Treatment of OPLL and OLF of the Cervical Spine:
Long-Term Results
Yoshiharu Kawaguchi
Introduction
Surgical intervention is indicated in patients with severe symptoms, mainly cervical myelopathy, due to ossifi ca- tion of the posterior longitudinal ligament (OPLL).
This chapter reviews the long-term surgical outcomes in patients with cervical OPLL. Operative methods are divided into two procedures: anterior decompression surgery and posterior decompression surgery. Com- bined surgery—anterior and posterior decompres- sion—is occasionally carried out. Most surgeons consider the patient’s general condition, the type of OPLL, and the severity of the cervical myelopathy to determine the surgical choice. Hirabayashi and Toyama reported indications for the particular operative method (Table 1) [1]. In general, anterior surgery is performed in patients with fewer than one- or two-level OPLL lesions, whereas posterior surgery is done in patients with lesions at more than three levels. Therefore, posterior surgery is predominantly performed for OPLL. In our clinic, the choice of surgery was anterior in 10%–20% of the patients with OPLL and posterior in 80%–90%.
There are numerous reviews regarding postoperative outcomes of anterior and posterior surgery for treating patients with OPLL. Several reports have described the long-term surgical results for each procedure.
Posterior Surgery
Decompression is achieved by shifting the spinal cord during posterior surgery, such as with cervical laminec- tomy or laminoplasty. Expansive cervical laminoplasty has become the standard procedure for patients with myelopathy attributable to multilevel spinal stenosis caused by OPLL or cervical spondylosis. Cervical lami- nectomy was carried out until the early 1980s. The
results of cervical laminectomy were poor during the early period, but the results improved after adding use of the high-speed air drill. Several reports have described the long-term results of cervical laminectomy in patients with OPLL. Kato et al. reported long-term results (mean follow-up 14.1 years) of laminectomy for cervical myelopathy due to OPLL [2]. They evaluated the surgi- cal results according to the Japanese Orthopaedic Asso- ciation (JOA) score in 44 patients and the neurological recovery rate by Hirabayashi’s method [recovery rate = (postoperative score − preoperative score) × 100 ÷ 17 (total score) − preoperative score], which was 44.2%
after 1 year, 42.9% after 5 years and 32.8% at the last follow-up. Neurological deterioration was observed in 10% of the patients; and the most frequent cause of deterioration was trauma due to a fall followed by thoracic ossifi cation of the ligamentum fl avum (OLF).
It has been reported that cervical laminectomy causes instability and progressive kyphotic deformity of the cervical spine, particularly when there has been extensive removal of the facet joints. A laminectomy membrane in the spinal canal is one of the causes of unfavorable sequelae after removal of the laminae.
Furthermore, possible trauma to the spinal cord might result from a lack of posterior bony protection. In an effort to eliminate these adverse effects of laminectomy, expansive cervical laminoplasty was developed during the 1970s. A variety of cervical laminoplasty techniques have been described since the reports of expansive Z- laminoplasty by Ohyama, Hattori, and Kawai in 1972.
The various types of expansive laminoplasty fall into two groups: unilateral hinge type and bilateral hinge type. In our institution, en bloc laminoplasty (the uni- lateral hinge type) proposed by Itoh and Tsuji has been used since 1982. During all of the cervical laminoplasty procedures, the laminae are preserved, but the size of the spinal canal is expanded because the freed or partially freed ends of the laminae are positioned more posteriorly. This cervical laminoplasty technique is applied in patients with myelopathy due to OPLL as well as in patients with cervical spondylotic myelopathy (CSM). Long-term results of expansive cervical lamino- plasty for the treatment of OPLL have been recently reported [3–7]. For the overall results, neurological Department of Orthopaedic Surgery, Toyama Medical and
Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan
219
increase in the thickness of the ossifi cation. Other causes of the cervical lesions are trauma and spinal cord atrophy [4]. Ossifi ed lesions in the thoracic spine, such as thoracic OLF and OPLL, are also frequent causes of neurological deterioration [6,7]. The thoracic ossifi ed lesions are frequently associated with cervical OPLL.
Patients with OPLL characteristically have general ossifi cation in the spinal ligaments [9]. Thus, the pres- ence of thoracic and lumbar ossifi ed lesions should be checked with caution. Lumbar spinal stenosis, cerebral infarction, peripheral neuropathy, and osteoarthritis in the lower extremities are considered noncervical lesions leading to late deterioration [6].
It has been reported that several factors infl uence the fi nal operative results (Table 4). Preoperative, intra- operative, and postoperative factors can be considered.
Age >60 years, long preoperative duration (>1 year), trauma onset, and severe myelopathy are poor prognos- tic preoperative general factors. These factors might be related to irreversible changes in spinal cord function. It has been reported that the cross-sectional area of the spinal cord affects postoperative recovery, but the rate of thickening of OPLL in the spinal canal does not.
Kyphosis of the cervical alignment and a small area of spinal cord have been suggested as preoperative local factors resulting in a poor prognosis in patients with OPLL or CSM because it may be diffi cult to achieve local shift of the spinal cord by laminoplasty in patients with cervical kyphosis. In several clinical studies, no differ- ence in postoperative recovery was found between patients with preoperative cervical lordosis and patients with kyphosis [5–7]. Iwasaki et al. stated that the post- operative kyphotic change of the cervical alignment is not related to the surgical outcome [5]. Therefore, we believe that laminoplasty is not contraindicated in patients with slight or mild kyphosis preoperatively. The recovery of patients with diabetes mellitus is signifi - cantly poorer than that in patients without diabetes mellitus [10]. It is controversial whether the type of OPLL, the area of ossifi ed lesions in the spinal canal, and the change of signal intensity shown by magnetic resononance imaging (MRI) are related to the postop- erative recovery. Several reports have noted that high intensity in the spinal cord on T2-weighted MRI indi- cates spinal cord damage and is a poor prognostic factor;
however, there are some objections to these opinions.
Table 1. Indications for operative methods Anterior decompression and fusion Favorable indications
Segmental type, fewer than three spinal bodies Localized type
Combined with disc hernia Relative indications
Mushroom type on CT, fewer than three disk levels, continuous or mixed type
Posterior decompression (expansive open-door laminoplasty)
Widely extended continuous or mixed type Multisegmental type, more than four spinal bodies Combined with spinal canal stenosis
Aged patients
Scheduled two-stage combined operation Favorable indications
Combined with spinal canal stenosis and locally dominant ossifi cation
Relative indications
Widely extended ossifi cation and locally dominant ossifi cation
Multisegmental type with more than four spinal bodies combined with spinal canal stenosis; locally kyphotic deformity
CT, computed tomography From Hirabayashi and Toyama [1]
Table 2. Long-term outcomes (>10 years) after cervical laminoplasty
Author Year No. of Method Follow-up length Maximum recovery Final recovery
patients (years) rate (%) rate (%)
Seichi et al. [4] 2001 32 Bilateral hinge type 12.8 48.8 39
Iwasaki et al. [5] 2002 64 Unilateral hinge type 12.2 64± 28 60± 32 Kawaguchi et al. [6] 2003 49 Unilateral hinge type 13.2 59.1± 30.9 49.8± 37.8 Ogawa et al. [7] 2004 72 Unilateral hinge type 12.9 63.1± 4.5 41.3± 7.5 recovery as evaluated by JOA score occurred rapidly
within a year and continued until 5 years after various cervical laminoplasties. The recovery rate after cervical laminoplasty for patients with OPLL has been reported to be approximately 50%–60% at the maximum score (Table 2).
The postoperative recovery is maintained through- out the long-term follow-up after cervical laminoplasty;
however it has been reported that 15%–30% of the patients show late neurological deterioration after surgery (Table 3) [3–7]. The types of late neurological deterioration are divided into cervical lesions and non- cervical lesions. Regarding the cervical lesions, progres- sion of cervical OPLL is one of the most common causes of deterioration [3–8]. In our previous study, 73%
(33/45 cases) of the patients had progression of OPLL over 10 years after en bloc laminoplasty [8]. Three patients had neurological deterioration following an
Regarding intraoperative factors, various cervical laminoplasty techniques have been established as safe procedures for decompressing the cervical spinal cord, although they have the potential risk of intraoperative complications related to spinal nerve injury. Traumatic damage to nerve roots or to the spinal cord might bring about motor palsy of the upper extremities or spinal cord injury. Postoperative hematoma develops acutely or sometimes subacutely after surgery, resulting in neurological deterioration. Matsumoto et al. estimated the prevalence of postoperative hematoma to be 0.6%
in their institution [11].
Postoperative intramedullary changes of the spinal cord are sometimes observed on MRI, even though effi - cient decompression of the spinal cord is achieved after surgery. These changes occasionally accompany post- operative neurological deterioration. The pathology of the lesions is yet unknown, but intramedullary edema, myelomalacia, and cavitation due to reperfusion of the spinal cord after decompression are suspected.
Segmental motor paralysis, mainly involving the C5 segment, has frequently been described. Chiba et al.
noted that the incidence of segmental paralysis has been reported to lie between 4% and 13% of surgical cases after a variety of cervical laminoplasties [12]. The precise etiology remains unknown, although surgical trauma, a tethering effect of the nerve root, impinge- ment of the stretched nerve root, and reperfusion injury of the spinal cord are thought to cause this paralysis.
The prognosis of this complication is usually good, with spontaneous regression within 1–2 years, although in some cases this unfavorable condition continues during the long-term follow-up. Therefore, preventive mea- sures and therapeutic strategies should be established.
Postoperative factors related to late neurological deterioration during follow-up have been previously described.
Although the neurological outcome is improved after expansive cervical laminoplasty, some patients com- plain of axial symptoms, such as pain or stiffness in the posterior neck and shoulder and limited neck range of motion (ROM) following surgery [13]. Evaluation of these complaints is not included in the JOA score, which was established in 1994. The complaints are observed not only in patients with OPLL but also in those with CSM after cervical laminoplasty. To date, there have been no data showing a difference in the incidence of axial symptoms for OPLL and CSM. Several articles have described the possible mechanisms of the axial symptoms, with some researchers believing that the axial pain is derived from damaged neck muscle and facet joints. Limited neck ROM might be due to inter- laminar fusion after laminoplasty. In fact, it has been reported that neck ROM was reduced to 30%–60% of the preoperative level after laminoplasty [14]. To prevent these unwanted effects, several intraoperative and postoperative measures have been developed. Min- imally invasive procedures, such as skip laminectomy and C7-preserving laminoplasty, have been reported.
Furthermore, early exercise of the posterior neck muscle is recommended after cervical laminoplasty.
Despite numerous articles describing the clinical rel- evance of expansive cervical laminoplasty for treatment of cervical myelopathy, Ratliff and Cooper published a critical review of cervical laminoplasty [15]. They stated that there is no benefi t to laminoplasty over laminec- tomy in adults in terms of spinal alignment, incidence of kyphotic deformity, or surgical outcome. Previous data suggested that the results of laminoplasty regard- ing clinical outcome, cervical alignment, and preserva- tion of spinal alignment are, at best, equal to those of laminectomy and fusion. However, many Japanese spine surgeons believe that cervical laminoplasty is superior to laminectomy based on their clinical experi- ence. Future research should focus on a prospective comparison of clinical and radiological outcomes of cervical laminoplasty versus laminectomy with long- term follow-up to confi rm the relevance of cervical laminoplasty over laminectomy.
Anterior Surgery
The anterior approach is essential for the surgical treat- ment of patients with OPLL because OPLL exists ante- riorly in the spinal canal. Anterior decompression is indicated in patients with massive OPLL (>6–7 mm thick) or a canal-narrowing ratio of more than 50%.
However, the anterior approach may require a long Table 3. Neurological deterioration after cervical
laminoplasty
Author Incidence of No. of patients
deterioration (%)
Seichi et al. [4] 31 10/32
Iwasaki et al. [5] 16 10/64
Kawaguchi et al. [6] 29 13/49
Ogawa et al. [7] 15 11/72
Table 4. Poor prognostic factors after cervical laminoplasty Age > 60 years old
Duration of preoperative symptoms > 1 year Trauma onset
Severe preoperative myelopathy Cross-sectional area of the spinal cord Preoperative kyphosis of cervical alignment
High intensity on T2-weighted magnetic resonance imaging Complication of diabetes mellitus
operating time, and it is sometimes associated with massive bleeding during surgery. Furthermore, cere- brospinal fl uid (CSF) leak is often encountered during removal of the OPLL because ossifi cation of the dura matter is frequently ossifi ed in OPLL patients. Yamaura, a pioneer in developing the anterior approach, initially attempted to remove OPLL directly. Later, however, he developed the anterior fl oating method for decom- pressing the spinal cord to minimize surgical interven- tion and the risk of massive bleeding and CSF leak.
With this technique the ossifi cation is gradually thinned with an air drill; the ossifi ed lesion is then transected at the cranial, caudal, and lateral edges, and the OPLL fl oats [16]. This results in decompression of the spinal cord. Matsuoka et al., at the same institution, reported long-term outcomes (mean follow-up 13.0 years) of the anterior fl oating method [17]. In their report, the surgi- cal indication was for OPLL located between C2 and T3.
It is diffi cult to approach above C2 and below T3. A halo vest is generally used after surgery. The maximum recovery rate evaluated by the JOA score was 74%, and it was 56.4% at the fi nal follow-up. The fi nal results are infl uenced by such factors as the interval from the onset of the initial symptoms, the minimum area of the spinal cord, the preoperative JOA score, and the age at opera- tion and at fi nal follow-up. There was no correlation with the canal narrowing ratio or the thickness of the OPLL.
Late neurological deterioration was found in 20%
(16/80) of the patients. The causes of deterioration were inappropriate decompression, OPLL progression, the presence of other ossifi ed lesions in the spinal canal, and disease in the adjacent segment. There was no evi- dence of signifi cant recurrent OPLL within the margins of a prior decompression in their study.
Future Research
Despite previous reports regarding the long-term surgi- cal outcomes after treatment of patients with OPLL, there are several points to be resolved in the near future.
First, the operative indications have not yet been well established. Most spine surgeons agree that surgery is considered for patients with severe symptoms of myelopathy. However, there have been no reports con- cerning the operative indications in patients with mild myelopathy or regarding preventive surgery for asymp- tomatic patients whose OPLL is extensive; these patients are expected to develop severe myelopathy, although at the time of diagnosis the OPLL is not causing any symp- toms. Matsunaga and Sakou, in an analysis of a large number of the patients (>300), reported that 20% of the patients who did not have myelopathy at the initial stage developed it during follow-up [18]. The important
factors in the development of myelopathy were the amount of OPLL compromising the spinal canal and the degree of ROM of the cervical segments. Based on their results, they concluded that prophylactic surgery for nonmyelopathic patients with OPLL may not be necessary. In contrast, the patients whose myelopathy was due to trauma tended to have a poor prognosis.
Therefore, proper operative indications should be established based on the characteristics of each patient with OPLL.
Second, there is no consensus for choosing anterior or posterior surgery for a patient. Each procedure has its own advantages and disadvantages. The surgical results seem to be similar for the two procedures, but to date there has been no comparative study. The anterior approach is technically demanding, and long- term postoperative treatment with a halo vest is required. Although the merits described above are reported for anterior surgery, the posterior approach is often indicated in patients with OPLL that extends over three vertebral levels. Goto and Kita reported the results of anterior and posterior surgery for patients with OPLL [19]. Tani et al. compared anterior micro- surgical decompression and posterior laminoplasty for extensive OPLL, with its thickness exceeding 50% of the bony canal diameter [20]. They stated that the anterior procedure provided a signifi cantly better functional result without neurological complications than did laminoplasty. However, these studies were based on a retrospective analysis, and the number of patients was small. The characteristics of OPLL (e.g., OPLL type, the extent in the longitudinal axis, OPLL thickness, the shape and canal-narrowing ratio) should be considered during the decision-making process to determine the surgical choice. A prospective random- ized analysis with a large number of patients should be carried out to clarify whether anterior or posterior surgery is indicated in individual patients with OPLL.
Thus, it is necessary to design a multicenter study in the future.
Third, the increase in the size of the ossifi cation worsened the neurological fi ndings in some patients.
Some preventive measures should be considered in patients who are at risk of OPLL progression, especially young patients with either mixed or continuous-type OPLL. However, no defi nitive measures have been con- fi rmed. A recent study has revealed that EHDP admin- istration may be effective in preventing progression of the ossifi cation following surgical decompression in OPLL patients. During laminoplasty, a wider laminar opening might effectively prevent postoperative neuro- logical deterioration. Another choice is that anterior decompression surgery should be carried out in patients who are at risk for OPLL progression. Further studies should be undertaken to resolve the problem of OPLL progression after surgery.
References
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