The Prediction Of Spinal Canal Expansion Following Open-door Cervical Laminoplasty And Double-door Cervical Laminoplasty

Open-door cervical laminoplasty (ODCL) and double-door cervical laminoplasty (DDCL) have become a popular treatment for patients with multilevel cervical compression myelopathy resulting from cervical spondylotic myelopathy (CSM), ossification of the posterior longitudinal ligament (OPLL), and/or cervical stenotic myelopathy. Excellent long-term results have been reported using this technique. In a DDCL, the spinous processes and laminae are centrally split with a burr or a threadwire saw (T-saw), and lateral hinges are created at the medial borders of the facet joints. The laminae are opened to both sides, and HA-Spacer are inserted to hold the laminae apart. In the open-door type, osteotomy is performed at one side of the lamina-facet junction, with troughs of the contralateral side at the facet-lamina junction leaving a thin rim of bone is created and acted as a hinge, elevation of the lamina, which is secured to the facet by sutures.Expansive open-door laminoplasty and double-door laminoplasty enlarge a stenotic cervical canal, while preserving the posterior elements of the spine and the activity and stability of the cervical spine, which expands the diameter and volume of the spinal canal by placing the laminae in a more posterior position, which alleviates posterior spinal cord compression. Because the spinal cord shifts backward, anterior compression is indirectly relieved, which allows for enhanced circulation.In expansive open-door laminoplasty and double-door laminoplasty, the laminoplasty opening size (LOS) or the laminoplasty opening angle (LOA) largely determines the magnitude of resulting canal expansion. On the one hand, if the laminoplasty opening size (LOS) or the laminoplasty opening angle (LOA) is smaller, inadequate increase in sagittal canal diameter (SCD) or canal volume does not relieve spinal cord compression and may lead to undesirable results after surgery; On the other hand, if the laminoplasty opening size (LOS) or the laminoplasty opening angle (LOA) is bigger, excessive opening of the lamina may cause the cord to migrate and extend posteriorly to an excessive degree, which can lead to the occurrence of postoperative C5 nerve root palsy. Tsuzuki et al show that traction, tethering, and/or kinking of the nerve root secondary to posterior shift of the spinal cord may result, which has been viewed as a main factor in postoperative C5 nerve root palsy. Hatta et al reported that the magnitude of postoperative posterior spinal cord shift is related to the occurrence of postoperative C5 nerve root palsy. Other authors have also expressed the idea that excessive opening of the lamina may lead to postoperative C5 nerve root palsy. Uematsu et al reported that the incidence of radiculopathy was significantly increased among patients with a large angle (≥60°) of the lamina after expansion or when the expansion was excessive. Wang et al pointed out that excessive opening also creates a wider epidural space and leads to the formation of more epidural scar tissues than normally expected.So in order to prevent postoperative spinal canal diameter and volume is insufficient or excessive, the laminoplasty opening size (LOS) or the laminoplasty opening angle (LOA) must be strictly controlled. However, the relationship between the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the amount of canal expansion has remained unclear.In this paper, the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the amount of canal expansion were act as the research object, The research content are as follows:(1) The formula, d=hx(sinβ/sina-1), describing the relationship between the angle of the opened lamina and increase of sagittal diameter was deduced by using trigonometry, a indicated preoperative lamina angle,β indicated the angle of the opened lamina, h indicated vertical distance which was from the split points before surgery to the wired of bilateral hinge gutters, d indicated the increase in sagittal diameter after double-door cervical laminoplasty, which was defined as the difference between post-surgical diameter and pre-surgical diameter. (2) To ratiocinate the formula of relationship between opening size of laminoplasty and the increment of sagittal vanal diameter following double. door cervical laminoplasty and to predict the increment of sagittal canal diameter and the cross sectional area of canal according to the opening size of laminoplasty. (3) To clarify the relationship between the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the increase in sagittal canal diameter (SCD) and to predict the amount of canal enlargement during open-door cervical laminoplasty (ODCL).Part one Relationship between the angle of the opened lamina and the increase of sagittal canal diameter following double-door cervical laminoplastyObjectives:To clarify the relationship between the angle of the opened amina and increase of sagittal canal diameter in double-door laminoplasty.Methods:The formula, d=h×(sinβ/sina-1), describing the relationship between the angle of the opened lamina and increase of sagittal diameter was deduced by using trigonometry, a indicated preoperative lamina angle, β indicated the angle of the opened lamina, h indicated vertical distance which was from the split points before surgery to the wired of bilateral hinge gutters, d indicated the increase in sagittal diameter after double-door cervical laminoplasty, which was defined as the difference between post-surgical diameter and pre-surgical diameter.32 patients with multilevel cervical spondylotic myelopathy underwent double-door cervical laminoplasty (C3-C7 in 20 patients and C3-C6 in 12 patients) in our institution between September 2010 and April 2014. At pre-operative and 1 week post-operative, axial CT was made at each pedicle level from C3 to C7 to measure the values of a, P, h by using software(picture archiving and communication system, PACS). The actual value of d was obtained by measuring the pre-and post-operative C3-C7 sagittal canal diameter by using PACS software. The computed value of d of C3-C7 in each patient was processing the formula d=h×(sinβ/sina-1). The differences between the data obtained by actual measurement and the data computed by the formula were compared by the paired t test. The correlation between the data obtained by actual measurement and computed by the formula was assessed by Pearson’s correlation coefficient. The accuracy of the formula was assessed.Results:The computed value of d at C3-C7 was 5.15±0.47mm, 5.39±0.47mm,5.22±0.37mm,5.25±0.25mm,4.35±0.35mm respectively; the actual measured value of d at C3-C7 using PACS measurement software was 5.17±0.40mm,5.43±0.52mm,5.27±0.44mm,5.29±0.28mm,4.38±0.33mm respectively. The data obtained by actual measurement and the data evaluated by the paired t test showed the value of t computed by the formula at C3-C7 was 0.42,0.68,1.58,1.38,1.11 respectively, which showed no significant difference(P>0.05). The value of r by Pearson correlation analysis computed by the formula at C3-C7 was 0.8953,0.8155,0.9159,0.7821,0.9238 respectively, which showed a very high degree of correlation(P<0.001).Conclusions:The formula accurately reveals the correlation between the angle of the opened lamina and the increase in sagittal canal diameter in double-door laminoplasty. Based on the angle of the opened lamina, increases in sagittal canal diameter following laminoplasty can be computed by using this formula.Part two Prediction of spinal canal expansion following double-door cervical laminoplastyObjective:To ratiocinate the formula of relationship between opening size of laminoplasty and the increment of sagittal vanal diameter following double. door cervical laminoplasty and to predict the increment of sagittal canal diameter and the cross sectional area of canal according to the opening size of laminoplasty.Methods:Twenty patients(12 males and 8 females)with multilevel cervical spondylotic myelopathy had undergone double-door cervical laminoplasty(C3-C7 in 9 patients and C3-C6 in 11 patients,89 segments)in our institution between September 2010 and January 2013. The formula describing the relationshin between the onening size of laminonlastv and the increment of sagittal diameter was deduced. The parameters of pre-and post-operative computed tomography scans of 20 patients who had undergone laminoplasty surgery were measured by picture archiving and communication system(PACS) software, and the increment of sagittal canal diameter and the cross sectional area of canal were predicted when the opening size of laminoplasty were 6 mm,8 mm,10 mm,12 mm,14 mm and 16 mm according to the formula.Results:Increment of sagittal canal diameter and canal area respectively showed significant difference in the same segment laminoplasty. Increment of sagittal canal diameter between various groups in the same segment(C3-C6) showed significant difference. Increment of sagittal canal diameter between the opening size of 14 mm and 16 mm in C7 laminoplasty showed no significant difference. Increment of sagittal canal diameter was increased steadily following C3-C7 double-door laminoplasty with opening sizes of 6 mm,8 mm,10 mm,12 mm,14mm and 16mm, but the increasing trend in sagittal canal diameter diminished gradually.Conclusion:Increment of sagittal canal diameter and Canal area following C3-C7 laminoplasty Can be accurately predicted according to the opening size of laminoplasty by this formula. The formula Can help operator to perform double-door cervical laminoplasty based on accurate individual laminoplasty opening size, which prevents inadequate or excessive opening.Part three Relationship between the laminoplasty opening size and the laminoplasty opening angle, increased sagittal canal diameter and the prediction of spinal canal expansion following open-door cervical laminoplastyObjective:To clarify the relationship between the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the increase in sagittal canal diameter (SCD) and to predict the amount of canal enlargement according to the laminoplasty opening size (LOS) during open-door cervical laminoplasty (ODCL).Methods:Thirty-six patients with multilevel cervical spondylotic myelopathy had underwent C3-C7 open-door laminoplasty between June 2012 and November 2013. The pre-and post-operative morphologic changes in the cervical spinal canal were studied, a formula describing the relationship between laminoplasty opening size, laminoplasty opening angle and the increase in sagittal canal diameter in open-door laminoplasty was deduced by applicating of trigonometric function. A validation study was undertaken in order to assess the accuracy of the formula. Increase in sagittal canal diameter and laminoplasty opening angle, increase in canal area was predictived by the formula, when C3-C7 laminoplasty opening angle was 8,10,12,14,16mm respectively.Results:When C3-C7 laminoplasty opening angles were 8-16mm, the magnitude of increase in the sagittal canal diameter and laminoplasty opening angle, increase in canal area were increased in a proportional manner. When C3-C7 laminoplasty opening size were equivalent, the magnitude of increase in sagittal canal diameter and laminoplasty opening size, increase in canal area differed throughout the cervical region. When C3-C7 laminoplasty opening size were 10mm, the magnitude of increase in sagittal canal diameter was ≥4.1mm, and the magnitude of increase in canal area in C3-C6 were> 88mm2, and the magnitude of increase in canal area in C7 were> 80mm2; When C3-C7 laminoplasty opening size were 12mm, the magnitude of increase in sagittal canal diameter was ≥5.2mm, and the magnitude of increase in canal area in C3-C6 were> 104mm2, and the magnitude of increase in canal area in C7 were> 94mm2.Conclusion:Formula accurately showed the relationship between the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the increase in sagittal canal diameter (SCD) achieved by open-door cervical laminoplasty (ODCL). The amount of canal enlargement following open-door cervical laminoplasty (ODCL) could be predicted according to the laminoplasty opening size (LOS) by the formula, which may allow preoperative determination of the optimal individual size of the opening needed to establish adequate space for the spinal cord.