* The author receives no compensation in any form from products discussed in this chapter.
“I often say that when you can measure what you are speaking about and express it in numbers, you know something about it; but, when you cannot measure it in numbers your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge but [you] have scarcely in your thought advanced to the stage of science whatever the matter may be.” —LORD KELVIN
Objective measurements provide a foundation for hand rehabilitation efforts by delineating baseline pathologic conditions from which patient progress and treatment methods may be assessed. A thorough and unbiased assessment procedure furnishes information that helps predict rehabilitation potential, provides data with which subsequent measurements may be compared, and allows medical specialists to plan and evaluate treatment programs and techniques. Conclusions gained from evaluation procedures guide treatment priorities, motivate staff and patients, and define functional capacity at the termination of treatment. Assessment through analysis and integration of data also serves as the vehicle for professional communication, eventually influencing the body of knowledge of the profession.
The quality of assessment information depends on the objectivity, sophistication, predictability, sensitivity, selectivity, and accuracy of the tools used to gather data. It is of utmost importance to choose assessment instruments wisely. Dependable, precise tools allow clinicians to reach conclusions that are minimally skewed by extraneous factors or biases, thus diminishing chances of subjective error and facilitating more accurate understanding. Instruments that measure diffusely produce nonspecific results. Conversely, instruments with proven accuracy of measurement yield precise and selective data.
The manner in which assessment tools are used is also critical. Deviations in recommended equipment, procedure, or sequence invalidate test results. A cardinal rule of assessment is that instruments must not be used as therapy practice tools for patients. Information obtained from tools that have been used in patient training is radically skewed, rendering it invalid and meaningless. Testing equipment also should not be substituted or altered from the original equipment on which reliability and validity statements were based, and test procedure and sequence must not vary from that described in administration instructions. Patient fatigue, physiologic adaptation, test difficulty, and length of test time also may influence results. Clinically, this means that sensory testing is done before assessing grip or pinch; rest periods are provided appropriately; and if possible, more difficult procedures are not scheduled early in testing sessions. Good assessment technique should reflect both test protocol and instrumentation requirements.
Communication is the underlying rationale for requiring good assessment procedures. The acquisition and transmission of knowledge, both of which are fundamental to patient treatment and professional growth, are enhanced through development and use of a common professional language based on strict criteria for assessment instrument selection. The use of “home-brewed,” evaluation tools that are unreliable and unvalidated is never appropriate because their baseless data may misdirect or delay therapy intervention. The purposes of this chapter are to (1) define measurement terminology and criteria, (2) identify factors that influence the development of an upper extremity battery, and (3) review current upper extremity assessment instruments in relation to accepted measurement criteria. It is not within the scope of this chapter to recommend specific test instruments. Instead readers are encouraged to triage the instruments used in their practices according to accepted instrument selection criteria, keeping those that best meet the criteria and discarding those that do not.
Assessment Terminology and Criteria
Standardized tests, the most sophisticated assessment tools, are statistically proven to be reliable and valid, indicating (1) that they measure consistently within their testing unit, between like instruments, between examiners, and from trial-to-trial, and (2) that they measure what they were designed to measure. “Reliability deals with whether a measurement consistently reflects something, whereas validity deals with how the measurement is used.” The few truly standardized tests available in hand rehabilitation are limited to instruments that evaluate hand coordination, dexterity, and work tolerance, and unfortunately, not all of these tools meet all of the requirements of standardization. The remaining hand/upper extremity assessment tools fall at varying levels along the reliability and validity continuums according to how closely their inherent properties match measurement criteria.
As consumers, medical specialists must require that all assessment tools have appropriate documentation of reliability and validity. “Data regarding reliability [and validity] should be available and should not be taken at face value alone; just because a manufacturer states reliability studies have been done, or a paper concludes an instrument is reliable, does not mean the instrument or testing protocol meets the requirements for scientific design.” Purchasing and using assessment tools that do not meet fundamental measurement criteria limits potential at all levels, from individual patients to the scope of the profession.
Standardized tests must have all of the following elements: (1) Statistical proof * of reliability; (2) statistical proof † of validity; (3) a statement defining the purpose/intent of the test; (4) detailed equipment criteria; (5) specific administration, scoring, and interpretation instructions; and (6) normative data, drawn from a large population sample, that is divided, with statistically suitable numbers of subjects in each category, according to appropriate variables such as hand dominance, age, sex, and occupation. A bibliography of related literature also may be included. Although many instruments are touted as “standardized,” most lack even the fundamental elements of statistical reliability and validity, relying instead on normative statements such as means or averages. Instruments without statistical reliability and validity have no basis for justifying either their consistency of measurement or their capability to measure the entity for which they were designed. Because relatively few evaluation tools fully meet standardization criteria, instrument selection must be predicated on satisfying as many of the listed requisites as possible.
* Correlation statistics or another appropriate measure of instrument reliability.
Correlation statistics or another appropriate measure of instrument validity.Through interpretation, standardized tests provide information that may be used to predict how a patient may perform in normal daily tasks. For example, if a patient achieves “x” score on a standardized test, it may be predicted that the patient would perform at an equivalent of the “75th percentile of normal assembly line workers.” Standardized tests allow deduction of anticipated achievement based on narrower performance parameters as defined by the test.
In contrast, observational tests assess performance through comparison of subsequent test trials and are limited to like-item-to-like-item comparisons. Observational tests are often scored according to how patients perform specific test items, that is, independently, independently with equipment, needs assistance, and so on. “The patient is able to pick up a full 12-ounce beer can with his injured hand without assistance.” Progress is based on the fact that he could not do this 3 weeks ago. However, this information cannot be used to predict whether the patient will be able to dress himself or herself or run a given machine at work. Assumptions beyond the test item trial-to-trial performance comparisons are invalid and irrelevant. Observational tests may be included in an upper assessment battery so long as they are used appropriately.
Computerized Evaluation Equipment
Computerized assessment tools must meet the same measurement criteria as noncomputerized instruments. Unfortunately, both patients and medical personnel tend to assume that computer-based equipment is more trustworthy than its noncomputerized counterparts. This assumption is erroneous. In hand rehabilitation, some of the most commonly used noncomputerized evaluation tools have been or are being studied for instrument reliability and validity (the two most fundamental instrumentation criteria). However, at the time of this writing, none of the computerized hand evaluation instruments have been statistically proven to have intrainstrument and interinstrument reliability, via comparison to National Institute of Standards and Technology (NIST) criteria. Some have “human performance” reliability statements, but these are based on the fatally flawed premise that human normative performance is equivalent to mechanized NIST calibration criteria. Who would accept the accuracy of a watch that had been “calibrated” by timing 20 “normal” individuals in a 20-yard dash? Human performance is not an acceptable criterion for defining the reliability, that is, the calibration, of mechanical devices such as those used in upper extremity rehabilitation clinics.
Furthermore, one cannot assume that a computerized version of an instrument is reliable and valid because its noncomputerized counterpart has established reliability. For example, although some computerized dynamometers have identical external components to those of their manual counterparts, internally they have been “gutted” and no longer function on a hydraulic system. Reliability and validity statements for the manual dynamometer are not applicable to the “gutted” computer version. Even if both dynamometers were hydraulic, separate reliability and validity data would be required for the computerized instrument.
Because of its inherent complexity, it is often difficult to determine instrument reliability of computerized test equipment without the assistance of qualified engineers and computer experts. Compounding the problem, stringent federal regulation often does not apply to “therapy devices.” Without sophisticated technical assistance, medical specialists and their patients have no way of knowing the true accuracy of the data produced by computerized therapy equipment.
Development of an Assessment Battery
An assessment battery must be reflective of the environment in which it is used. Types of patients, expectations and use of data, and physical setting should be considered to ensure that the selected group of tests meets the unique needs of the practice. Age, diagnosis, intelligence, socioeconomic background, language, and other patient population variables are important in selecting evaluation tools. Tests requiring high levels of cooperation may not be appropriate for a practice dealing primarily with children, mentally retarded individuals, or persons with limited language skills. The intent for gathering information is also important when creating an assessment battery. Requirements are often more stringent for research evaluation equipment than for instruments used in daily clinical testing. Staff qualifications, fiscal criteria, and state and federal regulations also influence selection of tests in an assessment battery.
An assessment battery should address the full spectrum of upper extremity performance, including physiologic status, motion, sensibility, and function. In addition, it should define a patient’s medical history, vocational and avocational information, and relevant administrative data that allow subsequent intervention to be tailored to the specific needs of patients. Specialized tests such as an upper extremity prosthetic check-out and a splint evaluation are also invaluable.
Because there is no single universal upper extremity assessment instrument, clinicians must rely on a variety of tools to measure the various parameters of hand condition and performance. A minimum of one instrument per area should be selected to measure each of the five basic domains: physiologic status, motion, sensibility, function, and patient satisfaction. Although this minimum-requirement five-instrument assessment battery is sufficient for cursory evaluation, practices specializing in hand/upper extremity dysfunction routinely include several instruments specific to each domain, generating gradation and verification of information.
The American Society for Surgery of the Hand (ASSH) and the American Society of Hand Therapists (ASHT) have established guidelines for clinical assessment of the hand and upper extremity. These guidelines are meaningful in defining the quality of professional communication and understanding of hand/upper extremity dysfunction. It is important that those responsible for developing evaluation protocols seriously consider these guidelines and generate assessment batteries that reflect the recommendations of these two professional organizations.
Timing and Use of Assessment Tests
Not all patients who are evaluated need to be given all of the tests within an assessment battery. Hand specialists routinely use a few quick tests to check hand function initially, adding more sophisticated testing procedures as dictated by the patient’s condition. For example, if a patient tests normal with the Semmes-Weinstein monofilaments, other sensibility tests can be eliminated in most cases. To conserve time and decrease frustration, tests within each domain should be scheduled according to type of information provided and degree of difficulty, beginning with an easy, dependable test that supplies basic data and working toward the more esoteric instruments.
Initial and final evaluations usually are comprehensive in scope, and intervening evaluations are less formal, concentrating on assessing progress in specific areas according to the problems exhibited by the patient. Frequency of reevaluation sessions depends on the patient, progress demonstrated, and the nature of the test itself. Range of motion (ROM) may be measured several times during a therapy session for an early postoperative tenolysis patient. However, grip strength measurements for this patient may not be appropriate because of wound healing and tensile strength limitations until 7 to 8 weeks postoperatively, and then strength measurements, because of the time required to effect change, are not measured as often as ROM.
Recording of assessment data also varies with the situation. For the early tenolysis patient, unless significant problems are encountered requiring frequent documentation to demonstrate lack of cooperation or other mitigating issues, only one set of ROM measurements are recorded per day, although multiple readings are taken. As change occurs less rapidly, motion values may be recorded two or three times a week, eventually decreasing to once every 2 weeks, once a month, and so on. Change in status is documented through objective measurements at appropriate intervals.
History and Physical Status
In addition to recording the patient’s condition, the initial history should contain information about how and when the injury occurred, including time and place. Documentation of changes in vocational, avocational, and daily living skills (DLS) is important, as is close observation of the patient’s spontaneous use of the extremity before, during, and after the evaluation session. When identifying the source of pain, obtaining the patient’s subjective assessment of its perceived intensity and its impact on his or life, helps provide insight into the patient’s attitude and ability to cope with the situation.
Obtaining a history is not only amassing of facts, it is also an opportunity to begin building a foundation of trust and communication between patient and examiner. Genuine concern and an unhurried manner facilitate discussion, yielding cooperation and understanding as the patient participates in his or her rehabilitation process.
The detail in which the examination is accomplished, and by whom, depends on the clinical setting and on the division of duties between surgeons and therapists. Regardless of who is responsible for conducting the formal intake evaluation, patients are assessed for general condition and configuration of the extremity, including skin and soft tissue; skeletal stability; articular motion and integrity; tendon continuity and glide; neurovascular status; isolated muscle function, sensibility, and vessel patency; and finally, general function, coordination, and dexterity.
The combination of clinical examination and precise measurement allows examiners to identify and make judgments regarding patient rehabilitative potential and need for therapeutic intervention. Assessment instruments delimit problems through numerical data, quantifying and adding definition to knowledge and understanding. Without measurement, perceptions are diffuse and unclear.
Current Hand/Upper Extremity Assessment Instruments
Assessment instruments may be divided into groups according to five basic domains: extremity condition, motion, sensibility, function, and patient satisfaction. (1) Condition involves the neurovascular system as it pertains to tissue viability; nutrition; vessel patency; and arterial, venous, and lymphatic flow. Noninvasive monitoring of extremity volume, skin color, and temperature, and arterial pulses provides important information about the status of skin and subcutaneous tissue and neurovascular function. (2) Measurement of motion depends on muscle-tendon continuity, contractile and gliding capacity, neuromuscular function, and volitional control. Goniometric measurements and isolated muscle strength testing are commonly used methods for evaluating upper extremity motion. (3) Relying on neural continuity, impulse transmission, receptor acuity, and cortical perception, sensibility assessment may be divided into sudomotor or sympathetic response and the ability to detect, discriminate, quantify, and identify stimuli. (4) Reflecting the integration of all systems, hand function is evaluated through measurements of grip and pinch; coordination and dexterity; and vocational, avocational, and DLS activities. (5) Patient satisfaction tests assess patients’ endorsement/approval of the therapeutic intervention they received.
Condition Assessment Instruments
Based on Archimedes’ principle of water displacement, the volumeter, as designed by Brand, measures composite extremity mass ( Fig. 16-1 ). Available in a range of sizes, volumeters monitor physiologic changes within the extremity as evidenced by changes in hand/extremity size, provided immersion of the extremity in water is not contraindicated. Although volumeter measurements are crucial for monitoring the inflammatory stage of wound healing, they also may be used to assess atrophy. Volumeter measurements are accurate to within 10 ml when used according to manufacturer specifications. Variables that reduce accuracy include use of an aerated faucet for tank filling, extremity motion post immersion, inconsistent pressure on the stop rod, and inconsistent placement of the volumeter for successive measurements. Measurements from both extremities are recorded initially with successive measurements of the symptomatic extremity recorded at appropriate intervals.
When volumeter assessment is contraindicated, circumferential or external diameter measurements, using a flexible tape measure or external millimeter caliper, may be used to assess extremity size. Although less exact and inclusive in scope, accuracy of these tools is improved with consistent placement and tension of the tape or caliper on the extremity. Suspension of a 10- to 20-g weight from the end of the tape measure allows consistent tension from trial to trial, and caliper measurements are more appropriate for monitoring smaller diameters as with digital joints or segments. Serial measurements are recorded ( Fig. 16-2 ) at appropriate intervals as dictated by patient progress.
Directly related to digital vessel patency, skin temperature is a valuable indicator of tissue viability. Used to monitor the status of early postoperative revascularized hands or digits, cutaneous temperature gauges are placed on three areas, on a revascularized digit, on a normal adjacent or corresponding digit, and on the dressing, to monitor the relative temperature differences in the reattached digit, a matching digit, and room temperature. It is important to report any decrease in temperature in the revascularized segment, with critical temperature being 30° C, with lower readings indicating possible vascular compromise. Normal digital temperature ranges between 30° and 35° C.
Doppler scanners are used to map arterial flow through audible ultrasonic response to arterial pulsing. Although inconsistencies continue to plague attempts to quantify Doppler readings, to date these scanners are accepted as important noninvasive assessment tools.
Motion Assessment Instruments
Goniometric evaluation of the upper extremity is essential to monitoring articular motion and musculotendinous function ( Fig. 16-3 ). Passive range-of-motion (PROM) measurements reflect the ability of a joint to be moved through its normal arc of motion, with limitations indicative of problems within the joint or capsular structures surrounding the joint. Active range-of-motion (AROM) measurements reflect the muscle-tendon unit’s ability to effect motion of the osseous kinetic chain. Limitations in AROM may be caused by lack of tendon continuity; adhesions; tendon sheath constriction; tendon inflammation; tendon subluxation, dislocation, or bowstringing; or tendon attenuation. With diminished PROM, AROM may seem impaired, although tendon amplitude and muscular contraction are normal. Conversely, normal PROM may seem limited when tendon gliding is reduced. Because AROM cannot exceed the passive capacity of joint motion, it is essential that both AROM and PROM are assessed and recorded ( Fig. 16-4 ). It is also important to analyze carefully the cause of limited motion to properly direct therapeutic intervention.
Proven more precise than visual estimates, goniometric measurements are accurate, provided standard procedures are followed. Accuracy of goniometric measurements differs according to joint complexity, between PROM and AROM measurements, between same and multiple examiners, and according to patient diagnosis. For both intraexaminer and interexaminer reliability, repeated measures under controlled conditions allow variance of 4 degrees and for intraexaminer measurements, a difference of 3 to 4 degrees indicates change in upper extremity joint status. Although further study is needed to address the validity of using a fixed-axis device to assess joints with nonfixed axes of motion that are influenced by articular glide and rotation, most clinicians accept the assumption of rotation around a central point axis when assessing joint motion. Normative data for goniometric measurements are available. Multiaxis goniometers, video recordings, and fiber optics may be the equipment of the future.
An adjunct to individual joint measurement, composite digital motion, is computed as total active motion (TAM) and total passive motion (TPM). TAM is the sum of simultaneous (full fist) active flexion measurements of the metacarpal, and proximal and distal interphalangeal joints of a digit, minus the simultaneous (full finger extension) active extension deficits of the same three joints. TPM is computed in a similar manner except that passive measurements are used. TAM and TPM each are expressed as single numerical values, reflecting both flexion and extension capacity of a single digit and providing a composite assessment of single digit function ( Fig. 16-5 ).
Torque range of motion (TQROM), as described by Brand, applies a series of increasing forces to a stiff joint to quantify measurement of PROM. When translated into torque-angle curves, the composite mechanical qualities of the restraining tissues are visualized, allowing better understanding of the pathologic condition involved ( Fig. 16-6 ). With good repeatability, TQROM provides a quantifiable method of predicting and monitoring stiff joint response to therapy intervention.
Manual muscle testing (MMT) appraises isolated muscle strength ( Fig. 16-7 ). MMT is used to evaluate nerve lesions, monitor nerve regeneration, and assess preoperative potential of tendon transfers. Although criteria for grading muscle strength have improved, portions of the test are subject to examiner interpretation. To increase interrater reliability, it is important to have a common method of conducting and interpreting manual muscle examinations. Various grading systems exist, but the two most commonly used are Seddon’s numerical system (from 0 to 5) and the method recommended by the Committee on After-Effects, National Foundation for Infantile Paralysis using “zero,” “trace,” “poor,” “fair,” “good,” and “normal.” The latter is further refined by a plus-minus system, determining half-ranges. Fluctuations of muscle tone and altered reflex activity make MMT of little value in upper motor neuron lesions such as cerebral palsy or cerebrovascular accidents.
Sensibility Assessment Instruments
When assessing sensibility, it is important to use a technique of recording that is accurate, that allows quick understanding by others, and in an age of computerization, that is readily adaptable to computerization to facilitate follow-up. Color helps define areas of diminished and impaired sensibility (see color plates that accompany Chapter 13 ). Also, using area identification coordinates ( Fig. 16-8 ) speeds communication and data transfer. The “numbers” illustrated in Fig. 16-8 are area coordinates of the palm of the hand, with the first number in each two-digit sequence representing ray longitudinal position; that is, the thumb is 1, the index finger is 2, and the small finger is 5. The second number in the two-digit sequence represents transverse position of an area; that is, 1 equals the distal phalanx area, 2 the middle phalanx, 3 the proximal phalanx, and so on. When combined, the two digits allow immediate identification of a specific area; that is, area 21 is the index distal phalanx, 31 is the long distal phalanx, 53 is the small finger proximal phalanx, and area 54 is the field distal to the distal palmar crease over the fifth ray. The “numbers” illustrated are not true integers. Instead, they are single-digit coordinates that, when combined, allow accurate definition of the areas of the palm. Each area may be further divided into radial and ulnar and proximal and distal. Area 11RP is the distal phalanx of the thumb, radial proximal side (quadrant); area 32UD is the ulnar (U), distal aspect (D) of the long (3) middle phalanx (2). Accurate recording is critical to good assessment technique.
Sympathetic response tests are applicable to patients with complete nerve disruption and who are within 6 months of initial injury. Volitional participation is required for motor, sensibility, and dexterity testing, but the problem is compounded in assessing sensibility because the stimulus, when received, is also interpreted by the patient, resulting in test information that is vulnerable to bias. Although most patients are cooperative, occasions arise when dealing with children, patients with language problems, or patients whose motives may be suspect, in which a test that relies on sudomotor or sympathetic response may be helpful. These tests should not be relied on as the primary sensibility test in an assessment battery.
The ninhydrin test identifies areas of disturbance of sweat secretion after peripheral nerve disruption. Denervated skin does not produce a sweat reaction because of involvement of sympathetic fibers in the distribution area of the injured peripheral nerve. Ninhydrin spray, a colorimetric agent, turns purple when it reacts with small concentrations of sweat. Unfortunately, sympathetic return after a peripheral nerve injury is variable, and on long-term follow-up, sudomotor response does not correlate with sensibility return.
The wrinkle test is based on a similar concept of sympathetic fiber involvement in peripheral nerve injuries, in that denervated palmar skin, as opposed to normal skin, does not wrinkle when soaked in warm water. As with sweating, palmar wrinkling has diminishing correlation to sensory function as the postinjury time increases, and it has no correlation to sensory capacity in nerve compression injuries.
Detection of a punctate stimulus is the most simple level of function in the hierarchy of sensibility capacity of the hand/upper extremity, requiring ability to distinguish a single-point stimulus from normally occurring atmospheric background stimuli. Normal touch force threshold using Semmes-Weinstein monofilaments is approximately 4.86 g/mm 2 (pressure). As testing devices, the monofilaments are uniquely important to clinicians and researchers alike in that they control the amount of force applied ( Fig. 16-9 ). These filaments consistently produce repeatable forces within a predictable range from set to set and from examiner to examiner, provided their lengths and diameters are correct. Clinical validity of the monofilaments is documented for assessment and monitoring peripheral nerve disruption, compression, and regeneration ; prediction and monitoring peripheral neuropathic diseases and their complications; and for prediction of function.
An experience related by Weinstein regarding collaborative work with a neurosurgeon provides important insight into face validity of the monofilaments and the inherent difference between sensibility detection and discrimination levels. During craniotomies on conscious patients, Weinstein tested sensibility using two tests: the monofilaments and two-point discrimination. As weak electrical stimulation was applied to the cortical areas representing the hands, normal threshold values remained constant bilaterally for the monofilament test. In contrast, ability to perceive two points from one point even at large distances was abolished in the hand associated with the stimulated side, while the hand associated with the nonstimulated cortex area retained normal two-point discrimination, indicating a major difference between the two tests. Neurologically, detection is more fundamental than discrimination, which requires cortical integrity. Interestingly, this concept may be obliquely substantiated by rat model research in which neurophysiologists use the monofilaments to test extremity acuity of their animal subjects.
Duration of contact time, speed of filament application, soaking the hand before testing, and sites tested alter monofilament test results. It is imperative that consistent procedures be used with monofilament assessment of sensibility. In addition, it has been shown that use of the monofilaments in combination with wrist flexion provocative testing provides more accurate and sensitive results when testing for median-nerve compression.
The monofilaments are available in the original 20-filament set and in a 5-filament mini set. Supplying a no-overlap range of reproducible stimuli from normal to absent light touch, the 5-filament set is quick and easy to use in the clinic. Normative data for the filaments are available. A touch-force assessment instrument should produce stimuli that measure lighter than normal threshold. The 20-filament kit has two filaments that are lighter than the normal 2.83 filament, satisfying this requisite. The WEST 5-filament set has specialized tip geometry to decrease slippage upon contact and is certified for calibration accuracy.
The Dellon-Curtis evaluation has four categories, assessing moving touch, constant touch, flutter (30-cps tuning fork), and vibration (256-cps tuning fork). Controversy exists concerning this test, with some neurophysiologists and neurologists questioning use of vibration because of lack of stimulus specificity to evaluate nerve status in a confined space such as the hand. Bell-Krotoski and Buford found that applied force produced by either size tuning fork is uncontrolled, and oscillation is influenced by random vibration of the examiner’s hand, strike force, and how long oscillation persists. In addition, they report that force amplitude of a tuning fork is more uncontrolled with side application than tip application. Physicists note that use of a tuning fork in attitudes other than perpendicular to the surface of application changes the vibratory stimulus to a compression stimulus and may elicit a pain response. Force control is also absent for both the moving and constant touch portions of the test. Lack of control of stimulus force and disputed recovery of sequence as originally described raises reliability and validity questions.
Product development in the area of sensibility testing is rapidly changing, and most experts now acknowledge that control of stimulus force is a fundamental concept. One area in which force control has not been associated with stimulus application is that of vibrometry. Although several variations of vibrometers currently are available, for most vibrometers the issue of control of stimulus force continues to be absent, making their reliability questionable.
Discrimination is the second level in the sensibility assessment continuum. The ability to perceive one stimulus from a second, different stimulus, involves the capacity to detect each stimulus separately and to differentiate between them. Discrimination requires finer reception acuity and more judgment by the patient than does detection, the first level on the continuum.
Two-point discrimination is the most commonly used method of assessing sensibility of the hand. In giving this test, disagreement exists as to whether it is preferable to begin the test with a large or small distance between the two points, and the number of correct responses required varies slightly among examiners. Moving two-point discrimination adds the variable of motion to the test.
The two-point discrimination test has some instrumentation problems. Bell-Krotoski and Buford found that even among experienced hand surgeons and therapists, differences between the amount of force applied to the one point and that applied to two points easily exceeded the resolution or sensitivity threshold for normal sensibility ( Fig. 16-10 ). Lack of force consistency is amplified with the introduction of motion in the moving two-point test. Directly influenced by cutaneous topography, applied forces were found to be 400 times the sensitivity of normal cutaneous receptors. They also discovered that because of the varying pressures applied, interrater reliability was poor, perhaps explaining the lack of agreement in reporting and the multiplicity of current clinical sensibility assessment tools.
In contrast, Dellon et al. reported high interrater reliability using standard testing methods and a commercially available two-point discriminator instrument. However, this study involved only two examiners. More study is needed with multiple examiners in different conditions before conclusive statements may be made regarding reliability. Even more important, before examiner reliability is addressed, instrument reliability first must be documented in the laboratory.
In 1995, Tassler and Dellon reported validity of a new computerized sensibility testing tool, the pressure-specified sensory device (PSSD). In clinical comparisons to electrodiagnostic testing (EDT) in nerve entrapment patients, they found this handheld instrument with metal probe tips connected via force transducer to a computer, to have high sensitivity but low specificity. Although several published clinical studies using the PSSD exist, instrument reliability studies for the PSSD were not found. A prerequisite for all mechanical device validity studies, intrainstrument and interinstrument reliability must first be established through independent laboratory analysis using NIST criteria. Once this is done, independent intrarater and interrater reliability needs to be defined. One study reported that PSSD results were “highly operator dependent and difficult to reproduce” but encouraged further investigation of the device. Although the PSSD eventually may be found to be a useful instrument for testing sensibility, currently much more information is needed in terms of instrumentation criteria.
The Ridge device * introduces the important concept of control of amount of tissue displacement rather than control of applied force. Sensibility instruments should control either the force or the displacement variable, and although most aesthesiometer designs involve force application, the ridge device is unique because of its displacement design. Consisting of a rectangular piece of plastic, from the center of which a narrow ridge gradually rises to a height of 1.5 mm, the ridge device is believed to be useful in identifying patients whose two-point discrimination is between 8 and 12 mm. Instrumentation problems with the ridge device include reliability and validity issues. More intelligent patients have higher scores and the device tends to “bounce” across the skin as it is pulled. In addition, lack of measurement specificity relating to the amount of tissue deformation is problematic, in that the ridge rises without interruption, decreasing accuracy and rater reliability.
* Although clinical use of the Ridge device has decreased, it is included in this chapter because of its unique tissue displacement design.Quantification is the third level of sensory capacity. This level involves organizing tactile stimuli according to degree. A patient may be asked to rank in order several alternatives according to roughness, irregularity, thickness, or weightiness. Identification, the final and most complicated sensibility level, is the ability to identify objects. At this time, no standardized tests are available for these two categories, although their concepts are commonly used in sensory reeducation treatment programs. Some observational, function-based, sensibility tests such as the Moberg picking-up test and the coin test are adapted to test identification by eliminating sight cues, but none of these have reliability or validity, and they lack even simple equipment standards.
The major problem in assessing sensibility is cortical modification of thresholds. With the exception of sudomotor tests, all of the sensibility evaluation instruments currently available have the potential for producing subjective information. Another variable is callous formation or the hardness of the cutaneous surface ( Fig. 16-11 ). Keratin layers alter the amount of force transferred to sensory receptors by increasing the area of force application. Therefore occupation is a factor in assessment of sensibility. Furthermore, studies indicate that specific receptors cannot be isolated with current unrefined assessment instruments.