Common surgical procedures for patients with cervical spondylotic myelopathy include anterior spinal fusion, cervical disc replacement, laminectomy and laminoplasty.1-5 Although laminoplasty has achieved promising results, previous long-term studies have shown some issues including axial neck pain, canal restenosis, nerve root palsy, reduced movement of the cervical spine and loss of cervical lordotic alignment.1-5 The paper by Motosuneya et al showed a favorable long term outcome (> 10 years follow-up) by tension-band laminoplasty in the treatment of patients with myelopathy due to cervical spondylosis (CSM) or ossification of the posterior longitudinal ligament (OPLL). Their Japanese Orthopaedic Association (JOA) scores improved with a final 52.1 ± 24.6% recovery rate at the expense of decreased range of movement (ROM) (32.8 ± 12.3o vs 16.2 ± 12.3 o) and axial pain (69%). The Ishihara curve index of cervical spine decreased slightly (5.6 ± 6.7 vs 4.6 ± 5.3). Patients with OPLL had a less satisfactory outcome. This article certainly shows the rationale behind preserving the entire spino-ligamentous complex. It is a good surgical option for patients requiring decompression at several levels, but not recommended for those with disc lesions and posterior spur formation, disc herniation with a normal spine canal, or severe kyphosis.
Decreased ROM in this paper is expected and related to the bony union needed at the hinge and around the spacers. The requirement for a Minerva jacket for three weeks followed by a soft cervical collar for three months, as well as compromised muscle strength due to detached paravertebral muscles bilaterally from the laminae may compromise the ROM further. It is worth noting that the loss of movement post-operatively was greater in OPLL patients (30.0 ± 13.4o vs 8.6 ± 7.1 o). The relative contribution of OPLL progression or muscle weakness warrant further investigation. However, only movement in the extension/flexion plane of the cervical spine was assessed.
Some types of laminoplasty have shown a significant decrease in cervical lordosis after surgery in 42% to 87% of the patients. 3-6 This study by Motosuneya et al showed satisfactory post-operative preservation of spinal curvature. The mean pre- and post-operative index was 7.8 ± 7.0 and 6.2 ± 6.1 for CSM patients and 2.9 ± 5.3 and 2.6 ± 3.2 for OPLL patients, respectively. The difference after operatopm was not statistically significant in either group. The authors showed that preserving the entire spino-ligamentous complex and avoiding reclosure of the canal by using spacers may contribute to favorable long-term radiographical results.
The high incidence of axial pain around the neck and shoulder after laminoplasty is high (6-% to 80%).1,7 Less post-operative axial neck pain occurred when C7 spinous process was preserved in the laminoplasty.7 This study by Motosuneya et al showed 69% of patients having post-operative axial pain. This was more frequent in patients with OPLL, those undergoing laminoplasty at several levels, and those with a reduced ROM. In most patients who have axial pain soon after surgery it may last for > 10 years. Some patients may develop late-onset axial pain or deformity following a satisfactory operation with progression of disease, either restensosis or progressive deterioration of the neurological deficit.8
A previous study of the prognostic factors showed that the number of segments, localised marginal pattern, rostral location of signal intensity changes with a high signal change in the T2 image and a low spinal cord compression ratio in cervical spondylotic myelopathy patients may indicate a poor prognosis when treated by laminoplasty.9 Other studies showed that pre-operative JOA score, age at the time of surgery, and the length of time between the onset of symptoms and surgery affected the clinical results.10
The major aim when undertaking laminoplasty is to provide adequate space for the spinal cord. However, plain radiographs cannot show the potential compromise by soft tissues such as ligmentum flavum, and the PLL. Computed tomography (CT) or magnetic resonance imaging (MRI) would be of value. MRI may reveal atrophy of the spinal cord.8 The MRI T2 image signal intensity ratio and clinical manifestation may help predict the prognosis after surgery for cervical spondylotic myelopathy.11
Finally, the procedure described in this paper is an asymmetrical open-door laminoplasty that may incur late muscle imbalance and weakness. They may be related to spinal alignment, ROM, and axial pain. Thus electrophysiological studies and assessment of muscle strength in these patients may be helpful. Muscle volume may be assessed by MRI and this is another important factor contributing to muscle strength. Such studies of risk factors may be helpful.
By Professor Rong-Sen Yang,
National Taiwan University & Hospital,
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