Roentgen Stereophotogrammetric Research Articles

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

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

Less wear in deep-dished mobile compared to fixed bearing total knee arthroplasty of the same design at 5-year follow-up: a randomised controlled model-based Roentgen stereophotogrammetric analysis trial.

The aim of this prospective randomised controlled study was to compare wear characteristics and functional outcome between deep-dished mobile bearing (MB) and fixed bearing (FB) cemented total knee arthroplasty (TKA). We hypothesised that deep-dished MB reduces polyethylene wear and improves patient-reported outcome measures. A total of 50 patients were randomised to receive a MB or FB tibia component of the same cemented TKA design. Patients were evaluated over a 5-year follow-up period. Medial and lateral wear were assessed using model-based Roentgen Stereophotogrammetric Analysis (RSA) and compared with the direct postoperative minimal joint space measurement. Functional outcome was assessed by the clinician-derived KSS and OKS, WOMAC, LEAS, and FJS-12. All data were derived using a general linear mixed model. At 5-year follow-up, decreased wear in the MB compared to the FB group was observed on the lateral side (0.07 ± 0.17mm, p = 0.026), but not on the medial side (0.31 ± 0.055mm, p = 0.665). Functional outcomes improved with a statistical significant effect over time, with no significant differences between groups (all p > 0.17). This model-based RSA study with 5-year follow-up showed that cemented deep-dished MB reduced lateral polyethylene wear as compared to FB in a single TKA system, whilst clinical outcomes were comparable. Longer follow-up is needed to establish clinical implications of these altered wear patterns and determine type of wear. Level 1 randomised controlled trial.

FIVE-YEAR RSA RESULTS ASSESSING SUBSIDENCE AND ROTATION OF THE PARAGON HIP SYSTEM CONFIRMING IMPLANT STABILITY

Roentgen Stereophotogrammetric Analysis (RSA) is the gold standard for measuring implant micromotion thereby predicting implant loosening. Early migration has been associated with the risk of long-term clinical failure. We used RSA to assess the stability of the Australian designed cementless hip stem (Paragon TM) and now report our 5-year results.Fifty-three patients were prospectively and consecutively enrolled to receive a Paragon hip replacement. Tantalum beads were inserted into the bone as per RSA protocol and in the implant. RSA x-rays were taken at baseline 1–4 days post-surgery, at 6 weeks, 6 months, 12 months, 2 years, and 5 years. RSA was completed by an experienced, independent assessor.We reported the 2-year results on 46 hips (ANZJS 91 (3) March 2021 p398) and now present the 5-year results on 27 hips. From the 2-year cohort 5 patients had died, 8 patients were uncontactable, 1 patient was too unwell to attend, 5 patients had relocated too far away and declined. At 5 years the mean axial subsidence of the stem was 0.66mm (0.05 to 2.96); the mean rotation into retroversion was 0.49˚ (−0.78˚ to 2.09˚), rotation of the stem into valgus was −0.23˚ (−0.627˚ to 1.56˚). There was no detectable increase in subsidence or rotation between 6 weeks and 5 years. We compared our data to that published for the Corail cementless stem and a similar pattern of migration was noted, however greater rotational stability was achieved with the Paragon stem over a comparable follow-up period.The RSA results confirm that any minor motion of the Paragon cementless stem occurs in the first 6 weeks after which there is sustained stability for the next 5 years. The combination of a bi-planar wedge and transverse rectangular geometry provide excellent implant stability that is comparable to or better than other leading cementless stems.

Preliminary Results of a Prospective Clinical and Radiological Study with Roentgen Stereophotogrammetric Analysis (RSA) after Implantation of a Posterior Dynamic Stabilization Device in the Lumbar Spine

Introduction: Posterior dynamic stabilization (PDS) can be based on interspinous distraction devices (IDD). The goals of these implants are maintaining or restoring intervertebral range of motion (ROM) in a controlled fashion and avoiding a complete restriction of mobility. Clinical and radiological data with the Wallis® spacer as one type of IDD have been rarely reported. The goal of this study was to present clinical and radiological data including roentgen stereophotogrammetric analysis (RSA) after a short- to mid-term follow-up period.
 Patients and Methods: 10 patients were included in this prospective monocentric study and had PDS of the lumbar spine with an IDD (Wallis® spacer). Before and soon after operation and 3, 6, and 12 months later clinical and radiological evaluations were performed. Pain and disability were analyzed by use of visual analog scale for back and leg pain, Oswestry Disability Index, Roland-Morris Disability Questionnaire and Short-Form-36 Health Survey. The ROM of the operated levels and the total lumbar spine was determined by use of lateral functional x-ray images with calculation of the differences of the segmental and total lumbar spine angles in flexion and extension. Furthermore, RSA was used to measure the segmental ROM.
 Results: After a follow-up of 12 months, the results of the pain intensity and the disability and health related quality of life scores showed statistical significant improvement. The segmental angles of the operated levels demonstrated statistical significant reduction in ROM during the different follow-up examinations. The discrepancy of the conventionally determined segmental angles and the data measured by RSA were low with a mean of 1.77°. The mean total lumbar spine angles did not change statistically significantly during the postoperative controls.
 Conclusions: According to the radiological results of this study, the used implant leads to a posterior dynamic stabilization. The clinical findings are promising, but they are to be interpreted with caution because of the small number of patients and the lack of a control group.

Five-Year Prospective Roentgen Stereophotogrammetric and Clinical Outcomes of the BioPro MTP-1 Hemiarthroplasty.

Mixed results for functional outcomes and long-term fixation have been reported for first metatarsophalangeal arthroplasty. This prospective study was designed to evaluate the migration of the BioPro metatarsophalangeal-1 (MTP-1) joint hemiprosthesis with Roentgen stereophotogrammetric analysis (RSA). Migration patterns of the prosthesis, prosthesis-induced erosion of the metatarsal bone, and clinical outcomes were evaluated sequentially to 5 years postoperation (PO). Eleven female patients received the BioPro-1 hemiprosthesis. Prosthesis translation and metatarsal erosion were measured with RSA at immediately PO, 6 weeks, and 3, 6, 12, 36, and 60 months postoperatively. Clinical assessment was done by patient questionnaires. RSA data of 9 patients were available for analysis. Median (range) number of markers used in RSA analysis, condition number, and mean error of markers around the prosthesis were 4 (3-7), 320 (208-862), and 0.13 (0.02-0.28), respectively. Progressive subsidence was seen up to 3 years PO (mean 2.1 mm, SE 0.32). Progressive metatarsal erosion was found from 1 year PO (mean 0.49 mm, SE 0.15). Pain, function, and quality scores improved after surgery and did not deteriorate at later follow-up moments. Model-based RSA of the BioPro-1 prosthesis shows nonstabilizing medial and distal translation and metatarsal erosion. Despite the measured migration and erosion, clinical outcomes improved and remained similar up to 5 years postoperation. Level II, prospective analysis of MTP-1 hemiprosthesis.

Model-Based Roentgen Stereophotogrammetric Analysis Using Elementary Geometrical Shape Models: Reliability of Migration Measurements for an Anatomically Shaped Femoral Stem Component

Elementary Geometrical Shape (EGS) models present an alternative approach to detect in vivo migration of total hip arthroplasty using model-based Roentgen Stereophotogrammetric Analysis (mbRSA). However, its applicability for an irregular-shaped femoral stem and the reliability of this mbRSA approach has not been proven so far. The aim of this study is to assess the effect of multi-rater and an anatomically shaped femoral stem design onto resulting implant to bone migration results. The retrospective analysis included 18 clinical cases of anatomically shaped stem with 10-year RSA follow-ups. Three raters repeatedly measured all RSA follow-ups for evaluating the rater equivalence and intra-rater reliability. The results proved the equivalence between different raters for mbRSA using EGS models (mbRSA-EGS), hence it simplified the investigation of rater reliability to intra-rater reliability. In all in-plane migration measurements, mbRSA-EGS shows good intra-rater reliability and small intra-rater variability (translation: <0.15 mm; rotation: <0.18 deg). However, the reliability is worse in the out-of-plane measurements, especially the cranial-caudal rotation (intra-rater variability: 0.99–1.81 deg). Overall, mbRSA-EGS can be an alternative approach next to surface models while the in-plane migration of femoral stem (e.g., the implant subsidence for loosening prediction) have more research interested than other directions.

Früherkennung des Risikos der späteren Implantatlockerung mittels der Röntgen Stereophotogrammetrischen Analyse (RSA)

Aseptic implant loosening is the most common cause of implant revisions in total hip and total knee arthroplasty. Roentgen Stereophotogrammetric Analysis (RSA) represents the current gold standard for the in-vivo assessment of implant fixation. Long-term clinical trials have shown that continuous implant migration within the first two postoperative years correlates strongly with alater aseptic loosening. Thus, the implant migration measured with RSA can be regarded as areliable surrogate marker for later implant loosening. Over the past 40years, RSA has been continuously further developed, and the model-based RSA approach has reduced the effort involved since markers attached to implant are no longer needed. The RSA method is gaining importance in the certification process of new orthopaedic implants-for example, the Dutch Orthopedic Society has recommended phased-introduction and RSA studies for new hip implants. Furthermore, in the context of the new EU Medical Device Regulation (MDR), which took effect in May 2017, RSA gained relevance for investigating clinically unproven implants. Critics who associate MDR with hindering innovation can be countered in that the RSA method provides apredictive assessment of implant fixation after only two years of follow-up, which is significantly shorter than standard long-term clinical trials.

Fixation of the short global tissue-sparing hip stem.

Short, bone-conserving femoral components are increasingly used in total hip arthroplasty (THA). They are expected to allow tissue-conserving implantation and to render future revision surgery more straightforward but the long-term data on such components is limited. One such component is the global tissue-sparing (GTS) stem. Following the model for stepwise introduction of new orthopaedic implants, we evaluated early implant fixation and clinical outcome of this novel short-stem THA and compared it to that of a component with established good long-term clinical outcome. In total, 50 consecutive patients ≤ 70 years old with end-stage symptomatic osteo-arthritis were randomized to receive THA with the GTS stem or the conventional Taperloc stem using the anterior supine intermuscular approach by two experienced hip surgeons in two hospitals in the Netherlands. Primary outcome was implant migration. Patients were followed using routine clinical examination, patient reported outcome using Harris Hip Score (HHS), Hip Disability And Osteoarthritis Outcome Score (HOOS), EuroQol five-dimension questionnaire (EQ5D), and Roentgen Stereophotogrammetric Analysis (RSA) at three, six, 12, and 24 months. This study evaluated the two-year follow-up results. In addition to the initial migration pattern of distal migration (subsidence, Y-translation) and retroversion (Y-rotation) also exhibited by the Taperloc stem, the GTS stem showed an initial migration pattern of varization (X-translation combined with Z-rotation) and posterior translation (Z-translation). However, all components stabilized aside from one Taperloc stem which became loose secondary to malposition and was later revised. Clinical outcomes and complications were not statistically significantly different with the numbers available. A substantially different and more extensive initial migration pattern was seen for the GTS stem compared to the Taperloc stem. Although implant stabilization was achieved, excellent long-term survival similar to that of the Taperloc stem should not be inferred. Especially in the absence of clinically proven relevant improvement, widespread usage should be postponed until long-term safety has been established. Cite this article: Bone Joint J 2020;102-B(6):699-708.

Model-Based Roentgen Stereophotogrammetric Analysis to Monitor the Head-Taper Junction in Total Hip Arthroplasty in Vivo-And They Do Move.

Model-based Roentgen stereophotogrammetric analysis (RSA) using elementary geometrical shape (EGS) models allows migration measurement of implants without the necessity of additional attached implant markers. The aims of this study were: (i) to assess the possibility of measuring potential head–taper movement in THA in vivo using model-based RSA and (ii) to prove the validity of measured head–taper migration data in vitro and in vivo. From a previous RSA study with a 10 years follow-up, retrospectively for n = 45 patients head–taper migration was calculated as the relative migration between femoral ball head and taper of the femoral stem using model-based RSA. A head–taper migration of 0.026 mm/year can be detected with available RSA technology. In vitro validation showed a total migration of 268 ± 11 µm along the taper axis in a similar range to what has been reported using the RSA method. In vivo, a proof for interchangeable applicability of model-based RSA (EGS) and standard marker-based RSA methods was indicated by a significant deviation within the migration result after 12-month follow-up for all translation measurements, which was significantly correlated to the measured head–taper migration (r from 0.40 to 0.67; p < 0.05). The results identified that model-based RSA (EGS) could be used to detect head–taper migration in vivo and the measured movement could be validated in vitro and in vivo as well. Those findings supported the possibility of applying RSA for helping evaluate the head–taper corrosion related failure (trunnionosis).

Validation of a method to measure three-dimensional hip joint kinematics in subjects with femoroacetabular impingement.

A kinematic measurement method combining dynamic motion and imaging, which captures the behaviour of the hip at terminal motion, may offer improved diagnostic accuracy and enhance our understanding of the mechanics of femoroacetabular impingement (FAI). 3 embalmed cadaveric hip/pelvis specimens with implanted Roentgen Stereophotogrammetric Analysis (RSA) beads were mounted on a custom rig and imaged with a fluoroscope in four poses to simulate a clinical impingement examination: in hip extension and in three positions: near impingement, early impingement and late impingement while simulating a flexion/adduction/internal rotation manoeuvre. Hip joint kinematics were measured using 2 methods and compared: RSA (gold standard) and a custom 3-dimensional to 2-dimensional (3D-2D) image registration method which matches 3D models developed from CT to 2D fluoroscopic images. Using RSA as the gold standard, bias and precision of hip joint rotations measured using 3D-2D registration demonstrated maximums of 1.64° and 3.96°, respectively. However, if the single outlier was removed, bias and precision were 0.55° and 1.38°. Bias and precision of translations had maximums of 0.51 mm and 0.77 mm, respectively. This 3D to 2D registration method may offer a clinically useful solution for dynamic assessment of hip impingement. If 5-mm translation and 10° of rotation represent a clinically significant difference in hip kinematics, the method's accuracy of approximately 1 mm displacement and 1° rotation should enable detection of significant clinical differences.

Feasibility of model-based Roentgen Stereophotogrammetric Analysis to evaluate early migration of the trapeziometacarpal joint prosthesis.

BackgroundThe purpose of this study was to determine the feasibility of Roentgen Stereophotogrammetric Analysis (RSA) in total joint arthroplasty of the trapeziometacarpal (TMC) joint of the thumb.MethodsIn five cadaveric hands the TMC-joint was replaced by the Surface Replacement Trapeziometacarpal prosthesis (SR™ TMC prosthesis; Avanta, San Diego, CA) and tantalum beads of 0.8 mm were implanted for RSA. RSA radiographs in two directions were made in ten positions to calculate the measurement error. Migration values from zero are indicative for the measurement error. The number of detected markers was recorded.ResultsThe accuracy analysis showed that for the translations the mean measurement error varied between 0.003 mm (SD 0.057) and 0.055 mm (SD 0.133). For the rotations values ranged from 0.034° (SD 1.759) to 0.502° (SD 1.617).ConclusionsRSA analysis of the SR™ TMC prosthesis is feasible. The measurement error is good for the translations but high for the rotations. The latter is due to the close position of the markers relative to each other. Level of evidence III.

Fixation of High-Flexion Total Knee Prostheses: Five-Year Follow-up Results of a Four-Arm Randomized Controlled Clinical and Roentgen Stereophotogrammetric Analysis Study

High-flexion total knee arthroplasty was introduced to meet the demands of daily activity requiring increased knee flexion. However, concerns have been raised regarding the fixation of high-flexion total knee arthroplasty components and increased rates of loosening have been reported. To date, migration, and thus fixation, of high-flexion total knee arthroplasty components has not been analyzed and the preferential bearing type (mobile or fixed) is unknown. Of eighty-six consecutive eligible patients, seventy-four patients (seventy-eight knees) scheduled for total knee arthroplasty were randomized to one of four Legacy Posterior Stabilized (LPS) total knee prosthesis designs: (1) LPS-Flex mobile, (2) LPS-Flex fixed, (3) LPS mobile, and (4) LPS fixed. The primary outcome was component migration measured with use of Roentgen stereophotogrammetric analysis, and secondary outcomes were postoperative knee flexion and extension and Knee Society Score. Patients were evaluated postoperatively at six, twelve, twenty-six, and fifty-two weeks and annually thereafter. At the five-year follow-up, eight patients had died and two patients were lost to follow-up. Seventy-seven tibial and forty-two femoral components were suitable for migration measurements. The overall five-year migration of the seventy-seven tibial components was not significantly different among the four total knee prosthesis designs (compared with the LPS fixed design, the range of overall mean differences for the other three designs was 0.02 to 0.25 mm) and migration was comparable at the two and five-year follow-up. Migration stabilized in all but three components (two LPS-Flex mobile and one LPS fixed); one of these components has already been revised and was aseptically loose. The overall five-year migration of the forty-two femoral components was comparable among the four designs (compared with the LPS fixed design, the range of overall mean differences for the other three designs was 0.01 to 0.18 mm) and was similar at two and five years postoperatively. One femoral component (LPS-Flex mobile) migrated excessively. In patients who had a mean postoperative flexion of ≥ 125° or a maximum flexion of ≥ 135° during the one to five-year follow-up period, migration of high-flexion components was comparable with that of conventional components and indicative of appropriate fixation. Postoperative flexion, extension, Knee Society Score, and Knee Society Score function were comparable during the five-year follow-up period and at the two and five-year follow-up. The LPS-Flex total knee prosthesis with either a mobile or a fixed bearing had migration comparable that of with its conventional counterpart and is expected to have similar (excellent) long-term survival in these patients. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Dependence of model-based RSA accuracy on higher and lower implant surface model quality

BackgroundModel-based Roentgen Stereophotogrammetric Analysis (MBRSA) allows the accurate in vivo measurement of the relative motion between an implant and the surrounding bone (migration), using pose-estimation algorithms and three dimensional geometric surface models of the implant. The goal of this study was thus to investigate the effect of surface model resolution on the accuracy of the MBRSA method.MethodsFour different implant geometries (knee femoral and tibial components, and two different hip stems) were investigated, for each of which two reversed engineering (RE) models of differing spatial digitizing resolution were generated. Accuracy of implant migration measurement using MBRSA was assessed in dependence on surface model resolution using an experimental phantom-model set up.ResultsWhen using the lower quality RE models, the worst bias observed ranged from -0.048 to 0.037 mm, and -0.057 to 0.078 deg for translation and rotation respectively. For higher quality reverse engineering models, bias ranged from -0.042 to 0.048 mm, and -0.449 to 0.029 deg. The pair-wise comparisons of digitizing resolution (higher vs. lower quality) within the different implant type revealed significant differences only for the hip stems (p < 0.001).ConclusionThe data suggest that the application of lower resolution RE models for MBRSA is a viable alternative method for the in vivo measurement of implant migration, in particular for implants with non symmetrical geometries (total knee arthroplasty). Implants with larger length to width aspect ratio (total hip arthroplasty) may require high resolution RE models in order to achieve acceptable accuracy. Conversely, for some axis the bias for translation are clearly worse for translation, and are marginally better for rotations using the lower resolution RE models instead of the higher ones. However, performed box plots ranges were well within what has been reported in the literature. The observed lower accuracy and precision of the measurements for hip stem components for rotations about the superior-inferior direction is presumably the result of the nature of the MBRSA method. This well known effect within MBRSA for rotations about the axis of symmetry of axially-symmetric objects do not change the contour of the projected image to as large a degree as motion about a non-symmetric axes. It is not possible to detected this small motion as accurately using pose-estimation methods. This may affect the “higher” accuracy for the applied lower resolution RE models.

Markerless Roentgen Stereophotogrammetric Analysis for in vivo implant migration measurement using three dimensional surface models to represent bone

Recent studies have shown that model-based RSA using implant surface models to detect in vivo migration is as accurate as the classical marker-based RSA method. Use of bone surface models would be a further advancement of the model-based method by decreasing complications arising from marker insertion. The aim of this pilot investigation was to assess the feasibility of a “completely markerless” model-based RSA in detecting migration of an implant using bone surface models instead of bone markers. A total knee arthroplasty (TKA) was performed on a human cadaver knee, which was subsequently investigated by repeated RSA measurements performed by one observer. The cadaver knee was CT scanned prior to implantation of the TKA. Tibia–fibular surface models were created using two different commercially available software packages to investigate the effect of segmentation software on the accuracy of repeated migration measures of zero displacement by one observer. Reverse engineered surface models of the TKA tibial component were created. The analysis of the RSA images was repeated 10 times by one individual observer. For the markerless method, the greatest apparent migration observed about the three anatomical axes investigated was between −2.08 and 1.35mm (SD≤0.88) for z-axis translation, and −4.57° to 7.86° (SD≤3.17) for Ry-axis rotation, which were well beyond out of the range of what is typically considered adequate for clinically relevant RSA measurements. Use of tibia–fibular surface models of the bone instead of markers could provide practical advantages in evaluating implant migration. However, we found the accuracy and precision of the markerless approach to be lower than that of marker-based RSA, to a degree which precludes the use of this method for measuring implant migration in its present form.

Validation of a New Method for Finding the Rotational Axes of the Knee Using Both Marker-Based Roentgen Stereophotogrammetric Analysis and 3D Video-Based Motion Analysis for Kinematic Measurements

In a previous paper, we reported the virtual axis finder, which is a new method for finding the rotational axes of the knee. The virtual axis finder was validated through simulations that were subject to limitations. Hence, the objective of the present study was to perform a mechanical validation with two measurement modalities: 3D video-based motion analysis and marker-based roentgen stereophotogrammetric analysis (RSA). A two rotational axis mechanism was developed, which simulated internal-external (or longitudinal) and flexion-extension (FE) rotations. The actual axes of rotation were known with respect to motion analysis and RSA markers within ± 0.0006 deg and ± 0.036 mm and ± 0.0001 deg and ± 0.016 mm, respectively. The orientation and position root mean squared errors for identifying the longitudinal rotation (LR) and FE axes with video-based motion analysis (0.26 deg, 0.28 m, 0.36 deg, and 0.25 mm, respectively) were smaller than with RSA (1.04 deg, 0.84 mm, 0.82 deg, and 0.32 mm, respectively). The random error or precision in the orientation and position was significantly better (p=0.01 and p=0.02, respectively) in identifying the LR axis with video-based motion analysis (0.23 deg and 0.24 mm) than with RSA (0.95 deg and 0.76 mm). There was no significant difference in the bias errors between measurement modalities. In comparing the mechanical validations to virtual validations, the virtual validations produced comparable errors to those of the mechanical validation. The only significant difference between the errors of the mechanical and virtual validations was the precision in the position of the LR axis while simulating video-based motion analysis (0.24 mm and 0.78 mm, p=0.019). These results indicate that video-based motion analysis with the equipment used in this study is the superior measurement modality for use with the virtual axis finder but both measurement modalities produce satisfactory results. The lack of significant differences between validation techniques suggests that the virtual sensitivity analysis previously performed was appropriately modeled. Thus, the virtual axis finder can be applied with a thorough understanding of its errors in a variety of test conditions.

Roentgen Stereophotogrammetric Analysis of Fixation of the Tibial Component in Uncemented Unicompartmental Knee Arthroplasties

Roentgen Stereophotogrammetric Analysis of Fixation of the Tibial Component in Uncemented Unicompartmental Knee Arthroplasties

Development of a Model-Based Roentgen Stereophotogrammetric Analysis System to Measure Polyethylene Wear in Unicompartmental Arthroplasty

One of the most important causes of failure in unicompartmental knee replacement (UKR) is polyethylene wear. The aim of this study was to develop and assess a novel Roentgen stereophotogrammetric analysis (RSA)-based method for the measurement of linear wear suitable for UKR. Model-based RSA was used to estimate the linear wear of polyethylene bearings in UKR. A phantom was used to validate the method using in vitro measured bearing thicknesses and the linear wear of ten control bearings was estimated in vivo. Computer aided design (CAD) models for the UKRs were used in the model-based RSA system. There was no statistically significant difference between the estimated and measured bearing thicknesses using the CAD models (p = 0.386). The precision of the linear wear measurement, expressed as the standard deviation of the difference between the estimated and measured bearing thickness was 0.163 mm. The bias (mean difference) was 0.030 mm. The use of RSA to measure in vivo wear in a UKR has been shown to be accurate in a phantom, and has been verified with in vivo measured controls. The technique does not require surgical implantation of marker balls and can be used retrospectively.

Assessment of Internal and External Prosthesis Kinematics during Strenuous Activities Using Dynamic Roentgen Stereophotogrammetric Analysis

ABSTRACT Optimal performance of artificial limbs is still largely dependent on the accurate evaluation of their biomechanical behavior. The accumulated expertise of the prosthetist and indirect measurements of socket and joint kinematics are currently used in a trial and error format for prosthesis-socket performance maximization. The accurate direct unobtrusive assessment of residual limb-skin slippage within the socket during dynamic high-speed activities remains an unresolved challenge till date. This assessment is further complicated in the case of transtibial amputees who have previously undergone joint arthroplasty surgery. This study uses a new method of assessment of the combination of three-dimensional (3D) total knee prosthesis kinematics and socket-residual limb kinematics/slippage during high-speed strenuous activities using Biplane Dynamic Roentgen Stereogrammetric Analysis (DRSA) instrumentation. Marker-based assessment of dynamic socket-residual limb and residual bone telescoping motion with as much as 0.03-mm translational and 1.3 degrees rotational accuracy was demonstrated. The in-vivo dynamic accuracy for the model-based (markerless) tracking (MBT) method to track the joint prosthesis was further improved from that reported previously. Quantitatively, measurement bias between DRSA and the MBT methods ranged from −0.012 to −0.11 mm (depending on coordinate axis) for the femoral prosthesis and from 0.004 to 0.048 mm for the socket. The results from this transtibial case study indicated that maximum 3D slippage for some socket-skin-marker pairs reached values of up to 16 mm for the fast-stop task and up to 8 mm for the step-down task. Maximum “deformation” of up to 12.5% is observed for the fast-stop trials and step-down trials between skin-to-skin marker pairs. The respective deformation between skin-to-socket marker pairs reached maximum values of almost 22%. The deformation between femur/tibia edges and skin/socket marker pairs reached maximum values of almost 100%. Relative skin strain calculated from skin-marker pairs reached values that range between 0.01 and 0.1 for step-down and fast-stop trials, respectively. The relative engineering shear (γ) between selected skin-marker clusters that form orthonormal meshes ranged between 81.5 and 129 degrees. This in-vivo, patient-specific, unobtrusive dynamic information is highly accurate and allows socket-residual limb interactions to be presented using 3D visualization tools that were until recently unavailable to the clinician prosthetist. These methods can significantly impact the iterative cycle of socket fitting and evaluation.

Precision assessment of model-based RSA for a total knee prosthesis in a biplanar set-up

Model-based Roentgen Stereophotogrammetric Analysis (RSA) was recently developed for the measurement of prosthesis micromotion. Its main advantage is that markers do not need to be attached to the implants as traditional marker-based RSA requires. Model-based RSA has only been tested in uniplanar radiographic set-ups. A biplanar set-up would theoretically facilitate the pose estimation algorithm, since radiographic projections would show more different shape features of the implants than in uniplanar images. We tested the precision of model-based RSA and compared it with that of the traditional marker-based method in a biplanar set-up. Micromotions of both tibial and femoral components were measured with both the techniques from double examinations of patients participating in a clinical study. The results showed that in the biplanar set-up model-based RSA presents a homogeneous distribution of precision for all the translation directions, but an inhomogenous error for rotations, especially internal–external rotation presented higher errors than rotations about the transverse and sagittal axes. Model-based RSA was less precise than the marker-based method, although the differences were not significant for the translations and rotations of the tibial component, with the exception of the internal–external rotations. For both prosthesis components the precisions of model-based RSA were below 0.2 mm for all the translations, and below 0.3° for rotations about transverse and sagittal axes. These values are still acceptable for clinical studies aimed at evaluating total knee prosthesis micromotion. In a biplanar set-up model-based RSA is a valid alternative to traditional marker-based RSA where marking of the prosthesis is an enormous disadvantage.

APPLICABILLITY OF MODEL-BASED RSA FOR AN AXIS SYMMETRIC HIP RESURFACING PROSTHESIS DESIGN

Roentgen Stereophotogrammetric Analysis (RSA) allows the detection of early implant migration, which is of particular clinical relevance because early migration in the first two post-operative years correlates well with a later aseptic loosening [Karrholm, 1994; Ryd, 1995]. Model-based RSA (MBRSA) represents a new approach, which does not require the placement of tantalum markers on the prosthesis [Valstar, 2002; Kaptein, 2003]. The accuracy of MBRSA depends on the geometry of implant design [Hurschler, 2007]. Hip resurfacing arthroplasty (HR), a bone sparing strategy for younger patients, has drawn significant clinical interest, despite some setbacks including revisions due to loosening. The goal of this study, especially in light of the known interaction between geometric design and MBRSA accuracy, was to determine the theoretical accuracy and precision for migration measurements of axis-symmetric implants such as HR. The working hypothesis was that MBRSA provides sufficient accuracy to detect translational migration of total-axis-symmetric implants, despite the fact that the rotation about its symmetry-axis is indeterminate.