Construct Validity of the Prosthetic Limb Users Survey of Mobility (PLUS-M) in Adults With Lower Limb Amputation

Objective: To assess construct validity of the Prosthetic Limb Users Survey of Mobility (PLUS-M), a self-report mobility measure for people with lower limb amputation (LLA).

Design: Cross-sectional study.

Setting: Private prosthetic clinics (n=37).

Participants: Current lower limb prosthesis users (N=199; mean age ± SD, 55.4±14.3y; 71.4% men) were assessed before receiving a replacement prosthesis, prosthetic socket, and/or prosthetic knee.

Interventions: Not applicable.

Main outcome measures: Convergent construct validity was examined using correlations between participants' PLUS-M T-scores and measures of physical function, mobility, and balance, including the Amputee Mobility Predictor (AMP), timed Up and Go (TUG), Patient-Reported Outcomes Measurement Information System-Physical Function (PROMIS-PF), Prosthesis Evaluation Questionnaire-Mobility Subscale (PEQ-MS), and Activities-specific Balance Confidence (ABC) Scale. Known-groups construct validity was evaluated by comparing differences in PLUS-M T-scores among participants grouped by Medicare Functional Classification Level (MFCL).

Results: PLUS-M T-scores demonstrated a moderate positive relationship with AMP scores (ρ=.54, P<.001) and a moderate negative relationship with TUG times (ρ=-.56, P<.001). The PLUS-M also showed a strong positive relationship with PEQ-MS scores (ρ=.78, P<.001), ABC Scale scores (ρ=.81, P<.001), and PROMIS-PF T-scores (ρ=.81, P<.001). Significant differences (P<.05) in PLUS-M T-scores were found among groups of people classified by different MFCLs.

Conclusions: Study results support the validity of the PLUS-M as a self-report measure of prosthetic mobility. Correlations between PLUS-M and measures of physical function, mobility, and balance indicate convergent construct validity. Similarly, significant differences in PLUS-M T-scores across MFCL groups provide evidence of known-groups construct validity. In summary, evidence indicates that PLUS-M has good construct validity among people with LLA.