Pedicle screws can be inserted in a true percutaneous manner as described by Foley et al. [14] or through an expandable tubular retractor. When a purely percutaneous technique is chosen, it is essential to have a high-quality fluoroscopic guidance, with properly aligned images (Fig. 36.2). The surgeon should place the C-arm in order to obtain a true AP view with no shadow on the superior end plates. The pedicles should be well seen and located at the cranial part of the vertebral body, and the spinous process observed must be strictly in the midline. The lateral view should be obtained with strictly superimposed pedicles and single posterior vertebral body wall. Once the surgeon ensured the reliability of AP and lateral views, a Jamshidi needle can be introduced in the pedicle. Under fluoroscopic guidance, the needle is introduced through a 2 cm skin incision and docked gently on the lateral margin of the pedicle. On AP view, the tip of the needle is at the lateral cortex of the pedicle while it appears at the posterior edge of the pedicle on the lateral view. The Jamshidi needle is then hammered deeper in the pedicle, targeting its centre on the AP view and the posterior wall of the vertebral body on the lateral view. Once the Jamshidi needle is correctly placed, a K-wire is then introduced in the vertebral body through the needle. The needle can be removed and a cannulated tap is used over the wire to prepare the placement of a cannulated screw. Once the screws are inserted on one side, the rod can be placed but not locked, before the placement of the interbody cage.

The major principle of the minimally invasive approach is to minimise muscle trauma by lessening the soft tissue dissection and retraction (Fig. 36.3). It is crucial to properly place the retractor to ensure adequate exposure, creating a “working corridor” for safe disk access with minimum muscle injury. On the other hand, this “working corridor” limits the anatomical exposure. There are two technical points to become familiar with: first, handling and placing properly the retractor and, second, identifying the global anatomy with minimum bone exposure. The side of the transforaminal approach is based on the side of the radiculopathy, in order to achieve a large decompression of the affected nerve root. The site of the skin incision must be identified on AP fluoroscopy. A 3 cm skin incision is done 1–2 cm to the lateral margin of the pedicles. Notice that the incision may be more lateral in overweight patients, to maintain an adequate obliquity. The lumbosacral fascia is opened sagittally, and a blunt dissection is carried on in the plane between the multifidus and the longissimus, as described by Wiltse et al. [15]. The paraspinal muscles are split parallel to their fibres, creating a route to the junction between the transverse processes and the facet joint. The entry points of the cranial and caudal pedicles, overlying the disk of interest, are then identified. Using this plane, serial dilatators are introduced in the direction of the disk and centred on the facet joint. An appropriate length retractor is introduced over the dilatators and secured against the facet joint. Many retractors dedicated to this procedure are currently available. We recommend expandable retractors that can accommodate to the patient’s anatomy and expand the exposure when needed. The retractor is secured to the operating table via a flexible arm. A mediolateral retractor can be used in combination to widen the exposure of the segment of interest. This mediolateral retractor maintains the muscle split during the procedure. It is recommended to loosen this mediolateral retractor every 30 min to release the pressure and to limit the risk of muscle trauma and necrosis. One of the main advantages of the expandable retractor is the direct visual access to the pedicle’s entry point. In this setting and according to the surgeon’s preference, an operating microscope or operating loupes could be used. We prefer the microscope for the improved visualisation, the quality of the light, the possibility of video transmission and teaching purposes.

The dorsal and lateral surfaces of the facet complex are exposed using electrocautery and forceps (Fig. 36.4). Typical exposure includes both pedicle entry points and the transverse processes achieving posterior fusion. A total facetectomy is then performed using high-speed drill or osteotomes. During this step, the resected bone must be saved as bone graft. That is why osteotomes should be preferred rather than the drill. The inferior facet of the above vertebra is completely removed. The lamina can be partially drilled or opened using Kerrison rongeurs to expose the canal. In case of spinal canal narrowing, it is also possible to perform a wide laminectomy using this approach. The superior facet of the below vertebra is also cut or drilled without breaching the caudal pedicle to not alter the screw anchorage. For better identification, the pedicles should be located and tapped first. Once the foramen is opened, ligaments are carefully removed to expose both exiting and passing nerve roots. The surgeon should be aware of the location of both nerve roots and especially the exiting root. Epidural dissection can be carried on using bipolar cautery and spatulas. At this step, bayoneted instruments are required for optimum visualisation with microscope, in a small working channel. Step by step, the surgeon ensures enough space between the lateral margin of the dural sac and the passing root and the medial margin of the exiting root. This is mandatory to have a safe and wide exposure of the disk and mobile roots to be manipulated safely. The disk is then incised to perform an ipsilateral diskectomy using bayoneted forceps and curettes.

The interbody space is gradually distracted using sequential distractors until reaching the optimal reduction and suited height (Fig. 36.5). Sometimes, an osteophyte must be resected first using osteotomes to access the disk space. Once the desired distraction is obtained, it is maintained by locking the rod on the other side. The distractor is removed and the diskectomy can be completed. The end plates must be carefully prepared using dedicated straight and angled curettes and scrapers. The disk space is filled with the graft material. In our experience, the graft is performed using resected bone expanded with BCP (biphasic calcium phosphate). The fusion rate reported using such graft material is up to 90 %. Currently some teams use rh-BMP-2 (bone morphogenetic protein) and report a fusion rate of 100 % [16]. However, many complications have been reported such as postoperative radiculitis, bone osteolysis and symptomatic ectopic bone formation. As its use is not without risk, the reader should be aware of the reported complications related to the off-label use of rh-BMP-2 in minimally invasive TLIF [17]. Once the graft is inserted in the disk space, a straight or shaped TLIF cage is introduced after proper sizing. During the cage insertion, care should be taken on the roots especially the exiting root. A nerve root retractor might be needed to protect the root during this step. Finally, the ipsilateral screws and rod are placed under direct vision. Before locking, a posterior contraction is needed to secure the cage and to increase the lordosis. The posterior graft is placed and a drain is suitable on the side of the transforaminal approach.