The shift of segmental contribution ratio in patients with herniated disc during cervical lateral bending

BACKGROUND Abnormal intervertebral movements of spine have been reported to be associated with trauma and pathological conditions. The importance of objective spinal motion imaging assessment in the frontal plane was frequently underestimated. The clinical evaluation of the segmental motion contribution could be useful for detecting the motion pattern of individual vertebrae. Therefore the purpose of this study was to investigate the shift of segmental contribution ratio in patients with herniated disc during cervical lateral bending to provide additional insights to cervical biomechanics. METHODS A total of 92 subjects (46 healthy adult subjects and 46 disc-herniated patients) were enrolled in this case-control study. The motion images during cervical lateral bending movements were digitized using a precise image protocol to analyze the intervertebral motion and contribution. RESULTS Our results showed that the intervertebral angulation during cervical lateral bending for the C2/3 to C6/7 segments were 7.66°±2.37°, 8.37°±2.11°, 8.91°±3.22°, 7.19°±2.29°, 6.31°±2.11°, respectively for the healthy subjects. For the patients with herniated disc, the intervertebral angulation for the C2/3 to C6/7 segments were 6.87°±1.67°, 7.83°±1.79°, 7.73°±2.71°, 5.13°±2.05°, 4.80°±1.93°, respectively. There were significant angulation and translational differences between healthy subjects and the patients with herniated disc in the C5/6 and C6/7 segments (P=0.001-0.029). The segmental contributions of the individual vertebral segments were further analyzed. There was a significant increase in segmental contribution ratio of C3/4 (P=0.048), while a significant decrease in contribution ratio of C5/6 (P=0.037) was observed in the patients with herniated disc. Our results indicated that the segmental contribution shifted toward the middle cervical spine in the patients with herniated disc. CONCLUSIONS The segmental contributions of cervical spine during lateral bending movement were first described based on the validated radiographic protocol. The detection of the shift of segmental contribution ratio could be helpful for the diagnosis the motion abnormality resulted from the disc or, facet pathologies, and arthritic changes of cervical spine.