Impacts of postoperative changes of segmental mobility on neurological improvement after laminoplasty for cervical ossification of the posterior longitudinal ligament.

ABSTRACT: Several studies have demonstrated that the dynamic factor at the mobile segment affects the severity of myelopathy in patients with cervical ossification of the posterior longitudinal ligament (C-OPLL), and posterior decompression supplemented with posterior instrumented fusion at the mobile segment provides good neurological improvement. However, there have been few reports of changes in range of motion at the mobile segment (segmental ROM) after laminoplasty (LP). The aim of this study was thus to retrospectively investigate changes in segmental ROM after LP and the impacts of these changes on neurological improvement in patients with C-OPLL.A total of 51 consecutive patients who underwent LP for C-OPLL since May 2010 and were followed for at least 2 years after surgery were included in this study. Neurological status was assessed using the Japanese Orthopaedic Association (JOA) score before surgery and at 2-year follow-up. Segmental ROM at the responsible level for myelopathy was measured preoperatively and at 2-year follow-up using lateral flexion-extension radiographs of the cervical spine.The mean JOA score improved significantly from 10.7 points preoperatively to 13.5 points at 2 years after surgery (mean recovery rate, 45.0%). The mean segmental ROM decreased significantly from 6.5 degrees before surgery to 3.2 degrees at 2 years after surgery. In the good clinical outcome group (recovery rate of the JOA score ≥50%; n = 22), the mean segmental ROM decreased significantly from 5.8 degrees preoperatively to 3.0 degrees postoperatively. It also decreased significantly from 7.1 degrees to 3.4 degrees in the poor clinical outcome group (recovery rate of the JOA score <50%; n = 29).This study showed that segmental ROM was stabilized after LP in most patients with C-OPLL. Neither preoperative nor postoperative segmental ROM showed significant differences between the good and poor clinical outcome groups and neither a postoperative increase nor decrease of segmental ROM significantly affected the recovery rate of the JOA score.

Introduction

Cervical ossification of the posterior longitudinal ligament (C-OPLL) is a common disease leading to myelopathy, especially in East Asian countries.[ Although laminoplasty (LP) is widely used and provides good surgical outcomes for most patients with progressive myelopathy due to C-OPLL,[ some patients have poor clinical outcomes. Several studies have demonstrated that the dynamic factor at the mobile segment affects the severity of myelopathy in patients with C-OPLL,[ and posterior decompression supplemented with posterior instrumented fusion at the mobile segment provides good neurological improvement.[ However, there have been few reports of changes in range of motion at the mobile segment (segmental ROM) after LP. The aim of this study was thus to retrospectively investigate changes in segmental ROM after LP and the impacts of these changes on neurological improvement in patients with C-OPLL.

Materials and methods

Patients

All patients with C-OPLL at our institute have been treated using LP, with the exception of those with cervical kyphosis ≥15 degrees and a single-level anterior lesion without a narrow spinal canal. This retrospective study included 51 consecutive patients (41 males and 10 females) who underwent LP for C-OPLL since May 2010 and were followed for at least 2 years after surgery. Their mean age at the time of surgery was 67.9 years (range, 40–89 years). Two surgeons performed only bilateral open-door LP in 30 patients. Four other surgeons performed only unilateral open-door LP in 21 patients. For the first 2 weeks after surgery, all patients wore a soft collar. The protocol of this study was approved by the institutional review board of the hospital, and written, informed consent was obtained from all participants.

Surgical methods

Under general anesthesia, the patients were placed in the prone position. After exposure of the posterior elements, the spinous processes were resected at the base. In bilateral open-door LP, the laminae were cut in half using a high-speed drill. Bone gutters at the medial margin of the facet were created bilaterally to serve as hinges. The remaining halves of the laminae were elevated, and autologous bone grafts and/or hydroxyapatite spacers were installed (Fig. 1). In unilateral open-door LP, bone gutters at the medial margin of the facet were created bilaterally, and the drilling of the gutter on the left side was completed. The laminae were elevated, and hydroxyapatite spacers were installed (Fig. 2).

Figure 1

Computed tomography (CT) and magnetic resonance imaging (MRI) of bilateral open-door laminoplasty. (A) Preoperative CT. (B) CT image after surgery. (C) Preoperative (D) MRI, MRI 4 months after surgery.

Figure 2

Computed tomography (CT) and magnetic resonance imaging (MRI) of unilateral open-door laminoplasty. (A) Preoperative CT. (B) CT image after surgery. (C) Preoperative MRI. (D) MRI 1 year after surgery.

Clinical and radiological evaluations

Neurological status was assessed using the Japanese Orthopaedic Association (JOA) score before surgery and at 2-year follow-up. The recovery rate of the JOA score was calculated by the following formula: The recovery rate of the JOA score (%) = (Postoperative JOA score - Preoperative JOA score) / (17 - Preoperative JOA score) × 100. History of diabetes mellitus, operation time, estimated intraoperative blood loss, and surgery-related complications were also examined.

Segmental ROM at the responsible level for myelopathy and C2–7 ROM were measured preoperatively and at 2-year follow-up using lateral flexion-extension radiographs of the cervical spine, as the angle formed by 2 lines drawn parallel to the posterior margin of the vertebral bodies (Fig. 3). The responsible level for myelopathy was comprehensively determined by clinical examinations and the level of the T2 high-intensity lesion on magnetic resonance imaging. Neurological status was assessed by one of the authors, and radiological measurements were performed by the first author.

Figure 3

Range of motion measured as the change in angle in the flexion and extension positions (A) (B).

Statistical analysis

The paired t-test, Wilcoxon signed-rank test, the unpaired t-test, and the Mann–Whitney U-test were used for statistical analysis with StatMate IV (ATMS Co., Ltd., Tokyo, Japan), as appropriate. Values of P < .05 were considered significant.

Results

The level of decompression was C3-C4 in 1 patient, C3-C5 in 1 patient, C3-C6 in 13 patients, C3-C7 in 30 patients, C3-T1 in 2 patients, C3-T2 in 2 patients, and C4-C7 in 2 patients. The overall mean JOA score improved significantly from 10.7 points before surgery to 13.5 points at 2 years after surgery (mean recovery rate of the JOA score, 45.0%). None of the patients showed neurological deterioration after surgery. The mean operation time and estimated blood loss were 118 ± 29 minutes and 112 ± 128 mL, respectively. No intraoperative complications occurred. C5 palsy occurred in 1 patient 2 days after surgery, but recovered fully within 1 week.

The mean segmental ROM decreased significantly from 6.5 degrees before surgery to 3.2 degrees at 2 years after surgery, and the mean C2–7 ROM also decreased significantly from 24.4 degrees to 17.4 degrees. Table 1 summarizes the clinical and radiological features of patients in the good clinical outcome group (recovery rate of the JOA score ≥50%; n = 22) and the poor clinical outcome group (recovery rate of the JOA score <50%; n = 29). In the good clinical outcome group, the mean segmental ROM decreased significantly from 5.8 degrees preoperatively to 3.0 degrees postoperatively. It also decreased significantly from 7.1 degrees to 3.4 degrees in the poor clinical outcome group. Neither preoperative nor postoperative segmental ROM showed significant differences between the 2 groups. On the other hand, the mean recovery rate was 57.4% in the postoperative increase of segmental ROM group (n = 9) and 42.3% in the postoperative decrease group (n = 42); the difference was not significant (Table 2).

Table 1

Comparison between good and poor clinical outcome groups.

Variable	Good outcome (n = 22)	Poor outcome (n = 29)	P value
Mean age at the time of surgery	64.8 ± 11.6	70.2 ± 9.9	.080
Male	26	15	.12
Diabetes mellitus rate	6/22 (27.3%)	7/29 (24.1%)	.80
Operation time	120 ± 29.8	117 ± 28.5	.35
Estimated blood loss	88 ± 78	131 ± 154.	.10
Mean preop JOA score	10.6 ± 2.6	10.7 ± 1.6	.77
Mean postop JOA score	14.9 ± 1.7	12.4 ± 1.4	<.001
Mean recovery rate (%)	70.4 ± 19.2	25.7 ± 15.1	<.001
Mean preop C2–7 ROM	23.5 ± 11.0	25.0 ± 11.2	.64
Mean postop C2–7 ROM	19.1 ± 10.2	16.1 ± 11.5	.33
Mean preop segmental ROM	5.8 ± 4.4	7.1 ± 4.5	.30
Mean postop segmental ROM	3.0 ± 3.1∗	3.4 ± 3.3∗	.59

Table 2

Comparison between postoperative increase and decrease of segmental ROM.

Variable	Postoperative increase of segmental ROM (n = 9)	Postoperative decrease of segmental ROM (n = 42)	P value
Mean age at the time of surgery	66.9 ± 10.3	68.1 ± 11.1	.77
Male	7	34	.81
Mean preop JOA score	9.7 ± 2.4	10.9 ± 1.9	.14
Mean postop JOA score	13.9 ± 2.0	13.4 ± 2.0	.48
Mean recovery rate (%)	57.4 ± 26.4	42.3 ± 27.9	.16
Mean preop C2–7 ROM	16.2 ± 8.0	26.1 ± 10.8	.0065
Mean postop C2–7 ROM	16.9 ± 12.9	17.5 ± 10.7	.89
Mean preop segmental ROM	2.1 ± 2.9	7.5 ± 4.2	.00061
Mean postop segmental ROM	4.8 ± 4.3	2.9 ± 2.9	.24

Discussion

In the present study, segmental ROM decreased significantly after LP. To the best of our knowledge, only 1 report in the English literature examined preoperative and postoperative segmental ROM after LP in patients with C-OPLL.[ The authors showed that segmental ROM at the responsible level for myelopathy decreased from 9.0 degrees before surgery to 5.5 degrees after surgery. Regarding cervical ROM, it is well-known that C2–7 ROM decreases after LP. Hyun et al reported that the mean C2–7 ROM decreased significantly by 31.6% at 2 years after LP compared with the baseline, and they suggested that laminar autofusion was one of the reasons for the loss of ROM.[ Fujimori et al mentioned that the loss of ROM was caused mainly by a decrease in the extension angle and speculated that the restriction of extension had occurred partly as a result of impingement of the opened lamina.[ Other studies also reported that C2–7 ROM could have decreased resulting from unexpected fusion of facet joints and scarring of the cervical extension muscles.[ Because of these reasons, segmental ROM, as well as C2–7 ROM, may be decreased after LP.

The indication for posterior instrumented fusion in patients with C-OPLL remains controversial. Several studies showed that the dynamic factor contributed to the development of myelopathy in patients with C-OPLL. A biomechanical analysis demonstrated that, under static compression, the stress distribution increased with the ROM at the responsible level.[Miyazaki et al showed that preoperative segmental ROM was negatively correlated with the JOA score recovery rate after LP.[ Chen et al reported that the preoperative JOA score was lower with segmental instability than without segmental instability, and lateral mass screw fixation at unstable levels provided better clinical outcomes than LP alone.[

In the present study, the overall mean JOA score was significantly improved postoperatively. Segmental ROM decreased significantly both in the good clinical outcome group and the poor clinical outcome group, and neither preoperative nor postoperative segmental ROM showed significant differences between the 2 groups. In addition, neither a postoperative increase nor decrease of segmental ROM significantly affected the recovery rate. Because segmental ROM decreased in most patients after LP without posterior fixation, and postoperative segmental ROM was not related to neurological outcomes, supplementary posterior instrumented fusion at the mobile segment may not be necessary.

The limitations of the present study include the relatively small number of patients. Recently, the K-line, which is a line between the midpoints of the spinal canal at C2 and C7, is widely used for determining the surgical strategy for C-OPLL. The K-line is defined as (-) when the peak OPLL exceeds the K-line, and K-line (-) is considered a factor related to a poor surgical outcome.[ However, only 13 patients were classified as K-line (-) in the present study. In addition, there was no posterior fixation group in this study. Another limitation was the short duration of the postoperative follow-up. Furthermore, neck pain scores were not evaluated. A further long-term follow-up study with a larger sample size is needed.

Conclusions

Segmental ROM decreased significantly after LP. Neither preoperative nor postoperative segmental ROM showed significant differences between the good clinical outcome group and the poor clinical outcome group. In addition, neither a postoperative increase nor decrease of segmental ROM significantly affected the recovery rate. Supplementary posterior instrumented fusion at the mobile segment may not be necessary in patients with C-OPLL.

Author contributions

Conceptualization: Hironobu Sakaura.

Data curation: Atsunori Ohnishi.

Formal analysis: Atsunori Ohnishi.

Supervision: Hironobu Sakaura, Yamagishi Akira, Tetsuo Ohwada.

Writing – original draft: Atsunori Ohnishi.

Writing – review & editing: Hironobu Sakaura.