Lab 3—Arm & Axilla Skeletal—Questions 1 of 2 1. The pectoralis major inserts on the lateral lip of this 3. A 52-year-old man is brought to the emergency room after being bone's intertubercular groove: found in the park, where apparently he had lain overnight after a fall. He complains of severe pain in the left arm. Physical examination A. Ulna suggests a broken humerus that is confirmed radiologically. The pa- B. Radius tient can extend the forearm at the elbow, but supination appears to C. Humerus be somewhat weak; the hand grasp is very weak compared with the D. Scapula uninjured arm. Neurologic examination reveals an inability to extend E. Clavicle the wrist (wrist-drop). Because these findings point to apparent nerve damage, the patient is scheduled for a surgical reduction of the frac- ture. The observation that extension at the elbow appears normal, but supination of the forearm appears weak, warrants localization of the nerve lesion to which of the following? A. Posterior cord of the brachial plexus in the axilla B. Posterior divisions of the brachial plexus C. Radial nerve at the distal third of the humerus D. Radial nerve in the midforearm E. Radial nerve in the vicinity of the head of the radius 2. The accompanying x-ray below shows the shoulder of 4. A 10-year-old boy is brought into your office by his an 11-year-old girl who fell off the monkey bars, extending mother. The boy is supporting his left arm at the elbow by her arm in an attempt to break her fall. The small arrows using his right hand because he thinks he has “broken his indicate the fracture area. The large arrows indicate which arm.” The 10-year-old had been playing tag and tripped of the following? over the curb and landed on the grass, catching himself A. A fracture at the anatomic neck of the humerus with his hands. Upon physical examination you note a B. The glenohumeral joint slight drooping of the left shoulder when unsupported, C. The joint space between the proximal humerus and the and tenderness over the midclavicular region but no pal- acromion of the scapula pable fracture or displacement. The jugular notch appears D. The proximal humeral epiphyseal plate symmetrical. The shoulder has normal movement, but the E. What is commonly called a shoulder separation boy is unwilling to lift his hand above his head because it hurts. Otherwise, hand and arm movements are relatively normal with normal sensation. You order an AP and lat- eral x-rays of the thorax and upper arm because you sus- pect which of the following? 2. A. Colles’ fracture B. Scaphoid fracture C. Fracture of the surgical head of the humerus D. Dislocated sternoclavicular joint E. Greenstick fracture of the clavicle 5. A 7-year-old boy falls from a tree house and is brought to the emergency department of a local hospital. On ex- amination, he has weakness in rotating his arm laterally because of an injury of a nerve. Which of the following conditions is most likely to cause a loss of this nerve func- tion? A. Injury to the lateral cord of the brachial plexus B. Fracture of the anatomic neck of the humerus C. Knife wound on the teres major muscle D. Inferior dislocation of the head of the humerus E. A tumor in the triangular space in the shoulder region 1 Lab 3—Arm & Axilla Skeletal—Answers 1. Answer C. (2) The pectoral muscles are distinctly 3. Answer C. (7) Radial nerve at the distal third of different. The minor inserts on the coracoid process of the the humerus. The clinical signs and findings in the scapula. The major is involved with horizontal flexion of patient presented in the question indicate radial the humerus; thus, it must insert on the humerus. Re- nerve damage. The evidence that extension (triceps member a bench press is horizontal flexion of the humer- brachii muscle) at the elbow appeared normal while us and extension of the forearm. People who train using supination appeared weak can be used to localize the bench press have well-developed pectoralis major the lesion. The innervation to the medial and long heads of the triceps brachii, principal extensor of the (and triceps brachii) muscle. arm, arises from the radial nerve (in the axilla) as the medial muscular branches. The innervation to the lateral head, and to a smaller portion of the medial head, arises from the radial nerve as it passes along the musculospiral groove at mid-humerus. 2. Answer D. (7) The large arrows indicate the 4. Answer E. The clavicle is the most frequently proximal humeral epiphyseal plate. The young girl broken bone in body. Greenstick fractures of the was only 11 and still growing. The epiphyseal plates clavicle are extremely common in children as a re- show up on x-rays as radiolucent cartilage and sult of falling on outstretched arms. Colles’ fracture should not be confused with a fracture. The epiphy- is also common from falling on outstretched arms, sis is located at the anatomic neck of the humerus but there are no physical findings to support a Col- but is notdiscoid-shaped like many epiphyseal plates les’ fracture [(answer a); fracture of the distal radius, in long bones. This plate is tent-shaped, which is occasionally including the ulna] in this boy, [nor why it is not clearly visible all the way across the scaphoid fracture (answer b)]. The sternoclavicular proximal humerus. The fracture at the anatomic joint (answer d) is extremely stable and is rarely dis- neck of the humerus is marked by the small arrows located. Fracture of the surgical head of the humer- (answer a). The glenohumeral joint is more medial us (answer c) is not indicated by the physical find- (answer b). The joint space between the proximal ings. humerus and the acromion of the scapula (answer c) is more superior. The shoulder is not dislocated or separated (answer e). 5. Answer D. (1) Inferior dislocation of the head of the humerus may damage the axillary nerve, which arises from the posterior cord of the brachial plexus, runs through the quadrangular space accompanied by the pos- terior humeral circumflex vessels around the surgical neck of the humerus, and supplies the deltoid and teres minor, which are lateral rotators of the arm 2 Lab 3—Arm & Axilla Muscles; Tendons — Questions 1 of 3 1. Which of the following muscles can perform arm and 5. Which of the muscles listed below is the rotator cuff elbow flexion along with forearm supination? muscle involved in medial rotation of the humerus? A. biceps brachii A. Teres minor B. brachialis B. Latissimus dorsi C. brachioradialis C. Biceps brachii D. coracobrachialis D. Supraspinatus E. supinator E. Subscapularis 2. Which of the following is a small muscle that originates 6. A rock climber falls on his shoulder, resulting in a chip- from the lateral epicondyle of the humerus and inserts on ping off of the lesser tubercle of the humerus. Which of the olecranon? the following structures would most likely have structural A. Biceps brachii and functional damage? B. Brachialis A. Supraspinatus muscle C. Brachioradialis B. Infraspinatus muscle D. Triceps brachii C. Subscapularis muscle E. Anconeus D. Teres minor muscle E. Coracohumeral ligament 3. Only its long head is a two-joint muscle: 7. A 10-year-old boy falls off his bike, has difficulty in A. Biceps brachii moving his shoulder, and is brought to an emergency de- B. Brachialis partment. His radiogram and angiogram reveal fracture of C. Brachioradialis the surgical neck of his humerus and bleeding from the D. Triceps brachii point of the fracture. Following this accident, the boy has E. Anconeus weakness in rotating his arm laterally. Which of the follow- ing muscles are paralyzed? A. Teres major and teres minor B. Teres minor and deltoid C. Infraspinatus and deltoid D. Supraspinatus and subscapularis E. Teres minor and infraspinatus 4. This muscle supinates the forearm and originates on 8. A patient has suffered a fracture of the surgical neck of the scapula. the humerus. Which muscle is most likely to have been A. Teres minor weakened? B. Latissimus dorsi A. Deltoid C. Biceps brachii B. Supraspinatus D. Supraspinatus C. Biceps brachii E. Subscapularis D. Teres major E. Latissimus dorsi 3 Lab 3—Arm & Axilla Muscles; Tendons — Answers 1. Answer A. (12) The biceps brachii muscle attaches proxi- 5. Answer E. (2) There are three rotator cuff muscles that mally by its short head to the coracoid process of the scapula stabilize the head of the humerus in the glenoid cavity of the and by its long head to the supraglenoid tubercle. Distally it at- scapula. The subscapularis inserts on the lesser tubercle of the taches by a strong tendon to the tuberosity of the radius and by humerus and medially rotates the humerus. The supraspinatus an aponeurosis to the ulna. It thus can perform arm and elbow abducts and the infraspinatus laterally rotates the humerus. flexion along with forearm supination. 2. Answer E. (2) These requirements mean that the muscle 6. Answer C. (1) The subscapularis muscle inserts on the would need to be an extensor, which rules out the brachioradial- lesser tubercle of the humerus. The supraspinatus, infraspina- is, biceps brachii, and brachialis. The triceps brachii has a much tus, and teres minor muscles insert on the greater tubercle of larger origination. The anconeus is a small muscle, easily pal- the humerus. The coracohumeral ligament attaches to the great- pated during extension, in the gap between the lateral condyle er tubercle.