There are two kinds of spondylolisthesis, isthmic and pseudo or degenerative. The isthmus is the part of the lamina that connects to the inferior facet joint. It may be congenitally absent or fractured. In pseudo- spondylolisthesis the facet joints have “worn out” and slippage occurs. Either kind can be stable or unstable. Instability can be determined by taking lateral spine X-rays in flexion and extension to look for abnormal movement in the spine. Displacement of one vertebra on another may have taken place slowly in the past and not be unstable.
If a fusion is needed, there are several various ways to do that, depending on the patient’s age and health, the level of the defect, and the surgeon’s experience. Also, a herniated disc causing pain should be ruled out
Lumbar Spine Fusion
Fusion means inducing vertebrae to grow together so the spine can function. Usually a graft of some kind is used to bridge a gap, Neither external bracing nor placing of internal rods and screws will hold in place unless the graft fuses; they will eventually work loose if the graft fails. Graft materials vary. A person’s own bone (autograft) fuses best. Allograft (cadaver bone) doesn’t do as well. Synthetic materials are also available. A growth hormone for bone, BMP (bone morphogenic protein) is also available to place on grafts and stimulate fusion, but care must be taken to use that only in certain locations.
MIS Pedicle Screws – Robotics
Pedicles are thick posts of bone connecting the lamina to the body of the vertebra. Long screws can be placed inside the pedicles into the body of the vertebra and connected with metal rods to form a very stable construct for fusion. In open surgery an X-ray fluoroscope is used to get real-time images for guidance of screw insertion. Some robotic systems are also now being used for insertion of the pedicle screws in a minimally invasive manner.
Anterior Lumbar Interbody Fusion – ALIF
A large graft placed between the vertebral bodies, where the disc is located, has a good chance of fusing. However, the surgery ust be done through the abdomen and carries some risk of injury to abdominal contents and the large blood vessels along the front of the spine.
Transverse Lumbar Interbody Fusion – TLIF
Similar to ALIF, but done from the side to avoid abdominal structures
360 Fusion – “360”
Entails doing a posterior laminectomy & fusion, then turning the patient over and doing an ALIF at the same time.