Fig. 24.1
Rib used as an inlay or a strut graft
Osteotomies
A bony fusion between two vertebrae represents an obstacle to allow a good surgical lordosis restoration.
The Smith-Petersen osteotomy is the easiest manner to obtain a mobilization of the spine when the anterior column is still mobile. We start the osteotomy by a Farcy’s osteotomy (Fig. 24.2), which is achieved by removing the superior articular process (the caudal part of the facet joint). After exposure of the superior articular process, a curette is passed along the lateral part of the facet joint in order to cut all soft tissues adherent to it and to separate the isthmic vessels from the bone. A saw is then used to cut the superior articular process straight ahead: the blade of the saw is set perpendicular to the facet in the transversal plane, adjacent to the cranial edge of the transverse process. The osteotomy is then completed using the chisel to ensure a safe separation of the facet towards the intervertebral foramen. Once the facet is cut, it is removed using a curette inserted in the articular cavity. The last insertions of the flavum ligament attached to the facet are removed. The same procedure is performed bilaterally. It is important to avoid electrocoagulation at the recessus and the foramen.
Fig. 24.2
Farcy’s osteotomy
24.3 Instrumentation
Hooks or pedicle screws are implants that facilitate lordosis reduction and fixation of the spine.
Hooks provide a posterior anchoring of the vertebrae. Compression on hooks at posterior spinal elements induces lordosis. On the other hand, posterior distraction has a kyphosing effect at the level of the disk. In the lumbar spine, hooks can only be used on the laminae. Hooks cannot be placed in a neutral position: a tension between the hook and the bone is required to ensure implant stability. For that reason, lamina hooks are used in claws bridging two adjacent vertebrae. Pedicle screws provide an anchoring in the three columns of the vertebra. As opposed to hooks, screws can be placed in a neutral position. Today, indications for hooks in lumbar spine are very restricted. Special situations and difficulties during pedicle screw placement may however require the use of hooks as a backup option.
Rods
It seems obvious that a rod in lumbar spine should be lordotic according to physiological sagittal curvatures of the spine. Therefore, it is not usually appropriate to use a straight rod in a curved spine. The shape of the rod and the amount of bending represent key factors in order to achieve the best possible lumbar lordosis. A rod that follows the spinal curvature is always better than a rod bridging the spine when low profile instrumentations are used.
24.4 Reduction
Compression
Hooks: As previously mentioned, the use of hooks required tension and posterior compression to achieve lordosis (Fig. 24.3). Compression of posterior vertebral elements induces a posterior narrowing of the intervertebral space and an anterior elevation of the superior vertebra.
Fig. 24.3
Posterior compression using hooks
Screws: The anchorage of the screws is posterior and anterior at each vertebra. Compression on monoaxial screws does not create or induce lordosis if the shape of the rods is straight or curved (Fig. 24.4). Therefore, a lordotic bending of the rods is mandatory to achieve sagittal alignment correction. The center of rotation is posterior with a rod-screw construct if the orientation is 90° between the rod and the monoaxial screw. Polyaxial screws work like hooks: a posterior compression on the screws induces a lordosis on the anterior column by distraction at the level of the disk (Fig. 24.5).
Fig. 24.4
Posterior compression using lordotic rod and monoaxial screws
Fig. 24.5
Posterior compression on polyaxial screws induce anterior distraction and segmental lordosis of the lumbar spine
Translation
Translation (approximation) is very popular today with instrumentations using persuader systems of the rod. This technique is used on a regular base with percutaneous instrumentation in MIS. With this practice, care should be taken that the vertebrae are not pulled backward to the rod, which might happen if the shape of the rod is too flat. It is mandatory to pull back the end vertebrae of the lordotic construct and to push the apical vertebrae anteriorly. Accurate bending of the rod is mandatory and is achieved by giving a lordotic shape to the rod prior translation and rotation of the apical vertebrae in the sagittal plane. Polyaxial screws facilitate the rod-screw connection with multilevel persuaders. However, the screws must be in line in the sagittal plane to allow lordotic opening of the spine by pushing the curved rod into the screws with the persuaders.
In situ bending
The principle is to mimic the shape of the spine and then to make the spine follow the shape of the rod. Instead making the vertebra following a prebent rod as with the approximation technique, the rod is inserted without any stress onto the uncorrected (flat) spine. The screws are closed but not locked once the rod is in place. Bending irons are set on the two rods, right and left symmetrically, and the rods are then bent inside the patient by pushing the bending irons together. This maneuver applied to the rod induces a movement of the screws, and subsequently of the vertebra, which are pushed anteriorly into a lordotic alignment. This maneuver is not dangerous while the screw is pushed anterior and not pulled back (Fig. 24.6). Bending has to be repeated along the rod, by little forces given in many times. The reduction is easily obtained by a 90° rod-screw connection with monoaxial screws, thus giving the spine the shape of the rod (Fig. 24.7).
Related posts:
Epidemiology of Lumbar Degenerative Disk Disease
To Fuse or Not to Fuse: That’s the Question
Lessons from a Life: The Journey of Spinal Neurosurgery in the United States
Minimally Invasive Transforaminal Lumbar Interbody Fusion (TLIF): Indications and Techniques
Oblique Lumbar Interbody Fusion
Compensatory Mechanisms Contributing to the Maintenance of Sagittal Balance in Degenerative Diseases of the Lumbar Spine
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
