Throughout our early clinical rotations, a common impairment that we noticed was forward shoulder posture (look around your classroom and you will see it as well!). In our program, we were taught to measure muscle strength using Kendall's technique. In her book, Muscles: Testing and Function, in Posture and Pain, Kendall demonstrates measuring the length of the pec minor, along with several other muscles, in the supine position, from the posterolateral border of the acromion to the table top (>3-4 finger lengths being an adaptively shortened muscle). In this position, the biceps brachii, coracobrachialis, and pectoralis minor could all contribute to the protracted/anteriorly tilted shoulder, due to the common attachment to the coracoid process. We commonly found that the scapula lowered to normal position with shoulder flexion, which would indicate adaptively shortened coracobrachialis, even though the common assumption is the pec minor being the culprit.
This article demonstrates that the pectoralis minor is indeed found to be adaptively shortened in many individuals and provides a much more reliable technique to measure the length of the pectoralis minor, as long as proper palpation skills are used. The key is to use a tape measure or caliper to measure the distance between the coracoid process and the sternal edge of the 4th rib. While there may not be sufficient evidence to start using this in the clinic right away, this new technique is something to consider when examining patients.
Pectoralis Minor Muscle:
Origin: Anterior surface of the sternal ends of ribs 3-5
Insertion: Coracoid Process of the scapula
Action: Protracts and depresses the scapula. Helps elevate the ribs (if O and I are reversed)
Innervation: Medial Pectoral Nerve (C8-T1)