ORIGINAL RESEARCH| Volume 102, ISSUE 8, P1576-1587, August 2021

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The Lower Extremity Physical Function Patient-Reported Outcome Measure Was Reliable, Valid, and Efficient for Patients With Musculoskeletal Impairments

Published:March 04, 2021DOI:


      • The newly developed regional lower extremity physical function (LEPF) patient-reported outcome measure (PROM) is reliable, valid, and efficient.
      • The LEPF computerized adaptive test and LEPF short form can be used for research and clinical care.
      • Clinicians may simplify PROM administration by using a single regional measure.



      To calibrate the Lower Extremity Functional Scale (LEFS) items into a regional lower extremity physical function (LEPF) item bank and assess reliability, validity, and efficiency of computerized adaptive test (CAT) and short form (SF) administration modes.


      Retrospective cohort.


      Data were collected from patients treated in outpatient rehabilitation clinics for musculoskeletal impairments of the hip, knee, foot, and ankle that responded to all 20 LEFS items at intake.


      Patients aged 14 years or older who started an episode of care during January 2016-October 2019 and identified the lower extremity region as the source of a primary musculoskeletal complaint. Total cohort included 78,186 patients (mean age, 53±19y, range, 14-89y).


      Not applicable.

      Main Outcome Measures

      Item response theory (IRT) model assumptions of unidimensionality, local item independence, item fit, and presence of differential item functioning (DIF) were studied. LEPF-CAT– and LEPF-SF–generated scores were evaluated.


      An 18-item solution was supported for its unidimensionality and fit to the IRT model, with reliability estimates >0.9 for all administration modes. No DIF impact on LEPF scores was identified. Scores discriminated between multiple patient groups in clinically logical ways and were highly responsive to change, with negligible floor or ceiling effects. CAT scores were generated using an average of 4.9 items (median, 4).


      The LEPF scores were reliable, valid, and efficient for assessing perceived physical function of patients with musculoskeletal impairments of the hip, knee, foot, and ankle; thus, it was found suitable for research and routine clinical administration. These findings are limited to the type of patients included in this study, with further validation needed to assess their generalizability.


      List of abbreviations:

      CAT (computerized adaptive test), CBFA (confirmatory bifactor analysis), CFA (confirmatory factor analysis), CFI (comparative fit index), DIF (differential item functioning), ECV (explained common variance), EFA (exploratory factor analysis), FOTO (Focus on Therapeutic Outcomes), IRT (item response theory), LEFS (Lower Extremity Functional Scale), LEPF (lower extremity physical function), omega-H (omega-hierarchical), PROM (patient-reported outcome measure), RMSEA (root mean square error of approximation), SF (short form), SRMR (standardized root mean square residual), TLI (Tucker-Lewis index)
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