Lumbar spinal fusion has evolved as a treatment option for symptomatic spinal instability, spinal stenosis, spondylolisthesis, and degenerative sco­liosis [1, 2]. Lumbar spinal fusion is often per­formed after a posterior decompressive procedure when there is evidence of preoperative lumbar spinal deformity or instability that could worsen after laminectomy alone [3]. When performing a lumbar spine fusion, attaining a solid interbody arthrodesis through the intravertebral disc space has distinct biomechanical advantages when

fusions [4]. The advantages of interbody fusions include increased surface area for fusion to occur, the ability to restore and/or maintain foraminal height, and the ability to restore segmental lordo­sis across the fused segment [4]. Restoration of disc space height through placement of structural interbody grafts increases foraminal size which allows for indirect neural decompression [5, 6]. The posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF)

surgery is superior to nonoperative treatment in patients with debilitating low back pain and/or radiculopathy that have failed conservative treat­ment [1]. Fusion is also indicated in patients with lumbar instability and for correction of spi­nal deformity including symptomatic spondylo­listhesis, degenerative scoliosis, and spinal stenosis associated with instability [1, 2, 12]. Circumferential fusions with interbody graft placement have several advantages over postero­lateral or intertransverse fusions. These advan­tages include greater surface area for fusion, restoration of disc space height for additional indirect decompression, and restoration of and/ or preservation of segmental lordosis. Recent evidence from the spine deformity literature demonstrates the importance of global and regional alignment on patient outcomes. Inadequate restoration of lordosis or loss of lor­dosis through these segments can have a dra­matic effect on the overall lumbar lordosis, which can impact sagittal alignment, patient out­comes, and need for revision surgery. Not restor­ing adequate lumbar lordosis during lumbar fusion may result in mechanical low back pain, sagittal malalignment, and increased risk of adjacent segment degeneration. Several short­term studies comparing posterolateral fusions to interbody techniques including TLIF have not reported a dramatic difference in short term out­comes. The ability to restore segmental lordosis with TLIF is a distinct advantage over PLF and may result in more durable long-term outcomes.

In order to facilitate the discectomy and inter­body placement, a temporary rod is placed oppo­site the side of the planned discectomy and distraction is applied. Use of an offset distraction device on the ipsilateral side may improve access to the disc space while maintaining distraction. With the disc space under distraction, the thecal sac and exiting nerve roots are identified and pro­tected, the disc space is identified, and discec­tomy is performed. First, the outer annulus fibrosis of the intervertebral disc is incised lateral to the traversing nerve root. If the medial aspect of the subjacent superior facet has been ade­quately resected, the discectomy can be accom­plished with minimal or no retraction of the exiting or the traversing nerve roots. Pituitary rongeurs and bone rasps are used to remove the great majority of disc material from the inter­space. Care is taken to preserve the ventral and lateral margins of the annulus to allow the graft material, both structural and morselized, to be contained.

In all cases, we use generous amounts of autolo­gous bone graft for both the intervertebral space and the posterolateral gutters. Autogenous iliac crest graft is combined with the previously pre­pared local autograft bone. Corticocancellous iliac crest autograft may be obtained, through either the same incision or a separate incision, using bone gouges. Recently, we have modified our technique and have started using bone marrow aspirates from the iliac crest. Using a large bore trocar, the bone marrow is aspirated and no inci­sion is necessary. A total of 20 mL of combined blood/bone marrow is removed for processing. This technology allows for concentration of the osteogenic precursor cells which are isolated from the bone marrow. These cells are combined with the previously obtained local bone graft to pro­duce a generous amount of fusion substrate bone for later grafting. The fusion substrate bone is packed within radiolucent, carbon- fiber rein­forced PEEK cages (CFRP cages; DePuy Synthes Spine). In our current technique, after a thorough discectomy, autologous morselized graft is packed into the ventral aspect of the disc space.

Attention is now directed to the lateral gutters. Generous amounts of morselized autograft are placed over the decorticated transverse processes and sacral alae. This is performed before con­necting the pedicle screws together to allow for the bone to be in direct apposition to the exposed donor sites.

Given the significant disc height loss causing severe foraminal stenosis, as well as the degen­erative spondylolisthesis at L4–L5, a two-level TLIF was offered to decompress the nerve roots, stabilize the L4–L5 and L5–S1 interspaces, restore the disc space heights, and attempt to restore the segmental lordosis across the L4–S1 segments (Figs.

• TLIF can be a powerful tool for restoration of segmental lordosis. This can be achieved by performing a posterior column osteotomy (chevron or Smith-Petersen osteotomy) fol­lowed by compression across the segment. This is facilitated by anterior placement of the interbody cages which acts as a fulcrum when compression is applied across the segment.