Author Response

Extract

Dr Wong questions the use of the sternocostal junction of the fourth rib as a landmark for the pectoralis minor muscle. This is a valid concern that I will address with some clarification of how the landmark was selected. I selected the fourth sternocostal junction landmark for several reasons—to accurately represent the pectoralis minor muscle’s origin,^1,2 to be in line with the muscle’s line of action,^1,2 and to be practical for in vivo data collection. I also considered another landmark, the junction between the fourth rib and its cartilage, which is likely closer to the muscle’s true insertion, but it was not consistently located during palpation, especially on female cadavers due to subcutaneous breast tissue overlying the junction. Therefore, because women were to be used for the in vivo study, moving to the sternocostal junction became the best alternative. Importantly, the use of this landmark was supported by the validation analysis with cadavers: landmarks were first palpated and digitized on a cadaver; the skin and fascia were incised to allow visualization of the actual insertion of the pectoralis minor muscle; and the actual muscle insertions were digitized to serve as the gold standard measurement. All cadavers showed muscle digitations on the fourth sternal cartilage, very near the proposed landmark. Visualizing the actual insertions of the muscle verified that the landmarks very closely represented the underlying pectoralis minor muscle. I am confident that the process used in selecting and verifying the pectoralis minor muscle landmarks for validating the measurement technique was sound.