Once causation is determined and there is probable cause related to the event, then apportionment is evaluated. If there is no causal relationship then apportionment is not necessary.
American Medical Association: Guides to the Evaluation of Permanent Impairment, fifth edition. Chicago, AMA 2001
The extent to which each of 2 or more probable causes are found responsible for an effect (injury, disease, impairment, etc..)
American Medical Association: Disability Evaluation, second edition. Chicago, AMA 2003.
A distribution of causation among multiple factors that caused or significantly contributed to the injury and resulting impairment.
American Medical Association: Guides to the Evaluation of Permanent Impairment, sixth edition. Chicago, AMA, 2008
Precipitation - Injury or exposure causes a “latent” or potential disease process to become manifested.
Acceleration - Injury or exposure hastens the clinical appearance of an underlying disease process.
Aggravation - A permanent worsening of a prior condition by a particular event or exposure.
Exacerbation - A temporary worsening of a prior condition by an exposure / injury.
Recurrence - Signs and symptoms attributable to a prior illness or injury occur in the absence of a new provocative event.
American Medical Association: Disability Evaluation, second edition. Chicago, AMA 2003, page 99 -100.
The phrase "pre-existing condition" often causes confusion.
There are only two types of pre-existing conditions. The first is known as an "inactive" or "dormant" pre-existing condition. The second is known as an "active" or "symptomatic" pre-existing condition.
The difference between an active vs. inactive pre-existing conditions is "like night and day."
This may require a detailed review of past and present medical records.
Inactive pre-existing condition is if there is no evidence that a pre-existing condition is causing pain or disability before trauma is sustained.
The "proximate cause" of the present symptoms is the recent trauma, even though the symptoms may be worse or healing may take longer because of a pre-existing condition.
Besides classifying the apportionment it may also be necessary and beneficial to relate the percentage that the present condition or impairment is attributable to the new injury or event. To do this there must be:
- Documentation of a prior factor.
- Current impairment is greater than the prior factor (prior impairment, prior injury or illness).
- There is evidence that the prior factor caused or contributed to the impairment, based on reasonable probability.