From an evolutionary perspective, when primates stood on their hind limbs the upper limbs were freed from weight bearing. The upper limbs of upright primates are thus able to function as both organs of prehension and as sensory probes of their environment. Many seemingly simple hand functions are only possible through the integration of the entire body, the upper limb, and the hand.

Kinesiology considers motion as it occurs under living conditions, analyzing mechanical forces on the body in motion. Motion is studied as activities are performed against extrinsic forces, such as gravity, or against the resistance of objects that are grasped, pushed, or hurled by the upper limb. Steindler¹ emphasized that in many situations, muscles are primarily used to achieve “stabilization and equilibrium rather than free motion.” Steindler also identified that the muscle contraction necessary to stabilize the skeleton is often not apparent as visible joint motion, yet these unseen muscle forces play an essential role in maintaining musculoskeletal equilibrium. This chapter focuses on the major pattern of upper limb activity and details the mechanical and nonmechanical factors essential to humans in efficient task performance. Sensory function, muscle strength, and skeletal stability are essential to effective integrated function.

Prehensile activity depends upon the stability of the trunk. Trunk or core stability creates the potential to create multiple integrated spheres of influence (Figure 1). Proximal limb stability, essential for secure hand placement, demands more than shoulder control. Spinal stability with attendant trunk control is essential to free the upper limb to perform effective prehensile activity. If the arms are being used to hold crutches or a walker, the hands cannot be spared for other activity. The paralyzed patient who uses a wheelchair may be unable to fully use his hands in the presence of trunk instability. Many wheelchair-bound patients are relatively well balanced in a static sitting position but become unstable by the simple forward shift of their center of gravity as they reach forward. This may occur when the combined mass of the upper limb and the object being held is shifted anterior to their sitting center of gravity. The arm must be retracted, and the object surrendered, or individuals risk tumbling out of the wheelchair. Many individuals will hook one arm over the back or the side of the chair for stability, sacrificing the opportunity for bimanual function. If hip or spinal extensor muscles are ineffective, the wheelchair-confined patient must be stabilized by a reclining backrest, retaining strap, or other spinal support so that both upper limbs can he free to reach away from the body.

Effective functioning of the upper limb requires flexibility and mobility as well as stability. The hand should be able to reach the mouth, hair, and perineum as well as the front of the body. Kapandji² delineated seven degrees of freedom of the upper limb as it positions the hand in space. The shoulder possesses three degrees of freedom, the elbow one, and the wrist and forearm have three, rotation, flexion/extension, and radioulnar deviation.

Because the shoulder is the most proximal joint, it plays the primary role in limb orientation. The shoulder’s substantial mobility is enhanced by the modest constraint in the articulation of the spherical humeral head with the shallow glenoid fossa. Flexion and extension occur around the transverse or coronal axis, abduction and adduction about the sagittal axis, and internal and external rotation about the vertical axis. Since the shoulder is loosely constrained by its bony configuration, it is particularly vulnerable to dislocation when soft-tissue constraints have been disrupted and to subluxation when musculo-tendinous coapting forces have been altered by paralysis or weakness (eg, a cerebrovascular accident).

The most frequently used arc of shoulder motion is in front of the body, a domain that allows visual input to optimize effective hand function. A greater arc of motion is employed for other bodily activities. Shoulder abduction is necessary for the hand to access the scalp for combing one’s hair. Shoulder abduction is not necessary for feeding or washing. Internal shoulder rotation is usually employed for posterior perineal hygiene. Combined shoulder extension and adduction can also be used to access the posterior perineum if an individual is unable to internally rotate the shoulder.

The shoulder girdle musculoskeletal complex provides attachment and suspension of the upper limb from the axial skeleton. The glenohumeral, acromioclavicular, and sternoclavicular joints, as well as the scapulothoracic interface govern shoulder mobility. The sternoclavicular joint is the sole point of direct contact of the upper limb appendicular skeleton with the axial skeleton. Motion through the sternoclavicular and acromioclavicular joints allows scapulothoracic motion either alone or combined with glenohumeral movement.

Scapular motion may be described in terms of the change in position of the scapula relative to the thorax.³ Scapular elevation and depression are readily appreciated. Upward scapular rotation is motion in which the inferior angle of the scapula moves anterolaterally, tilting the glenoid articular surface upward. Downward scapular rotation is the opposite motion, in which the inferior angle moves medially, tilting the articular surface of the glenoid downward. Scapular protraction refers to laterally and forward motion of the scapula around the thorax. Scapular retraction implies scapular movement medially and posteriorly about the thorax.

The normal glenohumeral joint flexes 180° and extends 60° (Figure 2). During the first 30° of shoulder abduction, the scapula is stabilized against the thorax so that all abduction takes place at the glenohumeral joint.⁴ Through the arc from 30° to 180°, every 2° of glenohumeral motion is associated with 1° of scapulothoracic motion.⁵ Thus, in full 180° of abduction, 130° of motion occurs at the glenohumeral joint while 50° of motion takes place at the scapulothoracic interface (Figure 3).

The elbow has a single primary arc of motion: flexion and extension. Constraint of the elbow arc is governed by the osseous contour of the olecranon and the trochlea and stabilizing ligaments. Recurrent dislocation of this constrained joint is infrequent. Because the elbow has a single arc of motion, it has been likened to a caliper functioning to regulate the distance between the hand and the trunk. The flexibility of the elbow to alter the length of the limb is critical to fundamental self-care activities including feeding and perineal care.

The biceps muscle has been termed the primary feeding muscle since it both flexes the elbow and supinates the forearm to bring the hand to the mouth. Biceps muscle strength should be sufficient to lift the weight of the hand, forearm, and any object in the grasp of the hand against the force of gravity.⁵ Although gravity may allow elbow extension in the absence of an active triceps muscle, it is essential that passive elbow extension be preserved if the limb is to be capable of reaching the perineum. Active elbow extension is necessary for reaching or placing the hand overhead as well for locomotion using a walker or propelling a wheelchair.

When triceps function is absent but full passive elbow motion is preserved, the elbow may be temporarily locked in a stable hyperextended position by shifting the weight of the trunk to that side. This strategy creates a stable limb by shifting the axis of weight bearing from the shoulder to the hand slightly posterior to the hyperextended elbow.⁶ The locked elbow position is particularly useful for transfer activity in paralyzed individuals. The limb is stable to axial load as long as the elbow remains extended.

The forearm and wrist are defined by three degrees of freedom that govern the orientation of the hand: forearm rotation, wrist flexion-extension, and wrist radial and ulnar deviation. The proximal and distal radioulnar articulations allow forearm pronation and supination. Though the interosseous space between analogous points on the radius and ulna is generally maintained throughout rotation, the space is maximal in neutral rotation and slightly narrowed in pronation (Figure 4).⁷

Because the olecranon of the ulna is stabilized against the humerus proximally, forearm rotation appears to occur as the radius (with the attached carpus and hand) rotates around the ulna. More precisely observed, the elbow is a loose hinge allowing rotation or rocking. When the forearm moves from pronation to supination, the distal ulna shifts radially and the ulna flexes (Figure 5). Pronation is the ideal position for body weight support activity, whereas supination is important in feeding as well as for balanced support of objects in the palm. Shoulder abduction is effective in substituting for absent forearm pronation. The usual strategy for compensating for a lack of supination, shoulder adduction and carpal supination is awkward and less effective since shoulder adduction is hindered by the trunk.

Both dorsiflexion and palmar flexion as well as radial and ulnar deviation occur through the radiocarpal and intercarpal joints (Figure 6).⁸ A limited degree of rotation is possible at the wrist, principally at the radiocarpal articulation. Because wrist dorsiflexion passively tightens the finger flexors by the tenodesis effect, dorsiflexion is an essential posture for strong grip activities. The ability of the wrist to passively palmar flex to release digital grip is important in hands possessing limited active motor units. In ulnar deviation the thumb becomes aligned with the long axis of the radius, a particularly effective posture for holding tools.