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.

Cadaveric study validating in vitro monitoring techniques to measure the failure mechanism of glenoid implants against clinical CT.

Definite glenoid implant loosening is identifiable on radiographs, however, identifying early loosening still eludes clinicians. Methods to monitor glenoid loosening in vitro have not been validated to clinical imaging. This study investigates the correlation between in vitro measures and CT images. Ten cadaveric scapulae were implanted with a pegged glenoid implant and fatigue tested to failure. Each scapulae were cyclically loaded superiorly and CT scanned every 20,000 cycles until failure to monitor progressive radiolucent lines. Superior and inferior rim displacements were also measured. A finite element (FE) model of one scapula was used to analyze the interfacial stresses at the implant/cement and cement/bone interfaces. All ten implants failed inferiorly at the implant-cement interface, two also failed at the cement-bone interface inferiorly, and three showed superior failure. Failure occurred at of 80,966 ± 53,729 (mean ± SD) cycles. CT scans confirmed failure of the fixation, and in most cases, was observed either before or with visual failure. Significant correlations were found between inferior rim displacement, vertical head displacement and failure of the glenoid implant. The FE model showed peak tensile stresses inferiorly and high compressive stresses superiorly, corroborating experimental findings. In vitro monitoring methods correlated to failure progression in clinical CT images possibly indicating its capacity to detect loosening earlier for earlier clinical intervention if needed. Its use in detecting failure non-destructively for implant development and testing is also valuable. The study highlights failure at the implant-cement interface and early signs of failure are identifiable in CT images. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 36:2524-2532, 2018.

Trauma whole-body MDCT: an assessment of image quality in conventional dual-phase and modified biphasic injection.

OBJECTIVE: To compare the image quality of conventional arterial and portal venous (PV) phase multidetector CT (MDCT) with two biphasic injection protocols in polytrauma patients. METHODS: 60 consecutive patients with polytrauma underwent body 256-slice MDCT with a conventional protocol or 1 of 2 single-pass biphasic protocols: Group A, arterial (30 s) and PV (60 s) phase acquisitions; Group B, "biphasic" contrast injection with a single acquisition at 60 s; and Group C, "modified biphasic" injection with a single acquisition at a 70-s delay. Images were analyzed for arterial, venous and parenchymal attenuation profiles with regions of interest in the major arteries, veins and solid abdominal organs. A 5-point scoring system was used to assess the image quality, with 5 representing excellent arterial, venous and parenchymal opacification and <3 representing non-diagnostic opacification. In addition, the effective dose (millisieverts) was compared between the groups. RESULTS: In 93% of patients, image quality was scored as good or excellent (≥4). All studies were of satisfactory diagnostic quality. Overall, venous and arterial attenuation profiles were comparable. Attenuation profiles in the solid abdominal viscera were significantly higher (p < 0.01) using both biphasic protocols than with arterial or PV phase of conventional protocols. Effective doses were higher in Group A. CONCLUSION: Comparable image quality can be achieved using a biphasic i.v. contrast injection protocol with single MDCT acquisition with less radiation and reduction in acquisition time. ADVANCES IN KNOWLEDGE: For these particular biphasic injection protocols, we have shown that image quality is comparable with a conventional protocol. This has been achieved by comparing enhanced densities of specific structures, as well as gestalt scoring by assessors, on a 256-slice MDCT.