Objective To investigate the correlation between subaxial cervical spine instability and cervical spondylotic sympathetic symptoms as well as the difference of cervical spondylotic subaxial instability between male and female patients. Methods We analyzed retrospectively 318 surgical cases of cervical spondylosis treated at Department of Orthopedic Surgery of Peking Union Medical College Hospital between July 2003 and December 2007. All cases were divided into group A without sympathetic symptoms （n=284） and group B with sympathetic symptoms （n=34）. Angular and horizontal translation values between two adjacent vertebral bodies from C2 to C7 were measured separately on hyperflexion and hyperextension lateral cervical spine radiographs. Fisher’s exact test was used to evaluate the correlation between subaxial cervical instability and sympathetic symptoms. Intragroup correlation between patient gender and subaxial cervical instability was also evaluated. Results Subaxial instability incidences in groups A and B were 21.8% （62/284） and 55.9% （19/34）

respectively. Statistical analysis indicated a definite correlation between subaxial cervical instability and sympathetic symptoms （P=0.000）. Among patients without sympathetic symptoms

subaxial instability incidences were 21.4% （37/173） in males and 22.5% （25/111） in females

respectively （P=0.883）. While among patients with sympathetic symptoms

subaxial instability incidences were 27.3% （3/11） in males and 69.6% （16/23） in females

respectively

indicating significant difference （P=0.030）. Subaxial instability was most commonly seen at C4-C5 intervertebral space in sympathetic cervical spondylosis patients. Conclusions High correlation exists between subaxial cervical spine instability and cervical spondylotic sympathetic symptoms

especially in female patients. Hyperextension and hyperflexion radiographs of cervical spine are important to assess sympathetic cervical spondylotic subaxial instability.