Long Fusion Arthrodesis Stopping at L5 for Adult Scoliosis: Fate of L5-S1 Disk and Risk Factors for Subsequent Disk Degeneration

Junctional Failures at Both Ends After Long Fusion Arthrodesis Stopping at L5: Incidences and Risk Factors

OBJECTIVE

Junctional failures after long fusion stopping at L5 can present at both proximal and distal ends. The purpose of this study was to investigate incidences and risk factors of proximal junctional failure (PJF) and distal junctional failure (DJF) after long lumbar instrumented fusion stopping at L5 for adult spinal deformity.

METHODS

Sixty-three patients who underwent long fusion surgery stopping at L5 with a minimum follow-up of 3 years were reviewed retrospectively. PJF and DJF were defined as newly developed back pain and/or radiculopathy with corresponding radiographic failures. The incidence and risk factors of each junctional failure were analyzed using a log-rank test and Cox proportional hazards model.

RESULTS

Twelve men and 51 women were included in our study. Their mean age was 68.5 ± 7.0 years and the mean follow-up period was 84.5 ± 45.3 months. PJF and DJF occurred in 17 (27%) and 16 patients (25.4%), respectively. PJF and DJF developed at median durations of 32.1 months and 13.3 months, respectively, showing no significant difference between the two. Three patients presented with both PJF and DJF. Risk factors for PJF included lower body mass index, higher preoperative lumbar lordosis, and higher postoperative sagittal vertical axis (SVA) (hazard ratio, 0.570, 1.055, and 1.040, respectively). For DJF, higher preoperative SVA was an independent risk factor (hazard ratio, 1.010).

CONCLUSIONS

After long fusion surgery stopping at L5, PJF and DJF occurred at similar rates. Lower body mass index, higher preoperative lumbar lordosis, and higher postoperative SVA were risk factors for PJF. Higher preoperative SVA was an independent risk factor for DJF.

Assessment of two entry points for S2 alar-iliac screw in a Japanese cohort using three-dimensional computed tomography scan

BACKGROUND CONTEXT

Lumbosacral fusion supplemented with sacropelvic fusion has recently been increasingly employed for correcting spinal deformity and is associated with lower incidence of pseudarthrosis and implant failure. To date, few studies have evaluated anatomical parameters and technical feasibility between different entry points for S2 alar-iliac screws.

PURPOSE

To compare anatomical parameters and technical feasibility of two entry points for the S2 alar-iliac screw (S2AIS) in a Japanese cohort using three-dimensional (3D) computed tomography (CT).

STUDY DESIGN/SETTING

Retrospective cohort study.

PATIENT SAMPLE

Fifteen men and 15 women aged 50-79 years who underwent pelvic CT at our hospital in 2013.

OUTCOME MEASURES

Screw length, lateral angulation, caudal angulation, angle range, distance from the entry point to the sacroiliac joint, distance from the S2AIS to the acetabular roof, distance from the S2AIS to the sciatic notch, and insertion difficulty.

METHODS

We used 30 pelvic CT images (15 men and 15 women). We selected two entry points from previous studies: one was 1 mm distal and 1 mm lateral to the S1 dorsal foramen (A group) and the other was the midpoint between the S1 and S2 dorsal foramen (B group). We resliced the plane in which the pelvis was sectioned obliquely from these entry points to the anterior inferior iliac spine in the sagittal plane. We placed the shortest and longest virtual S2AISs bilaterally in this plane using a 4-mm margin. We measured screw length, lateral angulation, caudal angulation, angle range, distance from the entry point to the sacroiliac joint, distance from the S2AIS to the acetabular roof, distance from the S2AIS to the sciatic notch, and insertion difficulty. These measurements were compared between Groups A and B.

RESULTS

In group A, the angle in the sagittal plane was significantly smaller and the distance from the entry point to the sciatic notch was significantly longer than in group B. Group B demonstrated a significantly longer screw length, longer distance from the entry point to the sacroiliac joint, and longer distance from the entry point to the acetabular roof than group A. The rate of insertion difficulty of S2AIS was much higher in group A.

CONCLUSIONS

Insertion of S2AIS from the midpoint between the S1 and S2 dorsal foramen compared with the entry at distal and lateral to S1 foramen enables insertion of longer screws with low insertion difficulty.

Radiological Evaluation of Pelvic Morphology for S2 Alar-Iliac Screw Insertion in the Japanese Samples: A Retrospective Cohort Study

Introduction

S2 alar-iliac screw (S2AIS) insertion for lumbosacral fixation is becoming a common procedure for deformity surgeries. However, studies that have reported the anatomy and morphometric features of the pelvis for S2AIS insertion in the Japanese samples are scarce. This study aimed to elucidate the morphometric features of the pelvis regarding S2AIS insertion in the Japanese samples.

Methods

We used 60 computed tomography scans of the pelvis (30 men and 30 women). The entry point for the S2AIS was determined as 1-mm lateral and 1-mm distal to the S1 dorsal sacral foramen. We resliced the plane in which the pelvis was sectioned obliquely from this entry point to the anterior inferior iliac spine in the sagittal plane. We bilaterally placed the shortest and longest virtual S2AISs in this plane using a 4-mm margin. We analyzed the length, angle, and safety of the determined trajectory and compared these measurements according to sex and age.

Results

The median longest and shortest screw lengths were 108.1 and 103.3 mm, respectively. The median longest and shortest distances from the entry point to the sacroiliac joint were 31.2 and 28.2 mm, respectively. The median smallest and largest lateral angulations were 40.7° and 47.3°, respectively. The median angle range was 4.2°. The median caudal angulation was -2.8°. The median shortest and longest distances from the S2AISs to the acetabular roof were 23.5 and 27.4 mm, respectively. The median distance from the S2AISs to the sciatic notch was 23.1 mm. Assuming the insertion of screw with a diameter of 8 mm, S2AIS insertion was difficult in 32 of 120 (27%) screws because the dorsal cortex of the sacrum was damaged.

Conclusions

Screw length and lateral angulation were similar to those in previous studies. Insertion difficulty occurred in 27% of screws.

Predictors and Correlative Factors for Low Back Pain after Long Fusion Arthrodesis in Patients with Adult Scoliosis

INTRODUCTION

Low back pain (LBP) still exists at the follow-up visit in some cases after long fusion arthrodesis for adult scoliosis. However, few available studies have elaborated the reasons and factors associated with this symptom. Therefore, the aim of the current study was to identify the correlative factors and predictors of postoperative LBP after long fusion arthrodesis and provide evidence to improve the surgical strategy.

METHODS

Seventy-nine patients with adult scoliosis who underwent long fusion arthrodesis were divided into a group with no or mild LBP (NLBP group) and one with moderate or severe LBP (MLBP group) according to the average Oswestry Dability Index (ODI) at the last follow-up visit. The Japanese Orthopaedic Association (JOA) score, ODI and complications were used to evaluate clinical outcomes. %Fat infltration area (%FIA), sagittal and coronal parameters were recorded to evaluate radiological outcomes. Multivariate logistic regression analysis was conducted to identify the predictors and correlative factors for postoperative LBP.

RESULTS

Thirty-three patients (41.77%) with ODI (30.06% ± 6.92%) higher than the average at the last follow-up were divided into the MLBP group, while the rest (58.23%) with last follow-up ODI (13.26% ± 5.31%) lower than the average were divided into the NLBP group. In multivariate logistic regression, the preoperative sagittal vertical axis (SVA) (P < 0.001), %FIA (P = 0.003) and osteoporosis (P = 0.016) were identified to be predictors and last follow-up SVA (P < 0.001), last follow-up lumbar lordosis (LL) (P = 0.031) and adjacent segment degeneration (ASD) (P = 0.043) were identified as correlative factors. The receiver-operating characteristic (ROC) curve showed satisfactory accuracy in preoperative SVA (P < 0.001) and %FIA (P < 0.001) to predict postoperative LBP.

CONCLUSION

Postoperative LBP after long fusion arthrodesis for adult scoliosis was common. Postoperative LBP was associated with increased SVA and decreased LL and ASD. Preoperative SVA > 3.54 cm, %FIA > 24.82% and osteoporosis showed good accuracy to predict the postoperative symptoms. Optimal surgical methods should be used for patients with these factors to decrease the incidence and degree of postoperative LBP.

Prognostic Factors for Adjacent Segment Disease After L4-L5 Lumbar Fusion

BACKGROUND

Adjacent segment disease (ASD) is an important consideration during decision making for lumbar spinal fusion.

OBJECTIVE

To identify risk factors for development of ASD after L4-L5 fusion and differences in incidence between rostral and caudal ASD.

METHODS

We retrospectively reviewed all consecutive patients at a single institution who underwent first-time spinal fusion at the L4-L5 level for degenerative spinal disease over a 10-yr period, using posterolateral pedicular screw fixation with or without posterior interbody fusion. ASD was defined as clinical and radiographic evidence of degenerative spinal disease requiring reoperation at the level rostral (L3-L4) or caudal (L5-S1) to the index fusion.

RESULTS

Among 131 identified patients, the incidence of ASD requiring reoperation was 25.2% (n = 33). Twenty-four cases (18.3% of the entire cohort) developed rostral ASD (segment L3-L4), 3 cases (2.3%) developed caudal (L5-S1), and 6 cases (4.6%) developed bilateral ASD (both rostral and caudal). Cumulatively, the incidence of caudal ASD was significantly lower than rostral ASD (P < .001). Following multivariate logistic regression for factors associated with ASD reoperation, decompression of segments outside the fusion construct was associated with higher ASD rates (odds ratio [OR] = 2.68, P = .039), as was female gender (OR = 3.55, P = .011), whereas older age was associated with lower ASD incidence (OR = 0.95, P = .011).

CONCLUSION

When considering posterior L4-L5 fusion, surgeons should refrain from prophylactic procedures in the L5-S1 level, without clinical indications, because ASD incidence on that segment is reassuringly low.

Contactless treatment for scoliosis by electromagnetically controlled shape-memory alloy rods: a preliminary study in rabbits

PURPOSE

To evaluate the safety and efficacy of a system aiming to correct scoliosis called "electromagnetically controlled shape-memory alloy rods" (EC-SMAR) used in a rabbit model.

METHODS

We heat-treated shape-memory alloy (SMA) rods to achieve a transition temperature between 34 and 47 °C and a C-shape austenite phase. We then developed a water-cooled generator capable of generating an alternating magnetic field (100 kHz) for induction heating. We next studied the efficacy of this system in vitro and determined some parameters prior to proceeding with animal experiments. We then employed a rabbit model, in which we fixed a straight rod along the spinous processes intraoperatively, and conducted induction heating postoperatively every 4 days for 1 month, while performing periodic X-ray assessments.

RESULTS

Significant kyphotic deformations with Cobb angles of about 45° (p < 0.01) were created in five rabbits, and no complications occurred throughout the experiment. The rabbits are still very much alive and do not show any signs of discomfort.

CONCLUSIONS

This is the first system that can modulate spinal deformation in a gradual, contactless, noninvasive manner through electromagnetic induction heating applied to SMA alloy rods. Although this study dealt with healthy spines, it provides promising evidence that this device also has the capacity to correct human kyphosis and even scoliosis in the future. These slides can be retrieved under Electronic Supplementary Material.

Comparison of long fusion terminating at L5 versus the sacrum in treating adult spinal deformity: a meta-analysis

Purpose

Choosing an optimal distal fusion level for adult spinal deformity (ASD) is still controversial. To compare the radiographic and clinical outcomes of distal fusion to L5 versus the sacrum in ASD, we conducted a meta-analysis.

Methods

Relevant studies on long fusion terminating at L5 or the sacrum in ASD were retrieved from the PubMed, Embase, Cochrane, and Google Scholar databases. Then, studies were manually selected for inclusion based on predefined criteria. The meta-analysis was performed by RevMan 5.3.

Results

Eleven retrospective studies with 1211 patients were included in meta-analysis. No significant difference was found in overall complication rate (95% CI 0.60 to 1.30) and revision rate (95% CI 0.59 to 1.99) between fusion to L5 group (L group) and fusion to the sacrum group (S group). Significant lower rate of pseudarthrosis and implant-related complications (95% CI 0.29 to 0.64) as well as proximal adjacent segment disease (95% CI 0.35 to 0.92) was found in L group. Patients in S group obtained a better correction of lumbar lordosis (95% CI − 7.85 to − 0.38) and less loss of sagittal balance (95% CI − 1.80 to − 0.50).

Conclusion

Our meta-analysis suggested that long fusion terminating at L5 or the sacrum was similar in scoliosis correction, overall complication rate, revision rate, and improvement in pain and disability. However, fusion to L5 had advantages in lower rate of pseudarthrosis, implant-related complications, and proximal adjacent segment disease, while fusion to the sacrum had advantages in the restoration of lumbar lordosis, maintenance of sagittal balance, and absence of distal adjacent segment disease.

Graphic abstract

These slides can be retrieved under Electronic Supplementary Material.