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

Complications, Monitoring, and Precautions

Approach-related Injuries

Anterior approach–related complications related to injury to the soft-tissue structures of the neck are well known. These include temporary or permanent dysphagia, recurrent laryngeal or superior laryngeal nerve injury, vertebral artery injury, esophageal perforation, and soft-tissue swelling that constricts the airway and necessitates prolonged intubation or tracheostomy.[4] Timing of extubation is particularly difficult in patients with previous operations, lengthy operations, obesity, or significant comorbid conditions. Elective tracheostomies, although rare, should be entertained in patients who cannot be safely extubated. While a posterior approach avoids many of these potential complications, commonly there is significant postoperative muscular spasm and pain related to the approach. Significant early and long-term axial neck pain may also occur after cervical laminoplasty.[7] The cause of this axial neck pain remains poorly understood; however, many authors have attempted to better preserve the paravertebral muscles in an attempt to reduce this type of pain.[28]

Dural Injury and CSF

In cases of OPLL, the anterior approach presents a significant risk of dural injury and subsequent CSF leak. Epstein et al.[19] reported that this can occur in up to 35% of patients treated by anterior corpectomy for advanced OPLL. Yamaura et al.[70] described the operative "anterior floating method" for focal decompression and fusion in OPLL. Any specific area that has suspected dural erosion is separated from the surrounding tissue and allowed to float free. This allows for adequate decompression while minimizing the risk of dural trauma associated with direct decompression. Dural ossification can be identified prior to the operation by using CT scanning,[24] and the surgeon should always have a high index of suspicion. In our experience, areas suspicious for dural ossification may be avoided during decompression. We do not believe that this jeopardizes the degree of cervical decompression. However, it may require a more extensive lateral exposure and potentially increases the risk of neurovascular injury. If a CSF leak is encountered, a lumbar drain is placed. In our experience, maintaining drainage for 5–7 days will ensure that the dura is sealed. Use of a small intraoperative ultrasongraphy device is often beneficial in confirming the adequacy of the decompression and restoration of the subarachnoid dural CSF pulsations.

C-5 Palsy Following Cervical Decompressive Surgery

Postoperative upper-extremity paresis is a well-known and troubling complication following cervical decompression surgery. It appears primarily to be associated with the C-5 nerve and can result in temporary, or less commonly permanent, deltoid weakness. While paresis of the other cervical nerves (C6–8) can occur in isolation or combination, these have been reported with a significantly lower incidence.[6,67] In patients with postoperative C-5 palsy, half of the affected patients will have primarily sensory deficits and/or severe pain in the C-5 dermatome (shoulder region) with motor weakness and the other half will have primarily weakness of the deltoid and biceps brachii muscles.[72] Sakaura et al.,[57] in an analysis of multiple reports, found the average incidence of postoperative C-5 palsy to be 4.6% (range 0%–30%). The frequency of this complication did not appear to correlate with the direction (anterior vs posterior) or exact type of approach. The average incidence was 4.3% for anterior decompressive techniques and there was a similar rate, 4.7%, for laminoplasty.[57] A recent review of more than 700 cases of instrumented cervical decompression also showed similar rates between ventral as opposed to dorsal decompressions (J Eck, presentation to the American Academy of Orthopaedic Surgeons, 2009).

Various mechanisms for the development of C-5 radiculopathy have been postulated; however, the precise mechanism remains controversial. The development of C-5 palsy immediately following surgery is presumed to be the result of direct nerve injury. However, this fails to explain the many cases of C-5 palsy that occur several days following an operation. Other reports have hypothesized either a traction or vascular phenomenon that contributes to nerve root injury. A traction hypothesis is supported by the unique anatomy of the C4–5 joint. The zygapophysial joint at C4–5 protrudes more anteriorly than the other joints, and the C-5 nerve root is shorter than adjacent segments. In addition, with a multilevel laminectomy, the C-5 root is the center of decompression. As a result, the greatest degree of posterior shift is believed to occur at this level.[62] Others have proposed either the development of local ischemia or reperfusion injury as a pathological mechanism. Chiba et al.[6] found that increased postoperative T2 signals occur more frequently in patients with upper-extremity palsy. This led to the proposal that reperfusion injury could contribute to damage to the proximal nerve root.

Patients with postoperative C-5 palsy generally have a good prognosis for functional recovery. Specific protocols for preventing these injuries have not yet been established. However, postoperative physical therapy, muscle strengthening exercises, and ROM exercises have been advocated to prevent the development of contractures and adhesive capsulitis (a clinical syndrome more commonly known as a "frozen shoulder"). In our own experience, these patients often show significant improvement in strength and ROM with time and physical therapy.

Graft-related Complications

Complications related to graft placement include the extrusion of the graft as well as the development of pseudarthrosis. Complications have been reported following multilevel ACC with and without the use of anterior plates. Saunders et al.[60] reported on 3 (9.7%) of 36 patients with acute graft extrusion following 4-level ACC. Vaccaro et al.[68] noted a 9% rate of graft extrusion with 2-level ACC and a significantly higher rate with 3-level anterior surgery. In these circumstances, immediate revision surgery is invariably required to replace the graft. However, when there is only partial extrusion, serial radiographic follow-up may be appropriate. These patients often will still develop a solid fusion without further complication.[3,9] However, with any radiographic signs of progression of graft displacement, further follow-up should likely include revision surgery. Reported rates of pseudarthrosis following ACCF for the treatment of OPLL are quite variable. In 76 patients with nonplated ACCF or multilevel nonplated ACC, Epstein[14] reported a 13% incidence of pseudarthrosis during the first 6 months. Swank et al.[63] noted a 31% rate of pseudarthrosis in 26 patients undergoing ACC. This rate was increased to 44% in patients with multilevel corpectomy constructs. Significantly better fusion rates were reported by Eleraky et al.,[11] who reported a 98.8% fusion rate in 87 patients with 1-level ACC and 98 patients with multilevel fixation. In the authors' experience, patients with asymptomatic nonunion can be clinically observed for evidence of graft extrusion. When pain is present in association with the nonunion, posterior cervical fusion may be chosen to relieve pain and to provide stability for fusion.

Postlaminectomy Kyphosis

The incidence of kyphotic change after multilevel laminectomy has been reported to be between 21% and 47% in larger retrospective series.[32,33] Although progressive kyphosis was seen in 47% of patients as reported by Kato et al.,[33] there appeared to be no effect on clinical outcomes. In a recent report by Cho et al.[8] in 14 patients treated by total laminectomy for OPLL, kyphosis was observed in all but 1 patient. However, similar to the series of Kato et al., progressive kyphosis did not lead to neurological deterioration. Facet injury is the most important contributor to postoperative kyphosis. An extension of the facetectomy to include greater than 50% is thought to result in significant kyphosis and resultant instability.[73]

Monitoring and Precautions During Cervical Spine Operations

It is our opinion that the patient with significant cervical compression due to advanced OPLL requires unique attention from the entire surgical team. Particularly difficult in these patients are the challenges of airway management following extensive anterior or combined anterior-posterior decompressive surgery. At our hospital, we recommend that all patients undergo awake, fiberoptic intubation to avoid injury due to hyperextension of the neck. We additionally have elected to extubate all patients on postoperative Day 1 or later when the patient has undergone multilevel corpectomy or combined anterior-posterior surgery. All patients are also evaluated for the ability to ventilate around a deflated endotracheal cuff.[3] Perioperative steroids are routinely administered. Intraoperative blood pressure is closely monitored throughout all cases to avoid any hypotension. We have found that fiberoptic evaluation of the vocal cords has been beneficial in high-risk patients (prior anterior surgery, obesity, chronic obstructive pulmonary disease, or significant blood loss). If significant airway edema is encountered, extubation is commonly delayed into the 1st postoperative week. The use of continuous intraoperative electrophysiological monitoring during either anterior or posterior cervical approaches for OPLL is used during all cases at our institution. The use of this monitoring, specifically motor evoked potentials, may serve as a sensitive means to diagnosis potential neurological injury during decompression.[56] In our opinion, the use of motor evoked potentials represents the current best clinical practice and is a sensitive real-time mechanism for detecting injury. This is especially important for anterior compression of the ventral horns.

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