Lumbar spinal fusion is commonly performed

23 Minimally Invasive Transforaminal Lumbar Interbody Fusion 137 Lumbar spinal fusion is commonly performed in the treatment of degenerative spinal disorders, trauma, spondylolisthesis, tumor and deformity cases. 34 In recent years, several studies has shown that instrumentation is needed and very important to achieve successful spinal fusion. 26,29 The use of spinal instrumentation requires wide and extensive exposure of the osseous anatomy of the lumbar spine to provide the adequate exposure to visualise anatomical landmarks. During this extensive muscle dissection, denervation of the paravertebral muscles, retractor induced muscle injury and bleeding take place. And also the dissection of the supporting ligamentous structures of the spine can result in iatrogenic instability. 12,13 Technological advancements on the development of surgical instruments and techniques have facilitated the development of the minimally invasive surgical (MIS) techniques for the treatment of spinal disorders. MIS surgical techniques performed from the minimal working corridors gives little harm to the surrounding tissue while the objectives of decompression and stabilisation can be achieved similar as the open techiques. 15,19 The minimally invasive variation of the transforaminal lumbar interbody fusion (TLIF) procedure (MIS-TLIF) was first described in 2003 by Foley et al. 4,7,27 This method has become very popular among the spine surgeons since it achieves circumferential fusion (360 degree) via posterior approach only when combined with the percutaneous pedicle screw systems. 3,11,33 Indications Similar with the indications of open TLIF surgery. Furthermore, surgeon should be familiar with the MIS techniques. 1) Grade 1-2 spondylolisthesis (Axial low back pain and/or leg pain) 2) Recurrent disk disease (Predominantly low back pain) 3) Degenerative disk disease 4) Postlaminectomy instability 5) Treatment of pseudoarthrosis Contraindications 1) Conjoined nerve root anomaly 2) High grade spondylolisthesis (grade 3 and 4) 3) Significant scoliosis 4) High level instability after laminectomy Relative Contrindications 1) Multiple level (>2 ) disease 2) Severe osteoporosis

138 Surgical Technique Following the induction of general endotracheal anesthesia, the patient is turned to the prone position on a radiolucent table. To maintain the lumbar lordosis, options include using a standard table with chest rolls or a Jackson type table that places the hips in extension. Surgeon is located to the symptomatic side of the patient or it is surgeon s choice to select the side if the symptoms are bilateral. Fluoroscopic image intensifier is set to the contrlateral side of the surgeon. Prior preparing and draping the patient, lateral (Lat) and antero-posterior (AP) images are obtained to identify the pedicle anatomy. After the patient is draped, the disc level of interest and facet complex is identified by a Kirschner (K) wire on lateral images. (figure 1) A 2-2,5 cm skin incision is centered over this point, approximately 4-4,5 cm lateral to the midline. A K-wire is placed toward the facet complex with a a lateral to medial trajectory through the incision. Serial dilators are passed over the wire creating a muscle splitting surgical corridor. The appropriate length tubular retractor (22 or 26 mm in diameter) or working cannula is passed over the dilators and set over the facet complex. The retractor is fixed to the table by the help of a flexible arm. There are also some other expandable Figure 1: AP (A) ve Lateral (B) Lumbar X-Ray. A. Under fluoroscopy, pedicles and disc space are identified on AP view. Lateral upper and lower aspects are marked. Starting from the disc level, approximately 15 mm cranial(black arrow) and 10 mm caudal(white arrow) vertical skin incision is performed. B. Disc space is identified on the lateral view. retractor systems that settles over the working cannula. (figure 2) After this stage, surgery is performed even under operating microscope or surgical loupe, depending on the surgeon s preference. Working cannula should be placed over the facet complex properly. (figure 3) It is paramount to carefully identify the midline spinous process and ipsilateral facet joint prior to any bone removal. Otherwise it is possible to enter the spinal canal inadvertently because of the oblique position of the working cannula. The facet should be visualised in the lateral half of the working cannula, with the laminofacet junction and lateral portion of the lamina in the medial half of the working cannula. Residual soft tissue is removed from the dorsal surface of the facet complex using electrocautery and pituitary forceps. A total facetectomy is performed using high speed drill or bayoneted osteotomes, curettes and rongeurs specifically designed for minimally invasive surgery. Ligamentum flavum and synovium are removed in piecemeal fashion using Kerrison rongeurs to expose the exiting and traversing nevre roots. Epidural bleeding is commonly encountered at this point and is easily controlled using gelfoam and bipolar coagulation. It is not obligatory to expose the entire exiting nevre root, but the surgeon should be aware of both the root s location beneath the superior pedicle and and the amount of space between the lateral margin of the traversing root and the medial edge of the exiting root. A standard ipsilateral discectomy is performed through the working cannula. The interspace is then distracted using one of two methods. In the first method, contlateral side is instrumented percutaneously and a rod is placed to distract the interspace and temporarily maintain the distracted position. In the second method, an interlaminar spreader is placed through the incision and used for interspace distraction. Once the optimal interspace distraction has been achieved, endplate preparation is performed

Minimally Invasive Transforaminal Lumbar Interbody Fusion made up of polyetheretherketon(peek), carbon fiber, allograft bone and titanium. The most important point is, major fusion is achieved via the bone chips located disc space anteriorly. So the surgeon should put the maximum amount of bone to the interspace to increase the rate of the fusion. (figure 4) Furthermore, in the literature there are several reports indicating the effective osteogenetic properties of rhbmp-2 in the interbody fusion. 30 Since this product is not allowed to use in Turkey by the national social security system, we only use local autograft for interbody grafting. Contrlateral pathology may be addressed indirectly on the basis of distraction of the intervertebral disc space, re- Figure 2: Preparation of MIS working corridor. Minimally invasive expandable retractor system is being placed over the sulting in ligamentotaxis and increase in working cannula the foraminal diameter. In cases of severe contrlateral foraminal stenosis and central canal stenosis, the surgeon has 2 options. First, the working cannula may be angled medially to decompress the central canal and contrlateral hemilamina. Second option is also to perform MIS decompression to the contrlateral side. 16 139 Figure 3: Lateral intraoperative X-Ray. Working cannula should be docked on the interested facet complex using special designed down pushing curettes and endplate scrapers. All of the cartilaginous endplate is removed, and the bone endplates are decorticated but left structurally intact. Based on the surgeon s preference, local autologous bone (bone chips obtained from the decompresion) and/or recombinant bone morphogenic protein (rhbmp) products can be placed contrlateral to the anulotomy in the ventral portion of the interspace followed by the placement of the cage. Cages can be Figure 4: Anterior part of the disc space is filled with the bone graft.

140 After completing decompression, percutaneous instrumentation is started. First operated side is instrumented and compressed under fluoroscopic control followed by the contrlateral side. (figure 5) 2) Dural tear (Managed succesfully with bed rest for 24h and dural onlay substitute with/without fibrin glue) Discussion TLIF is a well-known technique for achieving 360 degree fusion through a single, posterior approach. 6,18 The safety and efficacy of the TLIF procedure are well established. 8,24 Fortunately, advances in imaging technology and instrumentation have allowed for the procedure to be performed using MIS techniques. Fessler et al. were the first to perform a cadaveric feasibility study of MIS-TLIF procedure in 2002. They showed that the procedure could be performed safely and effectively. 14 In 2005, Isaacs et al. reported a significant decrease in intraoperative blood loss, postoperative narcotic use and hospital length of stay in patients who underwent MIS-TLIF vs patients who underwent an open lumbar fusion. 9 Schwender et al. also affirmed the feasibility of safely and effectively performing the TLIF procedure through a minimally invasive approach in a series of 49 patients with a mean of 22,6 months of follow-up. 27 There are various numbers of reports concerning MIS-TLIF procedure for the treatment of degenerative spinal disorders and spondylolisthesis. 5,21,22,25 The results compare favorably with open procedures for the same indication. 2,23 MIS-TLIF procedure may be routinely used in obese and elderly patients. 10,17,31 In their study, Karikari et al reported very low complication rate in the 70 years old and/or older patient group. 10 Similarly, Figure 5: Postoperative view of the incision scars that underwent bilateral decompression and MIS-TLIF surgery Lee et al did not find any statistically significant difference between the 65 years old patients and young patients who underwent single level MIS-TLIF surgery. 17 Wang et al did not report any complication except Complications increased X-ray exposure time in obese patients who 1) Screw and/or cage malposition underwent MIS-TLIF surgery. 31 MIS-TLIF procedure can easily be performed in revision cases since paramedian approach through naive muscle avoids scar tissue and reduces the risks of nerve injury or a spinal fluid leak. 28,32 Excellent results are obtained in selected patients. Increased X-ray exposure time, steep learning curve and the necessity for some custom made surgical instrument for performing MIS-TLIF procedure are the main disadvantages when compared open TLIF surgery. 1,20 Conclusion MIS-TLIF procedure significantly diminishes blood loss, postoperative narcotic use and length of stay in hospital when compared with open TLIF.

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