| Latissimus dorsi | |
|---|---|
 Latissimus dorsi originates from the mid to lower back | |
 Muscles connecting the upper extremity to thevertebral column. | |
| Details | |
| Origin | Spinous processes ofvertebraeT6-S5,thoracolumbar fascia,iliac crest, inferior 3 or 4ribs andinferior angle ofscapula |
| Insertion | Floor ofintertubercular groove of thehumerus |
| Artery | Thoracodorsal branch of thesubscapular artery |
| Nerve | Thoracodorsal nerve (C6, C7, C8) |
| Actions | Adducts, extends and internally rotates the arm when the insertion is moved towards the origin. When observing the muscle action of the origin towards the insertion, the lats are a very powerful rotator of the trunk. |
| Antagonist | Deltoid andtrapezius muscle |
| Identifiers | |
| Latin | musculus latissimus dorsi |
| TA98 | A04.3.01.006 |
| TA2 | 2231 |
| FMA | 13357 |
| Anatomical terms of muscle | |
Thelatissimus dorsi (/ləˈtɪsɪməsˈdɔːrsaɪ/) is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by thetrapezius on the back near the midline.
The word latissimus dorsi (plural:latissimi dorsi) comes fromLatin and means "broadest [muscle] of the back", from "latissimus" (Latin:broadest) and "dorsum" (Latin:back). The pair of muscles are commonly known as "lats", especially amongbodybuilders.
The latissimus dorsi is responsible forextension,adduction, transverse extension also known as horizontal abduction (or horizontal extension),[1] flexion from an extended position, and (medial)internal rotation of theshoulder joint. It also has asynergistic role in extension andlateral flexion of the lumbar spine.
Due to bypassing the scapulothoracic joints and attaching directly to the spine, the actions the latissimi dorsi have on moving the arms can also influence the movement of the scapulae, such as their downward rotation during apull up.
The number of dorsal vertebrae, to which it is attached, varies from four to eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium.
Amuscle slip, theaxillary arch, varying from 7 to 10 cm in length, and from 5 to 15 mm in breadth, occasionally springs from the upper edge of the latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of thepectoralis major, thecoracobrachialis, or the fascia over thebiceps brachii. This axillary arch crosses theaxillary artery, just above the spot usually selected for the application of a ligature, and may mislead a surgeon. It is present in about 7% of the population and may be easily recognized by the transverse direction of its fibers. Guyet al. extensively described this muscular variant using MRI data and positively correlated its presence with symptoms of neurological impingement.[2]
A fibrous slip usually passes from the upper border of the tendon of the Latissimus dorsi, near its insertion, to the long head of thetriceps brachii. This is occasionally muscular, and is the representative of the dorsoepitrochlearis brachii ofapes.[3][4] This muscular form is found in ~5% of humans and is sometimes termed the latissimocondyloideus.[5]
The latissimus dorsi crosses the inferior angle of thescapula. A study found that, of 100 cadavers dissected:[6]
The latissimus dorsi is innervated by the sixth, seventh, and eighthcervical nerves through thethoracodorsal (long subscapular) nerve.Electromyography suggests that it consists of six groups of muscle fibres that can be independently coordinated by thecentral nervous system.[7]
The latissimus dorsi assists in depression of the arm with theteres major andpectoralis major. It adducts, extends, and internally rotates the shoulder. When the arms are in a fixed overhead position, the latissimus dorsi pulls the trunk upward and forward.[8]
It has asynergistic role in extension (posterior fibers) and lateral flexion (anterior fibers) of the lumbar spine, and assists as a muscle of both forced expiration (anterior fibers) and an accessory muscle of inspiration (posterior fibers).[9]
Most latissimus dorsi exercises concurrently recruit theteres major, posterior fibres of thedeltoid, long head of thetriceps brachii, among numerous other stabilizing muscles. Compound exercises for the 'lats' typically involve elbow flexion and tend to recruit thebiceps brachii,brachialis, andbrachioradialis for this function. Depending on the line of pull, thetrapezius muscles can be recruited as well; horizontal pulling motions such as rows recruit both latissimus dorsi and trapezius heavily.
The power/size/strength of this muscle can betrained with a variety of different exercises. Some of these include:
Tight latissimus dorsi has been shown to be a contributor to chronic shoulder pain and chronic back pain.[10] Because the latissimus dorsi connects the spine to thehumerus, tightness in this muscle can manifest as either sub-optimalglenohumeral joint (shoulder) function which leads to chronic pain ortendinitis in the tendinous fasciae connecting the latissimus dorsi to the thoracic andlumbar spine.[11]
The latissimus dorsi is a potential source of muscle forbreast reconstruction surgery after mastectomy (e.g., Mannu flap)[12] or to correct pectoralhypoplastic defects such asPoland's syndrome.[13][14] An absent or hypoplastic latissimus dorsi can be one of the associated symptoms of Poland's syndrome.[15][16]
For heart patients with low cardiac output and who are not candidates for cardiac transplantation, a procedure calledcardiomyoplasty may support the failing heart. This procedure involves wrapping the latissimus dorsi muscles around the heart and electrostimulating them in synchrony with ventricular systole.
Injuries to the latissimus dorsi are rare.[17] They occur disproportionately in baseball pitchers. Diagnosis can be achieved by visualization of the muscle and movement testing. MRI of the shoulder girdle will confirm the diagnosis. Muscle belly injuries are treated with rehabilitation while tendon avulsion injuries can be treated surgically, or with rehab. Regardless of treatment, patients tend to return to play without any functional losses.[18]
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This article incorporates text in thepublic domain from the 20th edition ofGray's Anatomy(1918)
