MIS Treatment of Spondylolisthesis

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About Spondylolisthesis

Spondylolisthesis is a spinal disorder in which one vertebra slips forward over the vertebra below. (Figure 1) It usually affects the low back or lumbar spine. The condition may be classified as congenital, degenerative, or isthmic. Congenital means a disorder present at birth, degenerative is often age-related, and isthmic spondylolisthesis (Figure 2) occurs when there is a defect or fracture of the pars interarticularis. The pars interarticularis is a bone connecting the upper and lower facet joints.

Figure 1.
Vertebral slip

Figure 2.
Fracture of the pars interarticularis

Diagnosis and Slip Severity

Important to a proper diagnosis is the patient?s medical history, physical and neurological examination, and imaging studies.

  • Medical history includes symptoms, their severity, and treatments already tried.
  • Physical and neurological examination includes evaluating movement limitations, balance problems, pain, extremity reflexes, muscle weakness, and sensation. The exam may include a series of movements such as bending sideways, forward and backward at the waist, and walking.
  • Imaging studies may include standing x-rays (front/back, side). In addition, if necessary, a CT scan, or MRI is performed.

Using the patient's x-ray, CT scan, or MRI studies, the severity of the slip is graded using the Meyerding Grading System to classify the degree of vertebral slippage. This system is easy to understand. Slips are graded on the basis of the percentage that one vertebral body has slipped forward over the vertebral body below. Although, every spondylolisthesis does not require surgery, the degree of slip is important to surgical treatment considerations.

Grade I: 1-24%
Grade II: 25-49%
Grade III: 50-74%
Grade IV: 75%-99%
Grade V: 100%, spondyloptosis

When MIS is Recommended

Besides the severity of the slip, there are other considerations before surgery is considered. Although the indications for surgery vary, MIS may be recommended if:

  • Pain and other symptoms worsen and are unresponsive to nonoperative treatment
  • Pain and symptoms significantly affect quality of life
  • Neurologic problems develop, such as weakness, numbness, or bowel or bladder dysfunction
  • Imaging tests, such as x-ray or MRI demonstrate spinal instability or slip progression

MIS Goals

Surgical goals include:

  • Decompress spinal nerves (relieve pressure)
  • Stabilize the spine to prevent slip progression and nerve compression
  • Correct deformity and restore spinal alignment

Surgery may include combined procedures such as repair of the pars interarticularis, decompression, spinal fusion and instrumentation, and deformity correction.

  • Repair of the pars may involve removal of the bone combined with spinal fusion and instrumentation. This is best for children less than 16-years of age.
  • Decompression procedures relieve pressure on spinal nerves. Discectomy (disc removal), laminotomy, laminectomy, and foraminotomy are common procedures. Laminotomy (partial removal) and laminectomy (complete removal) involve removing the vertebral body?s lamina to increase the size of the spinal canal. The lamina is a section of bone near each facet joint covering access to the spinal canal. Foraminotomy expands the foramen or spinal nerve passageways.
  • Spinal fusion uses bone graft to fuse or join two or more vertebrae. Fusion is often combined with instrumentation, such as an interbody device (i.e. cage), pedicle screws and rods, to immediately stabilize the spine and stop slip progression until the construct fuses.
  • Deformity correction involves restoring the spine to a more normal alignment and fixing the spine in position using fusion and instrumentation.

MIS Treatment

Minimally spine surgery procedures approach the spine from the front (anterior), back (posterior), side (lateral), or back and side (posterolateral). Procedures such as those listed below share the same surgical goals:

  • Anterior Lumbar Interbody Fusion (ALIF)
  • Direct Lateral Interbody Fusion (DLIF / XLIF)
  • Transforaminal Lumbar Interbody Fusion (TLIF)
  • Trans-sacral Fusion at L5-S1

The interbody device, such as a Titanium cage or PolyEthylEther Ketone (PEEK) spacer, is implanted into the disc space. Bone graft is packed into and around the device to stimulate spinal fusion.

  • ALIF provides access to the spine and disc through the abdomen. This procedure is often combined with posterior fusion and instrumentation for better spinal fixation.
  • DLIF provides access to the spine through the side of the body. This procedure involves a transpsoas approach, which means the surgeon accesses the spine through the psoas muscle; a long muscle on both sides of the lumbar spine.
  • TLIF provides access to both sides of the disc through the intervertebral foramina, small passageways through which nerves exit the spinal canal. An interbody device, such as a cage or spacer is implanted into the disc space from one side of the spine. Pedicle screws and rods, with additional bone graft, secure the back (posterior) section of the spine. TLIF fuses the front and back sections of the spine.
  • Trans-sacral Fusion is a novel technique that uses a long screw inserted from the back. The L5-S1 level is reached through an incision near the tailbone. Behind the pelvis at the rectum dissection is performed; the L5-S1 disc is removed and bone graft inserted through the trans-sacral device. Usually, additional screws and rods are placed to ensure maintenance of spinal alignment.
Notice L5 is pulled back to normal position AND the disc height is restored


Above patient underwent a straightforward 1-level NAV MAST TLIF. Patient went home the following day and is very happy with the results so far. Note the minimal scarring

Risks and Complications

No patients are identical and risks and complications vary. Your surgeon will explain possible risks and complications related to your specific MIS procedure.

Updated on: 12/10/09
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