The quadratus lumborum muscle, informally called the ''QL'', is a paired muscle of the left and right

posterior abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity. The abdominal wall is split into the anterolateral and posterior walls. There is a common set of layers covering and forming all the walls: the deepest being the vi ...

. It is the deepest abdominal muscle, and commonly referred to as a back muscle. Each is irregular and quadrilateral in shape. The quadratus lumborum muscles originate from the wings of the ilium; their insertions are on the transverse processes of the upper four lumbar

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

plus the lower posterior border of the twelfth rib. Contraction of one of the pair of muscles causes '' lateral flexion'' of the

lumbar spine The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...

, ''elevation'' of the pelvis, or both. Contraction of both causes ''extension'' of the lumbar spine. A disorder of the quadratus lumborum muscles is pain due to

muscle fatigue Muscle fatigue is the decline in ability of muscles to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main ca ...

from constant contraction due to prolonged sitting, such as at a computer or in a car.Core Topics in Pain, p. 131, Anita Holdcraft and Sian Jaggar, 2005.

Kyphosis Kyphosis is an abnormally excessive convex curvature of the spine as it occurs in the thoracic and sacral regions. Abnormal inward concave ''lordotic'' curving of the cervical and lumbar regions of the spine is called lordosis. It can result ...

and weak

gluteal muscles The gluteal muscles, often called glutes are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus, gluteus medius and gluteus minimus. The three muscles originate from the ilium and sa ...

can also contribute to the likelihood of quadratus lumborum pain.

Structure

The quadratus lumborum muscle originates by

aponeurotic An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...

fibers into the

iliolumbar ligament The iliolumbar ligament is a strong ligament passing from the tip of the transverse process of the fifth lumbar vertebra to the posterior part of the inner lip of the iliac crest (upper margin of ilium). Course It forms the thickened lower bor ...

and the internal lip of the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poster ...

for about . It inserts from the lower border of the last rib for about half its length and by four small tendons from the apices of the transverse processes of the upper four

lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...

. The number of attachments to the vertebræ, and the extent of its attachment to the last rib, may vary. Also, occasionally, a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebræ, and is inserted into the lower margin of the last rib.

Relationships

File:Gray388.png, Cross-section of the posterior abdominal wall, showing on the right the relationship of the quadratus lumborum muscle to the

psoas major The psoas major ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the iliop ...

and

sacrospinalis The erector spinae ( ) or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes (gluteus maximus, gluteus medius and gluteus minimus) to maintain stable posture standing or sitt ...

muscles. Gray1124.png, Posterior view showing on the left the relationship of the left

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

to the left quadratus lumborum muscle. Anterior to the quadratus lumborum are the colon, the

, the psoas major muscle, (if present) the

psoas minor The psoas minor muscle ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long, slender skeletal muscle. When present, it is located anterior to the psoas major muscle.Tank (2005), p 93Gray (2008), p 1372 Structure The psoas minor mu ...

muscle, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves. The quadratus lumborum muscle is a continuation of

transverse abdominal muscle The transverse abdominal muscle (TVA), also known as the transverse abdominis, transversalis muscle and transversus abdominis muscle, is a muscle layer of the anterior and lateral (front and side) abdominal wall which is deep to (layered below) th ...

Nerve supply

Anterior branches of the ventral rami of T12 to L4.

Functions

The quadratus lumborum can perform four actions: # Lateral flexion of vertebral column, with

ipsilateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

contraction # Extension of lumbar vertebral column, with bilateral contraction (based on line of force passing ~3.5 cm posterior L3 rotation axisMcGill SM, Santaguida L, Stevens J: Measurement of the trunk musculature from T5 to L5 using MRI scans of 15 young males corrected for muscle fibre orientation, Clin Biomech (Bristol, Avon) 8:171-178, 1993.) # Fixes the 12th rib during forced expiration. The quadratus lumborum assists the diaphragm in inhalation # Elevates the

Ilium (bone) The ilium () (plural ilia) is the uppermost and largest part of the hip bone, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny ...

, with

contraction ("hip hiking") Additional functions: * Vertical stabilization of pelvis, lumbar spine, and lumbosacral junction. Prevents collapse of the vertebral column in the frontal plane (i.e. scoliosis) * Reserve mover actions: anterior pelvic tilt. * Contralateral lateral pelvic rotation.

Clinical significance

The quadratus lumborum muscles can be the source of back pain when overused, or in association with scoliosis or weak gluteal muscles.

Mechanism

The quadratus lumborum is a common source of unilateral or bilateral lower back pain, including localized pain and tenderness over the wing of the ilium.''Clinical Orthopaedic Examination'', Ronald McRae, 2004 (5th ed.). Because quadratus lumborum connects the pelvis to the spine and is therefore capable of extending the lower back when contracting bilaterally, the two quadratus lumborum muscles pick up the slack, as it were, when the lower fibers of the erector spinae are weak or inhibited (as they often are in the case of habitual seated computer use and/or the use of a lower back support in a chair). Given their comparable mechanical disadvantage, constant contraction while seated can overuse the quadratus lumborum, resulting in

.Core Topics in Pain, p. 131, Anita Holdcraft and Sian Jaggar, 2005. A constantly contracted quadratus lumborum, like any other muscle, will experience decreased blood flow, and, in time, adhesions in the muscle and fascia may develop, the end point of which is

muscle spasm A spasm is a sudden involuntary contraction of a muscle, a group of muscles, or a hollow organ such as the bladder. A spasmodic muscle contraction may be caused by many medical conditions, including dystonia. Most commonly, it is a muscl ...

Association with kyphosis

This chain of events can be and often is accelerated by

kyphosis Kyphosis is an abnormally excessive convex curvature of the spine as it occurs in the thoracic and sacral regions. Abnormal inward concave ''lordotic'' curving of the cervical and lumbar regions of the spine is called lordosis. It can result ...

, which is invariably accompanied by rounded shoulders, both of which place greater stress on the quadratus lumborum by shifting body weight forward, forcing the erector spinae, quadratus lumborum,

multifidi The multifidus (multifidus spinae : ''pl. multifidi'' ) muscle consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. While very th ...

, and especially the

levator scapulae The levator scapulae is a slender skeletal muscle situated at the back and side of the neck. As the Latin name suggests, its main function is to lift the scapula. Anatomy Attachments The muscle descends diagonally from its origin to its inserti ...

to work harder in both seated and standing positions to maintain an erect torso and neck. The experience of "productive pain" or pleasure by a patient upon

palpation Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine ...

of the quadratus lumborum is indicative of such a condition.

Association with weak gluteal muscles

Hip abduction is performed primarily by the hip abductors (gluteus medius and minimus). When the gluteus medius/minimus are weak or inhibited, the tensor fasciae latae or quadratus lumborum will compensate by becoming the prime mover. The most impaired movement pattern of hip abduction is when the quadratus lumborum initiates the movement, which results in hip hiking during swing phase of gait. Hip hiking places excessive side-bending compressive stresses on the lumbar segments. Thus, a tight quadratus lumborum may be another hidden cause of low back pain (Janda 1987). When the hip adductors are tight or hypertonic, their antagonist (gluteus medius) may experience reciprocal inhibition. The gluteus medius will become weak and inhibited. This in turn may cause hypertonicity of ipsilateral quadratus lumborum. Chronic hypertonicity of quadratus lumborum tends to cause low back pain due to its ability to create compressive stress on lumbar segment.

Treatment

While stretching and strengthening the quadratus lumborum are indicated for unilateral lower back pain, heat or ice applications as well as massage should be considered as part of any comprehensive rehabilitation regimen. Current studies show that application of heat or ice, massage, and estim will not leave long-term benefits. Careful assessment of muscular imbalances and movement impairments by a therapist is recommended in order to address the underlying issues mentioned.''Assessment and Treatment of Muscle Imbalances'', p. 100, Phil Page, 2010.

References

External links

* - "Posterior Abdominal Wall, Dissection, Anterior View" {{Authority control Muscles of the torso