Anterior Decompression Through Posterior Approach for Thoracic Myelopathy Caused by OPLL: Ohtsuka Procedure

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Anterior Decompression Through Posterior Approach for Thoracic Myelopathy Caused by OPLL: Ohtsuka Procedure

Kuniyoshi Abumi

¹

, Manabu Ito

²

, and Akio Minami

²

Introduction

The incidence of ossiﬁ cation of the posterior longitudi- nal ligament (OPLL) in the thoracic spine is lower than that of cervical myelopathy caused by cervical OPLL.

However, once compressive myelopathy appears at the thoracic spine, which is mechanically more stable than other spinal levels by nature, conservative treatment such as rest or immobilization by brace is considered ineffective [1–3]. Accordingly, decompression surgery is usually recommended for patients with severe or moderate thoracic myelopathy caused by OPLL. For thoracic myelopathy due to OPLL, it has been pointed out that the results of posterior decompression are uncertain or even poor in many patients [4,5]. The main reason for these poor results is that the thoracic spine is naturally kyphotic, and the spinal cord is compressed anteriorly. At the present time, choices of treatment for thoracic OPLL consist of anterior decom- pression through the anterior or posterior approach, posterior extensive laminectomy, and circumferential anterior and posterior decompression [6–13]. The choice of a surgical decompression procedure is still controversial among surgeons. In general, for patients with spinal cord compression caused by OPLL at the kyphotic portion of the thoracic spine, anterior decom- pression is recommended. However, for some patients with mild kyphosis at the thoracic spine, a simple, less invasive posterior extensive laminectomy may be indi- cated for decompression of the OPLL [4,6].

In this chapter, we focus on the indications, surgical technique, and results of anterior decompression through the posterior approach for thoracic myelopa- thy caused by OPLL.

Indications for Surgery

In the upper and middle thoracic spine, the thoracic vertebrae are connected to the rib cage by the costover- tebral joints, providing a stabilizing effect against tho- racic spinal motion; and the mechanical stability of the upper and middle thoracic spine is greater than that of the cervical and lumbar spine [14,15]. Therefore, con- servative treatment including rest or an orthosis, which one might expect to diminish the dynamic factor in the progression of myelopathy, is ineffective for myelopa- thy caused by thoracic OPLL. In addition, it has been pointed out that surgical decompression for advanced myelopathy caused by long-term compression is gener- ally ineffective because of the irreversible pathological changes in the spinal cord. Therefore, early surgical decompression should be considered for progressive myelopathy caused by thoracic OPLL. However, surgi- cal procedures for decompression of thoracic OPLL involve a risk of neurological complications during or after surgery, such as direct spinal cord damage or epi- dural hematoma [12].

Among the various symptoms caused by thoracic myelopathy, gait disturbance and bladder and bowel dysfunction are disabling and signiﬁ cantly affect the activities of daily living. Therefore, the severity of gait disturbance and bladder dysfunction must be the primary focus when considering surgical intervention.

Myelopathy that is mild with sensory disturbance in the trunk or lower extremities and abnormal reﬂ exes of the lower extremities is not an indication for surgical treatment.

Possible Decompression Procedures for Thoracic OPLL

Direct removal of the compressive elements is reason- able for decompressing the compressed spinal cord.

OPLL in the anterior portion of the spinal canal com- presses the spinal cord anteriorly, causing deformity and posterior shift of the spinal cord. In the cervical

1Health Administration Center, Hokkaido University, N8 W5, Kita-ku, Sapporo 060-0808, Japan

2Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, N15 W7, Kita-ku, Sapporo 060- 8638, Japan

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spine with physiological lordosis, posterior decompres- sion for OPLL provides posterior shift of the decom- pressed spinal cord, with the results being satisfactory in most patients. In contrast, it is difﬁ cult to shift the spinal cord posteriorly by a posterior unrooﬁ ng lami- nectomy for OPLL in the thoracic spine with kyphosis, and results of posterior decompression for thoracic OPLL have been uncertain [4,5,6,12]. For this condi- tion, anterior decompression of the spinal cord is the appropriate decompression procedure.

Several anterior decompression procedures for tho- racic OPLL using the anterior approach, posterior approach, and combined anterior and posterior approach have been developed [8–10,12]. However, because of the technical diffi culties and extensive sur- gical invasion necessary to perform anterior decom- pression in the thoracic spine, posterior decompression procedures have occasionally been utilized for thoracic OPLL. This posterior decompression, which is effective in some patients with a specifi c condition, may be indi- cated for a limited number of patients with thoracic OPLL. In our experience, an upper thoracic lesion is a good indication for cervicothoracic laminectomy because the lordosis in the decompressed cervical level allows an effi cient posterior shift of the spinal cord [6,11]. In addition, even patients with a long OPLL lesion (from the upper to lower thoracic spine) are possible candidates for laminectomy. However, patients with a large kyphotic angle in the thoracic spine, espe- cially those with OPLL at the apex of the thoracic kyphosis, cannot achieve suffi cient restoration of spinal cord function. Patients with posterior compres- sion of the spinal cord by ossifi ed ligamentum fl avum (OLF) regained better spinal cord function by poste- rior decompression than patients without posterior compression.

Anterior Decompressive Procedures for Thoracic OPLL

If laminectomy is not considered a favorable method because of a greater degree of kyphosis or an absence of posterior spinal cord compression by OLF, as delin- eated on radiographic images, anterior decompression should be selected as the treatment of choice for OPLL.

The choice of the anterior or posterior approach for anterior spinal cord decompression for thoracic OPLL depends mainly on the number of spinal segments that require decompression, the level of OPLL in the spine, and the experience of the surgeons.

Anterior decompression through the anterior approach for thoracic OPLL is generally limited to three or four spinal segments. For thoracic OPLL that requires decompression of more than four segments, anterior

decompression through the posterior approach, devel- oped by Ohtsuka [9], is often indicated. This procedure may also be indicated for decompression of thoracic OPLL requiring a shorter area of decompression, such as two to four spinal segments.

Anterior decompression through the posterior approach consists of three procedures: (1) posterior decompression by extensive laminectomy as the ﬁ rst step, which includes resecting any coexisting OLF and resecting the medial part of the facet joint and the pars interarticularis; (2) mining the vertebral body laterally to anteriorly to the anterior aspect of the spinal cord;

and (3) intertransverse bone grafting with reinforce- ment using spinal instrumentation. The mining creates a V-shaped space at the anterior aspect of the spinal cord in the vertebral body, allowing forward transposi- tion of the spinal cord into the V-shaped space and sufﬁ cient decompression effect on the spinal cord (Fig. 1).

There is no restriction to the number of spinal segments to be decompressed by the procedure. In addition, the procedure can be applied from the cervi- cothoracic junction down to the thoracolumbar junc- tion; and it can be used in patients with spinal cord compression by OLF at the same spinal levels as OPLL or at spinal levels adjacent to the OPLL. Furthermore, patients with OPLL from the cervical spine to the upper thoracic spine can be managed simultaneously by combining the procedure with cervical posterior decompression. This procedure, which provides sufﬁ - cient decompression in patients with thoracic OPLL, requires more extensive resection of the posterior spinal elements, including the major part of the bilat- eral facet joints in the thoracic spine, producing insta- bility at the decompressed spinal segments [14–16]. To obtain dependable clinical results, the authors recom- mend performing additional reconstructive surgery using spinal instrumentation with intertransverse bone grafting.

Surgical Technique of Anterior Decompression Through the Posterior Approach for

Thoracic OPLL

Positioning the Patient

The patient is placed prone on a Relton-Hall frame

using a horseshoe-type headrest or the Mayﬁ eld head-

holder. The Mayﬁ eld head-holder is recommended for

patents with cervical OPLL or a spinal canal narrowed

by cervical spondylosis, thereby avoiding aggravation

of the cervical myelopathy. The cranial portion of

the thorax must be held with the additional use of a

rectangular holder, which helps avoid spinal cord injury

due to extensive spinal instability after the second step

of this procedure.

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Posterior Decompression by Extensive Laminectomy The thoracic spine should be extended laterally to the tip of the transverse process, taking into consideration the oblique insertion of a high-speed burr to the ante- rior portion of the spinal cord in the vertebral body during the second step of this procedure and the instru- mentation and bone grafting during the third step.

Extensive laminectomy must be performed using a high-speed burr. The right-to-left width of the laminec- tomy must be narrower at the level of the pars inter- articularis than it is at the pedicles to maintain bony continuity of the pars interarticularis, preserving the bone graft bed. Therefore, the margin of the laminec- tomy takes on a wave-like shape after decompression (Fig. 1a,b). Great care must be taken not to injure the dura mater, especially in patients with associated OLF at the decompression levels.

Mining the Vertebral Body and Anterior Decompression

At the ﬁ rst stage of mining the vertebral body, a high- speed diamond burr must be inserted from the intra- medullary cavity of the each pedicle down to the posterior portion of the vertebral body (Fig. 1d). The wall of the pedicle must be shaved in the cranial, medial, and caudal directions until the epidural space is exposed. The nerve root must be protected during this technique especially when shaving the caudal portion of the pedicle. Mining in the caudal and cranial direc- tion is complete near the intervertebral disc level.

During the second stage of the mining, the direction of the burr must be changed to a medial direction toward the midline of the vertebral body. Compressive force is required on the burr to shave the endplate of the vertebral body. The burr must be shaken cranially

Fig. 1. Sequence of anterior decompression through the pos-

terior approach. First step: Posterior decompression by extensive laminectomy, which includes resection of coexisting ossiﬁ cation of the ligamentum ﬂ avum (OLF) and resection of the medial part of the facet joint and the pars interarticularis (a, b). The blue zone indicates the range of extensive laminec-

tomy. Second step: Mining the vertebral body, beginning laterally and proceeding anteriorly to the anterior aspect of the spinal cord in the second step (c–f ). Mining the vertebral body creates a V-shaped space in front of the anterior aspect of the spinal cord, which induces in the vertebral body forward transposition of the spinal cord into the V-shaped space

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to caudally to complete mining the central portion of the vertebral body (Fig. 1c). Complete excavation of both sides is obtained throughout the decompression segments using the above-described technique (Fig.

1 e).

During the ﬁ nal stage of the mining, the residual ossiﬁ ed ligament or the most posterior portion of the vertebral body must be amputated at the most cranial and most caudal levels of the decompressed segments.

The residual ossiﬁ ed ligament is completely separated

from the vertebral body at this stage and allowed to shift anteriorly with the spinal cord (Fig. 1f ). This ante- rior shift of the spinal cord provides a sufﬁ cient decom- pression effect in patients with kyphosis and thoracic OPLL (Figs. 2, 3).

Extirpation of the Ossified Ligament

As noted, the anterior shift of the spinal cord provides a sufﬁ cient decompression effect for the most kyphotic

Fig. 2. Segmental-type ossiﬁ cation of the posterior longitudinal ligament (OPLL) at the apex of the thoracic kyphosis.

a Vertebrae involved (5–8). Preoperative and postoperative computed tomography (CT) scans (b, c) demonstrate sufﬁ -

cient anterior decompression by the anterior shift of the spinal cord. Posterior instrumentation and fusion were not indicated for this patient considering the relatively small range of posterior vertebral mining

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at the apex of the thoracic kyphosis. The spinal cord was compressed anteriorly by OPLL and posteriorly by OLF.

(a–c). The patient underwent anterior decompression through the posterior approach followed by posterior instrumentation and fusion (b, e–g). The preoperative Japanese Orthopaedic Association (JOA) Score of 1.5 points improved to 9 points at the ﬁ nal follow-up

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patients with thoracic OPLL. However, suffi cient decompression occasionally cannot be achieved by shifting the ossifi ed ligament anteriorly in patients whose ossifi ed ligament is sharply protruding toward the spinal cord, resembling a bird’s beak. This sharply protruding ossifi ed ligament sometimes needs to be extirpated after anteriorly shifting the ossifi ed ligament.

This extirpation technique, however, is associated with a risk of complications, including aggravation of spinal cord function and cerebrospinal fl uid leakage. Even considering this possibility, though, extirpation of the ossifi ed ligament must be conducted as salvage surgery for patients with insuffi cient recovery of spinal cord function after anterior shifting of the ligament. It might also be considered as primary surgery for patients with an extremely sharply extruded ossifi ed ligament.

To extirpate the ossiﬁ ed ligament safely through the small space between the dura mater and the residual lateral mass, the size of the residual ossiﬁ ed ligament must be reduced as much as possible using a high-speed burr prior to pulling it out. The OPLL is sometimes adherent to the anterior aspect of the dura mater.

Therefore, the ossiﬁ ed ligament must be detached from the dura using a small nerve retractor or a dissector.

Great care must be taken with regard to the spinal cord during extirpation of the ossiﬁ ed ligament (Fig. 4).

Additional resection of the lateral portion of the facet joints and the pars interarticularis is recommended if the surgeon believes it is too risky to extirpate the ossi- ﬁ ed ligaments through the space created during the laminectomy and when mining the vertebral bodies (Figs. 5, 6).

Spinal Instrumentation and Fusion

Considering the possible neurological deterioration caused by progression of spinal instability and kyphosis after extensive posterior laminectomy and anterior decompression by resecting the posterior portion of the vertebral body [14–16], we recommend that additional reconstructive surgery be performed, including spinal instrumentation and intertransverse bone grafting.

However, if the patient has diminished spinal motion, additional posterior instrumentation may be omitted.

Clinical Results of Anterior Decompression Through the Posterior Approach

We managed 30 patients with thoracic myelopathy caused by OPLL using anterior decompression through the posterior approach between 1992 and 2003. Five of these patients had previously undergone extensive lam- inectomy for thoracic OPLL. There were 19 women and 11 men, with an average age of 53.5 years (range 37–72 years). For management of the ossiﬁ ed lesion, 15 patients underwent extirpation of the ossiﬁ ed liga-

ment—extirpation as primary surgery in 10 patients and as salvage surgery after a ﬂ oating procedure or extensive laminectomy in 5 patients. The remaining 15 patients were managed by ﬂ oating the ligament without extirpation. Of the 30 patients, 23 underwent spinal instrumentation and fusion.

Recovery of Nerve Function

Recovery of nerve function was satisfactory in most patients; among the others, however, there were several who could not achieve sufﬁ cient neurological recovery.

Moreover, the complication rate after this procedure was higher than with other decompression procedures

Fig. 4. Extirpation of ossiﬁ ed ligament. When the ossiﬁ ed ligament sharply protrudes toward the spinal cord, it sometimes must be extirpated after anteriorly shifting the ligament.

To extirpate the ossiﬁ ed ligament safely through the small space between the dura mater and the residual lateral mass, the size of the residual ossiﬁ ed ligament must be reduced as much as possible using a high-speed burr prior to the pull-out procedure

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Fig. 5. a Patient with spinal cord compression due to OPLL and OLF. b Preoperative and postoperative CT scans demon- strate successful extirpation of the ossiﬁ ed ligament and the anterior shift of the spinal cord. The preoperative Japanese

Orthopaedic Association (JOA) score of 3 points improved to 10 points at the ﬁ nal follow-up. Posterior instrumentation and fusion were undertaken in this patient

a

b

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for cervical OPLL. The average preoperative Japanese Orthopaedic Association (JOA) score was 3.3 (range 1–

6 ). The preooperative JOA score for thoracic myelopa- thy was 3.3 (range 1–6; full score is 11 points), which improved to 7.1 (range 1–11) at the ﬁ nal follow-up.

These results for neurological recovery exceeded the results achieved using posterior decompression alone in 37 patients with thoracic OPLL in our facility: 3.8 average preoperative JOA score that improved to 5.8 at the fi nal follow-up (Fig. 7). There were fi ve patients with insuffi cient nerve function recovery. Three of the fi ve patients remained at the same JOA score, and the remaining two patients had a worse score (Table 1). In these worsened two patients (patient land 3 in Table 1), the initial laminectomy surgery failed, and salvage surgery (fl oating and extirpation of the ossifi ed liga- ment) did not provide neurological recovery.

Complications

There have been several complications. Eight patients suffered from temporary or permanent aggravation of nerve function. Extirpation of the ossiﬁ ed ligament or additional ﬂ oating was therefore performed. With the salvage surgery, three improved and recovered to their preoperative JOA score, but two others did not achieve their preoperative JOA scores.

Two patients had delayed infection, which was managed by removing the instrumentation and apply- ing continuous irrigation. Leakage of cerebrospinal ﬂ uid (CSF) occurred in eight patients. Five of the eight underwent extirpation of the ossiﬁ ed ligament. Four of the eight patients had previously undergone extensive laminectomy at the same spinal level. The CSF leakage was successfully managed by lumbar drainage.

Discussion/Conclusions

Anterior decompression through the posterior approach for thoracic myelopathy is a reasonable decompressive procedure for patients with thoracic myelopathy caused by OPLL at the kyphotic portion of the thoracic spine.

However, this procedure is associated with a high risk of damaging the thoracic spinal cord and a high rate of complications. Simple, less invasive posterior decom- pression by laminectomy is indicated for patients with OPLL who have mild kyphosis in the thoracic spine.

This procedure should be done in patients for whom recovery of nerve function would not be expected if the less invasive procedure of extensive laminectomy were used. The need to extirpate ossiﬁ ed ligament for decom- pression is controversial among surgeons. Extirpation

Fig. 6. Salvage surgery for previously operated thoracic OPLL

by laminectomy. a–c This patient had undergone posterior decompression for thoracic OPLL, but myelopathy developed after the surgery, and the patient was referred to our clinic. d, e Posterior re-decompression and anterior decompression by

extirpation of the ossifi ed ligament. The JOA score of 3 improved to 8 at the fi nal follow-up. Postoperative magnetic resonance imaging (MRI) shows the anterior shift of the spinal cord. The high-intensity area behind the spinal cord on MRI indicates leakage of cerebrospinal fl uid

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of the OPLL, especially with beak-shaped ossifi cation, may provide a more adequate decompression effect than fl oating the ligament. However, extirpation of the ossifi ed ligament puts the spinal cord at greater risk.

Further investigation is required to establish the precise indications for extirpation of OPLL in the thoracic spine.

References

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Table 1. Five patients with poor results

JOA score^a Surgery

Patient Age/sex Preo Postop Final follow-up

1 57/F 3 2 2 1st: Laminectomy; 2nd: ﬂ oating

2 46/F 2 1 2 1st: Laminectomy; 2nd: ﬂ oating; 3rd: extirpation

3^b 4/3F 3 1 2 1st: Laminectomy; 2nd: ﬂ oating; 3rd: extirpation

4 37/M 3 1 3 1st: Extirpation

5 52/M 3 2 3 1st: Extirpation

JOA, Japanese Orthopaedic Association; ﬂ oating, anterior decompression through the posterior approach without extirpation of the ossiﬁ ed ligament

aFull score is 11 points

bPreviously underwent extensive laminectomy

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