To establish the surgical strategy for cervical myelopathy of patients with LSDs, the evaluation of upper cervical level could be critical. The main stenotic cervical level of the patients with MPS was C1 due to the hypoplasticity of the C1 lamina in our series; some types of LSDs are often accompanied by atlantoaxial instability 12,13. When atlantoaxial instability is evident, occipito-cervical fixation, rather than cervical laminoplasty, with C1 laminectomy should be indicated. Otherwise, the cervical myelopathy of patients with LSDs could be safely treated with laminoplasty with or without C1 posterior arch resection. In addition, the current study demonstrated that the atlantoaxial stability and the improvement of symptoms could be maintained at an average of 5 years postoperatively. The spinal cord compression at the upper cervical level could affect not only the movement of the whole extremity, but also the respiratory function. As the main cause of death of MPS is respiratory dysfunction, we strongly recommend surgically treating patients with LSDs at an earlier stage of myelopathy, such as only numbness as a symptom of myelopathy.
Regarding the surgical method of laminoplasty, open-door and double-door laminoplasties are two major methods 26,27. The distinct features of LSDs from those of adult CSM/OPLL include the small characteristic shape of the spine, presence of accumulation in the extradural space, and non-requirement of extradural resection of the accumulation. Based on our institution’s surgical strategy, open-door laminoplasty is employed to treat adult patients with CSM/OPLL owing to sufficient space available for spacers. However, for patients with LSDs, it is challenging to put spacers and treat extradural materials with one-side opening of the laminae due to the hypertrophic deformity of the laminae (Fig. 1). In addition, age could be an important factor for selecting the surgical method. We excluded two patients, a 3-year-old boy with MPS II and a 1-year-old girl with ML type III, who underwent total laminectomy of the cervical spine from the current series, as their spines were too small to undergo laminoplasty.
One of the advantages of laminoplasty is ROM preservation and kyphotic change prevention. In this series, the postoperative cervical ROM was significantly decreased compared with the preoperative ROM, which is in accordance with the previous report analyzing patients with adult CSM/OPLL 21–23. However, in our series, the cervical ROM at an average of 5 years postoperatively was still 36° on average. As the cervical ROM is one of important factors for achieving a high QOL and for preventing dysphagia 28, we recommend avoiding fusion surgery as much as possible. In addition, although patients with LSDs still have a much shorter life expectancy than the normal population, it could be prolonged owing to the development of patient care and interventions, such as ERT and HSCT 9–11. The prolonged life induces degenerative changes in the joint and spine, which may require additional surgical interventions. It is now significant to consider and introduce surgical methods that can prevent degenerative changes, such as adjacent disc degeneration observed after an ordinal spine surgery.
Another advantage of cervical laminoplasty compared with cervical laminectomy is the low incidence of kyphotic change postoperatively. Machino et al. reported that nearly 8% of patients are predisposed to cervical kyphosis 29. Moreover, McGirt et al. reported that laminoplasty for the resection of intramedullary spinal cord tumor in children was associated with a decreased incidence of progressive spinal deformity requiring fusion compared with laminectomy 30. In accordance with such studies, current results showed no significant change in the C2-7 angle at an average of 5 years postoperatively.
The disadvantage of the cervical laminoplasty is the limited indication for pediatric patients with LSDs, as their laminar size is too small to undergo laminoplasty and to allow placement of a spacer. In addition, although there are some types of spacers for cervical laminoplasty, all of them were designed for adult patients, and no spacers that could fit small pediatric patients were noted. Indeed, during the study period, we have two patients in whom laminectomy was performed, rather than laminoplasty, owing to the small laminae.
Several limitations to the present study need to be addressed. Firstly, the retrospective nature of the study makes it difficult to exclude bias, especially regarding the referral for a certain postoperative rehabilitation program and the particular surgical techniques utilized. Secondly, the number of patients is relatively small and the disease type is inconsistent. In addition, this study is a case series, not a comparative study. All these limitations prevent us from making a definitive conclusion regarding the safety and clinical outcomes of surgical treatment for patients with LSDs. However, the possibility for spine physicians to treat such patients is significantly increasing owing to the current advancement in medical treatment. Therefore, we believe that our data could be useful for spine physicians when treating cervical myelopathy in patients with LSDs.