Introduction
Principles
Applications
Conclusion
Lumbar interbody fusion is a surgery in which a disc between two vertebrae is removed and the vertebrae were subsequently fused together. This type of surgery, also known as spinal fusion surgery, may be the treatment option for some patients with degenerative disc diseases, persistent back pain due to a weak or unstable spine, some spinal deformities such as scoliosis, slipped vertebrae or certain spinal injuries.
Spinal fusion aims at stopping motion at the pathological segment, thereby controlling the pain and restoring spinal function. The spinal column can be approached for the procedure either anteriorly through the abdominal muscles or posteriorly through the thick back muscles. Conventional anterior and posterior open approaches to lumbar spine require a significant degree of soft tissue dissection in order to achieve appropriate exposure.
In recent years, minimally invasive techniques have been developed. Such techniques aim at reducing trauma to the soft tissues surrounding the spine and yet, allow surgeons to achieve the same surgical goal.
When compared with surgeries performed through conventional open approach, minimally invasive surgeries can significantly reduce the trauma experienced by soft tissues, cause much less blood loss, and make post-operative pain much easier to control.
The goal of minimally invasive surgeries for lumbar fusion is the same as traditional open interbody stabilisation procedures, namely, the decompression of neural elements followed by interbody fusion with or without instrumentation of internal fixation devices. The difference between these two methods is in the manner of operative exposure and soft tissue retraction to allow procedures to be performed on the spinal segments. Surgical invasiveness has been minimised mainly on surgical accesses but not on the target surgery.
Minimally invasive lumbar approaches are technically demanding. Before the surgeon can perform safely through small skin incisions with clinical success, he has to have extensive knowledge on spinal anatomy. The procedure also requires judicious use of intraoperative X-ray and other imaging techniques, as well as adequate lighting and magnification of the operative site at the depth of the wound.
1. Tubular retractor system in percutaneous micro-disectomy
The use of tubular retractor can minimise soft tissue dissection and trauma while providing adequate surgical exposure. A working corridor is established to allow decompression of the involved neural tissue, interbody fusion and pedicle screw placement. The tubular retractor system is commonly used in posterior and transforaminal lumbar interbody fusions (see photos below).
2. Minimally invasive Posterior Lumbar Interbody Fusion (PLIF)
Fluoroscopy is used to localise the disc space in question. A tubular retractor is inserted through natural muscle planes, again under fluoroscopic guidance. A “bone window” is opened, exposing the pathology and the neural tissue. With gentle medial retraction of the neural tissue, a complete discectomy (excision of an intervertebral disc) can be achieved. Bone grafts or some fusion spacer (cage) can be inserted through the working corridor and be placed between the vertebral bodies if spinal fusion is deemed necessary. Pedicle screws may be inserted under direct vision through the tubular retractor or via a separate percutaneous wound under fluoroscopy.
3. Minimally invasive Transforaminal Lumbar Interbody Fusion (TLIF)
Transforaminal Lumbar Interbody Fusion (TLIF) is a procedure very similar to the PLIF, except that the disc is removed from the side instead of from the back in this case. This procedure allows surgeons to limit the approach to only one side, further decreasing soft tissue dissection. The advantage is that the nerve root is decompressed and the disc space is accessed with minimal root retraction. This can avoid damage to the neural tissue during the operation.
As with PLIF, the procedure begins with fluoroscopic localisation of the disc space in question. Percutaneous pedicle screws were inserted through small stab incisions. Provisional fixation of the pedicle screw system allows temporarily distraction of the disc space and facilitates decompression and placement of interbody grafts or cage. A tubular retractor is placed to expose the entire facet complex. The facet joint and the surrounding soft tissue are removed for decompression of the neural tissue. Finally, pedicle screws may be placed via the tubular retractor as an adjunct to the interbody fusion construct.
4. Minimally invasive Anterior Lumbar Interbody Fusion (ALIF)
Capener described the first anterior approach to the lower lumbar spine in 1932. Unfortunately, this open approach is associated with profound morbidity. Less traumatic approaches for accessing the spine have since become desirable.
Currently, there are three common minimally invasive approaches for Anterior Lumbar Interbody Fsion (ALIF). They are laparoscopic transperitoneal, endoscopic retroperitoneal and mini-open retroperitonea. These approaches allow lumbar fusion be performed anteriorly while minimising potential injury to neural tissues and preserving the posterior spinal structures. Minimally invasive ALIFs can also be part of the spinal fusion surgery that is performed in conjunction with percutaneous pedicle screw instrumentation.
Minimally invasive techniques are currently applied in various spinal procedures and the early experience has been encouraging. These approaches may shorten hospital stays, diminish blood loss and help patients speed up their return to normal daily functions. However, surgeries that are minimally invasive do require meticulous pre-operative planning, thorough knowledge of the patient’s individual anatomy and respect for the tissue functions. These factors are essential for achieving good clinical outcomes.
Dr. SUN, Lun-kit