Quantification of Axial Chest Wall Slope Asymmetry in Healthy Females
Breast asymmetry is an established concern in both aesthetic and reconstructive surgery, with literature primarily focusing on soft tissue differences. Embryologically, the heart forms early in fetal development, requiring the left chest wall to extend farther than the right during endochondral ossification of the ribs. Therefore, we hypothesize that asymmetry in the adult chest can be attributed to inherent skeletal differences between the left and right chest walls. This study aims to quantify this chest wall asymmetry, proposing that the right chest has a steeper slope in the axial plane.
Methods/Technique
:Inclusion criteria captured healthy females between 18-45 years old and a BMI of 20-25. Patients were excluded if they had a prior diagnosis of scoliosis, pectus carinatum, pectus excavatum, any diagnosed congenital deformities, a history of trauma to the chest wall or ribs, or a history of breast cancer, reconstruction, or implants. After screening from a large database, a total of 25 randomly selected CT scans underwent Image Segmentation using Simpleware™ software (Version 2024.06; Synopsys, Inc., Sunnyvale, USA). Each segmentation started at the insertion of the fourth rib at the sternum. Caution was taken to exclude any underlying or overlying musculature. A centerline was created, and the x and y coordinates were transformed to a common cartesian plane with the median sternum set to (0,0). Statistics were performed between the left and right slopes using Chi –Squared analysis for the mean y-value at each standardized x-value along the curve. A significance level of 0.05 was used for all statistical analyses.
Results/Complications
:The right and left chest curves have significantly different slopes over their respective course in space (n = 25, p = 0.003). From the origin of the sternum moving laterally, the mean left chest curve was found to be more positive for a greater distance compared to the mean right chest curve. Looking at standardized points at distances away from the middle of the sternum, there were significant differences at 2 through 4 cm laterally. At 2 cm, 3 cm, and 4 cm, there was a 1.96 mm (p = 0.002), 2.56 mm (p = 0.006), and 2.85 mm difference (p = 0.02), respectively. From 0 to 2 cm, close to the sternum, and from 5 to 10 cm, as the chest wall turns towards the midaxillary line, the curves were more similar. Once the cardiac silhouette ends within the left chest, around 5cm from the sternum, the chest wall slopes measured were not significantly different.
Conclusion
:In this cohort of healthy females, the right rib cage has a significantly steeper slope in the axial plane when compared to the left rib cage. The slopes were statistically significant until the left lateral border of the heart. We posit that the presence of the heart and subsequent rib ossification during embryological development may explain this difference. In both aesthetic and reconstructive surgery, an understanding of these inherent skeletal asymmetries will allow surgeons to appropriately adjust their practice and patient expectations.