Functional Anatomy

Introduction

Anatomy is the study of the physical structures within the human body. The skeleton provides the foundation for the body; muscles attach by way of bony origins and insertions. Knowledge of the nervous system provides us with a practical understanding of muscle action, tendon excursion, and joint motion. Therefore, the assessment of key postural markers throughout the upper extremity provides an understanding of proper skeletal alignment and balance in the neuromusculoskeletal system as well as a basis for comparing the normal default of body conformation to that of abnormal alignment.

As hand therapy professionals, we rely on the functional anatomy of the upper extremity as the main determinant in grading the success of our client’s task performance. We can correlate abnormal postures to a client’s functional complaints. Fundamentally and simplistically, the observation and assessment of the body’s alignment is a measure of how the neuromusculoskeletal system is performing. The concept of balance and movement can provide a greater understanding of human anatomy and direct us to the contributions of soft tissue impairment. The important issue for us is that a postural assessment gives us the ability to evaluate the overall muscle balance and the response of the body as a whole to disease and trauma.

During purposeful activity, a client thinks more about what they want to do and less about how they do it. Frequently, unguarded movements lead to stressing joints and overloading muscles without knowing the consequences of their effects on healing tissues. When symptoms and functional limitations appear, pain is the body’s response to injury. As the first line of defense, movement is altered unconsciously to reduce pain. Whether the complaints are global and diffuse or pinpoint and local, we cannot be fooled into narrowly interpreting the origin of their symptoms as the source of pathology to a specific body structure. Altered body movements and imbalances in resting neuro-muscular-skeletal alignment can cause mechanical pathology and can be the secondary complications that result in the client’s chief complaint that is it “hurts.”

Due to a fixed time period allotted for our evaluation, it is imperative that we observe our client’s static body postures and movement patterns to understand the etiology of their physical impairment. Our efficiency and skill in evaluation is imperative to control health care dollars and, above all, to direct treatments to the best outcomes for each of our clients. During the initial interview of chief complaints and general medical history, you can simultaneously perform an assessment of posture. Observations can be done in static, resting positions while the client is sitting, standing, and lying down as well as during spontaneous, dynamic movements when the client first shakes your hand, takes off his/her coat, walks, sits down, or completes paperwork. These observations are the first quick functional anatomy screen of how the body is aligned, possible altered responses proximally and distally, and observations of the sites related to the client’s physical complaints.

Resting and dynamic postural assessments assist us in developing a plan of care that provides a clear relationship between the desired improvements of the neuro-muscular-skeletal balances and functional tasks. Self-reports are obtained every visit on the client’s satisfaction and ease of performance in doing purposeful daily activities. For example, the ability to wash hair will improve more efficiently and safely when scapular muscle stabilizers are strengthened and able to support free movement at the glenohumeral joint. Balanced scapulo-thoracic rhythm occurs at the normal starting position of retracted, downward rotation. This allows normal gliding of the rotator cuff tendons without impingement at the acromioclavicular joint and reduces subsequent pain. A systematic approach to screening the functional anatomy of the core and distal joints of the body combines the knowledge of kinematic chains, tissue imbalances, and compensatory movements in the recovery of the upper extremity from disease and trauma.

To enhance your clinical reasoning skills, this chapter will review anatomy and neurophysiology principles beyond the rote memorization of origins, insertions, nerves, and actions. Instead, the reader will be introduced to normal postural mechanics and the characteristics associated with healthy bones, joints, ligaments, muscles, tendons, and the neurovascular system of the upper extremity. Then, common clinical scenarios will illustrate abnormal deviations or faults in postural mechanics resulting from tissue imbalance and will provide suggestions for quick screens of the functional anatomy. An extensive review of anatomic features such as joint function, the lymphatic system, dermatome levels, sensory distributions, and pulleys for flexor tendons, are provided in other chapters of the book.

Normal Postural Mechanics

There are observable muscle behaviors that influence our posture and purposeful movements, also termed as our functional anatomy. Important distinctions should be made between anatomic characteristic of body positions, both at the initial static position of a kinematic event and then the return to our neuro-muscular-skeletal equilibrium of balance.¹ Static posture is the stationary position held against gravity, whereas dynamic posture refers to a series of positions that constantly change during movement and function. Both postures require equilibrium of the muscle system and are observed during relaxation, standing, sitting, or lying down.¹

The neutral resting balance of our anatomy is the state of default or the zero position of the body.² The zero position is different from the anatomical position of the body. It represents the normal resting balance position where the upper extremities align themselves in space against gravity and where movement ceases and loads are removed. In zero position, the upper extremities are positioned in the midrange of glenohumeral and forearm rotation, the wrist is positioned in approximately ten degrees of extension, and the finger joints are positioned in approximately 45 degrees of flexion. Abnormal changes in functional anatomy cannot be understood without knowledge of the normal resting balance position. Fig. 2-1 illustrates zero position.

FIGURE 2-1 The zero position of the body from the sagittal and coronal planes.
A, Anterior view. B, Posterior view. C, Lateral view. (Modified from Cameron MH, Monroe LG: *Physical rehabilitation: evidence-based examination, evaluation, and intervention,* St Louis, 2007, Saunders Elsevier.)

The upper extremities return to this default resting position, or zero position, in most static body postures. It is an assumed position of joint alignment where the tone of muscle activity is minimal, where the origins and insertions are in a “resting” tone, and where the tension of the joint is in a relaxed, balanced position. Tone is defined as the continuous and passive-partial contraction of the muscle or the muscle’s resistance to passive stretch during the resting state.³

Clinical Pearl

If the starting position of the body differs from the zero position of balance, the altered anatomy will create a disrupted kinematic chain of movement that adds stress to areas, such as the acromioclavicular joint or to the muscles that originate on lateral epicondyles.

Functional anatomy, defined by postural kinematic expressions, is fundamentally based on a predictable design. Skeletal conformation is observed and analyzed by envisioning the underlying bone positions. By knowing the preset configuration, or default design, you can visually construct the muscle anatomy and its contribution to posture. The gross structure, knowledge of fiber alignment, location, and the origins and insertions from your human anatomy references will assist you in understanding the natural tone and potential force of a specific muscle. The angles and lines that are produced as well as the conformation of our body are indications as to how synergistic muscles and peripheral nerves are performing. Typically, the points of reference are anatomical landmarks and are observed in two body planes. The coronal plane is vertical and divides the body into anterior and posterior halves.² From the coronal plane, we draw a linear line, or plumb line, that forms an axis of reference. From the lateral view of the client, the alignment of the ear, shoulder, lateral elbow, posterior hip, anterior knee, and lateral malleolus are body landmarks that are located close to, if not directly within, the axis of reference. From the axis, you can observe the flexion, extension, anterior, and posterior adaptations of the body. Similarly, the sagittal plane is vertical and divides the body into right and left right halves.² Postures viewed from all sides include obvious body markers, such as head position, shoulder height and glenoid orientation, clavicle angle, scapular position, antecubital fossa (carry angle), hand orientation, and hip height. Fig. 2-1, A and B, illustrates the body in the sagittal plane and provides the anterior and posterior views of the body. Fig. 2-1, C, illustrates the body in the coronal plane and provides a lateral view of the body with a clear view of the arm position.

A functional anatomy screen is performed by envisioning the points at the joints, the anatomic landmarks, and the bone segments as they create altered angles in contrast to those described in the zero position. The differences in these angles or projections are used to hypothesize the influence of the associated muscle function. To understand postural forces of human anatomy and to utilize these concepts in practice, we need to apply the normal orientation of the ideal balance for the skeleton and muscles at rest and during movement throughout the entire kinematic chain. These “normal” default postures can then be compared to the patient who has compensatory adaptation and restrictions in his/her anatomical structures.

Mapping is a technique of drawing using the design and angles of the body that create a picture of alignment. Positions of mapping are in movement planes. The body’s coronal and sagittal planes produce the lines of reference in static and dynamic body postures. The front and back views of the body allow the best view of symmetry. Landmarks are structures that identify a feature other than a joint. Examples of landmarks are the ear, forehead creases, palm and nail positions, the carry angle space, web spaces, and skin folds in the back and digital creases. Once the position of the joint articulation and landmarks are identified, the segments are drawn. The design is then analyzed using the expected functional anatomy as the reference point for identifying imbalances that can contribute to pain, weakness, and restrictions in movement.

The use of the two anatomic planes, axes of reference, and mapping techniques serve as a functional anatomy screening tool that allows the hand therapy professional to compare the ideal postural alignment to that of the assumed posture of the client. The deviation from the ideal can range from slight to severe and will guide the evaluator in understanding the problems associated with joint and muscle functions. Next, a review of the anatomical systems will be discussed in further detail including the characteristics associated with bones, joints, ligaments, muscles, tendons, and the neurovascular systems of the upper extremity and their the contribution to normal postural mechanics.

Bones, Ligaments, and Joints

Bones are responsible for the rigidity and structure of the entire foundation. The joint anatomy is designed to allow transmission of muscle force, at rest and during motion. Understanding the joint structure contributes to the overall whole of functional anatomy and posture configuration. The bone-to-bone connection meets to create the joint. The bone segments within the joint move in relation to each other. The configuration of the bony surfaces dictates the degree of freedom of a joint and creates a type of movement hinge.

The joint allows freedom of movement from one to three planes. Two bony segments move in relationship to each other. Usually one segment is stable while the other moves in relation to the base. At the joint there can be more than one articulation. For example, the glenohumeral joint has scapulo-humeral, sterno-humeral, and clavico-humeral articulations.² The control and stability of the joint’s axis of rotation directly relates to the articular orientation of the bones. Without rules of engagement for the joint, the simplest movement can become weakened by loss of mechanical advantage. This is seen in joint dislocation and a segmental bone fracture, whereby the movement is not guided and irregular angulations are observed. Conversely, if the segments of bone are not congruent and there is altered space that changes the axis of movement, the normal extrinsic muscle pull can be offset and the movement will present with distorted mechanics that are less than desired.

Throughout the body, there are many axes of rotation. In the upper extremity there are flexion-extension, abduction-adduction, internal-external, radial-ulnar, and pronation-supination axes. The wrist has two, the elbow joint has one at the ulnohumeral joint axis, and the glenohumeral joint is a ball and socket joint with three axes of rotation. The relationships of joint axes have a normal presentation of balance that is predictable and can be assessed at rest and during movement.

The normal skeletal system of the upper extremity can be mapped to determine the normal default state of zero position. An imaginary overlay of the skeleton on the conformation of the body creates the approximate location of the joints and bone segments. These structures assist you in recognizing important landmarks. An example of important landmarks from Fig. 2-1 is the space between the arm and body. Fig. 2-2 identifies the mapping specific to the hand. Important landmarks for the hand are nail positions, the space between the index and thumb, the cascading flexion of the fingers, the mass of the thenar eminence, and the prominence of the ulnar head.

FIGURE 2-2 Mapping of the hand at rest in a pronated **(A),** supinated **(B),** and neutral forearm position. (From Donatelli RA: *Orthopaedic physical therapy*, ed 4, St Louis, 2010, Churchill Livingstone Elsevier.)

Clinical Pearl

An understanding of normal anatomy and the ideal positions of balance is essential to recognize the imbalances in your client’s neuromusculoskeletal anatomy.

Altered configuration of the joint’s soft tissue matrix or bony constructs lead to the joint’s failure to glide and can result in various types of joint collapses and deformities.³ With joint laxity, the axis shifts into the direction of the weakened, degraded tissue integrity. Frequently, this is seen with attritional changes of the glenohumeral joint where the anterior capsulo-ligaments are weakened and attenuated. A shift in the joint axis results in changes in the anterior and posterior capsule and in the formation of adhesions.

Another example is seen with metacarpophalangeal (MP) joint subluxation and swan neck deformities in the hands of persons with rheumatoid arthritis. A common joint change is when the proximal phalanx segment shifts palmary toward the volar plate, descending and subluxing. What is observed at rest is the prominent head of the metacarpal. The forces from muscle contractions are transmitted through the altered axis and with changes in the moment arm of the tendon, the extensor becomes a flexor of the finger MP joint. The change in the axis of rotation alters not only the forces applied to the MP joint but also the kinematic chain of all joints that the muscle tendon unit controls. The shortening or lengthening of the long tendon, in conjunction with significant joint changes, presents with a zigzag of the fingers in proximal interphalangeal (PIP) hyperextension and distal interphalangeal (DIP) flexion joint postures.

FIGURE 2-3 Mapping of a normal and pathological carpometacarpal (CMC) joint of the thumb. (Photo by Lori DeMott.)

Clinical Pearl

The kinematic chain of mobility is controlled and primarily influenced proximally.

Mapping the skeletal alignment within the body conformation is a screening tool that you can utilize to assist with evaluation of the functional anatomy. The technique can be drawn on the client and, with practice, will be visualized as part of your observations during the functional anatomy screen.

Muscles and Tendons

Muscles work in groups and patterns of movement. Individual muscles have lengthening, contractile, excitable, and recoil characteristics. Contractility allows a muscle to shorten with force, to lengthen passively, and to move. Excitability allows a muscle to respond to a stimulus and to maintain chemical potentials across its cell membranes. Extensibility allows a muscle to be stretched, repeatedly and considerably, as needed, without being damaged. Elasticity allows a muscle to return to its normal length after being stretched or shortened. The end result is a force application. For example, a coordinated neuromuscular event occurs during the conscious decision to make a fist. The wrist extensors stabilize the wrist in approximately 35 degrees of extension, the extrinsic extensor digitorum communis (EDC) elongates into a full extensible position as the antagonist muscle, and simultaneously the extrinsic flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) contract in their role as agonist muscles. The coordinated muscle contractions differentiate the glide that allows terminal distal joint flexion. Simultaneously, contraction of the intrinsic lumbrical and interossei muscles increase metacarpal joint flexion, stabilize and control the joint, and allow the digits to converge into a tucked position within the palm. The characteristics of the musculotendinous structures that contribute to muscle balance are located in Box 2-1.³

BOX 2-1 Musculotendinous Characteristics that Contribute to Balance

1. The resting length of a muscle is the relationship and proportional stretch to the fully contracted muscle fiber.

2. At rest and even during sleep, there is a tendency of the muscle to contract and resist lengthening. This principle is influenced by the central nervous system and the intrinsic muscle structure and by definition is our muscle tone.

3. Ordinary normal range of motion at rest or during movement is influenced by the variability of length and pull of all of our contributing anatomy due to antagonist lengthening as well as synergistic coordination.

4. Gravity and the need for skeletal stability will change the resting muscle tone and therefore change distal joint position.

5. Length and cross-section of a muscle leads to predictable excursion and levels of muscle elasticity.

6. A muscle crossing multiple joints will provide a composite excursion; a proximal joint stability is necessary for increased distal joint mobility.

7. Passive joint mobility is without influence of soft tissue elastic characteristics.

8. Muscle balance is involuntary, and over time the resting length can change or be changed by an altered axis. As the joint moves, these altered forces create imbalances and lead to deformity.

Nervous System

The peripheral, central, and autonomic nervous systems all combine to form one internal communication system for sensing and responding to internal and external stimuli.⁴ The motor and sensory functions for the forearm, wrist, and hand are provided by the peripheral nervous system; consisting of the median, ulnar, and radial nerves. Each nerve has efferent motor and afferent sensory fibers arranged in bundles of axons. The axons are protected by layers of dense connective tissues called the epineurium, perineurium, and endoneurium. Each layer has a unique role to support the innermost structures of the nerve, modulate compressive and tensile forces, and allow gliding between nerve fascicles and the surrounding anatomical structures.⁵ Electrical impulses are rapidly conducted via the nodes of Ranvier along a neural pathway, which originates at the spinal cord and brainstem and terminates in the fingers and toes. Due to the continuous nature and physiology of the peripheral nervous system, motions at a distal site, such as the wrist joint, increase the strain at the cord level of the brachial plexus. Similarly, contralateral flexion of the cervical spine increases the strain in the cords of the brachial plexus and three major nerves in the arm.⁴ Under tension, the neural tissue may have difficulty conducting electrical impulses, assuring adequate blood supply, and providing adequate axonal transport especially during movement.⁵

Several biomechanical properties are necessary to protect the nerve from tensile, shear, and compressive forces that occur across multiple joints in various postures and dynamic movements of the upper extremity during everyday activities.⁵ The properties of the nerve protect it from the forces generated from whole body movements resulting from everyday activities. These protections are due to the nerve’s capacity to change its length during movement, slide or glide relative to the surrounding interfacing tissue during movement, and tolerate increases in pressure or compression from the surrounding interfacing tissue.⁵ When the nerve does not tolerate normal stresses, a “sensitized” protective state may result as the upper extremity joints usually adjust by flexion or extension to limit the nerve excursion. Symptoms can include increased pain or aberrant movements in the absence of altered nerve conduction.^4,5

Observations of static and dynamic postures are essential to evaluate the neurodynamics of the peripheral nervous system in its entirety and the changes which can result from limited excursion or traumatized segment(s) of the nerve.⁴ As simply observed in an acute nerve injury, the upper arm is held tightly in shoulder adduction, internal rotation, and elbow flexion. In the presence of long-standing trauma to the nerve, imbalances in motor function can be observed. For example, hyperextension of the thumb MP joint during resistive lateral pinch can be observed in persons with ulnar nerve palsy. A zigzag deformity is observed as a result of absent function of the adductor pollicis muscle and imbalances created from a weakened intrinsic extensor mechanism and overpowering extrinsic long flexor.

A neuromusculoskeletal screen of the upper extremity is critical to understanding the changes that impact functional anatomy. Several observations of normal postures can be made. At rest, clients with neural tension postures will limit movement that places the nerve in full excursion. The elbow joint has a high degree of contribution to nerve glide. In resting postures the elbow will flex, and the head will laterally tilt to the affected side. During movement, the head may increase the degree of tilt or the elbow joint increase its flexed position to offset the increased demand at adjacent joints.

Now that you have a better understanding of normal postural mechanics and the neuromusculoskeletal systems, common clinical scenarios are provided to illustrate abnormal deviations, or defaults, in the postural mechanics that result from tissue imbalances. Quick screens will also be provided in each scenario to assist you in applying the principles of balance.