Biomechanical comparison of different anchors (foundations) for the pediatric dual growing rod technique

Proximal foundation anchor variations and their correlation with unplanned return to the operating room (UPROR) in children with EOS treated with magnetically controlled growing rods (MCGR)

INTRODUCTION

The evolution of MCGR technique has led to modifications in the configuration of the proximal construct to decrease the incidence of implant-related complications (IRC) and revision surgeries. However, there is no data characterizing the performance of the most used configurations reducing the risk of complications.

METHODS

487 patients were identified from an international multicenter EOS database.

INCLUSION CRITERIA

EOS patients, primary dual MCGR, complete radiographs, and minimum of 2-year follow-up. 76 patients had incomplete X-rays, 5 had apical fusions, and 18 had inconclusive complications, leaving 388 patients for review. A digital spine template was created to document UIV; number of levels; number, type, and location of anchors; as well as implant configuration. First available postoperative and latest follow-up radiographs were reviewed by two senior surgeons and two spine fellows. UPROR due to IRC was defined as any change in proximal anchors between the postoperative and final follow-up radiographs.

RESULTS

The most common proximal construct configuration: UIV at T2 (50.0%) with 17.5% UPROR, followed by T3 (34.0%) with 12.1% UPROR; number of levels was three (57.1%) with 16.8% UPROR and two (26.0%) with 17.0% UPROR; number of proximal anchors was six (49.9%) with 14.1% UPROR and four (27.0%) with 18.3% UPROR. The most common anchors were all screws (42.0%) with 9.9% UPROR, and all hooks (26.4%) with 31.4% UPROR (P < 0.001). The construct with the lowest rate of UPROR was a UIV at T2, with six anchors (all screws) across three levels (42 cases), with 0% UPROR. Other construct combinations that yielded 0% UPROR rates were UIV of T3, six anchors (all screws) across three levels (25 cases), and a UIV of T3 with six anchors (screws and hooks) across three3 levels (9 cases).

CONCLUSION

Proximal anchor configuration impacts the incidence of UPROR due to IRC in MCGR. UIV at T2 and T3 compared to T4, and the use of all screws or combination of screws and hooks compared to all hooks were associated with a lower UPROR rate. The most common construct configuration was T2 UIV, three levels, six anchors, and all screws. The use of a combination of six anchors (screws or screws and hooks) across three levels with a UIV at T2 or T3 was associated with a lower UPROR rate. Additional research is needed to further evaluate the variables contributing to configuration selection and their association with IRC.

Do Pedicle Screws That Terminate in the Costovertebral Joint Compromise Proximal Anchor Fixation in a Dual Growing Rod Construct?

INTRODUCTION

Growing rods (GRs) are used to treat early-onset scoliosis (EOS) recalcitrant to bracing and casting. Proximal anchor pullout, a known complication of GR constructs, can result in spinal cord injury if pedicle screw anchors are placed with a lateral-to-medial trajectory. To mitigate this risk, a more straightforward and potentially safer trajectory may result in screws that terminate within the costovertebral joint (CVJ). We asked, how often does CVJ placement occur and does this technique increase the rate of failure in GR constructs?

METHODS

We retrospectively reviewed 35 patients with EOS treated with dual GR with >2-year follow-up excluding patients with skeletal dysplasia or history of previous posterior instrumentation. Patient demographics, radiographic parameters, and implant constructs were assessed.

RESULTS

Of patients meeting the inclusion criteria, 18/35 (51%) were females with an average age of 7.96 (range: 4.0 to 15.2) years at surgery with a follow-up of 3.7 (range: 2.0 to 7.7) years. Five (14%) patients had idiopathic EOS, 5 (14%) had congenital EOS, 12 (34%) had neuromuscular EOS, 10 (29%) had syndromic scoliosis, and 3 (9%) had another etiology for EOS. Among 195 proximal pedicle screws placed, 19 (10%) terminated within the CVJ, and 13 patients (37%) had at least 1 CVJ screw. Two patients (6%) experienced unilateral proximal pullout. In both patients, the anchors on the affected side included 1 of 2 screws within the CVJ. Both patients had constructs that included 2 screws on the side that pulled out and 3 screws on the side that did not. None of the remaining 17 CVJ screws led to implant failure.

CONCLUSION

Pedicle screw placement within the CVJ is common and does not appear to significantly contribute to proximal screw pullout; however, it may contribute to unilateral implant failure in constructs employing only 2 proximal screws, where 1 of those 2 screws terminates within the CVJ. Construct modifications should be considered in this scenario.

LEVEL OF EVIDENCE

Level III.

Is Final Fusion Necessary for Growing-Rod Graduates: A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

The need for definitive fusion for growing rod graduates is a controversial topic in the management of Early-onset scoliosis (EOS) patients. The authors performed a systematic review and meta-analysis on the available literature to evaluate the outcomes of growing rod graduates undergoing final fusion or observation with implants in-situ.

METHODS

An extensive literature search was carried out aimed at identifying articles reporting outcomes in growing rod graduates. Apart from the study characteristics and demographic details, the extracted data included Cobb's correction, trunk height parameters, and revision rate. The extracted data was analyzed and forest plots were generated to draw comparisons between the observation and fusion groups.

RESULTS

Of the 11 included studies, 6 were case-control and 5 were case series. The authors did not find any significant difference between the 2 groups with respect to the pre-index and final Cobb's correction, T1-T12 or T1-S1 height gain in either over-all, or sub-analysis with case-control studies. The meta-analysis showed a significantly higher revision rate in patients undergoing a definitive fusion procedure.

CONCLUSION

The current analysis revealed comparable outcomes in terms of correction rate and gain in the trunk height but a lesser need of revisions in observation sub-group. The lack of good quality evidence and the need for prospective and randomized trials was also propounded by this review.

Growing rods for early-onset scoliosis in Ehlers-Danlos disease

PURPOSE

To study the results and complications of Traditional Growing Rods (TGR) for the treatment of Early-Onset Scoliosis (EOS) in patients with Ehlers-Danlos syndrome (EDS).

METHODS

This is a retrospective study of patients with EDS treated for EOS between 2012 and 2018 by TGR. For each patient, we evaluated the evolution of the Cobb angle of the main coronal curve before the first surgery, postoperatively and at the last follow-up. We also noted every complication.

RESULTS

Four patients have been evaluated. Age at the index surgery ranged from 3- to 6-year-old. All the patients had a Kyphoscoliosis. The preoperative Cobb angle of the main coronal curve ranged from 70° to 104°. Prior to surgery, a progressive correction of the spinal deformity by Halo-gravity traction was performed for all patients. One patient had several complications with a poor result after final fusion. Three patients did not sustain any complication and presented good results. Follow-up ranged from 3 to 8 years. For two of our patients, further lengthening procedures are still needed.

CONCLUSIONS

TGR is a good surgical option for the treatment of EOS in EDS. A progressive preoperative correction is recommended. Anchor-related complications must be minimized in these patients with an important kyphosis. Level of evidence Level IV.

The Effect of Apical Vertebra Position on Growing Rod Treatment: A Clinical and Finite Element Study

BACKGROUND

Growing rods (GRs) is a commonly utilized technique for the management of early-onset scoliosis. The significance of the position of the apical vertebrae relative to the rods is not known. The purpose of this study is to analyze the potential effects of the position of the apical vertebrae in relation to the GRs on deformity control through plain radiographs and finite element analysis (FEA) modeling.

METHODS

We identified 140 patients treated with GR between 2000 and 2018. Patients who had a congenital vertebral anomaly or <2-year follow-up were excluded. Curve magnitude, traction radiograph under general anesthesia (TRUGA) flexibility, apical rotation, the lengths of T1-12, T1-S1, and the instrumented segments were recorded. Patients were divided into 3 groups according to the apical position on the postoperative radiographs: group 1 (both pedicles are between the rods), group 2 (convex rod is between the apical vertebra pedicles), group 3 (both pedicles are lateral to the convex rod). FEA models were created simulating the 3 groups. Both radiographic and FEA data were analyzed to compare the deformity control and growth in each group.

RESULTS

Fifty-eight patients were included in the final analyses (mean age 84 mo; range: 38 to 148). Ten patients (17%) were in group 1, 34 (59%) in group 2, and 14 (24%) in group 3. Difference between TRUGA flexibilities was statistically insignificant. Group 3 was the least successful in terms of both height gain and rotational control. FEA showed a decrease in rotation and displacement for every group, however, the residual rotation and displacement was highest in group 3.

CONCLUSIONS

Bringing the apex in line with the GR increases the capacity of growth preservation as it results in largest height gain and better deformity control. FEA model demonstrated that distraction alone is inadequate for controlling rotation, and with increasing apical translation, residual rotation after distraction also increases.

LEVEL OF EVIDENCE

Level III.

Current benchtop protocols are not appropriate for the evaluation of distraction-based growing rods: a literature review to justify a new protocol and its development

PURPOSE

Although distraction-based growing rods (GR) are the gold standard for the treatment of early onset scoliosis, they suffer from high failure rates. We have (1) performed a literature search to understand the deficiencies of the current protocols, (2) in vitro evaluation of GRs using our proposed protocol and performed a finite element (FE) model validation, and (3) identified key features which should be considered in mechanical testing setups.

METHODS

PubMed, Embase, and Web of Science databases were searched for articles published on (a) in vivo animal, in vitro cadaveric, and biomechanical studies analyzing the use of GRs as well as (b) failure mechanisms and risk factors for GRs. Both FE and benchtop models of a proposed TGR test construct were developed and evaluated for two cases, long tandem connectors (LT), and side-by-side connectors (SBS). The test construct consisted of five polymer blocks representing vertebral bodies, joined with springs to simulate spinal stiffness. The superior and inferior blocks accepted the pedicle screw anchors, while the three middle blocks were floating. After the pedicle screws, rods, and connectors were assembled onto this construct, distraction was performed, mimicking scoliosis surgery. The resulting distracted constructs were then subjected to static compression-bending loading. Yield load and stiffness were calculated and used to verify/validate the FE results.

RESULTS

From the literature search, key features identified as significant were axial and transverse connectors, contoured rods, and distraction, distraction being the most challenging feature to incorporate in testing. The in silico analyses, once they are validated, can be used as a complementing technique to investigate other anatomical features which are not possible in the mechanical setup (like growth/scoliosis curvature). Based on our experiment, the LT constructs showed higher stiffness and yield load compared to SBS (78.85 N/mm vs. 59.68 N/mm and 838.84 N vs. 623.3 N). The FE predictions were in agreement with the experimental outcomes (within 10% difference). The maximum von Mises stresses were predicted adjacent to the distraction site, consistent with the location of observed failures in vivo.

CONCLUSION

The two-way approach presented in this study can lead to a robust prediction of the contributing factors to the in vivo failure.

A biomechanical study on the effect of lengthening magnitude on spine off-loading in magnetically controlled growing rod surgery: Implications on lengthening frequency

Purpose: To assess whether the magnitude of lengthening in magnetically controlled growing rod (MCGR) surgeries has an immediate or delayed effect on spinal off-loading. Methods: 9 whole porcine spines were instrumented using two standard MCGRs from T9 to L5. Static compression testing using a mechanical testing system (MTS) was performed at three MCGR lengthening stages (0 mm, 2 mm, and 6 mm) in each spine. At each stage, five cycles of compression at 175N with 25 min of relaxation was carried out. Off-loading was derived by comparing the load sustained by the spine with force applied by the MTS to the spine. Micro-CT imaging was subsequently performed. Results: The mean load sustained by the vertebral body before lengthening was 39.69N, and immediately after lengthening was 25.12N and 19.91N at 2 mm and 6 mm lengthening, respectively; decreasing to 10.07N, 8.31N, and 8.17N after 25 minutes of relaxation, at 0 mm, 2 mm, and 6 mm lengthening stages, respectively. There was no significant difference in off-loading between 2 mm and 6 mm lengthening stages, either instantaneously (p = 0.395) or after viscoelastic relaxation (p = 0.958). CT images showed fractures/separations at the level of pedicle screws in six spines and in the vertebral body's growth zone in five spines after 6 mm MCGR lengthening. Conclusion: This study demonstrated MCGRs cause significant off-loading of the spine leading to stress shielding. 6 mm of lengthening caused tissue damage and microfractures in some spines. There was no significant difference in spine off-loading between 2 mm and 6 mm MCGR lengthening, either immediately after lengthening or after viscoelastic relaxation.

Traditional Dual Growing Rod Technique in the Management of Early Onset Scoliosis and Its Effects on Spinal Growth and Lung Development: The Mid-Term Prospective Results

OBJECTIVE

The purpose of this study was to investigate the safety and effectiveness of the traditional dual growing rod (TDGR) technique, using only pedicle screws for fixation with more frequent lengthening while evaluating scoliosis correction in the growing spine, spinal growth rates, and the differences in lung volumes.

PATIENTS AND METHODS

In this single-centre prospective study, 27 patients with a follow-up of over three years were included in the study. Only pedicle screws were used as foundations for fixation. Routine lengthening procedures were performed every six months. Data were recorded including the age of initial surgery, gender, number of lengthenings, follow-up, and complications. The Cobb angle of the major curve, kyphosis angle, T1- S1 length, space available for lung (SAL) ratio, coronal and sagittal balance, and the height of all patients were measured and recorded preoperatively, immediately postoperatively, and finally before and after every lengthening.

RESULTS

The average follow-up time was 46.3 months (36-64 months). The correction rate was 69.5% for Cobb angle and 43.2% for kyphosis between preoperative and final follow-up period. The time between two lengthenings was 6.9 months, and the mean T1-S1 length increase was 1.78 cm per year. The SAL ratio increased from 0.885 preinitially to 0.985 at the last follow-up. The complication rate was determined as 9.6% in 187 procedures. Acceptable improvements were determined in the specified parameters with low complication rates with the use of this technique.

CONCLUSION

The TDGR technique with proximal and distal pedicle screws as anchors is a safe and effective treatment for deformity control in selected patients with early onset scoliosis (EOS). Repetitive surgical interventions are the negative side of this technique.

Complications of dual growing rod with all-pedicle screw instrumentation in the treatment of early-onset scoliosis

BACKGROUND

Treatment of early-onset scoliosis (EOS) is still a challenge to patients, families, and surgeons. Previous studies have indicated that EOS patients are at high risk for complications following growth-friendly surgery. This study was performed to evaluate the results and complications of all-pedicle screw dual growing rod instrumentation in the treatment of EOS.

METHODS

In an IRB-approved retrospective study, we searched the electronic medical records of our institution for all patients who underwent posterior spinal instrumentation for scoliosis between March 2014 and March 2017. Patients under the age of 10 at the time of surgery who were treated with a growth-friendly technique were then selected. Patients with incomplete records and less than 2 years of follow-up were excluded. Charts, operative notes, clinic visits, and radiographs were extracted. Radiographs were reviewed, and the main curve Cobb angle, thoracic kyphosis, pelvic tilt, pelvic incidence, sacral slope, and proximal junctional angles were measured. We specifically looked for any intra-operative or post-operative complications. Statistical analysis was performed to determine the risk factors of complications.

RESULTS

A total of 42 patients with a mean age of 4.8 ± 2.1 years (range, 1.5-8 years) were included in the final analysis. Patients were followed for a median of 34 months (range, 24-55). The major curve was corrected from a mean of 42.9° ± 10.7° to 28.8° ± 9.6° at the latest follow-up. Proximal junctional angles and thoracic kyphosis increased significantly during the follow-up period (both P values < 0.001). A total of 7 complications (17%) were observed. Four patients (10%) developed superficial surgical site infections, all of which resolved with antibiotics and one round of surgical debridement. Three cases (7%) of proximal junctional kyphosis (PJK) were encountered during the study period, none of which required revision surgery. Pre-operative thoracic kyphosis was the only significant risk factor for the development of PJK.

CONCLUSIONS

Our findings suggest that in settings without access to magnetically controlled growing rods, dual growing rods with all-pedicle screw instrumentation is still a viable treatment strategy with comparable results and complications. The most common complications are infection and PJK, with the latter being associated with a larger pre-operative thoracic kyphosis.

The growth-friendly surgical treatment of scoliosis in children with osteogenesis imperfecta using distraction-based instrumentation

PURPOSE

The study was undertaken to determine the feasibility of growth-friendly distraction-based surgery in children with OI.

METHODS

Two multi-center databases were queried for children with OI who had undergone GR or VEPTR surgery. Inclusion criteria were a minimum 2-year follow-up and three lengthening procedures following the initial implantation. Details of the surgical techniques, surgical complications, and radiographic measurements of deformity correction, T1-T12 and T1-S1 elongation and growth were recorded.

RESULTS

Five patients were identified. There was one patient with type I OI and two patients each with type III and type IV. Four patients had GR constructs and one a VEPTR construct. The initial scoliosis deformity averaged 80° (70°-103°), and the subsequent corrections averaged 32% for initial correction, 48% at last follow-up, and 54% for the two patients that had a final fusion. The T1-T12 and T1-S1 growth averaged 31 mm and 44 mm respectively, and yearly growth averaged 4 mm and 6 mm, respectively. Growth was notably much less in those with more severe disease. There were 13 complications in 4 patients. Nine of the 10 surgical complications were anchor failures which were corrected in 7 planned and 2 un-planned procedures. Significant migration occurred in one patient with severe OI type III.

CONCLUSION

The results varied in this heterogeneous population. In general, satisfactory deformity corrections were obtained and maintained, modest growth was obtained, and complications were similar to those reported in other series of growth-friendly surgery. Limited growth and significant anchor migration are to be anticipated in this population.

LEVEL OF EVIDENCE

IV.

Five or more proximal anchors and including upper end vertebra protects against reoperation in distraction-based growing rods

STUDY DESIGN

Retrospective multi-center enrollment.

OBJECTIVE

To examine the impact of patient and surgical factors on proximal complication and revision rates of early onset scoliosis patients using a multicenter database. Proximal anchor pullout and junctional kyphosis are common causes necessitating revision surgery during growth friendly treatment of early onset scoliosis (EOS). Many options exist for proximal fixation and may impact the rate of these complications.

METHODS

Retrospective review of multicenter database of patients with growth friendly constructs for EOS. Inclusion criteria were patients with index instrumentation < 10 years of age and minimum of 2 year follow-up.

RESULTS

353 patients met the inclusion criteria and had the following constructs: growing rods with spine anchors = 303; growing rods with rib anchors = 15 and VEPTR = 35. Mean age at index instrumentation was 6.0 years. Mean preoperative Cobb angle was 76° and mean kyphosis was 54°. Mean follow-up was 6.0 years. 21.8% of patients (77/353) experienced anchor pullout. Lower anchor pullout rates were associated with a higher numbers of proximal anchors (p = 0.003, r = - 0.157), and 5 or more anchors were associated with lower rates of anchor pullout (p = 0.014). Anchor type (rib hooks vs spine anchors vs rib cradle) did not impact rate of anchor pullout (p = 0.853). Kyphosis data was available for 198 patients. 23.2% (46/198) of these patients required proximal extension of their construct after index surgery. Initial instrumentation below the upper end vertebrae (UEV) of kyphosis was associated with higher rates of subsequent proximal revision; 28.9% (20/69) compared to 20.1% (26/129) for those instrumented at or above the UEV (p = 0.035). Preoperative kyphosis and change in thoracic kyphosis were not associated with anchor pullout (p = 0.436, p = 0.115) or proximal revision rates (p = 0.486, p = 0.401).

CONCLUSION

Five or more anchors are associated with lower rates of anchor pullout. Proximal anchor placement at or above the UEV resulted in a significant decrease in rates of proximal extension of the construct.

Dual pitch titanium-coated pedicle screws improve initial and early fixation in a polyetheretherketone rod semi-rigid fixation system in sheep

Background:

Reports on the efficacy of modifications to the thread design of pedicle screws are scarce. The aim of the study was to investigate initial and early fixation of pedicle screws with a plasma-sprayed titanium coating and dual pitch in the pedicle region (dual pitch titanium-coated pedicle screw [DPTCPS]) in a polyetheretherketone (PEEK) rod semi-rigid fixation system.

Methods:

Fifty-four sheep spine specimens and 64 sheep were used to investigate initial (“0-week” controls) and early (post-operative 6 months) fixation, respectively. Sheep were divided into dual pitch pedicle screw (DPPS), standard pitch pedicle screw (SPPS), DPTCPS, and standard pitch titanium-coated pedicle screw (SPTCPS) groups. Specimens/sheep were instrumented with four screws and two rods. Biomechanical evaluations were performed, and histology at the implant-bone interface was investigated.

Results:

At 0-week, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (557.0 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.61, P < 0.05; 622.6 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.43, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (343.4 ± 16.5 vs. 237.5 ± 12.9 N, t = 3.52, P < 0.05; 343.4 ± 16.5 vs. 289.9 ± 12.8 N, t = 3.12, P < 0.05; 124.7 ± 13.5 vs. 41.9 ± 4.3 cycles, t = 2.18, P < 0.05; 124.7 ± 13.5 vs.79.5 ± 11.8 cycles, t = 2.76, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (1.8 ± 0.13 vs. 3.76 ± 0.19 mm, t = 2.29, P < 0.05; 1.8 ± 0.13 vs. 2.46 ± 10.20 mm, t = 2.69, P < 0.05). At post-operative 6 months, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (908.4 ± 33.6 vs. 646.5 ± 59.4 N, t = 3.34, P < 0.05; 925.9 ± 53.9 vs. 646.5 ± 59.4 N, t = 3.37, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (496.9 ± 17.9 vs. 370.3 ± 16.4 N, t = 2.86, P < 0.05; 496.9 ± 17.9 vs. 414.1 ± 12.8 N, t = 2.74, P < 0.05; 249.1 ± 11.0 vs.149.9 ± 11.1 cycles, t = 2.54, P < 0.05; 249.1 ± 11.0 vs.199.8 ± 7.2 cycles, t = 2.61, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (0.96 ± 0.11 vs. 2.39 ± 0.14 mm, t = 2.57, P < 0.05; 0.96 ± 0.11 vs. 1.82 ± 0.12 mm, t = 2.73, P < 0.05). Resistance to toggle testing (370.3 ± 16.4 vs. 414.1 ± 12.8 N, t = 3.29, P < 0.05; 149.9 ± 11.1 vs.199.8 ± 7.2 cycles, t = 2.97, P < 0.05) was significantly lower and maximum displacement in cyclic loading (2.39 ± 0.14 vs.1.82 ± 0.12 mm; t = 3.06, P < 0.05) was significantly higher for the SPTCPS than the DPTCPS. Bone-to-implant contact was significantly increased for the DPTCPS compared to the SPPS (58.3% ± 7.0% vs. 36.5% ± 4.4%, t = 2.74, P < 0.05); there was no inflammatory reaction or degradation of coated particles.

Conclusion:

DPTCPSs might have stronger initial and early fixation in a PEEK rod semi-rigid fixation system.

Magnetically Controlled Growing Rods in Treatment of Early-Onset Scoliosis: A Single Center Study With a Minimum of 2-Year-Follow up and Preliminary Results After Converting Surgery

STUDY DESIGN

Case series.

OBJECTIVE

To evaluate complications and radiographic parameters after magnetically controlled growing rod (MCGR) index surgery (IS), during lengthening and following converting surgery (CS) with a minimum of 2-year follow up (FU).

SUMMARY OF BACKGROUND DATA

MCGR are maintaining skeletal growth in treatment of early onset scoliosis (EOS). There is no data regarding correction potential after CS available.

METHODS

Twenty-four cases were included. Two patients with rib and pelvic hook fixation instead of pedicle screws and three patients with previous spinal surgery were excluded from radiographic analysis.

RESULTS

Twenty-one patients received grade 3 or 4 in Classification of Early-Onset-Scoliosis (C-EOS) for main curve severity. The kyphotic modifiers (-) were given to seven and (+) to seven patients. Mean age at IS was 10.5 ± 2.4 years with a mean FU time of 42.3 ± 11.3 months. Deformity correction was only achieved during IS (46%) and CS (36%). During MCGR treatment a 5° loss of correction seen, while 25 mm of T1-S1 length was gained during the lengthening period. An overall average lengthening of 1.6 mm per lengthening procedure was achieved. Possibility to gain length during distractions decreases over time. No major failure of the distraction mechanism was observed, only 16 lengthening procedures failed within a total of 264 lengthening procedures. A total of 19 revision surgeries in 10 patients were observed. Four patients received more than one revision surgery.

CONCLUSION

Applying MCGR results in a revision rate of 0.23 per patient and per one FU year, while making further lengthening procedures obsolete compared with conventional growing rod techniques. Correction of major curve is possible during IS und CS. The law of diminishing returns applies during the period of lengthening.

LEVEL OF EVIDENCE

4.

Mechanical Performance of Posterior Spinal Instrumentation and Growing Rod Implants: Experimental and Computational Study

STUDY DESIGN

Experimental and computational study of posterior spinal instrumentation and growing rod constructs per ASTM F1717-15 vertebrectomy methodology for static compressive bending.

OBJECTIVE

Assess mechanical performance of standard fusion instrumentation and growing rod constructs.

SUMMARY OF BACKGROUND DATA

Growing rod instrumentation utilizes fewer anchors and spans longer distances, increasing shared implant loads relative to fusion. There is a need to evaluate growing rod's mechanical performance. ASTM F1717-15 standard assesses performance of spinal instrumentation; however, effects of growing rods with side-by-side connectors have not been evaluated.

METHODS

Standard and growing rod constructs were tested per ASTM F1717-15 methodology; setup was modified for growing rod constructs to allow for connector offset. Three experimental groups (standard with active length 76 mm, and growing rods with active lengths 76 and 376 mm; n = 5/group) were tested; stiffness, yield load, and load at maximum displacement were calculated. Computational models were developed and used to locate stress concentrations.

RESULTS

For both constructs at 76 mm active length, growing rod stiffness (49 ± 0.8 N/mm) was significantly greater than standard (43 ± 0.4 N/mm); both were greater than growing rods at 376 mm (10 ± 0.3 N/mm). No significant difference in yield load was observed between growing rods (522 ± 12 N) and standard (457 ± 19 N) constructs of 76 mm. Growing rod constructs significantly decreased from 76 mm (522 ± 12 N) to 376 mm active length (200 ± 2 N). Maximum load of growing rods at 76 mm (1084 ± 11 N) was significantly greater than standard at 76 mm (1007 ± 7 N) and growing rods at 376 mm active length (392 ± 5 N). Simulations with active length of 76 mm were within 10% of experimental mechanical characteristics; stress concentrations were at the apex and cranial to connector-rod interaction for standard and growing rod models, respectively.

CONCLUSION

Growing rod constructs are stronger and stiffer than spinal instrumentation constructs; with an increased length accompanied a decrease in strength. Growing rod construct stress concentration locations observed during computational simulation are consistent with clinically observed failure locations.

LEVEL OF EVIDENCE

5.

Mechanical performance of traditional distraction-based dual growing rod constructs

BACKGROUND

Growing rod constructs are an important contribution in the treatment of children with early onset scoliosis even though these devices experience high rates of rod fracture. The mechanical performance of traditional, distraction-based dual growing rod constructs is not well understood, and mechanical models for predicting device performance are limited.

PURPOSE

Two mechanical models were developed and used to determine the mechanical performance of various growing rod configurations by increasing construct complexity.

STUDY DESIGN/SETTING

Mechanical bench testing and finite element (FE) analysis.

METHODS

Static and dynamic compression bending tests were based on an ASTM F1717 method modified to accommodate dual growing rod constructs. Six construct configurations were tested, mechanical properties were recorded, and statistical analyses were performed to determine significant differences between groups: (1) no connectors (rods only), (2) side-by-side connectors, (3) side-by-side connectors plus 4 crosslinks, (4) (40-mm long tandem connectors, (5) 80-mm long tandem connectors, and (6) 80-mm long tandem connectors plus 4 crosslinks. FE analysis was used to predict the stress distribution within the constructs.

RESULTS

The static results indicated greater stiffness, yield load, and peak load as the axial connector length increased (side-by-side to 40 mm tandem to 80 mm tandem). The dynamic results showed similar cycles to failure for side-by-side and tandem connector (40 and 80 mm) construct configurations without crosslinks. Crosslinks shifted the location of rod fracture observed experimentally and significantly reduced the fatigue life of the construct. The flexibility of the construct decreased significantly as the axial connector length increased. FE predictions were highly consistent with the experimentally measured values and provided information on stress distribution within the rod for comparison to experimental fracture locations.

CONCLUSIONS

This is the first study to evaluate mechanical performance of various configurations of pediatric growing rod constructs using preclinical models. The current study is consistent with a previous retrieval study in that rigid constructs lacking flexibility (ie, higher stiffness and lower displacement), such as those with 80-mm tandem connectors and multiple crosslinks, demonstrated decreased mechanical performance as shown through both experimental and computational models. Additionally, the experimental and computational findings suggest that surgeons should strategically consider the number of interconnecting components and subsequent stress concentrations along the posterior side of the rod. For example, changing the placement of crosslinks to low stress regions of the construct or not using crosslinks in the construct are options.

Creation of a Porcine Kyphotic Model

STUDY DESIGN

Large animal study.

OBJECTIVE

Create a thoracic hyperkyphotic deformity in an immature porcine spine, so that future researchers may use this model to validate spinal instrumentation and other therapies used in the treatment of hyperkyphosis.

SUMMARY OF BACKGROUND DATA

Although several scoliotic animal models have been developed, there have been no reports of a thoracic hyperkyphotic animal model creation in an immature animal. The present study was designed to produce a porcine hyperkyphotic model by the time the pig weighed 25 kg, which corresponds to the approximate weight of a child undergoing surgery for early-onset scoliosis (EOS).

METHODS

Successful surgical procedures were performed in 6 consecutive 10-kg (male, 5-week-old) immature Yorkshire pigs. Procedure protocol consisted of 1) a left thoracotomy at T10-T11, 2) screw placement at T9 and T11, 3) partial vertebrectomy at T10, 4) posterior interspinous ligament transection, and 5) placement of wire loop around screws and tightening. Weekly x-ray imaging was performed preoperatively and postoperatively, documenting progressively increasing kyphosis as the pig grew. Necropsy was performed 5-6 weeks after surgery, with CT, slab section, and histologic analysis.

RESULTS

Average T9-T11 kyphosis (measured by sagittal Cobb angle) was 6.1° ± 1.4° (mean ± SD) preoperatively, 30.5° ± 1.0° immediately postoperation, and significantly increased to 50.3° ± 7.2° (p < .0001) over 5-6 weeks in 6 consecutive pigs at time of necropsy.

CONCLUSIONS

An animal model of relatively more rigid-appearing thoracic hyperkyphotic deformities in immature pigs has been created. Subsequent studies addressing management of early-onset kyphosis with spinal instrumentation are now possible.

LEVEL OF EVIDENCE

Level V.

Construct Levels to Anchored Levels Ratio and Rod Diameter Are Associated With Implant-Related Complications in Traditional Growing Rods

INTRODUCTION

In addition to patient characteristics, consideration of length of construct to number of anchored levels ratio and rod diameter should be a part of preoperative planning to minimize implant-related complications (IRCs). IRCs including rod breakage, anchor dislodgement, and pullout are among the most common adverse events in traditional growing rods (TGRs). The current study hypothesized that anchor type and configuration are associated with IRC.

METHODS

Patients with (1) age ≤10 years at surgery; (2) spine-based dual TGR; (3) minimum 2-year follow-up; and (4) available imaging. Cephalad and caudal foundations were grouped based on the number of instrumented levels and anchor type. All radiographs were reviewed. Based on the results, a "construct levels / anchored levels" (CL/AL) ratio was calculated, which is the number of levels spanned by instrumentation divided by the number of levels with bone-anchor fixation. Receiver operating characteristic curve was used to define the CL/AL threshold.

RESULTS

274 patients divided into patients with complications (IRC+, n = 140) and without complications (IRC-, n = 134) groups. Mean follow-up was 6.3 years (2.1-18.0 years). No significant differences in age, gender, body mass index, ambulatory status, etiology, primary curve size, T1-S1 height, coronal and sagittal balance, and rod material were observed between the two groups. Comparative analysis showed that connector type, presence and location of crosslinks, number of levels instrumented, number and type of anchors, presence of pelvic fixation, and mirroring of cephalad and caudal foundations were not different. However, maximum kyphosis and rod diameter were significantly different. The CL/AL ratio threshold was 3.5. Multivariate analysis of kyphosis, rod diameter, and CL/AL ratio showed a significant association with IRC (p < .05).

DISCUSSION AND CONCLUSION

Although patient characteristics like kyphosis have been proven to be associated with instrumentation failure, it is a combination of characteristics that include rod diameter and CL/AL ratio that showed significant correlation with IRC. Validation of the CL/AL ratio is recommended.

Impact of Connector Placement and Design on Bending Stiffness of Spinal Constructs

OBJECTIVE

To evaluate the stability of multiple rod-connector construct designs using a mechanical 4-point bending testing frame.

METHODS

A mechanical study was used to evaluate the bending stiffness of 3 connectors across 12 different configurations of rod-connector-rod constructs. Stability was evaluated in flexion-extension and lateral bending. Combinations of rods having 1 of 3 diameters (4.0 mm, 5.5 mm, and 6.0 mm) connected by 1 of 3 connector types (parallel open, snap-on, and hinged) were compared. Configurations with single connectors and with double connectors with variable spacing were also compared to simulate revision surgery conditions.

RESULTS

Constructs consisting of 4.0-mm rods connected to 4.0-mm rods were significantly less stiff as the total number of connectors used in a series exceeded 2. When single-connector configurations were compared, parallel open rod connectors demonstrated greater stiffness in flexion-extension than hinged open connectors, whereas hinged open connectors demonstrated greater stiffness in lateral bending. Using double connectors increased stiffness of 4.0- to 4.0-mm rod configurations in flexion-extension and lateral bending, 4.0- to 6.0-mm rod configurations in flexion-extension, and 5.5- to 6.0-mm rod configurations in lateral bending. Spacing the double connectors significantly improved lateral bending stiffness of 4.0- to 4.0-mm and 5.5- to 6.0-mm rod configurations.

CONCLUSIONS

Our data indicate that the design, number, and placement of rod connectors have a significant impact on the bending stiffness of a surgical construct. Such mechanical data may influence construct design in primary and revision surgeries of the cervical spine and cervicothoracic junction.

Pull-out of Upper Thoracic Pedicle Screws Can Cause Spinal Canal Encroachment in Growing Rod Treatment

BACKGROUND

Proximal foundation failure is a common complication of growing rod (GR) treatment for early-onset scoliosis. Spinal canal encroachment due to pull-out of pedicle screw used as proximal foundation has been anecdotally reported in GR patients. The aim of this study is to report the prevalence of spinal canal encroachment of pedicle screws in GR treatment and determine risk factors using a single-center cohort.

METHODS

Inclusion criteria were: (1) GR for early-onset scoliosis and (2) pull-out of at least 1 proximal anchor pedicle screw. Patients were divided into 2 groups according to the presence of medial screw migration. Medial migration of the screw was confirmed by computed tomography. The extracted data included demographic, clinical, and radiographic information.

RESULTS

A total of 21 patients (of 96) met inclusion criteria (21.8%). None of the screws appeared malpositioned on early postoperative x-ray. Average follow-up until screw failure was 50.4 months (64 to 85 mo) and average number of lengthenings 8.1 (4 to 13). Computed tomography revealed canal encroachment in 11 patients (group 1), and no encroachment in 10 (group 2). There was no significant difference between groups for age, follow-up or number of lengthenings. At the time of screw pull-out, coronal plane deformity was increased compared with early postoperative x-ray in all; however, this increase was significantly higher in group 1 (45.7 vs. 35 degrees, P=0.002). Proximal junctional angle (PJA) was increased in both groups at the time of pull-out. While not statistically significant, PJA increased linearly in group 1 but spiked in group 2 at the time of pull-out. There was no neurological event preoperatively, intraoperatively or postoperatively. Failed screws were safely revised in either planned/unplanned surgeries.

CONCLUSIONS

In patients with proximal anchor failure of GR, especially if there is increase of coronal deformity and/or PJA, possible spinal encroachment should be kept in mind.

LEVEL OF EVIDENCE

Level IV-retrospective case series.

Staged insertion of growing rods in severe scoliosis

PURPOSE

The objective of this retrospective chart and radiographic review was to present the clinical outcomes and complication rate of a staged approach to modern dual growing-rod (GR) surgery when treating children with severe early onset scoliosis.

METHODS

Fifteen patients received a 6-mm dual GR system. During Stage 1, pairs of end vertebra were exposed in a subperiosteal fashion, instrumented, grafted, and fused. Stage 2 was performed, on average, 5 months later (range 8-35 weeks) and the fused foundations were connected with two growing rods under skull-femoral traction. Clinical and operative notes were reviewed and all complications were recorded. Radiographic measurements were assessed at pre-index, with intraoperative traction during Stage 1, post-Stage 2 and at most recent follow-up. Statistical analyses were performed to evaluate change in scoliosis and kyphosis.

RESULTS

At initial surgery, the average age was 8.17 ± 1.5 years. The mean Cobb angle was 88.1° ± 14.0°, corrected to 60.3° ± 8.7° (p < 0.001) with intraoperative traction in Stage 1, preserved after Stage 2 instrumentation (59.5° ± 9.6°, p = 0.69), and maintained with subsequent lengthenings (60.6° ± 12.8°, p = 0.73). Hyperkyphosis (11/15 patients) improved from 70.8° ± 15.7° to 46.6° ± 9.7° (p < 0.001). At minimum 2-year follow-up (range 24-80 months, mean 49.5), the complication rate was 14 (0.93 complications/patient), including 6 rod breakages, 6 superficial infections, and 2 deep infections. No anchor migration or pull-out was noted. Seven patients have undergone definitive posterior spinal fusion.

CONCLUSIONS

Staged insertion of dual GR systems permits strong distraction, with acceptable correction of severe deformities and minimal complications. These slides can be retrieved under Electronic Supplementary Material.

What's New in Pediatric Spine Growth Modulation and Implant Technology for Early-Onset Scoliosis?

BACKGROUND

Early-onset scoliosis (EOS) affects roughly 1 to 2 out of 10,000 live births per year. Because this subset of patients has a yet to achieve a majority of their skeletal growth, a number of treatment challenges need to be addressed before surgical intervention. If left untreated, EOS can cause a number of problems throughout the patient's lifespan, particularly in regards to the growth of the thorax and pulmonary development. A wide variety of surgical systems and techniques are available to the treating surgeon.

METHODS

A review of the orthopaedic literature from 2010 to 2015 relating to pediatric spine growth modulation was performed. Ninety-eight papers were identified and, following exclusion criteria, a total of 31 papers were selected for further review.

RESULTS

This paper summarizes the recently published literature regarding growth-friendly spinal implants, the status of their Food and Drug Administration approval labeling as well as the indications, applications, and complications associated with their implementation.

CONCLUSIONS

There are a growing number of options at the surgeon's disposal when treating patients with EOS. As surgeons, we must continue to be vigilant in our demand for sound clinical evidence as we strive to provide optimal care for our patients. The rapidly advancing field of spinal growth modulation is exciting. More work must be done to further enhance our ability to predictably modulate growth in the pediatric spine.

Unplanned Reoperations in Magnetically Controlled Growing Rod Surgery for Early Onset Scoliosis With a Minimum of Two-Year Follow-Up

STUDY DESIGN

A retrospective review of prospectively collected clinical and radiologic data of patients with magnetically controlled growing rods (MCGRs) from a multi-centered study with a minimum of 2-year follow-up.

OBJECTIVE

The aim of this study was to describe the incidence and causes of unplanned reoperations and to report the outcomes of patients treated with MCGR for early-onset scoliosis (EOS).

SUMMARY OF BACKGROUND DATA

Published clinical studies have demonstrated that MCGR is safe and effective for curvature control of EOS, and can avoid repeated surgeries for distractions. However, there have been no reports on the unplanned reoperations and complications of MCGR for EOS with a large series of patients.

METHODS

Between 2009 and 2012, 30 patients with EOS underwent MCGR implantation in six institutions. A retrospective review of prospectively collected clinical and radiologic data with a minimum of 2-year follow-up was conducted. Demographic data, radiologic measurements, unplanned reoperations, and other complications were noted. Risk factors for unplanned reoperations were analyzed.

RESULTS

Patients underwent MCGR implantation at the mean age of 7.2 years. The mean follow-up period was 37 months. Fourteen patients (46.7%) underwent an unplanned reoperation within the follow-up period, with a mean time to reoperation of 23 months after initial surgery (range, 5-48 months). Causes of unplanned reoperation were failure of rod distractions, proximal foundation failure, rod breakage, and infection. More frequent distractions (between 1 week and 2 months) were associated with a higher rate of reoperation than distraction frequencies between 3 and 6 months (71% vs. 25%).

CONCLUSION

This is the largest series with the longest follow-up to date that examines the need for additional unplanned surgery after the initial procedure. It highlights that MCGR surgery can be associated with unplanned reoperations, and more frequent distractions may be a risk factor. Long-term comparative studies with traditional growing rod are required to evaluate the effectiveness of this implant.

LEVEL OF EVIDENCE

4.

Safe corridor for the implantation of thoracolumbar pedicle screws in growing pigs: A morphometric study

The pig spine is widely used as a large animal model for preclinical research in human medicine to test new spinal implants and surgical procedures. Among them, pedicle screw is one of the most common method of fixation of those implants. However, the pedicle of the porcine vertebra is not as well defined and not as large as the pedicle of the human vertebra. Therefore, the position of the screw should be adapted to the pig and not merely transposed based on the literature on humans. The purpose of this study is to determine the characteristics of the optimum implantation corridors for pedicle screws in the thoracolumbar spine of piglets of different ages using computed tomography (CT) and to determine the size and length of these corridors in pigs of different ages. CT scans from five groups of age: 6, 10, 14, 18, and 26 weeks were reviewed. For each thoracolumbar vertebrae, the pedicle width, pedicle axis length, and the pedicle angle was measured for the left and right pedicle. A total of 326 thoracic vertebrae and 126 lumbar vertebrae were included in the study. Pedicles are statistically larger but not longer for the lumbar vertebrae. An important variation of the pedicle angle is observed along the spine. In all pigs, an abrupt modification of the pedicle angle between T10 and T11 was observed, which corresponds to the level of the anticlinal vertebra which is the vertebra for which the spinous process is nearly perpendicular to the vertebral body. In conclusion, this study provides a quantitative database of pedicle screw implantation corridors in pigs of different ages. When using pedicle screws in experimental studies in pigs, these results should be considered for selecting the most suitable implants for the study but also to ensure a correct and safer screw position. Improving study procedures may limit postoperative complications and pain, thereby limiting the use of live animals.

Graduation Protocol After Growing-Rod Treatment: Removal of Implants without New Instrumentation Is Not a Realistic Approach

BACKGROUND

The growing rod remains an effective option in the treatment of early-onset scoliosis, and has previously been likened to an internal brace. While details of growing-rod treatment have been largely agreed on, the appropriate end point remains a matter of controversy. A decision was made in 2004, at the beginning of growing-rod treatment at our institution, to remove longitudinal instrumentation when the period of lengthening concluded and, similar to discontinuing a brace, leave the spine free.

METHODS

From 2004, patients managed with a growing rod who were ≤10 years old at the time of the index surgery and had no previous surgery were enrolled in the prospective treatment pathway. For this report, the inclusion criteria were complete records and radiographs; regular lengthenings; no complications defined as SV (severity grade) IIA, IIB, III, or IV; and a minimum follow-up of 2 years after reaching the age of 14 years. At the age of 14 years, the patients were reevaluated and 1 of 3 treatments was undertaken. In Group 1, which included patients with adequate correction and no requirement for extension of fusion, the growing rods were removed. In Group 2, which included patients with inadequate correction and/or interval changes, the growing rods were removed and instrumented fusion was performed. In Group 3, which included patients with a Risser sign of 0 or who were otherwise immature, lengthening was continued.

RESULTS

Twenty-six patients met the inclusion criteria. The mean age at the time of the index operation was 82.6 months. There were 10 patients in Group 1, 9 patients in Group 2, and 7 patients in Group 3. Of the 10 patients whose rods were removed without additional instrumentation, 9 had clinically important worsening of the deformity and required reimplantation with fusion.

CONCLUSIONS

Despite the initial intention to remove the implants, allow the spine to regain motion, and observe patients when they turned 14, the results of this report reveal that only 10 of the initially included 26 patients met the criteria to do so. In 9 of these patients, the deformity worsened after removal, confirming that prolonged growing-rod treatment does not necessarily result in spontaneous, reliable fusion. Removal of spinal implants without new instrumentation is not a realistic graduation protocol following growing-rod treatment, and implants should be retained, or if extension is required, another procedure should be undertaken.

LEVEL OF EVIDENCE

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

Advances in growing rods treatment for early onset scoliosis

PURPOSE OF REVIEW

The goal of treatment in early onset scoliosis is to correct the deformity while allowing the thoracic growth for optimal cardiopulmonary functions. Growing rods treatment is a distraction-based, growth-friendly method that is commonly used in treatment of early onset scoliosis with its specific indications. Magnetically controlled growing rods (MCGR) method has been introduced to avoid morbidity of recurrent lengthening procedures. In this review, recent developments in traditional growing rods and MCGR are summarized.

RECENT FINDINGS

As the experience with growing rods increased and favorable results were reported, its indications have expanded. Recent studies focused on patient outcomes and complications. Another area of interest is the effects of growing rods in the sagittal spinal alignment. Midterm results demonstrated that MCGR treatment is promising but not free of complications. In MCGR, there is no consensus on the frequency and amount of distraction per session. Rod contouring and behavior of the magnet under MRI are major issues.

SUMMARY

Growing rods treatment successfully controls the deformity while preserving the growth of spine and thorax, despite high complication rates. Magnetically controlled systems are introduced to avoid repetitive surgical lengthening procedures. Although preliminary results are promising, there are still significant challenges and unknowns for MCGR.

Biomechanical Evaluation of a Growth-Friendly Rod Construct

BACKGROUND

Distraction-type rods mechanically stabilize the thorax and improve lung growth and function by applying distraction forces at the rib, spine, pelvis, or a combination of locations. However, the amount of stability the rods provide and the amount the thorax needs is unknown.

METHODS

Five freshly frozen and thawed cadaveric thoracic spine specimens were tested for lateral bending, flexion/extension, and axial rotation in displacement control (1°/sec) to a load limit of ±5 Nm for five cycles after which a growth-friendly unilateral rod was placed in a simulated rib-to-lumbar attachment along the right side. The specimens were tested again in the same modes of bending. From the seven Optotrak Orthopedic Research Pin markers (Northern Digital Inc., Waterloo, Ontario, Canada) inserted into the top potting to denote T1, and the right pedicles at T2, T4, T5, T8, T9, and T11 and the Standard Needle Tip Pressure Transducers (Gaeltech, Isle of Skye, Scotland) inserted into the T4/T5 and T8/T9 discs, motion, stiffness, and pressure data were calculated. Parameters from the third cycle of the intact case and the construct case were compared using two-tailed paired t tests with 0.05 as the level of significance.

RESULTS

With the construct attached, the T1-T4 segment showed a 30% increase in neutral zone stiffness during extension (p = .001); the T8-T12 segment experienced a 63% reduction in the in-plane range of motion during flexion (p = .04); and the T8/T9 spinal motion unit had a significant decrease of 24% in elastic zone stiffness during left axial rotation (p = .04).

CONCLUSIONS

It is clear the device as tested here does not produce large biomechanical changes, but the balance between providing desired changes while preventing complications remains difficult.

Frequent small distractions with a magnetically controlled growing rod for early-onset scoliosis and avoidance of the law of diminishing returns

PURPOSE

To assess the effect of frequent small distractions with a magnetically controlled growing rod (MCGR) on spinal length gain and achieved distraction length in children with early-onset scoliosis (EOS), and to determine whether the law of diminishing returns applies to this group of patients with MCGR.

METHODS

A consecutive series of 3 males and 4 females with EOS who underwent MCGR implantation at a mean age of 10.2 years and were followed up for a mean of 3.8 years were reviewed. Distraction was aimed at 2 mm monthly. The coronal Cobb angle, T1-S1 length gain, and achieved distraction length were measured at 6-monthly intervals.

RESULTS

The mean total number of distractions was 31. Four of the patients had problems that may have affected distractions. The mean coronal Cobb angle improved post-operatively and was maintained throughout the follow-up period. The mean T1-S1 length gain and achieved distraction length varied over the follow-up period and did not diminish with repeated lengthening.

CONCLUSIONS

Frequent small distractions with the MCGR for EOS enable T1-S1 and achieved distraction length gain without significant reduction in gain after repeated lengthening.

Flexible growing rods: a biomechanical pilot study of polymer rod constructs in the stability of skeletally immature spines

Background

Surgical treatments for early onset scoliosis (EOS) correct curvatures and improve respiratory function but involve many complications. A distractible, or ‘growing rod,’ implant construct that is more flexible than current metal rod systems may sufficiently correct curves in small children and reduce complications due to biomechanical factors. The purpose of this pilot study was to determine ranges of motion (ROM) after implantation of simulated growing rod constructs with a range of clinically relevant structural properties. The hypothesis was that ROM of spines instrumented with polymer rods would be greater than conventional metal rods and lower than non-instrumented controls.

Methods

Biomechanical tests were conducted on six thoracic spines from skeletally immature domestic swines (35–40 kg). Paired pedicle screws were used as anchors at proximal and distal levels. Specimens were tested under the following conditions: control, then dual rods of polyetheretherketone (PEEK) (diameter 6.25 mm), titanium (4 mm), and cobalt-chrome alloy (CoCr) (5 mm). Lateral bending (LB) and flexion-extension (FE) moments were applied, and vertebral rotations were measured. Differences were determined by two-tailed t-tests and Bonferroni for four primary comparisons: PEEK vs control and PEEK vs CoCr, in LB and FE (α = 0.05/4).

Results

In LB, ROM of spine segments after instrumenting with PEEK rods was lower than the non-instrumented control condition at each instrumented level. ROM was greater with PEEK rods than with Ti and CoCr rods at every instrumented level. Combining treated levels, in LB, ROM for PEEK rods was 35 % of control (p < 0.0001) and 270 % of CoCr rods (p < 0.01). In FE, ROM with PEEK was 27 % of control (p < 0.001) and 180 % of CoCr (p < 0.01). At proximal and distal adjacent non-instrumented levels in FE, mean ROM was lower for PEEK than for either metal.

Conclusions

PEEK rods increased flexibility versus metal rods, and decreased flexibility versus non-instrumented controls, both over the entire instrumented segment and at each individual level. Smaller mean increases in ROM at proximal and distal adjacent motion segments occurred with PEEK compared to metal rods, which may help decrease complications, such as junctional kyphosis. Flexible growing rods may eventually help improve treatment options for young patients with severe deformity.

Comparison of single and dual growing rods in the treatment of early onset scoliosis: a meta-analysis

Background

The growing rod technique was applied in the treatment of early onset scoliosis (EOS) with promising outcomes and many complications at the same time. We reviewed data from literatures to compare the results of single growing rods with dual growing rods to achieve a clear understanding of this technique.

Methods

PubMed, Embase, MEDLINE, ScienceDirect, CNKI, Wanfang Data, and CQVIP were searched electronically until March 2016 using “growing rod” and “early onset scoliosis” as major search terms. Also, we manually searched other relevant conference proceedings. Two reviewers independently finished methodological quality assessment, data extraction, and calculations.

Results

Six retrospective trials were adopted in data analysis including 126 and 119 patients in the single and dual rod groups, respectively. Significantly better coronal correction rates were observed immediately after the initial operation (MD = −14.67; 95 % CI −20.97 to −8.37; P < 0.01; I² = 0 %) and at the final follow-up (MD = −23.70; 95 % CI −45.87 to −1.52; P = 0.04; I² = 82 %) in the dual rod group. Similarly, better lengthening of the T1–S1 height occurred in the dual rod group immediately after the initial operation (MD = −1.74; 95 % CI −2.62 to −0.85; P < 0.01; I² = 0 %) and at final follow-up (MD = −3.8; 95 % CI −5.56 to −2.04; P < 0.001; I² = 36 %). There were more complications about the implant in the single rod group, while wound problems were common in the other group.

Conclusions

The data of the current meta-analysis showed advantages in the coronal correction rate and lengthening by dual growing rods with fewer implant-related complications and more wound complications.

Ultrasonic Structural Health Monitoring to Assess the Integrity of Spinal Growing Rods In Vitro

BACKGROUND

Rod fracture is a common complication of growing rods and can result in loss of correction, patient discomfort, and unplanned revision surgery. The ability to quantitate rod integrity at each lengthening would be advantageous to avoid this complication. We investigate the feasibility of applying structural health monitoring to evaluate the integrity of growing rods in vitro.

METHODS

Single-rod titanium 4.5-mm growing rod constructs (n = 9), one screw proximally and one distally connected by in-line connectors, were assembled with pedicle screws fixed in polyethylene blocks. Proximal and distal ends were loaded and constructs subjected to cyclic axial compression (0-100 N at 1 Hz), with incrementally increasing maximum compressive loads of 10 N every 9k cycles until failure. Four piezoceramic transducers (PZTs) were mounted along the length the constructs to interrogate the integrity of the rods with an ultrasonic, guided lamb wave approach. Every 9k cycles, an 80 V excitatory voltage was applied to a PZT to generate high-frequency vibrations, which, after propagating through the construct, was detected by the remaining PZTs. Amplitude differences between pre- and postload waveform signals were calculated until rod failure.

RESULTS

Average construct lifetime was 88,991 ± 13,398 cycles. All constructs failed due to rod fracture within 21 mm (mean = 15 ± 4.5 mm) of a screw or connector. Amplitude differences between pre- and postload increased in a stepwise fashion as constructs were cycled. Compared to baseline, we found a 1.8 ± 0.6-fold increase in amplitude 18k cycles before failure, a 2.2 ± 1.0-fold increase in amplitude 9k cycles before failure, and a 2.75 ± 1.5-fold increase in amplitude immediately before rod fracture.

CONCLUSION

We describe a potential method for assessing the structural integrity of growing rods using ultrasonic structural health monitoring. These preliminary data demonstrate the ability of periodic rod assessment to detect structural changes in cycled growing rods, which appear to correspond to subclinical rod fatigue before rod fracture.

Special article: Update on the magnetically controlled growing rod: tips and pitfalls

Magnetically controlled growing rods (MCGR) have become an important treatment option in young patients with spinal deformities. This device allows for gradual lengthening on an outpatient setting with continuous neurological monitoring in an awake patient. With its growing popularity and interest, this study reports the tips, pitfalls, and complications of the MCGR for management of scoliosis. On 3 June 2015 at the University of Hong Kong, 32 participants from 16 regions shared their experience with MCGR. Current indications for surgery include early-onset scoliosis patients. Adolescent idiopathic scoliosis and congenital scoliosis patients have less favourable outcomes. The number of instrumented levels should be minimised, as all instrumented levels must be included in the definitive fusion surgery. Rod contouring is important and owing to the straight portion of the rod housing the magnet, there is limited proximal rod portion for proper contouring, which may predispose to proximal junctional kyphosis. There is currently no consensus on the rod configuration, timing, frequency, technique, and amount of distraction. Risk factors for distraction failure include larger patients, internal magnets too close to each other, and magnets too close to the apex of the major curve. Future studies should resolve the issues regarding the technique of distraction, optimal frequency and amount of distraction per session. More comprehensive cost analyses should be performed.

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing

The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age) of the animal, the level of the vertebrae (lumbar or thoracic) and the type of screw anchorage (mono- or bi-cortical) on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old) tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level), the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.

Validation of cone-beam computed tomography and magnetic resonance imaging of the porcine spine: a comparative study with multidetector computed tomography and anatomical specimens

BACKGROUND CONTEXT

New spinal interventions or implants have been tested on ex vivo or in vivo porcine spines, as they are readily available and have been accepted as a comparable model to human cadaver spines. Imaging-guided interventional procedures of the spine are mostly based on fluoroscopy or, still, on multidetector computed tomography (MDCT). Cone-beam computed tomography (CBCT) and magnetic resonance imaging (MRI) are also available methods to guide interventional procedures. Although some MDCT data from porcine spines are available in the literature, validation of the measurements on CBCT and MRI is lacking.

PURPOSE

To describe and compare the anatomical measurements accomplished with MDCT, CBCT, and MRI of lumbar porcine spines to determine if CBCT and MRI are also useful methods for experimental studies.

STUDY DESIGN

An experimental descriptive-comparative study.

METHODS

Sixteen anatomical measurements of an individual vertebra from six lumbar porcine spines (n=36 vertebrae) were compared with their MDCT, CBCT, and MRI equivalents. Comparisons were made for the absolute values of the parameters.

RESULTS

Similarities were found in all imaging methods. Significant correlation (p<.05) was observed with all variables except those that included cartilaginous tissue from the end plates when the anatomical study was compared with the imaging methods.

CONCLUSIONS

The CBCT and MRI provided imaging measurements of the lumbar porcine spines that were similar to the anatomical and MDCT data, and they can be useful for specific experimental research studies.

Early-onset scoliosis: current treatment

Early-onset scoliosis, which appears before the age of 10, can be due to congenital vertebral anomalies, neuromuscular diseases, scoliosis-associated syndromes, or idiopathic causes. It can have serious consequences for lung development and significantly reduce the life expectancy compared to adolescent scoliosis. Extended posterior fusion must be avoided to prevent the crankshaft phenomenon, uneven growth of the trunk and especially restrictive lung disease. Conservative (non-surgical) treatment is used first. If this fails, fusionless surgery can be performed to delay the final fusion procedure until the patient is older. The gold standard delaying surgical treatment is the implantation of growing rods as described by Moe and colleagues in the mid-1980s. These rods, which are lengthened during short surgical procedures at regular intervals, curb the scoliosis progression until the patient reaches an age where fusion can be performed. Knowledge of this technique and its complications has led to several mechanical improvements being made, namely use of rods that can be distracted magnetically on an outpatient basis, without the need for anesthesia. Devices based on the same principle have been designed that preferentially attach to the ribs to specifically address chest wall and spine dysplasia. The second category of surgical devices consists of rods used to guide spinal growth that do not require repeated surgical procedures. The third type of fusionless surgical treatment involves slowing the growth of the scoliosis convexity to help reduce the Cobb angle. The indications are constantly changing. Improvements in surgical techniques and greater surgeon experience may help to reduce the number of complications and make this lengthy treatment acceptable to patients and their family. Long-term effects of surgery on the Cobb angle have not been compared to those involving conservative "delaying" treatments. Because the latter has fewer complications associated with it than surgery, it should be the first-line treatment for most cases of early-onset scoliosis.

Effects of posterior distraction forces on anterior column intradiscal pressure in the dual growing rod technique

BACKGROUND

Little evidence is available addressing biomechanical properties of posterior distraction forces and their effects on anterior spinal column in the growing rod technique. The question is often asked if posterior distraction forces may be kyphogenic. The goal of this study is to determine whether posterior distraction forces transmitted anteriorly through different foundation constructs (i.e., screws vs. hooks) affect intradiscal pressure.

METHODS

Six skeletally immature porcine spines were harvested leaving soft tissues and rib heads intact. Pedicle screws served as the lower foundation on a L3-L4 motion segment while pedicle screws and laminar hooks were randomly used at T3-T4 levels. Proximal constructs (hook vs. screw) were switched after initial distraction testing. The dual rod distractor was instrumented with strain gauges and calibrated using a custom force transducer. During distraction, intradiscal pressures immediately inferior to the superior foundation and the level equidistant between foundations were measured using needle pressure transducers. Maximum distraction force and maximum anterior disc pressure change were compared between hook and pedicle screw anchors using one-way ANOVA (p < 0.05).

RESULTS

Upper foundations with pedicle screws had significantly greater distraction forces (416 ± 101 N) than those with upper level hooks (349 ± 100 N). There were no significant differences in disc pressures between levels or between upper foundation constructs. Disc pressures adjacent to the upper foundation demonstrated greater reduction (disc expansion) than the level equidistant within the construct. Pedicle screw constructs demonstrated greater endplate separation (distraction) compared to hook constructs.

CONCLUSIONS

Posterior distraction forces result in anterior disc separation (distraction) and are distributed across multiple levels rather than delivered to the disc immediately adjacent to a foundation. Constructs with upper foundation hooks had lower distraction forces possibly due to hook motion during distraction. The load distribution at multiple levels may assist with curve control and may affect vertebral growth. The distraction forces may not be kyphogenic as is commonly believed.

Apical and intermediate anchors without fusion improve Cobb angle and thoracic kyphosis in early-onset scoliosis

BACKGROUND

The main goal of treatment in early-onset scoliosis is to obtain and maintain curve correction while simultaneously preserving spinal, trunk, and lung growth. This study introduces a new surgical strategy, called the modified growing rod technique, which allows spinal growth and lung development while controlling the main deformity with apical and intermediate anchors without fusion. The use of intraoperative traction at the initial procedure enables spontaneous correction of the deformity and decreases the need for forceful correction maneuvers on the immature spine and prevents possible implant failures. This study seeks to evaluate (1) curve correction; (2) spinal length; (3) number of procedures performed; and (4) complications with the new approach.

DESCRIPTION OF TECHNIQUE

In the initial procedure, polyaxial pedicle screws were placed with a muscle-sparing technique. Rods were placed in situ after achieving correction with intraoperative skull-femoral traction. The most proximal and most distal screws were fixed and the rest of the screws were left with nonlocked set screws to allow vertical growth. The lengthening reoperations were performed every 6 months.

METHODS

Between 2007 and 2011, we treated 19 patients surgically for early-onset scoliosis. Of those, 16 (29%) were treated with the modified growing rod technique by the senior author (AH); an additional three patients were treated using another technique that was being studied at the time by one of the coauthors (CO); those three were not included in this study. The 16 children included nine girls and seven boys (median, 5.5 years of age; range, 4-9 years), and all had progressive scoliosis (median, 64°; range, 38°-92°). All were available for followup at a minimum of 2 years (median, 4.5 years; range, 2-6 years).

RESULTS

The initial curve Cobb angle of 64° (range, 38°-92°) improved to 21° (range, 4°-36°) and was maintained at 22° (range, 4°-36°) throughout followup. Preoperative thoracic kyphosis of 22° (range, 18°-46°) was maintained at 23° (range, 20°-39°) throughout followup without showing any substantial change. There was a 47 mm (range, 38-72 mm) increase in T1-S1 height throughout followup. The mean number of lengthening operations was 5.5 (range, 4-10). The mean T1-S1 length gain from the first lengthening was 1.18 cm (range, 1.03-2.24 cm) and decreased to 0.46 cm (range, 0,33-1.1 cm) after the fifth lengthening procedure (p = 0.009). The overall complication rate was 25% (four of 16 patients) and the procedural complication rate was 7% (seven of 102 procedures). We did not experience any rod breakages or other complications apart from two superficial wound infections managed without surgery during the treatment period. The only implant-related complications were loosening of two pedicle screws at the uppermost foundation in one patient.

CONCLUSIONS

In this preliminary study, the modified growing rod technique with apical and intermediate anchors provided satisfactory curve control, prevented progression, maintained rotational stability, and allowed continuation of trunk growth with a low implant-related complication rate.

Biomechanical Evaluation of 4 Different Foundation Constructs Commonly Used in Growing Spine Surgery: Are Rib Anchors Comparable to Spine Anchors?

STUDY DESIGN

In vitro animal model.

OBJECTIVE

To compare the strength of 4 different anchor constructs commonly used as foundations in growing spine surgery.

SUMMARY OF BACKGROUND DATA

Children with progressive early-onset scoliosis often require surgical intervention to control the deformity and allow continued growth. The foundation sites of growing spine constructs take a significant load and can fail. This study compares the strength of 4 commonly used constructs applying the same load in a porcine model.

METHODS

Forty immature porcine specimens including soft tissues (10 per group) were instrumented with 1 of 4 bilateral proximal anchors at T5-T6. The four groups were: screw-screw (SS), lamina hook-hook (HH), rib hook-hook (RR), and transverse process to lamina hook-hook (TPL). The entire specimen was kept intact except for surgical site exposure. A unique fixture was designed to brace the specimen and provide a counterforce. The ultimate load was identified as the greatest load recorded for a construct and analyzed by a set of 1-way analysis of variance using the SPSS 12.0 statistical package.

RESULTS

All specimens eventually failed at the bone-anchor interface. No failures were observed in the instrumentation used. The means and standard deviations of ultimate loads were measured as RR (429 ± 133 N), SS (349 ± 89 N), HH (283 ± 48 N), and TPL (236 ± 60 N). There was no statistically significant difference between the following construct pairs: RR/SS, SS/HH, and HH/TPL. Young's modulus was calculated for each construct type and no statistically significant difference was determined.

CONCLUSIONS

This study showed that RR and SS constructs had the greatest ultimate strength but also the greatest variability among the foundations tested. However, the HH and TPL constructs had lower ultimate strength but were less variable. Rib-based anchors may be considered as an alternative in upper foundation constructs in growing rod techniques.

Dual Growing Rods for the Treatment of Early-Onset Scoliosis

INTRODUCTION

The dual growing-rod technique involves implantation of a set of two rods and two anchor groups (upper and lower foundations) to exert frequent distractions to allow for spinal growth.

STEP 1 INITIAL SURGERY POSITIONING

Pay special attention to the effect of positioning on sagittal alignment.

STEP 2 INITIAL SURGERY NEUROMONITORING

Use multimodality intraoperative neuromonitoring, including SSEPs, MEPs, EMG, and H-Reflexes.

STEP 3 INITIAL SURGERY EXPOSURE

Avoid broad exposure of uninstrumented levels to prevent the risk of spontaneous fusion.

STEP 4 INITIAL SURGERY PREPARATION OF FOUNDATIONS

The foundation is an assembly of at least four anchors at two or three vertebrae along with one or two rods.

STEP 5 INITIAL SURGERY CHOOSING THE ANCHORS

Use hooks or pedicle screws for the proximal foundation and use bilateral pedicle screws (a four-anchor construct) for the distal foundation.

STEP 6 INITIAL SURGERY ROD CONTOURING AND ROD ASSEMBLY

Cut two 4.5-mm rods and contour them to the appropriate sagittal and coronal alignment, being careful not to overcorrect in the sagittal and coronal planes.

STEP 7 INITIAL SURGERY TANDEM CONNECTOR ATTACHMENT

Place a tandem connector at the thoracolumbar junction to allow for future lengthening.

STEP 8 INITIAL SURGERY FINAL IMPLANT ASSEMBLY

Pass the preassembled rods and tandem connector from caudad to cephalad beneath the fascia, securing them to the foundation and performing the first lengthening.

STEP 9 INITIAL SURGERY WOUND CLOSURE

Gentle handling of the skin and associated deeper tissues is essential to avoid complications.

STEPS 1 AND 2 LENGTHENING POSITIONING AND NEUROMONITORING

These are the same as those for the initial surgery.

STEP 3 LENGTHENING EXPOSURE

Make one incision between the two connectors on or in line with the original incision.

STEP 4 LENGTHENING LENGTHENING INSIDE VERSUS OUTSIDE THE TANDEM CONNECTOR

Lengthening can be performed inside or outside the tandem connector.

STEP 5 LENGTHENING CLOSURE

See Step 9 for the initial surgery.

RESULTS

The quantity and quality of research on growth-sparing techniques for early-onset scoliosis have increased substantially in the past three years.

WHAT TO WATCH FOR

IndicationsContraindicationsPitfalls & Challenges.

Distractional failure forces comparison of different anchor sites for the pediatric growing rod technique

PURPOSE

To analyze the distraction load-to-failure force supported by pedicle, lamina or rib linked to different constructs in pediatric cadaveric thoracic spine.

METHODS

Eighteen pediatric cadaveric thoracic spines with rib cages were randomly assigned into three testing groups: A (lamina and pedicle), B (rib and pedicle), and C (rib and lamina). Each specimen was sectioned into six units from T1-T2 to T11-T12. A longitudinal load-to-failure test simulating growing rod distraction force was performed with an ElectroForce(®)3500 machine, and yield forces were statistically analyzed.

RESULTS

The results showed that pedicle and lamina anchors could provide a similar capacity against distraction force in group A (P > 0.05), which was almost double that of ribs in groups B and C (P < 0.05). The data showed that T5 and T7 pedicles and laminas seem to provide the lowest distractional force. Furthermore, break pedicle insertion provides 75.6 % of distractional force as compared to the same segments with intact pedicle insertion.

CONCLUSIONS

Our results suggest the lamina as a proximal thoracic anchor site for pediatric spinal deformity. The pedicle and lamina of T5 and T7 vertebrae seemed to provide a lower distractional force than other thoracic segments in our test.

Risk factors for complications associated with growing-rod surgery for early-onset scoliosis

STUDY DESIGN

A retrospective multicenter study.

OBJECTIVE

To identify risk factors for postoperative complications associated with growing-rod (GR) surgery for early-onset scoliosis (EOS).

SUMMARY OF BACKGROUND DATA

Results and complications of GR surgery for EOS have not been adequately studied.

METHODS

We evaluated clinical and radiographical results from 88 patients with EOS who underwent GR surgery in 12 spine centers in Japan. The mean age at the time of initial surgery was 6.5 ± 2.2 years (range, 1.5-9.8 yr) and the mean follow-up period was 3.9 ± 2.6 years (range, 2.0-12.0 yr). Risk factors for postoperative complications were analyzed using binomial multiple logistic regression analysis. We considered the potential factors of sex, age, number of rod-lengthening procedures, whether a pedicle screw foundation was used, the uppermost level of the proximal foundation and lowermost level of the distal foundation, Cobb angles of the proximal thoracic, main thoracic, and lumbar curves, and the kyphosis angles in the proximal, main thoracic, thoracolumbar, and lumbar spine. Kaplan-Meier analysis was used to determine the complication-free survival rate of GR surgery as a function of the number of surgical procedures.

RESULTS

Complications affected 50 of the patients (57%) and were associated with 119 of 538 surgical procedures, with 86 implant-related failures (72%), 19 infections (16%), 3 neurological impairments (3%), and 11 other complications. The most frequent implant-related failure was dislodged implant (71%) and 95% of the dislodgements occurred at the proximal foundation. Kaplan-Meier analysis demonstrated a linear decrease in complication-free rates as the number of rod-lengthening procedures increased. Binomial multiple logistic regression analysis found the following significant independent risk factors: 6 or more rod-lengthening procedures (odds ratio [OR], 6.534), an increase of every 20° in the proximal thoracic Cobb angle (OR, 3.091), and an increase of every 25° in the lumbar lordosis angle (OR, 2.607) in the preoperative condition.

CONCLUSION

Increases in the upper thoracic scoliotic curve, thoracic kyphosis, and number of rod-lengthening procedures are positively associated with an increased risk of complications after GR surgery for EOS.

Advances in nonfusion techniques for the treatment of scoliosis in children

Scoliotic deformity in young children is a challenge for the spinal surgeon. Though traditional spinal correction and fusion techniques can improve these deformities, they inhibit growth of the spine. Nonfusion technologies are an effective approach to this problem. They not only correct the spinal deformity, but also allow the spine to keep growing and developing. These techniques include the growing rod, stapling, pedicle screw tethering, the vertical expandable prosthetic titanium rib (VEPTR), and multi-vertebrae wedge osteotomy. This is a review of advances in nonfusion techniques for the treatment of scoliosis in children.

Growing rod concepts: state of the art

INTRODUCTION

Early-onset spinal deformities present multiple challenges to the surgeon. They may be rapidly progressive and unresponsive to conservative treatment, necessitating surgical intervention at an early age.

MATERIALS AND METHODS

This text attempts to provide a review of current literature and to summarize the authors' opinions.

RESULTS

This paper attempts to concisely review available literature regarding the growing rod's inception, evolution, technique, results, and complications and answers some of the controversy still surrounding it.

CONCLUSIONS

The growing rod is one of the first, most evolved, most popular and one of the most heatedly discussed technique of fusionless spinal instrumentation.

Early definitive spinal fusion in young children: what we have learned

BACKGROUND

Early-onset scoliosis, when left untreated, leads to severe deformity. Until the last decade, treatment of progressive curves in young children often consisted of definitive spinal fusion. The recognition of thoracic insufficiency syndrome associated with definitive early fusion has led to the development of new surgical techniques developed to preserve spinal and thoracic growth in young patients with progressive scoliosis.

QUESTIONS/PURPOSES

We asked: (1) Does early definitive fusion arrest progression of spinal deformity? To what extent does early definitive spinal fusion influence (2) pulmonary function and (3) thoracic growth?

METHODS

A Medline search of the published literature on early-onset scoliosis, congenital scoliosis, and infantile scoliosis between 2008 and 2010 was performed on spinal fusion for early-onset scoliosis, focusing on studies reporting pulmonary function at followup.

RESULTS

Spinal deformity is apparently not well controlled by early fusion since revision surgery has been required in 24% to 39% of patients who underwent presumed definitive fusion in early childhood. Restrictive pulmonary disease, defined as forced vital capacity less than 50% of normal, occurs in 43% to 64% of patients who undergo early fusion surgery with those children who have extensive thoracic fusions and whose fusions involve the proximal thoracic spine at highest risk. Thoracic growth after early surgery is an average of 50% of that seen in children with scoliosis who do not have early surgery. Diminished thoracic spinal height correlates with decreased forced vital capacity.

CONCLUSIONS

The literature does not support routine definitive fusion of thoracic spinal deformity at an early age in children with scoliosis.

VEPTR™ growing rods for early-onset neuromuscular scoliosis: feasible and effective

BACKGROUND

The Vertical Expandable Prosthetic Titanium Rib (VEPTR™; Synthes North America, West Chester, PA) reportedly controls spinal deformity associated with constrictive chest wall conditions.

QUESTIONS/PURPOSES

We asked whether spine-to-spine constructs using VEPTR™ instrumentation in combination with standard spinal instrumentation could be deployed to salvage failed rib-to-spine constructs used originally in patients with constricted chest walls and to primarily treat progressive spinal deformity without chest wall abnormalities.

PATIENTS AND METHODS

Fifty patients were treated with VEPTR™ constructs for thoracic insufficiency syndrome at our center between 2001 and 2007. Fourteen of these 50 patients had placement of a spine-to-spine construct using a VEPTR™ implant in combination with standard spinal implants and are the subject of this retrospective review. Five had prior rib-based VEPTR™ or growing implants with an average of two failures before this surgery. Radiographic variables, preceding treatment, complications, and changes in ambulatory status, were recorded. The minimum followup was 2 years (mean, 35 months; range, 2-4 years).

RESULTS

After an average of five expansions in these 14 patients, positive changes were recorded for Cobb angle, T1-S1 height, sagittal balance, and space available for the lung. Complications included two rod fractures, two superficial infections, and one deep infection with rod removal.

CONCLUSIONS

VEPTR™ instrumentation as a spine-to-spine growing-rod construct demonstrated ease of implantation and expansion, with complication rates similar to other reported devices. This study suggests growing constructs using VEPTR™ can be used with relatively few complications and extends the potential uses of this instrumentation system.

Complications of growing-rod treatment for early-onset scoliosis: analysis of one hundred and forty patients

BACKGROUND

Previous reports have indicated high complication rates associated with non-fusion surgery in patients with early-onset scoliosis. This study was performed to evaluate the clinical and radiographic complications associated with growing-rod treatment.

METHODS

Data from the multicenter Growing Spine Study Group database were evaluated. Inclusion criteria were growing-rod treatment for early-onset scoliosis and a minimum of two years of follow-up. Patients were divided into treatment groups according to rod type (single or dual) and rod location (subcutaneous or submuscular). Complications were categorized as wound, implant, alignment, and general (surgical or medical). Surgical procedures were classified as planned and unplanned.

RESULTS

Between 1987 and 2005, 140 patients met the inclusion criteria and underwent a total of 897 growing-rod procedures. The mean age at the initial surgery was six years, and the mean duration of follow-up was five years. Eighty-one (58%) of the 140 patients had a minimum of one complication. Nineteen (27%) of the seventy-one patients with a single rod had unplanned procedures because of implant complications, compared with seven (10%) of the sixty-nine patients with dual rods (p ≤ 0.05). Thirteen (26%) of the fifty-one patients with subcutaneous rod placement had wound complications compared with nine of the eighty-eight patients (10%) with submuscular rod placement (p ≤ 0.05). The patients with subcutaneous dual rods had more wound complications, more prominent implants, and more unplanned surgical procedures than did those with submuscular dual rods (p ≤ 0.05). The risk of complications occurring during the treatment period decreased by 13% for each year of increased patient age at the initiation of treatment. The complication risk increased by 24% for each additional surgical procedure performed.

CONCLUSIONS

Regardless of treatment modality, the management of early-onset scoliosis is prolonged; therefore, complications are frequent and should be expected. Complications can be reduced by delaying initial implantation of the growing rods if possible, using dual rods, and limiting the number of lengthening procedures. Submuscular placement reduces wound and implant-prominence complications and reduces the number of unplanned operations.

[Growth modulation in operative treatment of juvenile scoliosis by USS paediatric]

OBJECTIVE

Growth modulation in operative treatment of juvenile scoliosis can be done by USS paediatric instrumentation to control spinal growth in patients of small stature with juvenile scoliosis. The double-rod system has to be distracted every 4-6 months. The system is used in young patients too tall for VEPTR (vertical expandable prosthetic titanium rib) instrumentation. The system with a very low profile allows reduced soft-tissue pressure saving soft tissue from atrophy or the development of pseudocysts above the screws. With this procedure controlled growth with growth modulation of the spine is possible and final spondylodesis can be done later.

INDICATIONS

Congenital, idiopathic and neuromuscular scolioses. Children, who are too tall and big for a VEPTR instrumentation. Cobb angle > 40 degrees or progression > 10 degrees during brace therapy.

CONTRAINDICATIONS

Adults. Dysplastic pedicles with vertebral anomalies. Arthrogryposis.

SURGICAL TECHNIQUE

The patient should be positioned prone, lying flat on the table. Median skin incision with subperiosteal preparation of the paraspinal muscles is done to expose the vertebrae. Next, the pedicle is prepared with a tap, and the USS paediatric pedicle screw system with its very low profile is inserted under fluoroscopic control in anterior-posterior and lateral view. In the upper thoracic spine the authors use screws 4.2 mm in diameter, in the lower thoracic spine 5-mm screws, and in the lumbar spine 6-mm screws. Measurement of the rod length and insertion of the rod are performed. When spinal growth for > 4 years is expected, distraction of the double-rod system by the use of two dominos is done on the concave and convex side of the curve to modulate spinal growth. When spinal growth for 2-4 years is expected, distraction is done just at the concave side of the curve. For correction of the curve, either segmental correction or classic derotation by the Cotrel-Dubousset technique can be performed.

POSTOPERATIVE MANAGEMENT

Postoperative on block rotation. Mobilization of the patient on day 2 after surgery with a rigid brace. Individual rigid custom-made plaster brace for 3-8 months. During postoperative recovery, muscular efforts should be reduced for 6 months after first implantation. Distraction of the system is necessary every 4-6 months to modulate spinal growth.

RESULTS

From 2004 to 2008, 26 patients (15 girls, eleven boys) with a mean age of 9 years (6-13 years) were treated using this technique. Follow-up examinations were performed 3, 6, 12, and 24 months after surgery. The mean follow-up was 26 months (6-40 months). At first implantation of the scoliosis instrumentation, just little scoliosis correction was done depending on the quality of bone. At every distraction, an average correction of the Cobb angle of 5 degrees was reached. The Cobb angle could be reduced from 71 degrees to 34 degrees on average. Fusion rate in the cranial and caudal part was evaluated by X-ray. 5-mm rods have a reduced stiffness of 50% compared to USS 6-mm rods. Average spinal growth was about 5.6 cm (4.0-8.1 cm) over a period of 3.2 +/- 1.2 years. During 2-year follow-up, rod or pedicle screw breakage, dislocation, or loosening of the Cobb angle did not occur.

[Surgical treatment of early-onset scoliosis with the StarLock implant system]

OBJECTIVE

The problem of early-onset scoliosis is the progression of spine curvature. With the StarLock instrumentation a corrected spinal growth can be achieved. Distraction is necessary once or twice a year.

INDICATIONS

Idiopathic, congenital and neuromuscular scoliosis.

CONTRAINDICATIONS

Ostoeoporosis. Arthrogryposis. Kyphosis.

SURGICAL TECHNIQUE

The use of a C-arm (anterior-posterior and lateral view) has to be possible. Pedicle screws are placed at the proximal and distal end of the curvature. Through distraction of the rods which are screwed to each other via parallel connectors, correction of the scoliosis can be achieved.

POSTOPERATIVE MANAGEMENT

Mobilization should be started 1 day postoperatively using an individual corset for 6 months. Distraction has to be done once or twice a year.

RESULTS

From March 2003 to October 2005, 14 children with early- onset scoliosis were treated with the StarLock instrumentation. After the first operation, the Cobb angle improved from 65 degrees (42-80 degrees ) to 26.5 degrees (18-45 degrees ) in the thoracic spine and from 22 degrees (18-55 degrees ) to 15 degrees (10-32 degrees ) in the lumbar spine. Lenghtenings were done every 6.8 months (5-9 months). The follow-up time was 4.5 years (3-6 years).

COMPLICATIONS

three rods and two screws broke. Infections and neurologic deficits were not observed.

Pedicle screw surface coatings improve fixation in nonfusion spinal constructs

STUDY DESIGN

Biomechanical and histologic analysis.

OBJECTIVE

To compare the strength of the bone-screw interface of standard uncoated pedicle screws with screws treated with hydroxyapatite (HA), titanium plasma spray (TPS), and a composite HA-TPS coating.

SUMMARY OF BACKGROUND DATA

Transpedicular screw fixation has become the gold standard in the treatment of various thoracolumbar spinal conditions. Pedicle screw loosening, however, has been reported, especially in mechanically demanding constructs or in vertebrae with low bone mineral density.

METHODS

Six mature porcine were instrumented with 4 types of titanium monoaxial pedicle screws (uncoated, HA-only coated, TPS-only coated, and HA-TPS composite coated) in a systematically varied, single-blinded fashion. After a 3-month survival period, the spines were harvested en-bloc and "time zero" control screws were instrumented in adjacent vertebrae. Screw placement and bone mineral density were evaluated with a postharvest computed tomography, and the strength of the tissue-implant interface was evaluated with a torsional screw extraction analysis (60 screws) and a nondecalcified histologic analysis (16 screws).

RESULTS

At 3 months postoperative, peak torque increased for all 3 types of coated screws (increased fixation) and decreased significantly for the uncoated screws (P < 0.001). Although 3-month peak torque was not statistically different between the 3 screw coatings, 4 of 10 TPS-only coated screws had a peak torque that was nearly 0 (<0.1 N m) versus only 1 of 10 HA-only screws and 0 of 10 HA-TPS composite screws. Histologic analysis confirmed the biomechanical findings with improved osseointegration in the HA-only and HA-TPS composite screws.

CONCLUSION

Pedicle screw coatings that promote mechanical interlocking, TPS, or direct osteoblast bonding(HA) increased screw fixation in this nonfusion model. More non-HA coated screws, however, were thought to be "loose" with a nearly zero peak extraction torque and fibrous encapsulation. Increased osseointegration with HA may result in a decreased incidence of screw loosening and improved outcomes of transpedicular spinal instrumentation in nonfusion procedures.