Physical therapist assists patient with exercise ball.

Muscle Minute TUESDAY – Meet the Teres Minor

Anatomy diagram of shoulder muscles, teres minor highlighted.

The teres minor is the least torn rotator cuff tendon, as its tendon is not situated near the acromion. However, it may be the most important rotator cuff muscle. Teres minor denervation (TMD) is associated with 82% of rotator cuff tears, with subscapularis being the most common tear. TMD is also associated with over 80% of posterior labrocapsular tears and shoulder instability. Those stats alone should make us want to take a deeper dive. Let’s get started:

Originlateral border of scapula
Insertioninferior facet of greater tuberosity (humerus)
Actionhumeral external rotation (decelerates internal rotation), depress humerus during elevation
Innervationaxillary n. (C5, C6)
Antagonistssubscapularis

The Real World Teres Minor

Did you catch that? Possibly the most important role of teres minor is depress the humeral head during elevation, preventing impingement of the more exposed rotator cuff muscles: supraspinatus and infraspinatus. If this muscle takes a hike, bad things happen.

What causes denervation of this muscle? The most common thought was quadrilateral space syndrome, compression of the axillary in space bordered by the teres minor (superiorly), long head of tricep (medially), teres major (inferiorly) and the humerus (medially). But MRI’s have demonstrated compression in many cases beyond the quadrilateral space. Let’s take a look at the path of the axillary nerve.

Diagram of axillary nerve in shoulder anatomy.

As one of the terminal ends of the brachial plexus, compression of the axillary nerve may occur at the following points:

  1. C5, C6 – one of the most common areas of hypermobility in the cervical spine
  2. Between anterior and middle scalene – trigger points in the scalene are often associated with an elevated first rib
  3. Between the first rib and clavicle – an elevated first rib, often associated with impingement syndrome, is common when one shoulder is chronically higher than the other
  4. Behind pec minor – trigger points in pec minor are often associated with protracted a protracted scapula and limited thoracic rotation

Though that may seem overwhelming, there are a lot of options to check when confronted with possible TMD. It can be isolated in MMT with the Hornblower’s Sign (resistance of external rotation with the arm abducted 90Ëš).

Conventional thinking says: The teres minor is a small muscle and rarely torn so it is one of the least significant rotator cuff muscles.

Real World Thinking asks: Teres minor may be one of the most important rotator cuff muscles, as it acts as a primary depressor of the humeral head protecting the other rotator cuff tendons from impingement and the posterior capsule and labrum from tearing. Denervation may be due to compression in the quadrilateral space and/or compression of the brachial plexus proximal to the quadrilateral space. In our rotator cuff patients, assess each of the compression points and fix what you find.

Because nobody has time to be in pain.

Until next time…

Kind Regards,
MoveWell Academy
[email protected]

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