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1.  Does Wallis implant reduce adjacent segment degeneration above lumbosacral instrumented fusion? 
European Spine Journal  2009;18(6):830-840.
Delayed complications following lumbar spine fusion may occur amongst which is adjacent segment degeneration (ASD). Although interspinous implants have been successfully used in spinal stenosis to authors’ knowledge such implants have not been previously used to reduce ASD in instrumented lumbar fusion. This prospective controlled study was designed to investigate if the implantation of an interspinous implant cephalad to short lumbar and lumbosacral instrumented fusion could eliminate the incidence of ASD and subsequently the related re-operation rate. Groups W and C enrolled initially each 25 consecutive selected patients. Group W included patients, who received the Wallis interspinous implant in the unfused vertebral segment cephalad to instrumentation and the group C selected age-, diagnosis-, level-, and instrumentation-matched to W group patients without interspinous implant (controls). The inclusion criterion for Wallis implantation was UCLA arthritic grade UCLA grade II in the adjacent two segments cephalad to instrumentation. All patients suffered from symptomatic spinal stenosis and underwent decompression and 2–4 levels stabilization with rigid pedicle screw fixation and posterolateral fusion by a single surgeon. Lumbar lordosis, disc height (DH), segmental range of motion (ROM), and percent olisthesis in the adjacent two cephalad to instrumentation segments were measured preoperatively, and postoperatively until the final evaluation. VAS, SF-36, and Oswestry Disability Index (ODI) were used. One patient of group W developed pseudarthrosis: two patients of group C deep infection and one patient of group C ASD in the segment below instrumentation and were excluded from the final evaluation. Thus, 24 patients of group W and 21 in group C aged 65+ 13 and 64+ 11 years, respectively were included in the final analysis. The follow-up averaged 60 ± 6 months. The instrumented levels averaged 2.5 + 1 vertebra for both groups. All 45 spines showed radiological fusion 8–12 months postoperatively. Lumbar lordosis did not change postoperatively. Postoperatively at the first cephalad adjacent segment: DH increased in the group W (P = 0.042); ROM significantly increased only in group C (ANOVA, P < 0.02); olisthesis decreased both in flexion (P = 0.0024) and extension (P = 0.012) in group W. The degeneration or deterioration of already existed ASD in the two cephalad segments was shown in 1 (4.1%) and 6 (28.6%) spines in W and C groups, respectively. Physical function (SF-36) and ODI improved postoperatively (P < 0.001), but in favour of the patients of group W (P < 0.05) at the final evaluation. Symptomatic ASD required surgical intervention was in 3 (14%) patients of group C and none in group W. ASD remains a significant problem and accounts for a big portion of revision surgery following instrumented lumbar fusion. In this series, the Wallis interspinous implant changed the natural history of ASD and saved the two cephalad adjacent unfused vertebra from fusion, while it lowered the radiographic ASD incidence until to 5 years postoperatively. Longer prospective randomized studies are necessary to prove the beneficial effect of the interspinous implant cephalad and caudal to instrumented fusion. We recommend Wallis device for UCLA degeneration I and II.
PMCID: PMC2899653  PMID: 19387697
Adjacent segment degeneration; Wallis; Lumbar fusion; Disc degeneration
2.  Posterior lumbar interbody fusion using one diagonal fusion cage with transpedicular screw/rod fixation 
European Spine Journal  2003;12(2):173-177.
Posterior lumbar interbody fusion (PLIF) using threaded cages has gained wide popularity for lumbosacral spinal disease. Our biomechanical tests showed that PLIF using a single diagonal cage with unilateral facetectomy does add a little to spinal stability and provides equal or even higher postoperative stability than PLIF using two posterior cages with bilateral facetectomy. Studies also demonstrated that cages placed using a posterior approach did not cause the same increase in spinal stiffness seen with pedicle screw instrumentation, and we concluded that cages should not be used posteriorly without other forms of fixation. On the other hand, placement of two cages using a posterior approach does have the disadvantage of risk to the bilateral nerve roots. We therefore performed a prospective study to determine whether PLIF can be accomplished by utilizing a single diagonal fusion cage with the application of supplemental transpedicular screw/rod instrumentation. Twenty-seven patients underwent a PLIF using one single fusion cage (BAK, Sulzer Spine-Tech, Minneapolis, MN, USA) inserted posterolaterally and oriented anteromedially on the symptomatic side with unilateral facetectomy and at the same level supplemental fixation with a transpedicular screw/rod system. The internal fixation systems included 12 SOCON spinal systems (Aesculap AG, Germany) and 15 TSRH spinal systems (Medtronic Sofamor Danek, USA). The inclusion criteria were grade 1 to 2 lumbar isthmic spondylolisthesis, lumbar degenerative spondylolisthesis, and recurrent lumbar disc herniations with instability. Patients had at least 1 year of low back pain and/or unilateral sciatica and a severely restricted functional ability in individuals aged 28–55 years. Patients with more than grade 2 spondylolisthesis or adjacent-level degeneration were excluded from the study. Patients were clinically assessed prior to surgery by an independent assessor; they were then reassessed at 1, 3, 6, 12, 18, and 24 months postoperatively by the same assessor and put into four categories: excellent, good, fair, and poor. Operative time, blood loss, hospital expense, and complications were also recorded. All patients achieved successful radiographic fusion at 2 years, and this was achieved at 1 year in 25 out of 27 patients. At 2 years, clinical results were excellent in 15patients, good in 10, fair in 1, and poor in 1. Regarding complications, one patient had a postoperative motor and sensory deficit of the nerve root. Reoperation was required in one patient due to migration of pedicle screws. No implant fractures or deformities occurred in any of the patients. PLIF using diagonal insertion of a single threaded cage with supplemental transpedicular screw/rod instrumentation enables sufficient decompression and solid interbody fusion to be achieved with minimal invasion of the posterior spinal elements. It is a clinically safer, easier, and more economical means of accomplishing PLIF.
PMCID: PMC3784842  PMID: 12709855
Lumbar Fusion cage Implant Transpedicular screw Interbody
3.  Mid-term clinical results of minimally invasive decompression and posterolateral fusion with percutaneous pedicle screws versus conventional approach for degenerative spondylolisthesis with spinal stenosis 
European Spine Journal  2011;21(6):1171-1177.
In order to minimize perioperative invasiveness and improve the patients’ functional capacity of daily living, we have performed minimally invasive lumbar decompression and posterolateral fusion (MIS-PLF) with percutaneous pedicle screw fixation for degenerative spondylolisthesis with spinal stenosis. Although several minimally invasive fusion procedures have been reported, no study has yet demonstrated the efficacy of MIS-PLF in degenerative spondylolisthesis of the lumbar spine. This study prospectively compared the mid-term clinical outcome of MIS-PLF with those of conventional PLF (open-PLF) focusing on perioperative invasiveness and patients’ functional capacity of daily living.
Materials and methods
A total of 80 patients received single-level PLF for lumbar degenerative spondylolisthesis with spinal stenosis. There were 43 cases of MIS-PLF and 37 cases of open-PLF. The surgical technique of MIS-PLF included making a main incision (4 cm), and neural decompression followed by percutaneous pedicle screwing and rod insertion. The posterolateral gutter including the medial transverse process was decorticated and iliac bone graft was performed. The parameters analyzed up to a 2-year period included the operation time, intra and postoperative blood loss, Oswestry-Disability Index (ODI), Roland-Morris Questionnaire (RMQ), the Japanese Orthopaedic Association score, and the visual analogue scale of low back pain. The fusion rate and complications were also reviewed.
The average operation time was statistically equivalent between the two groups. The intraoperative blood loss was significantly less in the MIS-PLF group (181 ml) when compared to the open-PLF group (453 ml). The postoperative bleeding on day 1 was also less in the MIS-PLF group (210 ml) when compared to the open-PLF group (406 ml). The ODI and RMQ scores rapidly decreased during the initial postoperative 2 weeks in the MIS-PLF group, and consistently maintained lower values than those in the open-PLF group at 3, 6, 12, and 24 months postoperatively. The fusion rate was statistically equivalent between the two groups (98 vs. 100%), and no major complications occurred.
The MIS-PLF utilizing a percutaneous pedicle screw system is less invasive compared to conventional open-PLF. The reduction in postoperative pain led to an increase in activity of daily living (ADL), demonstrating rapid improvement of several functional parameters. This superiority in the MIS-PLF group was maintained until 2 years postoperatively, suggesting that less invasive PLF offers better mid-term results in terms of reducing low back pain and improving patients’ functional capacity of daily living. The MIS-PLF utilizing percutaneous pedicle screw fixation serves as an alternative technique, eliminating the need for conventional open approach.
PMCID: PMC3366131  PMID: 22173610
Minimally invasive spine surgery; Posterolateral fusion; Percutaneous pedicle screw; Degenerative spondylolisthesis; Lumbar spine
4.  Evaluation of efficacy of a new hybrid fusion device: a randomized, two-centre controlled trial 
The 360° fusion of lumbar segments is a common and well-researched therapy to treat various diseases of the spine. But it changes the biomechanics of the spine and may cause adjacent segment disease (ASD). Among the many techniques developed to avoid this complication, one appears promising. It combines a rigid fusion with a flexible pedicle screw system (hybrid instrumentation, “topping off”). However, its clinical significance is still uncertain due to the lack of conclusive data.
The study is a randomized, therapy-controlled, two-centre trial conducted in a clinical setting at two university hospitals. If they meet the criteria, outpatients presenting with degenerative disc disease, facet joint arthrosis or spondylolisthesis will be included in the study and randomized into two groups: a control group undergoing conventional fusion surgery (PLIF - posterior lumbar intervertebral fusion), and an intervention group undergoing fusion surgery using a new flexible pedicle screw system (PLIF + “topping off”), which was brought on the market in 2013.
Follow-up examination will take place immediately after surgery, after 6 weeks and after 6, 12, 24 and 36 months. An ongoing assessment will be performed every year.
Outcome measurements will include quality of life and pain assessments using validated questionnaires (ODI - Ostwestry Disability Index, SF-36™ - Short Form Health Survey 36, COMI - Core Outcome Measure Index). In addition, clinical and radiologic ASD, sagittal balance parameters and duration of work disability will be assessed. Inpatient and 6-month mortality, surgery-related data (e.g., intraoperative complications, blood loss, length of incision, surgical duration), postoperative complications (e.g. implant failure), adverse events, and serious adverse events will be monitored and documented throughout the study.
New hybrid “topping off” systems might improve the outcome of lumbar spine fusion. But to date, there is a serious lack of and a great need of convincing data on safety or efficacy, including benefits and harms to the patients, of these systems. Health care providers are particularly interested in such data as these implants are much more expensive than conventional implants. In such a case, randomized clinical trials are the best way to evaluate benefits and risks.
Trial registration
PMCID: PMC4161882  PMID: 25189113
5.  Titanium-alloy enhances bone-pedicle screw fixation: mechanical and histomorphometrical results of titanium-alloy versus stainless steel 
European Spine Journal  2000;9(2):97-103.
Several types of pedicle screw systems have been utilized to augment lumbar spine fusion. The majority of these systems are made of stainless steel (Ss), but titanium-alloy (Ti-alloy) devices have recently been available on the market. Ti-alloy implants have several potential advantages over Ss ones. High bioactivity and more flexibility may improve bone ingrowth and mechanical fixation, and the material also offers superior magnetic resonance imaging (MRI) and computed tomography (CT) resolution and significantly less signal interference. However, no data are available from loaded spinal constructs regarding bony ingrowth and mechanical fixation. The aim of this study was to analyse the effect of Ti-alloy versus Ss pedicle screws on mechanical fixation and bone ingrowth in a loaded mini-pig model. Eighteen adult mini-pigs underwent total laminectomy and posterolateral spinal fusion at L3-L4, and were randomly selected to receive either Ss (n = 9) or Ti (n = 9) pedicle screw devices. In both groups, the device used was compact Cotrel-Dubousset instrumentation (Sofamore Danek) of an identical size and shape. The postoperative observation time was ¶3 months. Screws from L3 were used for histomorphometric studies. Mechanical testing (torsional tests and pull-out tests) was performed on the screws from L4. The Ti screws had a higher maximum torque (P < 0.05) and angular stiffness (P < 0.07), measured by torsional testing. In the pull-out tests, no differences were found between the two groups with respect to the maximum load, stiffness and energy to failure. No correlation between removal torque and the pull-out strength was found (r = 0.1). Bone ongrowth on Ti was increased by 33% compared with Ss ¶(P < 0.04), whereas no differences in bone volume around the screws were shown. Mechanical binding at the bone-screw interface was significantly greater for Ti pedicle screws than for Ss, which was explained by the fact that Ti screws had a superior bone ongrowth. There was no correlation between the screw removal torque and the pull-out strength, which indicates that the peripheral bone structure around the screw was unaffected by the choice of metal.
PMCID: PMC3611362  PMID: 10823424
Key words Pedicle screw; Titanium; Stainless steel; Pull-out test; Torsion; Histomorphometry
6.  Endoscopic transforaminal decompression, interbody fusion, and percutaneous pedicle screw implantation of the lumbar spine: A case series report 
On the basis of the experiences gained from conventional open spinal procedures, a long list of desirable objectives have emerged with the evolution of the lesser invasive spinal procedures. At the top of that list is the desire to minimize the trauma of surgery. The rest of the objectives, which include reductions of operating time, surgical blood loss, hospital stay, postoperative narcotic medication, convalescence, complication rates, and escalating health care costs, as well as the desire of elderly patients to continue rigorous physical activities, largely depend on the ability to minimize the trauma of surgery. The purpose of this study was to investigate the feasibility of the least invasive lumbar decompression, interbody fusion and percutaneous pedicle screw implantation, to minimize surgical trauma without compromising the quality of the treatment outcome, as well as to minimize risk of complications.
In this case series, 60 patients with diagnoses of degenerative disc disease, degenerative motion segments with stenosis, and spondylolisthesis, in whom nonoperative treatments failed, were treated with endoscopic transforaminal decompression and interbody fusion by 1 surgeon in 2 centers. The outcome measures were as follows: operating time, intraoperative blood loss, hospital stay, Visual Analogue Scale (VAS) scores for back and leg pain, scores on the Roland-Morris Disability Questionnaire, and postoperative imaging studies. A consecutive series of patients who met the treatment criteria completed VAS forms and Roland-Morris questionnaires preoperatively. Surgical procedures included arthroscopic decompression of the foramina and the discs; endplate preparation and implantation of allograft bone chips and bone morphogenetic protein 2 on absorbable collagen sponge into the disc space; and percutaneous implantation of pedicle screws. Postoperatively, the patients again completed the VAS forms and Roland-Morris questionnaires. Their charts were reviewed for office notes, operative notes, hospital stay, medications, and imaging studies. The latest X-ray and computed tomography scan films were reviewed and analyzed. Patients were followed up for a minimum of 6 months. The literature was reviewed for comparison of outcomes.
Sixty patients met the inclusion criteria. The mean age was 52.8 years. The duration of illness averaged 5 years. Follow-up ranged from 6 to 25 months, with a mean of 12 months. Preoperative diagnoses included degenerative disc disease, degenerative motion segments with stenosis, and spondylolisthesis. The mean time in the operating room was 2 hours 54 minutes. Estimated blood loss averaged 57.6 mL. The duration of the hospital stay averaged 2.6 days. Preoperative back pain and leg pain were significantly reduced (P < .005). Forty-seven imaging studies obtained at the last visit, including X-ray and computed tomography scans, showed solid fusion in 28 patients (59.6%), stable fixation in 17 (36.2%), and osteolysis around the pedicle screws in 2 (4.2%). All patients had improvement of motor function, whereas 2 patients complained of residual numbness. In addition, 8 patients (13%) complained of residual discomfort on extension of the lumbar spine. Two patients had pedicle screw–related complications requiring surgery. A review of the literature showed that endoscopic transforaminal decompression and interbody fusion performed better than open transforaminal lumbar interbody fusion/posterior lumbar interbody fusion, minimally invasive transforaminal lumbar interbody fusion, and extreme lateral lumbar interbody fusion, with regard to most parameters studied.
The endoscopic transforaminal lumbar decompression, interbody fusion, and percutaneous pedicle screw instrumentation consistently produced satisfactory results in all demographics. It performed better than the alternative procedures for most parameters studied.
PMCID: PMC4300894
ETDIF; Arthroscopic; Posterolateral; Interbody; Percutaneous; BMP-2
7.  Accuracy and safety of free-hand pedicle screw fixation in age less than 10 years 
Indian Journal of Orthopaedics  2013;47(6):559-564.
Pedicle screws are being used commonly in the treatment of various spinal disorders. However, use of pedicle screws in the pediatric population is not routinely recommended because of the risk of complications. The present study was to evaluate the safety of pedicle screws placed in children aged less than 10 years with spinal deformities and to determine the accuracy and complication (early and late) of pedicle screw placement using the postoperative computed tomography (CT) scans.
Materials and Methods:
Thirty one patients (11 males and 20 females) who underwent 261 pedicle screw fixations (177 in thoracic vertebrae and 84 in lumbar vertebrae) for a variety of pediatric spinal deformities at a single institution were included in the study. The average age of patients was 7 years and 10 months. These patients underwent postoperative CT scan which was assessed by two independent observers (spine surgeons) not involved in the treatment.
Breach rate was 5.4% (14/261 screws) for all pedicles. Of the 177 screws placed in the thoracic spine, 13 (7.3%) had breached the pedicle, that is 92.7% of the screws were accurately placed within pedicles. Seven screws (4%) had breached the medial pedicle wall, 4 screws (2.3%) had breached the lateral pedicle wall and 2 screws (1.1%) had breached the superior or inferior pedicle wall respectively. Of the 84 screws placed in the lumbar spine, 83 (98.8%) screws were accurately placed within the pedicle. Only 1 screw (1.2%) was found to be laterally displaced. In addition, the breach rate was found to be 4.2% (11/261 screws) with respect to the vertebral bodies. No neurological, vascular or visceral complications were encountered.
The accuracy of pedicle screw placement in pedicles and vertebral bodies were 94.6% and 95.8% respectively and there was no complication related to screw placement noted until the last followup. These results suggest that free-hand pedicle screw fixation can be safely used in patients younger than 10 years to treat a variety of spinal disorders.
PMCID: PMC3868136  PMID: 24379460
Computed tomography; pediatric spine; pedicle screws
8.  Cervical pedicle screw placement: feasibility and accuracy of two new insertion techniques based on morphometric data 
European Spine Journal  2006;16(1):47-56.
This morphometric and experimental study was designed to assess the dimensions and axes of the subaxial cervical pedicles and to compare the accuracy of two different techniques for subaxial cervical pedicle screw (CPS) placement using newly designed aiming devices. Transpedicular fixation is increasingly used for stabilizing the subaxial cervical spine. Development of the demanding technique is based on morphometric studies of the pedicle anatomy. Several surgical techniques have been developed and evaluated with respect to their feasibility and accuracy. The study was carried out on six conserved human cadavers (average age 85 years). Axes and dimensions of the pedicles C3–C7 (60 pedicles) were measured using multislice computed tomography (CT) images prior to surgery. Two groups consisting of 3 specimens and 30 pedicles each were established according to the screw placement technique. For surgical technique 1 (ST1) a para-articular mini-laminotomy was performed. Guidance of the drill through the pedicle with a handheld aiming device attached onto the medial aspect of the pedicle inside the spinal canal. Screw hole preparation monitored by lateral fluoroscopy. In surgical technique 2 (ST2) a more complex aiming device was used for screw holes drilling. It consists of a frame with a fully adjustable radiolucent arm for carrying the instruments necessary for placing the screws. The arm was angled according to the cervical pedicle axis as determined by the preoperative CT scans. Drilling was monitored by lateral fluoroscopy. In either technique 3.5 mm screws made of carbon fiber polyetheretherketone (CF-PEEK) were inserted. The use of the CF-PEEK screws allowed for precise postoperative CT-assessment since this material does not cause artifacts. Screw placement was qualified from ideal to unacceptable into four grades: I = screw centered in pedicle; IIa = perforation of pedicle wall less than one-fourth of the screw diameter; IIb = perforation more than one-fourth of the screw diameter without contact to neurovascular structures; III = screw more than one-fourth outside the pedicle with contact to neurovascular structures. Fifty-six pedicle screws could be evaluated according to the same CT protocol that was used preoperatively. Accuracy of pedicle screw placement did not reveal significant differences between techniques 1 and 2. A tendency towards less severe misplacements (grade III) was seen in ST2 (15% in ST2 vs. 23% in ST1) as well as a higher rate of screw positions graded IIa (62% in ST2 vs. 43% in ST1). C4 and C5 were identified to be the most critical vertebral levels with three malpositioned screws each. Because of the variability of cervical pedicles preoperative CT evaluation with multiplanar reconstructions of the pedicle anatomy is essential for transpedicular screw placement in the cervical spine. Cadaver studies remain mandatory to develop safer and technically less demanding procedures. A similar study is projected to further develop the technique of CPS fixation with regard to safety and clinical practicability.
PMCID: PMC2198884  PMID: 16628443
Cervical spine; Cervical pedicle; Anatomical study; Fixation technique
9.  Transpedicular screw fixation in the thoracic and lumbar spine with a novel cannulated polyaxial screw system 
Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system.
Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision®, Stryker). The accuracy of placement was assessed postoperatively by CT scan, and the patients were followed-up clinically for a mean of 16 months.
The total medio-caudal pedicle wall perforation rate was 9.2% (30/326). In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more) was 3.37% (11/326). Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period.
We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.
PMCID: PMC3417908  PMID: 22915906
spinal instrumentation; pedicle screws; misplacement; pedicle wall perforation
10.  A review of interspinous fusion devices: High complication, reoperation rates, and costs with poor outcomes 
Interspinous fusion devices (IFDs) are increasingly offered to patients over the age of 50 with lumbar spinal stenosis and intermittent neurogenic claudication. Here, we review the literature on complication rates, reoperation rates, and outcomes for implanting IFD, and offer an assessment of IFD charges at a single institution in 2010.
The literature concerning IFD implants was reviewed with particular attention focused on complications, reoperation rates, and outcomes. Additionally, the costs of implanting 31 IFD devices in 16 patients at one to three levels at a single institution in 2010 are presented.
Reviewing the spinal literature concerning the postoperative status of IFD followed over an average of 23–42.9 postoperative months revealed that IFD resulted in 11.6–38% complication rate, 4.6–85% reoperation rate, and 66.7–77% frequency of poor outcomes. Additionally, the 31 devices implanted in 16 patients at a single university hospital in 2010 cost a total of $576,407.
With high maximal complication rates (38%), reoperation rates (85%), poor outcomes (77%), and high costs ($576,407 for 31 devices in 16 patients), the utilization and implantation of IFD remains extremely controversial and should be investigated further.
PMCID: PMC3280001  PMID: 22347676
Complications; high costs; interspinous fusion devices; lumbar stenosis; poor outcomes; reoperations
11.  Technical factors related to the incidence of adjacent superior segment facet joint violation after transpedicular instrumentation in the lumbar spine 
European Spine Journal  2008;17(11):1476-1480.
Segmental pedicle screw fixation is rapidly becoming a popular method of spinal instrumentation. Few studies have investigated the rates of adjacent superior segment facet joint violation. The purpose of our study were to investigate the incidence of superior segment facet joint violation after pedicle screw instrumentation in the lumbar spine and to evaluate technical factors related to the incidence. A prospective study including 96 patients who underwent lumbar and lumbosacral fusion was conducted between March 2006 and December 2007. All patients had bilateral or unilateral posterior pedicle screw-rod instrumentation with either CD-Horizon (top-loading screw) or TSRH (side-connecting screw) implants. Pedicle screws were instrumented according to the methods advocated by Roy-Camille (Group 1, 20 cases) or Weinstein (Group 2, 76 cases). All patients had computed tomography scan at 1 week post operation. CT scans were reviewed blind by an experienced spine research fellow and a consultant radiologist to determine violation of the adjacent superior segment facet joint. Superior segment facet joint violation occurred in all of the 20 patients (100%) and all of the top-level screws (100%) in Group 1. The spinal research fellow noted the incidence of facet joint violation to be present in 23.8% of the screws and 32.9% of the patients in Group 2, whereas the consultant radiologist noted this to be the case in 25.2 and 35.5%, respectively. The incidence of facet joint violation in patients with CD-Horizon screws was far lower than patients with TSRH screws (P < 0.001). In conclusion, it seems that meticulous surgical dissection without injuring the top-level facet joints, proper instrumentation of pedicle screws with the appropriate entry site (Weinstein’s method), trajectory, and use of top-loading screw heads are some ways that surgeons could minimize the risk of top-level facet joint violation.
PMCID: PMC2583192  PMID: 18795343
Pedicle screws; Facet joint violation; Lumbar spine
12.  Multilevel decompressive laminectomy and transpedicular instrumented fusion for cervical spondylotic radiculopathy and myelopathy: A minimum follow-up of 3 years 
Cervical laminectomies with transpedicular insertion technique is known to be a biomechanically stronger method in cervical pathologies. However, its frequency of use is low in the routine practice, as the pedicle is thin and risk of neurovascular damage is high. In this study, we emphasize the results of cervical laminectomies with transpedicular fixation using fluoroscopy in degenerative cervical spine disorder.
Materials and Methods:
Postoperative malposition of the transpedicular screws of the 70 pedicles of the 10 patients we operated due to degenerative stenosis in the cervical region, were investigated. Fixation was performed between C3 and C7, and we used resected lamina bone chips for fusion. Clinical indicators included age, gender, neurologic status, surgical indication, and number of levels stabilized. Dominant vertebral artery of all the patients was evaluated with Doppler ultrasonography. Preoperative and postoperative Nurick grade of each patient was documented.
No patients experienced neurovascular injury as a result of pedicle screw placement. Two patients had screw malposition, which did not require reoperation due to minor breaking. Most patients had 32-mm screws placed. Postoperative computed tomography scanning showed no compromise of the foramen transversarium. A total of 70 pedicle screws were placed. Good bony fusion was observed in all patients. At follow-up, 9/10 (90%) patients had improved in their Nurick grades. The cases were followed-up for an average of 35.7 months (30–37 months).
Use of the cervical pedicular fixation (CPF) provides a very strong three-column stabilization but also carries vascular injury without nerve damage. Laminectomies technique may reduce the risk of malposition due to visualization of the spinal canal. CPF can be performed in a one-stage posterior procedure. This technique yielded good fusion rate without complications and can be considered as a good alternative compared other techniques.
PMCID: PMC3190426  PMID: 22013372
Cervical laminectomies; degenerative; spondylotic myelopathy; transpedicular screw
13.  Accuracy of free-hand placement of thoracic pedicle screws in adolescent idiopathic scoliosis: how much of a difference does surgeon experience make? 
European Spine Journal  2009;19(1):91-95.
The use of thoracic pedicle screws for the treatment of adolescent idiopathic scoliosis (AIS) has gained widespread popularity. However, the placement of pedicle screws in the deformed spine poses unique challenges, and surgeons experience a learning curve. The in vivo accuracy as determined by computed tomography (CT) of placement of thoracic pedicle screws in the deformed spine as a function of surgeon experience is unknown. We undertook a retrospective review to determine the effect of surgeon experience on the accuracy of thoracic pedicle screw placement in AIS. In 2005, we started to obtain routine postoperative CT scans on patients undergoing a spinal fusion. From a database of these patients, we selected AIS patients, who underwent a posterior spinal fusion. Fifteen consecutive patients for each of the following three groups stratified by attending surgeon experience were selected (N = 45): A) less than 20 cases of all pedicle screw constructs for AIS (surgeons <2 years of practice), B) 20–50 cases (surgeons 2–5 years of practice), and C) greater than 50 cases (surgeons greater than 5 years of practice). Intraoperative evaluation of all screws included probing of the pedicle screw tract, neurophysiologic monitoring, and fluoroscopic confirmation. A total of 856 thoracic pedicle screws were studied. Postoperative CT scans were evaluated by two spine surgeons and a consensus read established as follows: (1) In: intraosseous placement or ≤2-mm breach, (2) Out: >2-mm breach, either medial or lateral. Of the 856 screws, 104 demonstrated a >2-mm breach, for an overall rate of 12.1% (medial = 55, lateral = 49, P = 0.67). When the breach rates were stratified by surgeon experience, there was a trend toward decreased rate of breach for the most experienced surgeons, although this did not attain statistical significance (Group A: 12.7%, Group B: 12.9%, Group C: 10.8%, P = 0.58). However, the most experienced group (C) had a markedly decreased rate of medial breaches (3.5 vs. 7.4% and 8.4% for groups A and B, respectively, P < 0.01). The breach rate for the concave periapical screws was not statistically different from the overall breach rate (13.0% vs. 12.1%, P = 0.93). In conclusion, the overall accuracy of placement of pedicle screws in the deformed spine was 87.9%, with no neurologic, vascular, or visceral complications. Meticulous technique allows spine surgeons with a range of surgical experience to accurately and safely place thoracic pedicle screws in the deformed spine. The most experienced surgeons demonstrated the lowest rate of medial breaches.
PMCID: PMC2899745  PMID: 19882179
Adolescent idiopathic scoliosis; Computed tomography; Surgeon experience; Thoracic pedicle screws
14.  Intraoperative 3-dimensional imaging (O-arm) for assessment of pedicle screw position: Does it prevent unacceptable screw placement? 
Pedicle screws are biomechanically superior over other spinal fixation devices. When improperly positioned, they lose this advantage and put adjacent structures at risk. Accurate placement is therefore critical. Postoperative computed tomography (CT) scans are the imaging gold standard and have shown malposition rates ranging from 2% to 41%. The O-arm (Medtronic Navigation, Louisville, Colorado) is an intraoperative CT scanner that may allow intervention for malpositioned screws while patients are still in the operating room. However, this has not yet been shown in clinical studies. The primary objective of this study was to assess the usefulness of the O-arm for evaluating pedicle screw position by answering the following question: What is the rate of intraoperative pedicle screw revision brought about by O-arm imaging information? A secondary question was also addressed: What is the rate of unacceptable thoracic and lumbar pedicle screw placement as assessed by intraoperative O-arm imaging?
This is a case series of consecutive patients who have undergone spine surgery for which an intraoperative 3-dimensional (3D) CT scan was used to assess pedicle screw position. The study comprised 602 pedicle screws (235 thoracic and 367 lumbar/sacral) placed in 76 patients, and intraoperative 3D (O-arm) imaging was obtained to assess screw position. Action taken at the time of surgery based on imaging information was noted. An independent review of all scans was also conducted, and all screws were graded as either optimal (no breach), acceptable (breach ≤2 mm), or unacceptable (breach >2 mm). The rate of pedicle screw revision, as detected by intraoperative 3D CT scan, was determined.
On the basis of 3D imaging information, 17 of 602 screws (2.8%) in 14 of 76 cases (18.4%) were revised at the time of surgery. On independent review of multiplanar images, 11 screws (1.8%) were found to be unacceptable, 32 (5.3%) were acceptable, and 559 (92.9%) were optimal. All unacceptable screws were revised to an optimal or acceptable position, and an additional 6 acceptable screws were revised to an optimal position. Thus, by the end of the cases, none of the 602 pedicle screws in the 76 surgical procedures was in an unacceptable position.
The new-generation intraoperative 3D imaging system (O-arm) is a useful tool that allows more accurate assessment of pedicle screw position than plain radiographs or fluoroscopy alone. It prompted intraoperative repositioning of 2.8% of pedicle screws in our series. Most importantly, it allowed identification and revision of all unacceptably placed pedicle screws without the need for reoperation.
PMCID: PMC4300877
Pedicle screw; Pedicle screw revision; Pedicle screw malposition; O-arm; Intraoperative 3-D imaging
15.  In vitro study of accuracy of cervical pedicle screw insertion using an electronic conductivity device (ATPS part III) 
European Spine Journal  2009;18(9):1300-1313.
Reconstruction of the highly unstable, anteriorly decompressed cervical spine poses biomechanical challenges to current stabilization strategies, including circumferential instrumented fusion, to prevent failure. To avoid secondary posterior surgery, particularly in the elderly population, while increasing primary construct rigidity of anterior-only reconstructions, the authors introduced the concept of anterior transpedicular screw (ATPS) fixation and plating. We demonstrated its morphological feasibility, its superior biomechanical pull-out characteristics compared with vertebral body screws and the accuracy of inserting ATPS using a manual fluoroscopically assisted technique. Although accuracy was high, showing non-critical breaches in the axial and sagittal plane in 78 and 96%, further research was indicated refining technique and increasing accuracy. In light of first clinical case series, the authors analyzed the impact of using an electronic conductivity device (ECD, PediGuard) on the accuracy of ATPS insertion. As there exist only experiences in thoracolumbar surgery the versatility of the ECD was also assessed for posterior cervical pedicle screw fixation (pCPS). 30 ATPS and 30 pCPS were inserted alternately into the C3–T1 vertebra of five fresh-frozen specimen. Fluoroscopic assistance was only used for the entry point selection, pedicle tract preparation was done using the ECD. Preoperative CT scans were assessed for sclerosis at the pedicle entrance or core, and vertebrae with dense pedicles were excluded. Pre- and postoperative reconstructed CT scans were analyzed for pedicle screw positions according to a previously established grading system. Statistical analysis revealed an astonishingly high accuracy for the ATPS group with no critical screw position (0%) in axial or sagittal plane. In the pCPS group, 88.9% of screws inserted showed non-critical screw position, while 11.1% showed critical pedicle perforations. The usage of an ECD for posterior and anterior pedicle screw tract preparation with the exclusion of dense cortical pedicles was shown to be a successful and clinically sound concept with high-accuracy rates for ATPS and pCPS. In concert with fluoroscopic guidance and pedicle axis views, application of an ECD and exclusion of dense cortical pedicles might increase comfort and safety with the clinical use of pCPS. In addition, we presented a reasonable laboratory setting for the clinical introduction of an ATPS-plate system.
PMCID: PMC2899545  PMID: 19575244
Cervical pedicle screw fixation; Accuracy; Electronic conductivity device; Insertion technique; ATPS
16.  Role of intraoperative Iso-C based navigation in challenging spine trauma 
Indian Journal of Orthopaedics  2007;41(4):312-317.
Pedicle screw fixation is the most preferred method of stabilizing unstable spinal fractures. Pedicle screw placement may be difficult in presence of fractured posterior elements, deformed spine, gross instability and spinal pathology. Challenging spine-fracture fixation is defined as the presence of one or more of the following: 1) obscured topographical landmarks as in ankylosing spondylitis, 2) fractures in occipitocervical or cervicothoracic regions and 3) preexisting altered spinal alignment. We report a series of pedicle screw insertion with guidance of navigation in difficult fixation problems..
Materials and Methods:
Fourteen patients [hangman's fracture (n=3), odontoid fracture (n=4), C1C2 fracture (n=1) and spinal fracture with coexistent ankylosing spondylitis (n=6)] underwent posterior stabilization. Intraoperatively after surgical exposure, images were acquired by Iso-C 3D C-arm and transferred to navigation system. Instrumentation was performed with navigational assistance. Postoperatively, placements of pedicle screws were evaluated with radiographs and CT scan.
Sixty-seven pedicle screws (cervical, n=33; thoracic, n=6; lumbar, n=26; sacral n=2) and 15 lateral mass screws were inserted with navigation guidance. The average time of image data acquisition by Iso-C 3D C-arm and its transfer to workstation was 4 minutes (range, 2-6 minutes). Postoperative CT scan revealed ideal placement of screws in 63 pedicles (94%), grade 1 cortical breaches (<2 mm) in 3 pedicles (4.5%) and grade 2 cortical breach (2-4 mm) in one pedicle (1.5%). There were no neurovascular complications. Deep infection was encountered in one case, which settled with debridement.
Intraoperative Iso-C 3D C-arm based navigation is a useful adjunct while stabilizing challenging spinal trauma, rendering feasibility, accuracy and safety of pedicle screw placement even in difficult situations.
PMCID: PMC2989511  PMID: 21139784
Computer-assisted surgery; neuronavigation; pedicle screw; spine fracture; challenging spinal trauma
17.  Symptomatic Adjacent Segment Pathology after Posterior Lumbar Interbody Fusion for Adult Low-Grade Isthmic Spondylolisthesis 
Global Spine Journal  2013;3(4):219-224.
The incidence of symptomatic adjacent segment pathology (ASP) after fusion surgery for adult low-grade isthmic spondylolisthesis (IS) has been reported to be relatively low compared with other lumbar disease entities. However, there has been no study of symptomatic ASP incidence using posterior lumbar interbody fusion (PLIF) with pedicle screw instrumentation. We investigated the incidence of symptomatic ASP after PLIF with pedicle screw instrumentation for adult low-grade IS and identified significant risk factors for symptomatic ASP. We retrospectively studied records of 40 consecutive patients who underwent PLIF with pedicle screw instrumentation at the Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Japan. The patients were followed for ≥ 4 years. Patients' medical records were retrospectively examined for evidence of symptomatic ASP. Age at time of surgery, sex, fusion level, whole lumbar lordosis, segmental lordosis, preexisting laminar inclination angle, and facet tropism at the cranial fusion segment were analyzed to identify risk factors for symptomatic ASP. Four patients (ASP group) developed symptomatic ASP at the cranial segment adjacent to the fusion. There were no significant differences in age, sex, fusion level, lumbar lordosis, segmental lordosis, or facet tropism at the cranial segment adjacent to the fusion between the ASP and the non-ASP groups. In contrast, laminar inclination angle at the cranial vertebra adjacent to the fusion was significantly higher in the ASP group than in the non-ASP group. Four patients (10%) developed symptomatic ASP after PLIF with transpedicular fixation for adult low-grade IS. Preexisting laminar horizontalization at the cranial vertebra adjacent to the fusion was a significant risk factor for symptomatic ASP.
PMCID: PMC3854583  PMID: 24436872
isthmic spondylolisthesis; posterior lumbar interbody fusion; adjacent segment pathology; laminar horizontalization
18.  Correlative radiological, self-assessment and clinical analysis of evolution in instrumented dorsal and lateral fusion for degenerative lumbar spine disease. Autograft versus coralline hydroxyapatite 
European Spine Journal  2005;14(7):630-638.
This prospective longitudinal randomized clinical and radiological study compared the evolution of instrumented posterolateral lumbar and lumbosacral fusion using either coralline hydroxyapatite (CH), or iliac bone graft (IBG) or both in three comparable groups, A, B and C, which included 19, 18 and 20 patients, respectively, who suffered from symptomatic degenerative lumbar spinal stenosis and underwent decompression and fusion. The patients were divided randomly according to the graft used and the side that it was applied. The spines of group A received autologous IBG bilaterally; group B, IBG on the left side and hydroxyapatite mixed with local bone and bone marrow on the right side; group C, hydroxyapatite mixed with local bone and bone marrow bilaterally. The age of the patients in the groups A, B and C was 61±11 years, 64±8 years and 58±8 years, respectively. The SF-36, Oswestry Disability Index (ODI), and Roland-Morris (R-M) surveys were used for subjective evaluation of the result of the surgery and the Visual Analogue Scale (VAS) for pain severity. Plain roentgenograms including anteroposterior, lateral and oblique views, and lateral plus frontal bending views of the instrumented spine and CT scan were used to evaluate the evolution of the posterolateral fusion in all groups and sides. Two independent senior orthopaedic radiologists were asked to evaluate first the evolution of the dorsolateral bony fusion 3–48 months postoperatively with the Christiansen’s radiologic method, and secondly the hydroxyapatite resorption course in the spines of groups B and C. The diagnosis of solid spinal fusion was definitively confirmed with the addition of the bending views, CT scans and self-assessment scores. The intraobserver and interobserver agreement (r) for radiological fusion was 0.71 and 0.69, respectively, and 0.83 and 0.76 for evaluation of CH resorption. T12−S1 lordosis and segmental angulation did not change postoperatively. There was no radiological evidence for non-union on the plain roentgenograms and CT scans. Radiological fusion was achieved 1 year postoperatively and was observed in all groups and vertebral segments. Six months postoperatively there was an obvious resorption of hydroxyapatite granules at the intertransverse intersegmental spaces in the right side of the spines of group B and both sides of group C. The resorption of hydroxyapatite was completed 1 year postoperatively. Bone bridging started in the third month postoperatively in all instrumented spines and all levels posteriorly as well as between the transverse processes in the spines of the group A and on the left side of the spines of group B where IBG was applied. SF-36, ODI, and R-M score improved postoperatively in a similar way in all groups. There was one pedicle screw breakage at the lowermost instrumented level in group A and two in group C without radiologically visible pseudarthrosis, which were considered as having non-union. Operative time and blood loss were less in the patients of group C, while donor site complaints were observed in the patients of the groups A and B only. This study showed that autologous IBG remains the “gold standard” for achieving solid posterior instrumented lumbar fusion, to which each new graft should be compared. The incorporation of coralline hydroxyapatite mixed with local bone and bone marrow needs adequate bleeding bone surface. Subsequently, hydroxyapatite was proven in this series to not be appropriate for intertransverse posterolateral fusion, because the host bone in this area is little. However, the use of hydroxyapatite over the decorticated laminae that represents a wide host area was followed by solid dorsal fusion within the expected time.
PMCID: PMC3489222  PMID: 15789231
Coralline hydroxyapatite; Lumbar spinal stenosis; Instrumented fusion
19.  Minimum 2-Year Follow-Up Result of Degenerative Spinal Stenosis Treated with Interspinous U (Coflex™) 
Clinical and radiological results of posterior dynamic stabilization using interspinous U (ISU, Coflex™, Paradigm Spine Inc.®, NY, USA) were analyzed in comparison with posterior lumbar interbody fusion (PLIF) in degenerative lumbar spinal stenosis (LSS).
A retrospective study was conducted for a consecutive series of 61 patients with degenerative LSS between May 2003 and December 2005. We included only the patients completed minimum 24 months follow up evaluation. Among them, 30 patients were treated with implantation of ISU after decompressive laminectomy (Group ISU) and 31 patients were treated with wide decompressive laminectomy and posterior lumbar interbody fusion (PLIF; Group PLIF). We evaluated visual analogue scale (VAS) and Oswestry Disability Index (ODI) for clinical outcomes (VAS, ODI), disc height ratio disc height (DH), disc height/vertebral body length ×100), static vertebral slip (VS) and depth of maximal radiolucent gap between ISU and spinous process) in preoperative, immediate postoperative and last follow up.
The mean age of group ISU (66.2 ± 6.7 years) was 6.2 years older than the mean age of group PLIF (60.4 ± 8.1 years; p = 0.003 ). In both groups, clinical measures improved significantly than preoperative values (p < 0.001). Operation time and blood loss was significantly shorter and lower in group ISU than group PLIF (p < 0.001). In group ISU, the DH increased transiently in immediate postoperative period (15.7 ± 4.5% → 18.6 ± 5.9%), however decreased significantly in last follow up (13.8 ± 6.6%, p = 0.027). Vertebral slip (VS) of spondylolisthesis in group ISU increased during postoperative follow-up (2.3 ± 3.3 → 8.7 ± 6.2, p = 0.040). Meanwhile, the postoperatively improved DH and VS was maintained in group PLIF in last follow up.
According to our result, implantation of ISU after decompressive laminectomy in degenerative LSS is less invasive and provides similar clinical outcome in comparison with the instrumented fusion. However, the device has only transient effect on the postoperative restoration of disc height and reduction of slip in spondylolisthesis. Therefore, in the biomechanical standpoint, it is hard to expect that use of Interspinous U in decompressive laminectomy for degenerative LSS had long term beneficial effect.
PMCID: PMC2773383  PMID: 19893715
Degenerative spinal stenosis; Lumbar; Dynamic stabilization; Interspinous U; Coflex™; Posterior lumbar interbody fusion
20.  Comparative study of PILF and TLIF treatment in adult degenerative spondylolisthesis 
European Spine Journal  2008;17(10):1311-1316.
This study is to compare the therapeutic effect of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) with pedicle screw fixation on treatment in adult degenerative spondylolisthesis. A retrospective analysis of 187 patients to compare the complications and associated predictive factors of the two techniques of one level lumbar fusion. Ninety-one had PLIF with two cages and pedicle fixation (group 1), and ninety-six had TLIF with one cage and pedicle fixation (group 2). The two groups had similar age and sex distribution, and level of pain. Inclusion criteria and outcome measurements were identical in both groups. The two groups were operated on with autograft and cage with pedicle fixation. Before surgery and at the 2-year follow-up, pain (VAS) and functional disability (JOA) were quantified. The results showed there were no intraoperative deaths in our study. In the end 176 cases had 2-year follow-up while 11 cases were lost to follow-up. The follow-up rate was 93.4% (85/91) in the PLIF group and 94.8% (91/96) in the TLIF group. All patients had bone fusion, and there were no cases of cage extrusion. The pain index improved from 7.08 ± 1.13 to 2.84 ± 0.89 in PLIF patients and improved from 7.18 ± 1.09 to 2.84 ± 0.91 in TLIF patients (P < 0.001). There were 42 cases of excellent, 29 cases of good, 11 cases of general, and 3 cases of poor results in PLIF group. There were 46 cases of excellent, 31 case of good, 12 case of general, and 2 cases of poor results in TLIF group. The JOA score in all patients was 84.1% of good or excellent (83.5% in PLIF and 84.6% in TLIF, P > 0.05). The average preoperative slip was 30.1 ± 7.2% in PLIF group while in the TLIF it was 31.4 ± 8.3%. Immediately post operatively it was reduced to 7.3 ± 2.1% and 7.4 ± 2.7% and at last F/U it was 8.1 ± 2.8% and 8.2 ± 2.6%, respectively. The average of reduction rate was 75.2 ± 6.4% in PLIF and 75.4 ± 6.2 in TLIF on the initial post operatively X-ray, and 72.6 ± 5.2% and 72.4 ± 5.4% on the follow-up. The percentage rate, reduction rate and lost of reduction rate between the two groups was similar (P > 0.05). The average pre operative disk and foramen height in the PLIF group improved from 6.8 ± 2.3 and 14.2 ± 1.7 preoperatively to 11.6 ± 1.5 and 18.7 ± 1.8 post operatively, respectively. At last follow up there was minimal lost of correction down to 11.24 ± 1.2 and 18.1 ± 1.8, respectively. Similarly in the TLIF group, pre operative disk and foramen height were improved from 6.7 ± 1.7 and 14.1 ± 1.8 to 11.4 ± 1.6 and 18.5 ± 1.6 immediately post operative. At last follow up minimal lost of correction was noted with average disc height of 11.3 ± 1.4 and 18.2 ± 1.7. Both techniques achieve statistical significance in restoration of disc and foraminal (P < 0.01); however, there was no statistical difference between the two techniques. In conclusion, interbody fusion with either a PLIF technique or a TLIF technique provides good outcomes in the treatment of adult degenerative spondylolisthesis. The TLIF procedure is simpler and is as safe and effective as the PLIF technique.
PMCID: PMC2556474  PMID: 18685873
Spondyolisthesis; Interverterbral fusion; Internal fixation
21.  Minimally invasive one-level lumbar decompression and fusion surgery with posterior instrumentation using a combination of pedicle screw fixation and transpedicular facet screw construct 
Minimally invasive lumbar spine fusion surgery has gained popularity in recent years. Routinely, this technique requires bilateral parasagittal incisions for decompression, interbody fusion, and posterior instrumentation. The following study is a description of a new minimally invasive technique for one-level transforaminal lumbar interbody fusion (TLIF) using a unilateral parasagittal incision (Wiltse approach), with placement of pedicle screws and then a percutaneous transpedicular facet screw insertion on the contralateral side. The biomechanical stability of this posterior construct will be discussed while the efficacy and complications of this technique have been examined.
Forty patients underwent this new technique of one-level TLIF with posterior instrumentation using unilateral pedicle screw fixation supplemented with contralateral percutaneous transpedicular facet screw construct. Data regarding surgical time, estimated blood loss (EBL), hospital length of stay (LOS), and complications related to the posterior instrumentation are recorded.
The average surgical time of this new procedure was 124 minutes; average EBL was 140 cc; average hospital LOS was 3 days. Two patients developed new leg pain on the side where the facet screw had been placed. Both patients had the facet screw removed.
This novel technique of unilateral pedicle screw fixation combined with contralateral percutaneous transpedicular facet screw construct has further reduced the amount of normal tissue injury while maintaining the same biomechanical advantages of bilateral pedicle screw fixation. However, caution is needed during the placement of the percutaneous facet screw in order to avoid nerve root injury.
PMCID: PMC3814991  PMID: 24255796
Minimally invasive spine surgery; percutaneous facet screw; transforaminal interbody fusion; Wiltse approach
22.  Assessment of CAOS as a training model in spinal surgery: a randomised study 
European Spine Journal  2006;16(2):239-244.
The objectives of this study were (1) to quantify the benefit of computer assisted orthopaedic surgery (CAOS) pedicle screw insertion in a porcine cadaver model evaluated by dissection and computed tomography (CT); (2) to compare the effect on performance of four surgeons with no experience of CAOS, and varying experience of pedicle screw insertion; (3) to see if CT with extended windows was an acceptable method to evaluate the position of the pedicle screws in the porcine cadaver model, compared to dissection. This was a prospective, randomised, controlled and blinded porcine cadaver study. Twelve 6-month-old porcine (white skinned Landrace) lumbar spines were scanned pre-operatively by spiral CT, as required for the CAOS computer data set. Computer randomisation allocated the specimens to one of four surgeons, all new to CAOS but with different levels of experience in spinal surgery. The usual anatomical landmarks for the freehand technique were known to all four surgeons. Two pedicles at each vertebral level were randomly allocated between conventional free hand insertion and an electromagnetic image guided surgery (NAVITRAK®) and 6.5 mm cancellous AO screws inserted. Post-operatively, spiral CT was blindly evaluated by an independent radiologist and the spine fellow to assess the accuracy of pedicle screw placement, by each method. The inter- and intra-observer reliability of CT was evaluated compared to dissection. The pedicle screw placement was assessed as perfect if within the pedicle along its central axis, or acceptable (within < 2 mm from perfect), and measured in millimetres from perfect thereafter. One hundred and sixty-six of 168 pedicles in 12 porcine spines were operated on. Complete data were present for 163 pedicles (81 CAOS, 82 freehand). In the CAOS group 84% of screws were deemed acceptable or perfect, compared to 75.6% with the freehand technique. Screw misplacement was significantly reduced using CAOS (P = 0.049). Seventy-nine percent of CAOS screws were ideally placed compared with 64% with a conventional freehand technique (P = 0.05). A logistic linear regression model showed that the miss placed pedicle screw rate was significantly reduced using CAOS (P = 0.047). CAOS benefited the least experienced surgeons most (the research registrars acceptable rate increased from 70 to 90% and the spine fellow from 76 to 86%). CAOS did not have a statistically significant effect on the experienced consultant spine surgeon increasing from 70 to 79% (P = 0.39). The experienced general orthopaedic surgeon did not benefit from CAOS (P = 0.5). CT compared to dissection showed an intra-observer reliability of 99.4% and inter-observer reliability of 92.6%. The conclusions of this study were as follows: (1) an increased number of pedicle screws were ideally placed using the CAOS electromagnetic guidance system compared to the conventional freehand technique; (2) junior surgeons benefited most from CAOS; (3) we believe CAOS (Navitrak®) with porcine lumbar spines evaluated by post operative CT, represents a useful model for training junior surgeons in pedicle screw placement; (4) experienced spine surgeons, who have never used CAOS, may find CAOS less helpful than previously reported.
PMCID: PMC2200694  PMID: 16683122
Pedicle screw insertion; Computer assisted orthopaedic surgery; Conventional fluoroscopic technique; Training model; Porcine cadaver lumbar spine study
23.  Short term outcome of posterior dynamic stabilization system in degenerative lumbar diseases 
Indian Journal of Orthopaedics  2014;48(6):574-581.
Decompression and fusion is considered as the ‘gold standard’ for the treatment of degenerative lumbar diseases, however, many disadvantages have been reported in several studies, recently like donor site pain, pseudoarthrosis, nonunion, screw loosening, instrumentation failure, infection, adjacent segment disease (ASDis) and degeneration. Dynamic neutralization system (Dynesys) avoids many of these disadvantages. This system is made up of pedicle screws, polyethylene terephthalate cords, and polycarbonate urethane spacers to stabilize the functional spinal unit and preserve the adjacent motion after surgeries. This was a retrospective cohort study to compare the effect of Dynesys for treating degenerative lumbar diseases with posterior lumbar interbody fusion (PLIF) based on short term followup.
Materials and Methods:
Seventy five consecutive patients of lumbar degenerative disease operated between October 2010 and November 2012 were studied with a minimum followup of 2 years. Patients were divided into two groups according to the different surgeries. 30 patients underwent decompression and implantation of Dynesys in two levels (n = 29) or three levels (n = 1) and 45 patients underwent PLIF in two levels (n = 39) or three levels (n = 6). Clinical and radiographic outcomes between two groups were reviewed.
Thirty patients (male:17, female:13) with a mean age of 55.96 ± 7.68 years were included in Dynesys group and the PLIF group included 45 patients (male:21, female:24) with a mean age of 54.69 ± 3.26 years. The average followup in Dynesys group and PLIF group was 2.22 ± 0.43 year (range 2-3.5 year) and 2.17 ± 0.76 year (range 2-3 year), respectively. Dynesys group showed a shorter operation time (141.06 ± 11.36 min vs. 176.98 ± 6.72 min, P < 0.001) and less intraoperative blood loss (386.76 ± 19.44 ml vs. 430.11 ± 24.72 ml, P < 0.001). For Dynesys group, visual analogue scale (VAS) for back and leg pain improved from 6.87 ± 0.80 to 2.92 ± 0.18 and 6.99 ± 0.81 to 3.25 ± 0.37, (both P < 0.001) and for PLIF, VAS for back and leg pain also improved significantly (6.97 ± 0.84–3.19 ± 0.19 and 7.26 ± 0.76–3.56 ± 0.38, both P < 0.001). Significant improvement was found at final followup in both groups in Oswestry disability index (ODI) score (both P < 0.001). Besides, Dynesys group showed a greater improvement in ODI and VAS back and leg pain scores compared with the PLIF group (P < 0.001, P = 0.009 and P = 0.031, respectively). For radiological, height of the operated level was found increased in both groups (both P < 0.001), but there was no difference between two groups (P = 0.93). For range of motion (ROM) of operated level, significant decrease was found in both groups (P < 0.001), but Dynesys showed a higher preservation of motion at the operative levels (P < 0.001). However, no significant difference was found in the percentage change of ROM of adjacent levels between Dynesys and PLIF (0.74 ± 8.92% vs. 0.92 ± 4.52%, P = 0.91). Some patients suffered from degeneration of adjacent intervertebral disc at final followup, but there was no significant difference in adjacent intervertebral disc degeneration between two groups (P = 0.71). Moreover, there were no differences in complications between Dynesys and PLIF (P = 0.90), although the incidence of complication in Dynesys was lower than PLIF (16.67% vs. 17.78%).
Dynamic stabilization system treating lumbar degenerative disease showed clinical benefits with motion preservation of the operated segments, but does not have the significant advantage on motion preservation at adjacent segments, to avoid the degeneration of adjacent intervertebral disk.
PMCID: PMC4232826  PMID: 25404769
Degenerative lumbar disease; dynamic neutralization system; posterior lumbar fusion; Spinal arthritis; spinal fusion; instrumentation lumbar vertebrae
24.  Harvesting local cylinder autograft from adjacent vertebral body for anterior lumbar interbody fusion: surgical technique, operative feasibility and preliminary clinical results 
European Spine Journal  2006;15(9):1352-1359.
Autogenous iliac crest has long served as the gold standard for anterior lumbar arthrodesis although added morbidity results from the bone graft harvest. Therefore, femoral ring allograft, or cages, have been used to decrease the morbidity of iliac crest bone harvesting. More recently, an experimental study in the animal showed that harvesting local bone from the anterior vertebral body and replacing the void by a radio-opaque β-tricalcium phosphate plug was a valid concept. However, such a concept precludes theoretically the use of posterior pedicle screw fixation. At one institution a consecutive series of 21 patients underwent single- or multiple-level circumferential lumbar fusion with anterior cages and posterior pedicle screws. All cages were filled with cancellous bone harvested from the adjacent vertebral body, and the vertebral body defect was filled with a β-tricalcium phosphate plug. The indications for surgery were failed conservative treatment of a lumbar degenerative disc disease or spondylolisthesis. The purpose of this study, therefore, was to report on the surgical technique, operative feasibility, safety, benefits, and drawbacks of this technique with our primary clinical experience. An independent researcher reviewed all data that had been collected prospectively from the onset of the study. The average age of the patients was 39.9 (26–57) years. Bone grafts were successfully harvested from 28 vertebral bodies in all but one patient whose anterior procedure was aborted due to difficulty in freeing the left common iliac vein. This case was converted to a transforaminal interbody fusion (TLIF). There was no major vascular injury. Blood loss of the anterior procedure averaged 250 ml (50–350 ml). One tricalcium phosphate bone plug was broken during its insertion, and one endplate was broken because of wrong surgical technique, which did not affect the final outcome. One patient had a right lumbar plexopathy that was not related to this special technique. There was no retrograde ejaculation, infection or pseudoarthrosis. One patient experienced a deep venous thrombosis. At the last follow up (mean 28 months) all patients had a solid lumbar spine fusion. At the 6-month follow up, the pain as assessed on the visual analog scale (VAS) decreased from 6.9 to 4.5 (33% decrease), and the Oswestry disability index (ODI) reduced from 48.0 to 31.7 with a 34% reduction. However, at 2 years follow up there was a trend for increase in the ODI (35) and VAS (5). The data in this study suggest that harvesting a cylinder of autograft from the adjacent vertebral body is safe and efficient. Filling of the void defect with a β-tricalcium phosphate plug does not preclude the use of posterior pedicle screw stabilization.
PMCID: PMC2438563  PMID: 16598484
Lumbar fusion; β-Tricalcium phosphate (β-TCP); Cage; Pedicle screw
25.  Screws versus hooks: implant cost and deformity correction in adolescent idiopathic scoliosis 
To compare the costs of two spinal implants—hook and hybrid constructs and pedicle screw constructs—in posterior spinal fusion for adolescent idiopathic scoliosis (AIS) as they relate to intraoperative deformity correction.
Study design and method
This retrospective study examined 50 patients with AIS who were treated with posterior spinal fusion using segmental hook-hybrid constructs (23) or pedicle screws (27). Radiographic parameters measured on immediate preoperative and initial standing postoperative scoliosis films were the coronal Cobb angles of the upper thoracic, middle thoracic, lumbar, and instrumented curves; global coronal and sagittal balance; thoracic kyphosis; lumbar lordosis; and type and number of implants used. Current implant cost data were obtained from three major spinal implant manufacturers to determine the total cost of the constructs, cost per degree of correction, cost per level fused, and cost per degree of correction of the major curve.
After surgery, the average percentage of correction for the middle thoracic curve or major curve was 57 % in the hook-hybrid group compared to 73 % in the pedicle screw group (P < 0.001). The average amount of correction of the major curve was 31.1° in the hook-hybrid group compared to 42.7° in the pedicle screw group (P < 0.001). The average number of fused levels was 10.7 in the hook-hybrid group compared to 12.2 in the pedicle screw group (P < 0.001). The average number of implants was 14.8 in the hook-hybrid group compared to 23.3 in the pedicle screw group (P < 0.001). The average total cost of implants was $11,248 in the hook-hybrid group compared to $22,826 in the pedicle screw group (P < 0.001), and the average cost per fused level was $1,058 in the hook-hybrid group compared to $1,878 in the pedicle screw group (P < 0.001). The average cost per degree of correction of the major curve was $415 in the hook-hybrid group compared to $559 in the pedicle screw group (P = 0.0014). The global coronal balance, global sagittal balance, thoracic kyphosis, and lumbar lordosis did not differ significantly between the two groups.
Pedicle screw instrumentation was shown to be more expensive overall, per fused level, and per degree of correction. Also, more implants were used and more levels were fused in the pedicle screw group than in the hook-hybrid group. Pedicle screws showed a statistically significantly greater percentage of correction of the major curve. Physicians must evaluate each patient individually and determine if the increased percentage of correction warrants the increased cost for pedicle screw constructs.
PMCID: PMC3364343  PMID: 23730345
Scoliosis; Cost; Pedicle screw; Spinal fusion; Implant

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