Anatomy Angel: Subclavius

Subclavius is an important muscle with a fairly misunderstood action and underestimated performance. 

This important muscle is located exactly where its name indicates. It’s anchored directly under the clavicle, anchoring itself below to the first rib. 

Since the anterior part of the first sternocostal joint is not synovial, the clavicle is pulled inferiorly by subclavius at the acromioclavicular joint. 

Subclavius is misconstrued as a breathing muscle. Since the anterior first sternocostal joint is a primarily cartilaginous joint, it plays the most minute of roles in respiration. 

However, it’s ability to alter shoulder mechanics must be the attention of the practitioner. 

Subclavius often has a musculotendinous slip attaching to the coracoid process. This allows for a medial pull of the scapula when depressing the clavicle. Thus, subclavius assists the scapular protraction executed by pectoralis minor and serratus anterior. 

Since subclavius is a one joint muscle, it tends toward facilitation and tightness. With modern slouching postures, it tends even more toward being locked short. 

In dissection, the muscle is so tight and fibrous that I have a difficult time disarticulating the clavicle from the sternoclavicular (SC) joint.  Since the SC joint permits overhead arm movements, subclavius may be a limiting factor in that motion. 

It’s no accident that subclavius is innervated by the same major spinal level as the rotator cuff. These C5 structures affect each other, and both sets of structures are a slave to what’s happening at the neck. 

Tight neck flexors and posterior triangle muscles (i.e., levator scapula, splenius) are covered in prevertebral fascia. This fascia can affect subclavius, since the prevertebral fascia has a looping connection around the clavicle before it connects to the axillary fascia. 

The opposite can also occur, where axillary fascial tightness can create a pull on subclavius or the posterior neck triangle muscles via prevertebral fascial connections. 

In cases of distal hand circulation issues, subclavius must always be assessed. The subclavian vein runs directly posterior to subclavius. A tight subclavius may result in hand and arm circulation issues. 

The suprascapular artery and vein also run posterior and slightly superior to subclavius. Thus, direct blood flow to major rotator cuff muscles can be altered, as well as indirect flow to the entire shoulder girdle due to suprascapular artery’s anastomotic connections for blood. 

Please study the subclavius and learn its functional connections.