The Sixth Edition¹, published in December 2007, introduces new approaches to rating impairment. An innovative methodology is used to enhance the relevancy of impairment ratings, improve internal consistency, promote greater precision and simplify the rating process. The approach is based on a modification of the conceptual framework of the International Classification of Functioning, Disability, and Health (ICF),² although the fundamental principles underlying the Guides remain unchanged. To appreciate the impact of the Sixth Edition, it is useful to understand the history and structure of the Guides, previous criticisms, and these new approaches.

Use of the Guides

The approach to impairment evaluation has evolved over the past fifty years since the Guides started in 1958 with publication by the American Medical Association (AMA) of the article, “A Guide to the Evaluation of Permanent Impairment of the Extremities and Back”³. In 1971 a compendium of 13 guides became the First Edition.⁴ The Second Edition⁵ was published thirteen years later in 1984, and the Third Edition⁶ was published in 1988. The Third Edition was the first to use the Swanson methodology⁷ which assigned discreet impairment ratings to specific range of motion (ROM) deficits of the upper extremities. It was replaced two years later by the Third Edition, Revised⁸, which is still used by the State of Colorado for workers compensation cases.

The Fourth Edition⁹, published in 1993, provided many refinements, including the Diagnosis-Related Estimates (DRE) or “injury” model for evaluation of spinal injuries, alternative approaches to assessing lower extremity impairment, and a pain chapter. The DRE model was unique in allowing for assignment of an impairment rating based solely on the diagnosis, even if maximum medical improvement (MMI) had not yet been reached. The Fourth Edition is still used for assessing workers' compensation cases in Alabama, Arkansas, Connecticut, Kansas, Maine, Maryland, Mississippi, South Dakota, Texas, and West Virginia.

The Fifth Edition¹⁰, published in 2000, was nearly twice the size of its predecessor. It provided more detailed directives in all chapters, and modified the approaches used for spinal impairment evaluation by providing guidance on the choice of the rating method and the impairment ranges for DRE categories. Prior to the availability of the Sixth Edition twenty-six states made use of the Fifth Edition, including Alaska, Arizona, California, Delaware, Georgia, Hawaii, Idaho, Indiana, Iowa, Kentucky, Louisiana, Massachusetts, Montana, Nevada, New Hampshire, New Mexico, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, Tennessee, Utah, Vermont, Washington and Wyoming. The Sixth Edition represents a continued evolution in impairment evaluation.

Many states require the use of the “most recent Edition” of the Guides either by statute or code; therefore, states that are expected to implement the Sixth Edition immediately include Alaska, Hawaii, Kentucky, Louisiana, Mississippi, Montana, New Hampshire, New Mexico, Ohio, Oklahoma, Pennsylvania, Rhode Island, Tennessee, Vermont and Wyoming¹¹. The most recent edition is also expected to remain the standard for automobile casualty and personal injury cases, both domestically and internationally. Some of the countries abroad that use the Guides include Australia, Canada, Hong Kong, Korea, New Zealand, and South Africa.

The Sixth Edition will also be the immediate new standard for Federal Long-shore and Harbor Workers' Act (LHWCA). Federal workers' compensation laws cover all federal employees (including postal workers) and citizens of Washington, DC. Federal systems include Federal Employees' Compensation Act (FECA), Energy Employees Occupational Illness Compensation Program Act, and Longshore and Harbor Workers' Compensation Act (LHWCA). Under the Federal Employees' Compensation Act (FECA 5 USC 8107) benefit is given for permanent impairment to specific body parts including extremities, hearing, vision, and loss of specific organs. Under the Longshore and Harbor Workers' Compensation Act ratings are performed for “scheduled injuries” (eg, a scheduled member of the body defined by section 8(c)(1)-(20) of the LHWCA).¹² Scheduled injuries include upper extremity injuries (with the exception of the shoulder), lower extremity injuries, and hearing loss.

The Guides are often used to quantify the extent of injuries resulting from an automobile casualty or personal injury. Insurers may use an impairment rating as one of the factors in determining the reserve or settlement value of a claim. Insurers and attorneys may also use this as a factor to be considered in quantifying the impact of an injury and the associated case value. In some states, suits under no-fault automobile insurance are limited to cases where a specific defined impairment threshold has been met; in states such as these the Guides play an important role in providing numerical data to indicate that the threshold has indeed been met. In Florida, as an insured's claims for pain and suffering (as a basis for recovery) are subject to limits outside the automobile no-fault system, the Guides are used to define permanent loss.

The Guides impairment ratings are applied in a variety of ways, depending on the type of case and the jurisdiction. Although impairment is a different concept than disability, some jurisdictions use impairment as a proxy for the latter (the Guides does not recommend this approach), while others use the impairment rating value in a formula that results in a disability rating. Still other jurisdictions are similar to motor vehicle insurers in using the impairment value as a threshold indicator for a more serious injury or illness.

It is anticipated that, because of the multiple settings in which the Guides are used, the Sixth Edition will significantly impact many stakeholders.

Challenges and Criticisms of Prior Editions

There are many challenges associated with the use of the Guides, including criticisms of the Guides themselves, the use of impairment rating numbers, and a high error rate.^{13,14,15,16,17,18,19,20} Previous criticisms include:

• Failure to provide a comprehensive, valid, reliable, unbiased, and evidence-based rating system.

• Impairment ratings do not adequately or accurately reflect loss of function.

• Numerical ratings are more the representation of “legal fiction than medical reality.”

In response to these criticisms, the following changes were recommended:

• Standardize assessment of Activities of Daily Living (ADL) limitations associated with physical impairments.

• Apply functional assessment tools to validate impairment rating scales.

• Include measures of functional loss in the impairment rating.

• Improve overall intrarater and interrater reliability and internal consistency.

Studies have demonstrated poor interrater reliability and revealed that many impairment ratings are incorrect, and more often rated significantly higher than is appropriate.²¹ Treating physicians, who by definition are advocates for their patients, have been particularly prone to overrate impairment. Physicians who have not been adequately trained in the use of the Guides also commonly provide erroneous ratings, more commonly overrating impairment than underrating it.

Sixth Edition Approaches and Developmental Process

The Guides defines the process for evaluating impairment. Clinical discussions among physician colleagues regarding potential severity of an illness or injury typically involve four basic points of consideration:

• 1) What is the problem (diagnosis)?

• 2) What symptoms and resulting functional difficulty does the patient report?

• 3) What are the physical findings pertaining to the problem?

• 4) What are the results of clinical studies?

In a similar manner, these same basic considerations are used by the physicians to evaluate and communicate about impairment. Ratings are often used as the basis for monetary awards, and therefore, physicians must recognize the importance of consistency among subjective and other objectively nonquantifiable aspects of the clinical presentation, the diagnosis and the patient's objective findings. The Sixth Edition expands the spectrum of diagnoses recognized in impairment rating, considers functional consequences of the impairment as a part of each physician's detailed history, and clarifies significant physical examination findings and clinical testing.

International Classification of Functioning, Disability and Health

The Sixth Edition uses the framework based upon the International Classification of Functioning, Disability and Health (ICF), a comprehensive model of disablement developed by the World Health Organization. This framework, illustrated in Figure 1 (Figure 1-1, 6th ed, 3), is intended for describing and measuring health and disability at the individual and population levels. The ICF is a classification of health and health-related domains that describe body functions and structures, activities and participation. The domains are classified from body, individual, and societal perspectives. The ICF systematically groups different domains for a person in a given health condition (eg, what a person with a disease or disorder does do or can do). “Functioning” is an umbrella term encompassing all body functions, activities, and participations; similarly, “disability” serves as an umbrella term for impairments, activity limitations or participation restrictions. Since an individual's functioning and disability occurs in a context, the ICF also includes a list of environmental factors.

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ICF Model of Disablement

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The following definitions are used in the ICF to facilitate communications and standardization:

• Body functions: physiological functions of body systems (including psychological functions).

• Body structures: anatomic parts of the body such as organs, limbs, and their components.

• Activity: execution of a task or action by an individual.

• Participation: involvement in a life situation.

• Impairments: problems in body function or structure such as a significant deviation or loss.

• Activity limitations: difficulties an individual may have in executing activities.

• Participation restrictions: problems an individual may experience in involvement in life situations.

The ICF model reflects the dynamic interactions between an individual with a given health condition, the environment, and personal factors. Impairment, activity limitations, and limitations in participation are not synonymous; an individual may have impairment and significant limitations in most activities but be able to participate in a specific life situation of relevance, have minor impairment and activity limitations with inability to participate in a specific life situation, or have any permutation of these three factors.

Use of the ICF model does not indicate that the Guides will now be assessing disability rather than impairment. Rather, the incorporation of certain aspects of the ICF model into the impairment rating process reflects efforts to place the impairment rating into a structure that promotes integration with the ICF constructs for activity limitations and limitations in participation. This effort is intended to enhance applicability of the ICF model to situations in which the impairment rating is one component of the “disability evaluation process.”

Impairment Classes and Diagnosis-based Grids

The ICF classification uses five impairment classes and permits rating of patients who range from having no problems to having significant problems. In the Sixth Edition “diagnosis-based grids” were developed for each organ system. These grids use commonly accepted consensus-based criteria to classify most diagnoses relevant to a particular organ or body part into five classes of impairment severity ranging from Class 0 (normal), to Class 5 (very severe). The final impairment is determined by adjusting the initial impairment rating by factors that may include physical findings, the results of clinical tests, and functional reports by the patient. The basic template of the diagnosis-based grid is common to each organ system and chapter. Although there is variation in the ancillary factors used to develop the impairment rating (depending on the body part), there is greater internal consistency between chapters than was formerly seen.

This uniform diagnosis-based approach is a significant change from the anatomical approach that was applied in many previous musculoskeletal assessments. However, there are similarities to other approaches used in the Fourth and Fifth Editions. For example, as mentioned previously, spinal impairment assessments have typically been based on the Diagnosis-Related Estimates Method, with specific findings or diagnoses used to assign the patient to a category. In the Fifth Edition the patient is assigned to one of five categories, with the first category having no ratable impairment and the other four categories having four possible impairment values. A patient with a lumbar radiculopathy would be assigned to a DRE Lumbar Category III associated with a whole person impairment (WPI) rating in the range of 10-13%. The examiner assigned an impairment value within this range, based on a judgment regarding limitations in activities of daily living (ADLs) as a result of the impairment. Although the Fourth Edition also used the DRE system, there was no allowance for the impact of a given diagnosis upon ADLs and the rating for Category III was fixed at 10% WPI. Likewise, although lower extremity impairments are based on thirteen possible approaches in the Fifth Edition, the most commonly used approach is the Diagnosis-Based Estimates where specific impairment values are provided for diagnoses. For example, a patient with a partial medial meniscectomy is assigned 1% whole person permanent impairment. Rating systems previously used for the lower extremity did not provide for adjustments based on functional difficulties, physical examination findings, or the results of clinical studies.

The Preface to the Sixth Edition states that the features of the new edition include²²:

• A standardized approach across organ systems and chapters.

• The most contemporary evidence-based concepts and terminology of disablement from the ICF.

• The latest scientific research and evolving medical opinions provided by nationally and internationally recognized experts.

• Unified methodology that helps physicians calculate impairment ratings through a grid construct and promotes consistent scoring of impairment ratings.

• A more comprehensive and expanded diagnostic approach.

• Precise documentation of functional outcomes, physical findings, and clinical test results, as modifiers of impairment severity.

• Increased transparency and precision of the impairment ratings.

• Improved physician interrater reliability.

The Sixth Edition reflects movement toward these features; however, these changes are not all immediately achievable. This new edition should be considered a step in the evolution of the Guides rather than as an end point.

Development Process

The process of writing the Sixth Edition involved many participants – including physicians who use the Guides and the staff of the AMA, all of whom were asked to develop the Sixth Edition in the context of the aforementioned principles. The process was guided by an Editorial Panel and an Advisory Committee, and featured an open, well-defined, and tiered, peer review process. The Editorial Panel was established to include a Medical Editor (Robert Rondinelli, MD, PhD), five Section Editors (Elizabeth Genovese, MD, Richard Katz, MD, Kathryn Mueller, MD, Mohammed Ranavaya, MD, and Tom Mayer, MD), and four core physician experts. The editorial process used an evidence-based foundation when possible, primarily as the basis for determining diagnostic criteria, and a Delphi panel approach to consensus building regarding the impairment ratings themselves. When there was no compelling rationale to alter impairment ratings from what they had been previously, ratings provided in prior editions were the default. The Section Editors led a group of 53 specialty-specific, expert contributors in developing the chapters and in conjunction with the Senior Contributing Editor wrote considerable portions of the revised chapters. The review process involved over 140 physicians, attorneys and other professionals.

An Advisory Committee was developed to provide ongoing discussion of items of mutual concern and current issues in impairment and disability. The group was comprised of representatives from medical specialty societies and experts from certification and teaching organizations and workers' compensation systems. The primary objectives of the Advisory Committee were to:

• Serve as a resource to the Guides Editorial Panel by giving advice on impairment rating as relevant to the member's specialty.

• Provide documentation to staff and the Editorial Panel regarding the medical appropriateness of changes under consideration for inclusion in the Guides.

• Assist in the review and further development of relevant impairment-related issues and in the preparation of technical education material and articles pertaining to the Guides.

• Promote and educate professionals performing impairment ratings on the use and benefits of the Guides.

Sixth Edition Structure

The Sixth Edition is 634 pages in length (the Fifth Edition is 613 pages) and is comprised of 17 chapters. Chapter 1, Conceptual Foundations and Philosophy and Chapter 2, Practical Applications of the Guides, define the overall approaches to assessing impairment. Most impairment ratings are performed for musculoskeletal painful conditions; therefore the most commonly used chapters will be Chapter 15, The Upper Extremities; Chapter 16, The Lower Extremities and Chapter 17, The Spine and Pelvis. Chapter 3, Pain-Related Impairment; Chapter 13, The Central and Peripheral Nervous System and Chapter 14, Mental and Behavioral Disorders will also be frequently referenced. Chapters 4 to 12 focus on the remaining organ systems and structures. A comparison of chapters and length is presented in Table 1.

The most significant change with the Sixth Edition is the development of Impairment Classification Grids based on the ICF model. The first two chapters of the Guides provide the structure to the other fifteen chapters. Chapter 3 defines the current Guides approach to pain, an issue dealt with in many impairment ratings and referred to in many chapters.

Chapter 1 Conceptual Foundations and Philosophy

The Sixth Edition commences with Section 1.1 History of the Guides (6th ed, 1–2) describing a history of compensation for personal injury and disability that dates to antiquity. Section 1.2 New Direction for the Sixth Edition (6th ed, 2-3), presents previous criticisms of the Guides and five new axioms of the Sixth Edition, as noted in Table 2.

The contemporary model of disablement adopted by the Sixth Edition is the International Classification of Functioning, Disability, and Health (ICF), as explained in Section 1.3, The International Classification of Functioning, Disability, and Health (ICF): A Contemporary Model of Disablement (6th ed, 3-6). The traditional model of disablement previously relied upon, the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) presented by the World Health Organization more than a quarter century ago, is characterized as a simplistic model providing a unidirectional depiction of the relationship among pathology, impairment, disability and handicap. This model did not acknowledge the dynamic relationships among these factors nor the role of important personal and environmental modifiers.

The Sixth Edition defines impairment as “a significant deviation, loss, or loss of use of any body structure or body function in an individual with a health condition, disorder, or disease.” (6th ed, 5) This is more refined than the definition in the Fifth Edition which was “a loss, loss of use, or derangement of any body part, organ system, or organ function.” (5th ed, 601); the Sixth Edition includes the term “significant” and then adds the phrase “in an individual with a health condition, disorder, or disease.” Disability is defined as “activity limitations and/or participation restrictions in an individual with a health condition, disorder, or disease” (6th ed, 5) reflective of the ICF terminology. The Fifth Edition definition of disability was “alteration of an individual's capacity to meet personal, social, or occupational demands, or statutory or regulatory requirements because of an impairment.” (5th ed, 600)

Impairment rating is a physician-provided process that attempts to link impairment with functional loss and continues to be defined as a “consensus-derived percentage estimate of loss of activity reflecting severity for a given health condition, and the degree of associated limitations in terms of activities of daily living (ADLs).” (6th ed, 5) The Sixth Edition differs in stressing the importance of causation assessment in performing a rating, as it is first necessary to determine if the health condition is related to an allegedly causal event or exposure. This represents a concerted attempt to prevent, or at least reduce, the common error of including factors that are not causally related to an injury in the rating (for example rating spinal degenerative disease not caused by an injury).

Since impairment ratings may be used inappropriately as a direct correlate of disability, the Sixth Edition addresses this issue by explaining:

“The relationship between impairment and disability remains both complex and difficult, if not impossible, to predict. In some conditions there is a strong association between level of injury and the degree of functional loss expected in one's personal sphere of activity (mobility and ADLs). The same level of injury is in no way predictive of an affected individual's ability to participate in major life functions (including work) when appropriate motivation, technology, and sufficient accommodations are available. Disability may be influenced by physical, psychological, and psychosocial factors that can change over time.” (6th ed, 5-6)

The Sixth edition specifically states, as did prior editions, “the Guides is not intended to be used for direct estimates of work participation restrictions. Impairment percentages derived according to the Guides' criteria do not directly measure work participation restrictions.” (6th ed, 6) The intent of the Guides is to develop standardized impairment ratings which involves defining the diagnosis and associated loss at maximum medical improvement, enabling a patient with an impairment rating to exit from a system of temporary disablement, and provide diagnosis and taxonomic classification of impairment as a segue into other systems of long-term disability. The process of assigning an impairment rating requires the evaluator to clearly delineate the diagnostic criteria (based on the history, including prior clinical course), physical examination findings, current and prior diagnostic test results, and functional status that places the patient in a given impairment class and warrants assignment of a specific number within the options for that class, with the understanding that the provision of an impairment rating does not directly equate to a permanent disability rating.

Assessment of the functional ramifications of a given diagnosis is used in assigning (or modifying) impairment ratings, and the Sixth Edition facilitates consideration of relevant factors by defining two domains of human personal function: mobility and self-care (illustrated in Figure 2). This definition is new to the Guides.

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Domains of Personal Function

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Mobility involves transfer (movement of one's body position while remaining at the same point in space) and ambulation (movement of one's body from one point in space to another). The Sixth Edition differentiates activities of daily living that relate to self-care performed in one personal sphere: bathing and showering, bowel and bladder management, dressing, eating, feeding, functional mobility, personal device care, personal hygiene and grooming, sexual activity, sleep/rest, and toilet (hygiene) and “instrumented” ADLs that are complex self-care activities (eg, financial management, medications, meal preparation) which may be delegated to others. Mobility and self-care activities may be performed independently or may require adaptive aids or helper assistance. The highest level of independence with which a given activity is consistently and safely performed is considered the functional level for that individual. This concept is critically important since function is a modifier of impairment in the Sixth Edition, and it is therefore important that raters be more precise in asking questions (or using questionnaires) in order to assess the ability to perform activities relevant to an overall assessment of function.

Measurement issues are important factors in defining impairment and are discussed in Section 1.4, Measurement Issues (6th ed, 6-8). Previous studies examining the validity of musculoskeletal impairment ratings have revealed equivocal results between impairment rating and functional losses. The Guides attempt to balance science and clinical judgment, as explained in Section 1.5, Balancing Science and Critical Judgement (6th ed, 8-9). Impairment ratings continue to be based largely on consensus and expert opinion since there is not yet adequate methodology or data to relate these ratings to functional loss. The validity of impairment percentages defined in the Sixth Edition must await further empirical testing. As much as possible the approaches in the Sixth Edition focused on simplicity and brevity (Section 1.6 The Case for Simplification and Ease of Application, 6th ed, 9), although finding an appropriate balance between these goals and providing the information (often complex) required to increase the accuracy and reliability remains difficult.

The Sixth Edition provides greater weight to functional assessment than prior Editions. The full impact of this approach is yet to be determined. Section 1.7, The Application of Functional Assessment (6th ed, 9-11), discusses earlier approaches that have worked well (such as the New York Heart Association classification). Guidance is then provided on the use of self-report assessment tools and the need for empirical validation through in-office applications. The rating physician is to consider all available information; however, there is a clear mandate to evaluate the reliability of the information presented, noting that patients may under-report or over-report their difficulties.

The Guides are often used in workers' compensation cases and other litigation as the basis for monetary awards, and patients and/or treating physicians may be inclined to overstate the severity of conditions or functional losses. Therefore, the Sixth Edition states that “examiners must exercise their ability to observe the patient perform certain functional tasks to help determine if self-report is accurate,” (6th ed, 10). If the examinee reports loss of certain abilities on a self-assessment questionnaire or during the clinical interview, the examiner should observe the patient to see if these losses are consistent with the physical examination, diagnostic tests, historical data and/or functional limitations that are “usually” associated with a given disorder; inconsistent and invalid data should not be used to define impairment. The use of functional assessment tools varies by chapter.

Section 1.8, The Need for Internal Consistency and a Uniform Template (6th ed, 11-16), explains the process used to develop a generic template for impairment grids that could be used across various organ systems to enhance uniformity and consistency. The Five Scale ICF Taxonomy (6th ed, 11) used by the Guides is provided in Table 3.

Impairment percentage ranges are provided for each class; the impairment values are dependent on the organ system and structure. Diagnosis and other historical or clinical information typically serve as the key factor used to place a patient within a specific class, although there are some exceptions. Each class is associated with a corresponding range of impairment ratings, typically divided into five impairment grades (A to E), with the mid-range grade (C) serving as the default value. The grade may be modified by non-key findings, which may include functional history, physical examination findings, and the results of clinical studies.

The structure of a typical diagnosis-based grid is presented in Figure 3 (based on Figure 1-5, 6th ed, 13). The grid used for the extremities (which differs in several ways) is presented in Figure 4. Not all chapters use the same key factors, and some chapters use information other than the physical examination, test results, and functional limitations in assigning a specific rating (eg, the endocrine chapter considers burden of treatment compliance). Nonetheless, the system used in the Sixth edition represents a dramatic change from prior editions. The non-musculoskeletal chapters in previous editions included classes with ranges of impairment ratings and little or no specific guidance regarding how to choose a discreet numerical value to reflect a patient's impairment. This significantly contributed to the lack of interrater (and even intrarater) reliability. Use of the new method should considerably reduce this problem. The generic system used as the basis for most of the non-musculoskeletal chapters, and modified for use in rating the extremities and spine, is as follows:

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Diagnosis-Based Grid Template

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Diagnosis-Based Grid Structure for Extremities

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Once the history is used to place a patient into a given impairment class (at the default level of Grade C), the modifiers for other relevant factors (which will differ between body parts and/or organ systems) will be used to shift the rating to a higher or lower grade. The degree to which this occurs will ordinarily be based on the number of classes by which the additional factor represents a higher or lower impairment than the key factor. For example, if the history is the key factor and places an individual in Class 2, Class 1 physical findings (one below the originally assigned class) will shift the rating down to grade B, and then with Class 4 test results (two above the original class), a net change of + 1 (-1 + 2) results in a final rating in Class 2 – Grade D.

The system used for the spine and extremities differs in that initial placement in the grid used to refine the impairment rating is based upon the diagnosis alone, and then modified based upon the results obtained from matching the patient's clinical presentation to information in additional adjustment grids.

For each of the non-key factors there are definitions of the severity of the findings which reflect the grade modifier (class equivalent) of these findings. This is reflected in a summary in Adjustment Grid: Summary (Figure 5) and tables providing specific definitions for defining the grade modifier values for functional history, physical examination, and clinical findings.

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Adjustment Grid: Summary

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The grade may be adjusted by comparing the relative difference between the class assigned by the key factor and the classes assigned by the non-key factors. Unreliable non-key factors are not used to modify the rating and in the musculoskeletal chapters only the most significant diagnosis for an extremity or spine is modified by functional history. If the grade modifier for the non-key factors is the same as the class number assigned by diagnosis, the default impairment value associated with Grade C is used to define the impairment. It is probable that some workers' compensation jurisdictions will modify the approach to functional adjustment, either requiring all diagnoses to be modified or prohibiting functional adjustments.

In the Diagnosis-Based Impairment method, appropriate Class assignment is the critical factor; Class assignment is made solely by the diagnosis and associated clinical information. Non-key factors may only be used to modify the grade within a Class and will not result in impairment ratings lower or higher than the values associated with the particular diagnosis and Class. With the Fourth and Fifth Editions, it appears that some patients and raters attempt to inflate ratings by reporting findings that result in higher ratable impairment, (eg, more restricted joint motion or less strength than actually exists). With the Sixth Edition it is more likely that controversies will result from the interpretation of diagnoses and clinical information that results in Class assignment since this will have more dramatic impact on the impairment values. For example, with spinal impairment assessments it will be important to determine the clinical significance of disk herniations and radiculopathy, two of the critical factors that define the impairment class.

Chapter 2 Practical Application of the Guides

Chapter 2 outlines the key concepts, principles, and rationale underlying the application of the Guides, therefore it is essential that all participants understand this content. With prior Editions, erroneous ratings often occur as a result of physicians failing to follow rules defined in Chapter 2. Fourteen fundamental principles are defined and many of these principles have a significant impact on the rating process. These principles are summarized in Table 4.

The wide use of the Guides in workers' compensation and other disability systems is discussed in Section 2.1, Use of the Guides in Worker's Copensation and Other Disability Systems (6th ed, 20-21). Section 2.2, Organ System and Whole Body Approach to Impairment Ratings (6th ed, 21-23) explains the concept of the whole body approach to impairment ratings. Although most ratings are provided as whole person permanent impairments, some jurisdictions require regional impairment values, and these are provided in order to serve the needs of these jurisdictions. The hierarchical relationship of extremity ratings to whole person ratings remains, with total loss of the upper extremity equaling 60% whole person permanent impairment and total loss of the lower extremity equaling 40% whole person permanent impairment. The approach to combining impairment values using the Combined Values Chart remains the same; however, specific guidance is now provided for circumstances when multiple impairments are combined; the largest values must be combined first. This is consistent with the approach used in the California Permanent Disability Rating Schedule, however, it is a change from directives provided in the Fifth Edition in Chapter 16, The Upper Extremities, in Section 16.1c Combining Impairment Ratings (5th ed, 438). Duplication and/or inflation of a rating by combining ratings that rely on a similar underlying factor is not permissible and is avoided by careful consideration of the underlying pathophysiology.

The use of the Guides is explained in Section 2.3 (6th ed, 23-24). As noted previously, the most important element is the physician's accurate diagnosis, particularly since this defines the class of impairment. In the absence of a diagnosis that captures a particular condition, a similar diagnosis may be used, only if there is no other method for rating objectively identifiable impairment. Although impairment ratings are performed by physicians, nonphysician evaluators may analyze an impairment evaluation to determine if it was performed appropriately. The physician's role is to provide an independent, unbiased assessment. Treating physicians are not totally independent and may not have received adequate training in the use of the Guides. Therefore, assessments by treating physicians may be subject to greater scrutiny than those provided by independent physicians or those with extensive training in the use of the Guides. Impairment ratings are only performed at maximum medical improvement.

The rules of application for the Guides presented in Section 2.4, Rules of Application for the Guides (6th ed, 24-25) are similar to those in prior Editions and essentially reiterate the fundamental principles and the need to base ratings on consistent objective criteria. Impairment values may be rounded, and impairment ratings in the body organ system chapters make allowance for most of the functional losses accompanying the use of prosthetic and similar devices. The Sixth Edition explicitly advises the physician to assess if an individual must regularly use a prosthesis, orthosis or other assistive device; the organ system should be tested and evaluated with that device. If the device is easily removed the physician does have the option of reporting findings with and without the device.

Section 2.5, Concepts Important to the Independent Medical Examiner (6th ed, 25-27) presents concepts important to the independent medical examiner, including definitions of medical possibility versus probability, causation, exacerbation, aggravation and apportionment. The process of apportionment is the same as previous editions in which the examiner determines the current total impairment rating (all-inclusive) and subtracts the baseline rating reflecting pre-existing impairment. Apportionment requires careful analysis of the alleged causative factors and may be challenging when ratings have been performed using different Editions. This may be particularly challenging with the Sixth Edition since the approaches used to define impairment may differ from earlier editions. If impairment was defined previously and there has been further injury of the same region, it may be appropriate to subtract that previous impairment number from the current rating by the Sixth Edition. In most circumstances the most appropriate method is to rate both the current total impairment and the pre-existing impairment (using clinical information about that condition prior to the more recent injury) by the Sixth Edition. If there is insufficient information to appropriately modify the previous rating and accurately determine the grade within a class, the default value (C) for that diagnosis is used for the previous impairment rating.

In this edition, maximum medical improvement (MMI) refers to “a status where patients are as good as they are going to be from the medical and surgical treatment available to them. It can also be conceptualized as a date from which further recovery or deterioration is not anticipated, although over time (beyond 12 months) there may be some expected change.” (6th ed, 26). Rating prematurely typically inflates ratings, and the Fifth Edition allowed for ratings to be performed after the benefits of treatment had accrued. With the Sixth Edition, diagnoses may be modified by the time the patient is at MMI, therefore, it is necessary to assure the patient is at MMI prior to rating, and that the correct diagnosis is being rated. The Guides does not permit the rating of future impairment. This edition presents a brief new discussion of the significance of cultural differences that may impact the evaluation process.

An impairment evaluation is a form of expert testimony, as explained in Section 2.6, Impairment Evaluation and the Law (6th ed, 27-28). Therefore, ratings must be fully supportable. If findings or impairment ratings based on these findings conflict with established medical principles, they cannot be used to justify an impairment rating.

The standards for reports are provided in Section 2.7, Preparing Reports, (6th ed, 28-29), including clinical evaluation, analysis of findings, and discussion of how the impairment rating was calculated. This continues to serve as an excellent basis to determine the quality of an impairment evaluation report.

Chapter 3 Pain-Related Impairment

Chapter 3, Pain-Related Impairment (6th, 31-46) discusses the challenges and controversies associated with assessing pain. If pain accompanies objective findings of injury or illness that permits rating using another chapter in the Guides, than pain-related impairments are not used as “add-ons.” The clear language to this effect should reduce a common problem of double-dipping seen with the Fifth Edition, ie, rating for a musculoskeletal condition and then providing further impairment for pain. It is probable that impairment ratings for pain will be less frequent with the Sixth Edition.

Pain not accompanied by objective ratable findings may be ratable resulting in a maximum of 3% whole person permanent impairment, the same limit assigned in the Fifth Edition. The actual impairment is based on the patient's self-reports on a Pain Disability Questionnaire (PDQ) with a lowering of the impairment if the examiner questions the credibility of the patient. Due to the subjective nature of pain and differing philosophies, this chapter was one of the most controversial. Although there was discussion of modifying the magnitude of the impairment due to pain, there was no new or compelling information to support a change from the precedent established in the Fifth Edition; the maximum rating of 3% remains. It is probable that the approach to pain-related impairment will continue to evolve with the Seventh Edition.

Conclusion

It is probable that it will be several months before physicians, claims professionals, attorneys and fact-finders become familiar with the significant differences in assessing impairment using the Sixth Edition. This learning curve is shortened by training and developing understanding of the evolving methodology. It is hoped that the Sixth Edition will benefit all stakeholders by minimizing conflict and improving decision making. The process of defining impairment or the complexities of human function is not perfect; however, the Sixth Edition approach was designed with the intent to simplify the rating process, improve accuracy and provide a solid basis for future editions of the Guides.