Oftentimes as physicians we are asked to calculate permanent partial impairment ratings. Impairment is defined as a significant deviation, loss or loss of use of any body structure or function in individual with a health condition, disorder or disease. Impairments are determined as a percentage of the body part involved and then converted to a percentage of the whole person. An injury may result in an impairment from 0 to 100% of the whole person depending on the severity of the condition. Impairment ratings are defined by anatomic, structural, functional and diagnostic criteria. An accurate exam is also important in determining impairment as is the specific diagnosis. Ultimately the system for determining impairment should be reliable so that different raters arrived at consistent impairment ratings when assessing the same individual.
To achieve consistency the American Medical Association has been publishing The Guides to Evaluation of Permanent Impairment since the 1950s. Every seven years a new edition is printed. The most recent edition is the Sixth Edition published in 2008. This addition continues to emphasize diagnosis as a key contributor to determining the impairment rating. There are also adjustments for the significance of the patient symptoms and functional abilities. The physical findings and diagnostic studies can also influence the impairment. In my opinion The 6th Edition provides a better template for determining impairment. However it is a more complicated process and physicians have been slow to accept and utilize this edition. Many physicians still rely on the Fifth Edition. Some jurisdictions require the use of specific references for determining impairment.
Generally impairment should not be determined until the patient has reached a point of maximum medical improvement (MMI). Until the patient reaches a point of maximum improvement their impairment may change. For instance if a patient needs surgery for an unstable joint their impairment prior to the surgery would be much higher as they would likely lack motion and stability of the joint. After the surgery they would potentially improve functionally and symptomatically. Furthermore their joint would become more stable and have greater range of motion. Their impairment would be much less after the surgery if the outcome was as described above. Similarly when determining impairment for brain or nerve injuries we need to wait until the patient has made maximum medical improvement. After they have fully benefited from therapy and time we can then accurately measure their neurologic findings which will help to determine the significance of their loss and resultant impairment.
When determining impairment the physician should cite the reference and include the page or tables that were used in calculating the percentage. Furthermore if a body part is converted to a larger part or whole person the methodology needs to be described. A properly calculated impairment rating should be easily understood by those reading the report. It should also be easily supported by the reference utilized to determine the PPI.