Semi-automatic Software-based 3D-Angular Measurement For Weight-Bearing CT (WBCT) is 97% Faster than Measurement by Hand and Provides Similar Angles

Abstract

Category: Basic Sciences/Biologics Introduction/Purpose: Weight-bearing CT (WBCT) has been proven to allow for more precise and valid measurement of bone position (angles) than conventional weight-bearing radiographs (R) and conventional CT without weight-bearing (CT)1. The measurement by hand (MBH) has demonstrated adequate inter- and intraobserver reliability but high time consumption1. Recently, a semi-automatic software-based angular measurement (SAM) has been developed (Disior Ltd, Helsinki, Finland). The purpose of this study was to compare SAM with MBH regarding angles values and time spent for the investigator. Methods: Fifteen bilateral WBCT scans (PedCAT, Curvebeam, Warrington, PA, USA) were randomly extracted from a local institutional database with more than 13,000 scans. Nineteen angles as shown in table 1 were measured with MBH as previously described and with SAM1. SAM includes software generated 3D models with semi-automatic bone specification of tibia, fibula, talus, calcaneus, navicular, cuboid, cuneiforms and metatarsals. The software automatically defines the longitudinal axes of these bones and automatically measures the angles between these axes. The time spent of the investigator for the measurements was recorded (total process MBH and specification of bones for SAM). The software calculation time for SAM was not measured or considered as investigator time spent. The angles and time spent of MBH and SAM were compared (t-test, homoscedatic). Results: Mean age of the subject was 58 years (range, 7-81), 12 (40%) were male. The pathologies were bilateral in 8 (54%), right in 4 (27%) and left in 3 (20%) subjects (23 feet in total) and were specified as follows, ankle osteoarthritis/instability in 6 (26%), Haglund deformity/Achillodynia in 4 (17%), Forefoot deformity in 7 (30%), Charcot arthropathy in 2 (9%), flatfoot in 4 (17%) feet. The angles did not differ between MBH and SAM (Table 1, each p>.05). The time spent for MBH / SAM was 780+-171s / 20+-8 s on average in total for 19 angles and 41+-9s / 1+-0.4 s per angle (p<.01). Conclusion: This is the first study comparing MBH with SAM. SAM shows similar angles as MBH and can be also considered as reliable measurement option. The investigator time spent is 97% lower for SAM (1 s per angle) than for MBH (41 s per angle). SAM is an important step forward for 3D-angle measurement of WBCT. The next desired is fully automatic software-based measurement. References1. Richter M, Seidl B, Zech S, Hahn S. PedCAT for 3D-Imaging in Standing Position Allows for More Accurate Bone Position (Angle) Measurement than Radiographs or CT. Foot Ankle Surg 2014;20:201-7.