Minimally invasive posterior lumbar fusion—a novel approach to facet fusion

Chapter 5: Minimally invasive posterior lumbar fusion—a novel approach to facet fusion

Michael Gyorfi, Omar Viswanath, Alaa Abd-Elsayed


First, in 1911, Albee created a primitive version of a PLF. In 1944 King described a procedure that included a crude posterior fusion with facet screws that crossed the facet joint.2 Then in 1953 Watkins and Campbell pioneered the contemporary style of PLF, which comprised fusing the facet joints, pars interarticularis, and bases of the transverse processes.3 It was not until the 1970s that a specialized treatment for facet joint discomfort was developed, and facet pain had been mostly ignored until then.4 Magerl was the first to use translaminar facet screws (TLFSs) in 1983.2

Facet screw fixation has become a standard treatment, but the methods and practice of combining it with fusion techniques have progressed. Until recently, doctors would dissect all the tissue from the posterior components of the vertebrae implicated in the fusion (including fascia, ligaments, and muscle). This included both vertebrae’s transverse processes, the lateral facet joints, and possibly the lateral lamina. Decortication (removal of the bony cortex) is conducted after this extensive dissection is completed, by grinding the outer covering (the cortex) off these bones to prepare the area for fusion. The exposed bone is required to provide blood, mesenchymal stem cells, and growth factors to the bone graft for fusion to occur. All three of these components are required for healing, as they offer osteoinduction, osteoconduction, and osteogenesis.5 Today, a new approach allows for the same bone decortication as before, but without the need for substantial tissue dissection. With advancements in medical technology, physicians can now execute this surgery in a less invasive manner, potentially reducing blood loss, scarring, and recovery time.

Facet-mediated low back pain

Facet-mediated low back pain is thought to account for 25% to 40% of all low back pain.6 With neighboring-level pathology from earlier fusions or spinal operations, this number rises even more. Kyphoplasty and spinal augmentation operations are two procedures that may aggravate facet discomfort. Disc degeneration, spondylolisthesis, inflammatory arthritis, instability, and traumatic injuries are all diseases that can cause facet-mediated low back pain.7 On a magnetic resonance imaging (MRI) or computed tomography (CT) scan, these findings can be seen as a facet cyst or facet arthritic changes. Prior surgery at the same level is responsible for a smaller subset of facet-mediated pain. Interspinous spacers and other spinal implants aid in resisting motion in flexion and extension, but they do not help with lateral bending or axial rotation. Facet joints may stay flexible, and facet pain may last for a long time. To diagnose this as a pain modulator, an MRI or diagnostic blocks of the facet joints are frequently required (Fig. 5.1). After surgery, the joint can become weakened, leading to arthritic changes or abnormal mobility, resulting in facet-mediated discomfort.

Facet-mediated low back pain is a common cause of disability. Common causes of facet-mediated low back pain include:

Understanding the anatomy of the lumbar spine is necessary to comprehend the natural history of facet-mediated back pain. Although most adults have five lumbar vertebrae, it is estimated that about 5% of adults have a sixth lumbar vertebrae.8 In a healthy person, this is known as a transitional vertebra and should not pose any problems. The lumbar disc is located between the lumbar vertebrae. Patients who have had one of the aforementioned events may develop low back pain over time. This is most commonly, but not always, the outcome of anterior column disc degeneration and loss of integrity. Facet joints may become a source of pain if the disc is unable to maintain the tension across the lower back.9 The facet joints located in the lumbar spine (Fig. 5.2) are most susceptible to facet damage, as the lumbar spine bears the most weight and endures the greatest amount of stress/strain. Years of tension and exertion can wear down the intervertebral discs and facet joints. Water is the biggest constituent of an intervertebral disc, and age-related degenerative changes impact disc hydration, resulting in disc height loss and changes in facet joint alignment. Facet joint discomfort can result from this degeneration and misalignment. Facet joint syndrome frequently occurs in the presence of other spinal degenerative illnesses, such as degenerative disc disease, spondylolisthesis, and spondylosis (spinal osteoarthritis), and is a prevalent cause of low back discomfort. The lower back, as well as the buttocks and/or thighs, may be painful.7 Stiffness and difficulties standing up straight or sleeping on a flat surface can be caused by inflammation of these joints. Leaning forward generally relieves problems, whereas extension often aggravates them.

Anatomy and biomechanics of the facet joints

The zygapophyseal joints, commonly known as facet joints, are biomechanically complicated joints in the spine. The ranges of motion in flexion, extension, lateral bending, and axial rotation are limited by these joints.10 They form a motion segment in conjunction with the spinal disc, and the disc and superior/inferior facet joints on the right and left sides make up each motion segment. The facet joint is a synovial joint that secretes synovial fluid to keep it lubricated. Capsular ligaments surround the joints and serve to support the joint capsule. Owing to the strong innervation of medial branch fibers, high stretch values are the likely cause of discomfort when instability occurs.10 Because of the abnormal gliding of the joints, arthritic joints are also a source of discomfort. In the neuroforamen, spinal nerves exit anterior to the facet joint. Nerves can become squeezed, inducing peripheral neurologic symptoms when osteoarthritis or disc height decrease occurs.

Modern facet procedures

The facet joints are operated on to relieve discomfort by stabilizing the mobility segment. TLFS fixation, transfacet screw fixation, and intrafacet bone allograft fusion are the most prevalent procedures used today.11 Depending on the physician’s preference, the three techniques can be performed bilaterally in an open or minimally invasive manner. The key difference between these methods is the trajectory through which the implant is inserted (Fig. 5.3). When it comes to implant safety and efficacy, the trajectory is crucial. The screw must pass across the facet joint and have purchase via the superior articular process and inferior articular process of a facet joint when conducting translaminar facet fixation or transfacet fixation. The screw exerts a compressive stress on the joint, stabilizing it. The implant is inserted into the facet joint during an intrafacet fusion, and it usually contains characteristics that give it purchase within the joint. This approach is popular because it eliminates the need for the implant to pass through any sensitive neurologic structures. The screw must be positioned extremely precisely in a translaminar approach so that the threads do not breach the lamina cortex and enter the vertebral foramen. Another advantage of the intrafacet technique is that it allows for fixing without the use of metallic hardware. The cortex of the articular surfaces of the facet joint is removed in most intrafacet methods, and a cortical bone allograft is implanted. To generate another point of possible fusion across the joint, a bone graft is often placed on top of the implant.

May 21, 2023 | Posted by in PAIN MEDICINE | Comments Off on Minimally invasive posterior lumbar fusion—a novel approach to facet fusion
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