S1L3 MSK (The Anterior Axilo-Appendicular Muscle) PDF

The anterior axio- appendicular Siraj hayder The upper limb consists of four major segments, which are further subdivided into regions for Shoulder: proximal segment of the limb that overlaps It includes the pectoral, scapular,...

The anterior axio- appendicular Siraj hayder The upper limb consists of four major segments, which are further subdivided into regions for Shoulder: proximal segment of the limb that overlaps It includes the pectoral, scapular, parts of the trunk (thorax and back) and lower lateral and deltoid regions of the upper neck. limb Arm (L. brachium): first segment of the free upper limb. It precise description extends between and connects the shoulder and the elbow, and consists of anterior and posterior regions of the arm, centered around the humerus. Forearm (L. antebrachium): It extends between and connects the elbow and wrist and includes anterior and posterior regions of the forearm overlying the radius and ulna. Hand (L. manus): part of the upper limb distal to the forearm that is formed around the carpus, metacarpus, and phalanges. It is composed of the wrist, palm, dorsum of hand, and digits (fingers, including an opposable thumb), and is richly supplied with sensory endings for touch, pain, and temperature.  The pectoral and scapular regions consist of various structures that include muscles, blood vessels, and nerves; which all act together to make our upper limbs functional. The muscles of the pectoral region are divided into groups based on their locations. There are axio-appendicular muscles, which extend between the axial and appendicular skeletons; and the scapulohumeral muscles, which specifically connect the scapula to the humerus.  First, let’s take a look at the axio-appendicular muscles, which are divided into two large groups: the anterior and posterior groups of muscles. The anterior axio-appendicular group is composed of four muscles: the pectoralis major, pectoralis minor, the subclavius, and the serratus anterior.  The pectoralis major is a relatively flat, fan shaped muscle, which covers the upper half of the thorax. This muscle has two proximal attachments also called heads. The first one is the clavicular head, which attaches proximally to the medial half of the clavicle. Below it, there’s another much larger part called the sternocostal head, which attaches proximally to the anterior surface of the sternum and the superior six costal cartilages. Both the clavicular and the sternocostal heads converge distally and then attach to the lateral lip of the intertubercular groove of the humerus.  The pectoralis major muscle is innervated by two nerves: the lateral pectoral nerve and the medial pectoral nerve. Alright, so when these two heads of the pectoralis major muscle contract simultaneously, they produce adduction, and medial rotation of the arm. Additionally, each muscle head can also contract independently. When the clavicular head contracts alone, it causes flexion of the arm, while the contraction of the sternocostal head extends it back from a flexed position The clavipectoral fascia is a strong fascial sheet deep to the clavicular head of the pectoralis major muscle, filling the space between the clavicle and the pectoralis minor muscle. STRUCTURES PIERCING THE CLAVIPECTORAL FASCIA Lateral pectoral nerve. Thoraco-acromial artery. Cephalic vein. Lymphatics from the breast  Alright, now let’s talk about the pectoralis minor muscle, which is a triangular muscle situated deep to the pectoralis major in the anterior axillary wall. The base of the pectoralis minor muscle attaches to the anterior surface of the third, fourth, and fifth ribs, at the point where they meet their costal cartilages. The fibers of pectoralis minor converge towards its apex superolaterally into a tendon that attaches to the coracoid process of the scapula  The pectoralis minor is innervated by the medial pectoral nerve. And when the pectoralis minor contracts, it pulls on the coracoid process inferiorly and anteriorly against the thoracic wall, providing stability to the scapula by holding it tight to the thorax. It also helps during deep inhalation because this muscle can elevate the ribs as it contracts, thus increasing the volume of the thoracic cavity, so more air can get into the lungs.  Next in the anterior axio-appendicular group is the subclavius, which is this small round muscle lying horizontally inferior to the clavicle and superior to the first rib. It’s best seen when the arm is in the anatomical position. Proximally, the subclavius attaches to the first rib and its costal cartilage, while distally, it attaches to the inferior surface of the middle third of the clavicle. This is where this muscle gets its name.  The subclavius is innervated by the nerve to subclavius, which receives fibers from the anterior rami of C5 and C6 via the superior trunk of the brachial plexus. The subclavius helps to stabilize the shoulder by anchoring and depressing the clavicle and also adding some strength to stabilize the acromioclavicular joint when you hit those heavy weights at the gym.  Last but not least, there’s the serratus anterior muscle, which forms the medial wall of the axilla and lies over the lateral part of the thorax. This is a fitting name for the muscle because “Serratus” means saw and the way this muscle’s fibers are arranged on its anterior border gives it a saw-like appearance. The muscle originates on the external surfaces of the lateral parts of the upper eight ribs and then prolong laterally and posteriorly to insert onto the whole length of the anterior aspect of the medial border of the scapula, along with the inferior angle of the scapula  The serratus anterior is innervated by the long thoracic nerve which originates from the anterior rami of C5, C6, and C7. When the serratus anterior contracts, it protracts the scapula, meaning it pulls it anteriorly and laterally along the back. This happens when you are trying to reach for something anteriorly or when making a punching motion, which is why this muscle is also referred to as the boxer’s muscle. The serratus anterior also helps to anchor the scapula by holding it close to the thoracic wall, like when doing push ups or pushing a car. Last but not least, this muscle also causes the scapula to rotate upwards, thus tilting its glenoid cavity like when abducting your arm above the head.  It passes over the chest wall and lies on the superficial surface of the serratus anterior muscle. The long (22-24cm) and superficial course of this nerve makes it susceptible to various injuries Injury to long thoracic nerve can cause weakness of the serratus anterior muscle and dynamic winging of scapula clinical case