Posterior decompression surgeries such as cervical expansive laminoplasty (EL) or laminectomy with fusion (LF) have been widely performed to adequately decompress the spinal cord, although they cannot directly remove ossification of the posterior longitudinal ligament (OPLL) [2,7,11]. In patients with cervical myelopathy with OPLL in more than three segments, posterior decompression is more attractive than anterior decompression because this procedure can avoid the need for an anterior route or major strut graft-related problems, such as cerebrospinal fluid leakage, pseudoarthrosis, or graft dislodgment [26,31]. Posterior decompression surgeries were reported to diminish cervical lordosis preoperatively, and postoperative kyphotic deformities have been considered a source of pain and disability [15,21,22,29,32]. Therefore, it is important to evaluate the correlation between clinical outcomes and cervical sagittal alignment after posterior cervical decompression. There have been several studies about the clinical outcomes of patients who underwent cervical EL to treat cervical spondylotic myelopathy [6,13,16,30]. However, few studies have evaluated whether posterior decompression techniques such as EL or LF lead to cervical kyphosis and if these procedures could be used to achieve favorable clinical outcomes in patients with multilevel cervical OPLL [13].

We compared cervical EL with LF to treat cervical compressive myelopathy (CCM) in patients with OPLL in more than three levels. The purpose of this study was to comparatively assess cervical sagittal alignment and clinical outcomes, including patient-reported pain and quality of life, between patients who underwent cervical EL and those who underwent cervical LF.

Eighty-four patients (63 men and 21 women) were evaluated. The average follow-up period was 27.7 months (range: 24-48.8; 27.32 for cervical LF patients and 28.08 for cervical EL patients). The mean age at the time of surgery was 59.36 years (range: 38-82). The mean ages of the patients in the LF and EL groups were 65.81±7.99 and 54.52±9.57 years, respectively. The mean age was significantly higher in the LF group than that in the EL group (p<0.0001). There were more male than female patients.

The mixed type of OPLL was the most prevalent in patients who underwent surgery. The average number of operated-upon levels was 3.42 in the LF group and 3.04 in the EL group. OPLL in the upper cervical (C2) or cervicothoracic area (C7) was more frequently observed in LF patients (13/36, 36.11%) than in EL patients (2/48, 4.17%). The preoperative occupying ratio was higher in the EL group than that in the LF group, while the prevalence of preoperative signal intensity changes on T2-weighted MRIs was higher in the LF group than that in the EF group. However, there was no statistically significant difference between the two groups. There was no significant difference regarding the operation time (p=0.0529) and amount of bleeding (p=0.8838) between the two groups. The demographic characteristics of the patients in this study are summarized in Table 1.

We performed this study to comparatively assess the cervical sagittal alignment and clinical outcomes, including patient-reported pain and quality of life, of patients who underwent EL and those who underwent LF. Cervical EL and LF were effective surgical techniques to improve the clinical outcomes of patients with OPLL in more than three levels. Improvements in the patient-reported outcomes and HRQOL were nearly the same for the two techniques. Cervical EL can preserve cervical lordosis and improve range of motion and neck pain, more than cervical laminectomy with fusion can. Cervical sagittal imbalance after posterior decompression surgery was related to axial neck pain. In terms of cervical sagittal alignment, preserving the posterior muscular-ligament complex in subaxial lesions was more important than preserving this complex in the upper cervical or cervicothoracic junction.

Many studies reported postoperative kyphotic changes in the cervical spine after posterior decompression surgery [15,18,29]. The loss of cervical lordosis or kyphotic deformity after laminectomy alone was reported to occur in 33% to 70.7% of cases [21,22]. In a long-term follow-up study, progressive kyphosis resulted in late neurological deterioration [26]. The EL technique was developed to avoid the complications of laminectomy alone, such as post-laminectomy kyphosis and segmental instability through the resected laminae, and to restore the posterior musculo-ligamentous complex [5]. However, other investigators found a rate (35%) of kyphosis deformity following expansive laminoplasty that was comparable to the reported rates of kyphotic deformity following laminectomy alone [25]. Therefore, for patients with significant preoperative kyphosis or a high risk of developing kyphosis after laminectomy, cervical laminectomy alone or laminoplasty should be avoided because of postoperative kyphotic deformity, and posterior laminectomy with instrumented fusion is indicated [12]. Some authors insisted that posterior screw augmentation after laminectomy could prevent postoperative kyphotic deformities, axial pain, and instability [1,12]. Anakwenze et al. reported that post-laminectomy kyphosis might be prevented in patients undergoing posterior screw fusion [1].

The current study showed that posterior decompression surgery caused loss of the preoperative cervical lordotic angle. Patients who underwent cervical LF had a higher incidence of postoperative kyphosis and loss of preoperative lordosis than did those who underwent EL.

Sakai et al. reported that the cervical C2-7 SVA increased and the cervical lordotic angle decreased after cervical laminoplasty [26]. In this study, we found that the C2-7 SVA increased after posterior decompression surgery. Particularly, the cervical C2-7 SVA increased more in patients who underwent cervical LF than in those who underwent EL. As a result, supplementation with screw fixation after cervical laminectomy did not allow us to maintain the preoperative cervical alignment. When cervical laminectomy with fusion is performed, the posterior neck muscles should be dissected extensively to confirm the screw’s entry point, compared with the muscle exposure procedure used in EL. As the level of surgical invasion of the posterior muscular-ligament complex increases, cervical sagittal balance decreases. Despite the use of posterior screw augmentation to stabilize the bony and joint structures, the compensatory mechanism did not work after the musculo-ligamentous complex was damaged. To reduce damage to the musculo-ligamentous complex, Kim et al. developed myoarchitectonic spinolaminoplasty without damaging the attachments of the semispinalis cervicis, multifidus, interspinalis, and rotator muscles, which could prevent postoperative instability, decrease the incidence of postoperative kyphosis, and preserve the ROM of the C2-7 angle at 1 year after surgery [7,27].

Maintaining the paraspinal musculature at C2 and C7 is important during a posterior cervical operation because involvement of the C2 and C7 vertebrae might affect the postoperative cervical sagittal balance [24]. We compared original data (in which the C2 and C7 level was included) with subtracted data (in which the C2 and C7 was not included) to assess the risk of kyphosis. The change (Δ) in the C2-7 SVA was significantly increased in the cervical LF group compared with that in the EL group. Postoperatively, the LF group had large alterations in the C2-7 lordotic angle compared with the preoperative angle. These results were similar to the original results.

Sagittal imbalance in one region of the spine can influence other regions. Damaged parts of the posterior cervical spine would affect the compensatory mechanism of the upper cervical or subaxial spine [17]. In the present study, the C2-7 SVA was positively correlated with the T1 slope and C0-2 angle and negatively correlated with the C2-7 lordotic angle. The C2-7 lordotic angle was negatively correlated with the C0-2 angle, which is consistent with the results of previous studies [17,29]. However, compensation was not enough to maintain the preoperative cervical alignment and prevent kyphosis from occurring postoperatively.

ROM of the cervical spine was reported to be restricted by posterior decompression surgeries such as EL or LF [6,20]. Several reports have described reductions in ROM of 30% to 70% of the preoperative ROM after cervical laminoplasty [6,20]. Blizzard et al. reported that the ROM was reduced by up to 27.11% of the preoperative ROM after cervical LF [2]. In our study, patients in the cervical LF group experienced a significant reduction in ROM compared with those in the EL group. Cervical laminoplasty is advantageous because it can preserve the cervical spine’s motions compared with multilevel LF.

Cervical EL preserved cervical lordosis and improved ROM and neck pain, more than LF for treatment of more than 3 levels of cervical OPLL. Sagittal imbalance after posterior decompression surgery of the cervical spine was related to the clinical outcome, particularly axial neck pain. We found that the preservation of the posterior musculo-ligamentous complex in subaxial lesions was more important in maintaining the sagittal alignment than the complex in the upper cervical or cervicothoracic junction.