Chapter 6: Humerus & Shoulder Girdle

Detailed Chapter Overview

Chapter 6 focuses on the humerus and shoulder girdle, a region characterized by incredible mobility and a high susceptibility to injury, making its radiography both common and complex. This chapter provides an in-depth anatomical and procedural guide essential for diagnosing conditions ranging from simple fractures to complex dislocations and rotator cuff pathologies. A key theme is the critical relationship between patient positioning, specifically humeral rotation, and the visualization of key anatomical structures. The chapter meticulously details the anatomy of the clavicle, scapula, and proximal humerus, emphasizing the landmarks that are vital for accurate positioning and image evaluation. Understanding the three distinct joints of the shoulder girdle—the glenohumeral, acromioclavicular (AC), and sternoclavicular (SC) joints—and their classifications is fundamental. The chapter thoroughly explains why different rotational views are necessary to profile the greater and lesser tubercles of the humerus and to open up specific joint spaces. It provides detailed, step-by-step instructions for a wide array of projections, from routine AP and lateral views of the humerus to specialized projections like the Grashey method for an open glenohumeral joint space and the Scapular Y lateral for assessing dislocations. Particular attention is given to trauma radiography, outlining techniques like the transthoracic lateral for patients who cannot move their arm. For every projection, rigorous evaluation criteria are presented, training the radiographer to become a discerning critic of their own work to ensure every image is diagnostically optimal.

In-Depth Study Guide

Anatomy of the Shoulder Girdle

The shoulder girdle consists of the clavicle and the scapula, which connect the upper limb to the trunk of the body.

Clavicle (Collarbone):

• A long, slender, S-shaped bone that acts as a strut to support the shoulder.
• Acromial Extremity: The lateral end, which articulates with the acromion of the scapula to form the AC joint.
• Sternal Extremity: The medial end, which articulates with the manubrium of the sternum to form the SC joint.

Scapula (Shoulder Blade):

A large, flat, triangular bone located in the upper posterior thorax. It has three borders, three angles, and several important processes.

• Borders: Medial (vertebral), Lateral (axillary), and Superior.
• Angles: Superior, Inferior, and Lateral. The inferior angle is a key landmark for positioning.
• Glenoid Cavity (Fossa): A shallow depression on the lateral angle that articulates with the head of the humerus. This is the socket of the ball-and-socket shoulder joint.
• Acromion: A large process on the posterior aspect of the scapula that extends laterally over the shoulder joint.
• Coracoid Process: A thick, beak-like process that projects anteriorly beneath the clavicle.
• Scapular Spine: A prominent ridge that runs across the posterior surface, separating the supraspinous fossa from the infraspinous fossa.

Anatomy of the Proximal Humerus

The proximal humerus consists of the head, neck, and two prominent tubercles.

• Head: The large, smooth, rounded proximal end that articulates with the glenoid cavity.
• Anatomic Neck: The narrow constriction located directly below the head, separating it from the tubercles.
• Greater Tubercle: The larger, more lateral prominence.
• Lesser Tubercle: The smaller, more anterior prominence.
• Intertubercular Sulcus (Groove): The deep groove that separates the two tubercles.
• Surgical Neck: The constriction below the tubercles where the head tapers to join the shaft. It is a very common site for fractures, hence its name.

Joints and Rotational Anatomy

The shoulder complex involves three synovial joints.

• Glenohumeral (Shoulder) Joint: A spheroidal (ball-and-socket) joint. It is the most freely movable joint in the body, which also makes it prone to instability and dislocation.
• Acromioclavicular (AC) Joint: A plane (gliding) joint.
• Sternoclavicular (SC) Joint: A plane (gliding) joint.

Importance of Humeral Rotation:

Rotating the humerus changes the relationship of the tubercles to the x-ray beam, allowing specific parts of the anatomy to be visualized in profile. The epicondyles of the distal humerus are used as a guide to determine the position of the proximal humerus.

• External Rotation (True AP): Achieved by supinating the hand and ensuring the epicondyles are parallel to the IR. This position places the **greater tubercle in profile laterally**.
• Internal Rotation (True Lateral): Achieved by pronating the hand and ensuring the epicondyles are perpendicular to the IR. This position places the **lesser tubercle in profile medially**.
• Neutral Rotation: Hand and epicondyles are at a 45-degree angle to the IR. Neither tubercle is in profile. This is often the natural resting position for trauma patients.

Routine and Special Projections

Humerus

• AP and Lateral: The entire humerus must be included, requiring visualization of both the shoulder and elbow joints. The AP is taken in external rotation, and the lateral requires abducting the arm slightly.

Shoulder (Nontrauma)

• AP External Rotation & AP Internal Rotation: These two projections form a standard routine shoulder series, providing AP and lateral views of the proximal humerus and glenohumeral joint.
• Grashey Method (AP Oblique): The patient is rotated 35 to 45 degrees toward the affected side. This rotation places the glenoid cavity parallel to the IR, opening the glenohumeral joint space and demonstrating it without superimposition. It is excellent for evaluating joint space narrowing.

Shoulder (Trauma)

• Scapular Y Lateral (AP Oblique): A crucial view for evaluating dislocations. The patient is rotated into an anterior oblique position (RAO or LAO). The "Y" is formed by the acromion and coracoid processes superiorly and the body of the scapula inferiorly. In a normal shoulder, the humeral head is superimposed on the junction of the Y. In an **anterior dislocation** (most common), the head will be seen beneath the coracoid process. In a **posterior dislocation**, it will be seen beneath the acromion.
• Transthoracic Lateral (Lawrence Method): Used when the patient cannot abduct the arm. The patient is positioned for a lateral, with the affected arm against the IR. The CR is directed horizontally through the chest from the unaffected side. An orthostatic (breathing) technique is used (low mA, long exposure time) to blur out the overlying ribs and lung markings, allowing the proximal humerus to be seen.

Clavicle & AC Joints

• Clavicle: Requires an AP projection and an AP axial projection with a 15-30 degree cephalic angle to project the clavicle above the ribs.
• AC Joints: An AP bilateral projection is taken **with and without weights**. The patient holds weights strapped to their wrists (not in their hands) to stress the AC joints. A widening of the joint space on the weighted view compared to the unweighted view indicates an AC separation.