Dynamic Cervical Radiographs in Patients with Hirayama Disease: An Unneglectable Factor on the Choice of Surgery Options

OBJECTIVE: To evaluate the cervical spine alignment and range of motion (ROM) of neck flexion in patients with Hirayama disease. METHODS: Fifty male patients were included, with dynamic radiographs and magnetic resonance imaging (MRI) analyzed retrospectively. The Cobb angles for the entire cervical spine (C2-C7) and each level (C2/3-C6/7) were measured, and the neck flexion ROM was defined as the neutral Cobb angle minus the flexion Cobb angle. Paired t tests and Wilcoxon signed-rank tests were used to compare the Cobb angles and ROM between radiographs and MK RESULTS: The neutral and flexion Cobb angles decreased from C2/3 to C5/6 but increased at C6/7 on radiographs and MRI. The neutral Cobb angle of C2-C7 from radiographs was significantly larger than that seen on MRI (5.27 degrees vs. 3,26 degrees; P < 0.0001). Neck flexion ROM seen with MRI tended to be lower than those of corresponding levels on radiographs. The ROM of C2-C7, C3/4, and C6/7 on radiographs was significantly larger than that seen with MRI (37.86 degrees vs. 26.59 degrees, P < 0.0001; 7.46 degrees vs. 5.10 degrees, P = 0.0071; and 10.45 degrees vs. 7.03 degrees, P = 0.0023, respectively). For the lower cervical levels, the largest and second largest ROM were seen in C5/6 and C6/7 on the radiographs but C5/6 and C4/5 on MRI CONCLUSIONS: The cervical spine alignment and neck flexion ROM in Hirayama disease differed between radiographs and MRI. Both imaging techniques should be examined comprehensively when planning an operation.