The prognostic value of functional capacity evaluation in patients with chronic low back pain: part 1: timely return to work.

STUDY DESIGN: Historical cohort study.

OBJECTIVES: We examined the validity of the Isernhagen Work Systems' Evaluation in predicting timely return to work.

SUMMARY OF BACKGROUND DATA: Functional Capacity Evaluations are used commonly to determine readiness for return to work, yet little is known of their validity.

METHODS: Workers' compensation claimants undergoing Functional Capacity Evaluations following work-related low back injury were studied. Two cohorts were formed, one on which exploratory analyses were conducted and a second for confirmation. Evaluation indicators were the number of tasks in the protocol rated as failed and performance during the floor-to-waist lift task. The primary outcome investigated was time receiving total temporary disability benefits (as a surrogate of return to work) and a secondary outcome was time until claim closure in the year following Evaluation. Cox proportional-hazards regression was used to determine the prognostic effect of Evaluation crudely and after controlling for potential confounders.

RESULTS: Few patients (4%) were found to pass all Evaluation tasks, yet most experienced total temporary disability suspension and claim closure within 1 year following Functional Capacity Evaluations. Better Evaluation performance was related to faster time to suspension of total temporary disability benefits and claim closure after controlling confounding factors, but explained little of the variation in these outcomes (approximately 10%). Performance on the floor-to-waist lift was as predictive as the number of failed tasks in the entire Functional Capacity Evaluations protocol.

CONCLUSIONS: Better performance on Evaluation was weakly associated with faster recovery; however, the amount of variation explained was small. One task in the Evaluation was as predictive as the entire protocol.