Background and Purpose. The gold standard for detection of implant wear and migration is currently radiostereometry (RSA). The purpose of this study is to compare a three-dimensional computed tomography technique (3D CT) to standard RSA as an alternative technique for measuring migration of acetabular cups in total hip arthroplasty.
Materials and Methods. With tantalum beads, we marked one cemented and one uncemented cup and mounted these on a similarly marked pelvic model. A comparison was made between 3D CT and standard RSA for measuring migration. Twelve repeated stereoradiographs and CT scans with double examinations in each position and gradual migration of the implants were made. Precision and accuracy of the 3D CT were calculated.
Results. The accuracy of the 3D CT ranged between 0.07 and 0.32 mm for translations and 0.21 and 0.82° for rotation. The precision ranged between 0.01 and 0.09 mm for translations and 0.06 and 0.29° for rotations, respectively. For standard RSA, the precision ranged between 0.04 and 0.09 mm for translations and 0.08 and 0.32° for rotations, respectively. There was no significant difference in precision between 3D CT and standard RSA. The effective radiation dose of the 3D CT method, comparable to RSA, was estimated to be 0.33 mSv.
Interpretation. Low dose 3D CT is a comparable method to standard RSA in an experimental setting.
BACKGROUND: Computed tomography (CT) has the potential to acquire the data needed for migration studies of orthopedic joint implants of patients who have had tantalum beads implanted at the time of joint replacement surgery. This can be accomplished with the same precision as radiostereometric analysis (RSA). Switching to CT would increase availability without the need for the specific facilities required for RSA. However, higher effective dose is a concern.
PURPOSE: To investigate if migration measurements can be done with CT with an accuracy and effective dose comparable to that of conventional RSA.
MATERIAL AND METHODS: Fourteen scanning protocols were tested in a hip phantom that incorporated tantalum beads and an uncemented femoral stem. The protocols were graded for clinical practice according to the three parameters of image quality, effective dose, and robustness of numerical data. After grading, the two protocols that graded best overall were applied to a pilot patient.
RESULTS: All protocols produced scans in which the numerical data were sufficient for a migration analysis at least as precise as would be expected using RSA. A protocol with an effective dose of 0.70 mSv was shown to be applicable in a pilot patient.
CONCLUSION: Low-dose CT scans with an effective dose comparable to a set of routine plain radiographs can be used for precise migration measurements.
Study Design: This was a randomized radiologic biomechanical pilot study in vivo. Objective: The objectives of this study was to evaluate if 3-dimensional computed tomography is a feasible tool in motion analyses of the lumbar spine and to study if preservation of segmental midline structures offers less postoperative instability compared with central decompression in patients with lumbar spinal stenosis with degenerative spondylolisthesis. Summary of Background Data: The role of segmental instability after decompression is controversial. Validated techniques for biomechanical evaluation of segmental motion in human live subjects are lacking. Methods: In total, 23 patients (mean age, 68 y) with typical symptoms and magnetic resonance imaging findings of spinal stenosis with degenerative spondylolisthesis (>3 mm) in 1 or 2 adjacent lumbar levels from L3 to L5 were included. They were randomized to either laminectomy (LE) or bilateral laminotomy (LT) (preservation of the midline structures). Documentation of segmental motion was made preoperatively and 6 months postoperatively with CT in provoked flexion and extension. Analyses of movements were performed with validated software. The accuracy for this method is 0.6 mm in translation and 1 degree in rotation. Patient-reported outcome measures were collected from the Swespine register preoperatively and 2-year postoperatively. Results: The mean preoperative values for 3D rotation and translation were 6.2 degrees and 1.8 mm. The mean increase in 3D rotation 6 months after surgery was 0.25 degrees after LT and 0.7 degrees after LE (P=0.79) while the mean increase in 3D translation was 0.15 mm after LT and 1.1 mm after LE (P=0.42). Both surgeries demonstrated significant improvement in patient-reported outcome measures 2 years postoperatively. Conclusions: The 3D computed tomography technique proved to be a feasible tool in the evaluation of segmental motion in this group of older patients. There was negligible increase in segmental motion after decompressive surgery. LE with removal of the midline structures did not create a greater instability compared with when these structures were preserved.
When a bone is broken for any reason, it is important for the orthopaedic surgeon to know how bone healing is progressing. There has been resurgence in the use of the fluoride (18F-) ion to evaluate various bone conditions. This has been made possible by availability of positron emission tomography (PET)/CT hybrid scanners together with cyclotrons. Absorbed on the bone surface from blood flow, 18F- attaches to the osteoblasts in cancellous bone and acts as a pharmacokinetic agent, which reflects the local physiologic activity of bone. This is important because it shows bone formation indicating that the bone is healing or no bone formation indicating no healing. As 18F- is extracted from blood in proportion to blood flow and bone formation, it thus enables determination of bone healing progress.
PURPOSE: To demonstrate the usefulness of positron emission tomography (PET)/computed tomography (CT) bone scans for gaining insight into healing bone status earlier than CT or X-ray alone.
METHODS: Forty-one prospective patients being treated with a Taylor Spatial Frame were recruited. We registered data obtained from successive static CT scans for each patient, to align the broken bone. Radionuclide uptake was calculated over a spherical volume of interest (VOI). For all voxels in the VOI, histograms and cumulative distribution functions of the CT and PET data were used to assess the type and progress of new bone growth and radionuclide uptake. The radionuclide uptake difference per day between the PET/CT scans was displayed in a scatter plot. Superimposing CT and PET slice data and observing the spatiotemporal uptake of 18F- in the region of healing bone by a time-sequenced movie allowed qualitative evaluation.
RESULTS: Numerical evaluation, particularly the shape and distribution of Hounsfield Units and radionuclide uptake in the graphs, combined with visual evaluation and the movies enabled the identification of six patients needing intervention as well as those not requiring intervention. Every revised patient proceeded to a successful treatment conclusion.
CONCLUSION: Numerical and visual evaluation based on all the voxels in the VOI may aid the orthopedic surgeon to assess a patient's progression to recovery. By identifying slow or insufficient progress at an early stage and observing the uptake of 18F- in specific regions of bone, it might be possible to shorten the recovery time and avoid unnecessary late complications.
Eighteen consecutive patients, treated with a Taylor Spatial Frame for complex tibia conditions, gave their informed consentto undergo Na18F− PET/CT bone scans. We present a Patlak-like analysis utilizing an approximated blood time-activity curveeliminating the need for blood aliquots. Additionally, standardized uptake values (SUV) derived from dynamic acquisitions werecompared to this Patlak-like approach. Spherical volumes of interest (VOIs) were drawn to include broken bone, other (normal)bone, and muscle. The SUV𝑚(𝑡) (𝑚 = max, mean) and a series of slopes were computed as (SUV𝑚(𝑡𝑖) − SUV𝑚(𝑡𝑗))/(𝑡𝑖 − 𝑡𝑗), forpairs of time values 𝑡𝑖 and 𝑡𝑗. A Patlak-like analysis was performed for the same time values by computing ((VOI𝑝(𝑡𝑖)/VOI𝑒(𝑡𝑖)) −(VOI𝑝(𝑡𝑗)/VOI𝑒(𝑡𝑗)))/(𝑡𝑖−𝑡𝑗), where p = broken bone, other bone, andmuscle and e = expected activity in aVOI. Paired comparisonsbetween Patlak-like and SUV𝑚 slopes showed good agreement by both linear regression and correlation coefficient analysis(𝑟 = 84%, 𝑟𝑠 = 78%-SUVmax, 𝑟 = 92%, and 𝑟𝑠 = 91%-SUVmean), suggesting static scans could substitute for dynamic studies.Patlak-like slope differences of 0.1 min−1 or greater between examinations and SUVmax differences of ∼5 usually indicated goodremodeling progress, while negative Patlak-like slope differences of −0.06 min−1 usually indicated poor remodeling progress in thiscohort.
Monitoring and quantifying bone remodeling are of interest, for example, in correction osteotomies, delayed fracture healing pseudarthrosis, bone lengthening, and other instances. Seven patients who had operations to attach an Ilizarov-derived Taylor Spatial Frame to the tibia gave informed consent. Each patient was examined by (NaF)-F-18 PET/CT twice, at approximately six weeks and three months after the operation. A validated software tool was used for the following processing steps. The first and second CT volumes were aligned in 3D and the respective PET volumes were aligned accordingly. In the first PET volume spherical volumes of interest (VOIs) were delineated for the crural fracture and normal bone and transferred to the second PET volume for SUVmax evaluation. This method potentially provides clinical insight into questions such as, when has the bone remodeling progressed well enough to safely remove the TSF? and when is intervention required, in a timelier manner than current methods? For example, in two patients who completed treatment, the SUVmax between the first and second PET/CT examination decreased by 42% and 13%, respectively. Further studies in a larger patient population are needed to verify these preliminary results by correlating regional (NaF)-F-18 PET measurements to clinical and radiological findings.
Background: Radiostereometric analysis (RSA) is often used for evaluating implanted devices over time. Following patients who have had tantalum beads implanted as markers in conjunction with joint replacements is important for longitudinal evaluation of these patients and for those with similar implants. As doing traditional RSA imaging is exacting and limited to specialized centers, it is important to consider alternative techniques for this ongoing evaluation. This paper studies the use of computed tomography (CT) to evaluate over time tantalum beads which have been implanted as markers. Methods: The project uses both a hip model implanted with tantalum beads, acquired in several orientations, at two different CT energy levels, and a cohort of seven patients. The model was evaluated twice by the same observer with a 1-week interval. All CT volumes were analyzed using a semi-automated 3D volume fusion (spatial registration) tool which provides landmark-based fusion of two volumes, registering a target volume with a reference volume using a rigid body 3D algorithm. The mean registration errors as well as the accuracy and repeatability of the method were evaluated. Results: The mean registration error, maximum value of repeatability, and accuracy for the relative movement in the model were 0.16 mm, 0.02 degrees and 0.1 mm, and 0.36 degrees and 0.13 mm for 120 kVp and 0.21 mm, 0.04 degrees and 0.01 mm, and 0.39 degrees and 0.12 mm for 100 kVp. For the patients, the mean registration errors per patient ranged from 0.08 to 0.35 mm. These results are comparable to those in typical clinical RSA trials. This technique successfully evaluated two patients who would have been lost from the cohort if only RSA were used. Conclusions: The proposed technique can be used to evaluate patients with tantalum beads over time without the need for stereoradiographs. Further, the effective dose associated with CT is decreasing.
As part of the 14-year follow-up of a prospectively randomized radiostereometry (RSA) study on uncemented cup fixation, two pairs of stereo radiographs and a CT scan of 46 hips were compared. Tantalum beads, inserted during the primary operation, were detected in the CT volume and the stereo radiographs and used to produce datasets of 3D coordinates. The limit of agreement between the combined CT and RSA datasets was calculated in the same way as the precision of the double RSA examination. The precision of RSA corresponding to the 99% confidence interval was 1.36°, 1.36°, and 0.60° for -, -, and -rotation and 0.40, 0.17, and 0.37 mm for -, -, and -translation. The limit of agreement between CT and RSA was 1.51°, 2.17°, and 1.05° for rotation and 0.59, 0.56, and 0.74 mm for translation. The differences between CT and RSA are close to the described normal 99% confidence interval for precision in RSA: 0.3° to 2° for rotation and 0.15 to 0.6 mm for translation. We conclude that measurements using CT and RSA are comparable and that CT can be used for migration studies for longitudinal evaluations of patients with RSA markers.
This study describes a 3D-CT method for analyzing facet joint motion and vertebral rotation in the lumbar spine after TDR. Ten patients were examined before and then three years after surgery, each time with two CT scans: provoked flexion and provoked extension. After 3D registration, the facet joint 3D translation and segmental vertebral 3D rotation were analyzed at the operated level (L5-S1) and adjacent level (L4-L5). Pain was evaluated using VAS. The median (±SD) 3D movement in the operated level for the left facet joint was 3.2 mm (±1.9 mm) before and 3.5 mm (±1.7 mm) after surgery and for the right facet joint was 3.0 mm (±1.0 mm) before and 3.6 mm (±1.4 mm) after surgery. The median vertebral rotation in the sagittal plane at the operated level was 5.4° (±2.3°) before surgery and 6.8° (±1.7°) after surgery and in the adjacent level was 7.7° (±4.0°) before and 9.2° (±2.7°) after surgery. The median VAS was reduced from 6 (range 5–8) to 3 (range 2–8) in extension and from 4 (range 2–6) to 2 (range 1–3) in flexion.
Background: Cervical total disc replacement (CTDR) is an alternative to anterior fusion. Therefore, it is desirable to have an accurate in vivo measurement of prosthetic kinematics and assessment of implant stability relative to the adjacent vertebrae. Purpose: To devise an in vivo CT-based method to analyze the kinematics of cervical total disc replacements (CTDR), specifically of two prosthetic components between two CT scans obtained under different conditions. Material and Methods: Nine patients with CTDR were scanned in flexion and extension of the cervical spine using a clinical CT scanner with a routine low-dose protocol. The flexion and extension CT volume data were spatially registered, and the prosthetic kinematics of two prosthetic components, an upper and a lower, was calculated and expressed in Euler angles and orthogonal linear translations relative to the upper component. For accuracy analysis, a cervical spine model incorporating the same disc replacement as used in the patients was also scanned and processed in the same manner. Results: Analysis of both the model and patients showed good repeatability, i.e. within 2 standard deviations of the mean using the 95% limits of agreement with no overlapping confidence intervals. The accuracy analysis showed that the median error was close to zero. Conclusion: The mobility of the cervical spine after total disc replacement can be effectively measured in vivo using CT. This method requires an appropriate patient positioning and scan parameters to achieve suitable image quality.