Dorsal instrumentation for idiopathic adolescent thoracic scoliosis: rod rotation versus translation

Surgical Outcomes of a New Technique Using a Convex Rod Rotation Maneuver for Adolescent Idiopathic Scoliosis

Introduction

Because of adolescent idiopathic scoliosis (AIS), most surgeons use rod rotation on the concave side for Lenke types 1 and 2 curves. Nevertheless, the accurate placement of pedicle screws within dysplastic pedicles, especially on the concave side, is sometimes challenging. Conversely, there is a concern that apical rotation might be exacerbated after convex rod rotation maneuver (RRM) because the rod is rotated in the same direction as vertebral rotation. This study aims to demonstrate the surgical technique and outcomes of a convex RRM with direct vertebral rotation (DVR) for the correction of AIS.

Technical Note

Multilevel pedicle screws were inserted into the vertebrae. The pre-bent pure titanium rod was set on the convex side and then derotated to nearly 90°. DVR was conducted for the desired vertebrae. Another pre-bent titanium alloy rod, for placement on the concave side, was contoured the same as the rod on the convex side. Using a reduction tube that allowed easier capture of the rod, the rod was connected to the concave side screws. DVR was again conducted for the desired vertebrae. Among the 59 patients, the correction rate of the main thoracic curve in Lenke types 1 and 2 AIS was 75.1% and 65.0%, respectively. The absolute value of the change in apical vertebral rotation between pre- and post-operative computed tomography (CT) scans in Lenke types 1 and 2 curves was 4.8° and 4.2°, respectively.

Conclusions

The convex RRM improved vertebral rotation in Lenke types 1 and 2 AIS. This procedure should be regarded as one of the surgical options for AIS, especially in patients with a narrow pedicle width on the concave side.

Effect of Direct Vertebral Rotation on the Uninstrumented Lumbar Curve in Thoracic Adolescent Idiopathic Scoliosis

Study Design

Retrospective study.

Purpose

To determine the effect and direction of direct vertebral rotation (DVR) in the lowest instrumented vertebra (LIV) on the uninstrumented lumbar curve depending on the lumbar modifier used for the correction of thoracic adolescent idiopathic scoliosis.

Overview of Literature

DVR in the LIV should be implemented in a different direction to obtain better spontaneous lumbar correction depending on the preoperative lumbar spine modifier.

Methods

We retrospectively analyzed 160 patients with thoracic adolescent idiopathic scoliosis treated by pedicle screw instrumentation and rod derotation. Patients who had a distal fusion level between T11 and L1 were divided into two groups: the DVR group versus the No-DVR group. Each group was divided into subgroups depending on the lumbar modifier used: the DVR-A, B, and C groups versus the No-DVR-A, B, and C groups. The DVR-A group was subdivided into two subgroups depending on the direction of screw rotation in the LIV: the DVR-A-O group (opposite direction) and the DVR-A-S group (same direction).

Results

There were no significant differences in the preoperative curve characteristics between the two groups. The preoperative lumbar curve was corrected in 70% of the patients in the DVR group and in 56% in the No-DVR group. Spontaneous coronal correction of the lumbar curve was better in the DVR-A-S group than that in the No-DVR-A group. However, the DVR-A-O group had the higher incidence of adding-on deformity. The DVR-B and C groups showed better spontaneous correction of lumbar coronal magnitude, apical vertebral translation, and rotation and the LIV tilting.

Conclusions

In lumbar modifiers B and C, screws in the LIV have to be rotated opposite to the direction of the screw rotation of the main thoracic curve; however, in modifier A, the screws have to be rotated in the same direction.

Direct Vertebral Rotation Versus Single Concave Rod Rotation: Low-dose Intraoperative Computed Tomography Evaluation of Spine Derotation in Adolescent Idiopathic Scoliosis Surgery

STUDY DESIGN

A comparative clinical study of two main corrective manoeuvres in scoliosis surgery.

OBJECTIVE

To compare the effectiveness of two main corrective manoeuvres: single concave rod rotation (SCRR) and direct vertebral rotation (DVR) in regard to apical vertebral rotation (AVR) and rib hump correction in adolescent idiopathic scoliosis (AIS) surgery.

SUMMARY OF BACKGROUND DATA

It remains unclear whether SCRR manoeuvre alone causes apical vertebral derotation (AVD) and rib hump correction. Although the influence of DVR on AVD and rib hump change has been described, it has been evaluated mainly with indirect methods. This is the first study to evaluate separately the derotational effectiveness of these two manoeuvres during the low-dose intraoperative computed tomography (ICT).

METHODS

A study group consisted of 38 AIS patients treated by posterior scoliosis surgery (PSS) with all pedicle screw constructs. All examined patients had dow-dose ICT evaluation (before correction, after SCRR, and after DVR).

RESULTS

We found SCRR ineffective - mean postcorrectional AVR increased insignificantly 1.5° (16.1% worsening) P = 0.170. On the contrary, an average postcorrectional AVR after DVR decreased significantly mean 3.1° (33.3% improvement) P = 0.049. Precorrectional rib hump angle was 19.3°, after SCRR 15°, and after DVR 12.3°. It was found that despite the lack of true derotation after SCRR there was a significant 22.3% decrease of the rib hump P = 0.043. Although the rib hump decreased significantly 36.3% after DVR as well P = 0.023. There was also significant difference between a rib hump angle after SCRR and DVR (P = 0.049).

CONCLUSION

SCRR does not lead to AVD. The true spinal derotation is possible only when DVR systems are used. The decrease of rib hump is achieved after both SCRR and DVR, but the improvement is significantly better after DVR.

LEVEL OF EVIDENCE

3.

Usefulness of Simple Rod Rotation to Correct Curve of Adolescent Idiopathic Scoliosis

Objective

To correct apical vertebral rotation for adolescent idiopathic scoliosis (AIS), direct vertebral derotation (DVD) or simple rod rotation (SRR) might be considered. The aim of the present study is to introduce the surgical experiences of AIS by a Korean neurosurgeon and to evaluate the effectiveness of SRR for apical vertebral rotation.

Methods

A total of 9 patients (1 male and 8 females) underwent scoliosis surgery by a neurosurgeon of our hospital. The Lenke classifications of the patients were 1 of 1B, 2 of 1C, 1 of 2A, 1 of 2C, 3 of 5C and 1 of 6C. Surgery was done by manner of simple rod rotation on the concave side and in situ coronal bending. Coronal Cobb's angles, vertebral rotation angles and SRS-22 were measured on a plain standing X-ray and CT before and after surgery.

Results

The mean follow up period was 25.7 months (range : 5–52). The mean number of screw positioning level was nine (6–12). The mean age was 16.4 years (range : 13–25) at surgery. The mean Risser grade was 3.7±0.9. The apical vertebral rotation measured from the CT scans was 25.8±8.5° vs. 9.3±6.7° (p<0.001) and the Coronal Cobb's angle was 53.7±10.4° vs. 15.4±6.5° (p<0.001) preoperatively and postoperative, respectively. The SRS-22 improved from 71.9 preoperatively to 90.3 postoperatively. There were no complications related with the operations.

Conclusion

SRR with pedicle screw instrumentation could be corrected successfully by axial rotation without complications. SRR might serve as a good option to correct AIS deformed curves of AIS.

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.

Sagittal curve and high metal density in adolescent idiopathic scoliosis

Objectives: To analyze radiographically the postoperative kyphosis from patients undergoing surgical treatment for AIS with pedicle screws in all vertebrae included in the arthrodesis. Methods: Retrospective study. The following measurements were evaluated: Cobb angle in anteroposterior radiograph of the three curves (proximal thoracic, main thoracic, and lumbar), Cobb angle in the lateral view of the two curves: thoracic kyphosis (T5-T12) and lumbar lordosis (T12-S1). Results: Of the 25 patients evaluated preoperatively, four (16%) were hypokyphotic, 20 patients (80%) were normokyphotic and only one (4%) was hyperkyphotic. For hypokyphotic and hiperkyphotic patients a satisfactory correction of thoracic kyphosis was obtained in 100% of cases, which was preserved in the final result. The same pattern of thoracic kyphosis was observed for all normokyphotic patients throughout the follow-up. Conclusion: Radiographic evaluation of thoracic kyphosis in patients with AIS treated surgically with pedicle screws in all vertebrae showed satisfactory results with respect to the correction of thoracic kyphosis.

Apical wiring technique in surgical treatment of adolescent idiopathic scoliosis: the intermediate outcomes between Lenke types

STUDY DESIGN

Retrospective cohort study of apical wiring technique for surgical treatment of adolescent idiopathic scoliosis patients.

OBJECTIVE

To evaluate the intermediate outcome of adolescent idiopathic scoliosis patients treated with apical wiring technique.

SUMMARY OF BACKGROUND DATA

Regarding surgical treatment for adolescent idiopathic scoliosis, there are reports of the superiority of coronal plane correction using all-screw constructs compared with all-hook or hybrid constructs. Major limitations of all-screw constructs are thoracic hypokyphosis and increased proximal junctional kyphosis. There are few reports about apical wiring technique outcomes and no reports of this surgical technique comparing Lenke types.

METHODS

Consecutive adolescent idiopathic scoliosis patients treated with apical wiring technique were analyzed. Inclusion criteria were patient 21 years old or younger, who underwent a posterior only surgical correction with a follow-up of at least 2 years. Radiographic data were analyzed according to the criteria given by Lenke and colleagues. The radiographic parameters included global balance, Cobb angle, curve flexibility, apical vertebral translation, tilt angle of lower instrumented vertebra, angle of caudal disk to the lower instrumented vertebra, thoracic kyphosis, lumbar lordosis, and proximal junctional angle preoperatively and postoperatively.

RESULTS

There was a significant improvement of Cobb angle in every Lenke type with an average correction of 74.6%. At latest follow-up, the average loss of correction was 3.5% (1.9 degrees). The greatest loss of correction for the minor curve of Lenke 2 was 14.1% (5.8 degrees). There was an improvement of thoracic kyphosis in hypokyphosis group (1.9-21.1 degrees; P<0.001) and hyperkyphosis group (49.8-33.2 degrees; P=0.001). Thoracic normokyphosis alignment was also preserved. No cases of abnormal proximal junctional kyphosis were noted in this cohort.

CONCLUSIONS

Apical wiring technique for surgical treatment of adolescent idiopathic scoliosis provides an average correction of 71.1% at 3.4 years of average follow-up with harmonious sagittal plane correction even with preexisting abnormal thoracic kyphosis.

Simultaneous translation on two rods to treat adolescent idiopathic scoliosis: radiographic results in coronal, sagittal, and transverse plane of a series of 62 patients with a minimum follow-up of two years

STUDY DESIGN

Retrospective analysis of a consecutive cohort of 62 adolescent patients treated by posterior spinal fusion (PSF) with a minimum follow-up of 2 years.

OBJECTIVE

To present sagittal and coronal results of a specific method of reduction: the simultaneous translation on 2 rods (ST2R).

SUMMARY OF BACKGROUND DATA

The long-term outcome of surgically treated scoliosis is dependent not only on the coronal correction but also on restoration of sagittal curves. Recent publications confirm the moderate correction of thoracic hypokyphosis by posterior instrumentation with hooks or pedicle screws.

METHODS

Radiographic parameters were measured preoperatively and at 6 weeks, 1 year, and last follow-up (between 2 and 7.4 years) in a consecutive cohort of 62 patients with adolescent idiopathic scoliosis (AIS) treated by PSF. All operative procedures were performed by the same surgeon using stable anchorages such as screws or self-stabilizing claws. The screws and claws included a polyaxial-threaded extension, which was fixed to the rod with connecting clamps. Reduction of the deformity was obtained by gradual and alternate tightening of the nuts on all threaded extensions on both rods, which allowed the vertebrae to gradually approach the rods while the translation maneuver was performed.

RESULTS

In the coronal plane, the average main curve was reduced from 51° to 16° and maintained 70% of correction at last follow-up. In the sagittal plane, for patients with hypokyphosis (27 cases < 20°), the average kyphosis angle was significantly improved from 9° to 29° and maintained during follow-up (32°) with a mean gain of 23° (P < 0.0001). Only 1 patient reported hypokyphosis (18°) at last follow-up. For patients with normal kyphosis, the average gain was 8°.

CONCLUSION

In a large consecutive cohort, reduction of scoliosis by ST2R is a simple method that allows 70% of correction in the coronal plane, equivalent to screw instrumentations, and a restoration of normal thoracic kyphosis.

Minimum 5-year follow-up results of skipped pedicle screw fixation for flexible idiopathic scoliosis

Object

The aim of this study was to evaluate after more than 5 years the outcome of surgical treatment for flexible idiopathic scoliosis using skipped pedicle screw fixation.

Methods

For patients with spine curves < 90° and flexibility > 20%, pedicle screws had been inserted into every other segment on the corrective side and 2–4 screws per curve had been inserted on the supportive side. The authors analyzed the results in 57 patients, including the correction rate of coronal curvature and rotational deformity, correction loss, sagittal balance, complications, blood loss, operation time, and implant costs.

Results

The mean Cobb angle was 54° preoperatively and 17° immediately after surgery (69% correction). At the last follow-up, the mean Cobb angle was 18° (2% correction loss). Rotation of the apical vertebra was corrected by 50% on average and showed only a 6% correction loss at the last follow-up. None of the patients had problems in maintaining sagittal balance. An adding-on phenomenon was detected in 4 patients (7%). Twelve of 14 patients with coronal decompensation showed improvement after surgery, whereas postoperative decompensation developed in 3 patients. Four patients had implant failures, and 4 had postoperative infections. The mean blood loss during surgery was 832 ml, and the mean operation time was 167 minutes. Compared with conventional methods, the authors' method used up to 48% fewer screws.

Conclusions

Skipped pedicle screw fixation of flexible idiopathic scoliosis showed satisfactory results. This method has several advantages, including reduced blood loss, shorter operation time, and reduced cost.

Use of the Universal Clamp in adolescent idiopathic scoliosis for deformity correction and as an adjunct to fusion: 2-year follow-up

PURPOSE

Among posterior surgical techniques for treating adolescent idiopathic scoliosis (AIS), hybrid constructs with pedicle-screw fixation in the lumbar spine and other anchors in the thoracic spine have been reported to provide to be of more physiological value in postoperative thoracic kyphosis than all-screw constructs. The Universial Clamp (UC) equipped with a soft sublaminar band is a relatively new thoracic anchor that can be used in hybrid constructs. A dedicated reduction tool that applies traction to the sublaminar band permits gentle translation of the thoracic curve to the precontoured fusion rods, which have been previously anchored distally by pedicle screws and proximally by hooks in a claw configuration. The aim of this study was to evaluate radiographic results of AIS treatment using UC hybrid constructs.

METHODS

This was a prospective case series in which 29 consecutive patients with Lenke type 1, 2 or 3 AIS operated on by two surgeons in two centers were followed for 24 months. Necessity for anterior release was an exclusion criterion.

RESULTS

A total of 5.4 ± 1.4 UCs were used per patient. The major thoracic curve was reduced from 55 ± 7° to 14 ± 6° at 1 month and 17 ± 6° at 24 months (correction 70%) without complications. In the patients who had less than 20° of T5-T12 kyphosis preoperatively, thoracic kyphosis improved from 14 ± 4° to 20 ± 3° at 3 months and 24 ± 9° at 24 months. In the other patients, preoperative thoracic kyphosis (27° ± 6°) was unchanged by the operation.

CONCLUSION

UC hybrid constructs appear to safely provide satisfying coronal correction while consistently improving thoracic kyphosis in patients who also have preoperative hypokyphosis. We hypothesize that diminution in thoracic kyphosis was consistently avoided due to the straightforward traction of the spine to the fusion rods into which the chosen kyphosis was contoured by the surgeon before applying the reduction tool to the sublaminar bands.

[Indications for deformity correction with minimally invasive spondylodesis]

The indications for surgical treatment of thoracic, lumbar, combined and thoracolumbar scoliosis are given for a curvature of the thoracic spine with a Cobb angle more than 50° and more than 45° in the lumbar spine. The maximum Cobb angle is 90°. The aim is the correction of more than 50% in the frontal plane and correction of scoliosis is possible in flexible curvatures up to 90%. By the minimally invasive surgical technique the muscular damage is completely avoided on the convex side but on the concave side this is only partly possible. This is the first report of a muscle preserving minimally invasive surgical technique for the convex side of scoliosis.

Comparação do desfecho radiográfico das escolioses idiopáticas do adolescente tratadas com instrumentação híbrida, parafusos pediculares ou ganchos

OBJETIVOS: comparar os resultados radiográficos dos pacientes portadores de escoliose idiopática do adolescente (EIA) tratados cirurgicamente, com instrumentação com ganchos, híbrida ou parafusos pediculares, com seguimento mínimo de um ano. MÉTODOS: avaliação radiográfica retrospectiva dos pacientes portadores de escoliose idiopática do adolescente tratados com diferentes instrumentações, nos períodos pré-operatório, pós-operatório imediato e pós-operatório de um ano utilizando o método de medição de Cobb. RESULTADOS: não houve diferença estatística no comportamento das curvas durante o primeiro ano de seguimento nas curvas torácica, lombar ou na cifose. Quando analisadas de forma quantitativa, não se encontrou diferença estatística nas curvas torácica (p=0,052) e lombar (p=0,332) no período pré-operatório entre os três grupos. Os três instrumentais apresentaram comportamento semelhante, não havendo diferença quantitativa na correção das curvas torácica (p=0,052) e lombar (p=0,267) nos períodos pós-operatório imediato e após um ano de seguimento. CONCLUSÕES: as três estratégias de instrumentação rendem resultados radiográficos similares em pacientes portadores de EIA flexíveis.

Spinal loop rectangle and sub laminar wiring as a technique for scoliosis correction

BACKGROUND

Most literature popularizes the efficacy of third generation instrumentation in the surgical correction of spinal deformities. A cheap and effective scoliotic deformity correction method is reviewed in this article. The aim of this study is to evaluate the efficacy of spinal loop rectangle and sub laminar wires as a modality for spinal deformity correction and its co-relation with patients' satisfaction and clinical outcome.

MATERIAL AND METHODS

Thirty six patients of scoliotic spinal deformities with various etiologies (congenital-4, idiopathic- 25, neurofibromatosis-3, neuromuscular-2 and 'syndromic'-3) with ages ranging from 8 to 23 years underwent corrective posterior spinal arthrodesis with stainless steel Hartshill loop rectangle and sublaminar wires. Clinicoradiological evaluation was done at an average follow-up of 6 (1/2) years (min-2 (1/2), years). Along with clinicoradiological outcome, patient satisfaction (as per the SRS 24), was accounted.

RESULTS

Average preoperative Cobb's angle were 73.25 degrees in the entire group and 66.48 degrees in the idiopathic group. Average percentage correction was 64.34% in the entire group and the (average degree of correction was 47.13). In the idiopathic group, the respective values were 69.19% and 46 degrees . Loss of correction in the whole group was 2.2 degrees at two year follow up. Sagittal profiles, truncal balance were well corrected too; minimal complications were seen. Patient satisfaction results were encouraging in 36 patients as per - SRS24). About 80.2% patients were ready to undergo the same surgery if required. (SRS24).

CONCLUSION

Segmental spinal fixation with locally made spinal loop rectangle and sublaminar wires is comparable as a modality to correct scoliotic spinal deformities.

Intraoperative three-dimensional correction during rod rotation technique

STUDY DESIGN

A numerical study was conducted by simulating the Cotrel-Dubousset (CD) surgery.

OBJECTIVE

To quantify intraoperative correction during CD surgery.

SUMMARY OF BACKGROUND DATA

Very few methods have been reported in literature to analyze the effect of intraoperative surgical gestures, and none considers the three-dimensional correction of the entire spine during the main surgical gestures. Intraoperative frontal radiographs limit analysis to two-dimensional correction, and movement tracking devices focus the kinematics study of specific vertebrae in the instrumented area only.

METHODS

This study included 20 patients, mean age 15 years, with severe idiopathic scoliosis treated by CD surgery. A patient-specific finite-element model (T1-L5 and pelvis), based on preoperative stereo-radiography and flexibility test radiographs, was constructed for each patient. An automated algorithm simulated all the main steps of the CD surgery. For each step, vertebral kinematics was exported to compute the evolution of various clinical parameters. Coherence of the simulations was evaluated by comparing the virtual postoperative spinal configuration with postoperative in vivo data.

RESULTS

The CD surgery affected the vertebral levels inside but also outside the fused spinal area, in a three-dimensional complex kinematics. Every intraoperative maneuver contributes to scoliosis correction. The second rod insertion, focused on the apical vertebra, leading to a global modification of all the curves.

CONCLUSIONS

The automated patient-specific simulation of CD surgery may improve our understanding of surgical biomechanics. Therefore, it could increase the relevance of preoperative surgery planning.

Restoration of thoracic kyphosis by posterior instrumentation in adolescent idiopathic scoliosis: comparative radiographic analysis of two methods of reduction

STUDY DESIGN

A retrospective comparison of radiographic results for 2 consecutive series of patients treated for adolescent idiopathic scoliosis (AIS) by posterior instrumentations with thoracic screws using 2 methods of reduction: sequential approximation by cantilever reduction (CR) and simultaneous translation technique on 2 rods (ST2R).

OBJECTIVE

To compare correction of thoracic hypokyphosis and coronal radiographic results between the 2 methods of reduction.

SUMMARY OF BACKGROUND DATA

Publications concerning AIS confirm the moderate correction of thoracic hypokyphosis by posterior instrumentation with hooks and also with pedicle screws.

METHODS

Forty-four patients with AIS (Lenke type 1, 2, 3) underwent a posterior spinal fusion and instrumentation (CR series: 21 patients--ST2R series: 23 patients). Three groups of preoperative kyphosis were generated: 12 patients with severe hypokyphosis (<or=10 degrees ) (5 in CR series and 7 in ST2R series); 12 patients with mild hypokyphosis (10-20 degrees ) (5 and 7 patients, respectively) and 20 with normal kyphosis (>20 degrees ) (11 and 9 patients, respectively). Thoracic kyphosis (T4-T12) and Cobb angle measurements of major and minor curves were evaluated by an independent observer. The minimum follow-up was 2 years.

RESULTS

At final follow-up, regarding patients with a severe preoperative hypokyphosis, the mean gain was 14 degrees in the CR series (8 degrees preoperative-22 degrees postoperative) and 27 degrees in the ST2R series (3-30 degrees ) (P = 0.018). Concerning patients with mild hypokyphosis, the mean gains were, respectively, 8 degrees (17-25 degrees ) and 18 degrees (16-34 degrees ) (P = 0.052). After surgery, 3 patients of CR series had hypokyphosis whereas the patients of the ST2R series all had normal kyphosis. In coronal plane, the mean correction of scoliosis was similar for both groups (75% vs. 69%; P = 0.177).

CONCLUSION

Simultaneous translation on 2 rods provides a better correction of thoracic kyphosis than the sequential approximation by CR on patients with preoperative hypokyphosis. This surgical technique restores normal thoracic kyphosis in all cases.

Thoracoplasty in thoracic adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective study.

OBJECTIVE

To evaluate the effect and outcome of thoracoplasty in conjunction with pedicle screw instrumentation in the treatment of thoracic adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Some spine surgeons recently think more correction of hump deformity using pedicle screws without thoracoplasty. Although thoracoplasty has been conventional treatment of rib hump, there are few papers about the results of pedicle screw instrumentation and concomitant thoracoplasty.

METHODS

Eighty-seven patients with thoracic AIS (mean age, 14.4 years) treated by pedicle screw instrumentation were retrospectively analyzed after a minimum follow-up of 2 years. Patients were divided into 3 groups; N-T group (no thoracoplasty with iliac bone graft, n = 37), T+N-DVR [thoracoplasty without direct vertebral rotation (DVR), n = 20] and T+DVR group (thoracoplasty with DVR, n = 30). In the T (T+N-DVR and T+DVR) group, 4 to 8 ribs were resected and used for bone graft. Patients were evaluated for deformity correction, balance, pulmonary function, height and angle of rib hump, clinical outcomes (SRS-30), and complications.

RESULTS

In the N-T group, the thoracic curve was corrected from 53 degrees to 16 degrees (69% correction), in the T+N-DVR group from 55 degrees to 18 degrees (69%) and in the T+DVR group from 54 degrees to 10 degrees (81%). There was no difference in postoperative spinal balance and pulmonary function among the 3 groups. The correction rates of hump height and angle were 35% and 38% in the N-T group, respectively, 57% and 58% in the T+N-DVR, and 70% and 72% in the T+DVR. The T group showed significantly better correction of rib hump and self-image score in the SRS-30 questionnaire than the N-T group. There were 8 iliac donor site problems in the N-T group and 3 hemothorax in the T group, which had no adverse effect in the final result.

CONCLUSION

Thoracoplasty showed significantly better rib hump correction, satisfactory clinical outcomes without pulmonary function compromise, or iliac bone graft site morbidity in the treatment of thoracic AIS with pedicle screw instrumentation.

A pedicle screw construct gives an enhanced posterior correction of adolescent idiopathic scoliosis when compared with other constructs: myth or reality

STUDY DESIGN

Tricenter retrospective cohort study of 72 patients who underwent posterior correction of Lenke 1 adolescent idiopathic scoliosis (AIS). Each center represented a single surgeon using only one type of construct.

OBJECTIVE

Compare the initial postoperative and 2-year follow-up correction of Lenke 1 AIS curves, after accounting for the preoperative flexibility of the curves.

SUMMARY OF BACKGROUND DATA

There are multiple reports in literature of the enhanced posterior corrective ability of the pedicle screw in the treatment of AIS. Unfortunately, none of these reports took into account the preoperative flexibility of the curve. It stands to reason that rigid curves will not correct as much as flexible curves irrespective of the nature of the construct.

METHODS

Groups were as follows: Group 1 (proximal and distal hooks and segmental intraspinous collar button wires), 24 patients; Group 2 (proximal hooks, distal screws, and apical sublaminar wires), 23 patients; and Group 3 (pedicle screws only), 25 patients. The postoperative correction percentage was expressed as a ratio of the preoperative flexibility and was termed Cincinnati correction index (CCI). Mathematically speaking the CCI equals (postoperative correction/preoperative erect Cobb angle) divided by (supine bending preoperative correction/preoperative erect Cobb angle). The postoperative sagittal correction was also measured.

RESULTS

CCI 2 (at 2-year follow-up) for Group 1 was 1.71, for Group 2 was 1.34, and for Group 3 was 1.41. The differences were not statistically significant. Within Group 1, however, there was a statistically significant difference between CCI (1.95) and CCI 2 (1.71), indicating a statistically significant loss of correction over 2 years. However, in terms of absolute values, there was only a 4 degree (average) difference between the initial and the 2-year postoperative Cobb measurement, rendering the loss off correction clinically insignificant. No such statistically or clinically significant differences were noted within Groups 2 and 3. Group 1 and Group 3 constructs further lordosed the curve by 8 degrees and 11 degrees, respectively, whereas the Group 2 construct retained or marginally increased the preoperative kyphosis.

CONCLUSION

The Group 3 (pedicle screw only) construct did not give an enhanced correction of Lenke 1 AIS, when the preoperative flexibility of the curve was considered. Also, contrary to popular belief, the pedicle screw construct has a lordosing effect on the thoracic spine. Therefore, we think that there is no significant advantage in using a relatively expensive pedicle screw construct in the correction of Lenke 1 AIS.

A biomechanical analysis of the self-retaining pedicle hook device in posterior spinal fixation

Regular hooks lack initial fixation to the spine during spinal deformity surgery. This runs the risk of posterior hook dislodgement during manipulation and correction of the spinal deformity, that may lead to loss of correction, hook migration, and post-operative junctional kyphosis. To prevent hook dislodgement during surgery, a self-retaining pedicle hook device (SPHD) is available that is made up of two counter-positioned hooks forming a monoblock posterior claw device. The initial segmental posterior fixation strength of a SPHD, however, is unknown. A biomechanical pull-out study of posterior segmental spinal fixation in a cadaver vertebral model was designed to investigate the axial pull-out strength for a SPHD, and compared to the pull-out strength of a pedicle screw. Ten porcine lumbar vertebral bodies were instrumented in pairs with two different instrumentation constructs after measuring the bone mineral density of each individual vertebra. The instrumentation constructs were extracted employing a material testing system using axial forces. The maximum pull-out forces were recorded at the time of the construct failure. Failure of the SPHD appeared in rotation and lateral displacement, without fracturing of the posterior structures. The average pull-out strength of the SPHD was 236 N versus 1,047 N in the pedicle screws (P < 0.001). The pull-out strength of the pedicle screws showed greater correlation with the BMC compared to the SPHD (P < 0.005). The SPHD showed to provide a significant inferior segmental fixation to the posterior spine in comparison to pedicle screw fixation. Despite the beneficial characteristics of the monoblock claw construct in a SPHD, that decreases the risk of posterior hook dislodgement during surgery compared to regular hooks, the SPHD does not improve the pull-out strength in such a way that it may provide a biomechanically solid alternative to pedicle screw fixation in the posterior spine.

Long-term clinical and radiographic results of Cotrel-Dubousset instrumentation of right thoracic adolescent idiopathic scoliosis

Little substantive data is available in the literature on the long-term clinical and radiological results of Cotrel-Dubousset instrumentation (CDI) for the treatment of adolescent idiopathic scoliosis. We therefore retrospectively investigated the long-term clinical and radiographic outcome of patients who underwent (CDI) for right thoracic adolescent idiopathic scoliosis. 54 consecutive patients (45 females, 9 males) who underwent CDI for right thoracic adolescent idiopathic scoliosis with an average age of 14 years (range 10-21 years) at surgery were included in this series. There were 18 King Type II, 19 Type III, 5 Type IV, 3 Type V and 9 double major curves. The average coronal Cobb angle of the primary thoracic curve preoperatively, postoperatively and at latest follow-up was 55 degrees, 17 degrees and 22 degrees, respectively. The lumbar curve (secondary and double major) averaged 40 degrees, 21 degrees and 23 degrees, respectively. Coronal balance (deviation from the central sacral line) was slightly improved from 13 mm to 11 mm. The average shoulder elevation increased from 3 degrees to 5 degrees, presumably as a result of the rod derotation maneuver. Thoracic kyphosis (20 degrees to 22 degrees) and lumbar lordosis (49 degrees to 54 degrees) was preserved or even improved by the instrumentation. All patients were doing well and had no complaints with regard to a substantial limitation of professional or sports activity. There were no apparent non-unions, infections or neurological complications. CDI of adolescent right thoracic idiopathic scoliosis provides encouraging clinical and radiographic results at an average follow-up of 9 years (2 to 16 years). Overall patient satisfaction, functional status and subjective cosmetic improvement is high.

Implant removal for late-developing infection after instrumented posterior spinal fusion for scoliosis: reinstrumentation reduces loss of correction. A retrospective analysis of 45 cases

A retrospective follow-up study of patients who, having undergone instrumented posterior spinal fusion for scoliosis, experienced late infection and then underwent either implant removal alone or implant removal and instrumented refusion. We conducted this study to determine whether it is possible to avoid loss of correction by a single-stage implant removal and reinstrumentation procedure. There have been a few reports of late-appearing infections after spinal instrumentation. Implant bulk, metallurgic reactions, and contamination with low-virulence microorganisms have been suggested as possible etiologic factors. The clinical symptoms include pain, swelling, redness, and spontaneous drainage of fluid. Complete instrumentation removal and systemic antibiotics is usually curative. We retrospectively reviewed 45 patients who underwent instrumented posterior spinal fusion for scoliosis and experienced development of late infections and, after a mean of 3 years after the initial procedure, either underwent implant removal alone [ n=35, instrumentation removal (HR) group] or additionally underwent reinstrumentation and fusion [ n=10, reinstrumentation and fusion (RI&F) group]. Three patients were reinstrumented 1.5 years after instrumentation removal, and seven underwent a one-stage rod removal and reinstrumentation/refusion procedure. Allergic predisposition, protracted postoperative fever, and pseudarthrosis appear to increase the risk of late-developing infection after posterior spinal fusion. All wounds in both groups healed uneventfully. Preoperative radiographic Cobb measurements showed no statistically significant between-group differences. At follow-up, however, outcome was clearly better in the RI&F group: Loss of correction was significantly smaller in reinstrumented patients. Thus, the thoracic Cobb angle was 28+/-16 degrees (range 0-55 degrees ) in the RI&F group versus 42+/-15 degrees (21-80 degrees ) in the HR group, and the lumbar Cobb angle was 22+/-11 degrees (10-36 degrees ) in the RI&F group versus 29+/-12 degrees (13-54 degrees ) in the HR group. The results of our study demonstrate that wound healing is usually uneventful after instrumentation removal for late infection, also when patients undergo instrumented refusion in a one-stage procedure. Reinstrumentation appears to achieve permanent correction of scoliosis.

Quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae of Chinese Singaporeans

This paper details the quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae (C3-T12) of Chinese Singaporean subjects based on 220 vertebrae from 10 cadavers. The purpose of the study was to measure the linear dimensions, angulations and areas of individual vertebra, and to compare the data with similar studies performed on Caucasian specimens. Measurements were taken with the aid of a three-dimensional digitiser. The means and standard errors for linear, angular and area dimensions of the vertebral body, spinal canal, pedicle, and spinous and transverse processes were obtained for each vertebra. Compared to the Caucasian data, all the dimensions were found to be smaller. Of significance were the spinal canal area, and pedicle width and length, which were smaller by 31.7%, 25.7% and 22.1% on average, respectively. A slight divergence, instead of convergence, was found from T8 to T12. According to the findings, the use of a transpedicle screw may not be feasible. The results can also provide more accurate modelling for analysis and design of spinal implants and instrumentations, and also allow more precise clinical diagnosis and management of the spine in Chinese Singaporeans.

Direct vertebral rotation: a new technique of three-dimensional deformity correction with segmental pedicle screw fixation in adolescent idiopathic scoliosis

STUDY DESIGN

A prospective study.

OBJECTIVES

To introduce a new technique, direct vertebral rotation, and to compare the surgical results of direct vertebral rotation with those of simple rod derotation.

SUMMARY OF BACKGROUND DATA

Pedicle screw fixation with a simple rod derotation maneuver enables a powerful coronal and sagittal plane correction in scoliosis surgery. However, the ability of achieving rotational correction is still unclear.

METHODS

Thirty-eight adolescent idiopathic scoliosis patients treated with segmental pedicle screw fixation were analyzed. The first group (n = 17) was treated by direct vertebral rotation; the second group (n = 21) was treated by simple rod derotation. All patients had a minimum follow-up of 2 years. Having similar preoperative curve patterns, both groups were evaluated for the deformity correction, lower instrumented vertebral tilt, and spinal balance. Apical vertebral rotation was evaluated by computed tomography scans. Surgical techniques of direct vertebral rotation were as follows: a precontoured rod was inserted into segmental screws on the concave side in thoracic scoliosis; a simple rod derotation was performed; and then the screws on the juxta-apical vertebrae, both on concave and convex sides, were rotated opposite direction to the rod derotation. Then, all the screws were sequentially tightened.

RESULTS

In the direct vertebral rotation group, the average preoperative apical vertebral rotation of 16.7 degrees was corrected to 9.6 degrees, showing 42.5% correction, whereas in the simple rod derotation group, the correction was negligible from 16.1 degrees to 15.7 degrees (2.4%). In the direct vertebral rotation group, the average preoperative thoracic curve of 55 degrees was corrected to 12 degrees (79.6%), and the lumbar curve of 39 degrees was corrected to 7 degrees (80.5%). In the simple rod derotation group, the preoperative thoracic curve of 53 degrees was corrected to 17 degrees (68.9%), and the lumbar curve of 39 degrees was corrected to 16 degrees (62.2%). The average lower instrumented vertebral tilt correction was 80.6% and 66.3% in the directvertebral rotation and the simple rod derotation group, respectively. There were statistically significant differences in the coronal curve, lower instrumented vertebral tilt, and rotational correction (P < 0.05, Mann-Whitney U test). Thoracic kyphosis was improved in both groups.

CONCLUSIONS

Segmental pedicle screw fixation with "direct vertebral rotation" showed better rotational and coronal correction than "simple rod derotation."

Axial and tangential fixation strength of pedicle screws versus hooks in the thoracic spine in relation to bone mineral density

STUDY DESIGN

In vitro biomechanical testing was performed to analyze the axial and tangential fixation strength of pedicle screws versus pedicle and laminar hooks in the human thoracic spine. Bone mineral density of each tested vertebra was determined.

OBJECTIVE

To study the fixation strength of pedicle screws and hooks in the thoracic spine in relation to bone mineral density.

SUMMARY OF BACKGROUND DATA

Biomechanical properties of pedicle screws have proven to be superior in the lumbar spine, but there is a paucity of data concerning the thoracic spine in particular with regard to bone mineral density.

METHODS

In 72 human thoracic vertebrae standard pedicle hooks between T4 and T8 and supralaminar hooks between T9 and T12 were tested against pedicle screws in pairs in one vertebra each. The bone mineral density of each vertebra was determined by means of quantitative computed tomography. Screws and hooks were loaded either axially strictly longitudinal to failure or in a coronal plane strictly perpendicular to the longitudinal axis nondestructively. A total of 78 pullout tests and 66 tangential loadings were performed.

RESULTS

The correlation of bone mineral density and fixation strength was significant for pullout strength of pedicle screws (P < 0.001) and pedicle hooks (P < 0.001). The average pullout strength of the pedicle screws was significantly higher than that of pedicle hooks (P = 0.003) and supralaminar hooks (P = 0.02). The difference was not significant if bone mineral density was <100 mg hydroxylapatite/mL. The average tangential elastic and permanent displacement of pedicle screws was significantly lower than that of pedicle (P < 0.001) and laminar hooks (P = 0.002).

CONCLUSION

Pedicle screws may be beneficial for instrumentation of the thoracic spine because they are significantly more resistant to axial and tangential loadings than pedicle and laminar hooks on the condition that bone mineral density is >100 mg/mL hydroxylapatite.