Essentials of the Musculoskeletal Exam Part I: Evaluating the Muscle
The patient’s chief complaint directs the musculoskeletal exam. Identical complaints often have different etiologies and require the exam to progress in different directions. Weakness, balance, changes in the appearance and functional ability of the muscles, and sensation are common complaints that may be primarily muscular or neurological in origin. Deciding which direction to pursue in terms of an evaluation depends first on a thorough exam and a logical approach. Abnormal postures and bodily asymmetries can be muscular or neurological in origin. Muscle weakness of the hand can indicate a nerve impingement that disrupts the information being conveyed from the brain to the hand, or the person being examined may be weak. A patient presenting with recurrent falls might suffer from the sequelae of weak trunk muscles or a lesion in the sensory system. While there is no substitute for understanding neurological pathways, dermatomes, muscle insertions, and other anatomical and physiological aspects of the musculoskeletal and nervous systems, it is essential to understanding how to perform and properly interpret the physical examination. In Part I of this article, strength testing and its implications are reviewed. In Part II, to be published in the December issue of Clinical Geriatrics, examining the neurological aspects of the musculoskeletal exam will be discussed.
Strength testing is a crucial part of diagnosing diseases of the muscles, connective tissue, and nervous system. During the evolution of medicine, the importance of muscle testing was evident. Ancient Egyptian medical papyri documented the usefulness of localizing weakness to correlate it to externally visible injuries. Hippocrates described a correlation of arm and leg weakness with “black bile.” A. Cornelius Celsus identified muscle weakness as part of paralysis. John Cooke pointed out the value of examining muscle tone and strength.1
Throughout history, it was clear that muscle testing was a valuable tool to provide the physician with information on the well-being of the patient. More recent studies also suggested that muscle weakness can offer evidence of disease within the muscle itself, joints, or neuronal processes. When evaluating strength, physicians can identify the risk of occurrence of common conditions such as falls, osteoarthritis, or chronic low back pain in their patients. Muscle weakness is correlated with falls in older adults.2
In a systematic review and meta-analysis of subjects 65 years and older using studies that measured muscle strength in patients and the occurrence of falls, lower-extremity weakness was statistically significant as a risk factor for falls. Whereas upper-extremity weakness may be a risk factor, it was also a marker of lower-extremity weakness. It is important to evaluate muscle strength in older individuals due to the comorbidity associated with falls. Lower-extremity strength in particular should be evaluated, and if weakness is detected its etiology should be evaluated and treated, if possible; falls can lead to further patterns of physical and mental deterioration. The question remains, however, as to whether strengthening exercises will prevent falls in older individuals with physically irreversible conditions.
Muscle weakness is also a harbinger of osteoarthritis. Evaluating for the presence of muscular weakness can indicate whether a preventive measure of strengthening should be implemented to thwart the development or slow the progression of osteoarthritis. Studies show that the quadriceps muscles are active in stabilizing the knee joint.3 With weakness in the quadriceps, disruption of the mechanics of the knee may lead to joint damage. It remains unclear, however, if quadriceps weakness is a result from pain in osteoarthritis or if quadriceps weakness precedes the onset of osteoarthritis. It is possible that both scenarios are true.
Patients with osteoarthritis were found to have significantly impaired quadriceps strength in a study that compared maximum voluntary isometric contractions to similarly aged, uninjured subjects.4 Having full strength of the quadriceps muscle and having maximally contracted muscle yielded higher volitional activity and less movement failure. With improved knee function and gait mechanics, the wear and tear that lead to osteoarthritis may be minimized. By identifying the possible causes of osteoarthritis, which include muscle weakness, patients can utilize strength exercises to improve their joint mechanics, thereby preventing degenerative joint disease. Some studies suggest that weakness of the vastus medialis obliquus may be an early sign of osteoarthritis, but other studies have reported no differences in temporal recruitment of the vastus medialis obliquus and vastus lateralis during stair climbing in patients with osteoarthritis.5
Rehabilitation of the quadriceps as a whole—not just the vastus medialis obliquus—appears to be of possible benefit for patients with osteoarthritis. Another indication for assessing muscle strength is in the presence of low back pain. Patients with chronic back pain were found to have weakness in both extensor and flexor muscles of the trunk.6 Although postural extensor muscles in these patients were weaker to a greater extent than the flexors, both muscle groups were found to be significantly weaker in women with chronic low back pain compared to normal controls. Hip extensors, such as the gluteus maximus, also play a role in low back pain. Functional changes were found in muscular activation patterns of patients with low back pain.7
In this study, 17 men with chronic, idiopathic low back pain were compared with 16 age-matched, healthy men. Student’s t-tests demonstrated significant differences for hip joint range of motion and stride time between healthy control individuals and those with back pain. There was a decrease in hip flexion and extension, as well as reduced gait cycle in those with back pain. This study confirms that low back disorders are related to changes in the hip extensor pattern that affect the physiological loading and alteration of the direction and magnitude of joint reaction forces. Questions still remain as to whether the muscle disturbances precede or are the consequence of idiopathic low back pain. Nevertheless, after identifying muscle weakness in patients with back pain, strengthening exercises have proven to be beneficial in reducing pain.6 Strengthening core muscle groups is an important approach to patients with chronic back pain.
EXAMINATION OF THE MUSCLES
Inspection by observation is the first step of the muscle exam. Looking at the muscle itself can determine whether atrophy, hypertrophy, fasciculations, joint swelling, or obvious trauma to the muscle and joint are present. Observation alone can be key to determining whether disease is present. A good place to start is by focusing on the thigh muscles and the thenar and hypothenar eminences. A number of conditions, both musculoskeletal and common medical problems, can cause muscle wasting. Patients who have diabetes, cancer, or AIDS, and astronauts in space, often exhibit muscle atrophy. Long-term use of cortico-steroids can cause catabolic effects that result in muscle wasting. Musculoskeletal diseases, nerve impingements, and osteoarthritis leading to disuse can also result in atrophy.
Muscle hypertrophy, with decreased strength, may be a result of genetic diseases, such as muscular dystrophy. Fasciculations (which will be discussed in Part II of this article) can suggest lower motor neuron disease, as in amyotrophic lateral sclerosis, as a reason for muscle weakness. Last, swelling of the joints may indicate arthritic changes. Muscle strength testing is achieved through identifying and isolating the individual muscles. Proper positioning during muscle testing is key to a successful exam. Testing muscle strength includes placement of the muscle in flexion and extension, internal and external rotation, adduction and abduction, or supination and pronation, depending on the action of the muscle. Both the right and left sides need to be compared and should be tested consecutively, one after the other. Discrepancies and asymmetry of strength between the two sides should be noted. If weakness is observed, it is important to identify whether it is proximal or distal weakness and if there are patterns of muscle weakness that reflect specific spinal nerve distributions. Proximal weakness may indicate diseases such as polymyalgia rheumatica, whereas distal weakness would suggest peripheral diseases such as carpal tunnel syndrome. If the weakness pattern is consistent with a spinal nerve distribution, entrapments and radiculopathies may be present. Techniques in evaluating the major muscles, with the spinal nerves indicated, are shown in Tables I and II; Table I indicates the upper-extremity muscles and Table II describes the trunk and lower-extremity muscle-testing techniques.
GRADING MUSCLE STRENGTH
When assessing the strength of a muscle, a numbering system has been devised to grade muscle strength based on manual testing. The score is dependent on the quality of muscle strength in relation to whether there is movement against resistance with or without gravity eliminated. During World War II, the grading of muscle strength was standardized by means of a scale developed by the British Medical Research Council (BMRC).8 Because the scale involves 6 categories (0-5), “plus” and “minus” can be utilized to further denote distinctions if a patient’s strength falls between two categories. Other studies have shown that condensing the scale from 12, which would include the “plus” and “minus,” to 4 categories would increase the discriminatory validity of manual strength testing.9 This case showed that manual muscle testing versus testing using a strength-measuring device, the dynamometer, supported the validity in using manual muscle testing when the two are compared. Table III shows the currently accepted testing scale used to categorize muscle strength.
One-leg stance Postural steadiness is an indicator of muscle strength and balance. The one-leg stance test is one method of testing postural steadiness. This involves instructing the patient to stand with two feet on the ground with weight equally distributed. Patients are then asked to stand freely on one leg for as long as possible. This common test performed in the primary care office measures two phases, a dynamic phase and a static phase.10 It is the first 5 seconds of the test, the dynamic phase, that suggests musculoskeletal weakness if a postural disturbance is detected. Rapid-finger tapping Rapid-finger tapping is a test that also identifies weakness. Patients are asked to tap the tip of their index finger with the interphalangeal joint of the thumb as fast as they can. The speed of movement is compared between the two hands. Asymmetries in speed indicate weakness in the slower hand.
Deterioration of hand movements, which may be characterized by segmented hand paths or unsmooth movements, as well as prolonged movement times, is seen in patients with Parkinson’s disease.11 Slowing of rapid-finger tapping is a sign of poor coordination due to cerebellar disease. Patients are asked to place the palms of their hands on their thighs and then flip to the backs of their hands against their thigh, flipping back and forth between the two as quickly as possible. The inability to carry this out efficiently is referred to as dysdiadochokinesia, and is a sign of cerebellar disease. Pronator drift Subtle weakness in the upper extremities that is detected by the presence of a pronator drift can tell physicians that a lesion in the motor system is present. Patients are asked to stretch out their arms in front of them with elbows extended and hands supinated. The eyes are then shut. If in this position one arm begins to drop or pronation of one hand occurs, weakness may exist in that extremity. This test can also indicate defects in proprioception.12 Without visual feedback, proprioception is necessary to maintain a limb position and to modify joint muscle torque. A defect in proprioception caused by a hemispheric lesion or defect at the joint and muscle level will result in a pronator drift.
Clearly, evidence of weakness found on physical exam can be muscular or neurological in origin. Determining the strength of a muscle and identifying weakness only presents a fraction of the picture. What is causing the inability of the muscle to function at its full capacity? Could it be disruptions of joint mechanics, a lesion in the central nervous system, a peripheral nerve palsy, or perhaps an autoimmune disease and mineral deficiencies? Looking at the patient as a whole—their medical history, laboratory tests, and their physical exam, including the neurological exam—can unmask the underlying cause of weakness. Targeting the root cause of muscle weakness can help physicians devise a plan for their patients to avoid injury. If the weakness is due to inappropriate joint mechanics and strength within the muscle itself, exercises and strength training may help patients escape debilitating conditions resulting from falls, osteoarthritis, and chronic back pain. However, if the etiology of weakness is neurological in origin, a different approach needs to be addressed. In the second part of this article, the neurological aspects of the musculoskeletal exam will be reviewed and discussed as a tool to clarify the etiology of muscular weakness.