Teres Major Anatomy

The teres major runs from the inferior angle of the scapula to the medial lip of the bicipital groove, sandwiched between the teres minor above and the latissimus dorsi wrapping around it below and in front. Functionally it is a modest muscle: electromyographic studies show it is essentially silent during unresisted movement and fires only against load, which is why it is described as "latissimus dorsi's little helper".

Anatomically and surgically it is anything but modest. It is the floor of the quadrangular space and the triangular space, and the roof of the triangular interval — three named spaces containing, respectively, the axillary nerve, the circumflex scapular artery and the radial nerve. Its lower border is the boundary at which the axillary artery becomes the brachial artery and at which the radial nerve leaves the axilla for the spiral groove. And with the latissimus dorsi it forms the posterior axillary fold and the standard donor pair for restoring external rotation to a shoulder that has lost it.

Actions by plane

• Adduction of the humerus.
• Extension of the humerus from a flexed position.
• Internal (medial) rotation of the humerus.
• Assists scapular stabilisation indirectly: because it originates on the mobile inferior angle rather than on the thorax, strong contraction with a fixed humerus rotates the scapula, and in climbing or pulling activity it contributes to drawing the trunk toward the arm.

The electromyographic point

• Teres major is electrically silent during unresisted movement. It recruits only against resistance, which distinguishes it from latissimus dorsi and explains why isolated teres major weakness or rupture is often clinically silent.
• This has two consequences. First, a teres major tear rarely produces measurable weakness in daily life. Second, after transfer, the patient must actively be taught to recruit it, because the muscle is not habitually engaged in low-load movement.

Moment arm and length-tension

• The moment arm for internal rotation is greatest with the arm abducted, since abduction brings the line of pull perpendicular to the humeral shaft.
• Excursion is short — the muscle is broad but not long, and the tendon is stiff. This is the mechanical reason teres major alone rarely provides sufficient excursion for a transfer, and why it is combined with the longer, more compliant latissimus dorsi.

Synergists and antagonists

• Synergists: latissimus dorsi (the dominant partner in every action), pectoralis major (adduction and internal rotation), subscapularis (internal rotation), posterior deltoid (extension).
• Antagonists: deltoid and supraspinatus (abduction), infraspinatus and teres minor (external rotation), the anterior deltoid and pectoralis major clavicular head (flexion).

Palpation and positioning

• Grasp the posterior axillary fold between thumb and fingers with the patient's hand on the hip and the arm pressed inward against resistance. The fold is composed of latissimus dorsi superficially and teres major deep to it; teres major is felt as the firmer, more cord-like structure closer to the humerus.
• Follow the lateral border of the scapula downward to the inferior angle with the arm across the chest; the origin becomes prominent as the patient adducts against resistance.
• The lower border of teres major can be traced as the oblique line that marks the top of the triangular interval, roughly at the level where the posterior axillary fold meets the arm.

Named tests and clinical assessment

Pitfalls

• The scapula must be stabilised when measuring passive external rotation, particularly in an infant with a birth palsy. An unstabilised scapula rotates on the chest wall and creates the illusion of a mobile glenohumeral joint.
• Do not mistake latissimus for teres major on palpation. Latissimus is the broad sheet reaching the iliac crest; teres major is the short thick cord confined to the scapular angle.

Radial nerve injury

• Mechanism: blind dissection at the lower border of teres major during transfer harvest, or traction on the nerve when routing the tendon.
• Consequence: wrist drop and loss of finger and thumb extension — a devastating result in a patient operated on to improve shoulder rotation.
• Avoidance: abduct and externally rotate the arm, release under direct vision from the humerus outward, and never sweep blindly inferior to the tendons.

Axillary nerve injury

• Mechanism: dissection in the quadrangular space at the upper border of teres major, or forceful passage of the tendon through a tunnel deep to the posterior deltoid.
• Consequence: deltoid and teres minor loss, which in a cuff-deficient shoulder removes the option of a reverse arthroplasty.
• Avoidance: create the tunnel bluntly with a finger under direct palpation, and confirm it is free before pulling the tendon.

Failure of the transfer

• Insufficient passive motion: the commonest cause. A transfer cannot move a stiff joint; the contracture must be released first.
• Inadequate tensioning: tensioning in internal rotation leaves the transfer slack. Tension with the arm in external rotation and neutral abduction, and immobilise in that position.
• Failure of re-education: teres major is habitually silent in unresisted motion, so the patient must be taught to fire it. Biofeedback and a structured programme are essential.
• Loss of internal rotation: rebalancing an internal rotation contracture can overshoot, leaving the patient unable to reach the midline or perform perineal care. This is a real and underappreciated trade-off, particularly in birth palsy.

Donor site morbidity

• Loss of latissimus dorsi and teres major function reduces adduction and extension power. Most patients do not notice, but it matters for wheelchair users, crutch users, climbers and swimmers, who depend on these muscles for transfers and propulsion.
• Seroma in the harvest bed, particularly with a wide latissimus dissection.
• Loss of the posterior axillary fold contour is a visible cosmetic change patients should be warned about.

Recurrence of contracture in the growing child

• After release and transfer for birth palsy, contracture can recur as the child grows if the underlying imbalance persists.
• Glenoid dysplasia may progress despite an apparently successful soft-tissue operation, which is why serial imaging and long-term follow-up to skeletal maturity are required rather than discharge at one year.

Related pages. Its inseparable partner: Latissimus Dorsi Anatomy, and Latissimus Dorsi and Teres Major Rupture for the throwing injury. The spaces it floors and roofs, and what runs in them: Quadrangular and Triangular Spaces, Quadrilateral Space Syndrome, Axillary Nerve Anatomy and Radial Nerve Anatomy — the last two explaining why its lower border matters in Humeral Shaft Fractures. Why it is transferred in the child: Brachial Plexus Birth Palsy. Why it is transferred in the adult, and the muscle that must be intact first: Massive Rotator Cuff Tears, Rotator Cuff Arthropathy, Subscapularis Anatomy and Subscapularis Tears.

Pathologies of the muscle itself

The Waters classification concept

Imaging

• MRI demonstrates the teres major muscle and tendon well on axial and coronal oblique sequences; the tendon is identified at the medial lip of the groove posterior to the latissimus dorsi tendon, separated by the bursa.
• In brachial plexus birth palsy, MRI or ultrasound assesses glenoid version, humeral head subluxation and the state of the internal rotators. Ultrasound is preferred in infants because it avoids anaesthesia.
• Rupture appears as myotendinous junction disruption with fluid signal and, in chronic cases, retraction and fatty change of the belly.
• Look for teres major hypertrophy in throwers as a contributor to quadrangular space narrowing.

The transfer family

Approaches in which teres major is the landmark

• Posterior approach to the humerus: the interval used is between the long head and lateral head of triceps, and the radial nerve is found in the spiral groove after it emerges from the triangular interval at the lower border of teres major. Identifying that border orients the surgeon to the nerve.
• Approach to the axillary artery: the transition from axillary to brachial artery is at the lower border of teres major, which defines whether exposure is an axillary or a brachial exploration.
• Posterior axillary fold flaps: the fold, composed of latissimus and teres major, is the basis of Z-plasty and local flap release of axillary burn contracture.
• Latissimus dorsi flap harvest: teres major is the muscle the surgeon must not take, and its recognition prevents inadvertent inclusion.

Anatomical variation across populations

• Fusion of teres major with the latissimus dorsi tendon at the insertion is described in cadaveric series with variable frequency, and where present it makes the transfer harvest considerably more difficult and increases the risk of taking both when only one is intended.
• Accessory slips from the inferior angle of the scapula to the latissimus dorsi (the axillary arch or Langer's arch when it crosses the axilla) are a recognised variant with reported prevalence differences between populations, and can compress the axillary neurovascular bundle or complicate axillary lymph node dissection.
• The level at which the lower subscapular nerve enters the muscle varies, which matters for the arc of rotation achievable at transfer.

Side-by-side guidance

Registry and outcome signals

• Tendon transfers about the shoulder are performed in low volume and are not captured by national joint registries; the evidence base is institutional cohorts and long-term case series rather than randomised trials.
• Where reverse arthroplasty is combined with a transfer, registries capture the arthroplasty component only, so the functional benefit attributable to the transfer is not visible at registry level.
• Brachial plexus birth palsy outcomes are tracked by specialist multidisciplinary networks rather than registries. The consistent message across those cohorts is that early recognition of the internal rotation contracture and rebalancing before fixed glenoid dysplasia develops is the single most important determinant of long-term shoulder function.

High-resource versus limited-resource practice

• Well-resourced settings: MRI assessment of glenoid morphology in infants, botulinum toxin to the internal rotators as a temporising measure, arthroscopically assisted release, and combined reverse arthroplasty with transfer in adults.
• Limited-resource settings: the essential assessment, passive external rotation with the scapula stabilised, requires no equipment and identifies the child who needs surgery. Open release and Hoffer-type transfer is an equipment-light operation with a strong track record.
• The L'Episcopo family of transfers remains globally relevant precisely because it requires no implants: the operation changes a lever, and the cost is surgical skill rather than technology.