Determination of Biodex Balance System Cutoff Scores in Older People With Nonspecific Back Pain: A Cross-sectional Study

Objective: The purpose of this study was to determine cutoff scores for the Biodex Balance System (BBS) and verify if they could be used to discriminate older people with nonspecific low back pain (NSLBP) with poor postural performance from those with good postural performance. Methods: This cross-sectional study included 52 participants with NSLBP older than 65 years. One level of stability (level 5; intraclass correlation ≥0.70) and 2 conditions (eyes open and eyes closed) were selected for the testing procedure. Anterior-posterior stability index (APSI), medial-lateral stability index (MLSI), and overall stability index (OSI) scores were calculated. The participants were classified into 2 groups: high risk of falling and low risk of falling. Both the receiver operating characteristic and the area under the curve were used to determine the best BBS cutoff values. Binary logistic regression analysis was used to investigate the ability of BBS scores to predict risk of falling. Results: BBS cutoff scores in the eyes-open condition (APSI = 2.60, MLSI = 1.95, OSI = 2.95) and eyes-closed condition (APSI = 3.05, MLSI = 2.17, OSI = 3.25) were found to be sensitive and specific in determining postural performance. Participants with index values lower than the cutoff scores had, respectively, 6.42, 4.20, and 3.72 times lower risk of falling in the eyes-open condition and 3.33, 5.50, and 3.00 times lower risk of falling in the eyes-closed condition. The predictive characteristics of the models for risk analysis were excellent and good to excellent. Conclusion: Our study shows that BBS cutoff scores are sensitive and specific in distinguishing between poor and good postural performance in older people with NSLBP.