THE HISTORY OF FUSION TECHNIQUES:

PLF: Posterolateral Fusion:

History: The grandfather of all flavors of fusion was a crude version of a posterolateral fusion (PLF), which was developed by Albee in 1911, for a patient suffering destructive tuberculosis of the spine (Pott’s disease) [1]. In order to stabilize and prevent the spread of the affected motion segment (i.e., to adjacent vertebrae), bone was taken from the patient's tibia (autologous bone), chopped up (morselized) into small fragments and then packed between adjacent spinous processes which had been surgically prepared by grinding off the bony cortex (this is called decortication). With the passage of time, the morselized bone hardened like cement (ossified) effectively immobilizing the painful/diseased motion segment. This type of procedure could be called an interspinous posterior fixation with autologous bone graft or just posterior fusion; this procedure is very rarely performed today. The procedure was improved upon over the next 10 years [65, 23, 25] and was first used for the treatment of degenerative spine conditions in 1929 by Hibbs and Swift [24].

In 1934, Massachusetts General Surgeons Mixter and Barr published a seminal paper in the New England Journal of Medicine [6] that concluded sciatica and back pain were frequently caused by a nerve-root-compressive disc herniation that was not a tumor of the disc as once believed. Instead, this herniation originated from the center (nucleus pulposus) of the disc. The pair of surgeons also suggested that the best way to correct the compressive disc herniations was by way of a crude fusion technique—the era of fusion was born.

The modern version of PLF was pioneered by Watkins and Campbell [59] who reported their twist of the procedure in 1953, which involved fusion of the facet joints, pars interarticularis, and bases of the transverse processes. Wiltse [62] described the final modification to the procedure, which simply included fusion of the lamina in addition to the previously mentioned posterior elements.

The Technique: In short, the surgeon dissects all the tissue (including fascia, ligaments and muscle) from the posterior elements of the vertebrae involved in the fusion (we shall use L4/L5 throughout this webpage). This includes the transverse processes of both vertebra and the lateral facet joints and maybe the lateral lamina. Once this extensive dissection is complete, decortication (removal of the bony cortex) is accomplished by grinding the outer covering (the cortex) off these bones to a point where they are oozing blood. The oozing blood is needed in order to supply the morselized bone with the blood and growth factors needed for osteoinduction and osteoconduction to occur ( or in layman speak; to allow the morselized bone to harden into real bone).

The Argument: Many argue this is a horribly invasive surgery because of the extensive dissection of muscle, tendon, and fascia involved, which in turn destroys the motion segment's ability to bend, extend, and turn. The counter argument is simple: the whole purpose of fusion is to eliminate the motion segment's ability to bend, extend, and turn so who cares that the muscle and ligaments are stripped off the motion segment – these muscles won't be used anyway.

Autograft vs. Allograft: Once the motion segment is prepared/decorticated, the next step in PLF is packing the morselized bone into the fusion bed, which is formed by the intertransverse ligaments.  Once the morselized bone is in place (in between adjacent transverse processes on each side of the spine), the larger erect a spinalis muscles are laid back down and act to hold the morselized bone in place. There are several options when it comes to creating the morselized bone: you can use the patient's own bone, which is preferred [21] because it boasts higher rates of fusion [32]. Or you can use donated bone/cadaver bone, which unfortunately is associated with risk of disease transmission and infection [29,30]. In the former situation, the procedure would be called an autograft, while in the latter procedure it would be called an allograft.

New Biologic Fusion Augmentation: for decades researchers have been searching for a way to increase the rate of successful fusion, and in 2002, rhBMP-2 (a powerful osteogenic growth factor, which is a member of the transforming growth factor-β superfamily) in combination with an absorbable collagen sponge (InFUSE™, Medtronic Sofamor Danek, Nashville, TN) was approved by the FDA for the treatment of symptomatic lumbar degenerative disc disease via anterior lumbar interbody fusion [we have not talked about that technique yet] in patients over 17 years of age who were affected at one motion segment from L2 through S1 [33]. It did not take long before spinal surgeons were using InFUSE™ for all of the different flavors of fusion, because of its remarkable ability to decrease fusion time, as well as prevent pseudoarthrosis (a.k.a. failure to fuse, nonunion) [34,35]. However, despite the initial industry sponsored trials reporting a 0% complication rate, subsequent nonindustry trials began reporting complications including fatal complications when used in the anterior cervical spine [Afghan] and ectopic bone formation in the spinal canal, which has been reported to necessitate decompressive revision surgery [36]. Although others have argued that the risk of rhBMP-2 complication is much less than the risk of patient morbidity secondary to the harvesting of iliac crest autograft.

When is PLF used? As mentioned previously, posterolateral fusion can stand alone or be combined with PLIF, TLIF or even the ALIF procedure. PLF is commonly employed alone for conditions such as symptomatic spondylolisthesis or for the correction of scoliosis [27] or any other condition where there is no compression of the neural elements within the central canal, lateral recess, or intervertebral foramen. If you need to decompress (i.e. perform laminectomy/facetectomy) for conditions such as stenosis or foraminal collapse, then PLIF or TLIF is often used in combination with PLF.

PLIF: Posterior Lumbar Interbody Fusion.

Posterior lumbar interbody fusion (PLIF) was a historic medical breakthrough for the treatment of degenerative spine disease, discogenic pain, spondylolisthesis, and spinal stenosis because it afforded much higher rates of fusion than the previous PLF technique.

What is the difference between PLF and PLIF? As the name implies, PLIF not only fuses the posterior elements (transverse processes, facets, and laminae), it also fuses adjacent vertebral bodies by the implantation of an intervertebral device (i.e. a graft or cage)!

The real pioneers of the procedure were Briggs and Milligan [4] who in 1944 had the brilliant idea to use the bone chips from the patient's laminectomy as the first interbody graft (they scraped out the disc and stuff these bone chips between the symptomatic vertebrae). A few years later, Jaslow [4] modified the technique by including spinous process fragments within the interbody graft.

The biggest breakthrough, however, was contributed by Robert Cloward who published a seminal paper in 1953 [3] that described a technique for removing blocks of bone from the patient's hip (iliac crest autograft) and inserting them into the disc space. Although a technical operation, the publication of this paper greatly increase the popularity of PLIF as a treatment intervention and boasted and fusion rates climbed to over 85%. However, compared to modern standards, the technique was fraught with complications such as blood loss, dural injury, nerve root damage, graphic extrusion, and arachnoiditis.

During the 1980s, Cloward [7] and others [8-15] improved the technique with the advent supplementary interbody implants and stabilizing posterior fixed instrumentation. Not only did these improvements boost the fusion rates, they also made the technique much easier to perform, which in turn further increased its popularity.
In 1988, Bagby reported that on the use of a stainless steel cylinder as an interbody implant device. The beauty of this system was that ground-up bone (autogenous bone) could be packed inside the device, as well as around the device. Not only did this device, which was affectionately called the "Bagby Basket," afford fusion rates near 90%, it also preserved the normal disc space height, which helped with exiting nerve root decompression as well as stabilization. The only problem with usage of a stainless steel device as an interbody graft, was the fact that its modulus of elasticity (Young's modulus) was far from that of natural bone, which in turn resulted in a problem with subsidence (the cages were sinking into the softer bone).

In the 1990s, Brantigan et al. [16] and Ray [17] modernize the technique even further by introducing synthetic interbody devices called “cages,” which were made out of carbon fiber and titanium respectively. These materials had a modulus of elasticity more similar to that of bone, which in turn mitigated the problem of subsidence.

Procedure description:

PLIF w/ PLF:

Arguably, the most common fusion performed in this day and age is a posterior lumbar interbody fusion (PLIF) with the addition of a posterolateral fusion (PLF). It can be used for treating discogenic pain, spondylolisthesis, and/or stenosis. Here is a description of the basic technique:

1) The surgeon will make a midline incision over the vertebrae that will be involved in the surgery.  He will then dissect his way down to the protective bony lamina, facet joints and transverse processes of the two vertebrae to be fused.  Dissected muscle and fascia are held off the bony structures by retractors.

2) In order to gain access to the disc space, the lamina on both sides of L4 are completely removed, which also means the spinous process is removed. The medial aspect of the facet joints are also taken (i.e., the inferior facets of L4); however, many surgeons spare the facet capsule. Usually modern surgeons will save this bone, grind it up, and use it later in the surgery as the cement which creates fusion (since it came from the patient, it’s called autogenous bone or autograft). The next soft tissue guard of the spinal canal is ligamentum flavum; this is also completely removed. Finally (here's the scary part), the entire thecal sac and traversing L5 nerve root must be pulled out of the way toward the midline. This is accomplished by a retractor. Now the surgeon has a clear view of the disc space (well, there is a nest of blood vessels and tiny nerve fiber that must be cut through but that's beyond the scope of this page).

3) The nucleus pulposus and end-plate of the L4 disc are now completely removed; much of the anterolateral annulus fibrosis is left intact as a barrier to protect the delicate anatomy anterior to the spine (sympathetic chain ganglia and vascular structures).

4) Next a tool is placed in the disc space to "jack-it-up,” which restores the normal disc height and increases the height of the IVF. The bony end-plate is now prepared by scraping the cortex off with a rasp like tool.

5) A graft of some sort—we shall use a “PEEK cage,” which is popular these days—is positioned in the interbody space (between the adjacent vertebrae).  I should back up: the PEEK cage, which has a hollow center, is first packed with that ground-up bone (morselized bone), which of course will act as the glue for the fusion. Once in its proper place, more morselized bone is packed all around the cage in a circumference approximately to that of the old disc.

6) Next, in order to ensure a solid fusion, a PLF is often performed (some surgeons don't do this depending on the circumstances).  The transverse processes and lateral aspect of the facet joints are decorticated (the outer cortex of bone is ground off) and then more morselized bone is packed between the adjacent transverse processes on both sides.
So the surgery is complete, right? Not! Remember all this morselized bone is like wet cement – it needs time to harden or ossified. The patient’s lumbar spine would be an unstable mass if we closed up right now. So we temporary, immediate solid fusion is created via rods, screws, and fasteners.

7) Special titanium screws are inserted into the strongest part of the vertebrae: the pedicles. More specifically, precise holes are drilled in each of the four pedicles and then the pedicle screws are screwed in place. The screws have special fasteners on their tops which hold lordotic titanium rods. Once everything is in place, the system (construct) is tightened down which not only creates a solid metal fusion, it also creates proper anatomical alignment (lordosis) between the adjacent vertebrae.

Now, the wound is closed up and we wait for the morselized bone to ossify and create a permanent fusion between the adjacent vertebrae.
By the way, once solid fusion is accomplished (this may take 6- 18 months depending on whether or not a special ossification accelerator was used (recombinant human bone morphogenetic protein-2 {BMP2}, which is a very controversial subject right now), the hardware may or may not be removed depending on whether or not it bothers the patient.

To be continued...

Transforaminal Lumbar Interbody Fusion:

REFERENCES:

1) Albee FH: Transplantation of a portion of the tibia into the spine for Pott’s disease. JAMA 57:885-86, 1911.
2) Carragee EJ, Hurwitz EL, Weiner BK. “A critical review of recombinant human bone morphogenetic protein-two trials: emergent safety concerns and lessons learned.” Spine J 2011; 6:471-491.
3) Cloward RB. “The treatment of ruptured lumbar intervertebral discs by vertebral body fusion. I. indications, operative technique, aftercare." J Neurosurg 1953; 10:154-168.
4) Jaslow I. Intracorporeal bone graft in spinal fusion after disc removal.” Surg Gynecol Obstet 1946; 82:215-22.
5) Yajun W, Yue Z, Xluxin H, Cui C. “A Meta-Analysis of Artificial Total Disc Replacement Versus Fusion for Lumbar Degenerative Disc Disease.” Eur Spine J 2010; 19:1250-1261.
6) Mixter WJ, Barr JS (1934) Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med 211:210-225.
7) Cloward RB. “Posterior lumbar interbody fusion updated.” Clin Orthop Relat Res 1985; 193:16-19.
8) Collis JS. “Total disc replacement: a modified posterior lumbar interbody fusion: report of 750 cases." Clin Orthop Relat Res 1985; 193:64-67.
9) Fraser RD. “interbody, posterior, and combined lumbar fusions." Spine 1995; 20:167S-177S.
10) Hutter CG. Posterior intervertebral body fusion. A 25 year study." Clin Orthop Relat Res. 1983; 179:86-96.
11) Lee CK, Vessa P, Lee JK. “Chronic disabling low back pain syndrome caused by internal disc derangements. The results of the disc excision and posterior lumbar interbody fusion." Spine 1995; 20:356-361.
12) Lin PM. "Posterior lumbar interbody fusion technique: complications and pitfalls." Clin Orthop Relat Res. 1985; 193:90-102.
13) Prolo DJ, Oklund SA, Butcher M. “toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to the posterior lumbar interbody fusion."
14) Steffee AD, Sitkowski DJ. “Posterior lumbar interbody fusion endplates." Clin Orthop Relat Res. 1998; 227:99-120.
15) Turner JA, Ersek M, Herron L, et al. “patient outcomes after lumbar spinal fusion." JAMA 1992; 268:907-911.
16) Guyer RD, Ohnmeiss DD. “Degenerative disc disease: fusion cages and dowels.” IN: The Lumbar Spine-3rd edition; Herkowitz HN, Dvorak J, Bell, G, et al. Lippincott, Williams & Wilkins, Philadelphia-2004.
17) Stromqvist B. “Operative Treatment of Anterior and Posterior Fusion.” In: IN: The Lumbar Spine-3rd edition; Herkowitz HN, Dvorak J, Bell, G, et al. Lippincott, Williams & Wilkins, Philadelphia-2004.
18) Greenough CG, Taylor LJ, Fraser RD. “anterior lumbar fusion: results, assessment techniques and prognostic factors." Eur Spine J 1994; 3:225-230.
19) Grob D, Scheier HJG, Dvorak J, et al. “circumferential fusion of the lumbar and lumbosacral spine." Arch Orthop Trauma Surg 1991; 111:20-25.
20) Herkovitz HN, Kurz LT. “degenerative lumbar spondylolisthesis with spinal stenosis: a prospective study comparing decompression with decompression and inter transverse processes arthrodesis." J Bone Joint Surg 1991; 73A: 802-808.
21) Ohtori S, Suzuki M, Koshi T et al. “Single Level Instrumented Posterolateral Fusion of the Lumbar Spine with a Local Bone Graft versus And Iliac Crest Bone Graft a prospective, randomized study with two-year follow-up." Eur Spine J (2011) 20:635-639.
22) Fernyhough JC, Schimandle JJ, Weigel MC, et al. “chronic donor site pain complicating bone graft harvesting from the posterior iliac crest for spinal fusion." Spine (1992) 17:1474-1480.
23) Hu R, Hearn T, Yang J. “bone graft harvest site as a determinant of iliac crest strength." Cin Orthop (1995) 310:252-256.
24) Kurz LT, Garfin SR, Booth RE Jr. “harvesting autogenous iliac bone grafts: a review of complications and techniques." Spine 14: 1324-1331.
25)Sasso RC, LeHuec JC, Shaffrey C. Spine Interbody Research Group (2005) "Iliac crest bone graft donor site pain after anterior lumbar interbody fusion: a prospective patient study outcome assessment."J Spinal Discord Tech 18:S77-S81.
26) Younger EM, Chapman MW “Morbidity at bone graft donor sites." J Orthop Trauma 3:192-195.
27) Violas P, chapuis M, Bracq H (2004) local autograft bone in the surgical management of adolescent idiopathic scoliosis. Spine 29:189-192.
28) Arrington ED, Smith WJ, chambers HG, et al. “complications of iliac crest bone graft harvesting." Orthop Relat Res 1996 300-309.
29) Buck BE, Malinin TI, Brown MD (1989) bone transplantation and human immunodeficiency virus. Clin Orthop Relat Res 240:129-136.
30) Muschler G, Lane J, Dawsonn E. “The Biology of spinal fusion. In: Cotler J, Cotler H (eds) Spinal Fusion, science and technique. Springer, Heidelberg.
31) Pelker RR, Friedlaender GE (1987) biomechanical aspects of bone autografts and allografts.” Orthop Clin North Am 1987; 18:235-239.
32) Floyd T, Ohnmeiss D. “A Meta-Analysis of Autograft versus Allograft in Anterior Cervical Fusion." Eur Spine J 2000; 5:398-403.
33) InFuse FDA Approval Letter. Available at http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprovalsandClearances/Recently-ApprovedDevices/ucm083423.htm. Accessed May 23, 2012.
34) cheng H, Jiang W, Phillips FM, Haydon RC, et al. Osteogenic activity of the 14 types of human bone morphogenetic proteins. J Bone Joint Surg Am. 2004; 86:141.
35) Mummaneni PV, Pan J, Haid RW, et al.  Contribution of recombinant human bone morphogenetic protein-2 to the rapid creation of interbody fusion when used in transforaminal lumbar interbody fusion: a preliminary report. Invited submission from the Joint Session Meeting on Disorders of the Spine and Peripheral Nerves, March 2004. J Neurosurg Spine 2004; 1: 19-23.
36) Wong DA, Kumar A, Sanjay J, Ghiselli G, Wong K. Neurologic impairment from ectopic bone in the lumbar canal: a potential complication of off-label PLIF/TLIF use of bone morphogenetic protein-2 (BMP-2). Spine J 2008; 8:1011-1018.