison of the components with each other. Measurements were taken along the medial-lateral and posterior-anterior axes for translations and around the cranial-caudal axis for rotations. The maximum total point motion was measured for comparison between the two components.

RESULTS

The effect of simulated patient motion was generally small, except in the cranial-caudal axis, but the induced imprecision associated with motion was larger in model-based RSA than it was in marker-based RSA. The mean ± standard deviation values of precision in model-based RSA were 0.035 ± 0.015 mm, 0.045 ± 0.014 mm, and 0.049 ± 0.036 mm greater than those in marker-based RSA, in accordance with the simulated motion protocol in translations along the medial-lateral axis (0.018 ± 0.004 mm; p = 0.01), along the posterior-anterior axis (0.018 ± 0.007 mm; p = 0.003), and rotations around the cranial-caudal axis (0.017 ± 0.006 mm; p = 0.02). Apparent differences in implant migration were the greatest for the maximum total point motion. The maximum total point motion increased from 0.038 ± 0.007 mm for the no-motion protocol to 1.684 ± 0.038 mm (p < 0.001) for the simulated motion protocol in marker-based RSA, and from 0.101 ± 0.027 mm for the no-motion protocol to 1.973 ± 0.442 mm (p < 0.001) for the simulated motion protocol in model-based RSA, and was the worst-case scenario regarding patient motion artifacts.

CONCLUSION

Patient motion exceeding 1 mm or 1° on nonsynchronized RSA images affects measurement errors regarding the detection of migration of a tibial component. In clinical RSA studies, the effect of patient motion on the assessment of implant migration should be of particular concern, even if clinical RSA systems have acceptable precision. Specially trained radiographers are crucial for correctly acquiring radiographs, especially when simultaneous radiography exposures are not electronically automated. In general, RSA requires synchronized image acquisition, and this should be the state-of-the-art.

CLINICAL RELEVANCE

In clinical RSA studies, precision assessed by repeat examinations may not be reliable using the current standards that are widely used in radiology departments. When assessing implant migration for reliability, comparison of the maximum total point motion between the tested (simulated motion) implant and baseline (no-motion) implant, as in this study, is advocated because of the accurate detection of patient motion artifacts.

Accuracy of radiostereometric analysis using a motorized Roentgen system in a pilot study for clinical simulation

Radiostereometric analysis (RSA) is routinely implemented with two paired Roentgen tubes for three-dimensional (3D) implant migration measurements. A conventional set-up of one stationary tube and one mobile could be time-consuming. Utilizing two customized ceiling-mounted tubes is normally associated with investment costs. Thus, a pilot set-up of a motorized system (single Roentgen source) for radiostereometric image acquisition may be a time-saving and space-efficient alternative. RSA using the motorized system is feasible in this study as a non-synchronized image acquisition technique, however, patient motion may occur and influence the assessment of implant migration. The phantom study aimed to assess accuracy of RSA using the motorized Roentgen system in this in vitro study. Accuracy values of translations and rotations were ±0.29 mm and ±0.48° for the single Roentgen source RSA set-up and ±0.26 mm and ±0.48° for the conventional RSA set-up. This study was also performed to simulate potential patient motion during exposure intervals between paired image acquisition. RSA using the motorized system is able to implement RSA with acceptable accuracy. In general, RSA with synchronized image acquisition is the gold standard to access in vivo implant migration with the highest accuracy. Patient motion exists in non-synchronized image acquisition techniques and results in RSA-related motion artifacts. Then we introduced what RSA-related motion artifacts are. The uniplanar calibration cage applied in the study has a few fiducial and control markers, and some of the markers were occluded in radiographs. Whereas, the number of markers in the calibration cage is correlated with accuracy of 3D implant reconstruction.

Precision of low-dose CT-based micromotion analysis technique for the assessment of early acetabular cup migration compared with gold standard RSA: a prospective study of 30 patients up to 1 year

BACKGROUND AND PURPOSE

Computed tomography micromotion analysis (CTMA) can be used to determine implant micro-movements using low-dose CT scans. By using CTMA, a non-invasive measurement of joint implant movement is enabled. We evaluated the precision of CTMA in measuring early cup migration. Standard marker-based radiostereometric analysis (RSA) was used as reference. We hypothesised that CTMA can be used as an alternative to RSA in assessing implant micromotions.

PATIENTS AND METHODS

We included 30 patients undergoing total hip arthroplasty (THA). Acetabular cup migration at 1 year was measured with RSA and CTMA. To determine the precision of both methods, 20 double examinations (postoperatively) with repositioning of the patients were performed. The precision was calculated from zero by assuming that there was no motion of the prosthesis between the 2 examinations.

RESULTS

The precision of RSA ranged from 0.06 to 0.15 mm for translations and 0.21° to 0.63° for rotations. Corresponding values for CTMA were 0.06 to 0.13 mm and 0.23° to 0.35°. A good level of agreement was found between the methods regarding cup migration and rotation at 1 year.

INTERPRETATION

The precision of CTMA in measuring acetabular cup migration and rotation is comparable to marker-based RSA. CTMA could possibly thus be used as an alternative method to detect early implant migration.

CT-based micromotion analysis method can assess early implant migration and development of radiolucent lines in cemented glenoid components: a clinical feasibility study

BACKGROUND AND PURPOSE

CT micromotion analysis (CTMA) has been considered as an alternative to radiostereometry (RSA) for assessing early implant migration of orthopedic implants. We investigated the feasibility of CTMA to assess early migration and the progression of radiolucent lines in shoulder arthroplasties over 24 months using sequential low-dose CT scans.

PATIENTS AND METHODS

7 patients were included and underwent 9 primary total shoulder arthroplasties. We made CT scans preoperatively, within 1 week postoperatively, and after 3, 6, 12, and 24 months. At each follow-up, postoperative glenoid migration and any development of radiolucent lines were assessed. Clinical outcomes were recorded at all time points except within 1 week postoperatively.

RESULTS

For the glenoid component, the median translation and median rotation were 0.00-0.10 mm and -1.53° to 1.05° at 24 months. Radiolucent lines could be observed around all glenoid components. The radiolucent lines developed from the periphery to the center of the implant for 6 glenoid components during follow-up. The Constant Score improved from a mean of 30 (21-51) preoperatively to 69 (41-88) at 24 months.

INTERPRETATION

CTMA can be used to identify early migration and the development of radiolucent lines over time in glenoid components. Clinical trials with a larger sample size and longer follow-up are needed to establish the relationship between migration, radiolucent lines, loosening, and clinical outcome.