Overview of Treatment for Ossification of the Longitudinal Ligament and the Ligamentum Flavum

Overview of Treatment for Ossification of the Longitudinal Ligament and

the Ligamentum Flavum

Motoki Iwasaki

Introduction

The Investigation Committee on Ossifi cation of the Spinal Ligaments, subsidized by the Japanese Ministry of Health, Labor, and Welfare, has conducted various studies of the ossifi cation of the posterior longitudinal ligament (OPLL) and ossifi cation of the ligamentum fl avum (OLF) since 1975. In 2002, the Committee estab- lished a subcommittee on clinical practice guidelines, which set out to systematically review articles on OPLL.

This review, presented in this chapter, is based on knowledge obtained by that subcommittee.

For cervical myelopathy secondary to OPLL, modali- ties that have been applied for myelopathy due to spondylosis and disc herniation have been adopted for the most part. When strictly classifying modalities for OPLL, the treatment is either conservative or surgi- cal; the former includes (1) a cervical orthosis and halter or skull traction that aims to avoid the effects of dynamic factors; (2) corticosteroids for spinal cord edema; (3) nonsteroidal antiinfl ammatory drugs (NSAIDs) for pain control; (4) bisphosphonates to prevent progression of the ossifi cation; and (5) alterna- tive medicine for pain control. The latter consists of spinal cord decompression by an anterior or posterior procedure and spinal stabilization.

Conservative Treatment

Studies have suggested that dynamic factors play an important role in the development of cervical myelopa- thy and radiculopathy in OPLL [1–3]. Cervical myelop- athy is recognized in all patients in whom more than 60 % of the spinal canal is compromised by OPLL. On the other hand, in patients with less than 60% spinal canal stenosis, the range of motion of the cervical spine is signifi cantly greater in patients with myelopathy

than those without myelopathy [2,3]. In a study of the natural history of OPLL in 207 patients, clinical symptoms did not change in 66% of patients, whereas preexisting myelopathy was aggravated in 7% [1]. In addition, a long-term follow-up cohort study of patients with OPLL reported a 71% myelopathy-free survival rate after 30 years in patients who did not have mye- lopathy at their fi rst presentation [3]. These studies of the natural history of the disease indicate that dynamic factors as well as static factors play an important role in the development of myelopathy, especially with mixed- or segmental-type OPLL [1–3]. Therefore, con- servative treatment of cervical OPLL is indicated to eliminate dynamic factors for patients whose predomi- nant complaint is neck/shoulder/arm pain (local pain, radicular pain, or both) without any symptoms of mye- lopathy or patients with mild ossifi cation in whom myelopathy is subclinical and not predominant. On the other hand, conservative treatment for thoracic OPLL or OLF is less effective because the thoracic spine is less mobile and has a narrower spinal canal than the cervi- cal spine.

Conservative treatment of cervical OPLL aimed at eliminating exposure to dynamic factors includes methods such as cervical orthosis, halter traction, and skull traction using a halo ring. Although no scientifi c evidence supports the effectiveness of such conserva- tive treatments, they are thought to have short-term benefi ts at most, and it remains unclear which conser- vative approach is preferable. Therefore, patients with obvious myelopathy cannot be treated adequately by nonoperative conservative treatment.

A positive head compression test is a good selection criterion for applying cervical traction [4]. When trac- tion is indicated for patients with cervical OPLL, it is important to keep patients comfortable with the cervi- cal spine in slight fl exion. If cervical traction increases the pain, the direction of the traction should be changed or the traction stopped entirely. Cervical traction in the neck-extended position should be avoided as it risks precipitating or promoting myelopathy. Alternative medical treatments such as acupuncture, massage, and spinal manipulation are considered effective for patients whose complaints consist solely of neck/shoulder/arm Department of Orthopaedic Surgery, Osaka University

Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565 -0871, Japan

165

166 M. Iwasaki

pain or stiffness (or both) without any symptoms of myelopathy [5]; however, there is no scientifi c evidence of benefi t. Physicians should also be aware that the lit- erature contains several reports on neurological risks during spinal manipulation in patients with OPLL and spinal canal stenosis [6–8]. Therefore, patients with moderate or severe myelopathy should not be treated with spinal manipulation.

With regard to medication, NSAIDs and muscle relaxants are considered effective for local pain and stiffness. However, the only medication available for OPLL and OLF is bisphosphonate [9], which is believed to prevent OPLL progression after surgery. In practice, when symptoms and signs of myelopathy are absent or are slight and do not limit activities of daily life, con- servative treatment is indicated. In particular, when patients with cervical OPLL complain mainly of neck pain, radicular pain, or both, physicians should select conservative treatment. It is important to advise patients with OPLL not to hyperextend the neck and to be vigilant regarding trauma and falls due to sports activities or excessive alcohol intake.

When disturbed circulation in and around the spinal cord is assumed to be an etiological factor for myelopa- thy, remedies that improve the circulatory condition may be applied, such as corticosteroids, recently pros- taglandin E

(PG

), and so on. However, no evidence has been established regarding the effi cacy of these drugs.

Surgical Treatment

Surgical decompression is indicated for patients who have long tract signs such as spastic gait disturbance and clumsiness of the hands. Surgical treatment is not generally recommended when the sole symptom is pain. Even among patients with myelopathy, surgical treatment is not always effective in patients whose pre- dominant complaint is pain.

Surgical decompression of the spinal cord is neces- sary for patients with obvious myelopathy because long-term compression of the spinal cord may cause irreversible degeneration. For patients with symptoms and signs of moderate or severe myelopathy, early sur- gical decompression is recommended, particularly for relatively young patients with a narrow spinal canal, because reports indicate that better neurological recov- ery is associated with younger age at operation and mild myelopathy [10]. Even if the myelopathy is mild, surgery may be indicated for patients with severe spinal stenosis (SAC: space available for the spinal cord <6 mm or an occupying ratio >60%) [2,11]. During the natural course of OPLL, all patients with a SAC of <6 mm suf- fered myelopathy [2]. However, there is no evidence indicating the effectiveness of prophylactic surgical decompression for patients who have no or slight

symptoms or signs of myelopathy [11]. Because myelop- athy is often exacerbated by minor trauma and hyper- extension of the neck, physicians should meticulously weigh the surgical indications, taking into consider- ation the occupying ratio of ossifi cation, space available for the spinal cord, and dynamic factors [3,11].

Some controversy exists over the appropriate method of surgery for myelopathy caused by cervical OPLL.

There are two surgical options: (1) an anterior proce- dure with extirpation or fl oating of the ossifi ed lesion or (2) a posterior procedure that includes various types of expansive laminoplasty. Regarding the anterior pro- cedure, extirpation of the ossifi ed lesion is not always necessary, and anterior fl oating with thinning of the ossifi ed lesion can work well [12,13]. Although these two procedures do not differ signifi cantly in terms of surgical outcome [10,13], the anterior procedure is usually selected when OPLL involves fewer than three intervertebral levels, whereas the posterior procedure is usually selected when more than three levels are affected. In addition, when preoperative alignment of the cervical spine is kyphotic or the preoperative occupying ratio of ossifi cation is relatively high, the anterior procedure with extirpation or fl oating of the ossifi ed lesion can yield outcomes superior to those achieved with posterior decompression [14]. For both procedures, a poorer prognosis is associated with older age at surgery, severe preoperative symptoms of myelopathy, and a history of trauma causing onset or progression of myelopathy [10,15]. Intramedullary hyperintensity on MR imaging (T2-weighted images) refl ects myelomalacia and neurological severity, although this fi nding does not indicate a poor outcome after decompression surgery [16].

The only surgical treatment currently available for OLF of the thoracic spine is posterior decompression.

However, the surgical outcome of this procedure for myelopathy caused by thoracic OPLL has generally been poor and inferior to that of myelopathy caused by cervical OPLL. The treatment of choice for thoracic OPLL depends on the spinal level of the ossifi cation, coexistence of OLF, and the degree of thoracic kypho- sis. The relative importance of these factors remains controversial among surgeons. For patients with OLF and thoracic OPLL, the most common choices of treatment are anterior decompression via a posterior approach, extensive cervicothoracic laminoplastic decompression, wide laminectomy with posterior instrumentation, lateral rachotomy, and combined anterior and posterior decompression [17–21].

Surgical Complications

Complications associated with the anterior procedure

include graft-related complications and adjacent

segment involvement after spinal fusion. On the other

Overview of Treatment for OPLL and OLF 167 hand, complications associated with posterior decom-

pression include postoperative neck/shoulder/arm pain, nerve root palsy (commonly C5), and progression of ossifi cation, although the causes of these complica- tions related to posterior decompression remain unclear. Regarding progression of the ossifi ed lesion, OPLL generally continues to progress after surgery. The incidence of OPLL progression after posterior decom- pression is approximately 50%–60% at 2 years and 70%

at 10 years or more. Younger patients ( <59 years of age) and patients with mixed- or continuous-type OPLL are at higher risk for progression [10,22].

With regard to surgical complications of thoracic myelopathy due to thoracic OPLL, postoperative para- plegia is unfortunately still sometimes associated with each procedure because of technical diffi culties and the vulnerability of the thoracic spinal cord. Surgical treat- ment of thoracic OPLL remains one of the most chal- lenging problems for spinal surgeons.

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