Measurement of Pectoralis Minor Muscle Length: Validation and Clinical Application

Study Design Clinical measurement validity study. Objectives To validate the measurement of the pectoralis minor muscle length using palpable landmarks and to explore the accuracy of the measurement using a clinical instrument. Background The pectoralis minor is believed to adaptively shorten. Individuals with a relatively short pectoralis minor demonstrate scapular kinematic alterations that have been associated with shoulder impingement. Methods and Measures A 3 dimensional electromagnetic motion capture system was used to calculate the length of the pectoralis minor in 11 cadavers, using 2 measurement techniques. In addition, a measurement with the electromagnetic system using palpable landmarks was compared to a measurement with both a caliper and tape measure in vivo. Results In cadavers, a measurement using palpable landmarks was determined to be a valid measure of the actual muscle length visualized and measured following dissection. There was a high intraclass correlation coefficient and a small root-mean-square error between these 2 measures. High intraclass correlation coefficients were also calculated in vivo when measurements with the clinical instruments were compared with the electromagnetic device measures. Conclusion A measurement using palpable landmarks for pectoralis minor length validly represents the muscle length in cadavers. A caliper or tape measure may be used clinically with high accuracy and may help clinicians determine the need for and the effectiveness of interventions for lengthening this muscle. J Orthop Sports Phys Ther 2008;38(4):169–174. doi:10.2519/jospt.2008.2723