Surgical outcome and associated factors of "cap uncovering" en-bloc removal of the spinal canal′s posterior wall surgery for single-level thoracic ossification of ligamentum flavum

English Keywords:Thoracic ossification of ligament flavum  Surgical outcome  Associated factors

English Abstract:

  【Abstract】 Objectives: To assess the efficacy of "cap uncovering" en-bloc removal of the spinal canal′s posterior wall and the prognostic associated factors for thoracic myelopathy caused by single-level thoracic ossification of ligamentum flavum(OLF). Methods: Patients with thoracic myelopathy induced by OLF underwent en-bloc removal of the spinal canal′s posterior wall termed as the "cap uncovering" technique between February 2005 and May 2013 and were retrospectively reviewed. Exclusion criteria were as follows: other tandem spinal diseases, OLF of more than one segment, cases caused by injury. A total of 44 cases was included. Among these 44 cases, there were 23 males and 21 females with a mean age of 56.8 years(range 24-76 years). Segmental distributions was as follows: 20 cases of T10/11, 14 cases of T11/12, 4 cases of T9/10, 2 cases of T8/9, 2 cases of T2/3, 1 case of T4/5, 1 case of T1/2. The modified JOA score and the recovery rate were used to measure the outcomes. The mean JOA score was 6.68±1.76 preoperatively. The follow-up results were classified according to the recovery rate and then the rate of excellent or good was calculated. The degree of spinal canal occupation was graded on axial T2 weighted MRI. The type of OLF and intramedullary high signal intensity on T2-weighted MRI was also evaluated. The spinal canal diameters were measured at the maximally stenosed level on axial and sagittal CT. The spinal canal diameter on axial CT was measured at three sites: the midline of the canal, the boundary of the canal, and the paramedian point. The canal diameter occupied ratio and the cross-section area occupied ratio were calculated. Sato′s classification and the growth position of OLF were observed on CT. Correlations between the surgical outcomes and various factors[age, gender, preoprative JOA scores, preoprative duration, unilateral/bilateral ossification, leakage of cerebrospinal fluid(CSF), the growth position, operative segment, high intensity signal in the spinal cord, shape on the sgittal MRI, dural ossification, Sato′s classification, degree of spinal canal occupation on axial MRI, canal diameter occupied ratio on sagittal and axial CT, the cross-section area occupied ratio] were analyzed through univariate linear correlation analysis, and multiple linear regression analysis was then used. Results: The mean follow-up period of these 44 cases was 40 months(range, 10-99 months). At final follow-up, the JOA score increased to 5-11(mean 8.84±1.83), and the JOA recovery rate was -20%-100%(mean 58.17%). Surgical outcomes were as follows: 13 excellent, 20 good, 9 fair and 2 poor. The rate of excellent or good was 75.0%(33/44). The univariate linear correlation analysis showed that preoprative JOA scores, unilateral/bilateral ossification, dural ossification, the growth position, high intensity signal in the spinal cord, Sato′s classification and degree of spinal canal occupation on axial MRI, canal diameter occupied ratio on sagittal CT, canal diameter occupied ratio on axial CT(boundary), canal diameter occupied ratio on axial CT(paramedian), the cross-section area occupied ratio might be correlated to JOA recovery rate(P＜0.05). Age, gender, preoprative duration, leakage of CSF, operative segment, shape on the sgittal MRI, canal diameter occupied ratio on axial CT(midline) were not associated with JOA recovery rate(P＞0.05). The multiple linear regression analysis revealed that only canal diameter occupied ratio(paramedian) on axial CT and preoprative JOA scores significantly correlated with recovery rate(P＜0.05). Unilateral/bilateral ossification, dural ossification, the growth position, high intensity signal in the spinal cord, degree of spinal canal occupation on axial MRI, Sato′s classification and other occupied index had no significant effect on surgical outcome(P＞0.05). Conclusions: "Cap uncovering" en-bloc removal of the spinal canal′s posterior wall surgery is effective for single-level thoracic OLF. Canal diameter occupied ratio(paramedian) on axial CT and preoperative JOA scores have significant effect on surgical outcome.