Conservative Treatment of Ossification of the Posterior Longitudinal Ligament in the Cervical Spine

Conservative Treatment of Ossification of the Posterior Longitudinal Ligament in the Cervical Spine

Masatoshi Sumi

, Minoru Doita

, and Kotarou Nishida

Introduction

The pathology of ossifi cation of the posterior longitu- dinal ligament (OPLL) is progressive stenosis of the spinal canal [1], which may cause compression myelop- athy, radiculopathy, or both. Thus, it is usually recom- mended that patients with OPLL undergo immediate surgical treatment; conservative treatment is not com- monly applied initially [2]. Surgical decompression is also recommended to prevent trauma-induced aggra- vation of myelopathy or spinal cord injury [3,4] by acci- dental external force. However, even among patients with large amounts of OPLL, cases have been observed with no incidence of myelopathy or with only mild myelopathy that improved or remained unchanged for a long period after the application of conservative treatment [1,5,6]. Because the indications and role of conservative treatment in OPLL are still obscure, it is important to understand both the natural course of OPLL and the pathology of the myelopathy resulting from OPLL so indications for conservative treatment can be extrapolated.

Progression of OPLL and Its Natural Course

OPLL develops in thickness and length during its natural course. A radiological study of OPLL progres- sion in 167 patients followed for more than 10 years after application of conservative treatment has been previously reported [7]. A distinct development in the thickness and length of OPLL was observed in 19%

and 35% of patients, respectively. Among patients who exhibited an onset or aggravation of myelopathy, 42%

showed an increase in the size of the OPLL. In other words, 58% of patients with an onset or aggravation of myelopathy did not show an increase in OPLL size.

Therefore, the gradual progress of static compression on the spinal cord in OPLL is estimated to be only one of many factors that affect the course of myelopathy.

The natural course of myelopathy is not yet under- stood regardless of its etiology (cervical spondylosis, disc herniation, OPLL). In terms of cervical spondylotic myelopathy (CSM), opinions are divided regarding long-term results between a benign, nonprogressive course [8–13] and a poor prognosis [2,14,15]. However, there has been only one randomized controlled pro- spective study published that did not show any impor- tant differences in outcomes between patients treated surgically and those managed conservatively after a 3- year follow-up [12]. This study was based on cases with mild myelopathy (JOA score of 12 points or more). In contrast, another prospective multicenter study noted that surgically treated patients appeared to have better outcomes than conservatively treated patients [15].

Unfortunately, the extent of myelopathy in the patients was not clarifi ed in this report. Articles that stress the importance of conservative treatment and the benign prognosis of myelopathy have tended to focus on patients with mild myelopathy or to cite the degree of disability at the time of initial evaluation as the main factor affecting prognosis [8,11,13]. These results indi- cate that the prognosis of mildly affected cases might be benign, whereas the prognosis for more severely dis- abled patients at the initial visit might be poor.

Matsunaga et al. [5] reported that the rate of onset of myelopathy was 17% after studying 323 OPLL patients without myelopathy at their initial visit during a 17.6- year follow-up. In contrast, aggravation of the myelopa- thy was observed in 64% of patients who exhibited myelopathy at the initial visit. Sawamura et al. [6]

reported aggravation of myelopathy at 39% by follow- ing 52 patients with mild myelopathy due to OPLL (average JOA score 12.7 points) after conservative treat- ment. One interesting result reported in their article was that “improvement of myelopathy” followed con- servative treatment in 44% of the patients.

1Department of Orthopaedic Surgery, Japan Labour Health and Welfare Organization, Kobe Rosai Hospital, 4-1-23 Kagoike-dori, Chuo-ku, Kobe 651-0053, Japan

2Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan

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The extent of myelopathy at the fi rst visit might affect the prognosis of myelopathy due to OPLL. One com- parative study showed no difference in fi nal disabilities related to daily living between the surgery group and the conservative therapy group among OPLL patients with mild myelopathy (grade 1 or grade 2 [16]), whereas conservative therapy has been reported not to be effi ca- cious in patients with moderate myelopathy (grade 3 or 4 [16]) [5]. These results suggest that OPLL patients with mild myelopathy are good candidates for conser- vative treatment. However, taking into account the relatively high rate of aggravation of myelopathy [5,6], surgeons should recognize that a larger amount of com- pression on the spinal cord by OPLL than is seen with CSM might be an indication of a worse prognosis.

Aggravating factors should be investigated, especially when considering whether to apply conservative treat- ment initially.

Dynamic Factors in Myelopathy Due to OPLL

In addition to a static compression factor, similar to CSM, dynamic factors may play an important role in the progression of myelopathy due to OPLL. Penning [17] reported a “pincer mechanism” that occurs in cases of retrolisthesis when the cervical spine is extended, causing spinal cord compression. Kataoka and Kurihara [18] stressed the importance of this mechanism as a dynamic factor in the pathology of CSM. Dynamic factors, including normal and abnormal movement and so-called spinal instability, are sug- gested as important etiological factors; and because these movements are changeable, they can be controlled to some degree. Thus, immobilizing the spine might be an effective conservative treatment.

The range of motion (ROM) of the cervical spine with OPLL, seen by radiography, has been reported to be one of the clinical factors affecting the onset and aggrava- tion of myelopathy [3,5]. Patients with myelopathy and mild stenosis ( <60%) had a more extensive ROM (75.6°) than patients without myelopathy and with mild steno- sis (only 36.5°) [5]. Furthermore, the type of ossifi cation was a factor that indicated prognosis. A signifi cantly higher risk of aggravating the myelopathy was found in the segmental and mixed types of OPLL than in the continuous type [1,6]. Because the mean ROM in the continuous type was signifi cantly lower than in other types [3], it is hypothesized that some movement adja- cent to the compression site due to ossifi cation might induce the onset or aggravation of myelopathy. The importance of dynamic factors is also verifi ed by articles on spinal cord injury associated with OPLL or trauma-induced myelopathy with OPLL [3,4,19].

Matsunaga et al. [19] indicated that there was a signifi - cantly higher risk of trauma-induced myelopathy in patients with the mixed type of OPLL (67%) than with the continuous type (3%). Koyanagi et al. [4] reported that spinal cord injury occurred frequently at the caudal edge of the OPLL in patients with continuous- or mixed- type OPLL and at the disc level in patients with the segmental type, where abrupt movements induce com- pression by an adjacent OPLL mass on the spinal cord.

Not only with trauma but also during ordinary daily life, movement at the edge of, or adjacent to, the OPLL can lead to the onset and aggravation of myelopathy;

this is known as the “dynamic factor.” Therefore, pre- venting movement of the cervical spine is indicated as a possible conservative treatment of OPLL.

Extent of Compression of the Spinal Cord and Prognosis

After investigating nine OPLL autopsy cases, Kameyama et al. [20] classifi ed the cross-sectional shape of the spinal cord at the most severely affected segment into two categories: boomerang shape and triangular. The boomerang shape was defi ned as a spinal cord with a convex lateral surface and a concave anterior surface.

The triangular-shaped spinal cord has an angular lateral surface and a fl at anterior surface. The boomerang shape indicates major pathological changes restricted to the gray matter with relatively well-preserved white matter even under severe compression. The triangular shape indicates more severe, irreversible pathological changes involving both white and gray matter.

Sawamura et al. [6] classifi ed the cross-sectional shape of the spinal cord, seen on the axial view in T1- weighted MR images at the most severely affected segment, into three categories: ovoid, boomerang, and triangular shapes (Fig. 1). The ovoid shape is added to Kameyama et al.’s categories by defi ning an additional shape with a convex or straight anterior surface and a convex lateral surface. Aggravation of myelopathy was observed in 86% of patients with triangular shaped spinal cords, in contrast to only 21% of patients with boomerang-shaped cords and 33% of patients with ovoid-shaped cords.

Although the importance of increased signal inten-

sity (ISI) in the spinal cord on T2-weighted images has

been discussed in correlation with myelopathy pro-

gnosis, the signifi cance of the pathology of ISI is not

yet understood. Therefore, up to now, the classifi cation

based on the cross-sectional shape of the spinal

cord [20] has provided the best indication of the extent

of destruction in the spinal cord and is the most

accurate method for predicting the prognosis of OPLL

patients.

Conservative Treatment Methods

Prevention of movement in the cervical spine appears to be the most effective conservative treatment for OPLL, and thus immobilization of the neck with an orthosis and intermittent bed rest has been shown to offer some relief of symptoms and signs. Immobiliza- tion diminishes irritation and compression, and iso- metric exercises can be used in conjunction with cervical immobilization [21]. The results of immobilization for patients with cervical myelopathy have been reported in only a few articles. Roberts [8] noted that 42% of his patients treated with immobilization of the neck in a plastic or metal frame collar accompanied by 2–3 weeks of bed rest in hospital experienced alleviation of their symptoms. Kadanka et al. [12] also reported a good prognosis for mild myelopathy after intermittent cervi- cal immobilization with a soft collar, similar to the degree of success achieved with surgery.

Borden [22] reported the effectiveness of continuous cervical traction in hospital for cervical spondylotic conditions. With this treatment, patients lie on the bed with their neck fl exed under continuous traction for as long as possible during the day for at least 2 weeks (Fig. 2). The advantage of this type of traction can be explained by the fl exed position and immobilization of the cervical spine. Our group has reported excellent results for cervical radiculopathy and relatively good results for cervical myelopathy using this continuous traction in hospital [6,10,13]. Eighty percent of CSM patients with a symptom duration of 3 months or less were reported to show improvement after traction [10].

Similarly, the results of this treatment for patients with mild myelopathy due to OPLL was also shown to be relatively good, with 62% of patients showing improve- ment immediately after treatment [6]. Although cervi- cal traction is recommended as a conservative treatment for OPLL, the cervical spine should be carefully immo- bilized in a fl exed, not extended, position as further hyperextension caused by inappropriate positioning could lead to additional spinal cord compression [21].

Although the results of conservative treatment seem to be favorable, especially for patients with mild myelopathy [6,11,12], careful follow-up is necessary after treatment. Risk factors for a poor prognosis after

conservative treatment or allowing the natural course of the disease to progress are the severity of the myelop- athy [5–7,11,12], a long duration of myelopathy [8,10], a triangular cross-sectional of the spinal cord at the most severely affected segment [6], segmental- or mixed-type OPLL [1,3,4,6,19], and more than 60% ste- nosis [5]. Patients with these factors should be followed especially carefully even after good outcomes following conservative treatment.

Conclusions

OPLL patients with mild myelopathy and without signs of worsening may be good candidates for conservative treatment. Immobilization of the cervical spine by various methods is an important principle of conserva- tive treatment for avoiding dynamic factors. If traction is selected as the method of immobilization, the cervical spine should be kept fl exed. Because some

spinal cord at the segment most severely affected by ossifi cation of the posterior longitudinal ligament (OPLL) on T1-weighted magnetic resonance imaging.

a Ovoid shape. b Boomerang shape. c Triangular shape. (Reprinted from Sawamura et al. [6], with permission)

Fig. 2. Continuous cervical traction in the hospital [22].

Patients lie on their backs with the cervical spine fl exed slightly and the apparatus applied to the neck. As the patient becomes accustomed to the traction, the duration of traction can be lengthened to one or a few hours. patients can read books or newspapers or watch television during traction.

Conservative Treatment of Cervical OPLL

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OPLL patients with mild myelopathy aggravate their myelopathy, and the surgical results of moderate myelopathy are superior to the results of conservative treatment, surgery should not be ruled out even if the outcome of conservative treatment is good, especially in patients with risk factors for a poor natural course or prognosis.

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