Multi-body simulations on flexion and extension for cervical segments with muscle contraction

Abstract

The neck is an important body part that links the head and chest sections. However, very few analyses of cervical movement derived from muscle contractions have been conducted with numerical simulation. This study aimed to construct a multi-body model of the neck comprising the bones, muscles, and ligaments (including the intervertebral disc) and to apply flexion and extension movements to analyze the behavior of each cervical segment. We created bone models (including cervical vertebrae C1-C7) from X-ray computed tomography (CT) images of the upper half of the human body. Each bone model was bound by 17 types of ligaments constructed as 51 wire models. We set six types of muscles as the protagonists for neck flexion and 12 types for the neck extension. Muscle strength was defined with a parallel contraction element model and an elastic element model. The intervertebral discs represented five spring models with repulsion characteristics on compression and attraction characteristics on extension. The neck section could flex up to 38.1° and extend up to 61.0° with contraction in the flexor and extensor models. The maximum cervical segment angles on flexion and extension were measured at C0-C1 and C4-C5, and their contribution rates were 20.7% and 19.3%, respectively. Each cervical segment angle when flexing and extending closely matched the experimental results measured by other studies. The centers of rotation for cervical segments from C2-C3 to C4-C5 on maximum flexion were different from those in previous experimental result. This may be because of the settings pertaining to the interspinous ligament, nuchal ligament and supraspinous ligament. On the other hand, our results for maximum extension were consistent with past experimental result. An improved neck model will allow the analysis of cervical segment movement through the joint restrictions based on damage to the ligaments and muscles or arthrodesis when flexing and extending.

Keywords

• center of rotation
• cervical segment motion
• ct images
• dynamic simulation
• flexion and extension
• kinematics
• musculoskeletal system
• neck