Ideas and technical innovations European Spree Journal

�9 Springer-Verlag 1993

Eur Spine J (1993) 1 : 249-253

Laminectomy combined with posterolateral stabilisation: a muscle-sparing approach to the lumbosacral spine

Robert D. Fraser and David J. Hall

Spinal Unit, Orthopaedic and Trauma Services, Royal Adelaide Hospital, North Terrace, Adelaide, South Australia 5000, Australia

Laminectomie associ6e ~ la stabilisation post6ro-latdrale: un abord lombo-sacr6 6pargnant les muscles

R6sum6. Nous rapportons notre exp6rience d 'une dd- compression postdrieure par vole mddiane associ6e une vole d'abord transmusculaire de Wiltse permettant l'arthrodase post6ro-latdrale et la raise en place de vis p6diculaires. Cette technique convient aux cas de st6nose rachidienne lombaire ainsi qu'aux hernies discales n6ces- sitant une stabilisation. Elle pr6sente des avantages signi- ficatifs sur les autres m6thodes rapport6es. Cette vole d'abord combinde a 6t6 utilis6e depuis 1990 chez 52 pa- tients, sans complications proprement li6es ?a la vole elle- meme.

Mots-cl6s: Lombalgie - St6nose du canal spinal - D6- compression du canal spinal - Vissage pddiculaire

Summary. We report our experience with a technique of midline posterior decompression in combination with the Wiltse muscle splitting approach for posterolateral spinal fusion and pedicle screw fixation. The technique is suitable for cases of lumbar spinal stenosis and disc her- niation where stabilisation is required and has significant advantages over other reported methods. This combined approach has been used in 52 patients since 1990 with no complications from the approach itself.

Key words: Low-back pain - Spinal stenosis - Spinal de- compression - Spinal fusion - Pedicle screw fixation

With the increased acceptance of pedicle screw fixation as an adjunct to lumbar spinal fusion, different methods of combining this with decompression have been de- scribed.

Most advocates of the posterior approach utilise a midline dissection with wide retraction of the erector spinae to each side. Following a decompressive laminec- tomy, the pedicle screw fixation system is inserted, and a posterolateral (apophyseal joint and/or intertransverse) fusion performed [5, 9, 12, 15, 20]. Others [13, 14] advo- cate a wide decompressive laminectomy and posterior

Correspondence to: R. D. Fraser

interbody fusion in combination with pedicle screw and plate fixation and posterolateral fusion.

In some cases adequate decompression can be achieved by anterior disc clearance and interbody fusion [1, 4, 7] although Combining this with pedicle screw and plate fix- ation and posterolateral fusion is favoured by some sur- geons [11].

Wiltse and others describe a method of combining de- compression and posterolateral fusion performed through a muscle-splitting approach [18]. This approach does have distinct advantages over a midline exposure for posterolateral fusion and pedicle screw fixation: the Wiltse approach is less destructive, being along an inter- muscular plane of cleavage, it requires a shorter incision for a given number of levels, reduces blood loss, and provides better exposure of the transverse processes, the ala of the sacrum and the lateral aspects of the apophyseal joints. While this approach is ideal for decompression of the lumbar intervertebral foramen, access to the spinal canal itself is somewhat limited.

In recent years there has been increased awareness of the need to preserve stability during laminectomy proce- dures. Great emphasis has been placed on the impor- tance of minimising muscle damage, protecting the pars interarticularis and maintaining the structural support of the apophyseal joints [3, 6]. Although laminoplasty is an accepted technique [16], it is only appropriate in a mi- nority of cases. Osteotomy of a spinous process to increase surgical exposure during lumbar laminectomy was first described by Yong-Hing and Kirkaldy-Willis [19]. With the aim of increasing the strength of wound closure, limit- ing dead space and improving stability, the spinous pro- cesses and midline ligaments can be retained as a central osteoligamentous band by osteotomising the spinous pro- cesses at their bases after retracting the erector spinae to each side [Crock, personal communication, 1985]. A mod- ification to this approach was suggested by Cornish (per- sonal communication, 1986) and later reported by Joson and McCormick [8], whereby the erector spinae is sepa- rated from the spinous processes and the laminae on one side only, the spinous processes osteotomised at their bases but left attached to the supraspinous and interspin- ous ligaments and the opposite erector spinae and then retracted laterally.

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A

B

C

D

E

( \

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Fig.la-e. The laminectomy approach (cross-sections at level of L4-5 intervertebral foreamen). A Mid-line posterior incision. B Spinous process osteotomy and retraction. C Spinal canal de- compression by undermining of lamina. D Closure of dorso-lum- bar fascia. E Posterior view after retraction of spinous processes to the right, showing L4-5 and L5-S1 decompression. The remaining bridge of L5 lamina has been undermined

Alternatively, many surgeons will leave the spinous processes intact while carrying out spinal decompression via multiple fenestrations. This has the limitation that access to the lateral spinal canal is hindered by the re- tained spinous processes, a major disadvantage in cases of nerve root canal stenosis.

The aim of this paper is to report our experience with a technique of midline posterior decompression in com- bination with the Wiltse muscle-splitting approach suitable for cases of lumbar spinal stenosis and disc herniation where stabilisation is required.

The combined approach

Whether the laminectomy or fusion is carried out first depends on the underlying pathology and the preference of the surgeon.

Laminectorny

A midline posterior incision is deepened to the supra- spinous ligament (Fig. 1A). On each side the subcutane- ous tissues are dissected from the dorsolumbar fascia for a distance of 5-6 cm and haemostasis is obtained.

Using cutting diathermy, the dorsolumbar and deep fasciae are separated from the supraspinous ligament on one side and the erector spinae is dissected from the spinous processes and interspinous ligaments and then stripped from the laminae with sharp dissection. The spinous processes at the levels to be decompressed are then osteotomised at their bases and retraced to the op- posite side by stripping from the laminae the erector spinae to which they remain attached (Fig. 1B). The use of Keon-Cohen self-retaining retractors provides wide and unrestricted access for the decompressive laminec- tomy. When multiple levels are to be decompressive laminectomy. When multiple levels are to be decom- pressed to favour, where possible, preservation of a horizontal bridge of lamina at each level to support the retained spinous process. In most cases the decompres- sion involves removal of the inferior one half of the lamina above and the superior one quarter of the lamina below, combined with undermining of the laminae and bilateral medial facetectomies at each level, taking care

251

D

B

Fig. 2a-e. Subsequent paraspinal approach for stabilisation (cross-sec- tions at level of L4 pedicle). A Wiltse paraspinal muscle-splitting ap- proach. B Harvesting bone graft from the posterior iliac crest in the distal end of the muscle-splitting approach. C Placement of pedicle screw facilitated by paraspinal approach. D Closure of both paraspinal wounds following laying of bone grafts and completion of screw and plate fixation. E Posterior view showing the area to be decorticated (hatched area) for L4-$I posterolaterat fusion and the final appear- ance after graft placement with plate and pedicle screw fixation

to preserve the pars interaarticularis (Fig. 1C, E). When it is not possible to preserve a horizontal bridge of lamina it is important to ensure that a sufficient amount of the base of each spinous process has been removed to avoid impingement on the dural sac. At the completion of the decompression the erector spinae is reattached to the spinous processes and midline ligments (Fig. 1D).

In cases of disc herniation a more limited exposure through a small fenestration approach may be all that is required.

Pedicle screw fixation and fusion

After closure of the midline fascial wound a bilateral muscle-splitting approach [18] is carried out (Fig. 2A). The dorsolumbar and deep fascia is divided in a longitu- dinal direction approximately 5 cm from the midline.

The oblique intermuscular plane in the midsubstance of the erector spinae is located at the level of the iliac crest, and blunt dissection with the gloved finger enables this relatively avascular plane to be developed proximally and distally for the required number of levels. Sharp dis- section is usually required to develop the distal end of the plane to the point where muscle fibres are attached to the posterior iliac crest. The ala of the sacrum, the transverse processes and the partes interarticulares are exposed by subperiosteal dissection, then decorticated, and the intervening apophyseal joints are partly excised. Muscle is cleared from the intertransverse ligaments. Bone graft is obtained from the posterior iliac crest which is exposed through the distal end of the muscle splitting approach (Fig. 2B). In males, where the inter- crestal distance is smaller, obtaining bone graft from the inner aspect of the posterior iliac crest on each side ira-

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proves exposure for screw and plate fixation into the sac- rum.

The entrance for pedicle screw placement is the mid- point of the transverse process at its junction with the lateral margin of the superior articular process [10, 17]. The $1 pedicle is entered through the base of the articu- lar process or just distal to the sulcus formed between this structure and the ala. A pedicle awl allows the nat- ural direction through the pedicle to be found, which from this point of entry usually lies along a line approxi- mately 20~ ~ to the sagittal plane. It is wise to check the size and direction of the pedicle in an axial view on a computed tomographic or magnetic resonance scan be- forehand. The muscle-splitting approach lies in the di- rection of the insertion of the pedicle screws and their in- sertion is not impeded by the edges of the wound (Fig. 2C). Following placement of the bone graft in the pos- terolateral gutters and over the apophyseal joints, and the attachment of the plates or rods (Fig. 2D, E), a suc- tion drain is positioned and the wound is closed in layers. To minimise the risk of haematoma formation the sub- cutaneous tissues are sutured down to the dorsolumbar and deep fasciae.

This combined approach has been used in 52 patients since 1990 with no complications of wound healing. The decompression involved a single-level unilateral fenestra- tion in 15 cases, while a wide decompression with spin- ous process osteotomy was performed at a single level in 25 patients, over two levels in 11 patients and over three levels in 1 patient. The spinal fusion with pedicle screw and plate fixation was carried out at one level in 22 pa- tients, two levels in 11 patients and three levels in 8 pa- tients.

Discussion

This combined approach for laminectomy and fusion has distinct advantages over other methods described. The main disadvantages with the commonly used midline posterior approach relate to the exposure of the trans- verse processes and lateral aspects of the apophyseal joints. To obtain reasonable access to these areas re- quires a lengthy incision with extensive stripping of the erector spinae on each side. This results in increased blood loss, partly due to the restricted view of the vascu- lar anastomosis arising from the posterior branches of the lumbar arteries and surrounding the apophyseal joints [2]. Pedicle screw placement may be difficult un- less the more medial entry point of Roy-Camille [12] is used or lateral puncture wounds are made [18]. Because of limited access it is more difficult to prepare the graft bed site thoroughly and position the bone graft accurately, thereby risking a technically inferior result.

The midline approach for laminectomy combined with posterior interbody fusion, favoured by Steffee and Sitkowski [14], requires a more destructive wide decom- pression with increased risk of neurological deficit from retraction of the cauda equina.

The muscle-splitting approach of Wiltse [18] provides superior access to the transverse processes and apoph-

yseal joints for the puposes of a posterolateral fusion. For a given number of levels to be exposed the length of the skin incision is shorter than when a midline approach is employed, and there is less stripping and damage to the erector spinae muscle, resulting in reduced blood loss. Although the approach is ideal for exposure of the intervertebral foramen, access to the laminae for decom- pression of the spinal canal is more restricted than through the standard midline approach.

The combined approach described above retains the advantages of the Wiltse muscle-splitting approach for fusion and pedicle screw fixation, while the midline poste- rior limited osteoplastic approach provides excellent ac- cess for decompressive laminectomy. Although on one side the midline attachments of the erector spinae are in- terrupted in addition to the separation of the muscle along the fascial plane, the shortened vertical expo- sure required means that this combined approach is less destructive than an extensive wide posterior mid- line approach. Additionally, separate approaches for decompression and fusion greatIy reduce the risk of bone graft fragments being displaced onto the exposed dura.

We agree with Wiltse that a single midline incision is superior to the previously used bilateral skin incisions [18], despite the higher risk of subcutaneous haematoma formation. When the bone graft is harvested through a distal extension of the muscle-splitting approach, the risk of developing a painful subcutaneous neuroma in the posterior cluneal nerves (lateral branches of the pos- terior primary rami) should be avoided.

Preservation of the spinous processes and midline lig- aments and their attachment to the erector spinae on one side minimises damage to the posterior midline structures and the erector spinae itself, while not imped- ing access for laminectomy. Provided a horizontal bridge of lamina is retained at each level the spinous process will usually reattach. By retaining the spinous processes and suturing the subcutaneous tissues to the dorsolum- bar and deep fasciae, the cosmetic result is enhanced with restoration of the normal median furrow.

Care must be taken with placement of the posterolat- eral bone graft, since the intertransverse membrane is a tenuous structure and we have observed cases where the underlying nerve root has been impinged by bone graft fragments which have been forced into the membrane by the overlying spinal plate. To minimise this risk when plates are used, we recommend fixing the plate a few millimetres away from the membrane to allow careful placement of cancellous bone graft. In addition, there is a tendency when tightening the screws onto the plate for the interpedicular distance to be shortened. To avoid foraminal entrapment of the nerve root by this mecha- nism we tighten the screws sequentially with slight dis- traction at each level.

This combined approach has been used extensively over a 3-year period and there have been no complica- tions attributable to the approach itself. We recommend this approach to facilitate the safe and adequate perfor- mance of decompressive surgery combined with postero- lateral fusion and pedicle screw fixation.

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