Minimally Invasive Spine Surgery

In general, the goal of the minimally invasive spine (MIS) surgery is to stabilize the vertebral bones and spinal joints and/or relieve the pressure being applied to the spinal nerves — often a result of conditions such as spinal instability, bone spurs, herniated discs, scoliosis or spinal tumors.

As opposed to open spine surgery, minimally invasive surgical approaches can be faster, safer, and require less recovery time. Because of the reduced trauma to the muscles and soft tissues (compared to open procedures), the potential benefits are:

• Better cosmetic results from smaller skin incisions (sometimes as small as several millimeters)
• Less blood loss from surgery
• Reduced risk of muscle damage, since less or no cutting of the muscle, is required
• Reduced risk of infection and postoperative pain
• Faster recovery from surgery and less rehabilitation required
• Diminished reliance on pain medications after surgery

In addition, some MIS surgeries are performed as outpatient procedures and utilize only local anesthesia — so there is less risk for an adverse reaction to general anesthesia.

As with any surgical procedure, no matter how minimal, there are certain risks associated that include, but are not limited to:

• Possible adverse reaction to the anesthetic
• Unexpected blood loss during the procedure
• Localized infections, no matter how small the incision area

And, though uncommon, there is always a small chance that the initial MIS surgery cannot be completed, requiring either a second procedure or full open surgery.

Conditions Treated Using MIS Procedures

• Degenerative disc disease
• Herniated disc
• Lumbar spinal stenosis
• Spinal deformities such as scoliosis
• Spinal infections
• Spinal instability, including spondylolisthesis
• Vertebral compression fractures
• Spinal tumors

How Minimally Invasive Spine Surgery Works
Because the spinal nerves, vertebrae, and discs are located deep inside the body, any approach to gain access to the spinal area requires moving the muscle tissue out of the way. In general, this is facilitated by utilizing a small incision(s) and guiding instruments and/or microscopic video cameras through these incisions. Contrary to popular belief, lasers are very rarely used in MIS surgeries.

A number of methods can be used to minimize trauma during MIS surgery. Some of the more common techniques are outlined here.

Using a Tubular Retractor
This technique involves progressive dilation of the soft tissues, as opposed to cutting directly through the muscles. By using tubes to keep the muscles out of the way, the surgeon works through the incision without having to expose the area widely. Sometimes, the surgeon will also utilize an endoscope or microscope focused down the tube to assist with performing the surgery through a minimal access strategy. Once the procedure is complete, the tubular retractor can be removed, allowing the dilated tissues to come back together. Depending on the extent and type of surgery necessary, incisions can often be small.

Percutaneous Placement of Screws and Rods
Depending on the condition of the patient, it may be necessary to place instrumentation, such as rods and screws, to stabilize the spine or to immobilize the spine to facilitate fusion of the spinal bones. Traditional approaches for the placement of screws require extensive removal of muscle and other tissues from the surface of the spine.

However, percutaneous (meaning “through the skin”) placement typically involves inserting rods and screws through relatively small skin incisions without cutting or dissecting the underlying muscle. With the aid of x-ray images, guidewires are placed through the skin and into the spinal vertebrae along the desired paths for the screws. Then, screws are placed over the guidewires and follow the path of the wires. These screws have temporary extenders that extend outside the skin and are subsequently removed after guiding the passage of rods to connect and secure the screws. With the use of spinal navigation and robots, spinal instrumentation is being placed more safely and accurately.

Direct Lateral Access Routes
In some cases, especially those involving the lumbar spine, approaching the spine from the side of the body results in reduced pain due to the limited amount of muscle tissue blocking the way. This approach is typically performed with the patient on his or her side. Then, tubular retractor docks on the side of the spine to enable access to the spine’s discs and bones.

Thoracoscopic Access Route
Depending on the patient’s condition, it may be necessary to access the front portions of the thoracic spine, located in the chest and surrounded by the heart and lungs. Traditional access approaches often involve opening the chest through large incisions that may also require the removal of one or more ribs. However, thoracoscopic access relies on multiple small incisions, through which working ports and cameras can be inserted to facilitate surgery.

Common MIS Surgery Treatment Options
A number of specific techniques have been deployed for MIS surgery. Though the field continues to develop, the list below highlights some of the most common options.

Discectomy: Spinal discs are essentially elastic rings with soft material inside that serve as cushions between the vertebral bones. If the elastic ring becomes weakened, the soft tissue inside can extrude — or herniate — outside of the elastic ring. The herniated disc material can compress the nerves passing by, thus causing pain. If surgical treatment is recommended to trim or remove the herniated disc, it may be possible to perform this procedure with MIS surgery using tubular dilators and a microscope or endoscope.

Spinal decompression: Spinal stenosis, which is a narrowing of the vertebral canal, is a common condition that can result in compression of the nerves. This can produce a variety of symptoms, including pain, numbness, and muscle weakness. If surgery is recommended, it may be possible to remove the bone and soft tissues causing the nerve compression through an MIS approach using tubular dilators and a microscope or endoscope. The more common decompressive procedures include laminectomy and foraminotomy.

Transforaminal Lumbar Interbody Fusion (TLIF): This is an MIS technique that is performed for patients with refractory mechanical low back and radicular pain associated with spondylolisthesis, degenerative disc disease, and recurrent disc herniation. The procedure is performed from the back (posterior) with the patient on his or her stomach. Utilizing two small incisions, screws and rods are placed between two or more vertebral levels. The intervertebral disc is removed, and a cage filled with bone is placed in that void with the goal of stabilizing the levels affected.

Candidates for MIS Surgery
A doctor will be able to tell which MIS surgeries, if any, might be an option for treating a spinal condition. In some situations, MIS surgery may not be as safe or effective as traditional open surgery. If so, the doctor will be able to inform you about the relative risks and benefits. In addition, there are some conditions that are not truly treatable with MIS surgery.

Spinal Fusion
Spinal fusion is an operation that creates a solid union between two or more vertebrae. This procedure may assist in strengthening and stabilizing the spine and may thereby help to alleviate severe and chronic back pain.

Almost all of the surgical treatment options for fusing the spine involve the placement of a bone graft between the vertebrae. Bone grafts may be taken from the hip or from another bone in the same patient (autograft) or from a bone bank (allograft). Bone graft extenders and bone morphogenetic proteins (hormones that cause the bone to grow inside the body) can also be used to reduce or eliminate the need for bone grafts.

Fusion may or may not involve the use of supplemental hardware (instrumentation), such as plates, screws, and cages. This fusing of the bone graft with the bones of the spine will provide a permanent union between those bones. Once that occurs, the hardware is no longer needed, but most patients prefer to leave the hardware in place rather than go through another surgery to remove it. Fusion can sometimes be performed via smaller incisions through MIS techniques. The use of advanced fluoroscopy, endoscopy, and navigation has improved the accuracy of incisions and hardware placement, minimizing tissue trauma while enabling an MIS approach.

MIS Fusion Procedures

• Minimally Invasive Lateral Interbody Fusion
• Minimally Invasive Posterior Lumbar Interbody Fusion (PLIF)
• Minimally Invasive Transforaminal Lumbar Interbody Fusion (TLIF)
• Minimally Invasive Posterior Thoracic Fusion

Source: https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Minimally-Invasive-Spine-Surgery