38In these circumstances, the following method must be applied:

38         In these circumstances, the following method must be applied:

a)      The assessor should, where possible, assess the degree of permanent impairment resulting from the pre-existing condition by reference to the available evidence (for example, clinical records, investigations, reported histories) and/or by using clinical judgment.

b)      Where it is possible to assess the degree of permanent impairment resulting from the pre-existing condition, the assessor should, where possible, isolate the permanent impairment resulting from the injury (for example, by comparing the degree of permanent impairment resulting from the pre-existing condition with the degree of permanent impairment resulting from the injury to assess whether there has been an increase in the employee’s whole person impairment). Only the permanent impairment resulting from the injury is to be included in the assessment of the degree of permanent impairment of the employee.

c)       Where it is not possible to assess the degree of permanent impairment resulting from the pre-existing condition, or it is not possible to isolate the permanent impairment resulting from the injury, the assessment of the degree of permanent impairment of the employee resulting from the injury is to be made by reference to the totality of effects of the pre-existing condition and the injury.

d)      The percentage of permanent impairment suffered by an employee as a result of a particular injury ascertained by applying this method may be 0%.

39         Where a pre-existing injury results in permanent impairment, and the employee subsequently suffers an injury which results in permanent impairment to the same body part, system or function (but the subsequent injury is not an aggravation of the pre-existing injury), the permanent impairment resulting from the pre-existing injury must be disregarded when assessing the degree of permanent impairment of the employee resulting from the subsequent injury. The subsequent injury should be assessed by reference to the functional capacities of a normal healthy person. The WPI rating for the pre-existing injury and the WPI rating for the subsequent injury may be added.

THE IMPAIRMENT TABLES

40         Division 1 of this Guide is based on the concept of whole person impairment which is drawn from the AMA5.

41         Division 1 assembles into groups, according to body system, detailed descriptions of impairments. The extent of each impairment is expressed as a percentage value of the whole, normal, healthy person. Thus, a percentage value can be assigned to an impairment by reference to the relevant description in this Guide.

42         It may be necessary in some cases to have regard to a number of chapters within this Guide when assessing the degree of whole person impairment which results from an injury.