Roentgen Stereophotogrammetric Analysis Method Research Articles

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.

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).

Improvement in the clinical practicability of roentgen stereophotogrammetric analysis (RSA): Free from the use of the dual X-ray equipment

After total knee replacement, the monitoring of the prosthetic performance is often done by roentgenographic examination. However, the two-dimensional (2D) roentgen images only provide information about the projection onto the anteroposterior (AP) and mediolateral (ML) planes. Historically, the model-based roentgen stereophotogrammetric analysis (RSA) technique has been developed to predict the spatial relationship between prostheses by iteratively comparing the projective data for the prosthetic models and the roentgen images. During examination, the prosthetic poses should be stationary. This should be ensured, either by the use of dual synchronized X-ray equipment or by the use of a specific posture. In practice, these methods are uncommon or technically inconvenient during follow-up examination. This study aims to develop a rotation platform to improve the clinical applicability of the model-based RSA technique. The rotation platform allows the patient to assume a weight-bearing posture, while being steadily rotated so that both AP and ML knee images can be obtained. This study uses X-ray equipment with a single source and flat panel detectors (FPDs). Four tests are conducted to evaluate the quality of the FPD images, steadiness of the rotation platform, and accuracy of the RSA results. The results show that the distortion-induced error of the FPD image is quite minor, and the prosthetic size can be cautiously calibrated by means of the scale ball(s). The rotation platform should be placed closer to the FPD and orthogonal to the projection axis of the X-ray source. Image overlap of the prostheses can be avoided by adjusting both X-ray source and knee posture. The device-induced problems associated with the rotation platform include the steadiness of the platform operation and the balance of the rotated subject. Sawbone tests demonstrate that the outline error, due to the platform, is of the order of the image resolution (= 0.145 mm). In conclusion, the rotation platform with steady rotation, a knee support, and a handle can serve as an alternative method to take prosthetic images, without the loss in accuracy associated with the RSA method.

Improved execution efficiency of model-based roentgen stereophotogrammetric analysis: simplification and segmentation of model meshes

Recently, the model-based roentgen stereophotogrammetric analysis (RSA) method has been developed as an in vivo tool to estimate static pose and dynamic motion of the instrumented prostheses. The two essential inputs for the RSA method are prosthetic models and roentgen images. During RSA calculation, the implants are often reversely scanned and input in the form of meshes to estimate the outline error between prosthetic projection and roentgen images. However, the execution efficiency of the RSA iterative calculation may limit its clinical practicability, and one reason for inefficiency may be very large number of meshes in the model. This study uses two methods of mesh manipulation to improve the execution efficiency of RSA calculation. The first is to simplify the model meshes and the other is to segment and delete the meshes of insignificant regions. An index (i.e. critical percentage) of an optimal element number is defined as the trade-off between execution efficiency and result accuracy. The predicted results are numerically validated by total knee prosthetic system. The outcome shows that the optimal strategy of the mesh manipulation is simplification and followed by segmentation. On average, the element number can even be reduced to 1% of the original models. After the mesh manipulation, the execution efficiency can be increased about 75% without compromising the accuracy of the predicted RSA results (the increment of rotation and translation error: 0.06° and 0.02 mm). In conclusion, prosthetic models should be manipulated by simplification and segmentation methods prior to the RSA calculation to increase the execution efficiency and then to improve clinical applicability of the RSA method.

Experimental Analysis of Model-Based Roentgen Stereophotogrammetric Analysis (MBRSA) on Four Typical Prosthesis Components

Classical marker-based roentgen stereophotogrammetric analysis (RSA) is an accurate method of measuring in vivo implant migration. A disadvantage of the method is the necessity of placing tantalum markers on the implant, which constitutes additional manufacturing and certification effort. Model-based RSA (MBRSA) is a method by which pose-estimation of geometric surface-models of the implant is used to detect implant migration. The placement of prosthesis markers is thus no longer necessary. The accuracy of the pose-estimation algorithms used depends on the geometry of the prosthesis as well as the accuracy of the surface models used. The goal of this study was thus to evaluate the experimental accuracy and precision of the MBRSA method for four different, but typical prosthesis geometries, that are commonly implanted. Is there a relationship existing between the accuracy of MBRSA and prosthesis geometries? Four different prosthesis geometries were investigated: one femoral and one tibial total knee arthroplasty (TKA) component and two different femoral stem total hip arthroplasty (THA) components. An experimental phantom model was used to simulate two different implant migration protocols, whereby the implant was moved relative to the surrounding bone (relative prosthesis-bone motion (RM)), or, similar to the double-repeated measures performed to assess accuracy clinically, both the prosthesis and the surrounding bone model (zero relative prosthesis-bone motion (ZRM)) were moved. Motions were performed about three translational and three rotational axes, respectively. The maximum 95% confidence interval (CI) for MBRSA of all four prosthesis investigated was better than -0.034 to 0.107 mm for in-plane and -0.217 to 0.069 mm for out-of-plane translation, and from -0.038 deg to 0.162 deg for in-plane and from -1.316 deg to 0.071 deg for out-of-plane rotation, with no clear differences between the ZRM and RM protocols observed. Accuracy in translation was similar between TKA and THA components, whereas rotational accuracy about the long axis of the hip stem THA components was worse than the TKA components. The data suggest that accuracy and precision of MBRSA seem to be equivalent to the classical marker-based RSA method, at least for the nonsymmetric implant geometries investigated in this study. The model-based method thus allows the accurate measurement of implant migration without requiring prosthesis markers, and thus presents new opportunities for measuring implant migration where financial or geometric considerations of marker placement have thus far been prohibitive factors.

Mechanical properties during healing of Achilles tendon ruptures to predict final outcome: A pilot Roentgen stereophotogrammetric analysis in 10 patients

BackgroundThere are presently few methods described for in vivo monitoring of the mechanics of healing human tendon ruptures, and no methods for prediction of clinical outcome. We tested if Roentgen stereophotogrammetric analysis (RSA) can be used to follow the restoration of mechanical properties during healing of ruptured Achilles tendons, and if early measurements can predict clinical results.MethodsAchilles tendon repair was studied with RSA in 10 patients with a total rupture. Tantalum beads were implanted in conjunction with surgical repair. The patients were evaluated at 6, 12 and 18 weeks, and after 1 year. RSA was performed with two different mechanical loadings, and the strain induced by increasing load was measured. The transverse area was determined by ultrasound. CT scan at 12 weeks confirmed that the tantalum beads were located within the tendons. Functional testing was done after 1 year. A heel raise index was chosen as primary clinical outcome variable.ResultsThe strain was median 0.90, 0.32 and 0.14 percent per 100 N tendon force at 6 weeks, 18 weeks and one year respectively. The error of measurement was 0.04 percent units at 18 weeks. There was a large variation between patients, which appears to reflect biological variation. From 6 to 18 weeks, there was a negative correlation between increase in transverse area and increase in material properties, suggesting that healing is regulated at the organ level, to maximize stiffness. Modulus of elasticity during this time correlated with a heel raise index at one year (Rho = 0.76; p = 0.02).ConclusionWe conclude that the RSA method might have potential for comparing different treatments of Achilles tendon ruptures.

A new model-based RSA method validated using CAD models and models from reversed engineering

Roentgen stereophotogrammetric analysis (RSA) was developed to measure micromotion of an orthopaedic implant with respect to its surrounding bone. A disadvantage of conventional RSA is that it requires the implant to be marked with tantalum beads. This disadvantage can potentially be resolved with model-based RSA, whereby a 3D model of the implant is used for matching with the actual images and the assessment of position and rotation of the implant. In this study, a model-based RSA algorithm is presented and validated in phantom experiments. To investigate the influence of the accuracy of the implant models that were used for model-based RSA, we studied both computer aided design (CAD) models as well as models obtained by means of reversed engineering (RE) of the actual implant. The results demonstrate that the RE models provide more accurate results than the CAD models. If these RE models are derived from the very same implant, it is possible to achieve a maximum standard deviation of the error in the migration calculation of 0.06 mm for translations in x- and y-direction and 0.14 mm for the out of plane z-direction, respectively. For rotations about the y-axis, the standard deviation was about 0.1° and for rotations about the x- and z-axis 0.05°. Studies with clinical RSA-radiographs must prove that these results can also be reached in a clinical setting, making model-based RSA a possible alternative for marker-based RSA.

Accuracy and repeatability of Roentgen stereophotogrammetric analysis (RSA) for measuring knee laxity in longitudinal studies

Roentgen stereophotogrammetric analysis (RSA) can be used to assess temporal changes in anterior–posterior (A–P) knee laxity. However, the accuracy and precision of RSA is dependent on many factors and should be independently evaluated for a particular application. The objective of this study was to evaluate the use of RSA for measuring A–P knee laxity. The specific aims were to assess the variation or “noise” inherent to RSA, to determine the reproducibility of RSA for repeated A–P laxity testing, and to assess the accuracy of these measurements. Two experiments were performed. The first experiment utilized three rigid models of the tibiofemoral joint to assess the noise and to compare digitization errors of two independent examiners. No differences were found in the kinematic outputs of the RSA due to examiner, repeated trials, or the model used. In a second experiment, A–P laxity values between the A–P shear load limits of ±60 N of five cadaver goat knees were measured to assess the error associated with repeated testing. The RSA laxity values were also compared to those obtained from a custom designed linkage system. The mean A–P laxity values with the knee 30°, 60°, and 90° of flexion for the ACL-intact goat knee (±95% confidence interval) were 0.8 (±0.25), 0.9 (±0.29), and 0.4 (±0.22) mm, respectively. In the ACL-deficient knee, the A–P laxity values increased by an order of magnitude to 8.8 (±1.39), 7.6 (±1.32), and 3.1 (±1.20) mm, respectively. No significant differences were found between the A–P laxity values measured by RSA and the independent measurement technique. A highly significant linear relationship ( r 2=0.83) was also found between these techniques. This study suggests that the RSA method is an accurate and precise means to measure A–P knee laxity for repeated testing over time.

Evaluation of accuracy and precision of bone markers for the measurement of migration of hip prostheses. A comparison of conventional measurements.

Our aim was to determine whether tantalum m arkers improved the accuracy and/or precision of methods for the measurement of migration in total hip replacement based on conventional measurements without mathematical correction of the data, and with Ein Bild Roentgen Analyse - Femoral Component Analysis (EBRA-FCA) which allows a computerised correction. Three observers independently analysed 13 series of roentgen-stereophotogrammetric-analysis (RSA)-compatible radiographs (88). Data were obtained from conventional measurements, EBRA-FCA and the RSA method and all the results were compared with the RSA data. Radiological evaluation was also used to quantify in how many radiographs the intraosseous position of the bone markers had been simulated. The results showed that tantalum markers improve reliability whereas they do not affect accuracy for conventional measurements and for EBRA-FCA. Because of the danger of third-body wear their implantation should be avoided unless they are an integral part of the method.

Evaluation of accuracy and precision of bone markers for the measurement of migration of hip prostheses

Our aim was to determine whether tantalum markers improved the accuracy and/or precision of methods for the measurement of migration in total hip replacement based on conventional measurements without mathematical correction of the data, and with Ein Bild Roentgen Analyse – Femoral Component Analysis (EBRA-FCA) which allows a computerised correction. Three observers independently analysed 13 series of roentgen-stereophotogrammetric-analysis (RSA)-compatible radiographs (88). Data were obtained from conventional measurements, EBRA-FCA and the RSA method and all the results were compared with the RSA data. Radiological evaluation was also used to quantify in how many radiographs the intraosseous position of the bone markers had been simulated. The results showed that tantalum markers improve reliability whereas they do not affect accuracy for conventional measurements and for EBRA-FCA. Because of the danger of third-body wear their implantation should be avoided unless they are an integral part of the method.

The Netherlands Orthopedic Society: S'Hertogenbosch, January 11–12, 1996

Micromoveinents of prostheses can be measured accurately by means of Roentgen Stereophotogrammetric Analysis (RSA). To this purpose, the prosthesis and the surrounding bone are marked with tiny metal pellets. The marking of the prosthesis, in particular, is regarded as disadvantageous. For this reason, for the Mallory Head hip prosthesis an adapted RSA method was developed, which requires no marking of the prosthesis but which uses prominent points of the prosthesis itself. A study was carried out in order to establish if the adapted RSA method is accurate enough for the measurement of micromovements of the Mallory Head hip prosthesis. Maferial and method: With the adapted RSA method, the spatial position of the prosthesis is determined using measuring points on the head, the stein and the tip of the prosthesis. To test the method, RSA photographs were made of a phantom placed in nine different positions. The phantom consisted of the femoral component of the Mallory Head hip prosthesis glued in a perspex cylinder. A number of tantalum markers were placed on the outline of the cylinder. The measurements of the positions of the markers and of the prominent measuring points of the prosthesis in the photograph were carried out using an accurate measuring table (Zeiss Planicomp 100). The calculated position of the cylinder in space was the golden standard with which the position of the prosthesis was compared. Results: As the prosthesis was bonded inside the cylinder with glue, no relative movement between the prosthesis and the cylinder proved possible. However, relative movements were nevertheless measured as the result of measuring errors. The magnitude of these relative movements was a measure of the magnitude of the measuring error. The relative movements of the prosthesis in relation to the cylinder were determined in eight cases, and expressed in spiral axis parameters. Two of the spiral axis parameters were the translation along and rotation round the spiral axis. The mean relative translation amounted to 0.005 inin, the mean relative ro-