Abstract
Background: Neck muscles stabilise the head, but muscle tension imposes high compressive forces on the cervical spine. Little is known about which structures resist these high forces.
Purpose: To quantify compressive load-sharing within the cervical spine.
Methods: Seventeen cervical “motion segments” from cadavers aged 54–92 yr (mean 72 yr), were subjected to 200 N compression while positioned in simulated flexed and extended postures. Up to 5 Nm of bending was applied in various planes. Vertebral movements were recorded at 50 Hz using an optical MacReflex system. Tangent stiffness was calculated in compression and in bending. Load-sharing was evaluated from compressive stress measurements obtained by pulling a pressure transducer through the intervertebral disc. All measurements were repeated after 2 hr of creep loading at 150 N, and following sequential removal of the spinous process, apophyseal joints and uncovertebral joints.
Results: Most compression was resisted by the disc. However, creep increased compressive load-bearing by the neural arch, from 21% to 28% in flexed posture, and from 27% to 45% in extended posture, with most of this loading being resisted by the apophyseal joints. Uncovertebral joints resisted 10% of compression in extended posture, and 20% in flexed posture. Flexion and extension movements were resisted primarily by ligaments of the neural arch, and by the apophyseal joints, respectively, whereas lateral bending was resisted mostly by the apophyseal and uncovertebral joints.
Conclusion: Cervical apophyseal joints play a major role in compressive load-bearing, and also offer strong resistance to backwards and lateral bending. Uncovertebral joints primarily resist lateral bending.
Conflicts of Interest: None
Source of Funding: Scholarship from the Greek Government
Correspondence should be addressed to: SBPR at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE, England.
