178


PART III THE UPPER EXTREMITY


Note to Students: It is recommended that you review the pretest questions before reading the chapter to better understand the critical elements of the text. As you complete each section, stop and answer the corresponding questions to test your comprehension. The pretest does not cover all the material in each chapter and should not be used as a sole means of self-assessment of knowledge.


This chapter studies the structures and functions of the elbow complex, which consists of the humeroradial and humeroulnar joints and the proximal and distal radioul- nar joints. The elbow complex functions to position the hand in space so that it can accomplish a multitude of tasks ranging from intrinsic fi ne motor manipulations to powerful grips. The elbow lengthens the arm for reach- ing and shortens the arm to enable the hand to bring objects to the face (e.g., for eating and grooming). By adding a rotational component of motion, the elbow complex provides a means for the hand to function in all planes. Finally, the elbow complex stabilizes the arm so that the wrist and hand can generate a strong grasp and links the function of the shoulder to the hand.


ELBOW COMPLEX STRUCTURES


The elbow complex consists of the articulations between the distal humerus, the radius, and the ulna. These bones form the joints of the elbow complex: humeroulnar joint, humeroradial joint, proximal radioulnar joint, and distal radioulnar joint (Fig. 9.1). The articulating structures along with the associated ligaments and joint capsules provide static stability to each of the joints. This section fi rst examines the structures and kinematics of each joint in the elbow complex and then looks at the role of the elbow complex muscles in elbow and forearm function.


BONY STRUCTURES Distal Humerus


The bony structures and landmarks of the proximal portion of the humerus are examined in Chapter 8. The shaft of the bone runs the length of the arm and fl ares at its distal aspect, forming the medial epicondyle and lateral epicondyle. These bony projections provide attachment sites for forearm and wrist muscles; this is discussed later in this chapter and in Chapter 10. The supracondylar ridges are bony ridges superior to the condyles. The hourglass-shaped trochlea and the rounded capitulum lie between the condyles. The trochlear groove divides the trochlea into medial and lateral sides, and the capi- tulotrochlear groove separates the trochlea from the capitulum. The coronoid fossa is the indentation on the humerus superior to the trochlea. The radial fossa is superior to the capitulum (Fig. 9.2A). On the posterior


Humerus


Humeroradial joint


Proximal radioulnar joint


Ulna Radius


Distal radioulnar joint


Humeroulnar joint


Figure 9.1 Articulations of the elbow complex.


surface of the humerus is an indentation called the olec- ranon fossa. The radial groove is located on the proximal one third of the humeral shaft (Fig.9.2B).


Radius and Ulna


The radius and ulna are the bones in the forearm that articulate with the proximal humerus. These bones lie parallel to each other in the forearm. The proximal radius is termed the radial head and has a concave surface called the fovea. The radial tuberosity is on the radial neck that lies just distal to the radial head. This bony area serves as the attachment site for the biceps brachii. The proximal articulating surface of the ulna is concave and is called the trochlear notch. The trochlear ridge divides the notch surface into halves. The olecranon process extends from the superior end of the trochlear notch, and the ulnar coronoid process extends from the lower end. Medial to the olecranon process is a groove through which the ulnar nerve transverses. Hitting your “funny bone” in this area can produce a tingling sensation as the ulnar nerve receives the mechanical stimulation.


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