A Biomechanical Study to Assess the Affect of Cervical Spine Posture on the Axial Load Bearing Ability

Introduction:

The cervical spine may lose its natural lordotic posture for many reasons (e.g. congenital, post–traumatic, postoperative, osteoporosis, postinfective, metabolic, and ankylosing spondylitis). Thus, it often assumes a straight or kyphotic posture. This alteration in cervical alignment obviously affects the location of the instantaneous axis of rotation (IAR) and the magnitude of bending moments. This contributes to eccentric spinal column loading and an exaggeration of the loads applied to the cervical spine. Therefore, the aim of this study was to assess the effect of cervical posture on the load bearing ability of the cervical spine.

Methods:

Twelve adult sheep cervical spines were tested. The specimens were randomly separated into two groups. Group I was fixed in a lordotic posture, and group 11 was fixed in a straight posture. Axial compressive loads were applied to both groups at a constant rate of 5cm/min. Load to failure, time to failure, piston displacement at failure, and failure modes were recorded. Statistical analyses were performed to detect differences between the groups.

Results:

There was no significant difference in load to failure values between the two groups (lordotic–3186N, straight–2584N). However, the time to failure and the piston displacement values for the straight spines were significantly less than for the lordotic spines, p<0.03. Additionally, the straight spines failed predominantly via ventral elements, whereas the lordotic spines predominantly failed dorsally.

Conclusions:

It is concluded that a loss of a lordosis increases the risk of injury to the cervical spine.