Etiology and Epidemiology

Evidence suggests that OPLL is a multifactorial disease with underlying genetic, environmental, and biomechanical contributions.⁴ Early epidemiologic and more recent genetic studies, for example, have identified numerous genes that may have causal associations with OPLL, including the genes for collagen 11,^5,6 nucleotide pyrophosphate,⁷ and transforming growth factor-β.⁸ Likewise, histochemical studies of OPLL show possible involvement of a number of cytokines and growth factors, such as bone morphogenetic proteins^9,10 and transforming growth factor-β.^8,11 It is proposed that these proteins may function by inducing osteogenesis in the PLL of patients with this condition.¹²

Other factors, such as diet and comorbidities, may also be related to the induction or progression of OPLL in individual patients. Vegetarian diets and diets high in salt and vitamin A have all been reported to be associated with OPLL,^13–17 although data are limited and further studies are necessary to clarify these associations. In addition, a higher incidence of OPLL has been reported in patients with endocrinologic comorbidities such as glucose metabolism disturbances, hypoparathyroidism, and acromegaly.^18–21

Epidemiologic studies have identified a modest radiographic frequency (1.9–4.3%) of OPLL in the Japanese population.²² Although similar ranges have been reported in other Asian populations, the incidence in the European and North America populations remains much lower (0.1–1.3%).²² Proportionally, however, patients with OPLL may represent up to one fourth of those presenting with signs and symptoms of myelopathy, regardless of their ethnic background.^23,24 Most studies also support a sex difference in the prevalence of OPLL, with a reported male-to-female ratio of 2 to 3:1.^22,25

Radiographic and Clinical Presentation

The diagnosis of OPLL is established by its pathognomonic radiographic characteristics. Most commonly, but not exclusively, identified in the cervical spine, a dense calcified strip of variable thickness (1–5 mm) can be found along the dorsal margins of the vertebral bodies and the intervertebral discs. The intervertebral discs in the involved area usually are well preserved, without evidence of disc space narrowing. The shape and volume of OPLL can be quite varied, compromising anywhere from a small fraction to greater than 50% of the spinal canal. Radiographically, OPLL has been classified into four groups: segmental (one or more separate lesions behind the vertebral body); continuous (a continuous lesion spanning several vertebral bodies); mixed (a combination of the two aforementioned types); and circumscribed (located primarily behind the intervertebral disc spaces).²³

Anatomically, the PLL consists of two layers, a deep and a superficial one. The deep layer fuses with the periosteum of the dorsal corner of the vertebral body.²⁶ This point of attachment is believed to be the site of initiation of OPLL in the segmental subtype. In the continuous form, the development is less clear. Although some authors advocate that it represents a continuous extension of the segmental subtype, others maintain that it results from progression of multiple scattered OPLLs.²⁶

The clinical presentation of patients with OPLL can be varied, largely because of the differing forms and extent of the pathologic process, as described previously. Approximately half the patients are asymptomatic when the diagnosis is made.²³ Typically, it presents in the fourth and fifth decades of life with an insidious onset of symptoms of cervical radiculopathy or myelopathy.²⁴ More commonly, up to two thirds of patients complain of neck pain or stiffness and/or pain or numbness in the upper extremities, with fewer (40%) complaining of motor symptoms in the arms.²⁷ Motor and sensory changes in the lower extremities are less common (40%), although the majority of patients (57%) are found to be hyper-reflexic. Less than 20% have bowel or bladder symptoms on presentation.²⁷

Natural History

An understanding of the natural history of OPLL is essential in managing patients, particularly in the subset of patients for whom the diagnosis was found incidentally. Not unexpectedly, reviewing recent studies on OPLL patients demonstrates a natural radiographic progression of the disease in the majority of patients regardless of treatment approach.⁴ In one recent study, Matsunaga et al.²⁸ observed an increase in PLL thickness in 70 (42%) of 167 patients managed conservatively; in 32 of these patients (19%) this increase was greater than 2 mm (marked development) over a mean follow-up of 11.2 years. There was a longitudinal increase in 144 (86%) in this same group, with 59 patients (35%) demonstrating ossification behind more than one vertebral level (marked development).

More recent studies by this same group examined the symptomatic progression of patients with OPLL in an effort to better delineate the clinical course of the disease as well as the radiographic predictors that might correlate to this course.^29,30 Following a small group of patients (N = 36) who presented with myelopathy, Matsunaga et al.³⁰ reported that 64% progressed over the study’s more than 10-year follow-up. Of the 323 patients who were not myelopathic on presentation, myelopathy developed in only 55 (17%). The Kaplan-Meier estimate of the myelopathy-free rate in the latter group was 71% at 30-year follow-up.

A severely narrowed spinal canal has been identified as a risk factor in the development of myelopathy in this condition, with 100% of patients with a canal diameter of less than 6 mm²⁸ or greater than 60% stenosis³⁰ experiencing this neurologic debility. In patients with canal diameters reduced by OPLL but not to such critical levels, presence of myelopathy does not appear to be correlated with diameter size per se.²⁸ Such findings have led authors to consider other factors that may contribute to the development of neurologic symptomatology in these patients. Instead, the pathology of cervical myelopathy in patients with OPLL can be explained in two different ways. In patients with significant canal compromise (>60%), the ossified ligament acts as a source of ongoing mechanical or static compression. In others with more moderate compression, cervical motion between adjacent ossified segments plays a role in the development of symptoms as a form of dynamic compression.^29,31,32

Management Strategies

The primary indication for surgical management in a patient with OPLL is cervical myelopathy. Variable combinations of motor, sensory, and reflex changes are usually present. Prophylactic surgery in mildly symptomatic or asymptomatic patients is controversial. As indicated previously, only a small proportion of these patients have been found to progress clinically,³⁰ suggesting that in the absence of known risk factors such as extreme canal compromise or evidence of increased cervical motion, conservative treatment may be preferable. And although trauma is a known risk factor for development of neurologic symptomatology in this patient population, this risk appears to be relatively low; in a recent prospective study only 6 of 368 asymptomatic patients with OPLL (2%) went on to develop trauma-induced myelopathy during a minimum 10-year follow-up period.³³ As a result, most authors do not recommend prophylactic surgery in this group, although a frank discussion with patients is warranted to involve them in the decision-making process.

Conservative management of OPLL is largely empirical. There exist no well-designed clinical studies systematically evaluating the efficacy of common treatment modalities. The mainstay of conservative therapy is immobilization together with anti-inflammatory medications, in an attempt to address modifiable sources of static and dynamic cord compression. Cervical traction has also been suggested by some based on their overall experience with patients with cervical spondylitic myelopathy.³⁴ In theory, immobilization of the grossly or microscopically unstable spine prevents ongoing dynamic compression and may facilitate resorption of degenerative osteophytes.

The goal of surgical intervention in patients with OPLL is to decompress the neural structures while stabilizing the spine: in effect, to eliminate the static and dynamic factors that are thought to be responsible for the clinical disease. Once the decision for surgical intervention is taken, the principal decision regarding surgical management is whether a ventral or dorsal approach should be used because comparable results have been achieved with both.^35,36 In general, a ventral decompressive procedure and fusion is the most appropriate surgical procedure in the presence of ventral compressive factors, such as OPLL, limited to three or fewer vertebral bodies. This procedure, combined with resectioning or floating of the ossified PLL, directly addresses the pathologic process and facilitates fusion with the use of bone graft. For many, it is the procedure of choice in patients with OPLL with significant canal stenosis (>60%), particularly if the lesion is focal or kyphotic angulation of the cervical spine is present. Compared with a dorsal approach, it may carry increased risk of surgical complications, including risk of cerebrospinal fluid leak as well as adjacent-segment disease due to progression of OPLL.^35,37 At 5-year follow-up, good to excellent clinical results have been achieved in as much as 80% of patients who underwent a ventral procedure, although 8% of these patients ultimately required further dorsal surgery.³⁵

Sir Victor Horsley is the neurosurgeon first credited with decompressing the cervical spine of a patient with progressive cervical spondylotic myelopathy using a dorsal approach.³⁸ This was once the procedure of choice for patients with cervical OPLL.³⁹ Although this procedure effectively enlarges the functional spinal canal area, thus allowing the spinal cord to move away from compressive elements and expand, it does so at the expense of dorsal stabilizing structures. Depending on preoperative spinal alignment and time since surgery, up to 50% of patients with OPLL who undergo a laminectomy for treatment develop spinal instability and a gradual kyphotic deformity.³⁹ Given these concerns, together with a considerable population suffering from a multilevel compressive pathologic process necessitating dorsal decompression, Asian surgeons developed the laminoplasty as a “tissue-sparing” procedure in the late 1970s to effectively remodel the spinal canal.^40,41 In theory, one can successfully enlarge the spinal canal while largely preserving dorsal stabilizing structures, thus reducing postoperative deformity or instability and alleviating the need to perform additional fusions.

Initial laminoplasty procedures were cumbersome and lengthy, requiring complex reconstruction of the dorsal arch.⁴¹ Numerous subsequent modifications have resulted in simplified, faster procedures with improved stability.^40,42–46 In particular, preservation of posterior elements was recognized significantly to increase the closing force on the elevated laminae, resulting in a “sinkage” effect with associated restenosis of the spinal canal.⁴⁷ To combat this problem, a variety of techniques have been used. These primarily involve the use of spacers to buttress the created gap or the use of sutures or titanium plates to “attach” the remaining spinous process(es) to the facet or soft tissue structures of the hinge side.^{40,46,48–50} We prefer the former, using fibular allograft, with the “closing forces” maintaining firm positioning of the graft and facilitating fusion. Further stability may be obtained, in addition to or in lieu of the aforementioned techniques, using onlay bone grafting at the hinge site(s).⁵¹

Animal studies have supported the presumed benefits of laminoplasty over laminectomy. In one study, laminectomies or laminoplasties were performed from C3-5 in goats, with monthly radiographic follow-up for 6 months. Radiographic results were compared with control animals, confirming that laminoplasties were biomechanically superior in maintaining alignment.⁵² An additional study in rabbits found that although postoperative range of motion was similar between groups, laminectomy was associated with increased angle deformity and poorer outcome.⁵³ Similarly, a biomechanical advantage of laminoplasty has been found in a retrospective study comparing different cohorts of patients.⁵⁴

Surgical Technique

Open-Door Expansile Cervical Laminoplasty

After the operative field is prepared and draped, the midline is infiltrated with commercially available 1% lidocaine with epinephrine to minimize skin bleeding. A midline incision is made and monopolar or bipolar electrocautery is used to control soft tissue bleeding. The midline fascia is then incised with monopolar electrocautery, and subperiosteal dissection is used to reflect the extensor cervical muscle groups, exposing the cervical lamina and mesial facets from the caudal portion of C2 to the rostral limit of T1, taking care to preserve the facet capsules (Fig. 221-1). The caudal one third of the C2 lamina and the rostral one third of the T1 lamina are removed, using a combination of a high-speed air drill and a 2-mm Kerrison punch, to visualize the underlying dura at this level. We also remove the spinous processes of C3 to C7 inclusively with Stille-Horsley bone-cutting forceps and morselize the bone for subsequent autografting.

FIGURE 221-1 After a midline skin incision is made, a subperiosteal dissection is performed to expose the spinous processes, laminae, and mesial facets of C2-T1. C2-6 is shown here.

The next phase of the procedure involves performing osteotomies of the C3-7 laminae. In so doing, one creates an “open” side and a “hinged” side of these laminae (Figs. 221-2 and 221-3). In general, the side with the greatest compression or the most clinically symptomatic side is the open side. If one is planning to perform foraminotomies in addition to the laminoplasty, the open side is best placed on the side of the intended foraminotomies. A high-speed air drill with a small bit is used to create troughs at the level of the laminofacet junction from C3 to C7. Drilling proceeds through the outer and inner cortical margins of the lamina on the side to be opened. On the hinge side, drilling proceeds through the outer cortical margin and cancellous bone; however, the inner cortex is not violated.

FIGURE 221-2 A small drill is used to create troughs at the laminofacet junction—bicortical on the open-door side and unicortical on the closed side. Shown here, the left trough has been drilled and the ink demarks the planned closed-door side.

FIGURE 221-3 Once drilled, upward-angled curettes are used to place tension on the open-door side and create a greenstick-type fracture on the contralateral side.

After the drilling is complete, bone allografts are prepared to stabilize the canal expansion. We prefer to use rib allografts for this purpose. Again using the drill, three separate grafts are cut, each approximately 10 to 18 mm long. Grooves are then made transversely along the cut surfaces of the rib grafts, approximating the thickness of the cut laminae.

After the grafts have been prepared, attention is turned to “opening the door.” Initially, two small curettes are introduced into the gap produced by drilling the laminae and advanced just deep to the outer cortex. By pulling the curettes upward, the laminar facet gap on the open side is slowly enlarged, and this creates a greenstick fracture along the previously created trough on the hinged side. Minimal advances are made before moving to other laminae in an effort to open all the involved laminae as a functional unit. The goal is to expand the anteroposterior diameter of the canal by approximately 4 mm (see Fig. 221-3). Great care must be taken to achieve this goal without fracturing the inner cortex of the hinge side.

Once this is accomplished, the rib allografts are placed in the gap that has been created at the C3, C5, and C7 levels, with the cut edges of the laminae resting in the cut grooves of the rib grafts (Fig. 221-4). If done properly, the grafts should fit snugly in the gap, there should be a slight “closing” force securing the grafts in position, and the inner cortex of the hinge side should be intact. We then use the morselized spinous process autograft and place it over the decorticated bone surfaces of the facet and lamina on the hinged side to promote intersegment fusion.

FIGURE 221-4 Rib allograft is cut into short segments (10–18 mm) and inserted into the gaps created in the open-door side at C3, C5 (as shown), and C7 (not shown).

Should the patient have radiculopathy as well as myelopathy, one can add one or several foraminotomies to the laminoplasty procedure. Typically, the foraminotomy is initiated once the lamina has been elevated and the ligamentum flavum excised. The mesial one third to one half of the facet over the exiting nerve root is drilled with a high-speed drill. The opening can be widened with 1- or 2-mm angled Kerrison punches.

Should rigid stabilization be required, facet cables with or without rib allograft can be inserted. Lateral mass screws attached to a plate or a rod can also be applied. It is sometimes difficult to position the rib allografts to hold open the laminae once additional hardware is placed, but it can be done. In this case, we perform the drilling and “opening the door” first, but no graft is inserted until the instrumentation is in place. Variations to the approach include use of the spinous process autograft instead of the rib allograft to hold open the lamina. Some surgeons prefer to use miniplates or sutures to stabilize the rib allograft to the adjacent lamina and facet on the open side.⁵⁰ The lamina can be split in the midline with a T-handled “Gigli-like” saw and the allograft spacers positioned between the greenstick-fractured hemi-lamina.⁵⁷

In our experience, an open-door expansile cervical laminoplasty (without additional stabilization procedures) takes approximately 90 minutes to complete, with an average blood loss of 200 mL. In general, the complication rate is low (see next section), particularly compared with decompressive procedures that attempt to achieve the same number of levels of decompression and stabilization from a ventral approach.⁵⁸

Conclusions

Management decisions in patients with OPLL must take into account a number of factors and are highly individualized. Although conservative management is warranted in asymptomatic patients with OPLL or those with only the mildest symptoms, surgical treatment is indicated in those patients with significant neurologic deficit or evidence of increased cervical motion; it has been shown to be effective in improving the neurologic status in the majority of patients. Dorsal decompression for patients with OPLL is specifically indicated when multisegment disease needs to be addressed, but should be undertaken with caution in individuals with marked loss of normal cervical lordosis or marked canal stenosis. It is particularly advantageous in that it avoids the additional risk of dural laceration associated with a ventral approach. Although laminectomy has traditionally been used for decompression of the spinal canal in North America, this is done at the expense of the dorsal stabilizing structures, and the resulting loss of cervical lordosis or the development of kyphosis may result in secondary cord compression and is associated with poorer outcomes. By leaving the dorsal stabilizing structures in situ, laminoplasty is believed to mitigate the development of kyphosis and, with subsequent bone fusion, stabilize the cervical spine, leading to improved outcomes. Although numerous variations on laminoplasty have been described, there is little comparative literature to support the advantage of one type over another.

Decisions regarding when to treat patients with OPLL and which approach to use should always be made in consultation with the patients themselves, such that reasonable expectations regarding outcomes as well as a proper understanding of the risks involved are achieved. This is particularly important in managing patients with OPLL, given the natural history of disease progression even in the face of aggressive surgical management.

Procedure

The patient is placed in the prone position and the head is secured in the Mayfield head holder. Intraoperative somatosensory and motor evoked potentials are used throughout the procedure. The procedure of exposing the spinous processes and laminae is the same as for a standard laminectomy. When the tips of the spinous processes are used for bone grafting, they are removed and preserved, and a midline osteotomy of the laminae is then performed. The spinous processes are drilled down with a high-speed drill after removing the interspinous ligament. Drilling should be performed with a small bur, usually 1.5 to 2 mm in diameter. Drilling is taken down to the inner cortex of the dorsal lamina.

While approaching the lamina through the spinous process, broader drilling is performed. This corresponds to the shape of the lamina and preserves the inner cortex of the lamina. The inner cortex of the lamina is then cut with a diamond bur. In each spinous process a hole is made on the side for wiring and later fixation.

Two gutters are drilled at both junctions between the lamina and the facet joints, leaving the inner cortex of the lamina elastic so that it will act as a hinge when each half of the lamina is lifted. Both halves of the lamina are lifted as if opening a saloon door, and the center of the laminae and ligamentum flavum are cut with Metzenbaum scissors, with care taken not to cause bleeding from the epidural vessels. The pulsation of the dura mater should be observed.

When the tip of the spinous process is used as a bone graft, the bone should be shaped to fit the spinous process. Enlargement of the spinal canal is determined by the size of the bone. The bone graft is usually 10 mm wide for use at C3-5, where the spinous processes are long. The length of the bone graft depends on whether interlaminar fusion is needed. When interlaminar fusion is planned, it is necessary for the bone graft to be of suitable length. A wiring hole is made in the grafted bone, and each spinous process is wired.

Discussion

Many different methods of performing laminoplasty have been described; each has its own advantages and disadvantages, and there is no consensus regarding the preferred method. Follow-up studies are required to determine the efficacy of each method. The major advantage of the French-door laminoplasty is not only its suitability for enlarging the spinal canal, but its utility in dealing with segmental instability by providing interlaminar fusion.

In the presence of an effective lordosis, cervical laminoplasty may be indicated in multilevel OPLL, congenital spinal canal stenosis, multilevel cervical stenosis, and dorsal ligamentous hypertrophy, and as part of a staged ventral/dorsal spinal canal expansion procedure.⁶ Most studies of laminoplasty for CSM and ossification of the posterior longitudinal ligament have reported postoperative enlargement of the spinal canal and an improved neurologic outcome. However, several recent studies suggest that there may be no significant postoperative difference between laminectomy and laminoplasty regarding decompression, neurologic recovery, kyphosis, and instability.^7,8 Laminoplasty was found to provide increased stability, with less translation, tilting, and range of motion, compared with laminectomy.⁹ Comparing the results of 28 cases (10 laminectomy and 18 laminoplasty with 5-year follow-up), Hukuda et al.⁷ did not find laminoplasty to be superior to laminectomy in CSM for functional recovery and enlargement of the epidural space. There was no difference in the occurrence of kyphosis or instability. They reported a reduction in neck extension in patients who underwent laminoplasty. Naito et al.⁵ compared the results of hemilateral open-door laminoplasty, bilateral open-door laminoplasty, and Z-plasty and found no difference among the three modifications. Yoshida et al.¹⁰ reported 50% limitation in flexion and extension of the neck after laminoplasty. On the other hand, Tsuzuki et al.¹¹ reported radiculopathies after laminoplasty procedures. They hypothesized that this was caused by extradural nerve root tethering. Sakaura et al.,¹² in a review of the incidence of C5 nerve root palsy after decompression surgery for CSM, found that C5 palsy occurred in 4.6% of patients after surgery for CSM, with no statistical differences between unilateral hinge laminoplasty and French-door laminoplasty. Patients with postoperative C5 palsy generally have a good prognosis for functional recovery, but the severely paralyzed cases required significantly longer recovery times than the mild cases.

Takeuchi and Yasuhiro¹³ evaluated the importance of preserving the C7 spinous process and attached nuchal ligament in French-door laminoplasty to reduce postoperative axial symptoms. They studied 41 patients and divided them into 2 groups, those in whom the whole structure of the C7 spinous process and nuchal ligament was preserved, and those in whom it was not. Significant differences were noted in the visual analogue pain scale questionnaire at 1- and 2-year follow-up, indicating the presence of fewer postoperative axial symptoms in the group in whom these structures were preserved intraoperatively. Recently, Okada et al.¹⁴ directly compared clinical outcomes in patients treated with open-door versus French-door laminoplasty and found perioperative complications occurred more frequently in the former than in the latter procedure. In this study, Japanese Orthopaedic Association (JOA) scores and recovery rates suggested that both procedures could be similarly effective in decompressing the spinal cord; however, axial pain was improved in French-door laminoplasty but became worse in open-door laminoplasty, suggesting that French-door laminoplasty could be more beneficial than open-door laminoplasty for patients with CSM. Although all laminoplasty techniques have been used for the prevention of kyphosis and instability, several authors have reported a rate of kyphosis development of up to 28% with the various different types of laminoplasty procedures.⁷ Hence, in view of the foregoing, French-door laminoplasty as a treatment for cervical stenosis continues to be controversial.

Indications

The indications for laminectomy are relative and may be surgeon specific. Most important is the preoperative spinal alignment. Laminectomy is indicated for those patients with an effective cervical lordosis. It may also be used cautiously for those with a straightened spine (see later discussion). Patients with multisegment involvement (i.e., three or more levels) may be more effectively managed with laminectomy than with a ventral approach.⁴ Older patients or those with medical comorbidities may benefit more from laminectomy compared with an extensive ventral procedure. This is related to the shorter operative time and lower morbidity of laminectomy compared with extensive ventral corpectomy. Finally, in patients with severe spinal stenosis accompanying OPLL, laminectomy may be indicated before performing ventral surgery.⁸

Defining Cervical Alignment

As previously mentioned, in our opinion the most important consideration for laminectomy is spinal alignment. Those patients with an effective cervical lordosis should undergo laminectomy, those with an effective cervical kyphosis should undergo ventral corpectomy or discectomy, whereas those with a straightened spine may be decompressed with either laminectomy or a ventral decompressive procedure. A midline lateral cervical radiograph or sagittal MRI may be used to determine spinal alignment.⁹ A vertical line is drawn from the dorsocaudal aspect of the C2 vertebral body to the dorsocaudal aspect of C7. A horizontal line is then drawn at the midpoint of the vertical line. The extent of this horizontal line depends on the surgeon’s preferences and biases. The lines drawn describe a shape similar to a kite, and will be referred to as such. If the dorsal aspects of the cervical vertebral bodies lie ventral to the kite, then the spine is in effective cervical lordosis. If the dorsal aspects of the cervical vertebral bodies lie dorsal to the kite, the spine is in effective cervical kyphosis. A “gray zone” exists when the dorsal aspects of the cervical vertebral bodies lie within the kite. In this circumstance, the spine is straight, and either a ventral or dorsal procedure may be performed (Fig. 221-6). Gwinn et al.¹⁰ recently evaluated this simple straight-line method of determining effective cervical lordosis and found it was superior to traditional methods used to make angular measurements of sagittal cervical alignment (e.g., Cobb angle). The traditional methods often failed to take into account ventral obstructions such as dorsally projecting osteophytes or spondylolisthesis, which may force the approach to be altered to a ventral decompression.

FIGURE 221-6 A midline lateral cervical radiograph or sagittal MRI may be used to determine spinal alignment. A vertical line is drawn from the dorsocaudal aspect of the C2 vertebral body to the dorsocaudal aspect of C7. A horizontal line is then drawn at the midpoint of the vertical line. The width of this horizontal line depends on the surgeon’s preferences and biases (see text). The lines drawn appear similar to a kite and will be referred to as such. A, If the dorsal aspects of the cervical vertebral bodies lie ventral to the kite, the spine is in effective cervical lordosis. Laminectomy is optimal for decompression in this situation. B, If the dorsal aspects of the cervical vertebral bodies lie dorsal to the kite, the spine is in effective cervical kyphosis and a ventral decompressive strategy should be chosen. C, A “gray zone” exists when the dorsal aspects of the cervical vertebral bodies lie within the kite. In this circumstance, the spine is straight, and either a ventral or dorsal procedure may be performed.

(Reprinted with permission from Benzel EC: Biomechanics of spine stabilization, ed 2, Rolling Meadows, IL, American Association of Neurologic Surgeons, 2001.)

Procedure

A few features of the procedure specific to OPLL should be mentioned. Ossification frequently spreads; it was seen in 70% of cases in the series reported by Kato et al.¹ In their series, deterioration due to spread of ossification was seen in paucilevel laminectomies (e.g., three-level laminectomy). Therefore, more extensive laminectomy is recommended in the management of OPLL, even when the disease is somewhat limited. The decompression should usually include C3-7, or at a minimum one to one-and-one-half segments above and below the radiographically abnormal segments. Because of the risk of postlaminectomy kyphosis, lateral resection should not incorporate more than the medial 25% of the facets on either side.¹¹

Sectioning of the dentate ligaments has been advocated by some,¹² but not by others.¹³ The benefit of sectioning the dentate ligaments is unclear and it necessitates opening the dura, which exposes the patient to the inherent risks of this procedure, such as cerebrospinal fluid leak and spinal cord injury. Therefore, we do not recommend this procedure.

Outcome

Outcome is adversely affected by older age and more severe myelopathy at the time of decompression.¹ Therefore, we recommend earlier surgery for patients with OPLL.

Miyazaki and Kirita¹² performed laminectomy on 155 patients with OPLL with at least 1 year of follow-up . Three patients developed quadriplegia after the procedure, whereas six demonstrated only transient quadriplegia during the first 24 hours after surgery. Functional outcome was evaluated by the Japanese Orthopaedic Association (JOA) score. Overall, 81.9% of the patients showed some improvement. Specifically, 36.8% were rated as excellent, 18.1% good, 27.1% fair, 7.1% unchanged, and 11% poor. Seventeen percent of the patients demonstrated postoperative kyphosis or a worsening of their kyphotic deformity. It was not reported if the new or worsened spinal alignment negatively affected their neurologic status.

Similar results were reported by Nakano et al.¹⁴ The authors performed laminectomy on 14 patients with OPLL and measured their outcomes using the JOA score. Overall, 81.1% of the patients demonstrated some improvement.

Complications

Spinal cord injury may be seen in up to 10% of cases, whereas nerve root injury has been seen in up to 12.8% of cases.^15–17 Spinal cord injury is most often directly related to surgery and should be minimized by meticulous attention to detail. Most important, perioperative and intraoperative hypotension should be avoided. This may result is cord ischemia and quadriplegia. The spinal cord may also be injured during surgical decompression, that is, when placing instruments under the laminae. This risk is mitigated by careful choice and usage of instruments. The C5 nerve root may be injured during the extensive cervical laminectomy required for decompression of OPLL. This is most likely due to tethering of the root during dorsal migration of the spinal cord after decompression,^15,16 and the deficit is usually temporary.

Postlaminectomy scar formation and kyphosis may develop, which has led to the development and widespread use of laminoplasty. The exact incidence of postlaminectomy kyphosis is unknown, but may be as high as 21%.¹⁸ Miyazaki and Kirita¹² noted that 17% of their patients developed either postoperative kyphosis or a worsening of their existing deformity. Although kyphosis and scar formation have been demonstrated after laminectomy, their clinical sequelae are unknown and often do not have a negative effect on the patient’s neurologic status.¹²

In our opinion, patient selection and surgical technique will avoid the potential complication of postoperative kyphosis. For example, a facet-sparing laminectomy in a patient with preoperative lordosis should minimize postoperative deformity.

Conclusions

Laminectomy is a highly effective surgical strategy in the management of OPLL. The procedure provides simultaneous multisegment decompression. The technique is familiar and the morbidity is low. It obviates the risk of neurologic injury and cerebrospinal fluid leak that may be seen after a ventral procedure. Furthermore, a simultaneous fusion is avoided.

Laminoplasty has been advocated as an alternative to laminectomy. The incidences of postoperative cervical deformity and scar formation with laminoplasty are claimed to be lower than with laminectomy. Despite these claims, there are some downsides to laminoplasty worth mentioning. Adequate decompression may be not achieved on the “hinged side” of the laminoplasty. Furthermore, the hinged laminae may fracture through the inner cortex, actually worsening the compression.¹³ Although increased kyphosis may be seen after laminectomy, it does not appear to have a negative impact on patient neurologic status. Nakano et al.¹⁴ compared laminectomy with laminoplasty for the management of OPLL and found that the outcome as measured on the JOA scale was no different between the two groups.

Laminectomy should be viewed as the procedure of choice for patients with a preoperative effective cervical lordosis and multisegment disease. Outcomes are favorable compared with other procedures, with less risk of cerebrospinal fluid leak and neurologic injury.

Rationale for Performing a Ventral Approach

A ventral approach to the cervical spine is favored by many surgeons because it provides excellent exposure, has a good cosmetic result, and has low rates of complication and discomfort. The ventral discectomy and fusion procedure done initially by Smith and Robinson involves removal of the cervical disc and placement of a tricortical iliac crest graft. Their approach focused on fusion and stabilization rather than decompression of the spinal cord. Modifications of the Smith-Robinson approach have since come to include decompression of the disc (discectomy) or vertebral body (corpectomy, which includes the removal of the vertebral body ventrally, as well as the complete removal of the discs above and below the offending level).^1–3 Complete excision of the vertebral body provides exposure of the posterior longitudinal ligament (PLL) for decompression along the length of the vertebral body and disc spaces, but the longer the corpectomy, the greater the risk of instability of the construct. Ultimately, the patient’s pathologic process and anatomy should influence selection of the optimal approach.

If a discectomy is performed, a spacer is recommended to maintain disc height, prevent deformity, and maintain foraminal height.^4–6 The likelihood of obtaining fusion in the cervical spine increases when using the ventral rather than dorsal approach.^7–9 Another benefit of the ventral over the dorsal approach is a potential decrease in blood loss because the surgeon uses the natural dissection planes in ventral loose connective tissue, compared with performing a dorsal subperiosteal dissection of paraspinal muscles.^10,11

Of the three surgical procedures (i.e., ventral, dorsal, and ventral combined with dorsal) for patients with ossification of the PLL (OPLL), corpectomy and resection of the OPLL is the most direct approach. Corpectomy is usually indicated for patients who present with less than 50% narrowing of the spinal canal and with three or fewer ossified segments. This is because the bone graft and plate construct becomes more susceptible to rotational torque as the number of levels increases. A dorsal approach such as a laminectomy or laminoplasty can also be considered if a longer multilevel procedure is necessary. Patients with bulky OPLL do not always present with cervical myelopathy.¹² However, in cases where OPLL causes spinal cord compression and myelopathy, surgical treatment may dictate ventral removal of the offending structures (osteophytes or the calcified PLL); otherwise, the cord may remain draped over the ventral structure even if a dorsal decompression is performed. Therefore, cases with prominent ventral impingement on the cord that spans over three levels may need a ventral approach for decompression combined with a dorsal fusion for stabilization of the construct.^13,14

A ventral approach is favorable in certain situations. Sakai et al. performed a prospective study of 44 patients, half of whom had a ventral decompression and fusion and half a French-door laminoplasty, with 5-year follow-up.¹⁵ The ventral group had improved Japanese Orthopaedic Association (JOA) scores and better recovery rates compared with the laminoplasty group, especially for cases with greater than 50% preoperative spinal canal compromise by OPLL or kyphotic alignment of the cervical spine. Progression of OPLL was observed in 5% of the ventral group compared with 50% of the laminoplasty group.

In cases limited to compression at the disc spaces, anterior cervical discectomy and fusion is the standard treatment. This includes treating cases with degenerative cervical disc disease associated with radiculopathy or myelopathy.^16,17 The original Smith-Robinson technique for achieving arthrodesis in the cervical spine after discectomy is a successful anterior cervical discectomy and fusion technique for managing OPLL, and remains quite popular.^18–21

Smith-Robinson Surgical Technique

After acquisition of intravenous access, induction of general anesthesia, and intubation, the patient is positioned in the supine position with the head in slight extension. At the time of original publication, nasal intubation was used to avoid neck hyperextension. Today, awake fiberoptic intubation, awake positioning, and neuromonitoring, including continuous intraoperative somatosensory evoked potential (SSEP) monitoring, are adjunct techniques that can be used if cord compression is particularly worrisome.²²

There is controversy as to which side to approach the ventral cervical spine.²³ Arguments supporting a left approach are based primarily on the theoretically increased risk of recurrent laryngeal nerve injury (which could lead to dysphagia and dysphonia) or the presence of a variant nonrecurrent right inferior laryngeal nerve. Arguments supporting a right approach are based on optimized surgeon comfort for right-handed surgeons, less risk of thoracic duct injury, and less esophageal retraction (i.e., the esophagus lies slightly to the left of midline). Although it remains a theoretical risk for operating on the right, there is as yet no clear evidence that the right recurrent laryngeal nerve is at greater risk than the left.²⁴

Once the patient is properly prepared and draped, a transverse incision is made following a natural crease in the skin around the C5 level. This can easily provide access to three to four levels and provides better cosmesis than a longitudinal incision following the sternocleidomastoid. The subdermal fat and platysma are exposed. The platysma is dissected free from subcutaneous tissue and incised with a transverse incision. The sternocleidomastoid and trachea are identified, and an avascular dissection plane is developed medially between these structures. Deeper, the carotid pulse is identified, allowing the carotid sheath to be reflected laterally using hand-held retractors, while the esophagus and trachea are retracted medially. The prevertebral compartment is then exposed, with the spine palpable under a thin layer of soft tissue, including the longus coli muscle. A spinal needle is placed in the disc space. The appropriate surgical level is confirmed using intraoperative fluoroscopy.

The longus coli is dissected laterally along the vertebral body from medial to lateral. The residual muscle forms a lip that helps to hold the retractor in place. The hand-held Cloward retractors are replaced by two medial and lateral self-retaining retractors (smooth or mildly serrated blades only). A second self-retaining retractor can be placed to retract soft tissue in the rostral-caudal direction. The annulus is then incised with a no. 15 blade, and the disc is removed with a pituitary forceps. The upper and lower end plates are prepared by removing the overlying cartilage with a curette while preserving the subchondral bone. If the disc space is too collapsed for entry, a partial corpectomy with a high-speed drill can be used to open the space.

The original Smith-Robinson technique calls for countersinking the graft into the vertebral body to prevent postoperative displacement of the graft. In the original technique, a 2-cm tricortical bone graft is removed from the ilium with an osteotome. Depressions or sockets are created in the end plates to fit the graft. The graft is trimmed and tamped into place between the two vertebral bodies in the sockets. Cervical traction with tongs is often also used to distract the cervical spine. The graft size is typically 10 to 15 mm because of the additional countersinking depth. The anterior longitudinal ligament is closed, followed by platysma and skin.

Modifications to the Smith-Robinson Surgical Technique

Over the years, many modifications to the Smith-Robinson technique have been used. Rather than cervical traction with tongs, Caspar vertebral body screws are inserted into the vertebral bodies rostral and caudal to the disc space to facilitate both disc space distraction and soft tissue retraction. Of note, distraction with Caspar vertebral body screws to open the disc space before OPLL resection can occasionally result in profound suppression or loss of SSEPs.

The original Smith-Robinson technique addressed fusion without decompression because it was thought that dorsal osteophytes would spontaneously resorb after fusion took place. Today, these osteophytes are now typically removed. In cases of severe OPLL, the calcified disc and PLL are removed with a high-speed drill to decompress the neural elements. This can be challenging because often the dura is adherent to the PLL, and aggressive drilling can result in a cerebrospinal fluid leak. Without cord decompression, however, the operation will have a poor result. Floating islands of calcified tissue can be left on the dura if the overall mass effect is removed. Hypertrophic end plates can be removed with either the drill or judicious use of a Kerrison punch, though there is a limit to how far the Kerrison can reach under the vertebral body. A partial corpectomy including only the dorsal vertebral body can also be attempted in order to preserve most of the end plate.

If the OPLL must be removed along the entire length of the vertebral body, then a corpectomy may need to be performed to provide access. After extensive removal of one or more vertebral bodies, a strut graft may be required to reconstruct the defect. In cases where OPLL occurs at adjacent interspaces, superior management may be obtained with a single strut graft rather than tandem interbody grafts. For example, in cases where both end plates of the intervening vertebral body have been extensively dissected to provide access for osteophyte removal, it may be suitable to remove the remaining cancellous bone and place a strut that spans that vertebral level and both disc spaces rostrally and caudally.

Modern techniques call for preservation of the end plates. Countersinking the graft was a useful technique before the availability of plating; however, breaking through the end plates creates a greater likelihood of graft subsidence over time through the exposed cancellous bone. Modern plating systems currently recommend end-plate preservation with placement of interbody grafts. After end-plate preparation and removal of the calcified disc and PLL, a spacer of appropriate size is inserted into the disc space.

Today, there are also several alternatives to the iliac crest bone graft used in the Smith-Robinson technique. Several studies have noted morbidity with harvest of iliac crest graft, including a 29% incidence of chronic pain, with other complications including arterial injury, ureteral injury, herniation, nerve injury, infection, fracture, pelvic instability, cosmetic defects, hematoma, and tumor seeding.²⁵ Alternatives today include but are not limited to fibular ring allograft, a milled bone graft, or a polyetheretherketone (PEEK) cage.

A significant depression or loss of SSEPs can indicate that the segment has been overdistracted and mandates removal and revision of the graft. The ideal graft size is determined as a function of preoperative disc space height, with typical sizes ranging between 6 and 10 mm, which is less than the original Smith-Robinson graft.⁷ After spacer placement, fixation is usually performed using a plate-and-screw system. This helps limit motion to facilitate fusion. The plate also helps prevent ventral displacement of the spacer.

Conclusion

The Smith-Robinson technique is an important approach for the surgical management of OPLL, particularly in settings of ventral spinal cord compression with short-segment pathology. Modifications to the original procedure have made the Smith-Robinson technique safer and significantly reduced its morbidity.

Surgical Technique

Patients are operated under general anesthesia in the supine position. Using a ventral approach, the posterior longitudinal ligament (PLL) is reached after performance of ventral discectomies. A variety of retractors may be used. The retractor I use is a practical and useful alternative to the existing self-retaining retractors designed especially for this operation, particularly for Smith-Robinson fusions.^26,27

A high-speed drill is used to drill upward from the connection of the PLL and the caudal surface of the vertebral body, under a surgical microscope. The hole is broadened with the help of the drill, and the OPLL is removed (Fig. 221-7). The same method is then applied to the upper discectomized intervertebral space in the downward direction (Fig. 221-8). Generally, the removal of the dorsal half of the vertebral body is sufficient to achieve an effective decompression. As a result, a space is formed at the dorsal aspect of the intervertebral discs and vertebral body that broadens the spinal canal (to approximately 15 mm; see Fig. 221-8). The removal of the intervertebral discs and the cartilaginous end plates and the creation of a mortise for graft material on both the rostral and caudal surfaces of the vertebral body result in diminished vertebral body height. However, this shortening of the vertebral body height does not influence graft placement. After obtaining an effective decompression, a Smith-Robinson fusion is applied to the intervertebral spaces (Fig. 221-9). In the surgical technique presented here, allograft fibula was used as the graft material. It is also possible to use autogenous iliac crest bone as a graft material. To minimize the incidence of graft dislodgment, the grafts are placed after distraction of the vertebral bodies, so that graft compression is achieved upon relaxation of the distraction. In addition, the grafts are shaped because the ventral height of the graft is a few millimeters (1–3 mm) greater than the height of dorsal surface. This minimizes dorsal dislodgment. Ventral spinal fixation is routinely used to increase the fusion rate.

FIGURE 221-7 After removal of the upper and lower discs, the rostral surface of the corpus is drilled toward the upper surface of the corpus.

FIGURE 221-8 The edges of the drilled sides are connected to each other and a window is made along the posterior surface of the vertebra. The spinal canal is enlarged without performing total corpectomy.

FIGURE 221-9 Schematic illustration of placement of Smith-Robinson fusion.

This OWC technique is particularly useful for moderately advanced cervical spondylosis or OPLL (Fig. 221-10). In general, excellent results are obtained with this technique.²⁸

FIGURE 221-10 Case 1 (A) and case 2 (B): Multilevel cervical spondylosis. Arrows depict the myelopathic areas at the affected levels. Note loss of subarachnoid space (arrowhead) in posterior border of C5 corpus, compared with upper and lower levels.

Rationale

Cervical spondylosis and OPLL cause progressive cervical stenosis and compressive myelopathy. Surgical treatment is designed to decompress the spinal cord and widen the spinal canal.

Laminectomy has been accepted as the most appropriate surgical approach to achieve these goals. However, instability and constriction of the dura mater after laminectomy are common complications.^1–6

Compression is generally from the ventral aspect of spinal cord in advanced spondylosis and OPLL, except for patients with a congenitally narrow spinal canal. The dura and the PLL are attached and even ossified in severe cases. The dentate ligaments, which connect the spinal cord to the ventral side of the spinal canal, and the nerve roots that bind the dura and the spinal cord ventrally, limit dorsal spinal cord movement. For these reasons, dorsal approaches are usually insufficient to relieve compression from the ventral side of the spinal column.^15,17–25

Total OPLL extirpation is currently one of the best surgical techniques to achieve a satisfactory outcome while avoiding the complications secondary to a dorsal approach. With this technique, the ossified annulus, the ossified cartilaginous end plates, and OPLL are totally extirpated after anterior corpectomy.^{15,17–20,22}

The ventral floating technique is another commonly used surgical approach for such cases. This technique frees the OPLL over the dura after corpectomy. Incisions are made to the level of the OPLL at the upper and lower aspects of the affected levels. Thus, the expanded dura pushes the attached OPLL segment inward to the removed vertebral body.^20,21,27

Both of these techniques are associated with pseudarthrosis, instability, and dislodgment owing to the use of anterior strut grafts, especially when three or more disc spaces are included in the operation.^21,27,29

Biomechanics

The technique described here removes only the dorsal aspect of the vertebral corpus after performance of appropriate ventral microdiscectomies. This provides a wide exposure of the spinal canal, along with the OPLL. After removal of the OPLL, the spinal cord is decompressed. This technique allows the ventral aspect and both lateral portions of the vertebral body to remain intact (Fig. 221-11). The importance of this is obvious with regard to the biomechanics of the spine. Biomechanically, the extent and location of ventral spinal decompression significantly affects spine instability.⁴ The ventral vertebral body cortex provides a significant advantage with regard to its buttressing effect; it bears axial loads much more effectively than the softer cancellous bone. The OWC technique allows the bone graft to contact the three cortical margins of the vertebral body (two lateral and ventral cortical margins).

FIGURE 221-11 Case 1 (A) and case 2 (B): The dorsal aspect of the vertebra has been drilled. Note the intact ventral vertebral body, sufficient decompression, and screw in the healthy corpus.

Graft Placement

Other advantages of this technique include the ease of appropriate bone graft placement. The location of the ventral interbody bone graft significantly affects the biomechanical efficacy of the construct. Biomechanically, the optimal location of interbody bone graft placement is inline or slightly ventral to the instantaneous axis of rotation if the dorsal elements of the spine are intact.³⁰ The instantaneous axis of rotation is usually located at the junction of the anterior and middle columns of Denis in the nonpathologic spine. The OWC technique thus allows the placement of the interbody bone graft in an optimal location. Obviously, this should result in a substantial increase in axial load-bearing ability.

Multilevel Fixation

Finally, in cases where ventral cervical fixation constructs are applied, this technique provides the option of multilevel fixation (Fig. 221-12). Removal of only the dorsal aspect of the vertebral body permits the surgeon to place screws ventrally (Fig. 221-13). Multilevel fixation distributes the fixation forces over multiple segmental levels. In other words, multilevel fixation applies the “load-sharing” principle.³¹ Although it is not yet proven experimentally, on a theoretical basis, the distribution of forces decreases the stresses applied to the metal-bone interface at each segmental level. As a result, this minimizes the incidence of construct failure.³² In addition, a rigid ventral construct can act as a fixed moment arm cantilever. In such an application, where two screws are used at each terminus of the implant (Fig. 221-14A), the construct bears axial loads relatively well. However, it does not resist translational forces well. The addition of intermediate points of fixation (Fig. 221-14B) allows the implant to resist these translational forces by using three-point bending forces. Therefore, the additional fixation points not only allow axial loads to be borne more effectively by adding additional points of fixation, but allow for resistance of translational forces. Moreover, a more stable construct is expected to provide a higher fusion rate. In my report,²⁸ a constrained construct with cancellous bone screws was used because this was the only implant available at the time. However, I believe that use of a dynamic construct may be more appropriate because it permits settling.

FIGURE 221-12 Case 1 (A) and case 2 (B): Plain lateral radiographs after surgery. Note the construct’s multiple points of fixation.

FIGURE 221-13 Cases 1 and 2 (A): Sagittal CT reconstruction studies show enlarged spinal canal after open-window corpectomy. Bony grafts are seen between the vertebral bodies. The advantage of this technique is that it is unnecessary to use long strut grafts for fusion. Note the use of multiple points of fixation. Cases 1 and 2 (B): Postoperative sagittal MRI studies show satisfactory decompression of the spinal cord.

FIGURE 221-14 A, Multilevel long strut graft with anterior plate. Note that this construct acts like a fixed moment arm cantilever construct (solid arrow depicts axial force, open arrows depict translational forces). B, Multilevel multigraft with anterior plate. Note that this construct applies three-point bending forces, thus offering better resistance to translational forces (solid arrow depicts axial force, open arrows depict translational forces).

Controversies

The use of multiple small grafts instead of a long strut graft is controversial. It is well known that an increase in the number of fusion sites decreases the fusion rates.^29,33 It has been also reported that placing an internal fixation implant significantly increases the fusion rate.^34–36 However, there are no data comparing plated multilevel, multigraft fusion rates with plated multilevel, single-graft rates. The OWC and similar techniques provide improved load sharing between the implant and the vertebral bodies, and a more stable construct (by using three-point bending fixation). Therefore, multiple grafts may be expected to be associated with a high union rate. As a result, problems such as dislodgment, pseudarthrosis, and construct failure may be infrequent with this method. The OWC technique provides a wide decompression (see Fig. 221-13) in a biomechanically sound manner.

Long-Term Results

Long-term results were investigated in 15 patients using both clinical and radiologic outcomes after OWC in cases of advanced cervical spondylosis and/or OPLL. The visual analogue scale scores (pain) and Japanese Orthopaedic Association (JOA) scores (upper extremity function) revealed significant clinical improvement from before surgery to the 15-month time point, and no significant changes from 15 to 92 months.³⁷ In accord with this, MRI and CT assessments revealed improvements in cervical lordosis, segmental lordosis, and cervical spinal canal diameter from before surgery to short-term follow-up, and no significant changes from 15 to 92 months (Fig. 221-15 and Table 221-1).

FIGURE 221-15 Schematic illustration of the lines used to measure the angles of cervical and segmental lordosis, and the method for measuring spinal canal diameter.

Ozer et al. also used the method developed by Hilibrand et al.³⁸ to assess the spinal segments adjacent to the operative site in long-term follow-up. All 15 of the patients underwent multilevel surgeries involving OWC, and 5 patients developed adjacent-segment disease (grade II, 4 patients below and 1 patient above the operated region) in the long term. This result is concordant with literature data.³⁸ Patient age was not part of the decision-making process with respect to performing OWC; however, only patients who had anterior compressive cervical spondylosis and/or OPLL were chosen.

Total and conventional corpectomy procedures may lead to complications such as graft or instrumentation failure, pseudarthrosis, neurologic deficits, vocal cord paralysis, and respiratory problems.^39,40 On the other hand, OWC is less destructive over the long term than other cervical corpectomy techniques. We also believe that the three-point fixation in OWC (the bone graft contacts both lateral portions and the ventral portion of the intact vertebral body) provides significant support for axial loads. Our long-term findings suggest that OWC is as safe and effective as anterior conventional corpectomy for patients with advanced cervical spondylosis and/or OPLL (Fig. 221-16).

FIGURE 221-16 Patient 13. A, Postoperative plain lateral radiograph shows the screws and grafts (arrows) in place. B and C, Sagittal and coronal CT reconstructions of the cervical spine at 15 months (short-term follow-up) demonstrate adequate decompression with multilevel open-window corpectomy. D, T2-weighted sagittal MRI at long-term postoperative study shows adequate decompression.

As mentioned, in OWC the inserted bone graft material contacts all three intact cortical margins of the vertebral body (both lateral portions and the ventral portion).²⁸ This is very important with respect to spinal biomechanics because the site and extent of anterior decompression can have a significant impact on spine instability.¹⁵ Three-point fixation and the small bone grafts used in OWC mean that there is lower risk of pseudarthrosis and infection compared with conventional corpectomy with strut-graft placement. None of the 15 OWC patients developed problems with pseudarthrosis, infection, chronic inflammation, screw loosening, screw avulsion, or plate breakage in long-term follow-up. However, a single screw broke in two cases and was attributed to incorrect plate selection. A single-screwed plate for each vertebra had been used, but after this problem occurred double-screwed plates were used.

Conclusion

Open-window corpectomy is a safe and effective technique for removing compressive spurs, osteophytes, and OPLL anterior to the cervical spinal cord. Currently, there are no data allowing fusion rates for plated, multilevel, multigraft placement to be compared with fusion rates for plated, multilevel, single-graft placement in patients with advanced cervical spondylosis and/or OPLL. However, OWC creates a more stable construct with three-point fixation and results in better load sharing between implants and healthy vertebrae. Our observations in long-term follow-up after OWC suggest that this is a good surgical option for patients with anterior compressive cervical spondylosis and/or OPLL.