Clinical outcomes of laminoplasty for patients with lysosomal storage disease including mucopolysaccharidosis and mucolipidoses: a retrospective cohort study

We conducted a retrospective cohort study to report the midterm clinical and radiological outcomes of patients with LSDs after cervical laminoplasty. Written informed consent was obtained from all participants. The study protocol was approved by the Institutional Review Board of our institution (No. 3170). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party directly or indirectly related to the subject of this manuscript. All procedures were performed in accordance with the Declaration of Helsinki and the Ethical Guidelines for Medical and Health Research Involving Human Subjects in Japan.

From December 2011 to March 2018, six patients with MPS (type I: 1, II: 3, VII: 1) or MLS type III underwent laminoplasty with or without C1 laminectomy for cervical myelopathy by a single surgeon in our orthopedic surgery department. All patients underwent MRI, CT, and dynamic cervical radiography preoperatively to evaluate the level of stenosis and segmental instability. One patient with atlantoaxial instability, defined as an ADI of > 3 mm measured on preoperative neutral radiography or CT images, was treated with fusion surgery and excluded from the current case series. Moreover, two patients aged ˂ 3 years were excluded as their laminae were too small to undergo laminoplasty; thus, they were treated with laminectomy instead. General conditions and airway status were carefully evaluated by a pediatrician and an anesthesiologist before the induction of general anesthesia. All patients required fiberoptic intubation due to airway management difficulty related to the narrowing of the oropharynx and airway or trismus.

Surgical methods of cervical laminoplasty are broadly divided into two types of osteotomy method to open the laminar: open-door type and double-door type [26, 27]. In the open-door type, an osteotomy is performed at one side of the lamina-facet junction. Meanwhile, in the double-door type, an osteotomy is performed at the central spinous process and lamina. Although each method has its advantages and disadvantages, its common purpose is to expand the narrowed spinal canal and afford the opportunity of reactivating the spinal cord [33]. In this series, we adopted the double-door laminoplasty due to the spacer size (see Discussion section).

Patients were carefully positioned prone while keeping the neck in a neutral position after fixing the head with a MAYFIELD fixator. Skull bone thickness was checked by CT scan before the MAYFIELD fixator was applied. For patients aged < 10 years or those with a thin skull, we used a halo vest instead of using the MAYFIELD fixator [34]. Intraoperative neurophysiological monitoring is recommended for the spinal surgery of LSDs [35]. A midline incision from the occipital to the T1 lamina process is created. Paraspinal muscles, including the semispinalis, are detached with a tiny bone chip and exposed laterally from the laminae. A midline cut is made; then, gutters are made on both sides inside the facet joint to leave a thin inner cortex to make hinges using a high-speed drill. This process is completed from C2 to C7. The dorsal wall of the foramen magnum is partially resected as necessary. As for C1, the posterior arch is resected until the lateral edge of the dura mater is visualized, followed by the subtotal resection of the atlanto-occipital membrane. The LSD-related accumulated materials are located in the extra-dural space between the dura mater and yellow ligaments. Hard and elastic accumulated materials on the dura mater should be carefully resected and removed to achieve adequate decompression. Durotomy or duroplasty is not required because the accumulation was outside the dura mater, although they are recommended in previous reports [34, 36]. After confirming dural pulsation, hydroxyapatite spacers are set to bridge the opened laminae on both sides. A drainage tube is placed after repeated saline irrigation. Postoperative care includes obligatory intensive care monitoring because of the high risk of respiratory/cardiac insufficiency in LSDs. Patients are mobilized freely without a brace because their neck lengths are too short to make adequate cervical collars. Patients are followed up clinically with MRI and functional cervical radiography.

Clinical evaluations were performed preoperatively, at 3 months, 1 year, and 2 years postoperatively, and at the final follow-up. The cJOA score, a physician-assessed score used to evaluate the severity of cervical myelopathy, was determined [37]. The VAS for upper extremity numbness was recorded as the component of the patient-oriented score [38]. The VAS scores were evaluated using a 100-mm long horizontal line with extremes indicated as “no symptoms: 0” and “worst symptoms imaginable: 100”. The patients marked the point on the line representing their perception of their current state.

Radiographic parameters were evaluated using preoperative and postoperative cervical plain radiographs. Each parameter was defined as follows: C2-C7 lordotic angle, the lordotic angle between the tangent lines of the lower endplates of C2 and lower endplates of the C7 vertebral body; ROM, defined as the difference in C2-C7 lordotic angles between the maximum flexion and extension positions [39]; ADI, the horizontal distance between the anterior arch of the atlas and the dens of the axis, and ADI was evaluated using weight-bearing radiographs at neutral, flexion, and extension positions and preoperative CT image at neutral position; and ⊿ADI, the differences in ADI on weight-bearing radiographs between flexion and extension positions. Observers reviewed the images and measured the parameters using computer software (Synapse; Fujifilm, Tokyo, Japan). The bone union of the gutter was evaluated using the CT scan taken within 12 months postoperatively, and the signal change of the spinal cord was evaluated using T2-weighted images of preoperative and postoperative MRI [40].

Average values were presented as average ± 1.0 standard deviation or range from minimum to maximum values. The values of the continuous variables, such as ROM, C2–C7 angle, ADI, and ⊿ADI, obtained preoperatively and at the final follow-up were compared using a paired t-test. In addition, the cJOA and VAS scores of upper extremity numbness obtained preoperatively and at the final follow-up were compared using a paired t-test. All analyses were performed using SPSS software (version 23; SPSS, Chicago, IL). A p-value < 0.05 was considered statistically significant.