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On “Lower Limb Functional Index…” Gabel CP, Melloh M, Burkett B, Michener LA. Phys Ther. 2012;92:98–110.

We were interested to read the article by Gabel and colleagues,1 who conducted a head-to-head comparison study of the psychometric properties of the Lower Extremity Functional Scale (LEFS),2 an instrument we developed in 1999, and the Lower Limb Functional Index (LLFI), an instrument developed by the authors. We have long been advocates of head-to-head comparisons of competing instruments to determine which has the greatest potential to positively affect clinical care.3 We would like to make some general comments regarding the conceptual framework, and then make more specific comments regarding the methods and literature interpretation in Gabel and colleagues' article.

We developed the LEFS2 based on the World Health Organization's model of disability and handicap.4 The more contemporary terms consistent with the current version of the International Classification of Functioning, Disability and Health (ICF)5 that guided instrument development are “activity limitations” and “participation restrictions.” Because our focus was on people with musculoskeletal disorders of the lower extremity, all of the items in our scale captured the person-level activity limitations and participation restrictions most relevant to people with disorders of the lower extremity. Notably absent from the LEFS are questions related to impairments (eg, pain, joint stiffness) or mental health status (eg, irritability, depression). Our rationale for this approach was that we saw problems with other functional status instruments available at the time because they combined questions related to impairments, such as pain and joint stiffness, with items dealing with person-level function and items related to psychological distress. An example of …