Validity and Reliability of an iPhone® Clinometer Application for Assessment of Joint Repositioning Error in Patients with Non-Specific Chronic Low Back Pain

Background: Non-specific chronic low back pain (NSCLBP) is a complex issue that impacts an individual's quality of life and functionality, leading to impairments in somatosensory and proprioception. Errors in proprioception are evaluated using specific tests such as joint reposition sense. Objective: This study aimed to validate and determine the reliability of the iPhone inclinometer application (Clinometer) in measuring the error in lumbar joint repositioning in patients suffering from NSCLBP. Materials and methods: In this cross-sectional study, 55 male and female patients diagnosed with NSCLBP were involved, with an average age of 25.51 ± 6 years. All patients underwent an active lumbar repositioning test using the Clinometer application and an isokinetic dynamometer to calculate the absolute angular error for a target angle of 30° lumbar flexion. This was done over two assessment sessions on different days, with each patient being evaluated by two examiners at each session. The intra-rater and inter-rater reliability were determined using the Intraclass Correlation Coefficient (ICC), and the concurrent validity was tested using Spearman’s correlation. Results: The Clinometer application demonstrated excellent concurrent validity with the isokinetic measurements at the same target angle (r= 0.83, p< 0.01), and exhibited excellent intra and inter-rater reliability (ICC values ranged from 0.88 to 0.93 for intra-rater reliability and from 0.82 to 0.88 for inter-rater reliability). Conclusion: The Clinometer app is a viable and reliable alternative to the isokinetic dynamometer for evaluating active lumbar reposition sensation in persons with NSCLBP at 30˚ of flexion.