Rating Spinal Impairment - Range of Motion Model of Injury Model???
 
Spinal impairment is common, symptoms related to the back and spine are among the most common of adults' everyday complaints.  Rating spinal impairment can be difficult.  Sorting out whether symptoms following an injury or illness are age-related or are related to the injury or the illness may be difficult of impossible due to the widespread occurrence of symptoms in the general population.
 
In the 4th edition of the American Medical Association Guides to the Evaluation of Permanent Impairment, assessment of permanent impairment can be done through one of two approaches.  One approach, which applied best to injuries, is call the Injury Model (also know as the DRE or Diagnosis Related Estimates Model).  The other is call the Range of Motion Model (also known as the Functional Model).
 
In the injury model, the examinee is assigned to one of 8 categories, on the basis of objective clinical findings.
 
In the other approach which was used prior to the 4th edition, impairment is based on assessing the degree of spine motion and assigning impairment percents according to limitation of motion combined with percents based on diagnoses, therapeutic approaches and neurological impairments.
 
The assessor should use the Injury Model if the patient's condition is one of the 8 categories listed in the Injury Model.  If none of the eight categories is applicable, then the evaluator should use the range of motion model.  The evaluator should use one or the other model, not both.
 
Whichever model is used, the examiner must perform a complete, accurate medical history, a  review of all pertinent records, a careful and thorough physical examination, list a complete description of the examinee's current symptoms, and document the relationship of any symptoms to daily activities, and review and record all findings of relevant laboratory, radiological and ancillary tests.  For the assessment to be valid, the impairment must be permanent (stable, not likely to change in the next year).
 
History: the history should be based on the patient's own statements.  Objective data from others can be considered.  It is not appropriate to question the patient's integrity, unless the information from the patient does not make sense, or is inconsistent.  The history should include the chief complaint, and pain, numbness, weakness, location, frequency and duration as well as how the condition interferes with daily activities.  Also included should be when the condition started, how the condition started, any relationship to previous spine problems, precipitating events or factors, and the impact of the problems on the examinee's daily activities.  The history should use the patient's description in their own words, how symptoms developed, the cause of the symptoms, and response to treatment.  Future plans should be noted.  Review of symptoms and past medical history is also helpful in terms of complicating problems and requirements for diagnosis and care.
 
Examination: The examination includes a complete neurological examination, as well as strength, reflexes, atrophy, tone and need for assistive devices.  Atrophy due to other causes must be excluded (old fractures, arthritis).  Vascular examination is important.  Inconsistent physical findings must be noted.  Subjective complaints must not be confused with objective findings.  Cervical, thoracic, lumbar and sacral regions must be separated.  The brachial plexus includes both the cervical and thoracic region, the lumbo sacral plexus includes the lumbo sacral spine.  With the injury or DRE Model, the main spinal regions are the cervico-thoracic, the thoraco-lumbar and the lumbo-sacral regions.  The cervico-thoracic region accounts for 35% of total body function, the thoraco-lumbar spine for 20% and the lumbo sacral spine for 75%.  Under the range of motion model, the regions are the cervical, for 80% of total body function, thoracic with 40% and the lumbo sacral spine with 90%.  Sciatic Nerve tension signs (straight leg raising) are important indicators of acute root compression, but may be absent with chronic conditions such as spinal stenosis.  Crossed straight leg raising, comparison with straight leg raising in the sitting and recumbent positions may be helpful.  Range of motion of the ankle and rotation of the hip can help validate straight leg raising findings.  Loss of motion segment integrity is an abnormal back and forth motion (translation) or abnormal angular motion between two vertebrae.  This is determined by x=ray.  AP motion (slipping) of more than3.5mm in the cervical or 5mm in the thoracic or lumbar spine, or angular motion greater than 11 degrees in flexion and extension defines loss of integrity.  Special studies such as x-rays, EMG and NCS, cystometric and other studies must be summarized, considered and included in an assessment.  Differentiators such as guarding, loss of reflexes, decreased muscle circumference, electrodiagnosis, lateral motion x-rays, loss of bowel or bladder control, bladder studies, may help the examiner choose the correct category of the injury model.  If the correct DRE category cannot be determined, the examiner may use the range of motion model.  In the range of motion model, the permanent impairment is based on the diagnosis, plus a percent based on motion, plus a percent based on neurological impairment.  The percent determined by the range of motion model can be used to determine the correct DRE category.  The proper DRE category being the one with the percent impairment closest to the percent determined by the range of motion model.  Structural inclusions, such as fractures that may not demonstrate any of the findings involving differentiators, are included in the DRE model.  Other criteria for that category need not be met if the structural inclusion is met!!!
 
Impressions, diagnoses and impairment estimates:  Impressions are expressed in a logical fashion, from symptoms to documented diagnoses, that may or may not be remediable.  Impairment estimates are based on all the data obtained, including the history, exam, testing data, the impression and any other data, including literacy, general capability, overall health and inconsistencies.
 
The Injury of DRE Model
In the Injury Model, medical data other than range of motion is considered.  Osteo-arthritis of the spine is considered to be more of an ageing phenomenon than a consequence of injury or illness due to its asymptomatic prevalence in the population as the population age increases.  The Injury Model attempts to document physiologic and structural impairments relating to insults other than common developmental findings such as spondylolysis, spondylolisthesis, herniated discs without radiculopathy and aging changes.  The Injury Model relies on evidence of neurological deficits, fractures, dislocations and loss of motion segment integrity.  DRE's are differentiated by clinical findings that are verifiable using standard medical procedures.  Surgery to treat an impairment does not modify the original impairment, despite any outcome from such surgery.  The general approach involves the history, exam and clinical workup to determine the appropriate impairment category.  Impairment is assessed based on the appropriate area of the spine.  Additional impairments may be assessed for long tract signs in the cervico-thoracic and thoraco-lumbar spine.  Bladder impairment is combined with the spine impairment using the combined values chart.  If there was a pre-existing condition causing a documented permanent impairment, that permanent impairment needs to be subtracted from the current permanent impairment.
 
The Range of Motion Model
Principles of inclinometry are observed.  Principles of "Ankylosis and Motion with Ankylosis" are observed.  This approach uses a diagnosis based component, based on Table 75, determining range of motion and a component based on a spinal nerve deficit.  The range of motion model should be used only if the Injury Model is not applicable or if more clinical data are needed to categorize the impairment.  The spine is considered to be the equivalent of the whole person, cervical is 80%, thoracic is 40%, lumbo sacral spine is 90%.  The impairment should be stable.  Reproducibility of findings is important.  There must be medical evidence of a documented injury or illness with a physiological residual.  
  • First the region is selected.
  • Using table 75 the estimated diagnosis related impairment is determined.
  • Range of motion is tested for Ankylosis or restricted motion.
  • Impairment must be judged regarding stability.
  • Motion is measured 3 times, averages are determined for reliability.
  • If measurements are inconsistent after 6 measurements, the examiner considers disallowing impairment for motion.
  • The examiner uses the maximum angle of a valid set of measurements to determine permanent impairment (use "Ankylosis and Motion with Ankylosis section if there is Ankylosis).
  • The examiner determines impairments due to neurological deficits.
  • The examiner combines the diagnosis based and range of motion based percents impairment using the combined values chart.
  • The examiner repeats the steps if additional areas are involved.
  • The examiner combines regional impairments using the combined values chart.
  • The examiner combines the whole person spine impairment with any whole person neurological impairment.
  • The examiner records and combines the results.
In short, there are challenges to the assessment of permanent impairment of the spine.  The first challenge is to separate changes due to aging from the effects of illness or injury.  The second challenge is to determine which mode of permanent impairment assessment is most appropriate for a particular examinee.  The American Medical Association Guides to the Evaluation of Permanent Impairment, 5th edition refines some of these issues and will be addressed in an upcoming newsletter.
 

Robert N. Phelps, Jr. MD

Fellow, American Academy of Orthopedic Surgery

Diplomate, American Board of Orthopedic Surgery

1-888-373-6388