Coronal and Sagittal Plane Correction in Patients With Lenke 1 Adolescent Idiopathic Scoliosis: A Comparison of Consecutive Versus Interval Pedicle Screw Placement

Implant density in adolescent idiopathic scoliosis: a meta-analysis of clinical and radiological outcomes

BACKGROUND

Adolescent idiopathic scoliosis (AIS) affects 1-3% of adolescents, and treatment approaches, including the density of constructs in surgical fusion, vary among orthopedic surgeons. Studies have sought to establish whether high-density or low-density constructs offer superior clinical and radiological outcomes, yet conclusive results are lacking. This meta-analysis aims to provide a definitive answer to the controversial and ambiguous question surrounding the efficacy of different pedicle screw densities in treating AIS.

METHODS

PubMed, Cochrane, and Google Scholar (page 1-20) were searched till December 2023. The studied outcomes were Major Cobb angle, major curve correction, lumbar curve, kyphosis (T5-T12), lumbar lordosis, coronal balance, LIV Tilt angle, TAV translation, LAV translation, apical trunk rotation, trunk shift, SRS-22, operative time, blood loss, complications and cost.

RESULTS

Twenty-four studies (total of 1985 patients, 1045 in LD group and 940 in HD group) were included in this meta-analysis. A statistically significant better improvement in ATR (p = 0.02) and LIV tilt angle (p = 0.02) was seen in the high-density group. On the other hand, longer operative time (p = 0.002), blood loss (p = 0.0004) and costs (p = 0.02) were seen in the high-density group. No difference was seen in the remaining radiographic and clinical outcomes between both surgeries.

CONCLUSION

Both low-density (LD) and high-density (HD) screw constructs show comparable and satisfactory radiographic and QOL for AIS patients. Furthermore, HD constructs had increased costs, operative time, and blood loss associated. However, a definitive conclusion cannot be made and more studies taking into account multiple additional variables are necessary to do so.

The Effect of Implant Density on Adolescent Idiopathic Scoliosis Fusion: Results of the Minimize Implants Maximize Outcomes Randomized Clinical Trial

BACKGROUND

Severe adolescent idiopathic scoliosis (AIS) can be treated with instrumented fusion, but the number of anchors needed for optimal correction is controversial.

METHODS

We conducted a multicenter, randomized study that included patients undergoing spinal fusion for single thoracic curves between 45° and 65°, the most common form of operatively treated AIS. Of the 211 patients randomized, 108 were assigned to a high-density screw pattern and 103, to a low-density screw pattern. Surgeons were instructed to use ≥1.8 implants per spinal level fused for patients in the high-implant-density group or ≤1.4 implants per spinal level fused for patients in the low-implant-density group. The primary outcome measure was the percent correction of the coronal curve at the 2-year follow-up. The power analysis for this trial required 174 patients to show equivalence, defined as a 95% confidence interval (CI) within a ±10% correction margin with a probability of 90%.

RESULTS

In the intention-to-treat analysis, the mean percent correction of the coronal curve was equivalent between the high-density and low-density groups at the 2-year follow-up (67.6% versus 65.7%; difference, -1.9% [95% CI: -6.1%, 2.2%]). In the per-protocol cohorts, the mean percent correction of the coronal curve was also equivalent between the 2 groups at the 2-year follow-up (65.0% versus 66.1%; difference, 1.1% [95% CI: -3.0%, 5.2%]). A total of 6 patients in the low-density group and 5 patients in the high-density group required reoperation (p = 1.0).

CONCLUSIONS

In the setting of spinal fusion for primary thoracic AIS curves between 45° and 65°, the percent coronal curve correction obtained with use of a low-implant-density construct and that obtained with use of a high-implant-density construct were equivalent.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Biomechanical Computational Study of Pedicle Screw Position and Density in Adolescent Idiopathic Scoliosis Instrumentation

STUDY DESIGN

Computer simulation of adolescent idiopathic scoliosis instrumentation.

OBJECTIVE

To test the hypothesis that different screw densities would result in different apical vertebral rotation (AVR) corrections and bone-screw forces in adolescent idiopathic scoliosis instrumentation.

SUMMARY OF BACKGROUND DATA

The "Minimize Implants Maximize Outcomes" Clinical Trial revealed that the use of more versus fewer screws resulted in similar coronal plane correction for Lenke 1A curves. However, the biomechanical impact of screw density on transverse plane correction is still unclear. Further investigation is needed to determine if and how transverse plane correction is correlated with screw density.

PATIENTS AND METHODS

We simulated apical vertebral derotation after segmental translation using patient-specific computer models of 30 patients from the "Minimize Implants Maximize Outcomes" Trial. For each case, 10 alternative screw patterns were tested with overall densities ranging between 1.2 and 2 screws per level fused, and local density at the 3 apical levels ranging between 0.7 and 2 (total: 600 simulations). Main thoracic (MT) Cobb angle, thoracic kyphosis (TK), AVR, and bone-screw forces were computed and compared.

RESULTS

The presenting MT (62 ± 11°; range: 45° to 86°), TK (27 ± 20°; -5° to 81°), and AVR (14±7°; -2° to 25°) were corrected through segmental translation to 22 ± 7° (10° to 41°), 26 ± 5° (18° to 45°), and 14 ± 7° (-4° to 26°). After apical vertebral derotation, they became 16 ± 8° (1° to 41°), 24 ± 4° (13° to 40°), and 4 ± 5° (-12° to 18°). There was no significant difference in MT among screw patterns; higher screw density had lower bone-screw forces ( P < 0.05). The apical vertebral derotation maneuver reduced AVR by an average of 70%, positively correlated with apical screw density ( r = 0.825, P < 0.05). There was no significant difference in TK.

CONCLUSION

Screw density had no significant effect on 3-dimensional correction through the primary segmental translation maneuver. Transverse plane correction through subsequent apical vertebral derotation was positively correlated with screw density at the apical levels ( r = 0.825, P < 0.05). Bone-screw forces were negatively correlated with overall screw density ( P < 0.05).

Is lower screw density associated with mechanical complications in adult spinal deformity surgery?

PURPOSE

To assess the impact of screw density on: (1) rod fracture/pseudarthrosis, (2) proximal/distal junctional kyphosis/failure (PJK/DJK/PJF), and (3) deformity correction judged by sagittal vertical axis (SVA) and T1-pelvic angle (T1PA).

METHODS

A single-center, retrospective cohort study of patients undergoing adult spinal deformity (ASD) surgery from 2013 to 2017 was undertaken. Screw density was calculated by dividing the number of screws placed by the total instrumented levels. Screw density was then dichotomized at our calculated mean density to ≥ 1.65 and < 1.65. Outcomes consisted of mechanical complications and the amount of correction obtained.

RESULTS

145 patients underwent ASD surgery with 2-year follow-up. Mean screw density (range) was 1.6 ± 0.3 (1.00-2.00). The most common levels with missing screws were L2 (n = 59, 40.7%), L3 (n = 57, 39.3%) and L1 (n = 51, 35.2%), located mainly along the concavity in 113(80.0%) patients and apices in 98 (67.6%) patients. Rod fracture/pseudarthrosis: 23/32 (71.8%) patients with rod fracture and 35/46 (76.0%) with pseudarthrosis had missing screws within two levels of the rod fracture/pseudarthrosis. Logistic regression showed no significant association between screw density and rod fracture/pseudarthrosis.

PJK/F

15/47 (31.9%) patients with PJK and 9/30 (30.0%) with PJF had missing screws within three levels of the upper instrumented vertebra (UIV). Logistic regression showed no significant association between screws density and PJK/F. Correction obtained: linear regression failed to show any significant association between screw density and SVA or T1PA correction.

CONCLUSION

These findings showed that no significant association was found between screw density and mechanical complications or the amount of correction obtained, though approximately 3 out of 4 patients with rod fracture/pseudarthrosis had missing screws at or within two levels of the pathology. The prevention of mechanical complications is likely multifactorial and subject to both patient's characteristics and surgical techniques.

LEVEL OF EVIDENCE

III.

Utilization of Offset Iliac Connectors as Anchoring Sites in Severe Rigid Scoliosis: New Technique

STUDY DESIGN

This was a prospective cohort study.

OBJECTIVES

To introduce the iliac connectors as fixation options in spinal constructs used for correction of severe scoliosis at locations other than the lumbopelvic region.

METHODS

Nine patients with severe rigid scoliosis undergoing surgical release and posterior instrumentation in the period between January 2013 and January 2015 were included in this prospective cohort study. Mean age was 18.4 years; 8 had triple structural curves, and the remaining patient had double structural curves. Cobb angles of the primary and compensatory curves were compared with the immediate, 1-year, and 2-year postoperative measurements using the F test, with P value ≤.05 indicating statistical significance. Screw densities of the final constructs were calculated and compared with the screw densities when the offset iliac connectors were not used.

RESULTS

One to 4 offset iliac connectors were used in all 9 patients, increasing screw density by a mean of 6.24 (P < .001). The mean Cobb angle of the major curve was corrected from 98.44° to 58.2° (P < .001), that of the first compensatory curve, from 56.55° to 38.33° (P < .001), and that of the second compensatory curve, from 40.75° to 26.63° (P < .001). There were no intraoperative neurological complications. After a mean follow-up of 30.6 months, the construct remained stable in all patients with no loss of correction.

CONCLUSION

Offset iliac connectors can be a valuable tool to increase screw density in correction of severe scoliosis, thus increasing overall biomechanical strength of the final construct.

A Retrospective Study of Factors Associated with Restoration of Thoracic Kyphosis in 43 Patients with Adolescent Idiopathic Scoliosis with Lenke Type 1 Curvature

BACKGROUND This retrospective study aimed to identify the factors associated with successful surgical correction of thoracic kyphosis (TK) in 43 patients with adolescent idiopathic scoliosis (AIS) with Lenke type 1 curvature, in which the major curve with the largest Cobb angle was mainly in the thoracic region. MATERIAL AND METHODS We collected data from patients with Lenke 1 AIS. The following parameters were measured: Cobb angle, side-bending Cobb angle, cervical lordosis (CL), TK, lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), the sagittal vertical axis (SVA), the center of a C7 plumb line to the center sacral vertical line (C7-CSVL), correction rate, Ponte osteotomy, flexibility, and screw density. Univariate analysis and multivariate logistic regression analyses were performed. RESULTS Among the 43 cases analyzed, the mean postoperative Cobb angle at the last follow-up, C7-CSVL, SVA, CL, TK, LL, PI, SS, and PT were respectively 21.33±9.47°, 10.41±8.45 mm, 19.68±14.33 mm, 16.19±7.45°, 23.12±7.45°, 50.33±11.37°, 49.70±9.83°, 39.42±8.11°, and 10.16±6.63°. Univariate analysis suggested that preoperative TK, preoperative LL, and Ponte osteotomy were statistically significant (P<0.05), and multivariate analysis suggested that preoperative LL and Ponte osteotomy were statistically significant (P<0.05). CONCLUSIONS The results of this study demonstrated that preoperative TK, preoperative LL, and Ponte osteotomy were related factors for maintaining normal TK. Multivariate analysis suggested that preoperative LL and the use of Ponte osteotomy with full-thickness segmental resection of the spinal posterior column resulted in the successful surgical correction of TK in patients with AIS with Lenke type 1 curvature.

The importance of curve severity, type and instrumentation strategy in the surgical correction of adolescent idiopathic scoliosis: an in silico clinical trial on 64 cases

Adolescent idiopathic scoliosis is a three-dimensional deformity of the spine which is frequently corrected with the implantation of instrumentation with generally good or excellent clinical results; mechanical post-operative complications such as implant loosening and breakage are however relatively frequent. The rate of complications is associated with a lack of consensus about the surgical decision-making process; choices about the instrumentation length, the anchoring implants and the degree of correction are indeed mostly based on personal views and previous experience of the surgeon. In this work, we performed an in silico clinical trial on a large number of subjects in order to clarify which factors have the highest importance in determining the risk of complications by quantitatively analysing the mechanical stresses and loads in the instrumentation after the correction maneuvers. The results of the simulations highlighted the fundamental role of the curve severity, also in its three-dimensional aspect, and of the instrumentation strategy, whereas the length of the fixation had a lower importance.

Correction objectives have higher impact than screw pattern and density on the optimal 3D correction of thoracic AIS: a biomechanical study

STUDY DESIGN

Assessment of screw pattern, implant density (ID), and optimization of 3D correction through computer-based biomechanical models.

OBJECTIVE

To investigate how screw pattern and ID affect intraoperative 3D correction of thoracic curves in adolescent idiopathic scoliosis, and how different correction objectives impact the optimal screw pattern. Screw pattern, ID, correction objectives and surgical strategies for posterior fusion of AIS are highly variable among experienced surgeons. The "optimal" instrumentation remains not well defined.

METHODS

10 patient-specific multibody models of representative adolescent idiopathic scoliosis Lenke 1A cases were built and used to compare alternative virtual correction surgeries. Five screw patterns and IDs (average: 1.6 screws/instrumented level, range: 1.2-2) were simulated, considering concave rod rotation, en bloc derotation, and compression/distraction as primary correction maneuvers. 3D correction descriptors were quantified in the coronal, sagittal and transverse planes. An objective function weighting the contribution of intraoperative 3D correction and mobility allowed rating of the outcomes of the virtual surgeries. Based on surgeon-dependent correction objectives, the optimal result among the simulated constructs was identified.

RESULTS

Low-density (ID ≤ 1.4) constructs provided equivalent 3D correction compared to higher (ID ≥ 1.8) densities (average differences ranging between 2° and 3°). The optimal screw pattern varied from case to case, falling within the low-density screw category in 14% of considered scenarios, 73% in the mid-density (1.4 < ID < 1.8) and 13% in the high-density. The optimal screw pattern was unique in five cases; multiple optima were found in other cases depending on the considered correction objectives.

CONCLUSIONS

Low-density screw patterns provided equivalent intraoperative 3D correction to higher-density patterns. Simulated surgeon's choice of correction objectives had the greatest impact on the selection of the optimal construct for 3D correction, while screw density and ID had a limited impact.

LEVEL OF EVIDENCE

N/A.

Risk and Predictive Factors for Proximal Junctional Kyphosis in Patients Treated by Lenke Type 5 Adolescent Idiopathic Scoliosis Correction

OBJECTIVE

Proximal junctional kyphosis (PJK) is a common sagittal complication of adolescent idiopathic scoliosis (AIS) after corrective surgery, leading to new deformities, pain, and, even, revision surgery. In the present study, we investigated the risk and predictive factors for PJK in patients who had undergone Lenke type 5 AIS correction to identify the parameters relevant to intraoperative guidance.

METHODS

A total of 35 patients with Lenke type 5 AIS who had undergone corrective surgery at our hospital from January 2008 to February 2016 were divided into the PJK (n = 15) and non-PJK (n = 20) groups. Correlation and receiver operating characteristic curve analyses were performed to screen the parameters for significance and calculate the thresholds. A survival analysis was performed to examine the differences between the 2 groups.

RESULTS

Independent t tests revealed significant differences between the 2 groups in the preoperative pelvic incidence, preoperative pelvic tilt, postoperative proximal junctional angle (PJA), and postoperative thoracic kyphosis (TK). The postoperative PJA, postoperative TK, and other parameters correlated significantly with changes in the PJA at the final follow-up. The receiver operating characteristic curves revealed that the postoperative PJA and postoperative TK effectively predicted for the occurrence of PJK, with a threshold of 9.45° and 25.25°, respectively. The estimated survival times were 14.7 months for a PJA >9.45° and TK >25.25°, 19.2 months for a PJA >9.45°, and 33.9 months for TK >25.25°.

CONCLUSIONS

The results of the present study have shown that the postoperative PJA and postoperative TK can be used to effectively predict for the occurrence of PJK in patients with Lenke type 5 AIS after corrective surgery, with a threshold of 9.45° and 25.25°, respectively.

A finite element analysis of different pedicle screw placement strategies for treatment of Lenke 1 adolescent idiopathic scoliosis: which is better?

OBJECTIVE

To simulate the process of curve correction with different strategies of pedicle screws placement, and then explore the ideal strategy. Materials and methods: A three-dimensional model was constructed using CT data from a Lenke 1 AIS patient for finite element analysis. Five screw-placement strategies were designed, including collocation of consecutive, interval and alternate screws instrumentation in convex or concave side. The whole surgical procedures of screw-placement strategies were simulated. And their influences in the curve correction as well as the biomechanics of the implants and implant-bone interface were analyzed. Results: The densities of pedicle screws were 100%, 79%, 64%, 57% and 50%, respectively. During curve correction, interval and alternate screws instrumentation demonstrated higher screws stress, while the higher rods and screw-rod interface was observed in consecutive screws instrumentation. When it referred to the interaction force between screws and vertebrae, a lower stress was observed in in consecutive screws instrumentation. After the fixation of rod at convex side, the maximum stress on screws in each strategy was observed in interval screws instrumentation. The higher stress of rods was observed in alternate screws instrumentation in both sides. However, the correction rate of each strategy was similar. Conclusion: There was little distinction on the curve correction rate in different screw-placement strategies. The screw-placement strategy with interval and alternate screws instrumentation has better biomechanics properties than others, except for higher maximum interaction force between screws and vertebrae.

Analysis of the Change Patterns of Sagittal Alignment Values After Selective Thoracic Fusion in Lenke 1 Adolescent Idiopathic Scoliosis According to Preoperative Thoracic Kyphosis Status

STUDY DESIGN

This was a retrospective study.

OBJECTIVE

The objective of this study was to demonstrate the different change patterns in reciprocal sagittal alignment values after selective thoracic fusion (STF) in Lenke type 1 adolescent idiopathic scoliosis (AIS) according to preoperative thoracic kyphosis (TK).

SUMMARY OF BACKGROUND DATA

Several studies have found significant increase in TK after STF, while other studies have reported decrease in TK postoperatively. Similar inconclusive results on changes in lumbar lordosis (LL) have been reported, showing LL increase, decrease, or no change.

MATERIALS AND METHODS

Ninety-three patients presenting with Lenke type 1 AIS treated by posterior STF with a minimum follow-up of 2 years were included in this study. Using whole spine radiographs, sagittal parameters including TK, LL, and upper lumbar lordosis (ULL) were compared preoperatively and at the last follow-up between a hypokyphosis group (preoperative TK<20 degrees) and a normokyphosis group (preoperative TK≥20 degrees). Health-related quality of life (HRQOL) was assessed using scoliosis research society health-related quality of life-30 (SRS-30) and short from health survey-36 questionnaire at the last visit.

RESULTS

The mean follow-up duration was 74.9 months. In the hypokyphosis group (35 patients), TK, LL, and ULL statistically significantly increased after surgery by mean 7.7, 5.1, and 3.7 degrees (P<0.001, <0.001, and 0.001). In the normokyphosis group (58 patients), these parameters did not show significant changes after STF. Final TK was significantly lower in hypokyphosis group than that in the normokyphosis group (21.2 vs. 30.9 degrees, P<0.001) while final LL did not differ between 2 groups (52.4 vs. 54.6 degrees, P=0.194). HRQOL did not differ significantly between the 2 groups.

CONCLUSIONS

After STF in Lenke 1 AIS, TK, and LL statistically significantly increased through an increase in the mean ULL in the hypokyphosis group while those mean values did not change in the normokyphosis group. Despite the final mean value of the TK in the hypokyphosis group increasing by 7.7 degrees, it was statistically significantly lower than the final mean TK value in the normokyphosis group which did not increase after STF surgery by posterior approach. However, HRQOL showed no significant difference between the 2 groups.

The implant density does not change the correction rate of the main and the accompanying curves: A comparison between consecutive and intermittent pedicle screw constructs

OBJECTIVE

The aim of this study was to evaluate the clinical outcomes and the coronal correction rate of the main and accompanying curves of adolescent idiopathic scoliosis (AIS) corrected with pedicle screws inserted consecutively or intermittently.

METHODS

The prospectively collected data of 60 patients (8 men and 52 women; mean age: 14.6±2.5 years) who underwent corrective surgery for AIS between January 2010 and December 2015 were reviewed retrospectively. Two groups were constituted according to the pedicle screw construct type: consecutive pedicle screw construct (CPSC) and intermittent pedicle screw construct (IPSC) groups. The preoperative, early postoperative, and 24-month follow-up radiographs and the Scoliosis Research Society-22 (SRS-22) scores were reevaluated. The Cobb angle of the main and accompanying curves, the correction rate, and the flexibility of the curves were calculated.

RESULTS

The mean preoperative Cobb angles were 57.03° and 57.46°, the mean postoperative Cobb angles were 14.93° and 14.4°, and the mean correction rates were 76.22% and 75.31% in IPSC and CPSC groups, respectively (p>0.05). The preoperative and postoperative accompanying curve magnitudes and correction rates were similar (p>0.05). These radiographic outcomes were also consistent with the SRS-22 scores.

CONCLUSION

Both the pedicle screw constructs had satisfactory outcomes following the surgery, which were confirmed by both the SRS-22 scores and radiographs taken perioperatively and at follow-ups. The IPSC and CPSC groups did not demonstrate a significant change in the correction rate of the main and minor or major accompanying structural and nonstructural curves, and also in the SRS-22 scores.

LEVEL OF EVIDENCE

Level III, Retrospective comparative study.

Impact of metal density on deformity correction in posterior fusions for adolescent idiopathic scoliosis: A retrospective cohort study

Introduction

Optimal implant density for posterior spinal fusion in adolescent idiopathic scoliosis (AIS) remains controversial. We aimed to examine radiographic outcomes of AIS cases treated with limited density pedicle screw constructs.

Methods

This is a retrospective analysis of 96 patients (89 females and 7 males with mean age of 13.8 ± 4.4 years) with AIS who underwent posterior spinal instrumentation at Ghurki Trust Teaching Hospital between 2014 and 2016. Construct characteristics and radiographic measurements were compared preoperatively and at 2 year follow-up using paired t-test. Pearson's correlation coefficient between curve characteristics and metal density was calculated.

Results

Preoperative coronal Cobb angle was 68.5 ± 6.9°. Flexibility of the curve was 47.5 ± 10.3% based on push-prone films. The mean number of vertebrae in the fusion was 10.7 ± 1.6. The implant density was 62%. The mean postoperative Cobb angle was 18.6 ± 4.2°, giving a mean correction of 72.5 ± 6.8%. Metal density was not correlated with preoperative coronal or sagittal radiographic variables; MT Cobb angle (r = 0.02, p = 0.847), MT curve flexibility (r = 0.129, p = 0.210), preoperative thoracic kyphosis (r = -0.119, p = 0.247) or lumbosacral lordosis (r = −0.048, p = 0.645). There was a significant correlation between the flexibility of the curve as assessed by push-prone radiographs with the percentage correction achieved (r = 0.368, p < 0.0001) as well as absolute correction in degrees (r = 0.643, p < 0.0001). No significant correlations were present between metal density and MT curve coronal correction rate/percentage (r = 0.086, p = 0.407) or postoperative Cobb angle (r = 0.098, p = 0.344).

Conclusion

Metal density does not influence the coronal and sagittal correction of AIS. Neither larger nor stiffer curves necessitate high metal density.

Level of evidence

IV.

•

Metal density does not influence either amount of main thoracic curve correction or post-operative Cobb angle.

•

We conclude that posterior fusion constructs with implant densities of approximately 60% can safely be used in moderate, flexible (45–80°, average 47% flexibility) idiopathic curves to attain and maintain correction in adolescent idiopathic scoliosis.

•

There is a significant correlation between the flexibility of the curve as assessed by push-prone radiographs with the percentage correction achieved as well as absolute correction in degrees.

•

We found that preoperative coronal or sagittal radiographic variables like main thoracic Cobb angle, curve flexibility, preoperative thoracic kyphosis or lumbosacral lordosis did not influence surgeon's decision for implant density.

•

Longer fusions were required for larger and less flexible curves.

Reciprocal Change in Sagittal Profiles After Adolescent Idiopathic Scoliosis Surgery With Segmental Pedicle Screw Construct: A Full-body X-ray Analysis

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

This radiographic analysis using a full-body x-ray evaluated the ways in which the sagittal profiles of the unfused spinal segments, pelvic, and lower extremities spontaneously change after adolescent idiopathic scoliosis (AIS) surgery with segmental pedicle screw constructs.

SUMMARY OF BACKGROUND DATA

Reciprocal lordotic changes in unfused spinal segments after corrective surgery for AIS have been reported. However, a full-body analysis has not been studied.

METHODS

The sagittal profiles of 51 (age ≤18) patients with AIS undergoing corrective surgery with segmental pedicle screw constructs were investigated. Patients were divided into two groups: group T; selective thoracic fusion and group L; fusion to the low lumbar spine. They were further subcategorized according to preoperative thoracic kyphosis (TK: T5-12): hypokyphotic (TK <20°) and normohyperkyphotic (TK >20°) groups. The postoperative change in the sagittal parameters and the correlation between the instrumented thoracic alignment change (ΔT2-12) and reciprocal changes of unfused segments were analyzed.

RESULTS

At baseline, the entire cohort had a relatively hypokyphotic thoracic spine (TK: 25.5° ± 13.7°), low T1 slope (13.6° ± 7.7°), and kyphotic cervical spine (C2-7 lordosis: 7.7° ± 13.1°). The lower extremities were in neutral alignment overall. Postoperatively, the cervical alignment changed significantly lordotic (average -13.4° increased lordosis) after the adequate preservation of TK (average 17.8° increased kyphosis) in the hypokyphotic group T. Linear correlations were observed between ΔT2-12 and spontaneous reciprocal changes in C2-7 lordosis, lumbar lordosis, and knee flexion angle in group T.

CONCLUSION

The sagittal profiles of patients with AIS can significantly change after adequate restoration of TK which averaged 17.8°, particularly in the cervical spine. Lordotic reciprocal change in the cervical spine as well as increase in lumbar lordosis can occur in a linear correlation after adequate restoration of TK. There were no significant changes that occurred in the pelvis or lower extremities after AIS corrective surgery.

LEVEL OF EVIDENCE

4.

Are inferior facetectomies adequate and suitable for surgical treatment of adolescent idiopathic scoliosis?

STUDY DESIGN

Retrospective review.

BACKGROUND

Inferior facetectomies, with the utilization of segmental pedicle screw constructs for corrective fixation, can provide adequate flexibility and post less risk of neural tissue and blood loss. We analyzed outcomes of surgical treatment for adolescent idiopathic scoliosis (AIS) using inferior facetectomies and segmental pedicle screw constructs. We hypothesized that adequate main curve correction and suitable surgical outcomes would be observed using this technique.

METHODS

We reviewed 38 AIS patients who underwent inferior facetectomies and segmental pedicle screw constructs by 2 surgeons at a single institution between May 2014 and December 2016. Coronal and sagittal radiographic measurements were evaluated over 1-year follow-up by 2 trained observers not associated with the surgeries. Surgical details, complications, and hospital length of stay (LOS) were also recorded.

RESULTS

Mean fusion levels were 11.0 ± 1.7. The mean Cobb angle of main AIS curves improved from 48.6± 10.1 degree preoperatively to 11.8± 6.2 degree postoperatively and 12.4± 6.2 degree at 1-year follow-up, which percentage correction was 75.9% and 74.6%, respectively. The mean thoracic kyphosis (T5-12) angle was 20.7± 11.6 degree preoperatively, 17.4± 8.0 degree postoperatively, and 16.8± 8.4 degree at 1-year follow-up. The mean surgical time, estimated blood loss, and LOS were 232.4 ± 35.7 minutes, 475.0 ± 169.6 mL, and 3.5 ± 1.3 days. Twelve patients received blood transfusion. There were no neurological or wound complications.

CONCLUSIONS

This case series demonstrated adequate correction of main AIS curves, acceptable thoracic kyphosis and blood loss, and short surgical time and LOS in AIS patients treated with inferior facetectomies and segmental pedicle screw constructs, potentially indicating that inferior facetectomies are adequate and suitable for AIS surgery when segmental pedicle screw constructs are utilized.

Periapical-dropout Screws Strategy For 3-Dimensional Correction of Lenke 1 Adolescent Idiopathic Scoliosis in Patients Treated by Posterior Spinal Fusion

STUDY DESIGN

This was a single-center, retrospective study.

OBJECTIVE

The objective of this study was to compare periapical-dropout screws strategy (PDSS) with traditional-multilevel pedicle screws strategy (TMSS) for 3-plane correction of Lenke 1 adolescent idiopathic scoliosis deformity.

SUMMARY OF BACKGROUND DATA

There are limited data in 3-plane correction and the optimal pedicle screw (PS) configuration for Lenke 1 adolescent idiopathic scoliosis surgery.

MATERIALS AND METHODS

Sixty-one consecutive patients with Lenke 1 curves (range: 50-80 degrees), undergoing single-stage posterior spinal fusion with PS fixation, were included. Patients with a minimum follow-up of 1 year were divided into 2 groups according to PS strategy. The PDSS group included 33 patients with PS placement bilaterally at both ends and apex of the construct. The TMSS group included 28 patients with conventional PS placement. Baseline, immediate, and last follow-up demographic, radiographic, and clinical outcomes were analyzed. Radiographic outcomes were assessed in axial (using rib index and apical vertebral rotation using Raimondi ruler and Upasani methods), coronal, and sagittal planes. The implant costs were also evaluated.

RESULTS

There were no differences in demographic, preoperative radiographic parameters and levels fused. The number of PSs per level fused was significantly lower in the PDSS group (1.3 vs. 1.4; P=0.0002). At last follow-up, major Cobb correction averaged 79% for the PDSS group and 69.5% for the TMSS group (P=0.001). T2-T12 kyphosis angle changes were 1 degree in the PDSS group and -2.5 degrees in the TMSS group (P=0.35). Rib index correction was 28.2% for the PDSS group and 17.7% for the TMSS group (P=0.02). Upasani grade apical vertebral rotation was significantly better in the PDSS group (0.7 vs. 1.4; P=0.0001). Clinical outcomes evaluated by Scoliosis Research Society-30 scores were similar in both groups. Total implant costs were significantly lower in the PDSS group ($16,852 vs. $18,926; P<0.001).

CONCLUSION

The PDSS construct provides better deformity correction in all 3 planes and helps decrease implant costs compared with the TMSS construct. Thus, the PDSS construct can be considered as a rational strategy and cost-effective technique when treating moderate Lenke 1 curves with posterior spinal fusion.

Anterior and Posterior Fusion for Large, Rigid Idiopathic Scoliosis: Does Implant Density Matter?

BACKGROUND

Despite advancements in surgical techniques, controversy remains regarding the optimal implant density for the correction of idiopathic scoliosis. Recent evidence has suggested that equivalent radiographic and clinical outcomes can be achieved with lower implant densities for those with moderate curves and good flexibility. Among the experts, the consensus has continued that higher implant densities should be used for larger, stiffer curves. The purpose of the present study was to compare the radiographic results between high-implant density (HID) and low-implant density (LID) constructs in patients with large (>65°), rigid (<50% flexibility) curves who had undergone anterior release and posterior spinal fusion.

METHODS

We reviewed the idiopathic scoliosis cases performed at a single institution from 2006 to 2014. Only those meeting the inclusion criteria were selected. The patients were divided into HID and LID groups. The postoperative radiographs were compared for coronal correction, thoracic kyphosis, pelvic tilt, lumbar lordosis, and sagittal vertical axis.

RESULTS

A statistically significant improvement in coronal correction was detected in the HID group at all follow-up points (final follow-up: HID, 81.1% vs. LID, 70.4%; P = 0.01). When preoperative thoracic kyphosis was considered, no differences were found between the 2 groups. No differences were found in the other sagittal parameters.

CONCLUSION

In patients with large, rigid idiopathic scoliosis undergoing anterior release and posterior spinal fusion, a small, but statistically, significant improvement in the coronal Cobb angle was seen. It remains to be determined whether this small difference in radiographic correction will have any influence on the clinical outcome.

Determination of optimal screw number based on correction angle for main thoracic curve in adolescent idiopathic scoliosis

BACKGROUND

Reducing the number of screw insertions while maintaining good clinical outcomes can improve the efficiency and cost-effectiveness of scoliosis surgery. However, the optimal minimum number of pedicle screws remains unclear. This study searched for factors to estimate the fewest number of pedicle screws required between end vertebrae in relation to preoperative main thoracic curve flexibility.

METHODS

Sixty-nine subjects (4 male and 65 female, mean age: 14.8 ± 2.5 years) who underwent skip pedicle screw fixation for Lenke type 1-4 or 6 curves and were followed for at least 1 year were enrolled. Intervention technique was selected according to the size and flexibility of the preoperative main thoracic curve. Surgery-related variables included pedicle screw number, rod material and diameter, and extent of Ponte osteotomy. The effect on postoperative correction angle (i.e., the difference between the preoperative supine position maximum bending and postoperative standing Cobb angles of the main thoracic curve) according to surgical intervention technique was estimated using multiple linear mixed regression models with the preoperative supine position maximum bending correction angle (i.e., the difference between the standing preoperative and supine position maximum bending Cobb angles) as a random effect.

RESULTS

The preoperative maximum bending correction angle was 8-42° and had a moderate negative correlation with postoperative correction angle (r = -0.65, P < 0.01). Multivariate analysis revealed a 1.7° (95% CI 0.7-2.6; P < 0.01) correction gain per single-screw insertion and a 1.8° (95% CI 0.5-3.1; P < 0.01) gain per intervertebral level in Ponte osteotomy.

CONCLUSIONS

The number of pedicle screws necessary to correct main thoracic adolescent idiopathic scoliosis curves can be estimated by calculating correction gains of 1.7° per pedicle screw and 1.8° per Ponte osteotomy intervertebral level. Based on these results, it may be possible to reduce invasiveness and cost for patients requiring a smaller degree of correction.

Long-term follow-up after surgical treatment of adolescent idiopathic scoliosis using high-density pedicle screw constructs: Is 5-year routine visit required?

PURPOSE

The objective of this study is to determine whether routine follow-up 5 years after adolescent idiopathic scoliosis (AIS) surgery is likely to affect postoperative care for patients treated with high-density pedicle screw constructs, when routine 2-year follow-up has been performed.

METHODS

We reviewed 80 patients undergoing surgery for AIS using high-density pedicle screw constructs and followed routinely 2 and 5 years after surgery. Quality of life (QOL) was assessed using the SRS-30 outcome questionnaire. Reoperations occurring between 2 and 5 years after surgery were identified.

RESULTS

Curve correction and QOL were similar between 2- and 5-year visits. Two patients required revision surgery after presenting during unplanned visits between the 2- and 5-year follow-ups. One patient presented at the routine 5-year visit with an asymptomatic undisplaced rod fracture without loss of correction, and it was decided to follow-up only as needed.

CONCLUSIONS

In AIS patients for whom routine follow-up 2 years after surgery using high-density pedicle screw constructs was uneventful, additional routine 5-year follow-up is not likely to affect postoperative care and revision rate. Patients developing complications and needing reoperation between 2 and 5 years after surgery will most likely present during unplanned visits rather than during routine follow-up appointments. Easy access to emergent visits on an as-needed basis is therefore important for this population if routine 5-year follow-up is not planned. These slides can be retrieved under Electronic Supplementary Material.

Sagittal Spinopelvic Alignment After Posterior Spinal Fusion in Adolescent Idiopathic Scoliosis: A Systematic Review and Meta-analysis

STUDY DESIGN

A systematic review and meta-analysis.

OBJECTIVE

The aim of this study was to determine the differences in the sagittal spinopelvic parameters between the nonscoliotic controls, preoperative, and different time points postoperative in Lenke 1 and 5 adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

The postoperative changes in the sagittal profile of Lenke 1 and 5 AIS at varying time points after posterior spinal fusion (PSF) has not been rigorously demonstrated; studies performed have had conflicting results.

METHODS

Sagittal spinal and pelvic parameters, T5-T12 thoracic kyphosis (TK), L1-S1 lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), and sagittal vertical axis (SVA), for Lenke 1 and 5 preoperatively, at immediate, less than 2-year, and more than 2-year postoperatively, and for nonscoliotic adolescents were searched. Differences in the sagittal spinopelvic parameters between preoperative and the follow-ups and between the nonscoliotic and pre- and postoperative AIS subtypes were calculated through meta-analysis.

RESULTS

A total of 22 studies on Lenke1 (1229 patients), 13 studies on Lenke5 (437 patients), and 18 studies on controls (1636 patients) were reviewed. Among all the measured variables, only PI in Lenke1 was significantly different between the final follow-up and controls, P < 0.05. In Lenke 1, SVA was significantly more anterior at the immediate postoperative than preoperative, but continued moving posteriorly up to 2-year postoperative resulting in no significant difference in the SVA position between the final follow-up and preoperative, P > 0.05. In Lenke 5, SVA was significantly more posterior at the immediate postoperative and more anterior at the final follow-up than the preoperative measurements, p < 0.05.

CONCLUSIONS

Continuous changes in the sagittal spinal parameters should be expected after PSF. Normalization of the sagittal spinal parameters appears to be the rule after PSF, and watchful waiting appears to be appropriate in this population when viewing the lateral X-ray postoperatively.

LEVEL OF EVIDENCE

4.

ADOLESCENT IDIOPATHIC SCOLIOSIS AND SIMILAR CONDITIONS: NEW TOOL TO MEASURE THE CORONAL PLANE

ABSTRACT Objective: To create a method to measure the overall coronal plane of the spine, called the sacral clavicular angle (SCA). Methods: A line is drawn at the base of the sacrum; a second central line is drawn perpendicular to the first one in the proximal extension of the spine. A third line is drawn passing through the intersections of the superior points of the clavicles with the two second ribs, forming two angles, the greater of which is measured. Therefore, the degrees exceeding 90° are the SCA values. This tool was tested retrospectively in a study of 46 patients with idiopathic scoliosis who underwent short, apical, single or multiple fixations. Third generation instrumentation was used and the SCA was evaluated in the pre- and postoperative periods, which were compared with another group of 46 patients treated with the traditional technique. Results: Patients submitted to the traditional fixation method presented a median SCA of 3° in the preoperative period, and in the postoperative period, the SCA remained in 3°. Therefore, there was a 0% reduction. Patients submitted to short, apical, single or multiple fixation method presented a median preoperative SCA of 6°, and a postoperative median SCA of 1°, a reduction of approximately 83%. Conclusions: The group treated with short, apical, single or multiple instrumentation presented a reduction in the SCA of approximately 83% in the postoperative period compared to the preoperative period. The difference between preoperative and postoperative values was considered statistically significant. Level of Evidence II; Retrospective study.

ADOLESCENT IDIOPATHIC SCOLIOSIS AND SIMILAR CONDITIONS: SHORT, APICAL, SINGLE OR MULTIPLE FIXATION

ABSTRACT Objective: To create a new instrumentation principle for the treatment of adolescent idiopathic scoliosis (AIS) and similar conditions. Methods: A new fixation format was created for the treatment of AIS using 3rd generation instrumentation in short, apical and single or multiple fixations. In patients presenting one scoliotic curve, one fixation is performed. In patients with two curves, two fixations are performed, and in those with three curves, three fixations are performed. To evaluate the new method, a retrospective study of 54 patients who had already undergone surgery for AIS and similar conditions using this innovation was conducted. Results: In this series, average corrections of 72% in the proximal curve, of 83% in the thoracic curve, and of 85% in the thoracolumbar curve were verified. Conclusions: It was concluded that the new fixation principle in the treatment of AIS and similar conditions using short, apical and multiple fixations presented excellent correction, better still in the curves that were more distal in relation to the spine. There was a significant statistical difference between the percentages of curvature correction. Level of Evidence III; Retrospective study.

Clinical and radiological outcomes of the multilevel Ponte osteotomy with posterior selective segmental pedicle screw constructs to treat adolescent thoracic idiopathic scoliosis

Background

To compare the clinical and radiological outcomes of the surgical correction of Lenke type 1 to 4 scoliosis by using a multilevel Ponte osteotomy procedure with posterior selective segmental pedicle screw constructs or posterior release and selective segmental pedicle screw constructs only in patients with adolescent thoracic idiopathic scoliosis.

Methods

Retrospective analysis of 65 patients, 32 treated with the multilevel Ponte procedure (Group A) and 33 with posterior soft tissue release only (Group B). The groups were compared with regard to the change in spinal alignment from preoperative to postoperative assessment and over the follow-up period.

Results

A correction rate of the main thoracic curve of 63.9 ± 4.5% was obtained for group A and 65.2 ± 2.4% for group B (P = 0.17). However, the Cincinnati correction index was greater for group A (1.8 ± 0.3) than that for group B (1.4 ± 0.2, P < 0.001), with a smaller change in angle over the period from 1 week postoperatively to the 2-year follow-up (P < 0.05). The operative time, volume of blood loss, and volume of transfusion were greater for group A than for group B (P < 0.05).

Conclusion

The multilevel Ponte osteotomy procedure, with posterior selective segmental pedicle screw constructs, improves the Cincinnati correction index and restores the thoracic kyphosis in patients with adolescent thoracic idiopathic scoliosis.

Significant variability in surgeons' preferred correction maneuvers and instrumentation strategies when planning adolescent idiopathic scoliosis surgery

BACKGROUND

Increased implant number is thought to provide better control on the scoliotic spine, but there is limited scientific evidence of improved deformity correction and surgical outcomes with high-density constructs. The objective is to assess key anchor points used by experienced spinal deformity surgeons and to evaluate the effect of implant density pattern on correction techniques.

METHODS

Seventeen experienced spine surgeons reviewed five Lenke 1 adolescent idiopathic scoliosis cases and provided their preferred posterior correction technique (implant pattern, correction maneuvers, and implants used for their execution) and an alternative technique with the minimal implant density they felt would be acceptable (170 surgical plans total). Additionally, for each case, they selected acceptable screw patterns for surgery from seven published implant configurations. Variability in the surgeons' plans was assessed, including instrumentation and correction strategies.

RESULTS

The preferred correction plan involved an average of 1.65 implants/vertebra, with 88% of the available anchor points at the apex ± 1 vertebra used for the execution of correction maneuvers and only 43% of possible anchor points used proximal and distal to the apical area. The minimal density that surgeons found acceptable was 1.24 implants/vertebra. The minimal density plan involved more in situ rod contouring (53 vs. 41%), fewer vertebral derotation maneuvers (82 vs. 96%), and fewer implants used for compression/distraction maneuvers (1.18 and 1.42 respectively) (p < 0.05). Implant placement at alternate levels or dropout of convex implants above and below the apical area was most frequently considered acceptable (> 70% agreement).

CONCLUSIONS

Implant position and number affect surgeons correction maneuvers selection. For low implant density constructs, dropout in the convexity and particularly in the periapical region is accepted by surgeons, with minor influence on planned correction maneuvers. Thus, preoperative implant planning must take into account which anchor points are needed for desired correction maneuvers.

Implant Density at the Apex Is More Important Than Overall Implant Density for 3D Correction in Thoracic Adolescent Idiopathic Scoliosis Using Rod Derotation and En Bloc Vertebral Derotation Technique

STUDY DESIGN

Biomechanical analysis of 3D correction and bone-screw forces through numerical simulations of scoliosis instrumentation with different pedicle screw patterns.

OBJECTIVE

To analyze the effect of different screw densities and distributions on 3D correction and bone-screw forces in adolescent idiopathic scoliosis (AIS) instrumentation.

SUMMARY OF BACKGROUND DATA

Instrumentation constructs with various numbers of pedicle screws and patterns have been proposed for thoracic AIS instrumentation. However, systematic biomechanical studies have not yet been completed on the appropriate screw patterns for optimal 3D correction.

METHODS

Patient-specific biomechanical models of the spine were created for 10 AIS cases (Lenke 1). For each case, surgical instrumentation patterns were computationally simulated using respectively a reference screw pattern (two screws per level fused) and six alternative screw patterns with fewer screws. Simulated surgical maneuvers and model definition were unchanged between simulations except the number and distribution of screws. 3D correction and bone-screw forces were compared.

RESULTS

A total of 140 posterior instrumentations were computationally simulated. Mean corrections in the coronal and sagittal planes with alternative screw patterns were within 4° to the reference pattern. Increasing screw density in the apical region from one to two screws per level improved percent apical vertebral rotation (AVR) correction (r = 0.887, P < 0.05). Average bone-screw force associated with the reference screw pattern was 243N ± 54N and those with the alternative screw patterns were 11% to 48% lower.

CONCLUSION

Compared with the reference maximal screw density pattern, alternative screw patterns allowed similar corrections in the coronal and sagittal planes. AVR correction was strongly correlated with screw density in the apical region; AVR correction varied significantly with screw patterns of the same overall screw density when an en bloc vertebral derotation technique was simulated. High screw density tended to overconstrain the instrumented spine and resulted in higher forces at the bone-screw interface.

LEVEL OF EVIDENCE

N/A.

Reciprocal Changes in Sagittal Alignment in Adolescent Idiopathic Scoliosis Patients Following Strategic Pedicle Screw Fixation

Study Design

Retrospective observational study.

Purpose

To analyze the effect of low-density (LD) strategic pedicle screw fixation on the correction of coronal and sagittal parameters in adolescent idiopathic scoliosis (AIS) patients.

Overview of Literature

LD screw fixation achieves favorable coronal correction, but its effect on sagittal parameters is not well established. AIS is often associated with decreased thoracic kyphosis (TK), and the use of multi-level pedicle screws may result in further flattening of the sagittal profile.

Methods

A retrospective analysis was performed on 92 patients with AIS to compare coronal and sagittal parameters preoperatively and at 2-year follow-up. All patients underwent posterior correction via LD strategic pedicle screw fixation. Radiographs were analyzed for primary Cobb angle (PCA), coronal imbalance, cervical sagittal angle (CSA), TK, lumbar lordosis (LL), pelvic incidence, pelvic tilt (PT), sacral slope (SS), C7 plumb line, spino-sacral angle, curve flexibility, and screw density.

Results

PCA changed significantly from 57.6°±13.9° to 19°±8.4° (p <0.0001) with 67% correction, where the mean curve flexibility was 41% and screw density was 68%. Regional sagittal parameters did not change significantly, including CSA (from 10.76° to 10.56°, p =0.893), TK (from 24.4° to 22.8°, p =0.145), and LL (from 50.3° to 51.1°, p =0.415). However, subgroup analysis of the hypokyphosis group (<10°) and the hyperkyphosis group (>40°) showed significant correction of TK (p <0.0001 in both). Sacro-pelvic parameters showed a significant decrease of PT and increase of SS, suggesting a reduction in pelvic retroversion SS (from 37° to 40°, p =0.0001) and PT (from 15° to 14°, p =0.025).

Conclusions

LD strategic pedicle screw fixation provides favorable coronal correction and improves overall sagittal sacro-pelvic parameters. This technique does not cause significant flattening of TK and results in a favorable restoration of TK in patients with hypokyphosis or hyperkyphosis.

Low-Density Pedicle Screw Constructs for Adolescent Idiopathic Scoliosis: Evaluation of Effectiveness and Cost

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To determine whether a low-density (LD) screw construct can achieve curve correction similar to a high-density (HD) construct in adolescent scoliosis.

METHODS

Patients treated operatively for idiopathic scoliosis between 2007 and 2011 were identified through a database review. A consistent LD screw construct was used. Radiographic assessment included percent correction of major and fractional lumbar curves, T5-T12 kyphosis, and angle of lowest instrumented vertebra (LIV). Costs were compared with HD constructs.

RESULTS

Thirty-five patients were included in the analysis. Ages ranged from 12 to 19 years (mean = 14.9 years). Average screw density was 1.2 screws per level (range = 1.07-1.5 screws). Mean percent curve correction at latest follow-up: major curve, 66.9%; fractional lumbar curve, 63%. Average postoperative thoracic kyphosis: 29.5°. Mean LIV angle: 5.6°. Average construct cost was $14 871 per case compared with $23 840 per case if all levels had been instrumented with 2 screws, amounting to an average savings of $9000.

CONCLUSIONS

Our LD screw construct is among the lowest density constructs reported and achieves curve correction comparable to HD constructs at substantially lower cost.

Current concepts in the surgical management of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a complex 3D deformity of the spine. Its prevalence is between 2% and 3% in the general population, with almost 10% of patients requiring some form of treatment and up to 0.1% undergoing surgery. The cosmetic aspect of the deformity is the biggest concern to the patient and is often accompanied by psychosocial distress. In addition, severe curves can cause cardiopulmonary distress. With proven benefits from surgery, the aims of treatment are to improve the cosmetic and functional outcomes. Obtaining correction in the coronal plane is not the only important endpoint anymore. With better understanding of spinal biomechanics and the long-term effects of multiplanar imbalance, we now know that sagittal balance is equally, if not more, important. Better correction of deformities has also been facilitated by an improvement in the design of implants and a better understanding of metallurgy. Understanding the unique character of each deformity is important. In addition, using the most appropriate implant and applying all the principles of correction in a bespoke manner is important to achieve optimum correction.

In this article, we review the current concepts in AIS surgery.

Cite this article: Bone Joint J 2018;100-B:415–24.

Does pedicle screw density matter in Lenke type 5 adolescent idiopathic scoliosis?

The aim of this study is to compare the effects of high versus low implant density on correction in Lenke type 5 adolescent idiopathic scoliosis (AIS) patients. A retrospective study of 59 Lenke type 5 AIS patients treated at a single institution were divided into to 2 groups according to implant density. Implant density, preoperative, early postoperative, and last follow-up thoracolumbar/lumbar (TL/L) curves were measured. Thirty-one constructs were high and 28 constructs were low density. The groups were similar in terms of age, sex, Cobb angle, and follow-up time. Mean implant density in low density group and high density group was 75.4% and 96.6%, respectively. High versus low-density comparison showed that there is no significant difference with regard to curve correction in early postoperative and last follow-up periods. The results show that pedicle screw density being low or high, does not affect curve correction rates in the short and long term in our patients.

Analysis of correlation between regional implant density and the correction rate in treatment of Lenke 1A and 1B adolescent idiopathic scoliosis with pedicle screws

A retrospective study.The optimal implant density in patients with Lenke type 1 adolescent idiopathic scoliosis (AIS) is undefined, and there is no study reporting the correlation between the partitional implant density and the correction outcome.To determine whether the implant density in structural and nonstructural regions would affect the coronal correction outcome of Lenke 1A and 1B AIS.Preoperative general data and postoperative follow-up data of Lenke 1A and 1B AIS patients who received posterior fusion with the pedicle screw system were analyzed. Correlations between the implant density in structural and nonstructural regions and the correction rate of coronal Cobb angle, as well as between the correction rate and loss of the coronal correction angle during a 2-year follow-up period were analyzed. According to the implant density, the patients were classified into 2 groups: structural region group (including A1 and A2), and nonstructural region group (including B1 and B2). Differences in related parameters between the 2 groups were compared statistically.Except for the mean implant density, there was no statistical difference in the other parameters between group A1 and A2. In group B1 and B2, the correction rate of the main thoracic (MT) curve was 63.0% and 71.6% (P = .022), and the loss of the correction angle was 2.1° and 4.2°, respectively (P < .01), showing a statistical difference in the correction rate and postoperative angle loss of the MT curve between group B1 and B2.The correction rate of the MT curve at the coronal plane and postoperative loss of the correction angle were not related to the implant density in structural regions but may be related to the implant density in nonstructural regions in the treatment of Lenke type 1A and 1B AIS with pedicle screw instrumentation.

Key Vertebral Pedicle Screw Strategy for the Correction of Flexible Lenke Type 1 Adolescent Idiopathic Scoliosis: A Preliminary Study of a 5-year Minimum Radiographic Follow-up

STUDY DESIGN

A retrospective clinical and radiographic study.

OBJECTIVE

The aim of this study was to evaluate outcomes of the key vertebral pedicle screw strategy (KVPSS) for the correction of flexible Lenke type 1 adolescent idiopathic scoliosis (AIS) with a minimum follow-up of 5 years.

SUMMARY OF BACKGROUND DATA

The KVPSS has been described as an alternative screw placement strategy for surgically treating the main thoracic curve in AIS patients. However, there have been no long-term, three-dimensional correction studies of selective thoracic fusion using the KVPSS in Lenke type 1AIS.

METHOD

Twenty consecutive patients with Lenke type 1 main thoracic AIS underwent one-stage posterior correction and fusion using the KVPSS. Preoperative and postoperative radiographic and clinical parameters were analyzed.

RESULTS

The mean preoperative major thoracic curve was 47.4° ± 5.8°, and mean corrections of 67.0%, 63.4%, and 61.5% were observed at the immediate, 2-year postoperative, and final follow-ups, respectively. Thoracickyphosis decreased significantly from the preoperative period to the immediate postoperative period (P = 0.042) but did not change significantly from the 2-year postoperative follow-up to the final follow-up (P = 0.067). Apical vertebral rotation achieved 34.7% correction and exhibited correction loss of 8.2% at the final follow-up. The average intraoperative blood loss was 802.3 mL, and the mean operative time was 138.6 minutes. SRS-22 scores for self-image and satisfaction improved significantly from the preoperative period to the final follow-up. No neurologic or implant-associated complications were observed in this study.

CONCLUSION

The KVPSS is an effective method for correcting Lenke type 1 AIS and achieves satisfactory correction of the deformity. Relative to other approaches, the KVPSS can not only achieve a satisfactory and cost-effective clinical outcome but also reduce both operative time and intraoperative blood loss.

LEVEL OF EVIDENCE

4.

Comparison of low density and high density pedicle screw instrumentation in Lenke 1 adolescent idiopathic scoliosis

BACKGROUND

The correlation between implant density and deformity correction has not yet led to a precise conclusion in adolescent idiopathic scoliosis (AIS). The aim of this study was to evaluate the effects of low density (LD) and high density (HD) pedicle screw instrumentation in terms of the clinical, radiological and Scoliosis Research Society (SRS)-22 outcomes in Lenke 1 AIS.

METHODS

We retrospectively reviewed 62 consecutive Lenke 1 AIS patients who underwent posterior spinal arthrodesis using all-pedicle screw instrumentation with a minimum follow-up of 24 months. The implant density was defined as the number of screws per spinal level fused. Patients were then divided into two groups according to the average implant density for the entire study. The LD group (n = 28) had fewer than 1.61 screws per level, while the HD group (n = 34) had more than 1.61 screws per level. The radiographs were analysed preoperatively, postoperatively and at final follow-up. The perioperative and SRS-22 outcomes were also assessed. Independent sample t tests were used between the two groups.

RESULTS

Comparisons between the two groups showed no significant differences in the correction of the main thoracic curve and thoracic kyphosis, blood transfusion, hospital stay, and SRS-22 scores. Compared with the HD group, there was a decreased operating time (278.4 vs. 331.0 min, p = 0.004) and decreased blood loss (823.6 vs. 1010.9 ml, p = 0.048), pedicle screws needed (15.1 vs. 19.6, p < 0.001), and implant costs ($10,191.0 vs. $13,577.3, p = 0.003) in the LD group.

CONCLUSIONS

Both low density and high density pedicle screw instrumentation achieved satisfactory deformity correction in Lenke 1 AIS patients. However, the operating time and blood loss were reduced, and the implant costs were decreased with the use of low screw density constructs.

Defining the number and type of fixation anchors for optimal main curve correction in posterior surgery for adolescent idiopathic scoliosis

BACKGROUND CONTEXT

The number and type of fixation anchors to use during posterior surgery for adolescent idiopathic scoliosis (AIS) is still debated, and the relationship with curve correction remains unclear.

PURPOSE

This study aimed to determine the number and type of fixation anchors associated with optimal curve correction following posterior surgery for AIS.

STUDY DESIGN

A retrospective study of the relationship between fixation anchors and main curve correction in AIS surgery was carried out.

PATIENT SAMPLE

A cohort of 137 AIS patients operated from a posterior-only approach using hooks and pedicle screws comprised the study sample.

OUTCOME MEASURES

Correction of the main scoliotic curve was the outcome measure.

METHODS

Implant density (ID) was defined as the number of fixation anchors divided by the number of available anchor sites within the main curve. Pedicle screw ratio (PSR) was defined as the number of pedicle screws divided by the total number of fixation anchors within the main curve. Multiple linear regressions were performed to analyze the influence of ID and PSR on main curve correction, while taking into account age, gender, curve type, preoperative main Cobb angle, main curve reducibility, number of fused levels, and number of levels within the main curve.

RESULTS

Main coronal curve correction was significantly related only to ID for all patients and for the subgroup of patients with a main thoracic curve. Constructs with an ID ≥70% and <90% provided a correction similar to that obtained with an ID ≥90%. However, main coronal curve correction was inferior for constructs with an ID <70%, when compared with constructs with ID ≥90%. Implant density and PSR were not related to the change in thoracic kyphosis in the multiple linear regressions.

CONCLUSIONS

Implant density is an important predictor of main coronal curve correction in posterior surgery for AIS. Increasing the number of fixation anchors within the main curve-rather than favoring screws over hooks-can lead to better correction in the coronal plane. However, after reaching an ID of ≥70% in the main curve, adding fixation anchors is not likely to result in significantly greater correction of the main curve in the coronal plane.

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

OBJECTIVE The radiographic and clinical outcomes of low-density (LD) versus high-density (HD) screw constructs in patients with adolescent idiopathic scoliosis (AIS) treated with all-pedicle screw constructs are still controversial. A systematic review and pooled analysis were performed to compare radiographic, perioperative, and quality-of-life (QOL) outcomes and complications in patients with moderate AIS treated with LD or HD screw constructs. METHODS The MEDLINE, Embase, and Web of Science databases were searched for English-language articles addressing LD versus HD screw constructs in AIS patients treated with all-pedicle screw constructs. The division of LD and HD groups was based on relative screw density and screw techniques. This systematic analysis strictly followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and all articles included in the analysis met the criteria specified in the guidelines. Two reviewers independently assessed the quality of the studies using the Newcastle-Ottawa Scale. Date on radiographic, perioperative, and QOL outcomes and complications were extracted from the included studies. RESULTS Twelve studies, involving a total of 827 patients (480 treated with LD constructs, 347 with HD), were analyzed-1 randomized controlled trial, 1 quasi-randomized controlled trial, and 10 retrospective studies. The patients' age at surgery, preoperative Cobb angle of the major curve, amount of thoracic kyphosis, and major curve flexibility were reasonably distributed, and no statistically significant differences were found. Regarding the outcomes at most recent follow-up, there were no significant differences in the Cobb angle of the major curve (mean difference 0.96°, 95% CI -0.06° to 1.98°, p = 0.06, I² = 1%), major curve correction (mean difference -0.72%, 95% CI -2.96% to 1.52%, p = 0.53, I² = 0%), thoracic kyphosis (mean difference -1.67°, 95% CI -4.59° to 1.25°, p = 0.26, I² = 79%), complications (odds ratio [OR] 0.66, 95% CI 0.31-1.42, p = 0.29, I² = 0%), and QOL outcomes. Reduced operative time (mean difference -48.56 minutes, 95% CI -82.69 to -14.43 minutes, p = 0.005, I² = 87%), blood loss (mean difference -77.85 ml, 95% CI -153.10 to -2.60 ml, p = 0.04, I² = 0%), and hospital charges (mean difference -$5.92K, 95% CI -$6.59K to -$5.26K, p < 0.00001, I² = 0%) were found in the LD group, compared with the HD group. CONCLUSIONS LD and HD screw constructs are both associated with satisfactory radiographic and QOL outcomes with few complications. This study supports the use of LD screw constructs for the treatment of moderate AIS, because they resulted in reduced operative time, blood loss, and hospital charges while maintaining radiographic and QOL outcomes and complication rates similar to those achieved with HD screw constructs.

Comparison of Consecutive, Interval, and Skipped Pedicle Screw Techniques in Moderate Lenke Type 1 Adolescent Idiopathic Scoliosis

OBJECTIVE

To compare perioperative, radiographic, and Scoliosis Research Society-22 (SRS-22) outcomes of consecutive, interval, and skipped pedicle screw techniques in patients with moderate Lenke type 1 adolescent idiopathic scoliosis (AIS).

METHODS

We retrospectively reviewed 65 consecutive moderate Lenke type 1 AIS patients at a single institution using all-pedicle screw constructs, with a minimum of 2 years of follow-up. In the consecutive group (C group, n = 22), pedicle screws were instrumented at consecutive levels bilaterally. In the interval group (I group, n = 18), pedicle screws were placed at every level on the concave side while skipping levels on the convex side. In the skipped group (S group, n = 25), pedicle screws were instrumented by skipping levels bilaterally. Perioperative, radiographic, and SRS-22 measurements were analyzed with a 1-way analysis of variance.

RESULTS

No significant differences were found in length of hospital stay, fused levels, coronal correction, and SRS-22 scores among the 3 groups. Increased surgery time was found in the C group compared with the I and S groups (P = 0.001 and P = 0.005, respectively). Decreased blood loss and blood transfusions were found in the S group compared with the C group (P = 0.04 and P = 0.047, respectively). Decreased implant costs were found in the S group compared with the C and I groups (P < 0.001 and P = 0.03, respectively).

CONCLUSIONS

Consecutive, interval, and skipped pedicle screw techniques all provide satisfactory deformity correction and SRS-22 outcomes with few complications. With better perioperative outcomes, interval and skipped pedicle screw techniques are the more cost-effective options for patients with moderate Lenke type 1 AIS.

Comparative Analysis of Interval, Skipped, and Key-vertebral Pedicle Screw Strategies for Correction in Patients With Lenke Type 1 Adolescent Idiopathic Scoliosis

Pedicle screw constructs have become the mainstay for surgical correction in patients with spinal deformities. To reduce or avoid the risk of pedicle screw-based complications and to decrease the costs associated with pedicle screw instrumentation, some authors have introduced interval, skipped, and key-vertebral pedicle screw strategies for correction. However, there have been no comparisons of outcomes among these 3 pedicle screw-placement strategies.The aim of this study was to compare the correlative clinical outcomes of posterior correction and fusion with pedicle screw fixation using these 3 surgical strategies.Fifty-six consecutive patients with Lenke type 1 adolescent idiopathic scoliosis were included in this study. Twenty patients were treated with the interval pedicle screw strategy (IPSS), 20 with the skipped pedicle screw strategy (SPSS), and 16 with the key-vertebral pedicle screw strategy (KVPSS). Coronal and sagittal radiographs were analyzed before surgery, at 1 week after surgery, and at the last follow-up after surgery.There were no significant differences among the 3 groups regarding preoperative radiographic parameters. No significant difference was found between the IPSS and SPSS groups in correction of the main thoracic curve (70.8% vs 70.0%; P = 0.524). However, there were statistically significant differences between the IPSS and KVPSS groups (70.8% vs 64.9%) and between the SPSS and KVPSS groups (70.0% vs 64.9%) in correction of the main thoracic curve (P < 0.001 for both). Additionally, there were no significant differences among the 3 strategies for sagittal parameters at the immediate postoperative and last postoperative follow-up periods, though there were significant differences in the Cobb angle between the preoperative and immediate postoperative periods among the 3 groups, but not between the immediate postoperative and last follow-up periods. The amount of hospital charges in the SPSS group was significantly higher than those in the IPSS (P < 0.001) and KVPSS groups (P < 0.001). There were also significant differences in operative time between the IPSS and KVPSS groups (P < 0.001) and between the SPSS and KVPSS groups (P < 0.001).Each of the 3 types of pedicle screw strategies for correction in patients with Lenke type 1 adolescent idiopathic scoliosis are effective, with satisfactory coronal and acceptable sagittal plane results. Although the KVPSS does not provide superior operative correction compared with the IPSS and SPSS, it can achieve a satisfactory clinical outcome and is more cost-effective.

Three-Dimensional Correction in Patients With Lenke 1 Adolescent Idiopathic Scoliosis: Comparison of Consecutive Versus Interval Pedicle Screw Instrumentation

STUDY DESIGN

A retrospective-matched cohort study.

OBJECTIVE

To assess the correction of the adolescent idiopathic scoliosis (AIS) deformity in three dimensions, comparing consecutive and interval pedicle screw (PS) instrumentation techniques.

SUMMARY OF BACKGROUND DATA

The number of the sites that should be implanted with pedicle screws in AIS surgery is controversial. Coronal and sagittal planes have been investigated thoroughly but there are very little data about transverse plane correction according to PS density.

METHODS

A total of 76 AIS patients who underwent posterior fusion with PS instrumentation were recruited in this study. Patients were divided into two groups according to PS density with 38 patients in each group. In group 1, consecutive PS instrumentation was used (CPS group), and in group 2 interval pedicle screw instrumentation (IPS group). Two groups were matched according to similar patient age, fusion levels, curve magnitude and flexibility, identical Lenke curve type, and identical operative methods. Patients were compared at 1-year follow-up according to radiographic changes in coronal, sagittal, and transverse planes. Clinical outcomes were assessed using Scoliosis Research Society-22 and spinal appearance questionnaires.

RESULTS

The two cohorts were well matched. At 1-year follow-up, major coronal Cobb angle changes were 45.4° in CPS group and 38.9° in IPS group (P = 0.049). T5-T12 sagittal Cobb angle changes were 5.1° and 5.9° in CPS and IPS groups, respectively (P = 0.897). Apical vertebral rotation changes were measured as 12.0° in CPS group and as 3.6° in IPS group, which demonstrated a significant difference (P = 0.001). Scoliosis Research Society-22 scores were similar in both groups, whereas spinal appearance questionnaire appearance domain was significantly better in CPS group at 1-year follow-up (P = 0.035).

CONCLUSION

CPS provides better deformity correction in AIS surgery in all three planes, compared with IPS. Improved deformity correction results in better appearance outcomes.

LEVEL OF EVIDENCE

3.

What would be the annual cost savings if fewer screws were used in adolescent idiopathic scoliosis treatment in the US?

OBJECT

There is substantial heterogeneity in the number of screws used per level fused in adolescent idiopathic scoliosis (AIS) surgery. Assuming equivalent clinical outcomes, the potential cost savings of using fewer pedicle screws were estimated using a medical decision model with sensitivity analysis.

METHODS

Descriptive analyses explored the annual costs for 5710 AIS inpatient stays using discharge data from the 2009 Kids’ Inpatient Database (Healthcare Cost and Utilization Project, Agency for Healthcare Research and Quality), which is a national all-payer inpatient database. Patients between 10 and 17 years of age were identified using the ICD-9-CM code for idiopathic scoliosis (737.30). All inpatient stays were assumed to represent 10-level fusions with pedicle screws for AIS. High screw density was defined at 1.8 screws per level fused, and the standard screw density was defined as 1.48 screws per level fused. The surgical return for screw malposition was set at $23,762. A sensitivity analysis was performed by varying the cost per screw ($600–$1000) and the rate of surgical revisions for screw malposition (0.117%–0.483% of screws; 0.8%–4.3% of patients). The reported outcomes include estimated prevented malpositioned screws (set at 5.1%), averted revision surgeries, and annual cost savings in 2009 US dollars, assuming similar clinical outcomes (rates of complications, revision) using a standard- versus high-density pattern.

RESULTS

The total annual costs for 5710 AIS hospital stays was $278 million ($48,900 per patient). Substituting a high for a standard screw density yields 3.2 fewer screws implanted per patient, with 932 malpositioned screws prevented and 21 to 88 revision surgeries for implant malposition averted, and a potential annual cost savings of $11 million to $20 million (4%–7% reduction in the total cost of AIS hospitalizations).

CONCLUSIONS

Reducing the number of screws used in scoliosis surgery could potentially decrease national AIS hospitalization costs by up to 7%, which may improve the safety and efficiency of care. However, such a screw construct must first be proven safe and effective.

Evaluation of Limited Screw Density Pedicle Screw Constructs in Posterior Fusions for Adolescent Idiopathic Scoliosis

STUDY DESIGN

Retrospective case series.

OBJECTIVES

To compare radiographic and clinical outcomes in posterior spine fusions with pedicle screw instrumentation of varying screw densities in the treatment of adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Posterior spinal fusion with pedicle screw instrumentation is the mainstay of surgical treatment for AIS. The most commonly used construct consists of screws placed at every level on the concave side of the deformity and nearly every level on the convex side. However, some surgeons have begun using constructs with fewer pedicle screws. The literature comparing outcomes of these differing pedicle screw constructs is limited.

METHODS

Fifty-two consecutive cases of posterior spinal fusions for AIS performed by four surgeons were reviewed. High screw density constructs were used in 26 cases and limited screw density constructs in 26 cases. Construct characteristics and radiographic measurements were compared preoperatively and at last follow-up. Operative time and estimated costs were also evaluated. Student t tests were used to compare the groups with p < .05 considered significant.

RESULTS

There was no significant difference in magnitude of correction for the high versus limited screw density group initially (38.5° vs. 34.9°, p = .093) or at final follow-up (36.9° vs. 32.2°, p = .054). Sagittal alignment, coronal balance, and translation of the major apical vertebra were comparable and stable in both groups. The high versus limited screw density group utilized significantly more pedicle screws (16.8 vs. 11.6 screws, p < .0001), had longer operative times (309 vs. 267 minutes, p = .007), and had additional estimated direct costs of $5,800.

CONCLUSIONS

Excellent curve correction, stability, and balance can be achieved using fewer screws than commonly used in posterior pedicle screw fusions for AIS. Operative time is reduced, and risk and cost are decreased with the use of limited screw density constructs.

LEVEL OF EVIDENCE

III.

The effect of metal density in thoracic adolescent idiopathic scoliosis

PURPOSE

Determine impact of metal density on curve correction and costs in thoracic adolescent idiopathic scoliosis (AIS). Ascertain if increased metal density is required for larger or stiffer curves.

METHODS

Multicentre retrospective case series of patients with Lenke 1-2 AIS treated with single-stage posterior only surgery using a standardized surgical technique; constructs using >80 % screws with variable metal density. All cases had >2-year follow up. Outcomes measures included coronal and sagittal radiographic outcomes, metal density (number of instrumented pedicles vs total available), fusion length and cost.

RESULTS

106 cases included 94 female. 78 Lenke 1. Mean age 14 years (9-26). Mean main thoracic (MT) Cobb angle 63° corrected to 22° (66 %). No significant correlations were present between metal density and: (a) coronal curve correction rates of the MT (r = 0.13, p = 0.19); (b) lumbar curve frontal correction (r = -0.15, p = 0.12); (c) correction index in MT curve (r = -0.10, p = 0.32); and (d) correction index in lumbar curve (r = 0.11, p = 0.28). Metal density was not correlated with change in thoracic kyphosis (r = 0.22, p = 0.04) or lumbosacral lordosis (r = 0.27, p = 0.01). Longer fusions were associated with greater loss of thoracic kyphosis (r = -0.31, p = 0.003). Groups differing by preoperative curve size and stiffness had comparable corrections with similar metal density. The pedicle screw cost represented 21-29 % of overall cost of inpatient treatment depending on metal density.

CONCLUSIONS

Metal density affects cost but not the coronal and sagittal correction of thoracic AIS. Neither larger nor stiffer curves necessitate high metal density.

Selective Thoracic Fusion of Lenke I and II Curves Affects Sagittal Profiles But Not Sagittal or Spinopelvic Alignment: A Case-Control Study

STUDY DESIGN

Literature review and retrospective case-control study (level 3 evidence) examining 50 adolescent idiopathic scoliosis (AIS) (Lenke I or II curve) cases with 32 healthy controls of the same age. The sagittal profiles were measured preoperatively, 6 months, and 2 years after surgery and compared with those of age-matched controls at baseline.

OBJECTIVE

The purpose of this study is to compare baseline sagittal profiles of AIS Lenke I and II curves with age-matched healthy controls and at 6 months and 2 years after surgery, as well as with previously published reports.

SUMMARY OF BACKGROUND DATA

Sagittal alignment and profiles have gained significant attention in spinal deformity outcomes. The sagittal profile of patients with AIS has been previously reported, as well as the effects of surgical correction, with inconsistent results and no clear references to nonscoliotic controls.

METHODS

Baseline sagittal profiles of 50 patients presenting with Lenke I or II AIS curves treated with selective thoracic fusion were compared with 32 age-matched controls without spinal pathology. These values were also measured at 6 months and 2 years postoperatively to examine effects of selective thoracic fusion over time. Sagittal parameters examined include pelvic incidence, pelvic tilt, C7 plumb line (sagittal vertical alignment), thoracic kyphosis, and lumbar lordosis. A literature review was performed comparing previously published data. Data are presented as mean (95% confidence interval). P value of less than 0.05 was considered significant.

RESULTS

Interobserver reliability (Cohen κ= 0.49-0.95). All demographic and preoperative sagittal alignment parameters were comparable between controls and patients with AIS prior to surgery. After selective thoracic fusion, thoracic kyphosis decreased significantly from baseline (25.4º [21.6-29.2] vs. 15.3º [12.8-17.8]; P < 0.001) at 6 months and at 2 years (10.3º [7.5-13.1]; P < 0.001). The lumbar lordosis significantly decreased at 6 months from baseline (54.5º [28.6-80.5] vs. 61.8º (33.4-90.1); P < 0.001) and at 2 years (55.4º [29.0-81.9]; P < 0.001). Sagittal vertical alignment, pelvic tilt, and pelvic incidence were comparable between controls and patients with AIS at baseline and did not change with surgery.

CONCLUSIONS

Adolescents with Lenke I or II curves have comparable sagittal profiles with those of healthy controls of the same age. This suggests that Lenke I and II curves may not be hypokyphotic as previously thought. After selective thoracic fusion, patients with AIS have a significantly decreased thoracic kyphosis, which is accompanied by reciprocal changes in the noninstrumented lumbar curve. Sagittal vertical alignment and pelvic tilt are not significantly affected. These results agree with previous reports, which suggest that constructs with pedicle screws have a higher impact on sagittal curves but do not affect sagittal or spinopelvic alignment. The long-term effects of abnormal sagittal profiles need further clarification.

LEVEL OF EVIDENCE

3.

Implant distribution in surgically instrumented Lenke 1 adolescent idiopathic scoliosis: does it affect curve correction?

STUDY DESIGN

Retrospective review of prospective multicenter database of patients with adolescent idiopathic scoliosis who underwent posterior spinal fusion.

OBJECTIVE

To analyze implant distribution in surgically instrumented Lenke 1 patients and evaluate how it impacts curve correction.

SUMMARY OF BACKGROUND DATA

Although pedicle screw constructs have demonstrated successful surgical results, the optimal pedicle screw density and configuration remain unclear.

METHODS

A total of 279 patients with adolescent idiopathic scoliosis treated with pedicle screws were reviewed. Implant density was computed for each side of the instrumented segment, which was divided into 5 regions: distal and proximal ends (upper/lower instrumented vertebra +1 adjacent vertebra), apical region (apex ± 1 vertebra), and the 2 regions in between (upper/lower periapical). Centralized measurement of Cobb angle and thoracic kyphosis was performed on preoperative and at 1-year postoperative radiographs as well as percent curve flexibility.

RESULTS

The mean implant density was 1.66 implants per level fused (1.08 to 2) with greater available pedicles filled on the concavity (92%, 53%-100%) compared with the convex side (73%, 23%-100%, P < 0.01). The concave distal end region had the highest density with 99% of pedicles filled (P < 0.01), followed by the other concave regions and the convex distal end region (88%-94%) (P > 0.05). Other convex regions of the construct had less instrumentation, with only 54% to 78% of pedicles instrumented (P < 0.01). Implant density in the concave apical region (69%, 23%-100%) had a positive effect on curve correction (P = 0.002, R = 0.19).

CONCLUSION

Significant variability exists in implant distribution with the greatest variation on the convex side and lowest implant density used in the periapical convex regions. Only instrumentation at the concave side, particularly at the apical region, was associated with curve correction. This suggests that for a low implant density construct, the best regions for planned screw dropout may be in the periapical convexity.

LEVEL OF EVIDENCE

3.

Main thoracic curve adolescent idiopathic scoliosis: association of higher rod stiffness and concave-side pedicle screw density with improvement in sagittal thoracic kyphosis restoration

OBJECT

The aim of this study was to evaluate the effects of rod stiffness and implant density on coronal and sagittal plane correction in patients with main thoracic curve adolescent idiopathic scoliosis (AIS).

METHODS

The authors conducted a retrospective study of 77 consecutive cases involving 56 female and 21 male patients with Lenke Type 1 main thoracic curve AIS who underwent single-stage posterior correction and instrumented spinal fusion with pedicle screw fixation between July 2009 and July 2012. The patients' mean age at surgery was 15.79 ± 3.21 years. All patients had at least 1 year of follow-up. Radiological parameters in the coronal and sagittal planes, including Cobb angle of the major curve, side-bending Cobb angle of the major curve, thoracic kyphosis (TK), correction rates, and screw density, were measured and analyzed. Screw densities (calculated as number of screws per fusion segment × 2) of < 0.60 and ≥ 0.60 were defined as low and high density, respectively. Titanium rods of 5.5 mm and 6.35 mm diameter were defined as low and high stiffness, respectively. Patients were divided into 4 groups based on the type of rod and density of screw placement that had been used: Group A, low-stiffness rod with low density of screw placement; Group B, low-stiffness rod with high density of screw placement; Group C, high-stiffness rod with low density of screw placement; Group D, high-stiffness rod with high density of screw placement.

RESULTS

The mean coronal correction rate of the major curve, for all 77 patients, was (81.45% ± 7.51%), and no significant difference was found among the 4 groups (p > 0.05). Regarding sagittal plane correction, Group A showed a significant decrease in TK after surgery (p < 0.05), while Group D showed a significant increase (p < 0.05); Group B and C showed no significant postoperative changes in TK (p > 0.05). The TK restoration rate was highest in Group D and lowest in Group A (A, −39.32% ± 7.65%; B, −0.37% ± 8.25%; C, −4.04% ± 6.77%; D, 37.59% ± 8.53%). Screw density on the concave side was significantly higher than that on the convex side in all the groups (p < 0.05).

CONCLUSIONS

For flexible main thoracic curve AIS, both rods with high stiffness and those with low stiffness combined with high or low screw density could provide effective correction in the coronal plane; rods with high stiffness along with high screw density on the concave side could provide better outcome with respect to sagittal TK restoration.

Skipped versus consecutive pedicle screw constructs for correction of Lenke 1 curves

PURPOSE

Thoracic pedicle screws provide superior curve correction to hook and wire constructs in adolescent idiopathic scoliosis, while increasing cost. The number of implants required for best correction and outcome has not yet been determined.

METHODS

We retrospectively reviewed pre- and post-operative radiographs and self-reported outcome measures in an age- and curve-matched cohort of 40 patients with Lenke I AIS who underwent selective fusions between T3/4 and L1. Twenty patients were treated with thoracic pedicle screws at every level bilaterally (CON) and 20 patients with screws at every level on the concave side and skipped levels on the convex side of the curve (SKP). All patients had a minimum 2-year follow-up. Radiographs were assessed for coronal and sagittal curvatures, as well as thoracic torsion and vertebral rotation. Health-related quality of life was assessed using the SRS-22 instrument. Instrumentation cost data were collected for each case.

RESULTS

Postoperative follow-up averaged 28 months for the CON group and 29 months for the SKP group. No statistically significant differences were found between groups with respect to age and pre- and post-operative radiographic parameters. Both constructs provided acceptable correction of the main thoracic curves (66.9 vs. 66.6 %, CON group and SKP group, respectively; p = 0.92), and spontaneous correction of the proximal thoracic (41.5 vs. 41.1 %; p = 0.92) and thoracolumbar/lumbar curves (54.8 vs. 54.3 %; p = 0.92). No significant difference was found in postoperative SRS-22 scores (96 vs. 94.3; p = 0.34). The CON group cost for instrumentation was significantly higher than the SKP group ($19,500 vs. $13,300; p = 0.002). There was no statistically significant difference in operating room times between groups.

CONCLUSION

Both construct types provide excellent coronal correction and sagittal balance, with no significant differences in radiographic findings or clinical outcomes. A significant decrease in cost was found with use of skipped screw constructs.

Posterior spinal fusion for adolescent idiopathic thoracolumbar/lumbar scoliosis

Clinical, radiological, and Scoliosis Research Society-22 questionnaire data were reviewed pre-operatively and two years post-operatively for patients with thoracolumbar/lumbar adolescent idiopathic scoliosis treated by posterior spinal fusion using a unilateral convex segmental pedicle screw technique. A total of 72 patients were included (67 female, 5 male; mean age at surgery 16.7 years (13 to 23)) and divided into groups: group 1 included 53 patients who underwent fusion between the vertebrae at the limit of the curve (proximal and distal end vertebrae); group 2 included 19 patients who underwent extension of the fusion distally beyond the caudal end vertebra.

A mean scoliosis correction of 80% (45% to 100%) was achieved. The mean post-operative lowest instrumented vertebra angle, apical vertebra translation and trunk shift were less than in previous studies. A total of five pre-operative radiological parameters differed significantly between the groups and correlated with the extension of the fusion distally: the size of the thoracolumbar/lumbar curve, the lowest instrumented vertebra angle, apical vertebra translation, the Cobb angle on lumbar convex bending and the size of the compensatory thoracic curve. Regression analysis allowed an equation incorporating these parameters to be developed which had a positive predictive value of 81% in determining whether the lowest instrumented vertebra should be at the caudal end vertebra or one or two levels more distal. There were no differences in the Scoliosis Research Society-22 outcome scores between the two groups (p = 0.17).

In conclusion, thoracolumbar/lumbar curves in patients with adolescent idiopathic scoliosis may be effectively treated by posterior spinal fusion using a unilateral segmental pedicle screw technique. Five radiological parameters correlate with the need for distal extension of the fusion, and an equation incorporating these parameters reliably informs selection of the lowest instrumented vertebra.

Cite this article: Bone Joint J 2014;96-B:1082–9.

Does higher anchor density result in increased curve correction and improved clinical outcomes in adolescent idiopathic scoliosis?

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To determine whether anchor density is associated with curve correction and patient-reported outcomes.

SUMMARY OF BACKGROUND DATA

There is limited information as to whether anchor density affects the results of adolescent idiopathic scoliosis surgery.

METHODS

A total of 952 patients with adolescent idiopathic scoliosis met inclusion criteria (Lenke 1, 2, and 5 curves) with predominantly screw constructs (no. of screws/no. of total anchors >75%). Anchor density was defined as the number of screws, hooks, and wires per level fused, with less than 1.54 considered low density. Analysis of covariance was undertaken to determine association of anchor density with percent curve correction, Scoliosis Research Society (SRS), and Spinal Appearance Questionnaire (SAQ) scores, controlling for flexibility, fusion length, demographics, and surgeon.

RESULTS

High- compared with low-anchor density was associated with increased percent curve correction in Lenke 1 curves at 1 year (69% vs. 66% correction, P = 0.0022), controlling for percent preoperative curve flexibility, length of fusion, and sex (model, P < 0.0001). Similar associations held at 2-year follow-up and for Lenke 2 curves. Decreased thoracic kyphosis was found with increased anchor density for Lenke 1 and 2 curve patterns. There were no associations found between anchor density and Lenke 5 curves. For Lenke 1 curve patterns at 2 years postoperatively, in the high- versus low-anchor density cohorts, there were statistically higher SRS Activity (4.3 vs. 4.2, P = 0.019), Appearance (4.3 vs. 4.1, P = 0.0005), Satisfaction (4.5 vs. 4.3, P = 0.028), and Total scores (4.3 vs. 4.2; P = 0.024). Similarly, the SAQ Appearance score at 1 year similarly was improved in the high-anchor density group (high: 14.1 vs. low: 15.0, P = 0.03) for Lenke 1 curve patterns only.

CONCLUSION

For Lenke 1 and 2 curve patterns, improved percent correction of major coronal curve was noted in the high-screw density cohort. Although statistical significance was reached, it is unclear whether screw density resulted in clinically significant differences in patient-reported outcomes.

Do anchor density or pedicle screw density correlate with short-term outcome measures in adolescent idiopathic scoliosis surgery?

STUDY DESIGN

Retrospective review.

OBJECTIVE

Determine if factors under surgeon control (anchor density or pedicle screw density) or those not under surgeon control (curve magnitude, levels requiring fusion, and curve flexibility) correlate with standard, short-term quality and outcome measures for adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Pedicle screw fixation has revolutionized posterior spinal instrumentation and fusion for adolescent idiopathic scoliosis and seems to provide greater radiographical coronal plane curve correction than less expensive constructs. Other clinically relevant improvements in outcome have been difficult to demonstrate.

METHODS

Retrospective review of 119 posterior spinal instrumentation and fusion cases for adolescent idiopathic scoliosis by 4 surgeons at 1 institution. Average follow-up was 586.7 days. Outcome measures were main thoracic curve correction, complications, reoperations, infection, intensive care unit days, length of stay, estimated blood loss, transfusion, procedure time, implant charges, and total hospital charges. "Surgeon-dependent" variables were implant density (fixation/instrumented level) and pedicle coefficient (implant density × percentage of anchors that are pedicle screws). "Surgeon-independent" variables were main thoracic curve magnitude, main thoracic curve flexibility, and levels fused. Correlations were estimated using Pearson correlation coefficients. One-way analysis of variance was used to estimate the effect of "type of surgeon" or "surgeon" on surgeon-dependent variables.

RESULTS

Complications, reoperations, and infections did not correlate with surgeon-dependent or surgeon-independent variables. Main thoracic curve correction correlated strongly with curve flexibility (correlation coefficient [cc] = 0.4089, P < 0.0001). Surgeon-independent variables were levels fused correlated significantly with procedure time (cc = 0.610, P < 0.001), hospital charges (cc = 0.309, P < 0.001), hospital length of stay (cc = 0.366 [P < 0.001]), implant charges (cc = 0.199, P < 0.047), and estimated blood loss (cc = 0.243, P < 0.013). Surgeon-dependent variables were implant density significantly correlated with implant charges (cc = 0.243, P < 0.015) and inversely with length of stay (cc = -0.236, P < 0.015). Pedicle coefficient was not significantly correlated with any outcome measure.

CONCLUSION

Levels fused, a surgeon-independent variable, had the most consistently strong correlations with standard short-term quality indicators. With physician grading by payers largely dependent on easily measured outcomes from medical records, hospital and billing records, physicians need to be aware of the surgeon-dependent and surgeon-independent variables that may affect their outcomes and cost-effectiveness profile.

LEVEL OF EVIDENCE

3.