OBJECTIVE: To develop an analytical model of the lumbar motion segment and to determine the following under the application of flexion physiological loads: (1) the force displacement relationships of the lumbar motion segment; (2) the forces in the ligaments, disc, and facet joints; (3) the strains in the ligaments; and (4) the effect of the transection of the ligaments.

 

DESIGN: Computer modeling.

 

SETTING: Spinal Ergonomics and Joint Research Laboratory at The National College of Chiropractic.

 

PROCEDURE: Computer model simulation of external loads and simulation of ligament transection.

 

MEASURES: The following parameters were predicted in flexion by means of a computer model: (1) the load-displacement relationships of the lumbar motion segment; (2) the loads in the ligaments, disc and facet joints; (3) the strains in the ligaments; and (4) the effect of the transection of the ligaments.

 

RESULTS: The load sharing among different ligaments predicted by this model under flexion load suggests that the supraspinous ligament carries the greatest load, followed by the yellow ligament, capsular ligament, intertransverse ligament, and interspinous ligament. The ligament strains indicate that the supraspinous ligament undergoes the maximum increase in length, followed by the interspinous ligament, yellow ligament, capsular ligament, and intertransverse ligament. The transection of ligaments increased the flexibility of the joint, the strains on the rest of the ligaments, the loads on all of the rest of the ligaments, as well as the moment on the disc, but does not significantly affect the compressive load on the disc.

 

CONCLUSIONS: The analytical model predicts results similar to the experimental data on cadaver motion segments reported in the literature under flexion moment loads.

 

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