A 3-year-old boy is brought to the emergency department after falling off a jungle gym. The boy tried to catch himself and landed on his outstretched arms. He did not lose consciousness and has been crying inconsolably since he fell. Pulse is 140/min; all other vital signs are within normal limits. Physical examination reveals tenderness and swelling over the anterior portion of his right shoulder with crepitus over the swollen area. An x-ray of his right shoulder is shown below. Tension from which of the following muscles is most likely responsible for displacement of the distal bone fragment?

Question

A 3-year-old boy is brought to the emergency department after falling off a jungle gym.  The boy tried to catch himself and landed on his outstretched arms.  He did not lose consciousness and has been crying inconsolably since he fell.  Pulse is 140/min; all other vital signs are within normal limits.  Physical examination reveals tenderness and swelling over the anterior portion of his right shoulder with crepitus over the swollen area.  An x-ray of his right shoulder is shown below.  Tension from which of the following muscles is most likely responsible for displacement of the distal bone fragment?

Quizplus · Accepted Answer

11ec160b_35e3_6977_9249_5bd9391834ea_MD0001_00 This patient has a displaced fracture of the distal clavicle, a commonly fractured bone. The clavicle is the only bone affixing the upper extremity and shoulder girdle to the thorax, and it can be subjected to significant forces during an injury, such as a fall onto the shoulder or outstretched arm. Because of their attachments on the clavicle, numerous muscles can apply tension on the proximal or distal bone fragments of a clavicle fracture. The anterior portion of the deltoid muscle originates on the distal clavicle and inserts onto the humerus. Normally, this part of the muscle acts to abduct, flex, and medially rotate the humerus. However, in a distal clavicle fracture, deltoid muscle tone and the weight of the upper extremity act to pull the distal fragment in the inferolateral direction. The proximal segment of the bone is pulled in the superomedial direction by the sternocleidomastoid and trapezius muscles. The net effect is to displace the fracture, which increases the risk of nonunion. (Choice A) The biceps brachii originates on the supraglenoid tubercle (long head) and coracoid process (short head) of the scapula. It inserts onto the radial tuberosity and bicipital aponeurosis of the forearm. (Choice C) The levator scapulae originates on the C1-C4 vertebrae and spans to the superomedial scapula. This muscle raises the scapula and rotates the acromion inferiorly. (Choice D) The pectoralis minor spans from the coracoid process of the scapula to the third, fourth, and fifth ribs and stabilizes the scapula against the thoracic wall. (Choice E) The teres minor spans from the lateral scapula to the greater tubercle of the humerus. It stabilizes the glenohumeral joint and laterally rotates the humerus. Educational objective: The clavicle is commonly fractured in children after a fall on an outstretched arm. In a distal clavicle fracture, the deltoid muscle and the weight of the arm cause inferolateral displacement of the distal fragment, whereas the sternocleidomastoid and trapezius muscles cause superomedial displacement of the proximal fragment. __________ References: Clavicle fractures: a review of the literature and update on treatment. (http://www.ncbi.nlm.nih.gov/pubmed/22030950)

A 3-Year-Old Boy Is Brought to the Emergency Department After