Introduction. The various problems that are managed with circular external fixation (e.g. deformity, complex fractures) also typically require serial plain x-ray imaging. One of the challenges here is that the relatively radio-opaque components of the circular external fixator (e.g. the rings) can obscure the view of the area of interest (e.g. osteotomy site, fracture site). In this presentation we describe how the geometry of the x-ray beam affects the produced image and how we can use knowledge of this to our advantage. Whilst this can be applied to any long bone, we have focused on the tibia, given that it's the most common long bone that is treated by circular external fixation. Materials & Methods. In the first part of the presentation we describe the known attributes (geometry) of the x-ray beam and postulate what effect it would have when we x-ray a long bone that is surrounded by a circular external fixator. In the second part we demonstrate this in practice using a tibia and a 3 ring circular external fixator. Differing x-ray beam orientations are used to demonstrate both how the geometry of the beam affects the produced image and how we can use this to our advantage to better visualise part of the bone. Results. The practical part of the study confirmed the theoretical part. Conclusions. Knowledge of the beam geometry can be used to minimise the obscuring nature of the circular fixator. This technique is simple and can be easily taught to the radiographer. It is a useful adjunct for the limb reconstruction surgeon

Introduction. In our institution, we started to perform THA with SuperPATH approach, including preservation of soft tissue around the hip (James Chow et al. Musculoskelet Med 2011) since July 2014, aiming for fast recovery and prevention of hip dislocation. For minimally-invasive approaches, however, there have been a few reports on malalignment of the implants related to shortage of operative field. The purpose of this study is to examine the short-term results of THA using SuperPATH, especially implant alignment. Materials and methods. We performed a study of 45 patients (45 hips) with osteoarthritis of the hip joint who had a THA with SuperPATH approach. There were 8 men and 37 women with an average age of 73 years, which were minimally 24 months followed. Dynasty Bioform cup and Profemur Z stem (Microport Orthopaedics) were used for all cases. Patients were clinically assessed with Merle d'Aubigne score and complications. Implant alignment and stability were radiologically evaluated by annual X-ray and CT acquired two months after surgery. Results. Merle d'Aubigne score was 10.2 (pain:2.8, mobility:4.4 walking ability:3.0) preoperatively and 16.6(pain:5.8, mobility:5.8, walking ability:5.0) at the latest follow-up. There were no dislocation and infection, but intraoperative proximal femoral fracture was found for two cases, which was managed to treat with additional circulating wire intraoperatively. Latest follow-up X-ray image showed 95% of the stem A-P alignment to be within 2 degrees and 5% to be more than 2 degrees and less than 5 degrees, while 44% of the stem lateral alignment to be within 2 degrees, 47% to be more than 2 degrees and less than 5 degrees, and 8% to be more than 5 degrees. From CT images averaged cup position found to be 40±5 degrees for inclination, and 19±5 degrees for anatomic anteversion, averaged stem anteversion to be 33±9 degrees. Annual X-ray evaluation showed no radiolucent line and less than Grade 2 stress-shielding (Engh classification) around the implants for all cases. One case had more than 5mm subsidence of the stem in early postoperative period, but not progressively subsided. No loosening of components was evident. Discussion and Conclusion. Many minimally-invasive approaches have developed, there have been many reports on fast recovery and low incidence of postoperative hip dislocation, however, the risk of complications or malalignment related to shortage of operative field has been pointed out. In this study, intraoperative proximal femoral fracture occurred for two cases. Also, though there were no loosening and the components position seemed excellent but lateral view of the X-ray showed 8% to be more than 5 degrees tilting alignment, resulting from femoral broaching required before femoral neck resection. SuperPATH approach, including pass way from between the Gluteus Medius and the piriformis tendon, can preserve the whole short external rotators and capsule of the hip joint, leading to fast recovery and low incidence of postoperative dislocation. Moreover, this approach may be friendly to the surgeons familiar with the posterior approach because of easily conversion to the conventional posterior approach

Radiostereometric analysis (RSA) allows for precise measurement of interbody distances on X-ray images, such as movement between a joint replacement implant and the bone. The low radiation biplanar EOS imager (EOS imaging, France) scans patients in a weight-bearing position, provides calibrated three-dimensional information on bony anatomy, and could limit the radiation during serial RSA studies. Following the ISO-16087 standard, 15 double exams were conducted to determine the RSA precision of total knee arthroplasty (TKA) patients in the EOS imager, compared to the standard instantaneous, cone-beam, uniplanar digital X-ray set-up. At a mean of 5 years post-surgery, 15 TKA participants (mean 67 years, 12 female, 3 male) were imaged twice in the biplanar imager. To reduce motion during the scan, a support for the foot was added and the scan speed was increased. The voltage was also increased compared to standard settings for better marker visibility over the implant. A small calibration object was included to remove any remaining sway in post-processing. The 95% confidence interval precision was 0.11, 0.04, and 0.15 mm in the x, y, and z planes, respectively and 0.15, 0.20, and 0.14° in Rx, Ry, and Rz. Two participants had motion artifacts successfully removed during post-processing using the small calibration object. With faster speeds and stabilization support, this study found an in vivo RSA precision of ≤ 0.15 mm and ≤ 0.20° for TKA exams, which is within published uniplanar values for arthroplasty RSA. The biplanar imager also adds the benefits of weight bearing imaging, 3D alignment measurements, a lower radiation dose, and does not require a reference object due to known system geometry and automatic image registration

Introduction. The correct anteversion of the acetabular cup is critical to achieve optimal outcome after total hip arthroplasty. While number of method has been described to measure the anteversion in plane anteroposterior and lateral radiograph, it is still controversial which method provides best anteversion measurement. While many of the previous studies used CT scan to validate the anteversion measured in plane anteroposterior radiograph, this may cause potential bias as the anteversion measured in CT scan reflects true anteversion while the anteversion measurement methods in plane radiograph are design to measure the planar anteversion. Thus, in the current study, we tried to find the optimal anteversion measurement method free from the previously described bias. Material and method. Custom made cup model was developed which enables change in anteversion and inclination. Simple radiograph was taken with the cup in 10° to 70° degree of inclination at 10° increments and for each inclination angle, anteversion was corrected from 0° to 30° at 5° increments. The radiograph was taken with the beam directed at the center of the cup (mimicking hip centered anteroposterior radiograph) and at 9cm medial to the cup (mimicking pelvis anteroposterior radiograph). The measurements were done by two orthopaedic surgeons using methods described by 1) Pradhan et al, 2) Lewinak et al, 3) Widmer et al, and 4) Liaw et al. For each measurements, the anteversion were compared with the actual anteversion. Result. Interoverver correlation (kappa value) were high in all measurements ranging 0.988 to 0.998. Regardless of how the radiograph was taken, Pradhan method was the most accurate measurement method showing difference of 2.17° ± 1.69° and −2.5° ± 1.93° compare to the actual anteversion respectively for hip centered radiograph and pelvis anteroposterior radiograph. The Widmer method showed the least accuracy (pelvis AP : −6.75° ± 4.62°, hip centered AP : −14.84° ± 4.36°). However, when the anteversion were measured in the safe zone with the inclination in 30° to 50° Liaw's method in hip centered radiograph showed the highest accuracy (1.63° ± 1.4°). Conclusion. The study indicates that the Pradhan's method may provide the most accurate anteversion measurement. However, with the hip in 30° to 50° inclination, Liaw's method measured from hip centred radiograph will provide most accurate anteversion measurement

Introduction. When performing a total hip arthroplasty (THA), some surgeons routinely perform an intraoperative anteroposterior (AP) pelvis radiograph to assess components. The purpose of this study was to evaluate the reliability of the intraoperative radiograph to accurately reflect acetabular inclination, leg length, and femoral offset as compared to the immediate postoperative supine AP radiograph. Methods. The intraoperative (lateral decubitus position) and immediate postoperative (supine position) AP pelvis x-rays of 100 consecutive patients undergoing primary THA were retrospectively reviewed. Acetabular inclination, leg length, and femoral offset were measured on both radiographs. We analyzed the correlation coefficient of the recorded measurements between the two films as well as the interobserver reliability of each measurement obtained. Results. Our data demonstrated a high positive correlation between the intraoperative and postoperative acetabular inclination measurements of both reviewers (r=.886 and .896). In addition, no significant difference was observed between the inclination measurements (p= .06 and .37). There was a moderate correlation among the leg length (r= .58 and .66) and poor correlation among the offset (r= .29 and .25) between the two radiographs. One observer generated a significant difference between leg length measurements while both reviewers generated a significant difference between offset measurements. Interobserver reliability was high for all measurements. Conclusion. Intraoperative AP radiographs are commonly obtained during THA to aid in evaluation of component position and size, femoral neck cut, femoral canal fill, and detection of occult fractures. Results from this study suggest that this film could also be used to accurately measure acetabular inclination, but is a less reliable indicator of femoral offset and leg length when compared to the immediate postoperative film. In addition, the high interobserver correlation illustrates the high reproducibility of the measurement methods utilized

Purpose. Leg length discrepancy after total hip arthroplasty (THA) sometimes causes significant patient dissatisfaction. In consideration of the leg length after THA, leg length discrepancy is often measured using anteroposterior (AP) pelvic radiography. However, some cases have discrepancies in femoral and tibial lengths, and we believe that in some cases, true leg length differences should be taken into consideration in total leg length measurement. We report the lengths of the lower limb, femur, and tibia measured using the preoperative standing AP full-leg radiographs of the patients who underwent THA. Materials and methods. From August 2013 to February 2017, 282 patients underwent standing AP full-leg radiography before THA. Of the patients, 33 were male and 249 were female. The mean age of the patients was 65.7±9.4 years. We measured the distances between the center of the tibial plafond and lesser trochanter apex (A-L), between the femoral intercondylar notch and lesser trochanter (K-L), and between the centers of the tibial plafond and intercondylar spine of the tibia (A-K) on standing AP full-leg radiographs before THA operation. We examined the differences in leg length and the causes of these discrepancies after guiding the difference between them. Results. The mean A-L was 674±44 mm on the right and 677±43 mm on the left. The mean difference between the left and the right was 6.2±7 mm. The differences of ≥5 and ≥10 mm between the left and right were confirmed in 131 (46%) and 39 cases (14%), respectively. The mean K-L was 343±23 mm on the right and 343±23 mm on the left, with a mean difference of 4.4±4 mm. The lateral differences of ≥5 and ≥10 mm were confirmed in 88 (31%) and 22 (8%), respectively. The mean A-K was 325±22 mm on the right and 327±22 mm on the left, with a mean difference of 4±4.5 mm. The differences of ≥5 and ≥10 mm between the left and right were confirmed in 24 (9%) and 67 cases (%), respectively. Discussion. Considering the total length of the lower limbs beyond the little trochanter and the leg length after THA, we confirmed that 46% of the leg length differences of ≥5 mm were admitted to 14%. Thus, THA appeared effective. Perthes head, Crowe classifications 3 and 4, history of childhood paralysis, and so on may be factors for leg length differences beyond the lesser trochanter. Conclusion. We think that it would be preferable to prepare a preoperative plan to measure leg length after THA by measuring the total length of the lower extremity before surgery and determining the difference between the left and right sides

Background. The full leg x-ray is a widely used imaging modality for post-operative assessment of total knee replacement (TKR). However, these assessments require controlled conditions and precise measuring in order to be accurate. inter-observer reliability remains a matter of concern as well. This study examines whether intersurgeon differences are significant. Method. Post-operative lateral and full-leg frontal x-rays of 26 patients were assessed by 6 surgeons according to a strict measuring protocol. Four measurements (Figure 1 and 2) were taken of which two were on the femur (Femoral Varus Angle FVA and Femoral Flexion Angle FFA) and two, on the tibia (Tibial Varus Angle TVA; Tibial Slope Angle TSA). A random effects, two-way ANOVA was performed on the data using Minitab (v 16.0, Minitab Inc., Pennsylvania, USA) to determine whether a surgeon has influence on the results (α = 0.05). Intra-class correlation coefficients (ICC) and standard error of measurements (SEM) resulting in smallest detectable changes (SDC) were also calculated [1]. Results. The resulting p-value for FVA is p = 0.246, p = 0.006 for FFA, p = 0.006 for TVA and p = 0.032 for TSA. The measured ICC of FVA is 0.88, 0.75 of FFA, 0.76 of TVA and 0.76 of TSA. Additionally, the SEM and SDC for FVA are respectively 0.26° and 0.72°, 0.84° and 2.36° for FFA, 0.45° and 1.26° for TVA and 0.66° and 0.86° for TSA. Discussion. The ANOVA shows for FFA, TVA and TSA a significant influence of the surgeon on the measurement result. Difficulty in indicating the implant line and the sensitivity of short lines to angular measurement could be reasons for the significant influence on FFA and TSA, which are measured on short lateral films. TVA measurements on the full frontal x-ray are also affected by difficulty in indicating implant line where for a femoral implant a line tangent to the condyles is more consistent. These results can be compared to the findings of Hirschmann et al [2] where, contrary to their data, our measurements on FVA and TVA correlate better, presumably because of the use of long leg film instead of short film. Our data is collected from 6 surgeons whereas the Hirschmann et al study represents 1 surgeon and 1 radiologist. SDC calculations based on this variability study show the smallest detectable changes on x-ray measurements for FVA, TVA and TSA are approximately 1° and approximately 2° for FFA. Conclusion. The results indicate that x-ray measurement variability should be taken into account when choosing a post-operative measurement technique. While x-ray measurement still has its place in daily practice, we advise more consistent methods of measuring for research

Aims. Leg length inequality following total hip replacement remains common. In an effort to reduce this occurrence, surgeons undertake pre-operative templating and use various forms of intra-operative measurements, including computer navigation. This study aims to delineate which measurement technique is most appropriate for measuring leg length inequality from a pelvic radiograph. Method. Three observers took a total of 9600 measurements from 100 pelvic radiographs. Four lines were constructed on each of the radiographs, bisecting the acetabular teardrops (Methods 1/2), ishial spines (Method 3/4), inferior sacroiliac joint (Method 5/6) and inferior obturator foramen (Method 7/8). Measurements were taken from these lines to the midpoint on the LT and to the tip of the GT. The effect of pelvic positioning was also assessed using radiographs of a synthetic pelvis and femur using the same eight methods by a single observer (ED). Intra-observer variability was analysed using within subject standard deviation. Inter-observer variability was analysed using the coefficient of inter-observer variability (CIV). Results. When considering the 100 pelvic radiographs measurement methods 3 (SD 3.5, CIV 0.34) and 8 (SD 3.3 CIV 0.33) showed the best inter and intra observer variability. Methods 4 and 6 performed badly for inter and intra observer variability (SD 3.8 CIV 0.4 and SD 4.6 CIV 0.4). Methods 1, 2, 5 and 7 performed well in one aspect but poorly in the other. When considering the effect of pelvic positioning using radiographs of the synthetic pelvis and femur construct, methods 3 and 7 performed best (SD 6.7 and SD 7.4). Discussion. Measuring from the ischial tuberosities to the LT has the best intra- and interobserver variability. It also performs well despite pelvic malposition. As techniques improve in the measurement of intra-operative leg length, a more accurate measurement of leg length is needed to validate these technologies by

Introduction. Well-balanced soft tissue is essential for achieving a good result when performing total knee arthroplasty. The preoperative planning is critical for ensuring a good operation. This study evaluated the preoperative distractive stress radiographs in order to quantify and predict the extent of medial release according to the degree of varus deformity in primary total knee arthroplasty. Methods. We evaluated 120 varus, osteoarthritic knee joints (75 patients). The association of the angle on the distractive stress radiograph with extent of medial release was analyzed. The extent of medial release was classified into the following 4 groups according to the stage: release of the deep medial collateral ligament (group 1), release of the posterior oblique ligament and/or semimembranous tendon (group 2), release of the posterior capsule (group 3) and release of the superficial medial collateral ligament (group 4). Results. Of the 120 cases for which medial release was performed, 30 (25.0%), 41 (34.2%), 20 (16.7%), and 29 (24.2%) cases were in group 1, 2, 3, and 4, respectively. After medial release, the difference between the medial and lateral gaps in flexion and extension was 0.1 mm (range, 0 to 1 mm) and 0.1 mm (range, 0 to 1 mm), respectively. The difference between the flexion and extension gaps was 0.6 mm (range, 0 to 1.5 mm). The mean femorotibial angle on the preoperative distractive stress radiograph was valgus 2.4° (group 1), valgus 0.8° (group 2), varus 2.1° (group 3) and varus 2.7° (group 4). The extent of medial release increased with increasing degree of varus deformity seen on the preoperative distractive stress radiograph.(Figure 1). Conclusions. The preoperative distractive stress radiograph was useful for predicting the extent of medial release when performing primary total knee arthroplaty. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Magnification of anteroposterior radiographs of the pelvis is variable. To improve the accuracy of templating, reliable and radiographer-friendly methods of scaling are necessary. We assessed two methods of scaling digital radiographs of the pelvis: placing a coin of known diameter in the plane of interest between the patient’s thighs, and using a caliper to measure the bony width of the pelvis. A total of 39 patients who had recently undergone hemiarthroplasty of the hip or total hip replacement were enrolled in the study. The accuracy of the methods was assessed by comparing the actual diameter of the head of the prosthesis with the measured on-screen value. The coin method was within a mean of 1.12% (0% to 2.38%) of the actual measurement, the caliper group within 6.99% (0% to 16.67%). The coin method was significantly more accurate (p < 0.001). It was also reliable and radiographer friendly. We recommend it as the method of choice for scaling radiographs of the pelvis before hip surgery

The verification of the alignment of the lower limb is critical for reconstructive surgery as well as trauma surgery in order to prevent osteoarthritis. The mechanical axis is a straight line defined by the center of the femoral head and the center of the ankle joint, ideally passing the knee joint in its center. Whereas the usual preoperative method to determine the mechanical axis of the lower limbs is still the long standing radiograph, common intra-operative methods are the use of an electrocautery cord or an X-ray grid consisting of wire lines underneath the patient. Both methods require the surgeon to bring the femoral head and the ankle joint exactly to overlay with a radiopaque line that passes through both points. The distance of the knee center from this line is defined as the mechanical axis deviation (MAD). In order to reduce the errors introduced by perspective projection effects, the joint centers must be placed in the center of the c-arm images, which definitely requires time, experience and additional radiation. We propose a computer aided X-ray stitching method that puts individual X-ray images into a panoramic image frame combining the Camera Augmented Mobile C-arm (CamC) system, which features a video camera with its optical center virtually coinciding with the origin of the X-rays, with an optical tracking marker pattern underneath the operating table. The camera image of the marker pattern is used to perform pose estimation of the C-arm, allowing the calculation of the x-ray source motion between the positions in which the individual X-rays were taken. By estimating the homography, the different X-rays can be registered into a panoramic frame, enabling perfect alignment and metric measurements. In order to reduce parallax effects that lead to axis and metric measurement errors, we applied a method requiring two constraints: The bone plane has to be roughly parallel to the planar marker pattern and the distance between the marker plane and the bone plane has to be estimated. In order to evaluate the method, we used a life-size synthetic skeleton leg. After tightening a straight wire between the centers of the hip and ankle joint, the knee joint was bent into a MAD of 55 mm, which was confirmed by measuring the distance between the knee center and the wire with a ruler. The leg phantom was then placed on a radiolucent operating table, parallel to the pattern plane 130 mm underneath. The operating table was moved through the C-arm while acquiring the three desired X-ray images. which were registered into a panoramic image frame. The centers of the femoral head, the ankle, and the knee were manually determined on the generated panoramic image by a surgeon. The mechanical axis was automatically displayed and the MAD was visualised in the image and computed as 55.23 mm. We presented a new solution to intra-operatively verify alignment of the lower extremity. When using the CamC system, only a marker pattern has to be used for tracking. No additional tracking devices and calibration procedures are needed. Furthermore, the presented method only requires three x-rays that cover the femoral head, the knee and the ankle and marking of the three spots. Due to the parallax correction, these spots do not have to be exactly in the center of the picture. For this reason, compared to using an X-ray grid or an electrocautery cord, our method allows the procedure to be much faster and reduces the number of x-ray images. However, for clinical evaluation, a patient study will be conducted in the future

Introduction. Various 2D and 3D surfaces are available for cementless fixation of acetabular cups. The goal of these surface modifications is to improve fixation between the metallic cups and surrounding bone. Radiographs have historically been used to evaluate the implant-to-bone fixation around the acetabular cups. In general, a well fixed cup shows no gaps or radiolucency around the cup's outer diameter. In post-operative radiographs, the presence of progressive radiolucent zones of 2mm or more around the implant in the three radiographic zones is indicative of aseptic loosening, as described by DeLee and Charnley [1]. In this cadaveric study, we investigated the X-ray image characteristics of two different types of acetabular shell surfaces (2D and 3D) to evaluate the implant-to-bone interface in the two designs. Methods. Six human cadavers were bilaterally implanted with acetabular cups by an orthopaedic surgeon. 2D surface cups (Trident, Stryker, Mahwah, NJ) and 3D surface cups (Tritanium, Stryker, Mahwah, NJ) were randomized between the left and right acetabula. The surgeon used his regular surgical technique (1 mm under reaming) to implant the acetabular cups. The cadavers were sent for X-ray imaging after the operation, Figure 1A. Following the X-ray imaging, the acetabular cups were carefully resected from the cadavers. Enough bone around the cups was retained for analysis of the implant-to-bone interface by contact X-ray. The acetabular cups with the surrounding bone were fixed in 70% isopropyl alcohol for about a week and subsequently embedded in polymethyl methacrylate. The embedded cups were sectioned at 30° intervals using a diamond saw in the coronal plane, as recommended by Engh et al [2], Figure 1B. The sectioning of the samples produced 6 slices of each cup where the implant-bone interface could easily be visualized for evaluation with contact X-ray. Results. The AP X-rays of the cadavers demonstrated radiolucent lines, as well as gap defects in some cases. The same phenomenon was observed on the contact X-rays of the embedded implant sections as well, where one could easily identify the gap between the metal cup and the surrounding bone. The most striking finding was that, in a few cases, the contact X-rays showed radiolucency around the metal cup whereas the physical section did not seem to have any gaps. This phenomenon is illustrated in Figure 2. Conclusions. The physical gap or radiolucent lines around the acetabular cups have been reported in literature; however, they seem to fill up with time as biological fixation progresses between the surrounding bone and the implant. In our study we found radiolucency that was not associated with the presence of a physical gap. In contrast, we found gaps on physical sections that were not correlated with radiolucencies. This phenomenon may be attributed to the interaction of X-rays with the cup surface modifications. The contact X-ray images demonstrated that radiolucency around cups may not always correlate with physical gaps. Further analysis is required to understand the implications of these findings

For a successful total knee arthroplasty (TKA) and long prosthesis lifespan, correct alignment of the implant components as well as proper soft tissue balancing are of major importance. In order to overcome weaknesses of existing imaging modalities for TKA planning such as radiation exposure and lack of soft tissue visualisation (X-ray and CT) and high cost, long acquisition times and geometric distortion (MRI), it is investigated if ultrasound (US) imaging is a suitable alternative. Currently, a reconstruction method of the bony knee morphology based on US imaging is developed at our research institute. For capturing the mechanical axis, being crucial for TKA planning, different approaches could be implemented. This work investigates whether a weight-bearing full leg X-ray registered with the local 3D-US knee dataset can be used for this purpose. Also, the impact of incorrect calibration data (i.e. uncalibrated X-rays) on the accuracy of the estimated mechanical axis is investigated. A 3D-2D projective, feature-based registration algorithm was used to spatially align the 3D US-based model to the 2D X-ray image before transferring the mechanical axis from the X-ray to the model. For validation, a CT-based local model and its projection were used and an initial error in translation and rotation was added. Also, calibration parameters such as the centre ray position and the source-to-image-detector distance were altered. The estimation error of the mechanical axis was less than 1°, the median error lower than 0.1° in the frontal plane. Even if the calibration data is not available, the accuracy remains sufficient for TKA planning. In this study, idealised 2D and 3D image information was used. In the future, this method should be tested using clinical X-ray images and 3D-US data

INTRODUCTION. Accurate knowledge of knee joint kinematics following total knee arthroplasty (TKA) is critical for evaluating the functional performance of specific implant designs. Biplane fluoroscopy is currently the most accurate method for measuring 3D knee joint kinematics in vivo during daily activities such as walking. However, the relatively small imaging field of these systems has limited measurement of knee kinematics to only a portion of the gait cycle. We developed a mobile biplane X-ray (MoBiX) fluoroscopy system that enables concurrent tracking and imaging of the knee joint for multiple cycles of overground gait. The primary aim of the present study was to measure 6-degree-of-freedom (6-DOF) knee joint kinematics for one complete cycle of overground walking. A secondary aim was to quantify the position of the knee joint centre of rotation (COR) in the transverse plane during TKA gait. METHODS. Ten unilateral posterior-stabilised TKA patients (5 females, 5 males) were recruited to the study. Each subject walked over ground at their self-selected speed (0.93±0.12 m/s). The MoBiX imaging system tracked and recorded biplane X-ray images of the knee, from which tibiofemoral kinematics were calculated using an image processing and pose-estimation pipeline created in MATLAB. Mean 6-DOF tibiofemoral joint kinematics were plotted against the mean knee flexion angle for one complete cycle of overground walking. The joint COR in the transverse plane was calculated as the least squares intersection of the femoral flexion axis projected onto the tibial tray during the stance and swing phases. The femoral and tibial axes and 6-DOF kinematics were defined in accordance with the convention defined by Grood and Suntay in 1983. RESULTS AND DISCUSSION. The offset in secondary joint motions at a given flexion angle was greater at larger knee flexion angles than at smaller flexion angles for abduction, anterior drawer, and lateral shift, whereas the opposite was true for external rotation. Significant variability was observed between subjects for the COR. The mean COR was on the lateral side during stance, consistent with results reported in the literature for the intact knee. Interestingly, the mean COR was on the medial side during swing. CONCLUSIONS. Our results suggest that secondary joint motions in the TKA knee, specifically, external rotation, abduction, anterior drawer and lateral shift, are determined not only by implant geometry and ligament anatomy but also by external loading, and are therefore task-dependent. The mean COR in the transverse plane shifted from the lateral to the medial side of the knee as the leg transitioned from stance to swing. Mobile dynamic X-ray imaging is a valuable tool for evaluating the functional performance of knee implants during locomotion over ground

Fractures of the clavicle are relatively common, occurring mostly in younger patients and have historically been managed non-operatively. Recent studies have shown an advantage to surgical reduction and stabilisation of clavicle fractures with significant displacement. Currently, fracture displacement is measured using simple anterior-posterior two-dimensional x-rays of the clavicle. Since displacement can occur in all three-dimensions, however, evaluation of the amount displacement can be difficult and inaccurate. The purpose of this study was to determine the view that provides the most accurate assessment. Nine CT scans of acute displaced clavicle fractures were analysed with AmiraDEV5.2.2 Imaging software. Measurements for degrees of shortening and fracture displacement of the fracture clavicle were taken. Using a segmentation and manipulation module (ITK toolkit), five digitally reconstructed radiographs (DRRs) mimicking antero-posterior x-rays were created for every CT, with each differing by projection angle (ranging from 20° upwards tilt to 20° downwards tilt). Measurements were taken on each DRR using landmarks of entire clavicle length, distance from vertebrae to fracture (medial fragment length), distance from fracture to acromium (lateral fragment length), and horizontal shortening, and then compared to the true measurement obtained from the original CT. For all 9 samples, after comparing the measurements of clavicle fracture displacement in each 2D image, we found that an AP view with a 20° downward tilt yielded displacement measurements closest to the 3D (“gold standard”) measurements. The results agree with previous data collected from cadaveric specimens using physical X-ray film images. DDRs enable creation of multiple standard AP radiographs from which accurate tilt can be measured. The large deviation in measurements on different DRR projections motivates consideration of standardising X-ray projections. A uniform procedure would allow one to correctly evaluate the displacement of clavicular fractures if fracture displacement information is to be utilized in motivating surgical decision-making

Accurate 3D pre-operative planning shows significance of improving the precision of Total Hip Arthroplasty (THA) and Total Knee Arthroplasty (TKA). Since CT acquisition leads to high radiation exposure to patients, it is clinically desirable to find an alternative to CT scan for planning THA or TKA such as patient-specific 2D–3D reconstruction from a limited number of 2D calibrated X-ray images acquired with much lower radiation dose e.g. EOS imaging. Feature-based 2D–3D non-rigid registration based on the construction of statistical shape model (SSM) as a priori has been applied to reconstruct the surface models of proximal femur, and also the surface reconstruction of lower extremity for TKA has been validated in a cadaveric study by Zheng et al. On the other hand, intensity-based 2D–3D non-rigid registration can reconstruct the patient-specific intensity volumes like CTs to allow an insight into lower extremity morphology such as intramedullary anatomy, which can provide more comprehensive information in routine clinical practice. In this study, we will present an atlas- based 2D–3D reconstruction method and introduce its application to reconstruct the intensity volumes of lower extremity. Moreover, we take the articulation in the knee joint into consideration so as to avoid the penetration between femur and tibia which is favourable for the pre-operative planning. The results of the experiments demonstrated the efficacy of the proposed method on reconstructing the lower extremity morphology as well as the intramedullary canal anatomy

Purpose:. To materialize 3D kinematic analysis of total knee arthroplasty (TKA), 2D/3D registration techniques, which use X-ray fluoroscopic images and the knee implants CAD, have been applied to clinical cases. However, most conventional methods have needed time-consuming and labor-intensive manual operations in some process. In previous study, we addressed a manual operations problem when setting initial pose of implants model for 2D/3D registration, and reported a semi-automated initial pose estimation method based on an interpolation technique. However, this method still required appropriate initial pose estimation of the model with manual operations for some X-ray images (key frames). Additionally, in the situation like fast knee motion and use of low frame rate, good registration results were not obtained because of the large displacement between each frame silhouette. To overcome these problems, this study proposes an improved semi-automated 3D kinematic estimation method. Methods:. Our 2D/3D registration technique is based on a robust feature-based algorithm. In improved initial pose estimation method, for the only first frame, the initial pose is manually adjusted as close as possible. That is, we automatically estimate appropriate initial pose of the model for X-ray images except for the first frame. To automatically estimate the initial pose of the model, we utilize a transformation with feature points extracted from the previous and next frames. A transform matrix which has three DOF (translations parallel to the image, and a rotation perpendicular to the image) is calculated by registration of corresponding feature points between the previous and next frame extracted with SURF algorithm. While, the corresponding point sets extracted by SURF sometimes include some error sets. Therefore, in this study, LmedS method was employed to detect the error corresponding sets and calculate a transform matrix accurately. In Fig. 1(a) and (b), the orange square shows the region defined with the boundary box of the model, and some lines show the combined corresponding point sets. The blue lines are correct corresponding point sets, and the pink lines are error corresponding point sets detected with LmedS method. Finally, 3D pose of the model estimated in previous frame is transformed with accurately calculated transform matrix, and the transformed pose is used as an initial 3D pose of the model in next frame. Experimental results:. To validate the feasibility of the improved semi-automated 3D kinematic estimation method, experiments using X-ray fluoroscopic images of 4 TKA patients during knee motions were performed. In order to assess the performance of the improved method, automation rate was calculated, and the rate was defined as the X-ray frame number of satisfying clinical required accuracy (error within 1 mm, 1 degree) relative to all X-ray frame number. As results of the experiments, 3D pose of the model for all X-ray images except for the first frame is automatically stably-estimated, the automation rate of the femoral and tibial component were 83.7% and 73.5%, respectively. Conclusions:. The present method doesn't need labor-intensive manual operations for 3D kinematic estimation of TKA, and is thought to be very helpful for practical clinical applications

To achieve 3D kinematic analysis of total knee arthroplasty (TKA), 2D/3D registration techniques which use X-ray fluoroscopic images and computer-aided design (CAD) model of the knee implants, have been applied to clinical cases. These techniques are highly valuable for dynamic 3D kinematic measurement of TKA implants, but have needed time-consuming and labor-intensive manual operations in some process. To overcome a manual operations problem of initial pose estimation for 2D/3D registration, this study proposes an improvement method for semi-automated 3D kinematic measurement of TKA using X-ray fluoroscopic images. To automatically estimate the initial pose of the implant CAD model, we utilise a transformation with feature points extracted from the previous and next frames. A transform matrix which has three degree of freedom (translations parallel to the image, and a rotation perpendicular to the image) is calculated by registration of corresponding feature points between the previous and next frame extracted with speeded up robust features (SURF) algorithm. While, the corresponding point sets extracted by SURF sometimes include some error sets. Therefore, in this study, least median of squares method is employed to detect the error corresponding sets and calculate a transform matrix accurately. Finally, the 3D pose of the model estimated (by the 2D/3D registration) in previous frame is transformed with the accurately calculated transform matrix, and the transformed pose is used as an initial 3D pose of the model (for the 2D/3D registration) in next frame. To validate the feasibility of the improved semi-automated 3D kinematic measurement method, experiments using X-ray fluoroscopic images of four TKA patients during knee motions were performed. In order to assess the performance of the improved method, automation rate was calculated, and the rate was defined as the X-ray frame number of satisfying clinical required accuracy (error within 1mm, 1 degree) relative to all X-ray frame number. As results of the experiments, 3D pose of the model for all X-ray images except for the first frame is automatically stably-estimated, the automation rate of the femoral and tibial component were 83.7 % and 73.5 %, respectively. The improved method doesn't need labor-intensive manual operations for 3D kinematic measurement of TKA, and is thought to be very helpful for actual clinical practice

Recent reports observe that orthopaedic surgeons lack essential knowledge about ionising radiation. We aim to demonstrate perceived use of image-intensifiers by surgeons and awareness of radiation doses used during fractured neck of femur surgery. Surgeons at a regional trauma centre were sent an online questionnaire. They were shown two neck of femur fracture radiographs and asked the total number of images they would use to reduce and fix the fracture with a dynamic-hip-screw / inter-medullary nail respectively. They were asked the maximum safe radiation dose, and that of ‘hip pining’ compared to CXR as outlined by the Ionising Radiation Regulations 1999. For a DHS, consultants and registrars estimate their image use similarly. For IM nailing, consultants estimated higher image use than registrars, and double the number of X-rays taken for IM nailing compared to DHS. Knowledge levels regarding radiation doses during orthopaedic hip procedures are very low. There is an expectation that more images will be used in IM nailing procedures. We plan to educate orthopaedic surgeons about radiation dose and safety. Correlating our findings with actual use of image in theatre when performing hip fracture surgery would extend the use of this study

Introduction. A full 3D postoperative analysis, i.e. a quantitative comparison between planned and postoperative positions of bone(s) and implant(s) in 3D, is necessary for a thorough assessment of the outcome of the surgery, as well as to provide information that could be used to optimize similar procedures in the future. In this work, we present a method of postoperative analysis based on a pair of X-ray images only, which reaches a level of accuracy that is comparable with the results obtained with a 3D postoperative image. Methods. The method consists in using 3D models of bones, segmented from 3D preoperative image (e.g. CT or MRI scans), and 3D models of implant, and aligning them independently to X-rays by matching contours manually drawn on the X-rays and projected contours. The result gives the relative postoperative position of bone and implant. The method was tested on a phantom consisting of commonly available femoral knee implant on a physical model of a femur (Sawbones®). Result was compared to the optical scan, considered as ground truth, of the implanted saw bone. Two studies were performed: inter-operator (six operators), and intra-operator (5 tests). In addition, the inter-operator study was repeated while asking all the operators to use the same pre-drawn contours. The results are presented by calculating the distance (anterior/posterior, proximal/distal, medial/lateral) between the centers of gravity, and the angles (varus/valgus, flexion/extension, external/internal rotations) of the implants from the X-ray based method and the ground truth. Results were also compared with the relative position of bone and implant extracted from a 3D CT postoperative image. Saw bone and implant were first segmented from this image. In order to determine the position of the implant, despite the metal artefacts in the CT images, the 3D model of the implant was registered on the segmented implant. All processing, including segmentation, registration of X-rays, and measurements, was performed using Mimics Innovation Suite 17.0 ®. Results. Results are shown in Figure 1. The inter-operator study showed a maximum error of 0,55 mm and 1°. The intra-operator study, performed by an experienced operator, showed the importance of the learning curve, as all the measurement errors decreased (except for the varus/valgus that increased from −0,07° to 0.13°)) up to 0,13 mm and 0,23°. Same trend was showed by the results of the inter-operator based on same drawn contours, showing the importance of contour drawing on the results, and thus again the importance of the training. In comparison, results from postoperative CT showed similar order of magnitude with a maximum error of 0,65 mm and 0,61°. Conclusion. The evaluation of our method gives preliminary good results, and was comparable with a postoperative analysis based on CT, while reducing the cost and the radiation dose of the analysis. A validation on cadaver and clinical data is planned to confirm our results