Ultrasonographic measurement indicated patients with chronic neck pain had reduced diaphragm thickness and mobility along with declined respiratory functions.

Background: Chronic neck pain (CNP) is a prevalent musculoskeletal condition including notable impairments in respiratory function. The diaphragm, serving dual roles in respiration and spinal stability, is intricately linked to the cervical spine through fascial, neurophysiological, and biomechanical connections. However, to date, none has investigated the diaphragm function in patients with CNP.

Objectives: To investigate the diaphragm function, respiratory muscle strength, and pulmonary function in patients with CNP. In addition, their associations were also examined.

Design: A case-control study.

Methods: A total of 54 participants were recruited including 25 patients with CNP (CNP group) and 29 healthy adults (CON group). Pulmonary function including forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV), and respiratory muscle strength represented by maximal inspiratory (MIP) and maximal expiratory pressure (MEP), as well as diaphragm function including ultrasonographic measures of mobility and thickness changes during maximal inspiration and expiration were assessed in all participants. Additionally, the intensity of pain and disability were evaluated using a Visual Analog Scale and Neck Disability Index only in patients with CNP.

Results: Significant reductions of the FVC, FEV, MIP, and MEP were found in the CNP group compared to the CON group (p < 0.05). The diaphragm mobility and thickness changes were also significantly decreased in the CNP group than the CON group with medium effect sizes (p < 0.05). Only diaphragm thickness change was positively correlated with FVC, FEV, and MEP in patients with CNP. Furthermore, MEP showed the strongest contribution to diaphragm thickness change based on the regression analysis.

Conclusions: Impaired diaphragm function, respiratory muscle strength, and pulmonary function were observed in patients with CNP. Patients with smaller diaphragm thickness change had poorer pulmonary function and reduced maximal expiratory muscle strength. Diaphragm assessment and intervention may be considered in CNP management.