Background and significance. Recovery from traumatic injuries is a complex process that varies significantly between individuals and is not predicted solely by injury severity. The International Classification of Function (ICF) describes disability as occurring at three levels: Impairments in Body Functions and Structures, Activity Limitations, and Participation Restrictions. This study uses Structural Equation Modeling (SEM) to examine structural relationships between these levels of function and test a model of disability following trauma based on the ICF.

Methods. Patients (N=1,013) from two longitudinal studies of severe lower limb trauma were followed at 3, 6, 12, and 24 months post-injury. Three variables describing Body Functions and Structures were developed: Pain, Physical Impairment, and Psychologic Distress. Exploratory factor analysis techniques were used to identify domains within the 136 items of the SIP that are consistent with the Activity and Participation domains of the ICF framework. These factors were labeled “Participation”, “Physical Activity”, and “Psychosocial Activity”. SEM techniques were used to examine the relationships among these variables over time.

Results. Physical and Psychosocial Activity were structurally related to Participation (standardized effects ranged between 0.25 and 0.34, p ≤ 0.01 in all models). Pain was structurally related to both Physical Impairment and Psychologic Distress. In contrast, neither Physical Impairment nor Psychologic Distress were structurally related to Pain or to each other. Overall, there was no evidence of a structural relationship between any of the Activity and Participation variables and any of the Body Function and Structure variables. On the other hand, Physical Impairment was structurally related to Physical Activity, Psychologic Distress was structurally related to both Psychosocial Activity and Participation, and Pain was structurally related to both Activity and Participation. Including the effects of direct and indirect relationships, Pain and Psychologic Distress had the highest total effects on Participation.

Conclusions, policy and program implications. The results lend considerable support to the hypothesis that within the ICF framework, Impairments are causally related to Activity Limitations, which in turn are causally related to Participation, and emphasize the central roles of Pain and Psychologic Distress in the etiology of disability following trauma. Secondary prevention interventions targeting sub-threshold levels of Pain and Psychologic Distress may be critical to achieving reductions in injury-related disability.