Wallis
This implant is designed to halt the disc degeneration in the spine after a disectomy. It operates as a posterior shock absorber and dampens motions of flexion and rotation. It is inserted between two vertebrae and attached to the spinal processes above and below via ligaments made of woven dacron.
Materials:
Spacer & clips in PEEK (PolyEtherEtherKetone) which provides:
- Excellent biocompatibility
- Mechanical properties unaltered by sterilization
• Autoclave
• Gamma radiation
- Elasticity: less stress between spacer and bone
- No bone degradation due to a contact with the implant
- Semi-crystalline polymer: good resistance to fatigue
Sizes:
10-16 mm
Surgical Procedure:
The patient is put in a prone position with slight lumbar lordosis. The spinal processes are exposed through an incision and the supraspinous ligament is detached from the two spinous processes of the operative level with a scalpel. The ligament is retracted laterally with being sectioned. The interspinous ligament is resected. The rough edges of the spinous processes are trimmed. The correct implant size is determined by trial and error test insertion. A band passer intstrument is used to push the band through the adjacent interspinous ligaments, flush with the spinous processes. The band cannot be twisted, and must lie flat against the spinous processes. The band is inserted into the clip. The clip is turned three hundred and sixty degrees and is snapped into place. The attachment is verified by listening for a snap, and visually inspecting the four studs. This is repeated for the second band. An implant holder is used to place the implant in the interspinous space. Band forceps are used to pull the slack out of the bands. A tightener rigging is used to align and tighten the bands. The ring passer and crimping ring are placed adjacent to the clip and then crushed. Each band is cut one to two millimeters from the crimping ring and then cauterized to prevent fraying. While using a backhaus towel clamp, an opening is created in the spinous processes. The supraspinous ligament is returned to its original position and reattached with a single suture.
Indications:
Isolated lumbar inter-vertebrae instability such as:
- Herniated disc
- Modic I degenerative lesions
- Degenerative disc disease at level adjacent to a previous fusion
- Narrow canal treated without laminectomy
Effect:
- Provides pain relief
- Preserves (controls) mobility
- Reversible
- Leaves all other options open
- Limits the amplitude of movement
- Increases the rigidity
- Increases the stability of the treated segment
- Unloading the posterior portion of the disc (to allow the annulus or disc to heal)
Studies:
In a study done by J. Senegas, the Wallis system had improved performance over a disectomy performed without the Wallis system. Also, there is currently a clinical study where stenosis one of the indications for treatment. There are no results for this study currently available.
Success Rates:
There is no controlled study of this device's success in treating lumbar spinal stenosis.
Availability:
This implant is not available in the US and the company producing wallis is currently seeking to gain approval to being a study in the US by the FDA.