The lateral thoracic region, located on the side of the human chest between the armpit and lower ribs, is a complex anatomical area. It contains a network of muscles, nerves, and blood vessels that facilitate various upper body movements and provide structural support.
Key Anatomical Structures of the Lateral Thoracic Region
The lateral thoracic region houses several anatomical components, each playing a role in the function of the chest and shoulder. These include the lateral thoracic artery, the long thoracic nerve, and the serratus anterior muscle. These structures are positioned in close proximity, allowing for coordinated movement.
Lateral Thoracic Artery
The lateral thoracic artery, also known as the external mammary artery, originates from the axillary artery. It descends along the lateral border of the pectoralis minor muscle, often beneath the pectoralis major, and terminates around the fifth intercostal space. It can also originate from the thoracoacromial or subscapular arteries.
Long Thoracic Nerve
The long thoracic nerve, also known as the nerve of Bell or posterior thoracic nerve, runs alongside the artery. It arises from the brachial plexus (spinal nerves C5, C6, and C7). The nerve descends behind the brachial plexus, continuing down the chest wall in the mid-axillary line. It lies directly on the surface of the serratus anterior muscle, which it solely innervates.
Serratus Anterior Muscle
The serratus anterior is a large, fan-shaped muscle located on the side of the ribcage, forming part of the armpit’s medial wall. It originates from the outer surfaces of the first to eighth or ninth ribs and inserts along the medial border of the scapula (shoulder blade). Its appearance is often described as “saw-toothed” or “serrated” due to its multiple rib attachments. This muscle is positioned deep to the scapula and pectoral muscles.
Functions and Importance of These Structures
The coordinated actions of the lateral thoracic artery, long thoracic nerve, and serratus anterior muscle are important for upper body movement and stability. Each component contributes to these functions, supporting daily activities.
Lateral Thoracic Artery Function
The lateral thoracic artery delivers oxygen-rich blood to the lateral chest wall and associated muscles. It supplies the serratus anterior, pectoralis major, pectoralis minor, and subscapularis muscles, along with the axillary lymph nodes. In females, it also supplies the breast.
Long Thoracic Nerve Function
The long thoracic nerve’s primary role is to provide motor innervation to the serratus anterior muscle. Without this nerve, the serratus anterior cannot function, directly impacting shoulder and arm movement.
Serratus Anterior Muscle Function
The serratus anterior muscle performs several functions related to scapular movement and stability. It protracts the scapula, pulling the shoulder blade forward around the thorax, a movement seen when pushing or throwing. It also works with the trapezius muscle to facilitate upward rotation of the scapula, necessary for lifting the arm overhead beyond 90 degrees. This muscle helps hold the scapula firmly against the ribcage, preventing it from “winging” or protruding. When stabilized, the serratus anterior can also assist in elevating the ribs, contributing to respiration.
Common Issues and Conditions
The lateral thoracic region can be susceptible to various issues that may result in pain, weakness, or altered movement.
Muscle Strains
Muscle strains, particularly affecting the serratus anterior, are common in this area. These strains often result from overuse in activities involving repetitive arm movements like swimming, throwing, or weightlifting. Poor posture, improper lifting techniques, or direct trauma to the ribcage can also contribute to serratus anterior pain. Symptoms include localized tenderness, discomfort along the side of the ribcage, and restricted shoulder range of motion.
Long Thoracic Nerve Palsy
Injuries to the long thoracic nerve can lead to long thoracic nerve palsy, commonly manifesting as “winged scapula.” This occurs when the serratus anterior muscle, which holds the scapula against the chest wall, weakens or paralyzes due to nerve damage. The medial border of the scapula then protrudes noticeably from the back, especially when the arm moves forward or pushes against a wall. Causes of long thoracic nerve injury include non-traumatic factors like viral illnesses or medical conditions, and traumatic factors such as direct blows, overstretching, or repetitive arm movements. Iatrogenic injuries from surgical procedures like mastectomy or axillary lymph node dissection are also recognized causes, often due to the nerve’s superficial course.
Referred Pain
Pain in the lateral thoracic region can also stem from referred pain, which is discomfort felt in an area different from the actual source. For example, issues in the thoracic spine, such as herniated discs or facet joint problems, can cause pain perceived in the side of the chest. Similarly, certain internal organ conditions, like those affecting the heart, may present as pain in the left shoulder or chest, which could be felt in the lateral thoracic area. This information is for general understanding and does not replace professional medical advice. If experiencing persistent pain, weakness, or altered movement in this region, consulting a healthcare provider for an accurate assessment is recommended.