02/12/2015
AO Technical Commission Approved

Facet Wedge Spine System

Facet Wedge Spine System
The treatment of chronic low back pain or any neurological deficit dueto degenerative conditions of the spine is well established. However,there remains no clear consensus on when a 360 fusion is required orwhen postero lateral fusion (PLF) will suffice. In patients with a high degree of degeneration and instability, a combined anterior and posterior column fusion is often appropriate.

When the degeneration is less and there is minimal instability, PLF may be more suitable.
With many of these surgical treatments, the posterior fixation may beperformed with translaminar facet screws (TFS) [1]. Posterior fixation of the lumbar motion segments with TFS is a less invasive option than the more commonly used pedicle screws and rods. It is also accurate to suggest that this technique helps to promote minimal soft tissue damage.
History of Translaminar Facet Screws (TFS) Use of TFS was first described by King [2] in 1948. His technique involved the insertion of short screws across the facet joint (Fig 1).
This approach was further modified by Boucher [3] in 1959 through
the useof a longer screw, the transfacet pedicle screw, directed towards thepedicle (Fig 2).
The approach most commonly used today, however, is Magerls technique,which involves the use of an even longer screw [4].

This screw enters through the base of the spinous process, traverses the length of the lamina, crosses the facet joint, and fixates in the base of the transverse process. This procedure, translaminar screw fixation, is discussed extensively in the literature [514] (Fig 3).
A second option for the achievement of primary stability is by lockingthe facet joints with a facet interference screw (FIS) (Fig 4).
Biomechanicalinvestigations have illustrated a similarity between
FIS fixation and TFS fixation in terms of primary stability.
Biomechanical studies [1, 1517] have provided evidence supporting
the use of TFS as a fixation technique for spinal motion segments.
Fusion rates associated with TFS range from 83% to 100% [5, 7, 11,18-20].
The number of re-operations for various reasons ranges from 2-37% [57, 13, 21].
TFS fixation is also associated with smaller incisions,
ease of procedure and learning curve, less instrumentation, andlower costs [7, 9, 12, 19, 22, 23]. Postero lateral fusion with TFS fixation should, similarly to pedicle screw fixation, only be performed with an intact anterior column. The disc therefore needs to be intact.

Facet Wedgedesign concept, benefits, and advantages

The Facet Wedge (FW) spinal system was developed to enhance
the advantages already offered by the Translaminar Facet Screws (TFS).

The intended use, indications, and contraindications for FW fixation are very similar to TFS fixation.
Facet Wedge is intended for the fixation of the spine as an aid to fusionthrough the immobilization
of the facet joints, with or without bonegraft, at single or multiple levels, from L1 to S1.
It can be inserted through a minimally invasive approach either to augment other fusion techniques or as a stand-alone device for cases without segmental instability.

The FW system is designed as a press fit block with friction rails to stop translational motion in the facet joints. In addition to the wedge, two screws are inserted divergently at 30 angles in order to increase pull out resistance.

The advantage of the FW design over the TFS is the direct visualization of the facet joint, which facilitates accurate implant insertion and may reduce the risk of damage to neural structures. The specific instruments used in conjunction with the FW allow facet joint preparation (eg, cartilage removal) to improve the likelihood of successful fusion.

Preclinical biomechanical tests demonstrate that the biomechanical
properties (stiffness and ROM) of FW are comparable to pedicle screw and rod fixation, as well as TFS fixation in all motion directions.

Indications
Stand-alone (bilateral) in situ facet fusion with or without decompression
Facet arthritis: fixation and fusion of facet joint
Supplementary fixation after anterior cage or nonunion of ALIF
Supplementary contra lateral fixation after MISS TLIF.

Contraindications
Unilateral application, except in combination with pedicle screw
fixation on the contralateral side
Compromised facets due to decompression techniques
Spondylolisthesis
Fracture or other instabilities of the posterior elements
Tumor
Acute or chronic systemic or localized spinal infections.

Tips for safety and effectiveness
The FW Spine System Risk Assessment identified that incorrect placement of the K-wire for rasp or FW positioning could result in damage to soft tissue, neural structures, or large blood vessels. A second risk involves the use of the facet opener. Excessive force or inappropriate manipulation may also lead to the damage of neural structures.
Several control measures are incorporated into the Facet Wedge system to minimize these risks and plans are also in place to conduct a study that will measure their occurrence.

Description
The Facet Wedge spine system includes the following implants and
features (Fig 5):
Kirschner wire hole enables guided insertion over K-wire (a)
Rails stop translational motion and generate contact between
subchondral bone and implant (a)
Low profile decreases muscle irritation (b)
Implant shoulder that controls insertion depth (b)
Teeth keep the implant in the desired position prior to screw
insertion (b)
Divergent angular stable locking screws for primary fixation (b)
Various implant sizes to accommodate patient anatomy (b)
Perforations create optimal fusion conditions (c).


Case 2

A 51-year-old female patient had been experiencing LBP for 3 years (Fig 10).
PNS right. Now L5 radiculopathy left.

Cases provided by Frank Kandziora, Frankfurt, Germany

Case 1

A 45-year-old healthy male patient had experienced load dependent lowerback pain (LBP) for 6 years, with no radicular pain and no neurologic deficit.
Multilevel facet pathology is shown in Fig 6. Intraoperative and postoperative images are shown (Figs 79).


Case2

A 51-year-old female patient had been experiencing LBP for 3 years (Fig 10).
PNS right. Now L5 radiculopathy left.


Case 3

A healthy 66-year-old female patient had been experiencing LBP for 5 years.


Cases provided by Maarten Spruit, Nijmegen, Netherlands

Case 4 : ALIF L4-5 non union

A 40-year-old man had ALIF L45 with SynFix 5 years previously. He had axial
low back pain. The CT scan showed locked pseudartrosis (Fig 17). Nonoperative treatment failed. The treatment option was bilateral Facet Wedge at L45.


Facet wedge surgery
A less invasive approach was used with Insight Retractor, and using the bilateral Facet Wedge. No bone graft. X-ray follow-up after 3 months and CT assessment after 6 months (Figs 1819).


Case 5 : Degenerative scoliosis

A female patient 66-years-old had back pain, leg pain, and degenerative deformity.The x-rays showed left convex degenerative scoliosis Cobb T12L3 38. Nonoperative treatment failed. Treatment option was posterior fusion T11L5, with URS, Facet Wedge L23 unilaterally.

URS/Facet Wedge surgery


A conventional approach for posterior correction was taken, with indirect foraminaldecompression and Facet Wedge fusion (apex curve). Facet Wedge introduction after curve correction with rod in situ. X-ray follow-up initially (Fig 20), with CT assessment of Facet Wedge fusion after 6 months (Fig 21).

 

Primary stability and permanent fusion through locking of the facet joints.

Presentation delivered by F. Kandziora (Germany) and Maarten Spruit (Netherlands) on facet fixation techniques.

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