Overview
Ossification of the posterior longitudinal ligament (OPLL) can manifest as myelopathy, radiculopathy, or myeloradiculopathy. Calcification and thickening of the posterior longitudinal ligament (PLL) in this disease leads to reduction in cross-sectional area of the spinal canal and subsequent compression of the neural elements.
Reported first in 1838, OPLL was only recognized as a pathologic condition in the 1960s. Recent advances in radiographic techniques, particularly computed tomography (CT) and magnetic resonance imaging (MRI), have made it easier to diagnose. Several surgical options for the treatment of OPLL have been developed over the past two decades. In this chapter, we will review the disease process, details of available surgical techniques, and their current predicted outcomes.
Epidemiology
Individuals in Asian populations are most commonly affected by OPLL, with an incidence that ranges from 1.9% to 4.3%. Other ethnic groups demonstrated much lower rates: for instance, North American Caucasians have a reported incidence of 0.01% to 1.7%. Despite the relatively low incidence, OPLL may account for up to 20% to 25% of cervical myelopathy seen in the United States and 27% of that observed in Japan. OPLL is twice as common in men and typically shows up during the fifth decade of life. The primary site of OPLL is in the cervical spine in 70% to 95% of patients, with the remainder divided between the midthoracic and upper lumbar spine. The spinal levels most often affected are C4–C6, T4–T7, and L1–L2.
Pathophysiology
Although the exact cause of OPLL remains uncertain, evidence is mounting that genetic susceptibility plays the most significant role in disease development. Early familial studies show the disease in more than 25% of first-degree relatives of affected individuals. Recently, more sophisticated in vitro and in vivo studies have identified potential candidate genes responsible for gene transmission. This increased understanding of the genetic susceptibility suggests that OPLL is probably transmitted in a complex multifactorial inheritance pattern. Clinical associations have also been reported between OPLL and other disorders, including diffuse idiopathic skeletal hyperostosis, ankylosing spondylitis, obesity, diabetes, acromegaly, and hyperparathyroidism.
Although it is clear OPLL is a multifactorial process, several genetic targets and key gene products have recently emerged as potential targets. One of the most studied genes is COL11A2, which encodes for the α-2 chain of type XI collagen. Multiple authors have demonstrated a clear link between several single-nucleotide polymorphisms and a susceptibility to OPLL development. Tumor growth factor β (TGFβ) has also been linked to OPLL because of its known role in regulating mesenchymal stem cells. Several authors have demonstrated both radiographic and clinical findings that link OPLL and several specific genetic polymorphisms. Another potential target is nucleotide pyrophosphatase, a known inhibitor of calcification, which in knockout mice has been shown to cause spontaneous development of OPLL. Although current treatment strategies continue to rely on surgical intervention, as our knowledge of genetic links to OPLL evolves, targeted gene therapy may ultimately prove to be an effective prophylactic.
In an early and commonly used classification system developed by Hirabayashi, four types of OPLL were identified: 1) continuous, with the ossified mass extending over several levels; 2) segmental, with ossification only behind each vertebral body; 3) mixed, a combination of the above; and 4) localized, which may present as anterior or circumferential ossification and stenosis ( Fig. 24-1 ). In a study of Japanese patients, these types of OPLL were found in 39%, 27%, 29%, and 7.5% of patients, respectively.
Clinical Presentation and Natural Course
Although presentation varies widely depending on levels and degree of involvement, myelopathy, radiculopathy, and neck pain are the most common symptoms of OPLL. In a meta-analysis of six series that compiled data from 120 patients, including 51 of her own, Epstein reported that 84% presented with myelopathy that caused severe neurologic dysfunction in Ranawat classes IIIA and IIIB. Radiculopathy with dysesthesias was seen in 47%, and neck pain was reported in 42%. These symptoms were present an average of 13.3 months (range, 7.5 to 22 months) at the time of presentation.
The majority of patients with OPLL (70% to 85%) report a gradual onset of symptoms. Another subset (15% to 30%) come to medical attention with sudden deterioration of neurologic function, often after only minor cervical trauma. While following 207 patients, Matsanuga and colleagues found that of those who presented with myelopathy, 37% experienced worsening of symptoms during a 10-year observation period. In 170 patients who were initially free of myelopathy, only 16% developed myelopathy over the same time course. In multiple reports, duration of symptoms correlated inversely with recovery.
Diagnostics and Radiographic Findings
Before the advent of CT, diagnosis of OPLL was based on findings observed on true lateral spinal radiographs. Dynamic lateral cervical spine radiographs remain a critical part of the evaluation of stability in the workup of OPLL, with instability defined by more than 3.5 mm of subluxation, 20 degrees of angulation, or 2 mm of motion between adjacent spinous processes.
High-resolution CT with sagittal reconstructions represents the definitive diagnostic tool for OPLL ( Fig. 24-2 ). CT also permits calculation of canal diameter and transverse area of the spinal cord, factors that may predict recovery after surgery. Preoperative CT has been shown to have a predictive value for OPLL incorporation or penetration of the dura and for risk stratification for postoperative cerebral spinal fluid (CSF) leakage. Additionally, CT myelography allows more detailed evaluation of the level and location of compression on neural elements.
The use of MRI contributes significantly to the evaluation of patients with OPLL by delineating the amount of cord compression and spinal cord edema, which when present on T2-weighted sequences have been shown to correlate with worse outcomes ( Fig. 24-3 ). The ossified ligament usually appears as an area of low signal intensity in the anterior aspect of the canal on both T1- and T2-weighted images. Flexion and extension MRI can also be obtained to evaluate the dynamic changes in canal diameter and cord compression.
Surgical Options and Outcomes
In those patients whose symptoms progress despite conservative therapy, surgical options include laminectomy, laminectomy plus fusion, laminoplasty, or anterior decompression and fusion. The decision is complex as to which surgical approach is the most appropriate, and no data are currently available to define a standard. Multiple factors must be considered in each case, including the patient’s age, anatomy of the lesion, degree of stenosis, extent of lordosis or kyphosis, and symptomatology.
Laminectomy
Laminectomy provides a relatively safe and simple approach to decompression of the neural elements when normal cervical lordosis is preserved. Posterior decompression in a lordotic spine allows the spinal cord to settle away from the compressive mass of the calcified PLL; however, the same procedure in a kyphotic spine will provide little relief, because the cord remains draped over the anterior elements. In addition, 30% to 40% of patients risk progression of the kyphotic deformity after elimination of the posterior tension band. Kato and colleagues reported a series of 52 patients who were treated with laminectomy alone. Patients initially had a 44.2% rate of neurologic recovery, yet long-term follow-up demonstrated a progression of kyphotic deformity in 47% of patients and radiographic progression of OPLL in 70% of patients.
Laminectomy alone is best reserved for older patients with multisegmental disease, preserved lordosis, limited cervical range of motion, and continuous OPLL. The details of laminectomy have been described in another chapter.
Laminectomy Plus Fusion
The addition of posterior instrumentation and fusion after decompressive laminectomy should be considered in cases of segmental instability, cervical kyphosis, or decompression extending across the cervicothoracic junction. The addition of a fusion construct produces similar clinical improvement to laminectomy alone, but it decreases the risk of subsequent kyphotic deformity and progression of spinal instability. The addition of lateral mass or cervical pedicle screws does carry the risk of potential vascular injury, nerve root injury, hardware failure, and adjacent segment disease and subsequent nonunion. Techniques for placement of lateral mass screws and those for posterior cervical fusion have been described elsewhere in this text.
Anterior Approaches
Anterior decompression of the spinal canal by partial or complete vertebrectomy and subsequent grafting and fusion represent an alternative to posterior approaches. Anterior corpectomy and fusion may help prevent progressive kyphotic deformity and allows for direct decompression of the calcified ligament. The anterior approach has several significant potential drawbacks, such as increased intraoperative blood loss, significant risk of durotomy, continued neurologic deterioration as a result of insufficient decompression, and high pseudarthrosis rates in fusions that involve more than three levels. In a recent systematic review by Li and Dai, the authors reported the surgical complications of anterior versus posterior approaches in the treatment of cervical OPLL and identified 27 studies that included more than 1500 patients. Although the overall incidence of surgical complications varied widely among studies (5.2% to 57.6%), interestingly, the overall incidence of complications was not significantly different in anterior surgery (24.3%) compared with posterior surgery (25.4%).
When an anterior approach is planned, several modifications should be considered. Preoperative placement of a lumbar drain and preparation for dural repair or grafting are recommended. The use of a small diamond burr with the high-speed drill and an operative microscope aids in minimizing dural and spinal cord injury. Although some surgeons advocate removal of all calcified elements, this increases the risk of dural violation. An alternative technique that may provide adequate decompression is the generation of a floating segment of bone. This can be achieved by thinning the posterior vertebral body and ossified PLL and then drilling small troughs at the lateral aspects of the canal ( Fig. 24-4 ). The midline bone is then free to “float” ventrally, away from the spinal canal.
Combined Anterior and Posterior Approaches
In cases of multisegmental OPLL in younger patients, Epstein advocated using circumferential surgery. She reported 25 successful fusions in 26 patients with multilevel anterior corpectomy with fusion followed by decompressive laminectomies and posterior fusion. Improvements of more than 3 Nurick grades were noted, with most patients rated at Nurick grades 0 or 1 at follow-up. This promising report must be weighed against the cumulative risks of combined procedures, and, as always, the approaches must be tailored to individual cases.
Laminoplasty
In an effort to prevent postlaminectomy kyphosis and repeat compression from postlaminectomy membranes, laminoplasty was developed as an alternative. In a recent meta-analysis of the laminoplasty data, Ratliff and Cooper attempted to evaluate the benefits of laminoplasty using the Japanese Orthopedic Association (JOA) scale for assessing myelopathy. They found wide-ranging results, with recovery rates of 20% to 80% with an average of 55%. These data were compared with those of laminectomy, which had a similar recovery rate of 54% in the immediate period and 48% at 5 years. Matz and colleagues recently reported the results of a meta-analysis, in which they concluded that class III evidence supports the use of laminoplasty as a treatment option for cervical OPLL. The authors reported a 55% to 60% improvement in JOA scores compared with those achieved with conservative therapy.
Other findings in the review by Ratliff and Cooper included a 10% rate of postlaminoplasty kyphosis and a 35% rate of worsening cervical alignment, although these data were not defined as loss of lordosis or progression of present kyphotic deformity. A 50% reduction in cervical range of motion and a 40% restenosis rate were also seen. Rates of postoperative axial neck pain were noted to range from 6% to 60%, and no evidence was found to indicate a slowing of posterior cervical muscle atrophy with laminoplasty versus laminectomy. As much as a 70% reduction in cross-sectional area of cervical musculature has been noted after laminoplasty, with no correlation between the degree of atrophy and spinal curvature. Similarly, it is unclear to what degree preservation of the posterior tension band preserves range of motion. From their review the authors concluded that the literature has yet to support the benefits of laminoplasty as a standard in all patients with OPLL. As with other procedures, laminoplasty must be applied and tailored to the individual patient and pathologic condition.
The incidence of postoperative C5 nerve paresis after cervical decompression for OPLL ranges from 4.6% to 16.3%. Although this a well-known complication after cervical decompression, the relative incidence of C5 palsy after surgery for OPLL seems to be higher than in degenerative cervical spondylosis. Although the exact pathogenesis of C5 palsy remains controversial, most authors report a good spontaneous functional recovery with conservative therapy.
Laminoplasty Techniques
Laminoplasty techniques were first popularized by Hirabayashi in the late 1970s. Since that time, many variations have been offered to lower the rates of postlaminectomy kyphosis. Many modifications of the original laminoplasty technique have subsequently been described in the literature and are schematically represented here ( Fig. 24-5 ).
Development of these earlier methods, in many cases, was driven by the lack of appropriate implantable stabilization hardware. The recent availability of allograft bone spacers and small titanium plating systems allows for a simple and effective fixation. Open-door laminoplasty using titanium miniplates avoids the use of stainless steel implants and allows for improved visualization on postoperative MRI. Precut allograft eliminates the morbidity of autograft. The detailed procedure for open-door laminoplasty using grafts and a plating system is outlined below. It should be kept in mind that outcomes of any type of laminoplasty may be more a function of the surgeon’s experience with a given technique than of anything else.
Indications and Contraindications for Laminoplasty
Indications
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Myelopathy
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Progressive or recurrent cervical radiculopathy
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Minimum of 10 degrees of cervical lordosis from C2 to C7
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Less than 7 mm of ventral OPLL
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Less than 50% canal stenosis
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Multilevel disease
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Younger patients (age <60 years)
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Preserved cervical mobility
Relative Contraindications
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Cervical kyphosis
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Single- or short-segment disease
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Segmental instability
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Older patients with other comorbidities
Operative Technique: Open-Door Laminoplasty
Equipment
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Radiograph-compatible operating table
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C-arm fluoroscopy
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Somatosensory-evoked potential and motor-evoked potential monitoring
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Headlight system
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Self-retaining retractors
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High-speed drill with fine-cutting and diamond burrs
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Straight and angled curettes: 3-0, 4-0, and 5-0 sizes
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1- to 3-mm Kerrison punches
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Bone graft source
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Autograft (spinous process, rib, iliac crest)
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Allograft (precut and presized fibula)
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Titanium laminar plating system
Patient Positioning and Intubation
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General endotracheal anesthesia is used. The use of awake, nasotracheal, or fiberoptic-aided intubation is preferred to minimize cervical extension and potential spinal cord injury.
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Baseline spinal cord monitoring is performed before turning the patient to the prone position.
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Mayfield three-pin head holder is placed.
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The patient is placed in the prone position, and the Mayfield head holder is attached to the bed, taking particular care to maintain neutral positioning of the neck.
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The shoulders are gently taped down to maximize visualization under fluoroscopy.
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Spinal cord monitoring is repeated to confirm maintenance of signals.
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If autograft harvesting is anticipated, the site is appropriately selected and prepped.
Location of Incision
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The C-arm is moved into position for verification of appropriate cervical positioning and marking of the appropriate surgical level.
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A midline incision is marked from one spinous process above to one spinous process below the planned levels of laminoplasty.
Preparation and Draping
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The incision is marked, and the cervical skin area is sterilely prepared.
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Draping is carried out in the usual manner.
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If autograft is to be used, a harvest site is draped separately.
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The anesthesiologist is at the head of the table, and the scrub nurse stands at the lower half of the table.
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The headlight and microscope are based on the side of the primary surgeon.
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Fluoroscopy is based on the side contralateral to the primary surgeon.
Incision and Soft Tissue Dissection
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Local anesthetic is injected subcutaneously at the incision site.
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A midline skin incision is made at the appropriate levels.
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Monopolar electrocautery is used to carry the dissection through the midline raphe to the spinous processes ( Fig. 24-6, A ).
Related posts:
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Thoracic Microdiskectomy: Lateral and Posterolateral Approaches
Lumbar Facet Screw Fixation Techniques
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Primary Malignant and Benign Tumors of the Spine
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