The scalene muscles are comprised of three pairs located in the lateral aspect of the neck which, collectively, form part of the floor of the posterior triangle of the neck. These muscles act as accessory muscles of respiration, performing flexion at the neck. In this article, we shall look more closely at the anatomy of the scalene muscles - their attachments, function, innervation and clinical importance.
The anterior scalene muscle is located deep to the sternocleidomastoid on the lateral aspect of the neck. It originates from the anterior tubercles of the transverse processes of C3-C6 and attaches onto the scalene tubercle (on the inner border of the first rib). Its function is elevation of the first rib, with ipsilateral contraction causing ipsilateral lateral flexion of the neck, and bilateral contraction resulting in anterior flexion of the neck. Its innervation is the anterior rami of C5-C6.
The middle scalene is the largest and longest of the three scalenes. It has several long, thin muscle bellies arising from the cervical spine, which merge into one large belly that inserts into the first rib. It originates from the posterior tubercles of the transverse processes of C2-C7 and attaches to the scalene tubercle of the first rib. Its function is again elevation of the first rib, with the ipsilateral contraction causing ipsilateral lateral flexion of the neck. Its innervation is the anterior rami of C3-C8.
The posterior scalene is the smallest and deepest of the scalenes. Unlike the anterior and middle scalene muscles, it inserts into the second rib. It originates from the posterior tubercles of the transverse processes of C5-C7 and attaches into the second rib. Its function is elevation of the second rib, with ipsilateral contraction causing ipsilateral lateral flexion of the neck. Its innervation is the anterior rami of C6-C8.
The brachial plexus and subclavian artery pass between the anterior and middle scalene muscles, providing an important anatomical landmark in anaesthetics for performing an interscalene block. The subclavian vein and phrenic nerve pass anteriorly to the anterior scalene - the subclavian vein courses horizontally across it, while the phrenic nerve runs vertically down the muscle. The subclavian artery is located posterior to the anterior scalene. In interscalene block, local anaesthetic is injected between these muscles at the level of the cricoid cartilage.
The scalene muscles collectively act to elevate the first and second ribs, and in doing so they increase the intrathoracic volume. This allows patients with respiratory distress to ventilate their lungs more effectively as the scalene muscles can be used as 'accessory muscles of respiration'. However, they are not required in the respiration of a healthy individual, and so the use of accessory muscles is an important clinical sign of respiratory distress.
The scalene muscles play an important role in respiration, flexion at the neck, and in providing an anatomical landmark for anaesthetics. Recognizing the use of the scalenes as accessory muscles of respiration in a patient with respiratory distress is an important clinical sign of the condition. In addition to their functional and clinical importance, understanding the anatomy of the scalene muscles is essential for the successful performance of an interscalene block.
The scalene muscles are an important part of the anatomy of the neck. They consist of three muscles that include the scalenus anterior, scalenus medius, and scalenus posterior. These muscles are located between and around several important structures which include the brachial plexus and subclavian artery. They originate from the posterior tubercles of the transverse processes of C5-C7 and attach into the second rib. The scalene muscles serve multiple functions including elevation of the second rib, ipsilateral lateral flexion of the neck, and acting as accessory muscles of respiration.
The scalene muscles are innervated by the anterior rami of C6-C8. Clinically, they are important in interscalene block, which is a regional nerve block. This procedure can be done to determine the level of nerve irritation and/or for post-operative pain relief. To perform an interscalene block, local anaesthetic is injected between the bellies of the anterior scalene and middle scalene muscles at the level of the cricoid cartilage in order to avoid the use of a general anaesthetic.
The scalene muscles are also important in respiration. In patients with respiratory distress, they can be used as accessory muscles to help ventilate the lungs and increase intrathoracic volume. These muscles can be identified as the scalenus anterior, medius, and posterior. The scalenus anterior attaches to the transverse process of the cervical vertebrae from C1-C4, while the medius and posterior attach to the transverse processes of C5-C7. The scalene muscles serve to elevate the first and second ribs and increase intrathoracic volume. The use of these muscles as accessory muscles of respiration is an important clinical sign of respiratory distress.
The scalene muscles are important structures in the anatomy of the neck that serve multiple functions. Clinically, they are important in interscalene block and in the respiration of patients with respiratory distress. Knowledge of the anatomical relationships, innervation, and clinical relevance of these muscles are essential for the proper diagnosis and treatment of various neck and shoulder conditions.
