CHAPTER 4

Assessment Tools for MusculoskeletalImpairment Rating and DisabilityAssessment

Mikel Cook, Rn: MP AAmi 1: Patel,MD Andrew J. Haig, MD

The AMA Guides encourages the disability physician examiner to utilize his orher "entire gamut of clinical skill and judgment in assessing whether or not theresults of measurements or tests are plausible and relate to the impairment beingevaluated."2 The purpose of this chapter is to clarify the applications andlimitations of physical tools and tests readily available to the clinician andtypically used in the assessment of musculoskeletal impairment and disability.The three main areas of interest and discussion include measurement tools toassess joint range of motion (ROM) and muscle strength, radiographic assess-ment of bone and joint pathology, and electrophysiological assessment ofneuromuscular function.

TOOLS FOR ASSESSING JOINT MOTION AND MUSCLE STRENGTHAND ENDURANCE

The disability examiner is frequently called on to objectively describe andidentify impairment to the musculoskeletal system in terms of joint flexibilityand muscle strength and endurance. There are a number of devices available toassist with the physical examination in this regard.

Range of Motion

Gon;ometersGoniometers are used to measure joint ROM (flexibility). The most commonand least expensive goniometer is the simple two-arm plastic or metal goniom-eter. The clinician can be trained to use this simple goniometer, and it remains byfar the most widely used tool for measuring ROM. Electrogoniometers,computerized goniometers, and the bubble goniometer (also known as thein.:;!inometer) are also used and have proved to be reliable.23.52 The simplegoniometer is the primary tool used in extremity ROM testing, whereas thesurface inclinometer (one inclinometer or two inclinometer methods) is primar-ily used in spine ROM testing.42. 53. 54 The Back Range of Motion (BROM)device has also been used in lumbar ROM research.9

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J60 Chapter 4 Assessment Tools for Musculoskeletal Impairment Rating and Disability Assessment

testing from smaller to larger grip and usually reveals greatest strengthmeasurement with the middle position. The subject is tested in all five positions,with resulting grip pressures recorded on a graph, which is expected to be bellshaped. If the bell-shaped curve is not generated, submaximal effort is sug-gested.68 This approach has been refined by examining peak and averageforce-time curves generated with side-to-side and gender-specific comparisonsfor normative data64 and for subjects with unilateral hand injuries.l1 However,the utility of hand-held dynamometers to determine maximal effort has beencritically reviewed,51,69 and results should be interpreted with considerablecaution by the clinician.

Computerized isometric and isokinetic dynamometers have also been used toassess consistency of effort. When performing a task, a strength curve isgenerated. In the normal or affected subject, this curve should remain consistentfrom test to test. If the affected subject shows marked weakness at a certainROM, it should be consistently reproducible. The computer program cancalculate a "coefficient of variation" (COV) as the standard deviation amongtrials, divided by the mean x 100 as a unitless measure of consistency ofeffort.41However, the range of acceptable COY varies by anatomical region, test mode(isometric versus isokinetic), and according to specificity of strength test (i.e.,whole body lift versus isolated muscle testing).61

Since there is no uniform agreement on norms and acceptable range of COY s,they should also be used only with considerable caution in interpretingconsistency of effort during isometric or isokinetic testing.

Summary of muscle strength and endurance testingMuscle strength and endurance testing is a key element of musculoskeletalassessment. The use of manual muscle testing and dynamometers can help theevaluator to objectively assess impairment and disability. Isokinetic and isomet-ric dynamometers are available to assist with strength and endurance assess-ments of complex movement and functional performance abilities. The appli-cation of such objective testing to the assessment of symptom magnification (interms of degree and consistency of effort) warrants considerable caution on thepart of the clinician at this time.

Radiological Assessment of Bone and joint Pathology

It is a common attorney strategy to show a radiograph at trial. The public putsstock in radiological examinations, and attorneys utilize that confidence topromote their cases. At face value, one might assume a strong correlationbetween disease, radiographic impairment, and disability or handicap. If thiswere true, however, then a simple interpretation of radiographic tests wouldoften be sufficient evidence for a disability determination. In reality, disabilitydetermination is a complex process that remains highly subjective, and thefunctional significance of radiographic and other objective indicators of impair-ment is likely to be debated in any given case. '

The purpose of this section is to review common radiographic procedures asthey apply to musculoskeletal impairment rating and to examine functionalinterpretations that may be drawn from radiographic findings when makingdisability determinations.

Plain-film radiographs are obviously useful in documenting the precise levelof amputation, fracture, nonunion, ankylosis, severe sprain, sur~cal interven-

Chapter 4 Assessment Tools for Musculoskeletal Impairment Rating and Disability Assessment 61

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tion such as rods or screws, and heterotopic ossification. The relationshipbetween these medical diagnoses and impairment is rather direct and unchang-ing. Still, when asked about disability or handicap, the physi~ian must use otherfactors to modulate the effect of these diagnoses on the tasks at hand.

A number of other diagnoses can be proved with radiography, but therelationship between the severity of radiographic findings and function is morevariable. For example, radiographic findings of recurrent patellar subluxationhave a highly variable relationship with actual function.14 Various arthritide~are also diagnosed with radiography. Although the extent of erosion, joint-spacenarrowing, or bony spurring correlates somewhat with functional disability, therelationship is not direct. For example, in rheumatoid arthritis (RA), there arethree common schemas foJ; r,ating radiological findings: the Steinbrocker Stage,Kaye Modified Sharp Score, and the Larsen Score.46 The Larsen systemappears to correlate with elbow disability59 and total disability,34 but not handfunction.57 Although these scales provide similar quantitative data concerningradiographic damage in patients with RA, weak correlations are seen betweenradiographic scores and joint count scores for tenderness.47 It is for this reasonthat indications for joint replacement surgery in arthritis include pain and

dysfunction.The presence of radiographic findings alone is often not sufficient to predict

extent of functional limitations. Radiographs may reveal disorders or condi-tions that put an individual at risk for future injury or illness despite adequatecurrent function. For example, severe osteopenia may be a relative contraindi-cation to heavy lifting or repetitive activity, regardless of current function. Theextent to which osteopenia warrants restrictions to protect the individual fromtrauma is further modulated by the individual's body habitus and strength, theparticular activity in question, and other factors that are difficult to measure,such as the physician's personal belief regarding acceptable risk. Joint disrup-tions, such as fractures through cartilage, spondylolisthesis, or avascularnecrosis of the femoral head, are thought to degenerate more quickly withincreased weight bearing and activity. Although radiographs can demonstratethese findings effectively, the relationship between future activity and jointdegeneration is variable.

Even with similar radiographs and levels of function, the extent of disabilitymay demonstrate an inverse relationship to age. Younger persons with hipreplacements will likely wear out the artificial joints, leading to multiple jointreplacements and possibly a girdlestone procedure requiring modified weightbearing or wheelchair use; older persons, in contrast, are likely to retainambulatory function with a single prosthesis for the duration of their life.

Radiographic findings can be used to document spinal impairment fromfracture, instability, or degenerative arthritis. Radiographs are less applicable inassessing spinal disability. For example, most research shows little correlationbetween more subtle spinal radiographic findings and pain (let alone disabilityor handicap). Functional outcome after surgical fusion has been shown to besimilar whether successful fusion or pseudoarthrosis occurs.20 Population-based studies have demonstrated little correlation between degenerativechanges shown on radiographs and pain21,45; however, some notable excep-tions occur. Radiographic findings that correlate somewhat with back paininclude disc-space narrowing at L4 without changes at L5, high-degree scoliosis(greater than 600 in an adult), large leg-length discrepancies (5 cm or more), andsevere multilevel degenerative changes. These findings reflect statistical signifi-

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62 Chapter 4 Assessment Tools for Musculoskeletal Impairment Rating and Disability Assessment

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cance of risk factors in a sample population that are insufficient criteria to"prove" pain or disability in the individual case, and are perhaps more useful tosupport the probability that an objective pain generator exists.

Radiological imaging during motion can det~rmine instability in someextremity joints. Radiological assessment of spinal instability is much morecomplex. The AMA Guides2 gives criteria for spinal instability, which it callsloss of motion segment integrity (LOMSI). This is based on comparison offlexion and extension views of lateral radiographs. Vertebral injury related totranslational (anterior-posterior) motion that is 5 mm or greater than that seenat an ~djacent intervertebral segment is the first diagnostic indicator of LOMSI.Angular motion is the second indicator. If comparing adjacent levels such asL4-LS or above, any angular motion 11° or greater at one level over anotheralso implicates LOMSI. When comparing the LS-SI interspace with L4-LS, thedifference must be greater than 15°. Strangely, these criteria are not widelyutilized by neuroradiologists, but are based on cadaver studies with no knownclinical correlate.49, 55 Simply put, the association between instability and pain

is yet undefined.48Advanced radiologic imaging tests, including computerized tomography

(CT), magnetic resonance imaging (MRI), and myelograms, are subject toadditional concern because they are highly sensitive to conditions of question-able clinical significance. There is a great potential for these tests to revealsoft-tissue lesions, but the clinical significance of these findings is variable.Although lesions such as supraspinatus tendon tear are fairly reliable findingson MRI,26 it is well documented that MR!, CT, and myelogram can demon-strate disc pathology in one third to two thirds of asymptomatic individualsstudied.5, 28 Clearly, imaging test results require clinical correlation, and theexaminer should avoid inappropriate weighting of nonspecific findings that arelikely to occur as a result of developmental changes or the normal aging

process}Bone scans are useful indicators of ongoing bone repair, thus providing

evidence of a fracture up to 1 year after an injury. They may be useful todocument the presence or absence of a fracture (including hairline fractures) orto determine that fracture healing is complete, and thus a permanent impair-ment rating of the healed fracture can be assigned. Other potentially useful testsinvolve the injection of radiopaque agents under fluoroscopy for diagnosticprovocation or palliation. Such tests include discography,62 facet injection,16sacroiliac joint injection,31 and selective nerve root block.63 For all of these tests,the actual photographic evidence of an abnormality is not considered patho-gnomonic for a disabling lesion. Instead, they all rely on the client's report thatthe test reproduced his or her symptoms. Some progress has been made inprotocols with placebo injections, injections at other "control" levels, blindedobservers, etc., to avoid suggesting responses to the client, but the clinicalapplications of tests to document impairment and disability appear limited atthis time.

Summary of radiological testingRadiographic procedures provide objective evidence of bone and joint pathol-ogy useful to the diagnosis of musculoskeletal impairment. However, thedisability examiner must exercise due caution when drawing functional infer-ences from radiographic findings as they penain to disability in the panicularcase. Clinical correlation of radiographic findings to appropriate subjective