Iliocostalis is one of the three thin and long muscles of the group called erector spinae (erigere: to erect, spina: spine) which are found parallel with the vertebral column. Erector spinae is the strongest muscle group of the back. Iliocostalis is found deeper than the other muscles of its group and takes most of its origin from sacrum, lower vertebrae and some of the upper vertebrae of thoracic region and is inserted into ribs generally.
Iliocostalis lies parallel and lateral to longissimus, which in Latin means as the ‘longest muscle’ and is present most laterally among the erector spinae muscles.
Unilateral Action: When one side of the iliocostalis contracts, it causes the vertebral column to bend to the same side (side-flexion).
Bilateral Action: When muscles of the both sides contract, it causes backward bending (extension) of the vertebral column.
Iliocostalis muscle is further divided into three branches lying very close to each other. However, some differences are found in their origin, insertion and actions in terms of their location.
- Iliocostalis cervices: It originates from the third, fourth, fifth and sixth ribs and inserts into fourth, fifth and sixth cervical vertebral bone.
- Iliocostalis dorsi (thoracis): It has its origin from the lower six ribs and inserts into the upper six ribs and the seventh cervical vertebral bone. It causes extension of thoracic spine when contracts from both sides of the back.
- Iliocostalis lumborum: Its fibers arise from sacral bone, eleventh and twelfth thoracic vertebrae, and all of the lumbar vertebrae. It inserts into the lower seven ribs.
Clinical Importance – Associated Diseases/Conditions
- Lower Back Pain (LBP) and Buttock Pain: Chief problem arises when the iliocostalis lumborum fibres undergo straining, or as a result of bone deformities as seen with aging. Other causes may include a bulging or a degenerative disc. Trigger factors include overloading of the back, prolonged sitting and constant bending and twisting, especially when lifting objects. Symptoms comprise of pain in the lower back, buttock, and may rarely radiate to lower abdomen. Patient may also experience nausea. Treatment strategy is wide and includes muscle relaxants and pain killers. For severe pain, epidural steroid injections may be advised, especially when inflammation is involved.
- Upper Back Pain: Upper back pain most commonly occurs due to over-activity or stretching of the iliocostalis thoracis (dorsi) muscle. Constantly sitting for several hours without exercise or rest may also trigger upper back pain. Other causes are almost the same as for lower back pain. Pain however, may radiate to shoulder and the chest, particularly the upper ribs.
- Iliocostalis Syndrome (Friction Syndrome): It is a painful condition in which the lower ribs rub against the iliac crest causing friction and leads to irritation or possibly damage of the muscles, tendons and other soft tissues around it. This syndrome most frequently occurs in patients of osteoporosis, scoliosis (side-way curve of the spine) and disc degenerative disorders. Treatment most often involves ice therapy, pain killers (NSAIDs) and perhaps steroid injections to suppress swelling and pain at the same time.