Assessment of the sacroiliac joint with computed tomography motion analysis: a diagnostic study of 12 patients.

BACKGROUND AND PURPOSE: Pain in the sacroiliac joint may be caused by abnormal joint motion. Diagnosis is mainly based on clinical tests. The aims of this study were to examine whether low-dose computed tomography with provocation of the hip could detect sacroiliac joint motion, and to study whether provocation of the hip results in greater sacroiliac joint motion in the ipsilateral than in the contralateral sacroiliac joint. PATIENTS AND METHODS: 12 patients with sacroiliac joint pain were examined with low-dose computed tomography scans of the sacroiliac joint, one with the hips in the neutral position, and one each in provocation with the left or the right hip in a figure-of-4 position. Accuracy was tested by comparing internal rotation of the sacrum with internal rotation in the sacroiliac joint. Motion in the sacroiliac joint was assessed by comparing the position of each of the ilia with the reference, the sacrum. Data is shown as mean with 95% confidence interval (CI). RESULTS: We observed greater motion in the sacroiliac joint than internally in the sacrum, i.e., 0.57° (CI 0.43-0.71) vs. 0.20° (CI 0.11-0.28). The motion of the geometric center of the moving object for the sacroiliac joint was larger on the provoked side; mean difference 0.17 mm (CI 0.01-0.33), P = 0.04. Corresponding figures for rotation were mean difference 0.19° (CI 0.10-0.28), P < 0.001. Compared with the sacrum, the largest motion was seen at the anterior superior iliac spine; mean difference 0.38 mm (CI 0.10-0.66), P = 0.001. CONCLUSION: Provocation in the figure-of-4 position of the hip results in sacroiliac joint motion measurable with computed tomography motion analysis. Provocation of the hip induces larger motion on the ipsilateral than on the contralateral sacroiliac joint.

Computed tomography-based radiostereometric analysis in orthopedic research: practical guidelines.

Early implant migration is an indicator of the long-term survival/failure of implants. CT-based radio-stereometric analysis (CT-RSA) is a precise method for measuring and visualizing implant migration in vivo using image processing of CT scans. This makes the method widely applicable to orthopedic researcher. Since its development in the early 2000s, CT-RSA has benefited from breakthroughs in CT and computing technology. These advancements have allowed for the acquisition of images with higher resolution at a much lower radiation dose. As a result, the measurement precision of CT-RSA is now comparable to that of the current gold standard technology while still compatible with most ethical considerations regarding radiation exposure. In this review we present bests practices for the successful execution of CT-RSA research projects. These practices are based on experience from projects on the hip, knee, shoulder, lower back, cervical spine, foot, pelvis, and wrist.

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

PURPOSE: High-energy pelvic fractures are complex injuries often requiring surgical treatment. Different radiological methods exist to evaluate the reduction and healing process postoperatively but with certain limitations. The aim of this study was to evaluate Computed Tomography Micromotion Analysis (CTMA) in a clinical setting for follow-up of surgically treated pelvic fracture patients. METHODS: 10 patients surgically treated for a pelvic fracture were included and prospectively followed with Computed Tomography (CT) at 0, 6, 12 and 52 weeks postoperatively. CTMA was used to measure postoperative translation and rotation of the pelvic fracture during the 52 weeks follow-up. Clinical outcomes were collected through the questionnaires EQ-5D index score and Majeed score. RESULTS: 10 patients were included with mean age (± SD, min-max) 52 (16, 31-80) years and 70% (n = 7) were males. The median (IQR, min-max) global translation from 0 to 52 weeks was 6.0 (4.6, 1.4-12.6) millimeters and median global rotation was 2.6 (2.4, 0.7-4.7) degrees. The general trend was a larger translation between 0 and 6 weeks postoperatively compared to 6-12 and 12-52 weeks. For the clinical outcomes, the general trend was that all patients started from high scores which decreased in the first postoperative follow-up and recovered to different extent during the study period. CONCLUSION: CTMA was successfully used in the follow-up of surgically treated pelvic fracture patients. Movement in the pelvic fractures after surgical fixation was largest between 0 and 6 weeks.

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

BACKGROUND AND PURPOSE: CT micromotion analysis (CTMA) has been considered as an alternative to radiostereometry (RSA) for assessing early implant migration of orthopedic implants. We investigated the feasibility of CTMA to assess early migration and the progression of radiolucent lines in shoulder arthroplasties over 24 months using sequential low-dose CT scans. PATIENTS AND METHODS: 7 patients were included and underwent 9 primary total shoulder arthroplasties. We made CT scans preoperatively, within 1 week postoperatively, and after 3, 6, 12, and 24 months. At each follow-up, postoperative glenoid migration and any development of radiolucent lines were assessed. Clinical outcomes were recorded at all time points except within 1 week postoperatively. RESULTS: For the glenoid component, the median translation and median rotation were 0.00-0.10 mm and -1.53° to 1.05° at 24 months. Radiolucent lines could be observed around all glenoid components. The radiolucent lines developed from the periphery to the center of the implant for 6 glenoid components during follow-up. The Constant Score improved from a mean of 30 (21-51) preoperatively to 69 (41-88) at 24 months. INTERPRETATION: CTMA can be used to identify early migration and the development of radiolucent lines over time in glenoid components. Clinical trials with a larger sample size and longer follow-up are needed to establish the relationship between migration, radiolucent lines, loosening, and clinical outcome.

Inducible displacement CT increases the diagnostic accuracy of aseptic loosening in primary total hip arthroplasty.

BACKGROUND AND PURPOSE: Inducible displacement CT compares 2 CTs acquired in series but with alternated rotation of the femur. This provides visual and quantitative clues as to the mechanical situation, i.e., loosening, of a total hip arthroplasty. We report the accuracy of this method as well as the experience of integrating it into a clinical workflow. PATIENTS AND METHODS: This was a retrospective single centre study of 72 cases of suspected aseptic loosening were the surgeon after reviewing a standard plain radiograph saw a need for more information. The displacement CT and plain radiograph were compared either to intraoperative findings or a 1-3 year follow up questionnaire for patients that did not have revision surgery. Patients reporting degradation in status since the time of the displacement CT were called for a follow up plain radiograph. Sensitivity and specificity were assessed, and user experience gathered. RESULTS: Of 72 enrolled patients 15 were lost to follow up. Of the remaining 57, 17 were judged by in-traoperative findings or follow-up to have had loose implants. For plain radiography the sensitivity and specificity were 59% (95% CI 35-82) and 85% (74-96). For displacement CT the corresponding values were 77% (56-97), and 100% (100-100) respectively. The tool was adaptable to clinical routine. CONCLUSION: Displacement CT with alternated rotations of the femur is a viable option to improve the diagnostic process for identifying aseptic loosening in a total hip arthroplasty.

Adverse Events due to Lack of Precision in Total Hip Arthroplasty: The Potential of Provocation-Based CT for Diagnosis of Implant Loosening.

Adverse events in total hip replacement (THR) may have several origins, one being lack of precision in diagnosis and/or during surgery. This study describes the pattern and frequency of avoidable injuries in THR and the potential value of a new tool for early diagnosis of implant loosening. This retrospective study was based on all (n = 1 456) settled claims regarding THR in the Swedish National Patient Insurance database from 2010 to 2017. The claims and medical records were analyzed for root causes, with special focus on adverse events where lack of precision could be the cause. In a second stage, we assessed in 10 patients (20 implants) the diagnostic precision of a new software tool based on provocation-CT. These were all patients where the implant loosening diagnosis was deemed as inconclusive after a first plain X-ray. The findings from the provocation-CT and plain X-ray were compared to the surgical findings at revision. While 3 of 20 implants were correctly diagnosed with plain X-ray, for dynamic CT, this number was 14 of 20 implants. The retrospective study showed that the most common types of injuries were infections (34%), nerve injury (29%), mechanical problems (14.5%), dislocation (6%), and miscellaneous complications (16.5%). Of the patients with mechanical complications, one-third had aseptic implant loosening. Statement of clinical significance: we estimated that almost 200 patients in our registry study had mechanical complications after THR, mainly implant loosening. A third of these could potentially have been diagnosed and treated if CT examination with a dedicated image analysis tool to assess implant loosening after THR had been available.

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

Background and purpose - CT (computed tomography) based methods have lately been considered an alternative to radiostereometry (RSA) for assessing early implant migration. However, no study has directly compared the 2 methods in a clinical setting. We estimated the precision and effective radiation dose of a CT-based method and compared it with marker-based RSA in 10 patients with hip arthroplasty.Patients and methods - We included 10 patients who underwent total hip replacement with a cemented cup. CT and RSA double examinations were performed postoperatively, and precision and effective dose data were compared. The CT data was analyzed with CT micromotion analysis (CTMA) software both with and without the use of bone markers. The RSA images were analyzed with RSA software with the use of bone markers.Results - The precision of CTMA with bone markers was 0.10-0.16 mm in translation and 0.31°-0.37° in rotation. Without bone markers, the precision of CTMA was 0.10-0.16 mm in translation and 0.21°-0.31° in rotation. In comparison, the precision of RSA was 0.09-0.26 mm and 0.43°-1.69°. The mean CTMA and RSA effective dose was estimated at 0.2 mSv and 0.04 mSv, respectively.Interpretation - CTMA, with and without the use of bone markers, had a comparable precision to RSA. CT radiation doses were slightly higher than RSA doses but still at a considerably low effective dose.

Accuracy and precision of a CT method for assessing migration in shoulder arthroplasty: an experimental study.

BACKGROUND: Radiostereometric analysis (RSA) is the gold standard to measure early implant migration which is a predictive factor for implant survival. PURPOSE: To validate an alternative computed tomography (CT) technique to measure implant migration in shoulder arthroplasty. MATERIAL AND METHODS: A cadaver proximal humerus and a scapula, which had tantalum beads incorporated within them, were prepared to accept a short-stemmed humeral component and a two-pegged glenoid component of a commercial total shoulder arthroplasty (TSA) system. A five degree of freedom micrometer and goniometer equipped rig was used to translate and rotate the implant components relative to the respective bone to predetermined positions. Double CT examinations were performed for each position and CT motion analysis software (CTMA) was used to assess these movements. The accuracy and precision of the software was estimated using the rig's micrometers and goniometers as the gold standard. The technique's effective dose was also assessed. RESULTS: The accuracy was in the range of 0.07-0.23 mm in translation and 0.22-0.71° in rotation. The precision was in the range of 0.08-0.15 mm in translation and 0.23-0.54° in rotation. The mean effective dose for the CT scans was calculated to be 0.27 mSv. CONCLUSION: In this experimental setting, accuracy, precision, and effective dose of the CTMA technique were found to be comparable to that of RSA. Therefore, we believe clinical studies are warranted to determine if CTMA is a suitable alternative to traditional RSA for migration measurements in TSA.

Implant migration and bone mineral density measured simultaneously by low-dose CT scans: a 2-year study on 17 acetabular revisions with impaction bone grafting.

Background and purpose - Early postoperative implant migration predicts failure of joint replacements. Bone mineral density reflects bone quality and bone-graft incorporation. Implant migration and bone densitometry analysis usually require special equipment. We investigated cup migration and bone mineral density changes simultaneously with low-dose CT scans after acetabular revision hip arthroplasty using impaction bone grafting.Patients and methods - We performed a low-dose CT postoperatively, after 6 weeks, and after 2 years in 17 patients, all revised using impaction bone grafting and a graft-compressing titanium shell in the acetabulum. 6 patients had combined segmental and cavitary acetabular defects. Cup migration was analyzed using CT-based micromotion analysis (CTMA). Bone mineral density was determined in the graft and in surrounding native bone using volumetric quantitative computed tomography (QCT). The bone graft volume was calculated from 3D reconstructions.Results - At 2 years, the translations were 1.5 (95% CI 0.4-2.6) mm in proximal direction, -0.6 (CI -1.6 to 0.4) in the medial direction and 0.3 (CI 0.0-0.6) in the anterior direction. The mean volume of impacted bone graft was 40 cm³ (CI 28-52). In the graft bone mineral density increased 14% after 6 weeks and 23% after 2 years. There was 1 mechanical failure.Interpretation - Proximal migration of the acetabular component was low and comparable to previous reports. There was a rapid increase of bone mineral density in the bone graft. Low-dose CT scans make migration analysis and bone densitometry measurements possible in the same setting, offering great diagnostic potential for hip arthroplasty patients.

Low-dose CT-based implant motion analysis is a precise tool for early migration measurements of hip cups: a clinical study of 24 patients.

Background and purpose - Early implant migration is known to be a predictive factor of clinical loosening in total hip arthroplasty (THA). Radiostereometric analysis (RSA) is the gold standard used to measure early migration in patients. However, RSA requires costly, specialized imaging equipment and the image process is complex. We determined the precision of an alternative, commercially available, CT method in 3 ongoing clinical THA studies, comprising 3 different cups.Materials and methods - 24 CT double examinations of 24 hip cups were selected consecutively from 3 ongoing prospective studies: 2 primary THA (1 cemented and 1 uncemented) and 1 THA (cemented) revision study. Precision of the CT-based implant motion analysis (CTMA) system was calculated separately for each study, using both the surface anatomy of the pelvis and metal beads placed in the pelvis.Results - For the CTMA analysis using the surface anatomy of the pelvis, the precision ranged between 0.07 and 0.31 mm in translation and 0.20° and 0.39° for rotation, respectively. For the CTMA analysis using beads the precision ranged between 0.08 and 0.20 mm in translation and between 0.20° and 0.43° for rotations. The radiation dose ranged between 0.2 and 2.3 mSv.Interpretation - CTMA achieved a clinically relevant and consistent precision between the 3 different hip cups studied. The use of different hip cup types, different CT scanners, or registration method (beads or surface anatomy) had no discernible effect on precision. Therefore, CTMA without the use of bone markers could potentially be an alternative to RSA to measure early migration.

Prosthetic liner wear in total hip replacement: a longitudinal 13-year study with computed tomography.

This case report follows a woman who had a total hip replacement in 1992 when she was 45 years old. Six serial computed tomography (CT) examinations over a period of 13 years provided information that allowed her revision surgery to be limited to liner replacement as opposed to replacement of the entire prosthesis. Additionally, they provided data that ruled out the presence of osteolysis and indeed none was found at surgery. In 2004, when the first CT was performed, the 3D distance the femoral head had penetrated into the cup was determined to be 2.6 mm. By 2017, femoral head penetration had progressed to 5.0 mm. The extracted liner showed wear at the thinnest part to be 5.5 mm, as measured with a micrometer. The use of modern CT techniques can identify problems, while still correctable without major surgery. Furthermore, the ability of CT to assess the direction of wear revealed that the liner wear changed from the cranial to dorsal direction.

Risk factors for periacetabular osteolysis and wear in asymptomatic patients with uncemented total hip arthroplasties.

Osteolysis is a silent disease leading to aseptic loosening. This has not been studied in a cohort of asymptomatic patients. The aim of this study was to detect factors that might be associated with the development of periacetabular osteolysis and wear around an uncemented cup. We assessed 206 patients with an uncemented cup, measuring wear and periacetabular osteolysis using computed tomography with a median follow-up of 10 years after surgery (range 7-14 years). EQ5D, pain from the hip, and satisfaction were assessed. The association between periacetabular osteolysis and wear, age, gender, activity, BMI, cup type, cup age, positioning of the cup, and surface coating was investigated with a proportional odds model. Wear and male gender were associated with an increased risk for periacetabular osteolysis. There was no association with periacetabular osteolysis for time from operation, patient age, UCLA Activity Score, liner thickness at time of operation, BMI, cup positioning, and type of implant. A thin liner at time of operation is correlated to increased wear. Linear wear rate was 0.18 mm/year and 46 of 206 patients had large periacetabular osteolysis. Asymptomatic patients with these implants should be followed up on a regular basis with a sensitive method such as CT in order to detect complications early.

A new automated way to measure polyethylene wear in THA using a high resolution CT scanner: method and analysis.

As the most advantageous total hip arthroplasty (THA) operation is the first, timely replacement of only the liner is socially and economically important because the utilization of THA is increasing as younger and more active patients are receiving implants and they are living longer. Automatic algorithms were developed to infer liner wear by estimating the separation between the acetabular cup and femoral component head given a computed tomography (CT) volume. Two series of CT volumes of a hip phantom were acquired with the femoral component head placed at 14 different positions relative to the acetabular cup. The mean and standard deviation (SD) of the diameter of the acetabular cup and femoral component head, in addition to the range of error in the expected wear values and the repeatability of all the measurements, were calculated. The algorithms resulted in a mean (± SD) for the diameter of the acetabular cup of 54.21 (± 0.011) mm and for the femoral component head of 22.09 (± 0.02) mm. The wear error was ± 0.1 mm and the repeatability was 0.077 mm. This approach is applicable clinically as it utilizes readily available computed tomography imaging systems and requires only five minutes of human interaction.

Can Na18F PET/CT be used to study bone remodeling in the tibia when patients are being treated with a Taylor Spatial Frame?

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 Na(18)F 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 Na(18)F PET measurements to clinical and radiological findings.

In vivo and ex vivo measurement of polyethylene wear in total hip arthroplasty: comparison of measurements using a CT algorithm, a coordinate-measuring machine, and a micrometer.

BACKGROUND: Determination of the amount of wear in a polyethylene liner following total hip arthroplasty (THA) is important for both the clinical care of individual patients and the development of new types of liners. PATIENTS AND METHODS: We measured in vivo wear of the polyethylene liner using computed tomography (CT) (obtained in the course of regular clinical care) and compared it to coordinate-measuring machine (CMM) readings. Also, changes in liner thickness of the same retrieved polyethylene liner were measured using a micrometer, and were compared to CT and CMM measurements. The distance between the centers of the acetabular cup and femoral head component was measured in 3D CT, using a semi-automatic analysis method. CMM readings were performed on each acetabular liner and data were analyzed using 3D computer-aided design software. Micrometer readings compared the thickest and thinnest regions of the liner. We analyzed 10 THA CTs and retrievals that met minimal requirements for CT slice thickness and explanted cup condition. RESULTS - For the 10 cups, the mean difference between the CT readings and the CMM readings was -0.09 (-0.38 to 0.20) mm. This difference was not statistically significant (p = 0.6). Between CT and micrometer, the mean difference was 0.11 (-0.33 to 0.55) mm. This difference was not statistically significant (p = 0.6). INTERPRETATION - Our results show that CT imaging is ready to be used as a tool in clinical wear measurement of polyethylene liners used in THA.

Computed tomography vs. digital radiography assessment for detection of osteolysis in asymptomatic patients with uncemented cups: a proposal for a new classification system based on computer tomography.

Digital radiographic images in the anterior-posterior and lateral view have been gold standard for evaluation of peri-acetabular osteolysis for patients with an uncemented hip replacement. We compared digital radiographic images and computer tomography in detection of peri-acetabular osteolysis and devised a classification system based on computer tomography. Digital radiographs were compared with computer tomography on 206 hips, with a mean follow up 10 years after surgery. The patients had no clinical signs of osteolysis and none were planned for revision surgery. On digital radiographs, 192 cases had no osteolysis and only 14 cases had osteolysis. When using computer tomography there were 184 cases showing small or large osteolysis and only 22 patients had no osteolysis. A classification system for peri-acetabular osteolysis is proposed based on computer tomography that is easy to use on standard follow up evaluation.

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

Background: Volar locking plate fixation (VLPF) is the most common method for operative fixation of distal radius fractures (DRF). The dorsal ulnar corner (DUC) can be difficult to stabilize as the fragment is small and not exposed when using the volar approach. The purpose of this study was to study fracture fragment migration after VLPF of AO type C DRF, using a volume registration technique of paired CT scans with special focus on the DUC fragment. Materials and Methods: This pilot study included ten patients with AO type C DRF, all operated with VLPF. The primary outcome was radiographic outcome. Postoperative and 1-year scans were compared and analyzed. Fragment migration was assessed with CT-based micromotion analysis (CTMA), a software technique used for volume registration of paired CT scans. Results: All plates were stable over time. Two patients showed signs of screw movement (0.2-0.35 mm and 0.35- > 1 mm respectively). Postoperative reduction was maintained, and there was no fragment migration at the 1-year follow-up except for one case with increased dorsal tilt. The DUC fragment was found in 8/10 cases, fixated in 7/8 cases, and not dislocated in any case at the 1-year follow-up. Conclusion: The CTMA results indicate that variable-angle VLPF after AO type C DRF can yield and maintain a highly stable reduction of the fracture fragments. The DUC fragment remained stable regardless of the number of screws through the fragment. CT volume registration can be a valuable tool in the detailed assessment of fracture fragment migration following volar plate fixation of DRFs.

A new technique for measuring wear in total hip arthroplasty using computed tomography.

Accurately estimating polyethylene wear in 3 dimensions, without the need for additional procedures or equipment, is of significant interest. We investigated the use of a high-resolution clinical computed tomographic (CT) scanner to estimate femoral head displacement relative to the cup as an indirect method of estimating polyethylene wear. A hip phantom was used to simulate the 3-dimensional displacement of a femoral head. The phantom was imaged in a high-resolution CT scanner. The mean difference between the true phantom displacement as positioned by micrometers and the calculated displacement based on the CT images was as follows: for the x-axis, 0 mm (SD, 0.213; SE, 0.058); y-axis, 0.039 mm (SD, 0.035; SE, 0.026); and z-axis, 0.039 mm (SD, 0.051; SE, 0.020).

Motion analysis of total cervical disc replacements using computed tomography: preliminary experience with nine patients and a model.

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.