Expansive open-door laminoplasty (EODL), developed and described by Hirabayashi et al in 1981 [1], has been widely used as a posterior decompression method for treating cervical spondylotic myelopathy (CSM), disc herniation, ossification of the posterior longitudinal ligament, and adjacent segment degeneration after anterior cervical decompression and fusion [2]. In the original method, the laminae are held open by stay sutures placed between the laminae and the muscles surrounding the facet joints [1], [2]. Although Hirabayashi et al's original method was simple and cost-effective, postoperative laminar closure is a major complication of this procedure [3], [4]. Therefore, several modified methods using autologous spinous processes [5], [6], anchoring screws [7], [8], plates [9], [10] [11] [12], or hydroxyapatite (HA) spacers [13] to hold the laminae open have been developed. These procedures can be divided into two groups according to the way the laminae are held together. In the first group, the anchor fixation group, the laminae are held together with strings, as in the original method, and suture anchor screws. In the second group, the spacer fixation group, the laminae are held together rigidly using spacers made by autologous spinous processes, metal plates, or HA blocks. Several studies have evaluated the differences between these two fixation methods [14]; however, their impact on the stability of the opened laminae is not well understood. Also, although cervical alignment is an important factor in EODL outcome [15], [16], [17], [18], to the best of our knowledge, there are no reports on the association between cervical alignment and efficacy of these fixation methods. The present study therefore aimed to (i) identify any differences in clinical and radiological outcomes between anchor and spacer fixation in regard to two cervical alignments: kyphosis and lordosis, and (ii) investigate the impact of laminar closure on clinical outcomes after EODL.
The present study was a retrospective analysis of prospectively collected data of patients who underwent EODL for CSM. The study protocol was approved by the Institutional Review Board of Osaka City University.Evidence & Methods
The authors present an interrupted time series comparing two types of fixation for open door laminoplasty in the treatment of patients with cervical kyphosis. At their center, suture anchors were used from 2001–2006 and hydroxyapatite spacers from 2007–2012.
The authors include 74 patients in the anchor group and 65 in the spacer group. Across cohorts, laminar closure greater than 20% was associated with inferior outcomes. The authors maintain superior outcomes were associated with spacer fixation as opposed to the use of suture anchors.
As an interrupted time series, there is the potential that the results could be confounded by evolving technical skills and surgical techniques as opposed to the type of fixation in and of itself. Nonetheless, for clinicians performing expansive open door laminoplasty in patients with cervical kyphosis, this study presents useful information in terms of selection of surgical fixation. Given the sample size as well as the potential for residual confounding, this study presents Level IV data.
—The Editors
The present study included 218 patients with CSM who underwent EODL at C3–C6 levels at our institution between 2001 and 2012 and were followed up for more than 2 years postoperatively. The patients were excluded if they had cervical disc herniation (n=15) or ossification of the posterior longitudinal ligament (n=29) and surgery performed at other levels (n=25). Finally, a total of 139 patients were included in the analysis (84 men, 45 women; mean age at surgery 64.2 years, age range 35–86 years). They were divided into two groups according to the method used to hold open the laminae. The anchor fixation group (Anchor group) consisted of 74 patients (296 laminae) who had undergone EODL with strings and anchor screws (Fig. 1). The spacer fixation group (Spacer group) consisted of 65 patients (260 laminae) who had undergone EODL with the HA spacer technique (Fig. 2). The operation used depended on the time period of the surgery: between 2001 and 2006, all patients underwent EODL with anchor screws, and between 2007 and 2012, all patients were treated with the HA spacer technique.
Anchor screws (Small Bone FASTak Suture Anchor; Arthrex Japan, Tokyo, Japan) and HA spacers (Boneceram P; Olympus Terumo Biomaterials Co., Ltd, Tokyo, Japan) were placed at each level. The day after surgery, all patients were allowed to sit up with a soft neck collar and, if possible, to stand and walk. Brace removal was allowed 1 week after surgery. All patients in both groups were then encouraged to start range of motion and isometric muscle strengthening exercises of the neck as early as possible. All patients followed the same postoperative clinical pathway, regardless of their fixation method. Patient demographics for both groups are shown in Table 1. There were no significant differences between the groups with respect to demographic data, including age and sex, and preoperative clinical status.
The Japanese Orthopaedic Association (JOA) score for cervical myelopathy (on a scale of 0=worst to 17 points=best) [19] was recorded preoperatively, and at 3 months, 1 year, and 2 years postoperatively by the patient's corresponding surgeon. The recovery rate was calculated using the formula established by Hirabayashi et al: (postoperative JOA score−preoperative JOA score)/(17−preoperative JOA score)×100 (%) [20].
Cervical alignment, considered in the present study as a radiographic parameter, was evaluated on plain radiographs in neutral position. Each patient's preoperative cervical alignment was categorized into one of four groups using a system proposed by Chiba et al [21] (Fig. 3). A total of 46.0% of the patients showed lordotic alignments and 24.5% showed kyphotic alignment of the cervical spine on preoperative plain radiographs (Table 1). Computed tomography (CT) was performed preoperatively, and at 1 week, 6 months, and 2 years postoperatively. After examining 1.0-mm axial CT scans, four reconstructed axial images that were parallel to each pedicle were obtained from each examination. The cross-sectional area (CSA) was measured at each level for each time period by a blinded researcher. The CSA was defined as the canal space area formed by the posterior wall of the vertebra, bilateral pedicle, and lamina. It was measured using computer software (ImageJ version 1.48, National Institutes of Health, Bethesda, MA, USA) (Fig. 4, Fig. 5).
To evaluate the impact of laminar closure after EODL on outcomes, we defined “the laminar closure group” as having a laminar closure rate reduction of over 20%. Laminar closure rate was calculated using this formula: 100—(Acquired CSA at 2 years postoperatively [CSA at 2 years postoperatively—CSA preoperatively]/acquired CSA at 1 week preoperatively [CSA at 1 week postoperatively—CSA preoperatively]×100) (%). We also compared the JOA scores between the closure and the non-closure groups.
Distribution of alignment of individual cervical segments was compared between the Spacer and the Anchor groups using the chi-square test. The JOA scores and the CSA values were compared between the two groups (Anchor group vs. Spacer group) and subgroups (kyphosis vs. lordosis alignment, closure vs. non-closure groups) using the Mann-Whitney U test. Statistical analysis was performed using SPSS (version 17; SPSS, Inc., Chicago, IL, USA). The level of significance was set at p<.05.
