Biomechanics of the lumbar spine--an experimental stress studies.

In order to estimate the strength of normal and spondylolytic vertebrae, vertebrae with laminectomy, anterior fusion, posterior fusion, and postero-lateral fusion, (vertebral) models were produced using acrylic resin (a composite of vinyl ester resin 70% and soft polyester resin 30%) for vertebrae and sponge rubber for intervertebral disc. Compression, flexion, and torsion tests were carried out on the various types of lumbar vertebral models with the following results. 1. Normal models are low in mechanical strength but highly flexible and resilient. 2. Anterior fusion models are mechanically stronger but inflexible. 3. Postero-lateral fusion models and posterior fusion models provide increased strength and retain some flexibility. 4. Laminectomy and spondylolysis models are the weaker than normal's in all mechanical strength tests.