Reliability of external caliper-based measurements for identifying severe pectus excavatum: Results from a...

Historically, methods for quantifying the severity of pectus excavatum (PE) have involved cross-sectional imaging. An external caliper-based metric, the Modified Percent Depth (MPD), has been described as a viable alternative to radiographic-based measurements such as the Pectus and Correction Indices for identifying severe PE in the clinic setting. The purpose of this study was to evaluate the reproducibility of the MPD among PE patients evaluated within a regional multicenter consortium of children's hospitals.

This was a prospective observational study of PE patients aged 6-25 years who underwent 2 sets of preoperative caliper measurements by independent raters during the same clinical encounter at one of eight member institutions between April 2021 and December 2023. Three caliper measurements were obtained: the deepest point of sternum to posterior midline and posterior midline to maximal point of the anterior chest protrusion bilaterally. These caliper measurements were used to calculate the MPD. Severe PE was defined as an MPD of ≥14 %. Interrater reliability for severe vs. non-severe PE was assessed by Gwet's chance-corrected agreement coefficient (AC1).

Among 202 patients, the mean (standard deviation) age was 15 ± 2 years and the majority were male (82 %). Both raters' measurements led to agreement in 174/202 (86 %) in categorizing severe vs. non-severe PE with an overall AC1 of 0.80 (95 % CI 0.72-0.91). Stratified by gender, the raters' measurements agreed in 146/65 (88 %) of males with an AC1 of 0.83 (0.75-0.91), and in 28/37 (76 %) of females with an AC1 of 0.62 (0.37-0.88).

This multicenter prospective study demonstrated excellent interrater reliability in the classification of severe vs. non-severe PE in male patients with the use of external chest calipers to calculate MPD. Females had lower interrater reliability compared to males but still showed good agreement. While further study of gender-based differences will be needed, the MPD can be considered a reliable, radiation-free alternative to routine cross-sectional imaging in the preoperative work-up of PE.