Kinematics of the cervical spine canal: changes with sagittal plane loads.
Spondylotic myelopathy is a result of decreased spinal canal space due to degeneration. The space also may change with physiological movements. The knowledge of the normal physiological changes is necessary for a better understanding of the clinical symptoms. Using a novel technique, we measured the changes in disk bulge, ligamentum flavum bulge, and anteroposterior canal diameter in response to tension-compression forces (up to 40 N each) and combined loading: 2 Nm of flexion or extension moment combined with 20 N compression force in five human cadaveric lower cervical spine specimens (C4-C7). From tension to compression, the average disk bulge changed 1.13 mm or 10.1% of the original canal diameter. The ligamentum flavum bulge changed 0.73 mm or 6.5% of the canal diameter. From flexion to extension the average disk bulb changed 1.16 mm or 10.8% of the canal diameter, whereas the ligamentum flavum bulge changed 2.68 mm or 24.3% of the canal diameter. Most of the changes in the bulges occurred with a small load application around the neutral position of the spine. The results of this study demonstrate that ligamentum flavum bulge can contribute significantly to canal encroachment in extension and that a flexed posture increases the sagittal diameter of the spinal canal.
Chen
I H
IH
Division of Neurosurgery, Veterans General Hospital, Taipei, Taiwan, Republic of China.
Vasavada
A
A
Panjabi
M M
MM
D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology; D006801:Humans; D017843:Ligamentum Flavum / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009038:Motion; D009333:Neck; D013115:Spinal Canal / Q000502:physiology*; D016474:Weight-Bearing