Choice of Surgical Procedure Motoki Iwasaki

Choice of Surgical Procedure

Motoki Iwasaki

and Kazuo Yonenobu

Introduction

With ossifi cation of the longitudinal ligament (OPLL), the pathological lesion lies in front of the spinal cord, and its removal has been thought to be a radical treatment from the time of its fi rst recognition. Thus, attempts to remove the ossifi ed lesion were abandoned because of the technical diffi culty. With the develop- ment of surgical instruments and techniques for spinal surgery, access to the ossifi ed lesion by resecting the vertebral body, such as the fl oating method described by Yamaura et al. [1], have been developed. Since then, the choice of procedure has been the subject of argu- ment among spine surgeons.

A surgical procedure that is most appropriate for the particular pathomechanism in each patient should be chosen. However, the mechanism behind the myelopa- thy in most patients with OPLL is multifactorial, so it is diffi cult clinically to clarify the exact pathomechanism of the myelopathy in a particular patient. Hence, argu- ments over the choice of surgical procedure for the condition have continued and are based on speculation about the pathomechanism and the clinical and labora- tory evaluations, including a neurological examination, radiographic examination, the degree of surgical inva- siveness, and possible surgical complications. This means that at this moment no criteria for choosing a surgical procedure have been established based on sci- entifi c evidence. In this chapter we summarize the long- time argument over this issue and discuss the choice of procedure for the condition.

Indications for Surgical Treatment

The goal of surgical treatment is to achieve adequate decompression of neural elements and to stabilize the

cervical spine to eliminate static compression factors and dynamic factors. Surgical treatment is indicated for patients who have long tract signs, such as spastic gait disturbance and clumsiness of the hands, whereas it is not always effective for pain relief in patients whose predominant complaint is neck/shoulder/arm pain, even if myelopathy is present. Therefore, surgical treat- ment is not generally recommended for patients in whom pain is the only symptom.

Surgical decompression of the spinal cord is necessary 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, however, early surgical decompression is recommended, particularly for rela- tively young patients with a narrow spinal canal, because reports indicate that better neurological recovery is asso- ciated with younger age at operation and milder myelop- athy [2]. 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 occupy- ing ratio of >60%), as all patients with SAC < 6 mm suffer from myelopathy [3,4]. Some controversy exists regard- ing surgical indications for patients with severe spinal stenosis due to OPLL but without any symptoms or signs of myelopathy. In patients with OPLL, trauma often induces myelopathy or infl uences neurological symp- toms. In addition, in patients with trauma-induced myelopathy, neurological symptoms tend to be severe and the surgical outcome poor [3,5–7]. However, there is no evidence of the effectiveness of prophylactic surgi- cal decompression for patients who have no or slight symptoms and signs of myelopathy [3].

Choice of Surgical Procedures for the Condition

Two opinions exist regarding the appropriate choice of surgical procedure for cervical myelopathy due to OPLL. The advantages of the anterior procedure are accomplishing effective decompression by removing the ossifi ed lesion, preventing progression of OPLL,

1Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan

2National Hospital Organization, Osaka Minami Medical Center, 2-1 Kidohigashi, Kawachinagano, Osaka 586-8521, Japan

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and stabilizing the cervical spine once the graft has attained solid fusion. On the other hand, the advantages of posterior decompression are a lower incidence of surgical complications and of additional surgery for the cervical spine [2,8]. Previous reports have not shown any signifi cant difference in long-term surgical outcome between the posterior and anterior procedures [2,9].

Hence, when surgical decompression is indicated for patients with cervical OPLL, most surgeons in Japan select expansive laminoplasty or anterior decompres- sion and fusion with extirpation or fl oating of the ossi- fi ed lesion, depending on the surgeon’s preference and the patient’s request. In general, the anterior procedure is selected when three or fewer intervertebral levels are affected, and the posterior procedure is selected when OPLL involves more than three levels and coexists with developmental canal stenosis. In addition, when the preoperative occupying ratio of OPLL is relatively high ( >60%), the sagittal ossifi ed lesion is hill-shaped (Fig.

1 A), or preoperative alignment of the cervical spine is kyphotic, the anterior procedure with extirpation or fl oating of the ossifi ed lesion can yield outcomes supe- rior to those achieved with posterior decompression [8,10,11]. Because no single procedure has yet been proven signifi cantly superior, the surgical procedure for a particular patient with cervical myelopathy due to OPLL should be chosen based on the following consid- erations [10,11]: age and general condition of the patient, extent of ossifi cation, OPLL type and sagittal shape of the ossifi ed lesion, OPLL occupying ratio, sag- ittal curvature of the cervical spine and spinal cord, and dynamic spinal instability between the interrupted ossi- fi ed lesions.

The pathological process causing OPLL occurs ventral to the spinal cord, and several surgeons have stated that posterior decompression alone does not achieve appropriate decompression of the spinal cord.

Such surgeons have accordingly attempted to remove ossifi ed lesions using the anterior approach. However, surgical results of anterior procedures are variable owing to insuffi cient decompression resulting from ossifi cation of the dura or massive bleeding from the epidural space. In 1975, Yamaura and colleagues con- sequently devised the anterior fl oating method in which the spinal cord was decompressed without total resec- tion of the ossifi ed lesion [1]. This anterior fl oating method, which is described in detail in another chapter, has made anterior decompression surgery safer and more reliable for cervical myelopathy due to OPLL. The advantages of this procedure include gradual decom- pression without extirpation but with an anterior shift of the OPLL to avoid dural tears caused by ossifi cation of the dura and lower risk of injury to neural tissues.

However, the main problem with anterior decompres- sion is restenosis at levels adjacent to the fusion area caused by postoperative progression of OPLL or spinal

instability. Matsuoka et al. reported that posterior decompression of the cervical spine was required post- operatively in 8% of the patients who underwent the anterior fl oating procedure [9]. Although anterior decompression and fusion is technically demanding and has a higher incidence of surgery-related complica- tions, anterior decompression and fusion has an advan- tage over laminoplasty for patients with the following characteristics [10,11]: (1) OPLL occupying ratio of

>60%; (2) hill-shaped ossifi cation; (3) locally kyphotic alignment of the cervical spine or the spinal cord; (4) dynamic spinal instability between the interrupted ossi- fi ed lesions.

With posterior procedures for OPLL (e.g., expansive laminoplasty), posterior shift of the anteriorly com- pressed spinal cord should provide decompression.

Laminectomy was once the procedure of choice for cer- vical OPLL [12]. However, because laminoplasty has biomechanical and clinical advantages over laminec- tomy [13–16], expansive laminoplasty has become the current major treatment of choice for posterior decompression—not only for OPLL but also for cervical spondylotic myelopathy [2]. In general, expansive lami- noplasty is effective and safer for most patients with the following characteristics [10,11]: (1) OPLL occupying ratio of <60%; (2) plateau-shaped ossifi cation (Fig. 1B);

(3) lordotic alignment of the cervical spine or the spinal cord. Our clinical experience indicates that lamino- plasty is not contraindicated for patients with preopera- tive kyphotic alignment of the cervical spine if the kyphosis is mild and reducible [2].

Internal rigid fi xation is rarely necessary for surgical treatment of OPLL. Utilization of spinal instrumenta- tion would not be recommended for laminoplasty because one of the advantages of laminoplasty is pres- ervation of some movement of the cervical spine.

Anterior plates and screws are rarely necessary for the anterior procedure if a halo vest is worn for 6–10 weeks.

However, posterior instrumentation is often used during salvage surgery for dislodgement or pseudar- throsis of a bone graft [8].

Long-term ( >10 years) results of laminoplasty [2]

and of the anterior fl oating method [9] are summarized

in Table 1. Statistical analysis indicates that the predic-

tive factors affecting clinical results of posterior decom-

pression are the preoperative severity of the myelopathy

[low total Japanese Orthopaedic Association (JOA)

score] and age at surgery [2,11,12]. These long-term

results demonstrate that the OPLL occupying ratio or

SAC is statistically unrelated to the surgical outcome of

posterior decompression [2,12], whereas retrospective

studies of OPLL with an occupying ratio higher than

50 %–60% demonstrate that anterior decompression

and fusion is safer than laminoplasty [10,11,17]. With

the anterior fl oating method, a good outcome is strongly

associated with the preoperative severity and the dura-

tion of the myelopathy, preoperative cross-sectional area of the spinal cord, and age at the last follow-up [9].

Thus, in general, a poor prognosis is associated with longer duration of symptoms, older age at surgery, more severe preoperative symptoms, and a history of trauma causing the onset or progression of myelopathy [2,6,7,18,19].

Progression of OPLL

OPLL generally continues to progress after surgery. In a Japanese nationwide multicenter study, the incidence of OPLL progression was 56.5% at 2 years after poste- rior decompression and 71% at 5 years (Kaplan-Meier

analysis) [20]. In this multicenter study, younger patients ( <59 years of age) had a higher risk of progres- sion [20]. Patients with mixed- and continuous-type OPLL had a higher rate of progression, whereas patients with the segmental type had the lowest incidence of progression [2,20,21]. In a long-term follow-up study, postoperative progression of ossifi cation was observed in 70%–73% of patients who underwent posterior decompression, but few were found to have related neurological deterioration [2,12,20,21]. Additional cer- vical surgery was required to treat progression of OPLL in only 1 of 64 patients (2%) undergoing laminoplasty [2]. On the other hand, the incidence of postoperative progression after anterior decompression and fusion has been found to range from 36% to 64%, which is lower than the rate for posterior decompression [9,22].

Fig. 1. Sagittal shapes of ossifi cation [8,11]. A Tomogram shows a hill-shaped ossifi ed lesion. B Radiograph shows a plateau- shaped ossifi ed lesion

A B

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References

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Laminoplasty versus laminectomy and fusion for multi- Table 1. Long-term (>10 years) results of laminoplasty and anterior fl oating procedure for cervical OPLL

Parameter Laminoplasty [2] Anterior fl oating method [9]

No. of patients 64 63

M/F (64/21) (45/18)

Follow-up (years) 12.2 13.0

Age at surgery (years) 56 57

Occupying ratio of OPLL 38% 54%

SAC (mm) 8.5 5.2

Preoperative JOA score 8.5 8.3

Postoperative JOA score 13.7 13.5

Recovery rate 60% 59%

Operating time (min) 179 323

EBL (g) 475 1099

Deterioration after surgery 0 0

Nerve root palsy 5% 10%

Progression of OPLL 70% 36%

Late deterioration of myelopathy 6 Cases (9%) 13 Cases (21%)

Cause Thoracic myelopathy (n= 3) Thoracic myelopathy (n= 6)

Progression of OPLL (n= 2) Inadequate decompression (n= 4) Spinal cord atrophy (n= 1) Progression of OPLL (n= 3)

Additional cervical surgery 1 Case (2%) 5 Cases (8%)

Data from Iwasaki et al. [2] and Matsuoka et al. [9]

JOA, Japanese Orthopaedic Association; EBL, estimated blood loss; OPLL, ossifi cation of the posterior longitudinal ligament

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