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Minimally Invasive Spine Surgery – Introduction
 
                Degenerative conditions such as disk herniations, spinal stenosis, spondylolisthesis (spinal slippage), scoliosis (curve of the spine) and facet cysts are potential causes of spinal pain (Figures 1-5).   These conditions may cause nerve compression leading to severe pain radiating down the arms or legs in addition to numbness, tingling and weakness as a result of dysfunction of a compressed nerve.  Patients with spinal stenosis often have difficulty with standing and walking as a result of compressed nerves in the lumbar region of the spine (low back).  Treatment for these conditions generally begins with non-surgical measures such as anti-inflammatory medications, physical therapy and spinal injections.  Patients with severe symptoms that are not relieved adequately with non-surgical treatment may be candidates for spinal surgery.  Thanks to recent advances in surgical technique and equipment, many spinal disorders can now be corrected with minimally invasive spinal surgery.

                Minimally invasive spinal surgery is a collection of surgical techniques that allows the spinal problem to be corrected using small surgical incisions.  Compared to traditional spine surgery, minimally invasive spinal procedures are less damaging to the muscles and other soft tissues around the spine.  Also, a quicker recovery from surgery is anticipated with minimally invasive surgery.  Other advantages of minimally invasive spinal surgery include less bleeding, shorter hospital stay and a lower rate of postoperative infection compared to traditional spinal surgery.

Minimally Invasive Spinal Surgery Techniques

                Minimally invasive spinal procedures may be done with general, spinal or even local anesthesia depending on specific type of surgery being performed.  Many minimally invasive spinal procedures can be performed in an outpatient setting while more complex minimally invasive operations may require postoperative hospitalization.  Minimally invasive spinal procedures require specialized equipment and should be performed by surgeons with substantial experience in spinal surgery and only after proper training and experience in each of the minimally invasive surgical techniques.  Each technique has a “learning curve” that must be overcome before the procedures can being reliably performed on patients.  For this reason, not all surgeons choose to include minimally invasive spinal procedures in their practices and only a small percentage of spinal surgeons specialize in minimally invasive spinal surgery.

                One of the major differences between minimally invasive and traditional spinal surgery is the use of small incisions to perform the surgical procedures.  To perform spinal surgery through small incision, the surgeon must utilize special equipment that is not routinely used with traditional spinal surgery.  To access the spine through a small incision, the minimally invasive spinal specialist uses a specialized tubular retractor or port to access the spine. 

                One important principle of minimally invasive spinal surgery is that the soft tissues surrounding the spine are not cut but rather are “dilated” using special instruments called serial dilators (Figure 6-8).  At the beginning of the procedure, the surgeon gently works the dilators through the incision to the spine, sequentially enlarging the space until the tubular port can be placed.  Once the tubular port is in place (Figure 9), the dilators are removed giving the surgeon an access channel to the spine.  The tubular port is secured to a flexible holder during the procedure (Figure 9).  The tubular port allows the surgeon to visualize the spine and to perform the corrective procedure (Figure 10).  During the surgical procedure, special instruments are used to remove pressure from the compressed nerve(s) (Figure 11 and 12).

                Visualization of the spine through the tubular port is achieved with the operative microscope (Figure 13).    The operative microscope allows the surgeon to focus and magnify the working zone at the floor of the tubular port and provides high intensity lighting which improves the surgeon’s view (Figure 14).  Use of the operating microscope allows the surgeon to achieve better differentiation between normal and abnormal tissues during the operation. 

                To precisely localize the spinal problem, the surgeon uses a mobile, real-time xray unit called a C-arm fluoroscopy machine (Figure 15 and 16).  This device is used prior to making the surgical incision to localize the site of the spinal problem and may be used a certain times during the procedure, such as when spinal implants are being placed. 

Minimally Invasive Spinal Decompression Surgery   

                The most common minimally invasive spinal procedure in our practice is spinal decompression surgery.  This type of surgery is used to treat patients suffering from disc herniations, spinal stenosis or from spinal cysts causing pressure on the nerve roots.  In this operation, the surgeon removes pressure from the spinal nerves caused by herniated disc fragments, bony arthritis (e.g. bone spurs) or spinal cysts. 

                To perform this type of surgery, the area of the spinal problem is precisely localized using the C-arm fluoroscopy machine (Figure 15 and 16).  Then, a small surgical incision (usually about 1/2 inch in length) is made directly over the level of the spinal problem.  Next, a series of small tubes (Figures 6-8) are used to dilate a working channel to the spine, allowing a tubular port (Figure 9 and 10) to be placed.  Using a microscope, the surgeon can then remove the pressure from the spinal nerves by trimming overgrown bone spurs, thickened ligaments or disc fragments that are compressing the spinal nerves (Figure 12 and 13).    

                In most cases, minimally invasive spinal decompression requires 30-60 minutes of surgery per level.  During the procedure, the surgeon can visualize the source of the nerve compression and can ensure that the nerve is fully decompressed at the conclusion of the procedure (Figure 17 and 18).  On imaging studies, the site of the spinal decompression will show a small passage to the spinal canal used to remove pressure from the nerve roots (Figure 19).  Importantly, the major spinal bony processes, muscles and ligaments remain intact and may help to prevent future instability of the spine. When a disc herniation is present, the surgeon can simply remove the herniated fragment, thus relieving pressure on the nerve (Figure 20 and 21).

                Following surgery, the tubular port is simply removed.  Because the soft tissues have not been cut, they simply naturally fold back together to close the passage used to access the spinal problem.  The skin and fascia are stitched beneath the skin and a small bandage is applied (Figure 22).  Local anesthesia is injected around the incision to lessen postoperative discomfort.    

                As soon as the patient is recovered from anesthesia, he/she is encouraged to walk and begin eating within a few hours of surgery.  Most patients are able to be discharged from the hospital within hours of surgery.  Normal light activities are encouraged after hospital discharge, especially a walking program.  Patients are allowed to shower on the second postoperative day.  Return to work and driving is generally allowed when the patient is no longer taking pain medications and able to function comfortable while doing the activities required of their job.  The first postoperative office visit is generally scheduled 2 weeks after surgery.  At that time, the healing of the wound is examined and the long term postoperative rehabilitation course is discussed (Figure 23).  Many patients benefit from a formal course of organized physical therapy which generally begins shortly after 2 week visit.

Minimally Invasive Spinal Fusion Surgery

                Certain spinal conditions such as spinal slippages (spondylolisthesis) (Figure 3) and spinal deformities (scoliosis) (Figure 4) require a spinal fusion due to the underlying instability of the spine.  Although spinal fusion surgery is generally more complex than spinal decompression surgery, many of conditions requiring spinal fusion can be successfully managed with a minimally invasive surgical approach.  A spinal fusion is an operation where the vertebrae are surgically linked together with bone graft that slowly heals much like a fractured bone until the bones become a single bony unit (Figure 24).  Several different types of spinal fusion can be performed using minimally invasive techniques.  The best type of fusion depends on the underlying spinal condition and other patient specific factors.  Some spinal fusions required the placement of spinal implants that are designed to support and immobilize the spine during the healing process (Figure 25).  Depending on the specific case, decompression of the spinal nerves may be done during the same operation that a spinal fusion is performed using techniques similar to those discussed above. 

                To perform a spinal fusion, the surgeon first localizes the area of the spine to be fused using fluoroscopy (Figure 16).  A tubular portal or retractor is then placed as described for spinal decompression, to visualize the area of the spine to be fused (Figure 26).  The vertebrae bones to be fused are then cleaned of local soft tissues and roughened to prepare the site to heal during the fusion process.  Bone graft material (either crushed bone or a related product that stimulates bone healing) is then packed between the vertebrae to bridge any gaps between the two bones.  In some cases, spinal implants may be placed to support and immobilize the area of the spinal fusion.  Examples of spinal implants would include bone screws, rods or fusion cages (Figure 27).  When placing spinal implants, the C-arm fluoroscopy unit is used correctly position and secure the implants to the spine (Figure 26).  At the end of the fusion procedure, the tubular portal or retractor is withdrawn and tissues naturally fold back together.  The fascia and skin are repaired with stitches under the skin and small bandages are applied. 

                Following surgery, the patient is allowed to recover from anesthesia and is then encouraged to walk and begin with a liquid diet.  Discharge from the hospital is allowed when the patient is walking, eating and comfortable on oral medications.  Spinal fusion patients are instructed not to bend the area of the spinal fusion until healing is confirmed on xrays. 

                X-rays are taken during office visits as specific time points to assess the status of the fusion.  A walking program and outpatient physical therapy are generally prescribed to assist in the healing and recovery from surgery.

	Figure 1- Lumbar disk herniation
	Figure 2- Lumbar stenosis
	Figure 3- Lumbar spondylolisthesis (slippage of the vertebrae)
	Figure 4- Lumbar degenerative scoliosis (spinal curvature)
	Figure 5- Lumbar facet cyst
	Figure 6- Sequential dilators and tubular retractor. Notice how each dilator has a slightly larger diameter allowing the tissues to be gently dilated open rather than cut.  The largest tube is the tubular retractor or port through which the procedure will be performed.
	Figure 7- Serial dilators and tubular port assembled as they would be during the initial stages of the procedure.
	Figure 8- Serial dilators in place to gain access to the spine without cutting the tissues.
	Figure 9- Tubular port placed over serial dilators and secured with flexible arm at the beginning of a lumbar decompression procedure.
	Figure 10- Tubular portal providing surgical view of the spine.
	Figure 11- Surgical instruments used for minimally invasive spinal surgery
	Figure 12- Surgeon operating through a tubular port.
	Figure 13- Operating with the operative microscope.  The operative microscope allows the surgeon to focus on and magnify the region of the spinal procedure under high intensity lighting.  This improves the surgeon’s visualization of normal and abnormal tissue and improves the safety and efficiency of the operation.
	Figure 14- Using the operative microscope, the surgeon is able to magnify and illuminate the area of the spinal disorder for precise surgical correction of the problem.
	Figure 15- C-arm fluoroscopy machine is used to visualize the spine with x-ray and localize the spinal problem.  It is also used during the placement of spinal implants that are applied during spinal fusion surgery.
	Figure 16- C-arm in place to localize the site of the spine problem.
	Figure 17- Picture of decompressed nerve sac following decompression surgery using a minimally invasive approach
	Figure 18- Picture decompressed nerve root following decompression surgery using a minimally invasive approach
	Figure 19- CT scan showing site of spinal decompression
	Figure 20- Picture of herniated disk fragment being removed at surgery
	Figure 21- Picture of herniated disk fragment after removal
	Figure 22- Surgical incision after closure is covered with special tape called steri-strips
	Figure 23- Surgical scar 2 weeks after surgery
	Figure 24- Spinal fusion- notice the bone linking the unstable vertebrae together on the sides of the spine
	Figure 25- Spinal implants consisting of screws linked by rods to immobilize the spinal segment undergoing fusion and assist with healing
	Figure 26- Tubular port position for spinal fusion as seen on an xray view
	Figure 27- Seven different types of fusion cages that may be used during a spinal fusion procedure

REFERENCES

1.         Asgarzadie F, Khoo LT.  Minimally invasive operative management for lumbar spinal stenosis: overview of early and long-term outcomes.  Orthop Clin N Am 2007, 38: 387-99.

2.         Khoo LT, Fessler RG.  Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis.  Neurosurgery 2002, 51(Suppl 2): 146-54.

3.         Palmer S, Turner R, Palmer R.  Bilateral decompression of lumbar spinal stenosis involving a unilateral approach with microscope and tubular retractor system.  J Neurosurg (Spine 2) 2002, 97: 213-7.

4.         Guiot BH, Khoo LT, Fessler RG.  A minimally invasive technique for decompression of the lumbar spine.  Spine 2002, 27: 432-8.

5.         Benz RJ, Garfin SR.  Current techniques of decompression of the lumbar spine.  CORR 2001, 384: 75-81.

6.         Rosen DS, O’Toole JE, Eichholz KM, et al.  Minimally invasive lumbar spinal decompression in the elderly: outcomes of 50 patients aged 75 years and older.  Neurosurgery 2007, 60: 503-8.

7.         Podichetty VK, Spear J, Isaacs RE, et al.  Complications associated with minimally invasive decompression for lumbar spinal stenosis.  J Spinal Disord Tech 2006, 19: 161-6.