Interrater reliability of the modified prone instability test for lumbar segmental instability in individuals with mechanical low back pain.

Objective: The purpose of this study was to establish the interrater reliability of measures obtained with a novel Modified Prone Instability Test (mPIT), which, like the original Prone Instability Test (PIT), is proposed to identify lumbar segmental instability. The mPIT has clinical feasibility advantages to the PIT, but its psychometric properties are yet to be determined.

Design: Repeated measures (test-retest) design, methods study.

Methods: The mPIT was administered by two blinded testers, an orthopedic physical therapy resident with < 1 year experience and board-certified orthopedic specialist physical therapist with >25 years' experience. Procedures were administered at an outpatient physical therapy clinic of a tertiary Medical Center. Participants included 50 adults (≥18 years old) with mechanical low back pain and no radicular (below the knee) symptoms (mean age 50.7 years, 66% female, 76% reported previous episodes of low back pain). Interrater reliability was measured via Fleiss' kappa coefficient.

Results: Assessments of the mPIT had moderate interrater agreement (κ = .579 [95% CI = .302 to .856],  < .001.).

Conclusion: Measures obtained using the mPIT demonstrated moderate interrater reliability between a new graduate and an experienced clinician, which aligns with several studies examining interrater reliability of the original PIT. Further study examining comparative validation of the mPIT with other lumbar instability measures is warranted.