Risk Adjustment of the Modified Low Back Pain Disability Questionnaire and Neck Disability Index to Benchmark Physical Therapist Performance: Analysis From an Outcomes Registry
Authors: Lutz Adam D , Brooks John M , Chapman Cole G , Shanley Ellen , Stout Chris E , Thigpen Charles A 
Published: January 2020

Background

Patient-reported outcomes (PROs) have been touted as the ultimate assessment of quality medical care and have been proposed as performance measures after appropriate risk adjustment. Although spine conditions represent the most common orthopedic disorders, the most used PROs for disabilities related to the back and neck—the Modified Low Back Pain Disability Questionnaire (MDQ) and the Neck Disability Index (NDI)—have not been evaluated as performance measures.

Objective

The objective of this study was to benchmark physical therapists’ performance in the management of spine conditions not involving surgery through the use of risk-adjusted MDQ and NDI outcomes.

Design

This was a retrospective observational study.

Methods

Data were accessed for patients seeking physical therapy with no history of related surgery for back or neck pain (315,274 treatment episodes) between January 2015 and June 2018. Patients with complete data, including initial and matched final MDQ or NDI, were considered for analysis (182,276 patients; 2799 physical therapists). Linear models controlling for baseline PRO and patient characteristics predicted PRO change for each patient. An aggregated performance ratio of actual PRO change to predicted PRO change was calculated for each physical therapist, and then empirical bootstrapping was used to develop the median performance ratio and its confidence intervals. Physical therapists who met a 40-patient threshold for either cohort (MDQ or NDI) were classified as “outperforming,” “meeting expectations,” or “underperforming” relative to predicted values using these 95% confidence intervals.

Results

Performance ratios indicated that 10% and 11% of physical therapists outperformed, 79% and 78% met expectations, and 11% and 11% underperformed relative to the risk-adjusted predicted change in the MDQ (1240 therapists; 97,908 patients) and NDI (461 therapists; 26,123 patients), respectively. To demonstrate the clinical importance of risk adjustment, clinical performance was evaluated in the seemingly homogeneous subset of 208 physical therapists within 0.5 SD of the median baseline MDQ and the median actual change in the MDQ. Following risk adjustment, 2 physical therapists were classified in each of the outperforming and underperforming cohorts.

Limitations

The secondarily obtained observational data used were not collected for research purposes. Additionally, the analyses were limited by missing baseline information and follow-up PROs.

Conclusions

The risk-adjusted performance ratios for the MDQ and NDI resulted in disparate conclusions regarding the quality of care compared with the raw, unadjusted change scores. According to the baseline and unadjusted change in the MDQ, even physical therapists in the most homogeneous sample were differentiated following appropriate risk adjustment. Clinically important improvements in actual PROs were observed in the outperforming but not in the underperforming physical therapists. Clinically meaningful differences in the performance ratio are unknown and are a limitation to clinical application and an opportunity for future research.