Neurosurg Rev (2001) 24:119–122

© Springer-Verlag 2001

O R I G I N A L A RT I C L E

Kazuhiro Ido · Yoshiyuki Asada · Takeshi Sakamoto Ryoichi Hayashi · Shinichi Kuriyama

Use of an autologous cortical bone graft sandwiched between two intervertebral spacers in posterior lumbar interbody fusion

Received: 19 September 2000 / Accepted: 15 November 2000

Abstract Various intervertebral spacers with or without posterior instrumentation use pedicle screw fixation in posterior lumbar interbody fusion (PLIF). Recently we harvested an autologous cortical bone graft from a spinous process by en bloc resection and inserted it between two intervertebral spacers during PLIF surgery. Due to better balance, this procedure provides greater mechanical strength, larger contact area, and better bilateral restoration of disc height than PLIF using intervertebral spacers only, and there is no need to take a bone graft from the iliac crest. This technique appears to result in effective spinal fusion in PLIF surgery. Keywords Surgery · Lumbar spine · Interbody fusion · Autologous bone graft

Introduction Posterior lumbar interbody fusion (PLIF), developed during the last decade, is indicated for many patients with pain and/or instability of the lumbar spine [1, 2]. The older technique of PLIF involved only insertion of an iliac bone graft after removal of the disc material. Newer techniques involve some kind of implant containing grafted bone with or without pedicle screw fixation. Although PLIF has several advantages over posterolateral or anterior interbody fusion, it also has some disadvantages such as high risk to neural tissues, longer operating time, bleeding from the epidural venous plexus, and perineural fibrosis [3, 4]. If these problems can be K. Ido (✉) Department of Orthopaedic Surgery, Kurashiki Central Hospital 1-1-1 Miwa, Kurashiki-city, Okayama, 710-8602 Japan Tel.: +81-86-4220210, Fax: +81-86-4213424 Y. Asada · T. Sakamoto · R. Hayashi · S. Kuriyama Department of Orthopaedic Surgery, Japanese Red Cross Society, Wakayama Medical Center, Wakayama, Japan

solved by advanced techniques, PLIF offers promising outcomes in low back surgery. Implants for insertion in the intervertebral disc space come in various configurations, ranging from a horizontal cylindrical cage [5–8], an upright cylinder like the Harms cage [9, 10], and an open box like the Brantigan cage [11, 12] to a solid rectangular parallel piped spacer like the intervertebral spacer made of glass ceramic containing apatite and wollastonite (A-W glass ceramic), one of the bioactive glass ceramics developed at Kyoto University in 1982 [13, 14]. The aims of using these implants are to correct the existing mechanical deformation, stabilize the segment until bone fusion occurs, and promote bone cell proliferation. Recently we harvested an autologous cortical bone graft from a spinous process by en bloc resection and inserted it between two intervertebral spacers with good postoperative outcome. The purpose of this report is to introduce our technique and discuss the characteristics of grafted boneendplate and intervertebral spacer-endplate interfaces based on our postoperative radiographic findings.

Materials and methods We performed nine PLIF procedures using autologous cortical bone grafts sandwiched between two intervertebral spacers. For this, A-W glass ceramic spacers and titanium mesh Harms cages were used as the intervertebral spacers in three and six cases, respectively. Seven patients had single PLIF and two underwent two-level PLIF. The clinical data are summarized in Table 1. Surgical procedure After exploring the spinous process and both sides of the lamina, en bloc resection of the spinous process and en bloc laminectomy were performed using an osteotome. All disc material and the superior and inferior apophyseal ring cartilage were removed until subchondral bone bleeding was seen. We explored the dura and nerve roots under the microscope. Pedicle screws were inserted and the disc space exposed using a retractor. Then, two intervertebral spacers and a piece of cortical bone of the same thickness harvested

120 Table 1 Summary of clinical data Patient

Age

Sex

Diagnosis

Fusion level

Spacer

Instrument

Follow-up (months)

1 2 3 4 5 6 7 8 9

60 57 57 55 69 53 47 53 36

F M F M M M F F M

Degenerative spondylolisthesis L4 spondylolytic spondylolisthesis L4 spondylolytic spondylolisthesis Spondylosis deformans Spondylosis deformans Degenerative spondylolisthesis L4 spondylolytic spondylolisthesis Degenerative spondylolisthesis L4 spondylolytic spondylolisthesis

L4-5 L4-5 L4-5 L2-3, L3-4 L2-3 L4-5 L4-5 L3-4, L4-5 L5-S

A-W A-W A-W Harms cage Harms cage Harms cage Harms cage Harms cage Ti mesh cage

Dynalok Dynalok Dynalok Moss Miami Moss Miami Moss Miami Moss Miami Moss Miami Moss Miami

31 29 28 25 25 18 18 15 14

graft were inserted, and bone union between the grafted bone and the endplate was seen in plain radiographs (Fig. 3). Case 8 This 53-year-old male underwent PLIF at L3-4 and L4-5 for degenerative spondylolisthesis. Harms cages and the autologous cortical bone graft were inserted and good positioning of the implants and grafted bone was seen on plain CT (Fig. 4).

Results Bone union between the sandwiched autologous cortical bone graft and the endplate of the vertebral body was seen in all eight patients in anteroposterior and lateral plain radiographs 6 months after the operations. Although good contact between the intervertebral spacers and endplates was observed just after operation, a radiolucent line was detected in two of three patients who received A-W glass ceramic spacers. However, micromotion or partial dislodgment was not observed. All patients reported pain relief postoperatively and there were no serious complications. Fig. 1 A scheme of two intervertebral spacers and sandwiched cortical bone graft insertion into intervertebral disc space from a spinous process by en bloc resection were inserted into the intervertebral space from both sides (Fig. 1). After completing these procedures, rods or plates were connected with screws and cross-link devices were fixed. Each patient was allowed to walk within a week after the operation wearing a hard corset. We examined the patients postoperatively by radiography. Radiolucent lines at the bone–implant interface and any micromotion of the intervertebral spacers were investigated. Case 3

Case 6 A 53-year-old male underwent PLIF at L4-5 for degenerative spondylolisthesis. Harm cages and the autologous cortical bone

Posterior lumbar interbody fusion has been widely accepted during the last decade because it provides total decompression of the lumbar neural elements as well as solid spinal fusion. It restores anterior column support and disc height, providing for nerve root decompression. A further advantage is that it allows treatment of associated nerve root or spinal cord disease during the same operation. With the introduction of pedicle screw fixation, there has been a resurgence of interest in PLIF surgery [1, 2, 15, 16].

Fig. 2A,B Case 3. Plain radiographs of a 57-year-old female 28 months after PLIF operation. A Anteroposterior view shows union between sandwiched cortical bone graft and endplates. B Lateral view Fig. 3A,B Case 6. Plain radiographs of a 53-year-old male 14 months after the operation. A Anteroposterior view shows union between sandwiched cortical bone graft and endplates. B Lateral view

▲

A 57-year-old female patient underwent PLIF surgery at L4-5 for spondylolytic spondylolisthesis. We used A-W glass ceramic spacers, and bone union between sandwiched grafted bone and the endplate was observed in plain radiographs (Fig. 2).

Discussion

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graft and the endplate can be easily confirmed by anteroposterior radiography. We expect that intervertebral disc height would be preserved even if an upright cylindrical spacer like the titanium mesh cage were to sink into the vertebral body. We think that the mechanical strength brought by our surgical technique is sufficient to support the anterior column. We are testing a wedge-shaped intervertebral spacer with 2 mm greater anterior than posterior thickness to achieve normal lumbar lordosis. The sandwiched cortical bone graft is trimmed to a wedge shape to obtain good contact with the endplate of the vertebral body, and posterior supports are added using pedicle screw fixation to maintain normal lumbar lordosis and obtain rigid initial stability. In conclusion, autologous cortical bone grafts sandwiched between two intervertebral spacers are useful for PLIF and provide effective spinal fusion.

References Fig. 4 Case 8. Postoperative CT scan of a 53-year-old male 10 months after operation shows good positioning of two spacers and grafted bone

To obtain good contact between the intervertebral spacers and the superior and inferior endplates, various spacers have been used in many ways. However, we expect any intervertebral spacer in PLIF surgery to have sufficient mechanical strength, provide initial stability, preserve intimate disc height, and have a large contact area at the endplate-implant interface [1–4, 15, 16]. Some intervertebral spacers that result in (highly desirable) early fusion at the endplate–implant interface have several disadvantages. For example, A-W glass ceramic spacers frequently become partially dislodged due to their mechanical weakness in anchoring to the bone. Cylindrical cages sometimes sink into the vertebral body or fail to result in fusion due to poor packing of the cancellous bone inside the cage. Furthermore, when using an upright cylindrical cage, it is difficult to confirm whether fusion has occurred at the endplate–implant interface. With titanium mesh cages like the Harms cage, we usually pack cancellous bone chips in front of the cage to monitor the bony fusion. However, this does not always clearly show whether bony fusion has occurred between the cage and the endplate, and cancellous bone chips are unable to support an anterior column because of their insufficient mechanical strength. We thought that cortical bone would have greater mechanical strength and be suitable for supporting an anterior spinal column when sandwiched between the intervertebral spacers. The surgical procedure described here has several advantages such as greater mechanical implant strength, large contact area between endplate and implant, no need to take a bone graft from the iliac crest, and bilateral restoration of disc height. Furthermore, bony fusion of the vertebral body between the sandwiched cortical bone

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