Posterior lumbar interbody fusion using B-Twin expandable spinal system achieves the same ultimate outcome as with the other devices but mitigates the above shortcoming and is more user-friendly to the surgeon. Mini abstract The authors present a novel technique for posterior lumbar interbody fusion based on a device capable of three-fold expansion once it has been installed in the disc space. Following a follow-up period of one year in 87 patients, the clinical outcome was comparable to other posterior lumbar interbody fusion techniques. However, the intraoperative hazards and post-operative morbidity were significantly reduced.
Expandable Spinal Fusion System Acquired degenerative disk disease (ODD) is manifested by progressive collapse and consequent bulging of the redundant disc surface, the ligamenta flava and the posterior longitudinal ligament. Narrowing of the inter-vertebral space causes subluxation and eventual arthrosis of the facet joints. Moreover, the involved unstable segment may slip backwards or forwards. These mechanical alterations may cause discogenic or facet induced pain and possible compressive radiculopathy (13). Structural solution of the problem requires reversing the process, i.e., re-expansion of the disc space and immediate stabilization of the segment in a balanced alignment to ensure gradual intervertebral welding. Posterior lumbar interbody fusion (PLIF) is bio-mechanically sound as it ablates the degenerated disc, restores the normal inter-vertebral height dynamically decompressing foraminal stenosis, and positions the bone graft along the weight-bearing axis (9). The immediate initial stability is provided through the tension it exerts upon the annulus fibrosus and inter-spinal ligaments. Moreover, a device enables fusion by a relatively small volume of bone graft, thereby minimizing donor-site morbidity. Application of this promising concept was pioneered by Briggs (6) in 1944 and popularized by Cloward shortly thereafter (7). However, the clinical reviews reported a high rate of graft failure (resorption, migration, non-union), and donor-site morbidity (17). In 1988, Bagby (3) introduced the concept of twin-cage support designed to neutralize the compressive forces and to provide immediate three-dimensional stability essential for successful incorporation of the fragile, cancellous bone graft housed within. But the devices since had major drawbacks as well: tension in the annulus, essential for immediate stability, dictated installation of large implants (3) and that, in turn, required excision
Expandable Spinal Fusion System of facets, the latter step subtracted paradoxically from the stability - that's conferred -mainly in respect to axial rotation (2). Supplementary pedicle screw fixation (5,11) or restoration of posterior elements (14) were advocated. Moreover, excessive retraction of the dural sac and roots posed an immediate risk of inadvertent dural laceration with potential neurologic deficit (1,5,8,19), or delayed epidural fibrosis (22). The purpose of the present study is to report early results of a novel B-Twin expandable spinal system (B-Twin ESS), free of all the drawback enumerated.
Expandable Spinal Fusion System Patients and Methods: Patient selection. Inclusion criteria were: disabling low back pain for 6 months or longer; non-response or inadequate response to conservative treatment; firm diagnosis of ODD on basis of typical symptoms plus diagnostic findings on MR1 or discogram, whenever required. Exclusion criteria included any disease that can adversely affect bone quality (e.g., spine infection, tumor, metabolic bone disease) or drugs or alcohol abuse and behaviour disorders that may affect patient's cooperation. Device description. (Disc-O-Tech Medical Technologies Ltd., Herzliya, Israel). The devise is made of unalloyed titanium. When collapsed, 5 wings are enclosed within a cylinder 5 mm in diameter (Fib. 1A). Following installation within the disc space by an expendable delivery system (Fig IB), the implant is expanded wing by wing until it is 25 mm long and 11-17 mm in diameter (Figs. 1C, ID). Final size is selected on the basis of preoperative x-rays and adjusted intra-operatively as necessary. When the expansion is completed, a blocking ring is then activated automatically. Operative procedure. Following a routine bilateral approach limited to flavectomy, discectomy and end-plate curettage are meticulously carried out. The inter-vertbral space is packed with cancellous iliac bone autograft delivered through a 5 mm diameter funnel. The B-Twin ESS is introduced into the inter-vertebral space bilaterally and then expanded, both stages are monitored by C-arm fluoroscopy. Since the first wing is opened perpendicularly to the end-plates, adjustments can be made at this stage by turning the delivery system 90 degrees and repositioning. No drilling, tapping or hammering is involved in the procedure. B-Twin ESS can be installed "stand-alone
Expandable Spinal Fusion System postero-lateral floating inter-transverse graft or with pedicle screw fixation, as may be needed, in the presence of spondylolisthesis or after previous facetectomy (Fig. 2). Postoperative radiological evaluation: Radiologic evidence of fusion required following criteria: no radiolucent gap at the device vertebral end-plate interface; no evidence of mobility in flexion-extension roentgenograms; presence of bridging trabeculae across the area or arthrodesis. In equivocal cases, a CT scan (2 mm thick slices) and sagittal reconstruction, as suggested (21), was performed. Data Acquisition: Preoperative information was elicited concerning the patient's medical history, social-economical status, physical examination and results of imaging studies. Pain and disability were scored by Visual Analog Scale and Oswestry Index (10) respectively. The operative notes included all difficulties and complications encountered. Data regarding each follow-up visit - 1,3,6,12 and 24 months after surgery included neurological examination, x-ray findings, repeat Visual Analog Scale and Oswestry Index scores. Upon termination of follow-up, the entire protocol on each patient was submitted to a clinical monitor for review. Statistical Methods: Descriptive statistics was applied to determine means and standard deviations, scoring binomial test was applied for VAS and Oswestry index.
Expandable Spinal Fusion System Results: The study was based on 87 participating patients, 46 men and 41 women, who ranged in age from 17 to 77 years (mean, 45.2 + 13.7). Length of disability ranged from 5-180 months (mean, 48.6 + 39.8). A total of X levels was surgically treated: In 54 cases, the B-Twin ESS was implanted "stand-alone floating inter-transverse fusion and in 23 by pedicle screws and rod constructs. Mean operative time was 148 + 64 minutes (range, 60-330), mean blood loss was 410 + 330 ml (range, 300-1500). Disc space height averaging 7.53 (+2.42) mm before surgery was increased to 10.03 (+2.00) mm at surgery and subsided to 9.47 (+2.10) mm at final follow-up. Procedure related complications included two inadequate implant positioning, which required intraoperative repositioning, one implant migrated postoperatively and had to be removed. No dural laceration, deep wound infection or neurological damage was reported. The minimal follow-up was 12 months (range 12-26 , average 15mos.). No patient has dropped-out to date. Imaging tests did not show evidence of non union in any of the said patients. The mean VAS score dropped from 8.5 to 3.3, 60% (p less than 0.01). The mean Oswestry Index score dropped from 31.0 to 12.7, 58% (p less than 0.01). On the last follow-up visit, 86.2% of the patients stated that the operation had been worthwhile.
Expandable Spinal Fusion System Discussion: PLIF is increasingly advocated as the treatment of choice for disabling LBP due to ODD. Fusion rates up to and over 90% were reported, 70-90% of the patients were satisfied (1,5,16,20) and 75 95% went back to work (12,16). Similar results were achieved in the present series. They are comparable to a far more extensive surgery of 360 degree fusion (12). Inter-series differences in the correlation between fusion rates and clinical outcome may be attributable to the unreliability of plain x-ray evaluation effusion (4,21) and/or the influence of varying socio-economic conditions (1) and litigation issues (1,5) on the way the patients describe their postoperative status. The superior degree of immediate stability conferred by the B-Twin ESS can be attributed to preservation of the most important spinal stabilizers, namely the facets (2) and the annulus fibrosus (15). In the present series, the mean inter-vertebral distraction of the segment treated was 1.94 mm. The B-Twin ESS expands the intervertebral space by gradual "jacking-up and tapping technique. None of the patients showed radiographic signs of non- union. Meticulous curettage of the nucleus, rather than installation of the implant within reamed channel, was proved by others to promote fusion (18). We would emphasize that the cardinal merit of the B-Twin ESS is the relative freedom from complications. No dural laceration, neurologic deficit or delayed symptomatic epidural scarring were reported. In comparison to other systems, the 5-mm diameter implant minimizes the retraction of the cauda equina (5-mm as compared to 20 mm in Threaded Fusion Cages (TFC) system when inter-vertebral distraction of 12 mm is required).
Expandable Spinal Fusion System In summary, bearing in mind that PLIF has established itself as a competer procedure, the issue of safety became most relevant. A recent review concernin PLIF system in current use, reports major complications in 45% and seconi operations in 25% (8). Similar complication rates have been reported in the use o 360 degree fusion which included PLIF: as many as 40% required further surgery mainly for revision of original constructs, repair of dural tears and removal of pedicl screws (5). PLIF using B-Twin ESS achieves ultimate outcome comparable to othe devices, but does not share the handicaps and hazards of the latter and is more user friendly to the surgeon.
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