Range of motion after 1, 2, and 3 level cervical disc arthroplasty.

Background: Motion of a solid body involves translation and rotation. Few investigations examine the isolated translational and rotational components associated with disc arthroplasty devices. This study investigates single- and multi-level cervical disc arthroplasty with respect to index and adjacent level range of motion. The investigators hypothesized that single- and multilevel cervical disc replacement will lead to comparable or improved motion at implanted and adjacent levels. Methods: Seven human cervical spines from C2 to C7 were subjected to displacement-controlled loading in flexion, extension, and lateral bending under intact, 1-Level (C5-C6), 2-Level (C5-C6, C6-C7) and 3-Level (C5-C6, C6-C7, C4-C5) conditions. 3D motions sensors were mounted at C4, C5, and C6. Motion data for translations and rotations at each level for each surgical condition and loading mode were compared to intact conditions. Results: 1-Level: The index surgery resulted in statistically increased translations in extension and lateral bending at all levels with statistically increased translation observed in flexion in the superior and inferior levels. In rotation, the index surgeries decreased rotation under flexion, with remaining levels not statistically different to intact conditions. 2-Level: A device placed inferiorly resulted in statistically increased translations at all levels in extension with statistically increased translations superior and inferior to the index level in flexion. Lateral bending resulted in increased nonsignificant translations. Rotations were elevated or comparable to the intact level for all loading. 3-Level: Translations were statistically increased for all levels in all loading modes while rotations were elevated or were comparable to the intact level for all loading modes and levels. Conclusions: Micromotion sensors permitted monitoring and recording of small magnitude angulations and translations using a loading mechanism that did not over constrain cervical segmental motion. Multilevel cervical disc arthroplasty yielded comparable or increased overall motion at the index and adjacent levels compared to intact conditions.

Solvents and malignancy.

Despite the number of substances that fall under the rubric of solvent, only a few are considered to be potential carcinogens. The purpose of this article is to provide readers with an overview of the cancer data that exist for a number of solvents currently in commercial use. These solvents include chloroform, carbon tetrachloride, methylene chloride (dichloromethane) trichloroethylene, tetrachloroethylene (perchloroethylene), and 1,4-dioxane. Although benzene also would be considered a solvent, the data concerning its carcinogenic potential are presented in another article in this issue and are not discussed in this article.