Examination of Regional Interdependence Theory in Chronic Neck Pain: Interpretations from Correlation of Strength Measures in Cervical and Pain-Free Regions.

OBJECTIVE: Impairments present in chronic pain conditions have been reported not to be limited to the painful region. Pain-free regions have also been proposed to be adversely affected as a cause or consequence of the painful condition. The aim of this study was to investigate the association between muscle strength in painful and pain-free regions and chronic neck pain.

DESIGN: A cross-sectional study.

SETTING: Rehabilitation hospital laboratory.

SUBJECTS: One hundred twenty-two patients with chronic neck pain (87 female) and 98 asymptomatic volunteers (52 female) were included in the study.

METHODS: Maximal isometric strength measures of the neck, scapulothoracic, shoulder, trunk, and hip muscles were assessed using a hand-held dynamometer in all participants. Pain intensity and pain-related disability were also assessed in patients through visual analog scale and Neck Disability Index scores, respectively.

RESULTS: Principal component analysis revealed one component for each of the studied regions. Multivariate analysis of variance found neck (d = 0.46), scapulothoracic (d = 0.46), shoulder (d = 0.60), trunk flexor (d = 0.38), extensor (d = 0.36), and hip (d = 0.51) strength components to be lower in the neck pain patients compared with asymptomatic participants (P < 0.01). Logistic and linear regression analyses found the shoulder strength component both to be a significant predictor for neck pain occurrence (β = 0.53, P < 0.01) and to have a considerable effect on pain intensity score (β=-0.20, P = 0.02), respectively.

CONCLUSIONS: The results found that some pain-free regions in addition to the cervical spine to exhibit lower levels of muscular strength in neck pain patients. These findings support the regional interdependence theory, which proposes that impairments are not limited to the painful area and are possibly mediated by central mechanisms.