The quadratus lumborum muscle, informally called the ''QL'', is a paired muscle of the left and right posterior abdominal wall. 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 plus the lower posterior border of the twelfth rib. Contraction of one of the pair of muscles causes '' lateral flexion'' of the lumbar spine, ''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 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 and weak gluteal muscles can also contribute to the likelihood of quadratus lumborum pain.

Structure

The quadratus lumborum muscle originates by aponeurotic 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 bord ...

and the internal lip of the iliac crest for about . It inserts from the lower border of the last

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

for about half its length and by four small tendons from the apices of the transverse processes of the upper four lumbar vertebrae. 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 ilio ...

and sacrospinalis 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 muscle, and the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

; between the fascia and the muscle are the twelfth thoracic,

ilioinguinal The ilioinguinal nerve is a branch of the first lumbar nerve (L1). It separates from the first lumbar nerve along with the larger iliohypogastric nerve. It emerges from the lateral border of the psoas major just inferior to the iliohypogastric, a ...

, and

iliohypogastric The iliohypogastric nerve is a nerve that originates from the lumbar plexus that supplies sensation to skin over the lateral gluteal and hypogastric regions and motor to the internal oblique muscles and transverse abdominal muscles. Structure ...

nerves. The quadratus lumborum muscle is a continuation of transverse abdominal muscle.

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

contraction Contraction may refer to: Linguistics * Contraction (grammar), a shortened word * Poetic contraction, omission of letters for poetic reasons * Elision, omission of sounds ** Syncope (phonology), omission of sounds in a word * Synalepha, merged ...

# 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 ti ...

, with ipsilateral

("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 The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

to the

spine Spine or spinal may refer to: Science Biology * Vertebral column, also known as the backbone * Dendritic spine, a small membranous protrusion from a neuron's dendrite * Thorns, spines, and prickles, needle-like structures in plants * Spine (zoolo ...

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 muscle fatigue.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 muscle ...

Association with kyphosis

This chain of events can be and often is accelerated by kyphosis, 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, and especially the levator scapulae 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 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