Biomechanical study of the lumbar spine using a unilateral pedicle screw fixation system

Successful outcomes of unilateral vs bilateral pedicle screw fixation for lumbar interbody fusion: A meta-analysis with evidence grading

BACKGROUND

Whether it’s better to adopt unilateral pedicle screw (UPS) fixation or to use bilateral pedicle screw (BPS) one for lumbar degenerative diseases is still controversially undetermined.

AIM

To make a comparison between UPS and BPS fixation as to how they work efficaciously and safely in patients suffering from lumbar degenerative diseases.

METHODS

We have searched a lot in the databases through 2020 with index terms such as “unilateral pedicle screw fixation” and “bilateral pedicle screw fixation.” Only randomized controlled trials and some prospective cohort studies could be found, yielding 15 studies. The intervention was unilateral pedicle screw fixation; Primarily We’ve got outcomes of complications and fusion rates. Secondarily, we’ve achieved outcomes regarding total blood loss, operative time, as well as length of stay. Softwares were installed and utilized for subgroup analysis, analyzing forest plots, sensitivity, heterogeneity, forest plots, publication bias, and risk of bias.

RESULTS

Fifteen previous cases of study including 992 participants have been involved in our meta-analysis. UPS had slightly lower effects on fusion rate [relative risk (RR) = 0.949, 95%CI: 0.910 to 0.990, P = 0.015], which contributed mostly to this meta-analysis, and similar complication rates (RR = 1.140, 95%CI: 0.792 to 1.640, P = 0.481), Δ visual analog scale [standard mean difference (SMD) = 0.178, 95%CI: -0.021 to 0.378, P = 0.080], and Δ Oswestry disability index (SMD = -0.254, 95%CI: -0.820 to 0.329, P = 0.402). In contrast, an obvious difference has been observed in Δ Japanese Orthopedic Association (JOA) score (SMD = 0.305, 95%CI: 0.046 to 0.563, P = 0.021), total blood loss (SMD = -1.586, 95%CI: -2.182 to -0.990, P = 0.000), operation time (SMD = -2.831, 95%CI: -3.753 to -1.909, P = 0.000), and length of hospital stay (SMD = -0.614, 95%CI: -1.050 to -0.179, P = 0.006).

CONCLUSION

Bilateral fixation is more effective than unilateral fixation regarding fusion rate after lumbar interbody fusion. However, JOA, operation time, total blood loss, as well as length of stay were improved for unilateral fixation.

Awake Percutaneous Fixation for Unstable Fractures of the Spine in High-risk Patients: A Retrospective Study

INTRODUCTION

Unstable fractures in sick or elderly patients are on the rise. These patients who are at high risk for surgery present a challenge for surgeons and anesthesiologists. In patients with American Society of Anesthesiologists (ASA) scores 3 to 4, the risk is even higher because of the high rate of intraoperative complications.

METHODS

All patients with ASA scores 3 to 4 who presented with unstable fractures of the spine to a level-one trauma center were assessed, and they underwent awake spinal percutaneous fixation, with mild sedation and local anesthesia. Demographics, radiology, and the outcome were collected.

RESULTS

Nineteen patients were operated between the years 2019 and 2021. Average follow-up was 12 months (range 8 to 24 months); six patients were female and 13 males. The average age was 77.7 years; the ASA score was 3 to 4 in all patients. There were 10 extension-type injuries, six unstable burst injuries, two chance fractures, and one teardrop fracture. All patients underwent unilateral fixation, and just one patient underwent bilateral fixation; cement augmentation was done in 16 of the patients. No neurologic complication was observed. One case of infection presented 4 months after surgery. All patients were discharged ambulating.

CONCLUSIONS

Awake fixation in extreme cases is safe and feasible; a dedicated team including an anesthesiologist and radiologist is needed to treat these cases safely and quickly.

Clinical and radiographic analysis of unilateral versus bilateral instrumented one-level lateral lumbar interbody fusion

Lateral lumbar interbody fusion (LLIF) is a widely applied and useful procedure for spinal surgeries. However, posterior fixation has not yet been decided. We compared the radiographic and clinical outcomes of unilateral versus bilateral instrumented one-level LLIF for degenerative lumbar disease. We conducted a prospective cohort study of 100 patients, who underwent unilateral (group U) or bilateral (group B) instrumented one-level LLIF for degenerative lumbar disease. Forty-one patients in group U were undergoing unilateral pedicle screw instrumentation, and 59 patients in group B were undergoing bilateral pedicle screw instrumentation. Clinical characteristic and demographic data before surgery were compared. The intraoperative data, including operative time with changes in positions, intraoperative blood loss, and X-ray exposure time, as well as the perioperative data, including postoperative hospital stay and clinical and radiographic data were compared. As a result, Group U required a significantly shorter operating time than group B. The subsidence grade and fusion rates exhibited no significant differences in the postoperative radiographic evaluation. Group U had better results in clinical assessments than group B. However, group U required more additional surgeries owing to complications.

Device solutions for a challenging spine surgery: minimally invasive transforaminal lumbar interbody fusion (MIS TLIF)

INTRODUCTION

Lumbar interbody fusion remains a mainstay in the treatment of degenerative spinal pathology. Interbody devices are often used in an attempt to improve fusion rates and outcomes. Minimally invasive techniques lend unique advantages, but are challenging and often plagued with complications. Specifically, minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) has a steep learning curve and there is a lack of concise information on solutions to optimize outcomes.

AREAS COVERED

This review details an appropriate surgical technique of MIS TLIF and includes an overview of the components that go into a successful procedure. A thorough literature search of the PubMed database was completed to provide a comprehensive analysis of the interbody devices, posterolateral fixation, and osteobiologics.

EXPERT OPINION

MIS TLIFs have demonstrated successful clinical and radiographic outcomes and have become a mainstay for treating various degenerative lumbar pathologies. As minimally invasive techniques continue to evolve, devices and biologics will continue to expand the indications for MIS TLIFs and will optimize long-term outcomes.

Do we need a transforaminal lumbar interbody fusion cage to increase the stability of functional spinal unit when comparing unilateral and bilateral fixation?

Transforaminal lumbar interbody fusion was an alternative to posterior lumbar interbody fusion for decompression surgeries. This study investigates the biomechanical responses of the unilateral and bilateral pedicle screw fixations with/without transforaminal lumbar interbody fusion cages under axial compression, flexion, and torsional loads. Ovine vertebrae were used in this study. Cadavers, randomly divided into five, were intact control group, bilateral pedicle screw fixation group, bilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage, unilateral pedicle screw fixation group, and unilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage. Axial compression, flexion, and torsion tests were performed on specimens. All study groups provided higher stiffness and yield load values than control group under axial compression. Addition of transforaminal lumbar interbody fusion cage to bilateral fixation increased the stiffness under axial compression. Moreover, additional use of transforaminal lumbar interbody fusion in unilateral fixation increased the yield load values under axial compression. Control group was the stiffest in flexion test. Placing a transforaminal lumbar interbody fusion cage to both unilateral and bilateral fixations did not significantly change the stiffness values. Additional transforaminal lumbar interbody fusion cage increased the yield moment of the bilateral fixation. In torsion test, control group had the highest stiffness and yield torque. The facet joints are the most important parts of the vertebrae on the stability. When comparing the bilateral and unilateral fixations with transforaminal lumbar interbody fusion addition, the more facet preserving approach has significantly higher stability under axial compression, flexion, and torsion. Unilateral fixation with transforaminal lumbar interbody fusion cage can be said biomechanically stable and advantageous fixation system because of the advantage on the less facet and soft tissue resection compared to bilateral fixation with transforaminal lumbar interbody fusion.

State Recognition of Bone Drilling Based on Acoustic Emission in Pedicle Screw Operation

Pedicle drilling is an important step in pedicle screw fixation and the most significant challenge in this operation is how to determine a key point in the transition region between cancellous and inner cortical bone. The purpose of this paper is to find a method to achieve the recognition for the key point. After acquiring acoustic emission (AE) signals during the drilling process, this paper proposed a novel frequency distribution-based algorithm (FDB) to analyze the AE signals in the frequency domain after certain processes. Then we select a specific frequency domain of the signal for standard operations and choose a fitting function to fit the obtained sequence. Characters of the fitting function are extracted as outputs for identification of different bone layers. The results, which are obtained by detecting force signal and direct measurement, are given in the paper. Compared with the results above, the results obtained by AE signals are distinguishable for different bone layers and are more accurate and precise. The results of the algorithm are trained and identified by a neural network and the recognition rate reaches 84.2%. The proposed method is proved to be efficient and can be used for bone layer identification in pedicle screw fixation.

Post-operative bracing after pedicle screw fixation for thoracolumbar burst fractures: A cost-effectiveness study

PURPOSE

While frequently prescribed to patients following fixation for spine trauma, the utility of spinal orthoses during the post-operative period is poorly described in the literature. In this study, we calculated rates of reoperation and performed a decision analysis to determine the utility of bracing following pedicle screw fixation for thoracic and lumbar burst fractures.

METHODS

Pubmed was searched for articles published between 2005 and 2015 for terms related to pedicle screw fixation of thoracolumbar fractures. Additionally, a database of neurosurgical patients operated on within the authors institution was also used in the analysis. Incidences of significant adverse events (wound revision for either dehiscence or infection or re-operation for non-union or instability due to hardware failure) were determined. Pooled means and variances of reported parameters were obtained using a random-effects, inverse variance meta-analytic model for observational data. Utilities for surgical outcome and complications were assigned using previously published values.

RESULTS

Of the 225 abstracts reviewed, 48 articles were included in the study, yielding a total of 1957 patients. After including patients from the institutional registry, together a total of 2081 patients were included in the final analysis, 1328 of whom were braced. Non-braced patients were older then braced patients, although this only approached significance (p=0.051). Braced patients had significantly lower rates of re-operation for non-union or clinically significant hardware failure (1.3% vs. 1.8%, p<0.001) although the groups had comparable rates of operative wound dehiscence and infection (p=1.000). These two approaches yielded comparable utility scores (p=0.120). Costs between braced and non-braced patients were comparable excluding the cost of the brace (p=0.256); hence, the added cost of the brace suggests that bracing post-operatively is not a cost effective measure.

CONCLUSIONS

Bracing following operative stabilization of thoracolumbar fracture does not significantly improve stability, nor does it increase wound complications. Moreover, our data suggests that post-operative bracing may not be a cost-effective measure.

Minimally invasive unilateral pedicle screws and a translaminar facet screw fixation and interbody fusion for treatment of single-segment lower lumbar vertebral disease: surgical technique and preliminary clinical results

BACKGROUND

Conventional open transforaminal lumbar interbody fusion (TLIF) using unilateral pedicle screws and a translaminar facet screw has been performed for many years with good results. The outcomes of minimally invasive TLIF (MIS TLIF) are similar to the good outcomes of open TLIF, with the additional benefits of reducing iatrogenic injury, shortening hospital stays, and reducing the recovery duration. Instead of using small cuts on both sides, we performed MIS TLIF through a single cut using unilateral pedicle screws and a translaminar facet screw. The operative feasibility, efficacy safety, and benefits of single-level MIS TLIF of such techniques require further clarification.

METHODS

A total of 60 patients with various single-segment lower lumbar vertebral diseases were treated in our department from January 2010 to March 2013. All the patients were initially performed single-level MIS TLIF using a hybrid construction of unilateral pedicle screws and a translaminar facet screw. Patient demographics and operative data were collected. The clinical outcomes were assessed before surgery and 3, 6, 12, and 24 months after surgery using the visual analog scale (VAS) for back and leg pain and the Oswestry Disability Index (ODI). Radiologic assessment of the lumbar spine with static and dynamic plain radiographs was performed 3, 6, 12, and 24 months after surgery. The fusion rates were assessed by an independent radiologist 2 years after surgery according to the Bridwell interbody fusion grading system.

RESULTS

No patients experienced significant postoperative complications. Excepting two cases, 58 cases were followed up for 24-38 months, averaged 29.9 ± 4.1 months. The patients' average age was 46.6 ± 11.5 years, operative time 109.7 ± 17.8 min, intraoperative blood loss 67.3 ± 29.7 ml, length of incision 29.0 ± 3.2 mm, fluoroscopy time 31.1 ± 7.2 s, time to ambulation 20.3 ± 7.0 h, length of hospital stay 5.1 ± 1.1 days, and length of the translaminar facet screw 51.7 ± 3.4 mm. Screw position results: type I, 54 cases with 54 segments; type II, four cases with four segments. There were two (3.4%) translaminar facet screw failures, which were intraoperatively converted to a bilateral pedicle screw fixation procedure and excluded from the research. The postoperative images showed good positioning of the hybrid internal fixation, and all of the translaminar facet screws penetrated the facet joint. Two (3.6%) translaminar facet screws penetrated the lateral lamina and two (3.6%) translaminar facet screws penetrated the medial lamina without any serious neural complications. During the follow-up, there was no screw loosening or pedicle fracture observed. The VAS and ODI scores were significantly improved compared with the preoperative scores (P < 0.05), and the symptoms disappeared gradually. Fifty-one patients (87.9%) achieved grade I fusion radiographically at the final follow-up.

CONCLUSIONS

MIS TLIF using a hybrid construction of unilateral pedicle screws and a translaminar facet screw is safe and effective in the treatment of single-segment lower lumbar vertebral disease, and it can be used as an optimal choice for fixation and fusion of some single-segment lower lumbar vertebral diseases.

Do the Position and Orientation of the Crosslink Influence the Stiffness of Spinal Instrumentation?

STUDY DESIGN

Biomechanical study of double-level pedicle screw constructs with or without crosslinks (CL) in an unstable model.

OBJECTIVES

The purpose of this study is to investigate the optimal position and orientation of the CL.

SUMMARY OF BACKGROUND DATA

Several reports have described biomechanical research on such CL, but no definite consensus has been reached regarding the effects. Very few studies have examined the position and orientation of the CL. The question of where and how the CL should be clinically set remains unanswered.

METHODS

Ten cadaveric lumbar spines (L3-L5) of boars were used and 7 models were prepared by the sequential damage and spinal instrumentation of each specimen. Bending stiffness was measured in flexion, extension, lateral bending, and axial rotation for each model using 6-axis material tester under torque of 0 to ±3 N m. Results for each configuration were compared using analysis of variance and the Turkey-Kramer test.

RESULTS

In flexion, extension, and lateral bending, 7 models showed similar stiffness with no significant differences. In axial rotation, stiffness increased significantly (P<0.05) in the cephalic, central, caudal, and oblique CL models in comparison with that of the no CL model, and stiffness of the horizontal 2 CL and oblique 2 CL models was significantly higher than that of cephalic, central, caudal, and oblique CL models (P<0.05). However, no significant differences in stiffness were seen between cephalic, central, and caudal CL models, between the central and oblique CL models, or between the horizontal and oblique 2 CL models.

CONCLUSIONS

Concomitant use of CLs significantly increased axial rotational stiffness, even though stiffness in flexion, extension, and lateral bending was not increased. In addition, stiffness in axial rotation significantly improved with the use of 2 CLs instead of a single CL, and stiffness was unchanged by position and orientation of CL.

Biomechanical effect of interspinous process distraction height after lumbar fixation surgery: An in vitro model

Pedicle screw fixation may induce abnormal activity at adjacent segment and accelerate the degeneration of lumbar vertebrae. Dynamic stabilizers could provide an intermediate solution between conservative treatment and fusion surgery. Lumbar vertebral segment cephalad to instrumented fixation was the most common localization of adjacent segment degeneration. The aim of this study is to explore the use of interspinous process devices in the lumbar vertebral segment cephalad to fixation segment in changing the mechanical distribution and limiting abnormal activity of the spine. Eight specimens were tested in the following groups: intact group, instability group (bilateral facetectomy at L3-L4), fixation group (bilateral facetectomy and pedicle screw fixation at L3-L4), and hybrid fixation group (fixation at L3-L4 and simulating interspinous device implantation of 6, 8, 10, 12, 14, 16, and 18 mm at L2-L3). Range of motion, motion of vertebral body, and strain distribution change were recorded. The range of motion in extension with 16- and 18-mm hybrid constructs was significantly lower than intact, instability, and fixation groups. In flexion and lateral bending, the strain values of L4 inferior articular process with 18-mm hybrid construct have a significant difference compared with other groups. In axial rotation, under the condition of a contralateral state, the strain values of L2 superior articular process with 18-mm hybrid construct have a significant difference compared with intact and fixation groups. The strain value of the L4 inferior articular process had negative correlation with height distraction in three dimensions, except extension. A negative correlation between the strain value of the L2 superior articular process and distraction height was found in contralateral bending and contralateral axial rotation. Interspinous process devices above the fixation segment can change the mechanical distribution of the spine and limit activity in some of the segments of the spine, which may delay the degeneration of the adjacent segment.

Clinical efficacy of lumbar interbody fusion using a channel system combined with ozone therapy for the treatment of central-type L3-L4 lumbar disc herniation

The clinical efficacy of minimally invasive lumbar interbody fusion via the intervertebral foramen combined with ozone (O₃) therapy for the treatment of L3-L4 central-type lumbar disc herniation was explored. We recruited patients with sciatica who attended our hospital between July 2013 and October 2015 and underwent lumbar X-ray (anteroposterior and lateral view), lumbar flexion-extension radiographs, computed tomography, and magnetic resonance imaging after admission. Seventy-four patients with central-type lumbar disc herniation but no other complications were randomly selected and divided into the observation and control groups. The observation group comprised 37 patients treated with lumbar fusion using a channel system combined with O₃ therapy, whereas the control group comprised 37 patients treated with lumbar fusion alone. The effects of the two therapies were evaluated using visual analog scale, Japanese Orthopaedic Association, and MacNab scores. There was no significant difference in scores between the two groups before surgery (P>0.05). The scores of the observation group after treatment were significantly lower than those before surgery and those of the control group (P<0.05). One patient in the observation group experienced no obvious improvement in symptoms after surgery, and two patients in the control group experienced postoperative recurrence; these three patients subsequently underwent laminectomy combined with planted bone fusion and internal fixation. There was no significant difference in total efficacy rates between the two groups (P>0.05). Lumbar fusion using a channel system combined with O₃ therapy for the treatment of L3-L4 central-type lumbar disc herniation is safe and effective. It has the advantages of reduced trauma, fewer complications, and rapid pain relief, and it promotes the recovery of lumbar function. Strict mastery of the surgical indications is key to the success of the procedure; however, it is worth expanding its use in the clinical setting.

Biomechanical assessment of the effects of vertebral distraction-fusion techniques on the adjacent segment of canine cervical vertebrae

OBJECTIVE To assess effects of vertebral distraction-fusion techniques at a treated segment (C5-C6) and an adjacent segment (C4-C5) of canine cervical vertebrae. SAMPLE Cervical vertebrae harvested from cadavers of 10 skeletally mature Beagles. PROCEDURES Three models (intact, titanium plate, and polymethylmethacrylate [PM MA]) for stabilization of the caudal region of the cervical vertebrae (C4 through C7) were applied to the C5-C6 vertebral segment sequentially on the same specimens. Biomechanical assessments with flexion-extension, lateral bending, and axial rotational tests were conducted after each procedure. Range of motion (ROM) for a torque load applied with a 6-axis material tester was measured at C4-5 and C5-6 and calculated by use of a 3-D video measurement system. RESULTS In both the plate and PMMA models, ROM significantly increased at C4-5 and significantly decreased at C5-6, compared with results for the intact model. The ROM at C5-6 was significantly lower for the plate model versus the PMMA model in lateral bending and for the PMMA model versus the plate model in axial rotation. Conversely, ROM at C4-5 was significantly higher in axial rotation for the PMMA model versus the plate model. No significant differences were identified in flexion-extension between the PMMA and plate models at either site. CONCLUSIONS AND CLINICAL RELEVANCE Results of this study suggested that vertebral distraction and fusion of canine vertebrae can change the mechanical environment at, and may cause disorders in, the adjacent segment. Additionally, findings suggested that effects on the adjacent segment differed on the basis of the fusion method used.

Biomechanical study of rotational micromovement of the pedicle screw

Background

In regard to the fixation using a pedicle screw (PS) and rod system, the mechanism from the onset of the clear zone up to the development of loosening of the pedicle screw is not completely clarified. The purpose of this study is to determine the cause of the pedicle screw loosening by performing a biomechanical study with three-dimensional movie analysis.

Methods

Ten PS fixation model of the lumbar spines (L3–4) of boar cadavers were used. The rotational angles of the L3 and L4 vertebral body and the screw at the time of applying a ±5 Nm load in the left anterior and right posterior flexion directions respectively were calculated based on those at the time of applying no load. The absolute value of the difference in the rotational angles between each vertebral body with left anterior flexion and right posterior flexion and the inserted screws was defined as rotational micromovement.

Results

In both the left anterior and right posterior flexion directions, there were significant differences (p < 0.05) in the rotational angles between the screw and the vertebral body for both the L3 and L4 vertebral bodies.

Conclusion

Our biomechanical results showed that rotational micromovement occurred between the PS and the vertebral body, and repeated rotational micromovement might cause loosening of the screw or pullout of PS fixation.

Mixed Fixation and Interbody Fusion for Treatment Single-Segment Lower Lumbar Vertebral Disease: Midterm Follow-up Results

OBJECTIVE

To investigate the midterm outcomes of unilateral pedicle screws combined with contralateral gunsight-guided translaminar facet screw fixation and interbody fusion for treatment of single-segment lower lumbar vertebral disease.

METHODS

A total of 78 patients with various lower lumbar single-segment vertebral diseases were treated in our department from January 2008 to December 2011. There were 21 males and 57 females, with an average age of 52.5 years, including lumbar disc degeneration (28 cases), local recurrence of lumbar disc herniation (9 cases), huge lumbar disc herniation (11 cases), lumbar disc herniation with spinal stenosis (13 cases), and lumbar degenerative spondylolisthesis (degree I) (17 cases). All patients were treated by unilateral pedicle screws in the median incision combined with contralateral gunsight-guided translaminar facet screw fixation and interbody fusion.

RESULTS

No wound infection or skin necrosis around incision was observed after operation. No leakage of cerebrospinal fluid or nerve injury occurred during and after operation. Excepting 4 cases, 74 cases were followed up for 18-60 months, averaged 33.5 months. All but one patient (98.6%) received interbody fusion. The intervertebral height of the indexed level was well restored and maintained. At final follow-up. During follow-up, there was no screw loosening or pedicle fracture observed. No apparent degeneration of adjacent segments. The mean Japanese Orthopaedic Association (JOA) scores was increased significantly from 12.79 ± 2.12 preoperatively to 25.8 ± 2.87 at the final follow-up.

CONCLUSION

Unilateral pedicle screw fixation combined with contralateral translaminar facet screw fixation and interbody fusion showed good mid-term outcomes in the treatment of single-segment lower lumbar vertebral disease, and can be used as an optimal choice for fixation and fusion of some single-segment lower lumbar vertebral diseases.

Biomechanical comparison of unilateral semi-rigid and dynamic stabilization on ovine vertebrae

Using the unilateral pedicle screw fixation was thought to decrease the stiffness of the fixed segments. Various prospective, randomized studies were performed to determine whether unilateral pedicle screw fixation provides the necessities of bilateral fixation in one- or two-segment lumbar spinal fusion. In this study, four different unilateral pedicle screw fixation systems were evaluated to determine which one best approximated an intact spine with respect to biomechanics and kinematics. The four groups included an intact group, a unilateral facetectomy group with no fixation, a unilateral semi-rigid pedicle screw fixation group with a poly-ether-ether-ketone rod, and a unilateral dynamic pedicle screw fixation group. The bone mineral densities of all specimens were measured and specimens were matched with groups randomly. Flexion, lateral bending, and axial rotation tests were performed to compare the groups. For the flexion, lateral bending, and axial rotation tests, the best biomechanical outcomes were in the control group. The unilateral facetectomy group had the poorest performance and was not stable enough, compared with the control group. The dynamic and semi-rigid groups showed performance closer to that of the control group. The biomechanical responses of these two groups were also in good agreement, showing no significant statistical differences. Based on these test results, it is concluded that the unilateral dynamic and semi-rigid pedicle screw fixations can be used to provide stability to the vertebrae.

Biomechanical study of unilateral pedicle screw combined with contralateral translaminar facet screw in transforaminal lumbar interbody fusion

BACKGROUND

The biomechanical stability of unilateral pedicle screw (UPS) combined with contralateral translaminar facet screw (TLFS), especially long-term stability, still needs to be compared to traditional UPS or bilateral pedicle screws (BPSs) in details.

METHODS

Twenty-four porcine spines (L2-L5) were tested for flexibility with pure moments of 5Nm under intact status and transforaminal lumbar interbody fusion status using UPS+TLFS, UPS or BPS at L3-L4. After short-term (3cycles) and long-term cyclic loading (18,000cycles), the range of motion was obtained and analyzed for single-level constructs in flexion/extension, lateral bending and axial rotation modes. In addition, the relative displacement of contralateral articular processes was recorded in a real time fashion.

FINDINGS

The range of motion was significantly reduced in all instrumented constructs. In all movement directions, UPS+TLFS achieved similar range of motion to BPS after short and long-term loading, which were significantly lower than that in UPS. A significantly larger displacement of contralateral articular process was recorded in UPS than UPS+TLFS and BPS during extension/flexion, lateral bending and axial rotation, suggesting its compromised stability.

INTERPRETATION

The hybrid construct of UPS+TLFS showed instant and long-term equivalent biomechanical ability to that of traditional BPS, making it an alternative option to BPS that could be less invasive while maintains a stable and effective instrumentation.

Limited Unilateral Decompression and Pedicle Screw Fixation with Fusion for Lumbar Spinal Stenosis with Unilateral Radiculopathy: A Retrospective Analysis of 25 Cases

OBJECTIVE

Lumbar spinal stenosis is conventionally treated with surgical decompression. However, bilateral decompression and laminectomy is more invasive and may not be necessary for lumbar stenosis patients with unilateral radiculopathy. We aimed to report the outcomes of unilateral laminectomy and bilateral pedicle screw fixation with fusion for patients with lumbar spinal stenosis and unilateral radiculopathy.

METHODS

Patients with lumbar spinal stenosis with unilateral lower extremity radiculopathy who received limited unilateral decompression and bilateral pedicle screw fixation were included and evaluated using visual analog scale (VAS) pain and the Oswestry Disability Index (ODI) scores preoperatively and at follow-up visits. Ligamentum flavum thickness of the involved segments was measured on axial magnetic resonance images.

RESULTS

Twenty-five patients were included. The mean preoperative VAS score was 6.6±1.6 and 4.6±3.1 for leg and back pain, respectively. Ligamentum flavum thickness was comparable between the symptomatic and asymptomatic side (p=0.554). The mean follow-up duration was 29.2 months. The pain in the symptomatic side lower extremity (VAS score, 1.32±1.2) and the back (VAS score, 1.75±1.73) significantly improved (p=0.000 vs. baseline for both). The ODI improved significantly postoperatively (6.60±6.5; p=0.000 vs. baseline). Significant improvement in VAS pain and ODI scores were observed in patients receiving single or multi-segment decompression fusion with fixation (p<0.01).

CONCLUSION

Limited laminectomy and unilateral spinal decompression followed by bilateral pedicle screw fixation with fusion achieves satisfactory outcomes in patients with spinal stenosis and unilateral radiculopathy. This procedure is less damaging to structures that are important for maintaining posterior stability of the spine.

Minimally invasive unilateral versus bilateral technique in performing single-segment pedicle screw fixation and lumbar interbody fusion

Purpose

The minimally invasive transforaminal lumbar interbody fusion procedure with percutaneous pedicle screws was adopted in clinical practice, but the choice between a unilateral pedicle screw (UPS) or bilateral pedicle screw (BPS) fixation after lumbar fusion remains controversial. The purpose of the present retrospective study was to compare the clinical outcomes and radiological results of unilateral and bilateral pedicle screw fixations.

Methods

The retrospective study recruited seventy-eight patients with a single-level pedicle screw fixation and lumbar interbody fusion at L4–L5 or L5–S1 from January 2010 to January 2013. The patients were treated with MIS TLIF with BPS fixation, and since May 2012, all patients were treated with UPS fixation. The perioperative outcomes including operative time, blood loss, hospital-stay length, and complication rates were accessed. Radiological outcomes regarding fusion were determined with the Bridwell grading system. Clinical outcomes were evaluated with the Oswestry Disability Index (ODI) and visual analog scale (VAS) during the mean follow-up of 2 years.

Results

According to perioperative assessments, the operative time was significantly shorter for group UPS (84.7 ± 6.4 min) than for group BPS (103.6 ± 10.6 min; p < 0.0001), and similar results were found with regard to the mean blood loss (UPS, 96.3 ± 17.5; BPS, 137.4 ± 32.9, p < 0.0001). With regard to the hospital-stay period, though the UPS group seems shorter, there is no statistical significance (UPS, 10.0 ± 2.1; BPS, 10.4 ± 2.4, p = 0.428). There were four in the BPS group and six in the UPS group defined as unfused at 6 months pest-operative, but at 12 months post-surgery, all patients achieved solid fusion. Regarding clinical outcomes, the VAS and ODI scores were significantly lower in the UPS group than the BPS group at 7 days post-surgery, but there was no difference at 1 month post-surgery and during the later follow-up.

Conclusion

There was no difference between the UPS and BPS flexion techniques about the clinical outcomes at 24 months post-surgery. However, because the UPS involves a shorter surgical time, less blood loss, faster pain relief, and faster functional recovery, UPS might be more suitable in performing single-segment pedicle screw fixation and lumbar interbody fusion.

Clinical and radiological outcomes of unilateral versus bilateral instrumentation in two-level degenerative lumbar diseases

PURPOSE

To compare the clinical and radiological outcomes of unilateral versus bilateral instrumented in two-level degenerative lumbar diseases after minimally invasive transforaminal lumbar interbody fusion (MITLIF).

METHODS

We conducted a prospective cohort study of 74 patients, who underwent unilateral or bilateral instrumented in two-level MITLIF for degenerative lumbar diseases from May 2010 to June 2012. There were 35 patients in group A undergoing unilateral pedicle screw fixation and 39 patients in group B undergoing bilateral pedicle screw fixation. Demographic data and clinical characteristics were compared between the two groups before surgery. Perioperative data, clinical and radiological outcomes of the two groups were also compared.

RESULTS

The mean follow-up period was 32.1 ± 7.5 months for group A and 31.7 ± 8.0 months for group B (p > 0.05). Group A required a significantly shorter operating time, lower implant costs and less intraoperative blood loss and X-ray exposure time than group B (p < 0.01). However, no statistical differences were identified in the amount of transfusion and postoperative hospital stay between the two groups (p > 0.05). Clinical outcomes assessed by visual analog scores for back and leg pain (VAS-BP and VAS-LP, respectively) and Oswestry Disability Index (ODI) improved significantly in both groups after surgery, and no significant differences existed between the two groups at each postoperative follow-up (p > 0.05). There were significant differences within groups for Cobb angles of the whole lumbar [Cobb (a)] and the whole lumbar lordosis at each time point before and after surgery (p < 0.05). No significant differences existed between groups in relation to Cobb (a), Cobb angle of the fused segments, lumbar lordosis and the segmental lordosis at any time point before and after surgery (p > 0.05). There were no significant differences in fusion rate and total complication rate between the two groups (p > 0.05).

CONCLUSIONS

Unilateral instrumentation after two-level MITLIF provided similar clinical and radiological outcomes to bilateral fixation in two-level degenerative lumbar diseases. Compared with bilateral fixation, unilateral fixation shortens operation time, reduces intra-operative blood loss and X-ray exposure time, and saves medical expenses with similar postoperative hospital stay and complication rate.

Unilateral versus bilateral pedicle screw fixation for degenerative lumbar diseases: a meta-analysis of 10 randomized controlled trials

Background

The common and effective treatment for degenerative lumbar diseases is lumbar spinal fusion. Controversy still exists on the choice for instrumentation with spinal fusion procedures. Therefore, we conducted this meta-analysis exclusively of RCTs to compare the clinical outcomes of patients receiving bilateral versus unilateral pedicle screw fixation (PSF).

Material/Methods

After systematic review of published and unpublished literature, a meta-analysis was conducted to compare the 2 treatment strategies. The methodological quality of the literature was assessed using the PEDro critical appraisal tool.

Results

Data synthesis showed less blood loss (P<0.001) and shorter operative time (P<0.001) in patients receiving unilateral PSF compared to bilateral PSF. However, there was no significant difference in fusion rates and functional outcomes between the 2 groups.

Conclusions

The meta-analysis indicated no significant difference in fusion rates and functional outcomes between the 2 treatment procedures, but unilateral PS fixation reduced blood loss and operative time.

The current testing protocols for biomechanical evaluation of lumbar spinal implants in laboratory setting: a review of the literature

In vitro biomechanical investigations have become a routinely employed technique to explore new lumbar instrumentation. One of the most important advantages of such investigations is the low risk present when compared to clinical trials. However, the best use of any experimental data can be made when standard testing protocols are adopted by investigators, thus allowing comparisons among studies. Experimental variables, such as the length of the specimen, operative level, type of loading (e.g., dynamic versus quasistatic), magnitude, and rate of load applied, are among the most common variables controlled during spinal biomechanical testing. Although important efforts have been made to standardize these protocols, high variability can be found in the current literature. The aim of this investigation was to conduct a systematic review of the literature to identify the current trends in the protocols reported for the evaluation of new lumbar spinal implants under laboratory setting.

A meta-analysis of unilateral versus bilateral pedicle screw fixation in minimally invasive lumbar interbody fusion

STUDY DESIGN

Meta-analysis.

BACKGROUND

Bilateral pedicle screw fixation (PS) after lumbar interbody fusion is a widely accepted method of managing various spinal diseases. Recently, unilateral PS fixation has been reported as effective as bilateral PS fixation. This meta-analysis aimed to comparatively assess the efficacy and safety of unilateral PS fixation and bilateral PS fixation in the minimally invasive (MIS) lumbar interbody fusion for one-level degenerative lumbar spine disease.

METHODS

MEDLINE/PubMed, EMBASE, BIOSIS Previews, and Cochrane Library were searched through March 30, 2014. Randomized controlled trials (RCTs) and controlled clinical trials (CCTs) on unilateral versus bilateral PS fixation in MIS lumbar interbody fusion that met the inclusion criteria and the methodological quality standard were retrieved and reviewed. Data on participant characteristics, interventions, follow-up period, and outcomes were extracted from the included studies and analyzed by Review Manager 5.2.

RESULTS

Six studies (5 RCTs and 1 CCT) involving 298 patients were selected. There were no significant differences between unilateral and bilateral PS fixation procedures in fusion rate, complications, visual analogue score (VAS) for leg pain, VAS for back pain, Oswestry disability index (ODI). Both fixation procedures had similar length of hospital stay (MD = 0.38, 95% CI = -0.83 to 1.58; P = 0.54). In contrast, bilateral PS fixation was associated with significantly more intra-operative blood loss (P = 0.002) and significantly longer operation time (P = 0.02) as compared with unilateral PS fixation.

CONCLUSIONS

Unilateral PS fixation appears as effective and safe as bilateral PS fixation in MIS lumbar interbody fusion but requires less operative time and causes less blood loss, thus offering a simple alternative approach for one-level lumbar degenerative disease.

Biomechanical and anatomical considerations in lumbar spinous process fixation--an in vitro human cadaveric model

BACKGROUND CONTEXT

Although multiple mechanisms of device attachment to the spinous processes exist, there is a paucity of data regarding lumbar spinous process morphology and peak failure loads.

PURPOSE

Using an in vitro human cadaveric spine model, the primary objective of the present study was to compare the peak load and mechanisms of lumbar spinous process failure with variation in spinous process hole location and pullout direction. A secondary objective was to provide an in-depth characterization of spinous process morphology.

STUDY DESIGN

Biomechanical and anatomical considerations in lumbar spinous process fixation using an in vitro human cadaveric model.

METHODS

A total of 12 intact lumbar spines were used in the current investigation. The vertebral segments (L1-L5) were randomly assigned to one of five treatment groups with variation in spinous process hole placement and pullout direction: (1) central hole placement with superior pullout (n=10), (2) central hole placement with inferior pullout (n=10), (3) inferior hole placement with inferior pullout (n=10), (4) superior hole placement with superior pullout (n=10), and (5) intact spinous process with superior pullout (n=14). A 4-mm diameter pin was placed through the hole followed by pullout testing using a material testing system. As well, the bone mineral density (BMD) (g/cm(3)) was measured for each segment. Data were quantified in terms of anatomical dimensions (mm), peak failure loads (newtons [N]), and fracture mechanisms, with linear regression analysis to identify relationships between anatomical and biomechanical data.

RESULTS

Based on anatomical comparisons, there were significant differences between the anteroposterior and cephalocaudal dimensions of the L5 spinous process versus L1-L4 (p<.05). Statistical analysis of peak load at failure of the four reconstruction treatments and intact condition demonstrated no significant differences between treatments (range, 350-500 N) (p>.05). However, a significant linear correlation was observed between peak failure load and anteroposterior and cephalocaudal dimensions (p<.05). Correlation between BMD and peak spinous processes failure load was approaching statistical significance (p=.08). 30 of 54 specimens failed via direct pullout (plow through), whereas 8 of 54 specimens demonstrated spinous process fracture. The remaining cases failed via plow through followed by fracture of the spinous process (16 of 54; 29%).

CONCLUSIONS

The present study demonstrated that variation in spinous process hole placement did not significantly influence failure load. However, there was a strong linear correlation between peak failure load and the anteroposterior and cephalocaudal anatomical dimensions. From a clinical standpoint, the findings of the present study indicate that attachment through the spinous process provides a viable alternative to attachment around the spinous processes. In addition, the anatomical dimensions of the lumbar spinous processes have a greater influence on biomechanical fixation than either hole location or BMD.

Minimally invasive transforaminal lumbar interbody fusion with unilateral pedicle screw fixation: comparison between primary and revision surgery

Minimally invasive surgery with a transforaminal lumbar interbody fusion (MIS TLIF) is an important minimally invasive fusion technique for the lumbar spine. Lumbar spine reoperation is challenging and is thought to have greater complication risks. The purpose of this study was to compare MIS TLIF with unilateral screw fixation perioperative results between primary and revision surgeries. This was a prospective study that included 46 patients who underwent MIS TLIF with unilateral pedicle screw. The patients were divided into two groups, primary and revision MIS TLIF, to compare perioperative results and complications. The two groups were similar in age, sex, and level of operation, and were not significantly different in the length of follow-up or clinical results. Although dural tears were more common with the revision group (primary 1; revision 4), operation time, blood loss, total perioperative complication, and fusion rates were not significantly different between the two groups. Both groups showed substantial improvements in VAS and ODI scores one year after surgical treatment. Revision MIS TLIF performed by an experienced surgeon does not necessarily increase the risk of perioperative complication compared with primary surgery. MIS TLIF with unilateral pedicle screw fixation is a valuable option for revision lumbar surgery.

Unilateral versus bilateral percutaneous pedicle screw fixation in minimally invasive transforaminal lumbar interbody fusion

OBJECT

Clinical results for unilateral pedicle screw fixation after lumbar interbody fusion have been reported to be as good as those for bilateral instrumentation. However, no studies have directly compared unilateral and bilateral percutaneous pedicle screw fixation after minimally invasive surgery (MIS) for transforaminal lumbar interbody fusion (TLIF). The purpose of this study was to determine whether unilateral percutaneous pedicle screw fixation is comparable with bilateral percutaneous pedicle screw fixation in 1-segment MIS TLIF.

METHODS

This was a prospective randomized study of 53 patients who underwent unilateral or bilateral percutaneous pedicle screw fixation after MIS TLIF for 1-segment lumbar degenerative disc disease. Twenty-six patients were assigned to a unilateral percutaneous pedicle screw fixation group and 27 patients were assigned to a bilateral percutaneous pedicle screw fixation group. Operative time, blood loss, clinical outcomes (that is, Oswestry Disability Index [ODI] and visual analog scale [VAS] scores), complication rates, and fusion rates were assessed using CT scanning 2 years after surgical treatment.

RESULTS

The 2 groups were similar in age, sex, preoperative diagnosis, and operated level, and they did not differ significantly in the length of follow-up (27.5 [Group 1] vs 28.9 [Group 2] months) or clinical results. Both groups showed substantial improvements in VAS and ODI scores 2 years after surgical treatment. The groups differed significantly in operative time (unilateral 84.2 minutes; bilateral 137.6 minutes), blood loss (unilateral 92.7 ml; bilateral, 232.0 ml), fusion rate (unilateral 84.6%; bilateral 96.3%), and postoperative scoliotic change (unilateral 23.1%; bilateral 3.7%).

CONCLUSIONS

Unilateral and bilateral screw fixation after MIS TLIF produced similar clinical results. Although perioperative results were better with unilateral screw fixation, the long-term results were better with bilateral screw fixation, suggesting bilateral screw fixation is a better choice after MIS TLIF.

Comparison of unilateral versus bilateral pedicle screw fixation in lumbar interbody fusion: a meta-analysis

PURPOSE

This is a meta-analysis to compare the clinical results between unilateral and bilateral pedicle screw (PS) fixation in lumbar interbody fusion.

METHODS

We included published studies with no language and year restrictions. The criteria which Koes et al. designed in 1995 were used to evaluate the risk of bias of the included studies. All data were analyzed by Review Manager 5.1. The primary outcomes included fusion rate and screw complications, and the secondary outcomes were operative time, blood loss, and hospital time.

RESULTS

A total of five prospective studies with 407 patients were included in the current meta-analysis, and four of them were randomized controlled trials. There was no significant difference between unilateral PS fixation and bilateral PS fixation group in fusion rate and screw complications (fusion rate: OR 0.54, Z = 1.33, P = 0.18, I (2) = 0 %; screw complications: OR 1.45, Z = 0.71, P = 0.48; I (2) = 44 %). In the secondary outcomes, the operative time (Z = 3.35, P = 0.0008; I (2) = 95 %) and blood loss (Z = 4.35, P < 0.0001; I (2) = 98 %) was significantly higher in bilateral PS fixation group than in unilateral PS fixation group. Besides, no significant difference was found in hospital time (Z = 1.19, P = 0.24; I (2) = 99 %).

CONCLUSIONS

In our meta-analysis, we found that unilateral PS fixation in lumbar fusion was as effective as bilateral PS fixation for lumbar degenerative diseases without major instability, no significant difference was found in hospital time, fusion rate and screw complications. In terms of operative time and blood loss, unilateral PS fixation even produced better results.

Comparison of lumbar interbody fusion performed with unilateral or bilateral pedicle screw

Currently, bilateral pedicle screw fixation is the standard of instrumentation, providing rigid fixation and an increased fusion rate. However, due to the excessive rigidity of the system, this instrumentation has been suspected to cause degeneration of adjacent segments. Alternatively, less rigid unilateral pedicle fixation is considered to be as effective as bilateral constructs. Few studies have compared unilateral and bilateral constructs in the treatment of lumbar degenerative disease. The purpose of this retrospective study was to evaluate possible differences between unilateral and bilateral pedicle screw fixation for single-level lumbar degenerative disease.Between October 2006 and October 2010, sixty consecutive patients were treated with unilateral pedicle screw fixation (28 patients) or bilateral pedicle screw fixation (32 patients) at the authors' institution. Oswestry Disability Index and visual analog scale scores showed a statistical difference between preoperative values and 3- and 6-month postoperative values (P<.05). Unilateral fixation resulted in shorter operative times and less intraoperative blood loss. No significant difference was found between the 2 fixation methods in terms of fusion rate and complication rate (P>.05).Lumbar interbody fusion with unilateral pedicle screw fixation was an effective and convenient method of treatment of single-level lumbar degenerative disease, with little surgical trauma.

Comparative study of unilateral and bilateral pedicle screw fixation in posterior lumbar interbody fusion

A prospective, randomized clinical study was performed to determine whether unilateral pedicle screw fixation was comparable with bilateral fixation in 1- or 2-segment lumbar interbody fusion. One hundred eight patients with lumbar degenerative diseases were randomly assigned to the unilateral (n=56) or bilateral (n=52) pedicle screw fixation group. Interbody fusion was performed in 1 or 2 levels with 1 cage. Operative time, blood loss, duration of hospital stay, functional outcome, fusion rate, and complication rate were recorded and compared statistically. The patients were followed for 3 years postoperatively.Successful radiographic fusion was documented in all patients. No flexion-extension hypermobility or pedicle screw loosening or breakage occurred during the follow-up period. No significant difference existed between the 2 groups when comparing the union rate, complication rate, and functional outcome scores (P>.05). However, compared with the bilateral pedicle screw group, a significant decrease occurred in operative time, duration of hospital stay, and blood loss in the unilateral group (P<.01). Unilateral pedicle screw fixation was as effective as bilateral fixation when performed in addition to 1- or 2-level lumbar interbody fusion. The authors recommend the use of unilateral fixation in lumbar interbody fusion with 1 cage for lumbar degenerative diseases without major instability.

A prospective randomized controlled study comparing transforaminal lumbar interbody fusion techniques for degenerative spondylolisthesis: unilateral pedicle screw and 1 cage versus bilateral pedicle screws and 2 cages

OBJECT

Many surgeons currently prefer to use transforaminal lumbar interbody fusion (TLIF), placing 1 unilateral pedicle screw (PS) and 1 cage. However, no study has examined whether unilateral fixation improves surgical outcome. The authors conducted a prospective randomized controlled trial with a minimum 2-year follow-up to analyze TLIF outcomes for 2 techniques: placement of a unilateral PS and a cage compared with placement of bilateral PSs and 2 cages.

METHODS

Fifty patients with degenerative spondylolisthesis undergoing single-level TLIF were randomly assigned to receive either unilateral or bilateral fixation. Parameters compared between the groups were surgical invasiveness, severity of intermittent claudication, pre- and postoperative visual analog scale (VAS) scores (from 0 to 10 for back pain, lower-extremity pain, and lower-extremity numbness), postoperative disability scores for lumbar spinal disorders (Japanese Orthopaedic Association Back Pain Evaluation Questionnaire [JOABPEQ]), and fusion rates.

RESULTS

The mean operative time for TLIF was significantly (p = 0.05) shorter and mean estimated blood loss was significantly lower in the unilateral than in the bilateral group. Intermittent claudication improved in response to each technique, but there was no significant intergroup difference. The unilateral group had a nonsignificant tendency toward less improvement in VAS score for back pain (1.5 vs 3.7 for the bilateral group) and exhibited significantly less improvement in VAS score for lower-extremity pain (2.1 vs 5.1, respectively) and numbness (1.7 vs 4.4). There were no significant differences between the groups in postsurgical scores for all 5 items of the JOABPEQ. The fusion rates were 87.5% (21 of 24 patients) in the unilateral group and 95.7% (22 of 23) in the bilateral group.

CONCLUSIONS

Transforaminal lumbar interbody fusion involving unilateral PS fixation and a single-cage technique is less invasive than a 2-cage technique and bilateral fixation, and it improved patients' symptoms. However, it resulted in less improvement in back pain, lower-extremity pain, and lower-extremity numbness. When considering unilateral PS fixation and a single cage, the surgeon should be aware of the potential limitations of this technique. Clinical trial registration no.: UMIN000007833 (UMIN).

Posterior interbody fusion using a diagonal cage with unilateral transpedicular screw fixation for lumbar stenosis

Few reports have described the combined use of unilateral pedicle screw fixation and interbody fusion for lumbar stenosis. We retrospectively reviewed 79 patients with lumbar stenosis. The rationale and effectiveness of unilateral pedicle screw fixation were studied from biomechanical and clinical perspectives, aiming to reduce stiffness of the implant. All patients were operated with posterior interbody fusion using a diagonal cage in combination with unilateral transpedicular screw fixation and had reached the 3-year follow-up interval after operation. The mean operating time was 115 minutes (range=95-150 min) and the mean estimated blood loss was 150 mL (range=100-200 mL). The mean duration of hospital stay was 10 days (range=7-15 days). Clinical outcomes were assessed prior to surgery and reassessed at intervals using Denis' pain and work scales. Fusion status was determined from X-rays and CT scans. At the final follow-up, the clinical results were satisfactory and patients showed significantly improved scores (p<0.01) either on the pain or the work scale. Successful fusion was achieved in all patients. There were no new postoperative radiculopathies, or instances of malpositioned or fractured hardware. Posterior interbody fusion using a diagonal cage with unilateral transpedicular fixation is an effective treatment for decompressive surgery for lumbar stenosis.