The effect of nucleotomy on facet joint loading - a porcine in vitro study.

Abstract

Lumbar facet joints have been cited as a possible origin of low-back pain. A relationship between disc height decrease and facet joint degeneration has been reported. Facet joint degeneration may also be triggered by nucleotomy, performed on prolapsed discs, which might change the natural load sharing between the anterior and posterior structures of the spine. In this study load bearing of the facet joints was compared between natural and nucleotomised spinal segments. Nine porcine lumbar motion segments were tested quasi-statically in ±1.5° extension-flexion under 700 N constant compression loading. The kinematics of the spinal segments were recorded as a response to the applied load. These kinematics were subsequently applied to the segments with the ligaments and disc sequentially removed and the reaction forces measured. This was performed in samples with and without nucleotomy. Comparison of the reaction forces allowed a direct comparison between healthy and pathological force transmission over the facet joints. Load sharing was related to the proportion of removed nucleus. The proportion of applied compression force supported by the facets increased from a mean of 40.7% (standard deviation, SD 10.0%) to 82.0% (SD 7.2%) after nucleotomy averaged over the entire extension-flexion regime. No correlation was observed between facet loading and the proportion of the nucleus removed. Increased facet loading after nucleotomy might cause greater cartilage wear, which may be related to facet joint degeneration. The independence of facet loading on the proportion of nucleus removed might be due to a complete pressure loss once the annulus is incised.