Essentials of the Musculoskeletal Exam; Part II: Evaluating the Nervous System

When examining the musculoskeletal system, neurological aspects must be considered. Strength testing, as discussed in Part I of this article (Clinical Geriatrics 2005;13[11]: 16-24), helps to assess whether a pattern of muscular weakness is due to a spinal nerve problem, or other musculoskeletal diseases. Examining the reflexes and the sensory system helps to differentiate neuronal damage from musculoskeletal pathology. Weakness associated with reflexive changes and discrepancies within the sensory system may indicate the nervous system as the culprit that is causing disease. Furthermore, evidence gathered from the neurological exam can determine if a lesion originates in the central nervous system versus the peripheral nervous system.

REFLEXES

Reflexes are involuntary contractions of a muscle brought out by the activation of muscle spindles. They are elicited by a sudden stretch of the muscle induced by a brisk hammer strike on the muscle tendon or the muscle itself. The hammer should strike with a quick, smooth, and direct motion. Note the speed, force, and amplitude of the reflex response, and compare the right and left sides. Decreased reflexes are a sign of spinal nerve and peripheral nerve damage. Entrapment neuropathies, such as that occurring in radial palsies or polyneuropathies in HIV and Guillain-Barré syndrome, present with diminished reflexes. On the contrary, patients presenting with hyperreflexia, clonus, or a Babinski sign may have an upper motor neuron lesion of the central nervous system. This is seen in patients with brain tumors, strokes, and multiple sclerosis. Fasciculations, or muscle twitches that are too weak to move limbs but are easily seen and felt by patients, should not be confused with a muscle reflex. These tiny contractions of individual muscle fibers are usually benign and can also be present in patients with mineral deficiencies. When accompanied by muscle weakness, fasciculations are a sign of lower motor neuron disease and are characteristic in patients with neurological diseases, such as amyotrophic lateral sclerosis (ALS). They tend to appear in the proximal muscles early on in the disease, and then more distally as ALS progresses.¹ Methods of reflex testing of major muscles and their associated spinal nerves are shown in Tables I and II. It is important to note that there are different ways of testing reflexes, as in the ankle reflex. The sensitivity and reproducibility of reflex testing using the different techniques are poor.² Therefore, interpretations of the reflexes made in light of other physical signs, such as muscle strength or sensory loss, can provide a clearer picture of whether deficits are real. If patients are having difficulty relaxing for the examiner to check the reflexes, a distracting method, called reinforcement, is used to bring out the reflex. For instance, when checking the patellar reflex patients are asked to hold their hands together with the tips of their fingers and pull outward. This is called the Jendrassik’s maneuver, which isometrically activates the muscles in the upper extremities, causing the patellar reflex to be brought out. The mechanism of potentiation of the reflex remains uncertain.³

GRADING OF MUSCLE REFLEXES

In addition to comparing reflex responses on the right and left side of a patient’s extremities, it is important to observe the amplitude and velocity of the response. The National Institute of Neurological Disorders and Stroke (NINDS) created a scale to describe the myotatic reflex (Table III).⁴ Its reliability and reproducibility has been studied and accepted internationally. Four neurologists, who received training from different countries, randomly and blindly evaluated the deep tendon reflexes of 80 subjects.⁵ They were trained with the same type of reflex hammer and employed the same techniques. Results of the study found that intraobserver reliability was substantial to near-perfect, and agreement between the neurologists was moderate to substantial. In particular, reliability of lower extremities was better. The authors of the study concluded that the NINDS Myotatic Reflex Scale has sufficient reliability to be adopted as a universal scale.

ASSESSMENT OF MUSCLE TONE

Flaccidity and rigidity When assessing muscle tone, the goal is to feel for abnormal resistance to passive stretching of the muscles. One method is to flex and extend the knee while supporting the thigh. In the upper extremity, the patient’s hand is placed in the examiner’s hand. The elbow is supported, and the shoulder joint is placed into moderate range of motion. Too little resistance, where the movements are markedly “floppy,” indicates flaccid or hypotonic muscles. Too much resistance or jerkiness in the movement suggests rigidity. This along with the presence of bradykinesia and tremor are found in Parkinson’s disease. Rigidity in Parkinson’s disease can be uniform or can be the cogwheel-type rigidity that is often accompanied by tremor.⁶ This extrapyramidal sign of “cogwheeling” may give way intermittently when resistance is placed on a joint. Spasticity Spasticity is characterized by overactivity of a muscle. It indicates hypertonic states secondary to hyperexcitable tonic stretch reflexes. An upper motor neuron lesion can result in spasticity, as occurs frequently in patients with multiple sclerosis. The “clasp-knife” phenomenon is one example of spasticity, in which once a joint nears full extension it suddenly “springs” into its final position, similar to a pocket-knife. Spasticity is differentiated by rigidity in that it is dependent on the speed of muscle stretch and often occurs in the presence of other upper motor neuron signs, such as clonus and a positive Babinski sign.⁷

SENSORY EXAM

A complete sensory exam is part of the musculoskeletal examination. A sensory deficit can be a disorder of the central or peripheral nervous system. Patients with strokes in the thalamus or parietal lobe can exhibit sensory loss. When testing patients for changes in their sensory system, loss of specific senses can help to confirm whether a lesion is present at a particular spinal level. Because different sensory modalities run in various pathways, it is important to check whether the sensory loss includes soft touch, vibration, proprioception, pin prick, or temperature. When localizing the lesion, it is important to note that touch, vibration sense, and proprioception arise from the dorsal columns that cross at the level of the medulla in the brainstem. Pin-prick and temperature sense follow the pain pathways in the spinal-thalamic tract, which decussate at the level of the related spinal root or a few levels above it. These points are relevant in that patients with spinal cord lesions that cause a hemisection of the cord, as in a Brown-Séquard’s lesion, may have loss of soft touch and proprioception on the side ipsilateral to the lesion and loss of temperature and pin-prick sensation contralateral to the lesion. Recent studies have suggested that a hemisection of the cord is not the only cause of Brown-Séquard’s syndrome, but that cervical disc herniations can produce a similar finding.⁸ Testing touch Touch is tested qualitatively using the clinician’s finger, a cotton swab, or even a piece of gauze. Patients can be asked to say “on” when they feel the sensation against their skin. The left and right sides are compared, and major spinal nerve distributions can be assessed. Testing vibration A tuning fork, either 128 Hz or 256 Hz, is used to assess the vibratory sensation. To test the vibratory sense, strike the tuning fork against an object and place it against the patient’s skin. Compare the left and right sides and ask the patient if it feels equal. Alternatively, the examiner can hold the tuning fork against the patient’s skin and ask him or her when the vibration disappears. Then compare it to the opposite side, and note whether there is a discrepancy in the patient’s ability to feel when the vibration disappears. As this type of assessment is not as reliable or sensitive compared to standardized evaluations, more quantitative measures, such as a Rydel-Seiffer graduated 64 Hz tuning fork, are more useful than standard tuning forks.⁹ Testing pain and temperature Pain is tested by using a pin prick. A safety pin can be used and then discarded to test whether patients feel the “sharp” sensation. A tip of a broken wooden applicator stick can also be utilized. When testing temperature, tubes of warm and cold water are traditionally used. More practical is the use of the cold tuning fork as opposed to the examiner’s warm fingers. Testing proprioception When testing proprioception, or joint position, patients are asked to shut their eyes. The examiner should hold the sides of a patient’s finger or toe and place it in an “up” or “down” position. Before testing, the examiner should place the finger or toe in the particular position and say whether it is “up” or “down.” Then, testing should begin. The Romberg sign is another method to test for proprioception in patients. This involves observing a patient’s postural stability with the patient’s feet together while the eyes are open, and then with them closed. A positive Romberg test is indicated when the patient is able to stand with the feet together when the eyes are open, but loses his or her balance when the eyes are closed.¹⁰ Whereas testing for proprioception reveals neurological deficits in the sensory and cerebellar system, a positive Romberg test can help to tease out the differences between weak muscles that cause imbalance and imbalance secondary to neurological processes.

CONCLUSION

Testing strength, reflexes, and sensory systems is part of a neurological exam, but it is also part of a complete musculoskeletal exam. It is clear that the musculoskeletal system receives numerous inputs from the nervous system in order to function. The two systems are intertwined, and it would be incomplete to test strength in the muscle without investigating possible deficits in reflexes and sensation. Together, findings from the musculoskeletal and neurological exams help to uncover the origin of the deficit. At various levels of muscle action, the nervous system plays a role in maintaining its activity. Even at the most basic functional unit of a muscle, the motor unit, the nerves play a role in muscle contraction. The muscle fibers contract when the alpha motor neuron signals them to do so. Reflex arcs that cause a contraction of a muscle to move a limb are dependent on neuronal feedback. Muscle spindles formed by sensory fibers detect stretch and synapse to alpha motor neurons to cause the excitation and the contraction of extrafusal muscle. These reflexes are carried out within the spinal cord. If there is damage to the central nervous system, and the damage is great enough, then the ability to contract muscle is diminished. With the addition of gamma motor neurons, the level of muscle contraction is further controlled. Gamma motor neurons enervate the poles of the muscle spindle and serve to respond to shortening or contraction of a muscle. When firing, it provides feedback used in reflex arches and sends information to the somatosensory cortex. The gamma motor neuron ensures that the sensory fibers continue to fire in spite of muscle shortening. Like the gamma motor neuron, the Golgi tendon organ is another type of sensory receptor that aids in providing appropriate muscle contraction. It delivers information on the force and tension of a muscle contraction. Activation of the Golgi tendon causes the inhibition of alpha motor neurons and reduces contraction of the muscle fiber. With feedback from both gamma motor neurons and Golgi tendon organs, proper functioning of the muscle is maintained and movement of the musculature is preserved. Therefore, when examining the musculoskeletal system, it is imperative that a thorough exam of the nervous system is made as well. The two systems work on feedback loops to allow for appropriate gait and movement. Disruptions in the sensory system may affect muscle contraction and can lead to compensatory mechanisms causing muscle aches and joint damage. To ensure a healthy musculoskeletal system, the flow of electrical transmission of the nervous system and the firing rates and synapses of the neurons must be at their most optimal setting. Exercises, strength training, and even alignment of the spine may help maintain muscle function as well as the well-being of the individual.