Effects of positioning on radiographic measurements of ankle morphology: a computerized tomography-based simulation study

Abstract

BackgroundMeasurements of the morphology of the ankle joint, performed mostly for surgical planning of total ankle arthroplasty and for collecting data for total ankle prosthesis design, are often made on planar radiographs, and therefore can be very sensitive to the positioning of the joint during imaging. The current study aimed to compare ankle morphological measurements using CT-generated 2D images with gold standard values obtained from 3D CT data; to determine the sensitivity of the 2D measurements to mal-positioning of the ankle during imaging; and to quantify the repeatability of the 2D measurements under simulated positioning conditions involving random errors.MethodFifty-eight cadaveric ankles fixed in the neutral joint position (standard pose) were CT scanned, and the data were used to simulate lateral and frontal radiographs under various positioning conditions using digitally reconstructed radiographs (DRR).Results and discussionIn the standard pose for imaging, most ankle morphometric parameters measured using 2D images were highly correlated (R > 0.8) to the gold standard values defined by the 3D CT data. For measurements made on the lateral views, the only parameters sensitive to rotational pose errors were longitudinal distances between the most anterior and the most posterior points of the tibial mortise and the tibial profile, which have important implications for determining the optimal cutting level of the bone during arthroplasty. Measurements of the trochlea tali width on the frontal views underestimated the standard values by up to 31.2%, with only a moderate reliability, suggesting that pre-surgical evaluations based on the trochlea tali width should be made with caution in order to avoid inappropriate selection of prosthesis sizes.ConclusionsWhile highly correlated with 3D morphological measurements, some 2D measurements were affected by the bone poses in space during imaging, which may affect surgical decision-making in total ankle arthroplasty, including the amount of bone resection and the selection of the implant sizes. The linear regression equations for the relationship between 2D and 3D measurements will be helpful for correcting the errors in 2D morphometric measurements for clinical applications.

Proposal of a magnetic resonance technique for the evaluation of the calcaneofibular ligament minimizing false positive results

“…However, subjective evaluation might contribute to distorted results. Other authors [ 16 ] showed that ankle morphological measurements are very sensitive to the positioning of the joint during imaging.…”

Validity and reliability of ankle morphological measurements on computerized tomography-synthesized planar radiographs

“…The conformity of the TAA design to the bone morphology, including proper sizing of the components, is an important factor for the prosthesis to replicate the function of the ankle joint [ 8 ]. Using implants of sizes and shapes precisely matching the osteotomies is expected to be of value for the long-term fixation of the implants [ 13 , 19 , 20 ], and can substantially reduce complications and increase survival rates [ 12 – 14 ]. Therefore, errors in the measurement of the patient-specific morphological parameters may have critical effects on the pre-surgical decision-making in TAA, including the selection of the size of the implants.…”

“…These can also be used for estimating patient-specific morphological parameters and for selecting the size of the prosthesis, particularly owing to their convenience, low cost, and low radiation dose compared with other modalities such as Magnetic Resonance Imaging or Computerized Tomography (CT) [ 21 ]. However, since planar radiographs are two-dimensional (2D) projective images, bones at different distances from the projection plane produce bone images of different size, position and intensity, critically affecting the measurement accuracy [ 19 ]. In addition, the intrinsic articular surfaces of the ankle joint are not symmetrical, and are often oblique with respect to the anatomical planes of the shank and foot.…”

“…For example, markers placed on the bony landmarks for 3D measurements will also appear on the planar radiographs, which will affect the subsequent independent repeated measurements on the radiographs. By taking advantage of CT-based computer simulation, gold standard values can be established by 3D CT measurements and the repeated planar measurements can be made on 2D radiographs concurrently synthesized using the CT data [ 19 ]. Comparisons between known gold standards based on 3D data and corresponding 2D repeated measurements will help assess quantitatively the validity and reliability of standard ankle morphology measurements based on routine planar images.…”

Tomosynthesis can facilitate accurate measurement of joint space width under the condition of the oblique incidence of X-rays in patients with rheumatoid arthritis

“…When the centre of the incident X-ray beam does not coincide with the target joint, detected JSW in the projected image contains perceptional or measured errors caused by bony overlap resulting from the oblique incidence of the X-rays. 14,15 Although this phenomenon is unavoidable clinically, to the best of our knowledge, the assessment of the effects caused by the oblique incidence of Xrays has not yet been performed. We therefore performed an assessment using phantoms simulating joints for radiography and tomosynthesis.…”