An Anatomical Study of the Feasibility of the Pectoralis Minor Transfer for Subscapular Deficiency: An Investigation of the Association Between the Transferred Muscle and the Musculocutaneous and Axillary Nerves

Abstract

Introduction The purpose of this study was to evaluate the feasibility of transferring the pectoralis minor (PM) in its entirety and assess its relationship with the musculocutaneous nerves (MCN) and axillary nerves (AXN). Methods Sixteen fresh transthoracic cadaver specimens were used. After PM transfer, the following measures were obtained: (a) the distance between the coracoid process (CP) and the subscapularis insertion on the lesser tubercle during external, neutral, and internal rotation. (b) The distances between the CP and PM, PM and musculocutaneous nerve, and PM and the axillary nerve. All measurements were performed using a precision caliper by two independent and blind-to-each-other findings observers. Results The median distance between the CP and PM muscles was 24 ± 7.7 mm, while the width of the coracoid was 24 ± 5.2 mm. PM-MCN distance was 23.25 ± 21.9 mm, CP-MCN distance was 72.1 ± 32.4 mm, and PM-AXN distance was 4.9 ± 0.7 mm. The distance between the coracoid process and lesser tuberosity varied by rotation: 29.2 ± 5.5 mm in internal rotation, 41.1 ± 8.9 mm in neutral rotation, and 51.1 ± 10.7 mm in external rotation. The distance significantly increased between internal and neutral or external rotation (p <0.05), but no significant difference was observed between neutral and external rotation (p > 0.05). Conclusion The distance between the coracoid process and lesser tuberosity increased considerably only between internal and neutral or external rotation positions. Additionally, the importance of identifying the musculocutaneous and axillary nerves and their branches when transferring the pectoralis minor should be highlighted.

Keywords: axillary nerve; coracoid process; musculocutaneous nerve; pectoralis minor; transfer.

Figure 1. Anatomical cadaver shoulder dissection via deltopectoral approach.

The conjoined tendon has been exposed and the inferior border of the coracoid process (CP) has been identified. The pectoralis minor has been detached from the CP, its tendon has been pointed out with forceps and displaced below the conjoint tendon into the lesser tuberosity. BB: biceps brachii, CB: coracobrachialis.

Figure 2. Anatomical specimen with the transfer in place in order to make the examined measurements.

The following landmarks were recognized: the inferior border of the coracoid process, the entry point of the most proximal muscular branch of the musculocutaneous nerve in the conjoined tendon, the cranial edge of the pectoralis minor at the medial edge of the conjoined tendon and the caudal edge of the pectoralis minor at the same level. CP: coracoid process, LT: lesser tuberosity, PM: pectoralis minor, MCN: musculocutaneous nerve, AXN: axillary nerve, Distance A (CP-LT) External rotation, Distance B (CP-LT) Neutral rotation, Distance C (CP-LT) Internal rotation, Distance D (CP-PM), Distance E (PM-MCN), Distance F (CP-MCN), Distance G (PM-AXN).