Effect of the Decompressive Extent on the Magnitude of the Spinal Cord Shift after Expansive Open-door Laminoplasty

Abstract

A retrospective study to analyze the effect of decompressive extent on the posterior shift of spinal cord after expansive open-door laminoplasty (ELAP). To investigate the effect of decompressive extent on cord shift distance after ELAP, and determine the morphologic limitations of posterior approach when the cervical alignment is lordotic or straight. It is still controversial on the effect of space available for spinal cord at the level cephalad to the decompression with cord shift. Moreover, there is less understanding regarding the significance of decompressive extent of laminoplasty in relation to spinal cord shift and clinical outcome. Preoperative and postoperative MRIs of 76 patients with a straight or lordotic cervical spine who had undergone cervical laminoplasty were reviewed and evaluated retrospectively. Radiographic parameters including cervical sagittal alignment, space available at the level cephalad, the thickness of compressive mass, and the average anterior subarachnoid space were measured. Laminoplasty was performed from C1 to C7 in 11 cases (CI group), C2 to C7 in 30 cases (CII group), and C3 to C7 in 35 cases (CIII group). According to whether the anterior indirect decompression was adequate or not, CII and CIII groups were further divided into two subgroups, the noncontact group in which the spinal cord was completely separated from the anterior compressive mass after laminoplasty, and the contact group in which there was residual cord compression after laminoplasty. The recovery rate that based on the Japanese Orthopedic Association score was calculated for each patient. There were statistically significant differences in the average anterior subarachnoid space among CI, CII, and CIII groups (P < 0.05);the average anterior subarachnoid space was the largest in CI group, and the smallest in CIII group. The space available at the level cephalad had strong sigmoidal correlation with cord postoperative shift in CIII group (R = 0.91). A higher neurologic recovery rate (69% ± 20% vs. 29% ± 11%; P < 0.05) in the noncontact group after surgery than in the contact group, with a similar follow-up period. The posterior decompression extent is a main factor affecting cord shift distance after laminoplasty in the context of a straightened or lordotic cervical curvature. The space available at the levels cephalad is a key factor to predict cord shift distance in laminoplasty from C3 to C7. Neurologic recovery rate after ELAP is affected by whether the anterior indirect decompression was adequate or not.