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The development of the Functional Capacity Index
E J MacKenzie1, A Damiano, T Miller
1Center for Injury Research and Policy, Johns Hopkins School of Public Health, Baltimore, Maryland, USA.
Objective:
This paper describes the development of the Functional Capacity Index (FCI) and compares it to the Abbreviated Injury Scale (AIS) and the Injury Impairment Scale (IIS).
Methods:
The FCI maps 1990 AIS injury descriptions into scores that reflect expected levels of reduced functional capacity at 1 year after injury. Its development involved three steps. First, an expert clinical panel identified 10 relevant dimensions of function and defined levels of capacity within each dimension. A group of 114 individuals then rated the relative severity of different levels of function in terms of their impact on daily living. The third step involved clinical experts assigning FCI scores to AIS '90 injury descriptions based on their knowledge of the likely 1-year consequences associated with each injury. As a first step in validating the FCI, 1 year postinjury levels of impairment (based on range of motion and strength) were correlated with FCI, IIS, and AIS scores derived for 301 patients with severe lower extremity fractures.
Results:
Consistency of FCI scores derived within and across dimensions of function argue for the conceptual integrity of the index. Non-zero FCI scores were assigned to only 26% of the 1,272 AIS injury descriptions, indicating that, for most of the injuries in the AIS dictionary, very little or no residual impairment is expected for the average person at 1 year. FCI scores derived for 301 patients with lower extremity fractures ranged from 0 to 63 (out of a possible 100 points). A modest correlation was found between FCI scores and actual levels of impairment observed at 1 year. Compared with the AIS and the IIS, the FCI appeared to discriminate somewhat better among different levels of function.
Conclusions:
Although further empirical validation of the FCI is essential before it can be broadly applied, its development represents an important first step in the generation of an AIS-based measure of expected functional outcome. Its validation is encouraged across a variety of settings and injury types.