Development and Initial Validation of the Orthotic Patient-Reported Outcomes – Mobility (OPRO-M): An Item Bank for Evaluating Mobility of People Who Use Lower-Limb Orthoses

October 8, 2024

Hanger Clinic

Journal

Authors

Geoffrey Balkman¹, Alyssa Bamer¹, Phillip Stevens^2,3, Eric Weber², Sara Morgan^1,4,5, Rana Salem¹, Dagmar Amtmann¹, Brian Hafner¹

Department of Rehabilitation Medicine, University of Washington, Seattle, Washington, United States of America.
Hanger Institute for Clinical Research and Education, Austin, Texas, United States of America.
Department of Physical Medicine and Rehabilitation, University of Utah, Salt Lake City, Utah, United States of America.
Gillette Children’s Specialty Healthcare, St. Paul, Minnesota, United States of America.
University of Minnesota, Minneapolis, Minnesota, United States of America.

Background

Lower limb orthoses (LLOs) are external leg braces designed to improve or maintain mobility in individuals with a variety of conditions affecting lower limb function. Despite the recognized benefits of LLOs, there is limited evidence measuring their comparative effectiveness.^1,2 In a prior study, orthotists reported that time constraints and the lack of instruments designed for LLO users were significant barriers to routine patient mobility outcomes measurement.²

Patient-reported outcome measures (PROMs) can provide insights into important aspects of a LLO user’s mobility and selecting and assessing the effectiveness of LLOs. This study conducted by the Hanger Institute for Clinical Research and Education in partnership with the University of Washington aimed to create a population-specific item bank for measuring the mobility of LLO users. The set of final calibrated items, termed the Orthotic Patient-Reported Outcomes—Mobility (OPRO-M) item bank, was evaluated for initial evidence of convergent, divergent, and known groups’ construct validity. OPRO-M was strongly correlated with existing PROMs designed to measure aspects of physical function.

Results from this study indicate that OPRO-M can effectively measure the mobility of LLO users. This illustrates the opportunity to successfully quantify clinical intervention and identify where possible improvements can be made. As a result, several versions of the instrument are now available to the field to incorporate into clinical practice and research studies.

Objective

To develop a validated outcome measure that is relevant to LLO users.

Design

A cross-sectional study surveyed LLO users. A total of 1,036 subjects reported their functional mobility with their orthotic device(s) through a pool of candidate questions. Individual questions were then evaluated for independent validity and reliability.

Results

A total of 39 questions were found to be unidimensional, indicating that they measure a single primary trait (i.e., mobility) with minimal redundancy. There was no evidence of floor or ceiling effect, suggesting that few LLO users will receive scores at the lowest or highest extremes of the measurement scale. Strong positive correlations were observed between the OPRO-M question bank and previously validated functional outcome measures. These 39 questions were fashioned into a 12- and 20-item short form to be utilized in clinic. Additionally, the OPRO-M items showed no significant differential item functioning (DIF), suggesting the tool measures mobility in LLO users without bias from variables generally unrelated to mobility.

Evaluation of Initial Construct Validity

ANOVA (Analysis of Variance) is a statistical test used to compare means across multiple groups. One-way ANOVA testing revealed that there were statistically significant differences in OPRO-M full bank T-scores, between at least two groups for all characteristics, including orthosis level (F(2, 2) = [25.08], p < 0.001), paresis type (F(2, 2) = [27.59], p < 0.001), assistive device use (F(2, 2) = [286.45], p < 0.001), fewer falls in the prior 12 months (F(2, 2) = [15.02], p < 0.001) and number of comorbidities (F(2, 2) = [7.08], p < 0.001).

Conclusion

OPRO-M is a novel, item response theory (IRT)-based PROM designed to measure the mobility of LLO users, revealing the functional impact these orthoses have on individuals. Calibrated to a national sample representative of a typical clinical population, it includes relevant activities and situations for respondents and can be administered efficiently in a clinical setting.

Additionally, OPRO-M:

Validates a reliable outcome measure that is specific for LLO users, focusing on activities and aspects of mobility that are most relevant to this population, and is the first study of its kind to do so.
Demonstrates to patients how their mobility improves with the use of their device(s).
Offers the potential to measure the effectiveness of clinical interventions and identify areas for enhancement.
Provides outcome measures to support the medical necessity of LLOs.

More Published Research

This publication is just one of the studies conducted by the Hanger Institute for Clinical Research and Education, in collaboration with leading researchers, clinical, and academic institutions.

Learn More