The Reproducibility and Convergent Validity of the Walking Index for Spinal Cord Injury (WISCI) in Chronic Spinal Cord Injury

Abstract

Background. The Walking Index for Spinal Cord Injury II (WISCI II) is a hierarchical scale that measures improvements in walking following spinal cord injury (SCI). The WISCI II has good face validity, concurrent validity, and reliability following acute SCI; however, psychometric properties need to be determined for chronic SCI. Because prior studies have demonstrated a relationship between lower-extremity motor scores (LEMS) and walking, outcome measures for walking should demonstrate a linkage between the underlying impairment (weakness) and walking—convergent validity. Objective. To determine convergent validity and reproducibility of the WISCI II. Methods. Self-selected and maximum WISCI levels were assessed for 76 patients with chronic SCI (34 paraplegia, 42 tetraplegia); 10-m walking speeds were calculated. Convergent validity was assessed by correlating WISCI II levels to LEMS and walking speed. Reproducibility was assessed with the intraclass correlation coefficient (ICC) and the smallest real difference (SRD). Results. Convergent validity of the self-selected and maximum WISCI II with LEMS was moderate for paraplegia (ρ = 0.479 and ρ = 0.533) and strong for tetraplegia (ρ = 0.852 and ρ = 0.816). Tetraplegia, but not paraplegia, demonstrated convergent validity of walking speed at the self-selected and maximum WISCI levels with LEMS (ρ = 0.752 and ρ = 0.813). WISCI reproducibility was excellent (self-selected ICC = 0.994; maximum ICC = 0.995), resulting in SRDs of 0.785 (self-selected) and 0.597 (maximum), suggesting that a change of one WISCI level can be interpreted as real in a chronic patient. Conclusions. Results suggest that the WISCI II should be a very useful outcome measure for detecting changes in walking function following chronic SCI.