36 Microscopically Assisted Percutaneous Technique as a Minimally Invasive Approach
to the Posterior Spine
R. Greiner-Perth, H. Boehm, H. El Saghir
36.1
Terminology
The approach introduced here, the “microscopically assisted percutaneous technique” (MAPN = micro- scopically assisted percutaneous nucleotomy), is appli- cable to all regions of the posterior spine. MAPN de- scribes an atraumatic percutaneous transmuscular ex- posure of the interlaminar window. Muscle trauma re- lated to the approach is reduced to the minimum by the so called “transmuscular dilatation” (see Sections 36.2 and 36.9).
36.2
Surgical Principle
The aim of this technique is the minimising of the ap- proach trauma especially in paraspinal muscles. The technique of transmuscular dilatation allows gentle spreading of the fascia and the fibres of the paraspinal muscles. Detachment of muscles from the spinous pro- cess, the lamina and the facet joint can be avoided. The target area is exposed through a working tube through which lumbar disc herniations can be removed with the help of a surgical microscope.
36.3 History
The incidence of lumbar disc herniation in Germany is about 4.5 % and from 100,000 inhabitants 87 will be subjected to surgical treatment [18, 22]. These figures illustrate the need for an operative modality that offers the patient the maximum safety and at the same time is associated with minimal trauma related to the ap- proach. This ultimately should result in earlier rehabili- tation of the patients.
The open lumbar discectomy was gradually replaced in the 1970s by the microdiscectomy techniques intro- duced by Yasargil [26] and Caspar [1]. The latter is still considered the “gold standard” for the operative treat- ment of lumbar disc herniation due to the relatively
minimal trauma related to the (mini-open) approach and the excellent illumination and visualisation provid- ed by the surgical microscope. In inexperienced hands, the disadvantage of this technique, however, is the dis- section of the short segmental paraspinal muscles (mul- tifidi) from their bony attachments, which can result in scarring as well as segmental denervation. In associa- tion with a postoperative height loss of the interverte- bral space the motion segment can destabilise [23].
As an attempt to further minimise the trauma relat- ed to the approach, Hijikata [16] in 1975 described the method of percutaneous discectomy. The indications for this technique as well as for the automated discecto- my described by Onik [21, 22] are very limited. Auto- mated percutaneous lumbar discectomy (APLD) [21, 22] is obsolete due to the lack of proven efficacy. Percu- taneous endoscopic intradiscal discectomy has never become an international standard procedure due to the restricted indication just for contained disc hernia- tions.
The introduction of endoscopically assisted proce- dures by Destandeau [7] and Foley [5, 9] is considered a further advance in the armamentarium of minimally invasive lumbar disc surgery. The main disadvantage of this method, however, is the lack of three-dimensional vision.
Our concept is based upon minimising the surgical trauma related to the approach by splitting of the para- vertebral muscles combined with use of the operative microscope which offers the surgeon three-dimension- al vision. Accordingly, this approach can be generally applied for all types of lumbar disc herniations and for decompressive procedures in all areas of the posterior spine (see Section 36.6) [12, 13].
36.4 Advantages
1. Less surgical trauma to the muscles.
2. Three-dimensional visualisation of operative field.
3. Reduced bleeding from the approach area.
4. Good possibilities for inclination of the working channel in sagittal and transversal planes.
5. The approach can be extended in every instance, if needed, to enable the surgeon to do a standard microdiscectomy or even an open discectomy.
6. The procedure can also be performed under local anaesthesia.
7. Excellent cosmetic outcome.
36.5
Disadvantages
It is a demanding technique, which requires experience in microsurgical techniques. The learning curve may be long.
36.6 Indications
The technique is applied mainly for access to lumbar disc herniations. All kinds of lumbar disc herniations which require a standard midline approach can be managed by this technique [13]. Above that additional indications for the approach technique proposed here include: lateral (intraforaminal) disc prolapse [3, 14]
and central and/or lateral stenosis in the lumbar spine as well as the thoracic and cervical spine [4, 12, 15]. An overview of indications is shown in Fig. 36.1.
36.7
Contraindications
Segmental stability is a prerequisite for successful ap- plication of the MAPN technique in posterior decom- pressions of the spine. Accordingly, the presence of seg- mental instability in functional studies constitutes a contraindication for this technique. In addition, the technique is not applicable for anterior stenosis caused
Fig. 36.1. Overview of indications for the microscopically assisted percutaneous approach in the posterior spine
by anteriorly located lesions. The presence of facet joint arthrosis with massive hypertrophy is considered a rel- ative contraindication.
36.8
Patient’s Informed Consent
As for other operations, the patient should be informed about the possible general and local complications. In addition, the possibility of conversion to traditional microdiscectomy should be pointed out.
36.9
Surgical Technique
36.9.1
Paramedian Approach
The approach is done with the patient in the prone or in the knee-chest position. The lateral decubitus position can be an alternative in certain cases (as in old poly- morbid patients) where the procedure is done under lo- cal anaesthesia.
After skin disinfection and draping, the space be- tween the two laminae at the desired level is deter- mined and documented by the image intensifier. A stab incision of 15 mm length, about 2.5 cm paramedian, is made and two soft tissue dilators are applied in se- quence. This allows gentle spreading of the fascia and the fibres of the paraspinal muscles to the extent that al- lows the introduction of the working channel (Figs.
36.2 – 36.4). These steps are performed under C-arm guidance, to prevent approaching the wrong level. The working channel has blunt threads on its outer surface which enables it to pass tightly through the paraspinal muscles while spreading them apart. The working channels (Medicon, Tuttlingen, Germany) are available in three different lengths (45, 55 and 65 mm) and two
Fig. 36.2. Intraoperative X-ray control with first dilator in place at level L5/S1
outer diameters (11 and 14 mm). A handle on the work- ing channel allows angulating movements, providing optimum direction of vision and access. In all posterior spine regions a good anatomical landmark is the inferi- or edge of the laminar arch. The angle of the working tube to the midline is about 10°. All further steps of the operation are executed through this channel.
The interlaminar space is exposed under vision of the operative microscope. The opening to the ligamen- tum flavum varies from simple splitting for removal of free sequestrated disc fragments to partial flavectomy in cases with hypertrophy of the ligamentum flavum causing canal stenosis. The possibility of tilting the working channel in the sagittal and transversal planes permits elimination of stenosis of the lateral recess of the ipsilateral as well of the contralateral side (cross- over technique). Generally speaking, the type and ex- tent of surgical decompression varies according to the surgical indication and the intraoperative findings. The procedure entails removal of the free disc fragments in cases with sequestrated prolapse (Fig. 36.5), nucleoto- my when loose disc fragments are present in the inter- vertebral disc, radiculolysis for periradicular fibrosis, decompression of the lateral recess in cases with lateral stenosis flavectomy for ligamentum flavum hypertro- phy and osseous decompression for central stenosis. In addition, through this approach it is possible to access intradural lesions, and thus we resort to this approach in cases needing diagnostic or therapeutic myeloscopy.
The principles of the technique are more or less the same in all spinal regions when midline approaches are needed. However, there are differences in the patient’s
Fig. 36.3. First dilator in situ, spinal needle contralaterally for marking of the level
Fig. 36.4. Insertion of the working channel
Fig. 36.5. View through operative microscope, the disc hernia- tion is being mobilised
Fig. 36.6. Intraoperative X-ray control with second dilator in si- tu at level C3/4
position. In the lumbar region, we prefer the knee- chest position. The lateral decubitus with the thighs flexed is resorted to when the operation is done under local anaesthesia. The standard prone position is used for lesions in the posterior thoracic spine. The same is applied to approaches of the cervical spine but an in- clined neck facilitates the decompression (Fig. 36.6).
36.9.2
Transforaminal Approach
The approach is ideal for intraforaminal and extrafo- raminal disc herniations (Fig. 36.7) as well as for fo- raminal stenosis. The angle between the lateral part of isthmus region and the lower border of transverse pro- cess is marked under fluoroscopic control in the anteri- or-posterior view. The stab incision is done usually
a b
Fig. 36.7. Intraforaminal disc herniation at level L3/4 left side in transversal (a) and sagittal (b) MRI scan
Fig. 36.8. Working channel placement in X-ray control (AP view) for transforaminal approach at level L3/4
about 5 – 6 cm away from the midline. Two dilators are applied in sequence to allow insertion of the working channel. The latter should be inclined 10° towards the midline. After correct positioning of the working chan- nel (Fig. 36.8), the next steps are done using illumina- tion and visualisation of the operating microscope.
Dissectors and probes are used to search for the nerve root in the extraforaminal region (lateral to the pars in- terarticularis). Usually the nerve root can be identified caudad to the inferior border of the transverse process and, sometimes, resection of a small part of the inter- transverse ligament may be necessary. After cranial mobilisation of the nerve root and the accompanying branch of the segmental lumbar artery (cave!!), the her- niated disc can be exposed and removed. In case of par- tial intraforaminal disc herniation, trimming of the yellow ligament will be necessary.
After removal of the herniated part of the nucleus, the nerve root is probed all around by using blunt
hooks of different lengths. In case of neural foramen stenosis as a result of facet joint hypertrophy, careful undercutting can be done from this lateral position without damaging the facet joints. A difficulty with this technique can arise at the level of L5/S1, due to high ili- ac wings.
36.10
Postoperative Care and Complications
In general, mobilisation of the patients is started 4 hours after surgery. A postoperative spinal support is not required. In our first series of 43 patients with lum- bar disc herniation treated using the aforementioned technique we found an incidence of intraoperative du- ral injury of 9 %. Recurrent disc herniation was evident in 4.5 % (1 year follow up) [13].
In a study including 38 patients suffering from spi- nal canal stenosis the incidence of dural injury was 5 % and reoperation was necessary in 8 % of them due to re- sidual stenosis and one epidural hematoma [12, 15].
The lateral approach for foraminal and extraforami- nal pathology was completely safe and recurrent disc herniation was encountered in two cases (7 %). Both
a b
Fig. 36.9. MRI scan with se- questrated disc herniation (a) in level L5/S1 and post- operative situation after dis- cectomy using the micro- scopically assisted percuta- neous technique (b) Table 36.1. Comparison be- tween results of microdiscec- tomy and microscopically assisted percutaneous tech- nique in lumbar disc hernia- tion
Parameter Microscopically assisted percutaneous technique
Microsurgical discectomy
References
Operative time 69 min 60 min [11]
Revisions 4.3 % 4 – 9 % [6, 10, 17, 19, 26]
Clinical results (good and excel- lent outcome)
80 % (3 months postoperative) 75 % (1 year postoperative)
80 – 90 % (6 – 66 months postoperative)
[10, 11, 17, 19, 26]
Postoperative hospital stay
4 days 4 days [25]
Return to work 100 % in 8 weeks ?
were successfully reoperated on using the same tech- nique [14].
No complications were encountered in the series done for cervical spine posterior decompressions [4].
In summary dural violations, recurrent disc hernia- tions and residual stenosis are the main complications in the learning curve of this technique
36.11 Results
36.11.1
Results in Lumbar Disc Herniations via the Paramedian Approach
In the period between May 1998 and May 2003, 485 pa- tients with lumbar disc herniations were operated on using this technique (Fig. 36.9). The first consecutive 43 cases done in the period between May and September 1998 were evaluated and the results were compared with those of the traditional microdiscectomy (Ta- ble 36.1) [13]. The male to female ratio was 3 : 2. The mean age was 54 years (range 22 – 77 years). The affect- ed level was L4-5 in 21 patients, L5-S1 in another 21, and L2-3 in the remaining patient. The patients were
examined 3 months after the operation at the outpa- tient clinic and a questionnaire was done 1 year after the surgery. The subjective perception of pain using the visual analogue scale (VAS) [2], the neurological defi- cits, the need for analgesics and the ability to return to work were analysed. The operative time and the blood loss in this series were compared with those encoun- tered in 86 microdiscectomies done by the same sur- geons 1 year before the introduction of the microscopi- cally assisted percutaneous technique.
The mean operative time in the cases treated by the microscopic percutaneous assisted technique was 69 minutes, which is slightly longer than that reported for conventional microdiscectomy (63 minutes). The mean blood loss with the MAPN technique was 30 ml in comparison with 90 ml in the standard microdiscecto- my. Apart from dural injuries in four cases, no other in- traoperative complications were encountered in the microscopically assisted percutaneous technique.
Early recurrent disc herniations necessitating surgi- cal reintervention was encountered on two (4.5 %) occa- sions. The early postoperative follow up 3 months after the operation showed that 50 % of the patients were free from any symptoms, 30 % had minimal symptoms (< 2 in VAS), 18 % had pain resembling sciatica but was tol- erable, while the remaining 2 % (one patient) had per- sistent symptoms without evidence of recurrent hernia- tion. Apart from those without a job, all employed pa- tients returned to their work within 4 – 8 weeks after surgery. Eighty percent of the patients reported that they no longer need any analgesics. The motor function improved from an average 3/5 preoperatively to an aver- age of 4/5 (according to Janda).
It was possible to contact 32 out of the 43 patients and ask them about their medical condition with refer- ence to the local symptoms. Of those, 75 % gave values between 0 and 2 while the remaining 25 % gave values between 2 and 5 VAS because of sciatic pain.
A randomised prospective study is presently being conducted in cooperation with the department of or- thopaedics in Otto-von-Guericke-University Magde- burg. The main aim is to study the effect of minimising the approach on the extent of muscle injury and local epidural fibrosis depending upon MRI done at regular intervals after surgery. The control group comprises cases treated by conventional microdiscectomy.
36.11.2
Results in Lumbar Intraforaminal Disc Herniations via the Transforaminal Approach
A prospective study includes 27 patients treated in the period between February 1999 and October 2002 [14].
The mean age was 59.4 years and 53 % were women.
The average operative time was 43 minutes and the mean blood loss was 40 ml. The VAS and Oswestry Dis-
Table 36.2. Results of transforaminal approach. (VAS leg Visual analogue scale leg pain, VAS back visual analogue scale back pain, ODI Oswestry Disability Index)
Study parameters
Preoperative Postoperative Significance
VAS leg 7.2 (SD 1.15) 3 (SD 1.78) P < 0.001 VAS back 6.1 (SD 1.75) 4.1 (SD 2.1) P < 0.001 ODI 29.3 (SD 4.9) 11.5 (SD 8.2) P < 0.001
ability Index (ODI) [8] improved significantly (Table 36.2) after a mean follow up of 10 months (4 – 24 months). Recurrent disc herniations were encountered on two occasions, 2 and 6 months after primary sur- gery, and were successfully treated by the same tech- nique.
36.11.3
Results of the Treatment of Lumbar Canal Stenosis Thirty eight patients (13 women and 25 men) with symptomatic lumbar stenosis were treated during the period between November 1998 and December 2001 uti- lising the aforementioned approach [12, 15] The mean age of the patients at the time of surgery was 73.2 years.
The number of segments to be decompressed was 56.
The mean operative time for each segment was 74 min- utes, while the mean blood loss measured 32 ml. The mean follow up was 32 months (18 – 55 months). The VAS for leg and back pain and the Oxford Claudication Score (OCS) [20] had improved significantly (Table 36.3). Dural tears were encountered on two occasions (5 %). Three patients (8 %) needed to be revised using open technique, one due to epidural bleeding causing symptoms and the other two because of residual steno- sis. Because of advanced comorbidity in two patients, the operation had to be done under local anaesthesia.
36.11.4
Results of Surgical Treatment of Cervical Radiculopathy Thirteen patients suffering from cervical radiculopathy (4 patients) and myelopathy (9 patients) were operated according to this technique during the period October 1998 to October 2001 [4]. The patients were strictly se- lected according to the offending pathology. Nine pa-
Table 36.3. Results of operative treatment of lumbar canal ste- nosis. (VAS leg Visual analogue scale leg pain, VAS back visual analogue scale back pain, OCS Oxford Claudication Score)
Study parameters
Preoperative Postoperative Significance
VAS leg 6.8 (SD 1.2) 3.1 (SD 1.9) P < 0.001 VAS back 7 (SD 1.2) 4 (SD 2.1) P < 0.001 OCS 29.4 (SD 5.2) 14.1 (SD 7) P < 0.001
Table36.4.Resultsoftreatmentofcervicalradiculopathyandmyelopathy.(VASneckVisualanaloguescaleneckpain,VASarmvisualanaloguescalearmpain,NDINeckDisabilityIndex) Patient num- ber Age (years)SexNeurological deficits (preoperative) ImagingfindingsLevelOperati- vetime (min) NDI (preope- rative) NDI (postope- rative) VASneck (preope- rative) VASarm (preope- rative) VASneck (postope- rative) VASarm (postope- rative) Neurological deficits(po- stoperative)
Followup period (months) 165MaleSensoryC8BonyforaminalstenosisC7/T16065107832Complete recovery42 251MaleSensory+ motorC8BonyforaminalstenosisC7/T17070506856Improved36 376FemaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C3-69070408823Improved25 480MaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C5/68555208741Improved19 543MaleSensoryC8BonyforaminalstenosisC7/T1456506721Complete recovery16 669FemaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C2/35065259764Improved14 776MaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C3/44580455554Improved12 852FemaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C5/610570458664Improved11 972FemaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C5/6656003511Complete recovery12 1073MaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C3-511075–96–––Died 9months postope- rative 1157FemaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C3/46060205713Improved9 1255FemaleSensory+ motorC7Intraforaminaldisc prolapseC6/7806056822Completere- covery7 1375MaleMyelopathyCentralstenosis(ligamen- tumflavumhypertrophy)C3/44565307735Improved5
a b Fig. 36.10. MRI scan with
posterior stenosis at level C3/4 preoperative (a) and af- ter microscopically assisted percutaneous decompres- sion (b)
Fig. 36.11. Cosmetic outcome 3 months postoperative after de- compression at level C6/7
tients (7 monosegmental, 1 bisegmental and 1 triseg- mental pathology) suffered from cervical myelopathy resulting from hypertrophied ligamentum flavum (Fig. 36.10). The other 4 patients presented with mono- radicular symptoms due to either bony foraminal ste- nosis or intraforaminal disc prolapse. The mean follow up period was 17 months (1 patient died after 9 months postoperatively due to unrelated causes). Patients were evaluated using a modified version of the Oswestry In- dex, called the Neck Disability Index (NDI) [24], and the VAS for neck and arm pain. The average operation
time per segment was 61 minutes. The mean NDI im- proved from 13.2 (preoperatively) to 4.8 (postopera- tively). The VAS for arm pain and for neck pain also showed marked postoperative improvement (Ta- ble 36.4). Complete recovery of the preoperative neuro- logical deficit was found in 4 patients while the remain- ing 8 patients showed improvement of the neurological symptoms during the follow up period. There were no intraoperative or postoperative complications and no reoperations (Fig. 36.11).
36.12
Critical Evaluations
Surgery for lumbar disc herniations represent the main indication for the use of the so-called microscopically assisted percutaneous technique. After a decisive learning curve, the procedure offers substantial advan- tages which makes it an alternative to the standard mi- crosurgical procedures. Certainly a smaller skin inci- sion is not the cause for a better clinical result therefore subsequent studies need to be done to evaluate the po- tential advantages as well the limitations of the proce- dure introduced here. We believe that this minimally invasive approach is a good alternative, especially to the open techniques, in the treatment of lumbar canal stenosis where polymorbidity is a considerable prob- lem. In our series, the mean age of the patients was 73.2 years. The patients are characterised by an in- creased surgical risk because of the commonly associ- ated diseases. The minimal trauma related to the ap- proach and the early mobilisation of the patients are advantages of this approach.
Finally we must understand that the presented stud- ies includes a small number of patients with a limited follow up.
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