Posterior lumbar interbody fusion for adult isthmic spondylolisthesis

Fusion Surgery for Lumbar Spondylolisthesis: A Systematic Review with Network Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

This study aimed to systematically evaluate the optimal surgical fusion approach for lumbar spondylolisthesis, to provide the latest and most reliable evidence for future clinical practice.

METHODS

A comprehensive search of the PubMed, Ovid-Embase, Web of Science, Cochrane, and Scopus databases was conducted from inception to September 1, 2023, to identify relevant records. Two independent reviewers performed the literature screening, data extraction, and assessment of study quality.

RESULTS

Fifteen randomized controlled trials involving 892 patients met the inclusion criteria. The network evidence plot showed that posterolateral fusion and posterior lumbar interbody fusion (PLIF) were the most used fusion techniques. The network meta-analysis results revealed that minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) had a significantly greater improvement in the Oswestry Disability Index (ODI) compared to endoscopic-TLIF, while PLIF had a significantly better fusion effect than posterolateral fusion. Furthermore, no statistically significant differences were observed between other fusion surgeries in terms of improving ODI, fusion rate, complications, or the improvement of visual analog scale-low back pain. The surface under the cumulative ranking curve results indicated that MIS-TLIF had the greatest potential for improving ODI, visual analog scale-low back pain, and complications, while PLIF had the greatest potential for increasing fusion rates. However, the existing selection bias, measurement bias, reporting bias, and publication bias may have reduced the reliability of the meta-analysis results.

CONCLUSIONS

Among the various fusion surgeries for lumbar spondylolisthesis, MIS-TLIF appears to provide the greatest benefit to patients. However, more high-quality, large-scale studies are needed to further investigate the treatment efficacy of different fusion surgeries for lumbar spondylolisthesis.

Comparison of Fusion Rates among Various Demineralized Bone Matrices in Posterior Lumbar Interbody Fusion

Background and Objectives: Posterior lumbar interbody fusion (PLIF) plays a crucial role in addressing various spinal disorders. The success of PLIF is contingent upon achieving bone fusion, as failure can lead to adverse clinical outcomes. Demineralized bone matrix (DBM) has emerged as a promising solution for promoting fusion due to its unique combination of osteoinductive and osteoconductive properties. This study aims to compare the effectiveness of three distinct DBMs (Exfuse®, Bongener®, and Bonfuse®) in achieving fusion rates in PLIF surgery. Materials and Methods: A retrospective review was conducted on 236 consecutive patients undergoing PLIF between September 2016 and February 2019. Patients over 50 years old with degenerative lumbar disease, receiving DBM, and following up for more than 12 months after surgery were included. Fusion was evaluated using the Bridwell grading system. Bridwell grades 1 and 2 were defined as 'fusion', while grades 3 and 4 were considered 'non-fusion.' Clinical outcomes were assessed using visual analog scale (VAS) scores for pain, the Oswestry disability index (ODI), and the European quality of life-5 (EQ-5D). Results: Fusion rates were 88.3% for Exfuse, 94.3% for Bongener, and 87.7% for Bonfuse, with no significant differences. All groups exhibited significant improvement in clinical outcomes at 12 months after surgery, but no significant differences were observed among the three groups. Conclusions: There were no significant differences in fusion rates and clinical outcomes among Exfuse, Bongener, and Bonfuse in PLIF surgery.

Comparison of Fusion Rate and Functional Outcome Between Local Cancellous Bone Plus Demineralized Bone Matrix and Local Bone in 1-Level Posterior Lumbar Interbody Fusion

STUDY DESIGN

Retrospective study with prospectively collected data.

OBJECTIVE

The purpose of this study is to investigate the difference in fusion rate and clinical outcome of patients with local bone as filler for the graft and demineralized bone matrix (DBM) plus only the cancellous bone from local bone as a filler for cage in 1-level posterior lumbar interbody fusion (PLIF) with cage.

SUMMARY OF BACKGROUND DATA

Cancellous bone is more advantageous than cortical bone in the local bone for improving bone formation in spine fusion surgery. There are little studies on the difference in fusion rate and reduction of fusion time using only these cancellous bones.

METHODS

Of the 40 patients who underwent 1-level PLIF using cage, 20 patients in group A used local bone and 20 patients in group B used mixture of cancellous bone extracted separately from local bone and commercially available DBM as filler for cage. Changes in fusion rate and intervertebral spacing were measured using lateral radiography, and fusion was determined as nonunion using the Brantigan-Steffee classification. The clinical outcome was evaluated.

RESULTS

There was no difference in height change over time between the two groups. Regarding union grade, group B showed better union grade than group A. However, no difference in union grade change over time was observed between the 2 groups. In group B, Oswestry Disability Index (ODI), Rolland-Morris Disability Questionnaire (RMDQ), and SF-36 mental component score (MCS) significantly decreased, but there was no difference in change over time.

CONCLUSIONS

In 1-level PLIF for degenerative lumbar disease, better fusion rate was observed in the group that used only cancellous bone from local bone plus DBM than that in the group that used local bone; however, there was no difference in fusion grade change over time in the 2 groups.

Modified Lumbosacral Angle and Modified Pelvic Incidence as New Parameters for Management of Pediatric High-grade Spondylolisthesis

STUDY DESIGN

Retrospective clinical study.

OBJECTIVE

We aimed to introduce new parameters that can better describe the pelvic morphology and lumbosacral segmental deformity in children with high-grade spondylolisthesis of the L5 vertebra: modified pelvic incidence (mPI) and modified lumbosacral angle (mLSA). Also, we aimed to establish the mLSA as a convenient, reliable measurement method and criteria to evaluate the reduction of L5 vertebral slippage.

SUMMARY OF BACKGROUND DATA

Numerous parameters and methods exist to evaluate segmental deformity and reduction of L5 vertebral slippage, but no definitive standard for accurately and conveniently describing lumbosacral kyphosis and degree of reduction exists.

METHODS

A total of 24 children with high-grade spondylolisthesis (S group) and 152 children without spondylolisthesis (non-S group) underwent standard lateral radiography of the spine in our hospital between June 2009 and June 2014. We compared mPI and mLSA between the S and non-S groups. The agreement and repeatability of mPI and mLSA were also assessed. Preoperative and postoperative Japanese Orthopaedic Association (JOA) and Scoliosis Research Society (SRS)-22 scores were compared to assess clinical outcomes in the S group. The correlations between modified parameter applications and clinical outcomes were also assessed.

RESULTS

While mPI did not differ between groups, mLSA differed significantly. In the non-S group, mLSA was lordotic (25.51±6.41 degrees). In the S group, mLSA was kyphotic (25.85±5.17 degrees) before surgery and lordotic (20.74±7.04 degrees) postoperatively. The agreement and repeatability of mPI and mLSA were good, and clinical outcomes of the S group were satisfactory. Positive correlations were found between modified parameter applications and the improvement rates of JOA scores.

CONCLUSIONS

mPI and mLSA can better describe the pelvic morphology and local deformity of pediatric high-grade L5 spondylolisthesis, and mLSA can serve as a useful index for correcting lumbosacral kyphosis, rebalancing the sagittal spinal profile and predicting clinical outcomes.

Cross-Sectional Area of the Lumbar Spine Trunk Muscle and Posterior Lumbar Interbody Fusion Rate: A Retrospective Study

STUDY DESIGN

A retrospective study.

OBJECTIVE

To investigate the relationship between trunk muscle cross-sectional area (MCSA) and fusion rate after posterior lumbar interbody fusion using pedicle screw fixation (PLIF-PSF).

SUMMARY OF BACKGROUND DATA

Although trunk muscles of the lumbar spine contribute to spinal stability and alignment, effect of trunk muscles on spinal fusion rate and time to fusion is unclear.

METHODS

A total of 192 adult patients with degenerative lumbar disease who underwent PLIF-PSF at L3-L4 or L4-L5 were included. The MCSA of the flexor (psoas major, PS), extensor (erector spinae, ES; multifidus, MF) were measured using preoperative lumbar magnetic resonance imaging at 3 segments. Bone union was evaluated using lumbar dynamic plain radiography. Patients were divided into 2 groups according to the presence of bone fusion.

RESULTS

Most PS MCSAs in the fusion group were significantly larger than in the nonfusion group, except for MCSA at the L2-L3 segment (all P<0.05). In cases of ES and MF MCSAs, 4 of 6 segments were significantly large. Multivariate analysis revealed that the PS MCSA at L4-L5 was an independent factor for decreased possibility of nonfusion status in both segments (OR=0.812, P=0.028). Pearson analysis demonstrated that the most trunk MCSAs were negatively correlated with time to fusion for both segments and PS MCSAs exhibited a significant correlation with time to fusion except for MCSA at the L2-L3 segment.

CONCLUSIONS

Trunk MCSAs were significantly larger for a fusion group than a nonfusion group. As trunk MCSAs increased, fusion timing decreased.

Posterior Only Approach for Lumbar Pyogenic Spondylitis With Short Instrumentation and Prolonged Suction Drainage

STUDY DESIGN

A single-institution, single-surgeon retrospective review.

OBJECTIVE

To assess the efficacy of posterior only approach with short instrumentation and prolonged suction drainage in managing lumbar pyogenic spondylitis.

SUMMARY OF BACKGROUND DATA

Several methods of posterior surgical treatment for pyogenic spondylitis have been reported, there have been few reports regarding the efficacy of posterior only approach with short instrumentation including even inflamed segment.

METHODS

Thirty-three patients with lumbar pyogenic spondylitis who underwent posterior decompression and lumbar interbody fusion with short instrumentation including the inflamed segment and catheter drainage were enrolled. Clinically infection control (erythrocyte sedimentation rate and C-reactive protein normalization time) and onset of ambulation were reviewed. Moreover, achievement of fusion and changes of sagittal alignment were investigated radiologically.

RESULTS

In all 33 cases, infection was controlled successfully without any recurrence. There was no breakage of implant. Postoperative interval to normalization of erythrocyte sedimentation rate was average 69.4 days and C-reactive protein was 25.4 days, respectively. Ambulation was started at average 5.8 postoperative days. Successful interbody fusion was confirmed radiologically in all the cases at a mean of 5.4 months. Sagittal angle of fixed segment was average 6.9 degrees of lordosis before operation, which became more lordotic to 11.5 degrees just after operation, but decreased to 4.7 degrees of lordosis at the final follow up. Actually final sagittal alignment was almost same as preoperative status (P = 0.24).

CONCLUSION

By achieving favorable clinical and radiological results, short instrumentation and prolonged suction drainage with posterior only approach seemed to be an effective method in managing lumbar pyogenic spondylitis.

LEVEL OF EVIDENCE

3.

National Trends in the Surgical Management of Adult Lumbar Isthmic Spondylolisthesis: 1998 to 2011

STUDY DESIGN

A retrospective review.

OBJECTIVE

Isthmic spondylolisthesis (ISY) is a common orthopedic condition. Our objective was to identify trends in the surgical management of adult ISY in the United States and to evaluate trends in the surgical techniques utilized.

SUMMARY OF BACKGROUND DATA

Various surgical approaches have been described for ISY but preferred trends are not known.

METHODS

Using the Nationwide Inpatient Sample (NIS), 47,132 adult patients (≥ 18 years) with ISY undergoing lumbar spine fusion from 1998 to 2011 were identified. Our primary outcome of interest was the national trend in use of anterior (ASF), posterior (PSF), posterior with interbody (P/TLIF), and combined anterior-posterior fusion (A/PSF) surgeries for ISY patients. Poisson regression, modified Wald's test, and linear and logistic regression analysis with P < 0.05 were used for statistical analysis.

RESULTS

The annual rate of fusion surgeries for ISY increased 4.33 times-from 28.31 surgeries in 1998 to 122.69 surgeries per million US adults per year in 2011. Over the study period, annual rates of ASFs increased 2.65 times (P < 0.001), PSFs increased 1.03 times (P = 0.24), P/TLIFs increased 4.33 times (P < 0.001), and A/PSF increased 2.93 times (P < 0.001). In 2010 to 2011, the complication rate was significantly higher for A/PSF (18.86%, P < 0.001). PSFs had a higher complication rate of 3.61% and P/TLIFs (2.58%). The risk of complications was lower for females, elective admissions, and in hospitals in the South. Mean hospitalization charges adjusted to 2011 dollars were significantly higher for A/PSF ($157,560; 95% CI [95% confidence interval]: 14,480-170,360; P <  .001), followed by P/TLIFs ($103,700; 95% CI: 9840-109,030) and PSFs had lower mean hospitalization charges ($87,420; 95% CI: 8210-92,770).

CONCLUSION

Use of fusion for ISY has significantly increased and interbody fusion has become the most preferred approach over the study period. Hospital charges and complications were highest for combined anterior-posterior fusions.

Cost-Effectiveness of Lumbar Spondylolisthesis Surgery at 2-Year Follow-up

OBJECTIVES

The purpose of this study was to determine the cost/quality-adjusted life-year (QALY) of the operative treatment of lumbar spondylolisthesis and identify factors associated with cost-effectiveness at 2 years.

METHODS

We evaluated patients who underwent surgery for spondylolisthesis. The QALY was determined from the EQ5D. Outcomes were also assessed using the Oswestry Disability Index (ODI). Surgical, neuromonitoring, and anesthesia Current Procedural Terminology (CPT) codes as well as hospital Diagnosis-Related Group codes were used to determine the Medicare direct care costs of surgery. Indirect costs were modeled based on existing literature. A discounting rate of 3% was applied. Analysis was performed to determine which factors were associated with a cost/QALY less than $100,000.

RESULTS

There were 44 patients who underwent surgery for either degenerative (30) or isthmic spondylolisthesis (14). There were 27 women and 17 men, with an average age at surgery of 59.7 years (standard deviation [SD] = 14.69) and an average follow-up of 2 years (SD = 0.82). The average postoperative improvement in ODI was 24.77 (SD = 23.9), and change in QALY was 0.43 (SD = 0.30). The average cost/QALY at 2 years for direct care costs was $89,065. The average cost/QALY at 2 years for direct plus indirect costs was $112,588. Higher preoperative leg pain and greater leg pain change was associated with a cost/QALY <$100,000 (p < .005, p < .028). The cost-effective group had a higher proportion of patients with disease extent of two or more levels (p = .021). When comparing surgical techniques of anterior-posterior and posterior only, there was no difference in cost-effectiveness.

CONCLUSIONS

Spondylolisthesis surgery is cost-effective at 2 years, with a QALY change of 0.43 and a direct cost/QALY of $89,065. Higher preoperative leg pain and larger extent of disease was associated with cost-effectiveness.

LEVEL OF EVIDENCE

IV.

Biomechanical and clinical study of single posterior oblique cage POLIF in the treatment of degenerative diseases of the lumbar spine

INTRODUCTION

Aim of the study was to evaluate the biomechanical stability and the clinical efficacy of a lumbar interbody fusion obtained by single oblique cage implanted by a posterior approach.

METHOD

Through the realization of three finite element models (FEMs), the biomechanics of POLIF was compared to PLIF and TLIF. Ninety-four patients underwent interbody fusion by POLIF with instrumented posterolateral fusion. Clinical and radiographic outcomes were evaluated at regular intervals for at least 6 months.

RESULTS

The FEMs showed no statistically significant differences in stability in compression and flexion-extension. Mean preoperative VAS score was 7.1, decreased to 2.1 at follow-up. Mean preoperative SF-12 value was 34.5 %, increased to 75.4 % at follow-up. All patients showed a good fusion rate and no hardware failure.

DISCUSSION

POLIF associated to instrumented posterolateral fusion is a viable and safe surgical technique, which ensures a biomechanical stability similar to other surgical techniques.

Restoration of the spinopelvic sagittal balance in isthmic spondylolisthesis: posterior lumbar interbody fusion may be better than posterolateral fusion

BACKGROUND CONTEXT

More and more orthopedic surgeons recognize the importance of the sagittal balance of the spine.

PURPOSE

To analyze the pre- and postoperative sagittal and deformity parameters of low-grade isthmic spondylolisthesis and evaluate the effect of posterolateral fusion (PLF) and posterior lumbar interbody fusion (PLIF) on spinopelvic sagittal balance.

STUDY DESIGN

Nonrandomized controlled prospective study with a historical control.

PATIENT SAMPLE

A total of 99 patients with low-grade L5-S1 isthmic spondylolisthesis were treated surgically; 36 patients (mean age, 60.2±5.2 years) received the PLF operation, and 63 patients (mean age, 57.1±6.9 years) chose the PLIF operation. The healthy control group was composed of 60 volunteers (mean age, 44.5±8.4 years).

OUTCOME MEASURES

The pre- and postoperative spinopelvic and deformity parameters.

METHODS

All patients had radiographs that allowed measurement of spinopelvic parameters before and after the operation. All the spinopelvic and deformity parameters were measured. Two radiologists measured the parameters with the Cobb method.

RESULTS

All of the preoperative spinopelvic parameters showed no difference between the PLIF and PLF groups in this study (p>.05). In both of the operation groups, the preoperative pelvic incidence, pelvic tilt (PT), sacral slope, lumbar lordosis (LL), and L5 incidence (L5I) were significantly higher than in the control group (p<.01); the height of the intervertebral disc (HOD) was significantly lower than the controls. There were no significant differences in PT among PLIF, PLF, and control groups after the operation (p>.05). LL increased in the PLIF group and decreased in the PLF group. The slip degree (SD) and L5I were restored significantly in both groups. The HOD of the PLIF group increased 5.04 mm, the postoperative HOD of the PLF group had no significant change. In both PLIF and PLF groups, the correction of SD was correlated with the change of LL (r=-0.398, p=.007; r=0.365, p=.022). The restoration of HOD in the PLIF group correlated with the change of LL (r=0.334, p=.011). No significant differences could be found between the short-term clinical outcomes of the PLF and PLIF.

CONCLUSION

Either PLF or PLIF would lead a great change in spinopelvic parameters and deformity parameters. The decrease of PT may be an important role for the short-term surgical outcome. The PLIF could increase the LL and form a more reasonable sagittal alignment. From the point of the sagittal spinopelvic balance, the PLIF may be better than the PLF for patients with isthmic spondylolisthesis.

A Comparative Radiographic Analysis of Fusion Rate between L4-5 and L5-S1 in a Single Level Posterior Lumbar Interbody Fusion

Objective

This study aimed to investigate radiographic fusion rates at L4-5 and L5-S1 after single level posterior lumbar interbody fusion (PLIF) and evaluate the relationship between fusion rates and preoperative disc slope angle (DSA), lumbar lordosis (LL), segmental angle (SA), and pelvic parameters.

Methods

We conducted a retrospective review of patients who underwent single level PLIF at L4-5 or L5-S1 during May 2003-December 2012 at our institution. 73 patients were finally enrolled. Fusion was assessed by use of the Brantigan-Steffee classification, less than 2mm translation and less than 5° motion on the flexion-extension lateral radiographs. We analyzed the radiographic fusion rates, risk factors, and relationship of fusion rates with DSA, LL, SA, and pelvic parameters.

Results

There were 59 patients (80.8%) in the L4-5 group and 14 (19.2%) in L5-S1 (average follow-up, 34 months). The radiographic fusion rates were 89.8% in the L4-5 group (53/59) and 42.9% in L5-S1 (6/14) (p<0.001).The preoperative DSA was significantly lesser in the L4-5 group than in the L5-S1 group (13.1±8.1° vs. 27.2±6.7°, p<0.001). The LL, SA, and pelvic parameters were not related with radiographic fusion rates in both groups. Risk factors for non-union were not identified between the two groups except for the surgery level (p<0.001).

Conclusion

The radiographic fusion rate at L5-S1 was less than half that at L4-5 after single level PLIF. This may be due to the anatomical and biomechanical differences between the two levels. More vigorous effort to achieve successful fusion at L5-S1 should be considered.

Comparison of one versus two cages in lumbar interbody fusion for degenerative lumbar spinal disease: a meta-analysis

OBJECTIVE

To systematically compare the fusion rate and safety of lumbar interbody fusion using one cage versus two cages for the treatment of degenerative lumbar spinal diseases.

METHODS

All randomized controlled trials (RCTs) and comparative observational studies written in English comparing the outcome of lumbar interbody fusion using one or two cages in patients with degenerative lumbar spinal diseases were identified by a comprehensive search of PubMed Central, MEDLINE, EMBASE, BIOSIS and the Cochrane Central Registry of Controlled Trials. An exhaustive electronic search up to July 2013. The quality of the methodology was assessed and relevant data retrieved independently by two reviewers, after which the resultant data were subjected to meta-analysis. All meta-analyses were performed using Review Manager 5.0, which is recommended and provided by the Cochrane Collaboration.

RESULTS

Our systematic search yielded 745 studies from the selected databases. After duplicate studies had been identified and the titles and abstracts screened, 736 studies were excluded because they were irrelevant to our topic. The full texts of the remaining nine potentially relevant references were comprehensively evaluated and four excluded for the following reasons: two studies involved co-interventions and the other two lacked control groups. Two relevant RCTs and three comparative observational studies involving 384 patients and 501 spinal segments with at least one year follow-up were identified. Analysis of the pooled data demonstrated no significant difference in fusion rate between the one-cage and two-cage groups. However, intraoperative blood loss and operating time were less and the complications rate lower in the one-cage group.

CONCLUSION

In patients with degenerative lumbar spinal diseases, lumbar interbody fusion using one cage has an equal fusion rate and is safer compared with using two cages. However, because this meta-analysis had some limitations, more high quality RCTs are needed to strengthen the evidence.

Slip Reduction Rate between Minimal Invasive and Conventional Unilateral Transforaminal Interbody Fusion in Patients with Low-Grade Isthmic Spondylolisthesis

OBJECTIVE

To compare the slip reduction rate and clinical outcomes between unilateral conventional transforaminal lumbar interbody fusion (conventional TLIF) and unilateral minimal invasive TLIF (minimal TLIF) with pedicle screw fixation for treatment of one level low-grade symptomatic isthmic spondylolisthesis.

METHODS

Between February 2008 and April 2012, 25 patients with low-grade isthmic spondylolisthesis underwent conventional TLIF (12 patients) and minimal TLIF (13 patients) in single university hospital by a single surgeon. Lateral radiographs of lumbar spine were taken 12 months after surgery to analyze the degree of slip reduction and the clinical outcome. All measurements were performed by a single observer.

RESULTS

The demographic data between conventional TLIF and minimal TLIF were not different. Slip percentage was reduced from 15.00% to 8.33% in conventional TLIF, and from 14.15% to 9.62% in minimal TLIF. In both groups, slip percentage was significantly improved postoperatively (p=0.002), but no significant intergroup differences of slip percentage in preoperative and postoperative were found. The reduction rate also not different between conventional TLIF (45.41±28.80%) and minimal TLIF (32.91±32.12%, p=0.318).

CONCLUSION

Conventional TLIF and minimal TLIF with pedicle screw fixation showed good slip reduction in patients with one level low-grade symptomatic isthmic spondylolisthesis. The slip percentage and reduction rate were similar in the conventional TLIF and minimal TLIF.

Long-term Follow-up of Minimal-Access and Open Posterior Lumbar Interbody Fusion for Spondylolisthesis

BACKGROUND:

Although posterior lumbar interbody fusion (PLIF) is regarded as an effective treatment for spondylolisthesis, few studies have reported comprehensive, long-term outcome data, and none has investigated the incidence of deterioration of outcomes.

OBJECTIVE:

To determine and compare the success rates and long-term stability of outcomes of open PLIF and minimal-access PLIF in the treatment of radicular pain and back pain in patients with spondylolisthesis.

METHODS:

Forty-three patients were followed for a minimum of 3 years. They completed a Short-Form Health Survey and visual analog scores for back pain and leg pain and underwent lumbar spine radiography. Outcomes were compared with baseline data and 12-month data.

RESULTS:

Surgery succeeded in reducing listhesis and increasing disc height, but had little effect on lumbar lordosis or the angulation of the segment treated. At 12 months after surgery, listhesis was reduced, disc height was increased, leg pain was reduced or eliminated, and physical functioning restored. Back pain was less often relieved. These outcomes were largely maintained over the ensuing 2 years. Only 5% to 10% of patients reported deterioration in their relief of pain. Depending on the definition adopted for success, the long-term success rate of PLIF may be as high as 70%.

CONCLUSION:

For the relief of leg pain, the success rates of open PLIF (70%) and minimal-access PLIF (67%) for spondylolisthesis are high and durable in the long-term. PLIF is less often successful in relieving back pain, but the outcomes are maintained. The outcomes of open PLIF and minimal-access PLIF were statistically indistinguishable.

Stress distribution on the screws in posterior lumbar fusion of isthmic spondylolisthesis with 2- or 3-vertebra fixation techniques: a biomechanical cadaveric study

BACKGROUND

Two- or three-vertebra fixation techniques are both used in the treatment of spondylolisthesis. However, the number of spinal segments that should be implanted in spondylolisthesis reduction and fixation is still controversial, and there are no published reports on stress distribution on the screws with 2- or 3-vertebra fixation techniques. Understanding stress distribution in screws would be of potential great clinical importance and supply more biomechanical evidence in surgery. The aim of this study was to compare and quantitatively analyze the stress distribution on the screws in 2- or 3-vertebra fixation techniques in cadaveric models of spondylolisthesis.

MATERIALS AND METHODS

Sixteen fresh specimens of human lumbar spines were used in this study. The spondylolisthesis model was generated by Panjabi method and fixed with the SINO universal spine system by 2- (group A) or 3-vertebra (group B) fixation technique. Rectangular electrical resistance strain gauges were fixed at upper and lower surface of the root of screws bilaterally. The samples were tested under flexion/extension, left/right lateral bending, and axial compression loading. Stress on the screws was measured by strain gauge monitor, respectively.

RESULTS

Under the five different loading conditions, the stress could be compressive stress or tensile stress. Under the compression, flexion, and bending loading condition, the stress in reduction screws in group A is higher than in group B (P < 0.01). However, under the extension loading condition, stress of lower surface in reduction screws in group A is 49% lower than in group B. With regard to the anchor screws, under flexion and lateral bending conditions, stress in group A is lower than in group B (P < 0.05). Under compression and extension loading conditions, stress in group A is slightly higher than in group B, but no significant difference is detected.

CONCLUSIONS

In most loading conditions, stress in reduction screws in 2-vertebra fixation technique was higher than in 3-vertebra fixation technique. The 3-vertebra fixation technique might effectively reduce stress on the reduction screws, and decrease the probability of fatigue fractures of the screws.