The optimal method for multilevel OPLL remains controversial. Anterior decompression and direct removal of the ossified posterior longitudinal ligament seems to be radical since the major pathomechanism of OPLL is anterior neurological compression. However, anterior approach becomes more technically demanding and has higher risk of complications such as spinal cord injury, dural tears, or hemorrhoea, with the increasing narrowing extent of ossification. Therefore, posterior decompression is the preferred choice of surgical treatment for multilevel cervical OPLL due to its a relatively safer procedure for severe canal stenosis or 3 or more levels of OPLL.
Laminoplasty (LP) and LF are considered as reliable and effective posterior approach, of which LF can increase spinal canal volume more effectively and has lower risk for kyphotic and OPLL progression than that with LP. However, LF may result in the backward shifting of the spinal cord which leads to the stretching of the nerve root. Therefore, it is difficult to relieve the radiculopathy only by LF approach. Up to our best knowledge, this study is first time to compare the clinical and radiological outcomes between LF and LFF for treating cervical OPLL with radicular pain of upper limbs. Our results demonstrated that the VAS for arm pain decreased more in LFF group than that in LF group, which evaluated radiculopathy caused by nerve root compression at the intervertebral foramina. For the potential mechanism, foraminal stenosis at the anterolateral corner of the spinal canal will put more compression on the corresponding nerve roots, which is one of the most common clinical courses of cervical radiculopathy. Tanaka et al reported that the intervertebral foramina is shaped like a funnel, where the entrance zone (medial half of the intervertebral foramen) was the narrowest part and exit zone (lateral half of the intervertebral foramen) was the widest. Therefore, when the OPLL occurs, compression of the nerve roots often occurred at the entrance zone of the intervertebral foramina. In posterior cervical foraminotomy, the nerve roots can be decompressed by resecting the medial half of the facet joints.
Foraminotomy is usually performed for one or two-level unilateral upper extremity radiculopathy due to posterolateral or foraminal disk herniation or disk/osteophyte complex. Theoretically, cervical instability would occur after the resection of facet joint following foraminotomy. However, this study showed no significant trend toward cervical kyphosis, angulation or slippage in LFF group compared with LF group. The possible reasons are as follows: (1) Zdeblick et al found segmental hypermobility of the cervical spine occurs if a foraminotomy involves resection of more than 50% of the facet. In this study, the posterior wall of intervertebral foramen was removed less than 50% to ensure the stability of the cervical spine for the patients in the LFF group. (2) Posterior fixation with local bone graft fusion was performed for each patient. This may provide stronger biomechanical strength and reduce post-laminectomy kyphosis and instability. Hence, we suggest that LFF could achieve good surgical results for OPLL with radiculopathy without segmental kyphosis or instability.
C5 nerve palsy is one of the most common complications after posterior cervical surgery . The intervertebral foramen tends to be narrower at C4 and C5 while the ossified posterior longitudinal ligament is often the thickest at the C5 segment . In addition, a high incidence of anterior osteophyte formation of the superior facet joint; and the posterior ramus proper is shortest at the C4 and C5 nerves. These features might lead to a “tethering effect” that stretches and compresses the C5 nerve root at the intervertebral foramen and radiculopathy pain. The lower occurrence of C5 nerve palsy in LFF group may be attributed to the foraminotomy of the C4-C5.
There are few limitations that are associated with this study. First, the retrospective nature of this study did not allow us to prospectively test our hypothesis. Moreover, the case series was limited based on a single center’s experience. The follow- up period was relatively short (mean 31.1 months). Future studies including prospective, randomized study with longer follow up period will be required to determine the durability of these findings.
In conclusion, LFF can provide satisfactory results in OPLL patients with myelopathy and radicular symptoms of upper limbs. LFF method can achieve satisfied clinical efficacy in improving neurological proper cases.