BIOMECHANICAL ALTERATIONS INDUCED BY MULTILEVEL CERVICAL LAMINECTOMY

Study Design. The biomechanical responses of the cervical spine undergoing a combined loading vector within the physiologic range and after multilevel laminectomy were evaluated. The experimental conditions were designed to more closely replicate the typical clinical situation than accomplished by previous studies. Objective. To determine the biomechanical alterations induced by multilevel cervical spine laminectomy using an in vitro model. Summary of Background Data. The few previous laboratory studies concerned with the effects of cervical laminectomy have generally indicated a lack of significant change in strength or flexibility induced by the procedure. These studies have been limited by a variety of factors, including the use of pure loads under low physiologic loading conditions, restriction of the laminectomy to one or two segments, and the evaluation of a small number of specimens. Methods Twelve fresh human cadaver cervical spine segments from C2-T1 were used. A custom-designed fixture was attached to the proximal end of the specimen to apply a flexion-compression load. Retroreflective targets were positioned in bony landmarks for localized temporal kinematics of the entire cervical column. Testing was performed before (intact) and after a three-level (C4-C6) laminectomy, and data regarding the force, displacement, and kinematics at every level of the column were obtained. Results. The mean stiffness of the intact cervical column was significantly greater (P < 0.05) than the mean stiffness for the laminectomized specimen. Sagittal rotation angle had significant (P < 0.05) differences between intact (3.6 degrees) and laminectomy (8.0 degrees). Laminectomized speciments consistently responded with higher rotations compared with the intact specimen at every cervical spine level. Conclusion, Multilevel cervical laminectomy induces significant increases in total column flexibility associated with increased segmental flexural sagittal rotations. These motion changes were generalized with a tendency to show the greatest change at the lower level of laminectomy. Such biomechanical changes may constitute part of the underlying basis for failure of laminectomy to offer sustained good therapeutic results of the myelopathy associated with cervical stenosis and cervical spondyloarthropathy.