Outcomes of Instrumented and Noninstrumented Posterolateral Lumbar Fusion

Revision after spinal stenosis surgery

PURPOSE

To make a literature review on spinal stenosis recurrence after a first surgery and edit rules to avoid this complication.

METHODS

We conducted two separate PUBMED searches to evaluate the revision post-stenosis and degenerative scoliosis surgery using the terms: lumbar vertebrae/surgery, spinal stenosis, spine, scoliosis and reoperation. The resulting papers were categorized into three groups: (1) those that evaluated reoperation post-simple decompression; (2) those that evaluated spinal decompression and fusion for short (3 levels or less) or long (more than 3 levels) segment spinal fusion; and (3) those diagnosing the stenosis during the surgery.

RESULTS

(1) We found 11 relevant papers that only looked at revision spine surgery post-laminectomy for spinal stenosis. (2) We found 20 papers looked at reoperation post-laminectomy and fusion amongst which there were two papers specifically comparing long-segment (> 3 level) and short-segment (3 or less levels) fusions. (3) In the unspecified group, we found only one article. Fifteen articles were excluded as they were not specifically looking at our objective criteria for revision surgery. In regard to revision post-adult deformity surgery, we found 18 relevant articles.

CONCLUSIONS

After this literature review and analysis of post-operative stenosis, it seems important to provide some advice to avoid revision surgeries more or less induced by the surgery. It looks interesting when performing simple decompression without fusion in the lumbar spine to analyse the risk of instability induced by the decompression and facet resection but also by a global balance analysis. Regarding pre-operative stenosis in a previously operated area, different causes may be evocated, like screw or cage malpositionning but also insufficient decompression which is a common cause. Intraoperatively, the use of neuromonitoring and intraoperative CT scan with navigation are useful tool in complex cases to avoid persisting stenosis. Pre-op analysis and planning are key parameters to decrease post-op problems. These slides can be retrieved under Electronic Supplementary Material.

Numerical simulations of bone remodelling and formation following nucleotomy

Nucleotomy is the gold standard treatment for disc herniation and has proven ability to restore stability by creating a bony bridge without any additional fixation. However, the evolution of mineral density in the extant and new bone after nucleotomy and fixation techniques has to date not been investigated in detail. The main goal of this study is to determine possible mechanisms that may trigger the bone remodelling and formation processes. With that purpose, a finite element model of the L4-L5 spinal segment was used. Bone mineral density (BMD), new tissue composition, and endplate deflection were determined as indicators of lumbar fusion. A bone-remodelling algorithm and a tissue-healing algorithm, both mechanically driven, were implemented to predict vertebral bone alterations and fusion patterns after nucleotomy, internal fixation, and anterior plate placement. When considering an intact disc height, neither nucleotomy nor internal fixation were able to provide the necessary stability to promote bony fusion. However, when 75% of the disc height was considered, bone fusion was predicted for both techniques. By contrast, an anterior plate allowed bone fusion at all disc heights. A 50% disc-height reduction led to osteophyte formation in all cases. Changes in the intervertebral disc tissue caused BMD alterations in the endplates. From this observations it can be drawn that fusion may be self-induced by controlling the mechanical stabilisation without the need of additional fixation. The amount of tissue to be removed to achieve this stabilisation remains to be determined.

Comparison of synthetic bone graft ABM/P-15 and allograft on uninstrumented posterior lumbar spine fusion in sheep

BACKGROUND

Spinal fusion is a commonly used procedure in spinal surgery. To ensure stable fusion, bone graft materials are used. ABM/P-15 (commercial name i-Factor™ Flex) is an available synthetic bone graft material that has CE approval in Europe. This peptide has been shown to improve bone formation when used in devices with fixation or on bone defects. However, the lack of external stability and large graft size make posterolateral lumbar fusion (PLF) a most challenging grafting procedure. This prospective randomized study was designed to evaluate early spinal fusion rates using an anorganic bovine-derived hydroxyapatite matrix (ABM) combined with a synthetic 15 amino acid sequence (P-15)-ABM/P-15 bone graft, and compared with allograft in an uninstrumented PLF model in sheep. The objective of this study was to assess fusion rates when using ABM/P-15 in uninstrumented posterolateral fusion in sheep.

METHODS

Twelve Texas/Gotland mixed breed sheep underwent open PLF at 2 levels L2/L3 and L4/L5 without fixation instruments. The levels were randomized so that sheep received an ABM graft either with or without P15 coating. Sheep were euthanized after 4.5 months and levels were harvested and evaluated with a micro-CT scanner and qualitative histology. Fusion rates were assessed by 2D sections and 3D reconstruction images and fusion was defined as intertransverse bridging.

RESULTS

There was 68% fusion rate in the allograft group and an extensive migration of graft material was noticed with a fusion rate of just 37% in the ABM/P-15 group. Qualitative histology showed positive osteointegration of the material and good correlation to scanning results.

CONCLUSIONS

In this PLF fusion model, ABM/P15 demonstrated the ability to migrate when lacking external stability. Due to this migration, reported fusion rates were significantly lower than in the allograft group. The use of ABM/P15 as i-Factor™ Flex may be limited to devices with fixation and bone defects.

Spinal fusion without instrumentation - Experimental animal study

BACKGROUND

The number and cost of instrumented spinal fusion surgeries have increased rapidly, primarily for the treatment of lumbar segmental instabilities. However, what if the organism itself is able to restore segmental stability over time? This large-animal study using sheep aimed to investigate whether the reparative response after destabilization via facetectomy and nucleotomy without instrumentation can effectively fuse the spinal segment comparable to instrumented standard fusion surgery.

METHODS

The following four surgical interventions were investigated: dorsal fixation via internal fixator, ventral fixation via cage as well as facetectomy and nucleotomy without additional instrumentation. Six months postoperatively, the animals were sacrificed, and the lumbar spines were used for biomechanical tests.

FINDINGS

Spinal stability was restored to the destabilized spinal segments at six months postoperatively and was comparable to the results of conventional surgery via screws and cages. Iatrogenic hypomobilization caused significant reductions in facet joint space and intervertebral disc height of segments at index and adjacent level. Restabilized segments after iatrogenic hypermobilzation also significantly decreased facet joint space and disc height at index level, but revealed no influence on adjacent segments.

INTERPRETATION

These findings in the sheep model question the necessity of costly instrumentation and suggest the alternative possibility of stimulating the reparative capacity of the body in human lumbar spine fusion surgery.