2: Functional Anatomy

INTRODUCTION

The study of functional anatomy—human anatomy as it relates to function—is an undertaking vital to physiatrists and any medical professionals who care for patients with disabilities or injuries of the musculoskeletal system. This chapter provides an overview of functional anatomy organized by common clinical problems framed from the perspective of anatomic study. There are many excellent resources for further study, which is essential for mastery of this topic. Some of these are listed within this chapter.

THE UPPER LIMB

CLINICAL PROBLEM: SCAPULAR WINGING

Pertinent Anatomy

The trapezius muscle (Figure 2–1) performs the following functions:(Figure 2–1)

• It stabilizes the scapula (Figure 2–2) proximally in the coronal plane via retraction toward the rib cage and ­spinous processes.

• It rotates the scapula upward in the coronal plane to maximize upward and outward reach of the arm.

• It rotates the scapula to optimize the length–tension relationship for the other shoulder abductor muscles, including the deltoids and the rotator cuff, allowing for the most efficient and forceful contraction.

The serratus anterior muscle (Figure 2–1) stabilizes the scapula in the sagittal plane, rotates the scapula upward in the sagittal plane, and protracts the scapula. This produces a combination of lateral excursion in the coronal plane, internal rotation, and anterior translation in the sagittal plane. Weakness of the serratus produces scapular dyskinesis in the sagittal plane, most notably during flexion of the arm.

Management Considerations

The arm can be abducted 180 degrees in the coronal plane. Of this motion, 120 degrees occurs at the glenohumeral joint and 60 degrees occurs at the scapulothoracic joint. Weakness of the trapezius causes impairment in arm abduction and produces a form of scapular dyskinesis. Scapular dyskinesis, or alteration in the normal scapulohumeral rhythm, results in a counter-rotation of the scapula downward, due to the direction of deltoid pull and the unopposed force of gravity on the upper limb. Humeral abduction in the coronal plane can be limited to as little as 60 degrees of abduction due to the limitation of scapulothoracic joint motion. Shoulder abduction in the upright position causes the scapula to wing laterally in a patient with trapezius weakness.

A patient with serratus weakness may not have noticeable winging when standing upright with the arms at the sides. However, when posterior force is exerted through the humerus onto the scapula, medial winging of the ...