Ossification of the Posterior Longitudinal Ligament

Pathogenesis, Management, and Current Surgical Approaches: A Review

Zachary A. Smith, M.D.; Colin C. Buchanan, M.D.; Dan Raphael, P.A.-C.; and Larry T. Khoo, M.D.

Disclosures

Neurosurg Focus. 2011;30(3):e10 

In This Article

Posterior Cervical Approaches

While anterior cervical discectomy or anterior corpectomy are excellent options for younger patients and those with inadequate cervical lordotic curve, dorsal procedures can often be used in patients with a well-maintained cervical lordotic curve. This can include patients with multilevel cervical spondylosis as well as those with OPLL. Cervical laminectomy and decompression can often be augmented by lateral mass fusion to correct instability or to prevent loss of future sagittal alignment. Laminoplasty is also offered as an alternative to lateral mass fusion. In patients undergoing posterior decompression surgery, there should be evidence of preoperative cervical lordosis of at least 10° and less than 7 mm of anterior-posterior OPLL for indirect decompression to be successful.[71] The most significant advantage of a posterior approach is that it avoids the potential soft-tissue complications of the anterior approach. Furthermore, there is no risk of graft extrusion, but there is a decreased incidence of postoperative pseudarthrosis. It has additionally been proposed that OPLL is associated with a "dynamic myelopathy" in which the cervical spinal cord is progressively injured by repeated movement of the cord parenchyma over the ossified ventral mass.[21] Arthrodesis and simple collar immobilization in these patients may serve to "stiffen" the cervical spine and decrease deleterious motion.

Laminectomy With or Without Fusion

Laminectomy is done through a midline posterior cervical incision. A subperiosteal dissection of the underlying ligaments and paracervical muscles will expose the spinous processes as well as laminae of the subaxial cervical spine. In cases in which posterolateral fusion is planned, the dorsal surface of the bony lateral masses and the facet joints are exposed. In most circumstances, the laminectomy is planned to allow for decompression rostral and caudal to the most severe area of cervical canal narrowing. In doing so, the cord will have the ability to migrate dorsally away from any areas of compression caused by degenerative osteophytes or ossified ligament.

The laminectomy can be undertaken by developing 2 bony troughs through the lateral lamina at the junction of the lamina and bony lateral mass. Under microscopic or loupe magnification, a high-speed drill can be used to cut through the anterior and posterior cortex of the lamina. This exposes the underlying ligamentum flavum overlying the cord. In cases of severe compression or an atretic ligament, we also advocate the use of a lower-speed diamond drill following initial removal of the outer cortex. After the bony troughs are developed, residual bone may be removed using either a 1- or 2-mm Kerrison rongeur. Following this step, the dorsal lamina should be unattached, constituting a mobile, "floating" segment relative to native cervical spine. Removal of any residual ligamentous attachments using a small-caliber Kerrison punch allows the entire segment of bony lamina to be removed together.

Following removal of the lamina, careful medial facetectomy and multilevel foraminotomy are completed. We are careful to avoid removing more than 25% of the medial facet joint at any level to prevent postoperative instability. However, we have found that in cases of severe lateral recess stenosis, partial facetectomy is required for adequate decompression. Furthermore, unroofing of the foramen using an undercutting technique with a small-caliber (2 mm or less) Kerrison punch allows for cervical nerve root decompression and mobilization of the cord. The cord can be covered (and protected) by placement of a collagen matrix on the dura and an epidural drain is placed prior to closure.

Laminectomy alone is chosen by some surgeons to decompress the cervical spine in OPLL. In general, when a posterior decompression is chosen, it is our practice to undertake either laminectomy with fusion or laminoplasty. This is in line with the philosophy of decreasing the "dynamic" component of myelopathy. However, if a laminectomy is chosen, the extent of medial facet resection should be kept to 25% or less to avoid postoperative instability. Long-term results from laminectomy are, however, generally positive. Kato et al.[33] noted a 44% rate of neurological recovery at 1 year in 44 patients with OPLL. Despite a high rate of kyphosis (47%), there was no associated decline in the patients' clinical state. We believe that this approach may be appropriate in select, older patients with maintained cervical lordosis and little evidence of instability or motion. However, posterior decompression should be avoided in patients with a kyphotic alignment, spondylolisthesis, suggested instability, or high disc spaces.

Laminectomy With Fusion

In patients with at least 10° of lordosis, a multilevel laminectomy will allow a release of the cord and promotes subsequent dorsal migration in cases of OPLL.[17] It will also decrease cervical ROM across an anterior ossified bar. There are multiple fusion techniques that can be used, including facet wiring, lateral mass screws, and pedicle screws. Epstein[19] demonstrated that posterior decompression with facet wiring can be successful in geriatric patients with OPLL and an appropriately lordotic cervical spine. Houten and Cooper[29] demonstrated that laminectomy and posterior lateral mass fusion can result in high rates of fusion, preserved lordosis, and clinical results comparable or superior to those seen with ACC. While many series show fusion rates near 100%, there is a defined morbidity for lateral mass screw placement. In a single study of lateral mass screw complications, nerve root injury was 0.6%, cord injury 2.6%, and screw loosening or avulsion was 1.3%.[23] It is also important to note that a stable pseudarthrosis will often yield the same clinical result as a solid fusion.

Cervical Laminoplasty

Cervical laminoplasty was described in the 1970s as an alternative to laminectomy in patients with myelopathy.[26] It is the opinion of many surgeons that laminoplasty is optimally designed to treat patients with multilevel OPLL. It offers dorsal decompression of the cervical spine without decreasing stability. However, it obviates the need to achieve a formal fusion and there is a placement of segmental spinal hardware. This segmental hardware helps to decrease range of motion. Biomechanically, when compared with laminectomy without fusion, laminoplasty has been shown to have an equivalent or even superior ability to maintain cervical alignment without the development of delayed postoperative kyphosis.[2] However, despite this increase in stability, in certain cases, kyphosis may still occur. Another theoretical advantage of the technique is that laminoplasty avoids the development of the postlaminectomy membrane and delayed restenosis.[25]

Multiple different approaches have been developed for cervical laminoplasty. These include the open-door or "hinge," midline "French window," and the Z-plasty techniques.[26,53] Each technique is aimed to allow expansion of the cervical canal with simultaneous preservation of a dorsal laminar cover. With these separate techniques, multiple reports have been able to clearly demonstrate that each technique of laminoplasty increases the functional diameter of the cervical canal.[37,48] In a recent review of the existing clinical literature, it was found that an approximately 55%–60% recovery rate was found for Japanese Orthopaedic Association scores following laminoplasty in patients with myelopathy in the setting of myelopathy or OPLL.[43] However, the predominance of the clinical data are retrospective in nature and any recommendations in favor of this technique are based on Class III evidence.[43]

The typical cervical laminoplasty performed in our practice is similar to the technique first described by Hirabayashi and Satomi.[26] This involves a standard dorsal exposure that includes the lamina and extends out to the facets bilaterally. A high-speed drill is used to make a unilateral bony trough on one side in a fashion similar to our standard laminectomy technique. This is the "open door" side of our laminoplasty. On the contralateral side, the drill is used to create a "greenstick" fracture and the "hinge" side of the trough is only developed to partial depth (Figs. 5 and 6). Gentle tension is then applied with a Kocher or other instrument and allows the spinous process and laminar complex to be hinged dorsally, away from the thecal sac. This effectively increases the volume of the cervical canal (Fig. 7). The decompression is then maintained with the application of titanium miniplates. Selective cervical foraminotomies can be performed as needed to relieve cervical radicular compression in an effort to prevent postoperative C-5 deltoid palsy.

Figure 5.

Illustrations showing the surgical steps in cervical laminoplasty using a modification of the open-door method first described by Hirabayashi and Satomi. A and B: A full-thickness trough is developed on one side while a "greenstick" fracture is prepared on the other side. C: A small bone graft is placed following angled "hinging" of the lamina and this is held in place with segmental hardware. Reprinted with permission from Aesculap, Inc.

Figure 6.

Intraoperative photograph showing a standard final construct following placement of segmental bone grafts and titanium miniplates (Aesculap, Inc.) for a C3–7 laminoplasty. The lateral mass of C-7 and lamina and spinous process at this same level can be seen clearly. Rostral exposure begins to the left side of the image.

Figure 7.

Postoperative axial CT showing positioned bone graft. Increased axial dimension at this level is shown with the dotted line corresponding to the initial dimensions of the cervical canal.

A description of our view of the advantages and disadvantages of anterior versus posterior surgical approaches is shown in Fig. 8.

Figure 8.

Chart showing our perceived advantages and disadvantages of anterior versus posterior techniques for decompression in OPLL. The merits of each approach should be weighed for each unique case. Dec. = decreased.

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