3-D joint space mapping at the ankle from weight-bearing CT: reproducibility, repeatability, and challenges for standardisation

Abstract

Objectives We present a 3-D approach to joint space width (JSW) measurement across the ankle from weight-bearing CT (WBCT) to demonstrate inter-operator reproducibility, test-retest repeatability, and how differences in angulation affect ankle JSW distribution. Methods One side from repeat WBCT imaging of both feet and ankles was analysed from 23 individuals as part of their routine clinical care pathway. Joint space mapping was performed at four facets across the talus: talonavicular, talar dome and medial gutter (dome-medial), lateral gutter, and posterior subtalar. Inter-operator reproducibility was calculated for two users, while test-retest repeatability was calculated by comparing the two visits, both presented as Bland-Altman statistics. Statistical parametric mapping determined any significant relationships between talocrural joint space angulation and 3-D JSW distribution. Results The average ± standard deviation interval between imaging was 74.0 ± 29.6 days. Surface averaged bias ± limits of agreement were similar for reproducibility and repeatability, the latter being: talonavicular 0.01 ± 0.26 mm, dome-medial 0.00 ± 0.28 mm, lateral gutter − 0.02 ± 0.40 mm, and posterior subtalar 0.02 ± 0.34 mm. Results are presented as 3-D distribution maps, with optimum test–retest repeatability reaching a smallest detectable difference of ± 0.15 mm. Conclusions Joint space mapping is a robust approach to 3-D quantification of JSW measurement, inter-operator reproducibility, and test–retest repeatability at the ankle, with sensitivity reaching a best value of ± 0.15 mm. Standardised imaging protocols and optimised metal artefact reduction will be needed to further understand the clinical value of these 3-D measures derived from WBCT. Clinical relevance statement Weight-bearing computed tomography is an increasingly important tool in the clinical assessment of orthopaedic ankle disorders. This paper establishes the performance of measuring 3-D joint space width using this technology, which is an important surrogate marker for severity of osteoarthritis. Key Points • Joint space width values and error metrics from across the ankle measured from weight-bearing CT can be presented as 3-D maps that show topographic variation. • The best sensitivity for detecting meaningful change in 3-D joint space width at the ankle was ± 0.15 mm, a value less than the isotropic imaging voxel dimensions. • Standardised imaging protocols and optimised metal artefact reduction will be needed to understand the clinical value of 3-D measures from weight-bearing CT.

Recent Innovations Brought about by Weight-Bearing CT Imaging in the Foot and Ankle: A Systematic Review of the Literature

“…• 3D bone absolute and relative relationships reporting [16,21,22,26,[52][53][54][55][56][57][58][59][60][61][62][63][64] • 3D Joint space width (3D-JSW) mapping: distance mapping [65][66][67][68][69] • Coverage mapping [70] • Surface measurements…”

“…The authors would be happy to revise or replace the proposed classification as progress is made, new methods arise and the technical landscape evolves in the future. Finally, we have only considered the foot and ankle field in the present work, but we fully acknowledge that WBCT devices already encompass the knee [20,65,78], with devices already available to image the pelvis and the upper limbs. There is no doubt that soon, devices able to image the full weight-bearing skeleton will be available.…”

“…This tool is based on analyzing the surfaceto-surface distance map within any given weight-bearing joint. The sum of all these point-by-point distances adds up to a 3D joint space width map, which explains why it has been dubbed 'distance mapping' [66,67,69], '3D joint space width' [65,68,89,90] or a mix of both in the literature. Originally developed as way to visualize regions of bony approximation, authors presented ways to also use it as a quantification tool for such conditions as PCFD or cavovarus deformity, by averaging the distances in reproducible in pre-defined anatomical quadrants within the joints of interest (Figure 9).…”