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, published online 21 November 2007. doi:10.2519/jospt.2008.2723

Study Design: Two-group comparison. Objective: To compare scapular kinematics during arm elevation between groups distinguished by pectoralis minor resting length. Background: Studies have demonstrated that individuals with subacromial impingement have altered scapular kinematics, such as loss of posterior tipping and increased internal rotation. One proposed mechanism for these alterations is an adaptively short pectoralis minor. This anterior scapulothoracic muscle may impact normal scapular kinematics if adaptively short. Methods and Measures: Fifty volunteers without shoulder pain were divided into long or short groups according to normalized pectoralis minor resting length. An electromagnetic motion capture system determined the angular orientation of the scapula, humerus, and trunk during arm elevation in 3 separate planes. Groups were compared for 3-dimensional scapular orientation relative to the trunk at arm elevation angles of 30°, 60°, 90°, and 120°, using a mixed-model analysis of variance (ANOVA). Results: There were statistically significant interaction effects between group and arm elevation angle for scapular tipping in all planes of arm elevation, with the scapula for the short group staying anteriorly tipped at higher angles. There was also a significant interaction for scapular internal rotation at lower arm elevation angles in the coronal plane only, with individuals with a shorter pectoralis minor demonstrating a more internally rotated scapula. Conclusions: The group distinguished by a short pectoralis minor demonstrated scapular kinematics similar to the kinematics exhibited in earlier studies by subjects with shoulder impingement. These results support the theory that an adaptively short pectoralis minor may influence scapular kinematics and is therefore a potential mechanism for subacromial impingement.

J Orthop Sports Phys Ther. 2005;35(4):227-238. doi:10.2519/jospt.2005.1669

Key Words: biomechanics, impingement, muscle, shoulder, 3-dimensional