Rod fracture and lengthening intervals in traditional growing rods: is there a relationship?

The Minimally Invasive Bipolar Fixation for Pediatric Spinal Deformities: A Narrative Review

Growing rod techniques are increasingly used for early-onset scoliosis in children. Unfortunately, they are associated with many complications, particularly neuromuscular scoliosis, favored by the poor general condition of these patients and the fragility of their osteoporotic bones. Furthermore, these interventions are often iterative and usually followed by vertebral fusion at the end of growth. This is a review of the literature on a recent fusionless technique, minimally invasive bipolar fixation, which is more stable than the traditional growing rod techniques and less aggressive than vertebral arthrodesis. It allows the avoidance of arthrodesis, owing to the solidity of the construct and the stability of the results, leading to progressive spinal stiffening that occurs over time. The results of this technique have been published with a long follow-up period and have confirmed that it can completely replace posterior vertebral arthrodesis, especially in the most complicated scoliosis. Because it preserves growth, this technique should be recommended for early-onset scoliosis before the age of 10 years. The use of a self-expanding rod can avoid the need for repeated surgery, thereby reducing the risk of complications and the overall cost of treatment.

The Clinical and Imaging Outcome of the Tandem Growing Rod Technique in Early-Onset Scoliosis With the Proximal Upper Thoracic Curve Progression: A Modified Technique of Growing Rod

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

The orthopaedic ability of traditional GR for severe EOS is limited. The proximal upper thoracic curve may progress during the lengthening procedure, which may lead to coronal imbalance and inhibit the longitudinal growth of the spine. In this retrospective cohort study, we investigated the clinical outcome of tandem GR.

METHODS

We modified the traditional technique by using two groups of GR devices to control the major and the proximal upper thoracic curve, connected the two groups of GR in series, and named it tandem GR. The clinical and imaging outcomes of the new technique were evaluated and compared with traditional technique.

RESULTS

Twenty one patients were enrolled in the tandem GR group, and 30 patients were treated with traditional GR as the control. The baseline parameters were consistent between the two groups. In the tandem GR group, the secondary curve progressed from 24.9 ± 3.9° to 31.4 ± 3.2° (P = .006) in the procedure with the traditional GR and improved to 18.4 ± 4.5° (P = .001) after the switch. Meanwhile, the clavicular angle aggravated from 1.6 ± 1.0° to 2.6 ± .7° (P = .041), and improved to 1.7 ± .8° after changed to the tandem GR (P = .033). At the final of the follow-up, the secondary curve was higher in the control group (27.1 ± 8.3° vs 18.4 ± 4.5°, P = .034), the clavicle angle was 2.4 ± 1.1° in control and 1.7 ± .8° in the tandem GR group (P = .028), the T1-S1 height was 28.2 ± 4.8 cm in the control and 33.3 ± 3.0 cm in the tandem GR group (P = .027). The average growth rate was 1.0 ± .3 cm/year in the control and 1.2 ± .4 cm/year in the tandem GR group (P = .046).

CONCLUSION

Tandem GR can effectively improve the proximal upper thoracic curve progression during the treatment of EOS. Compared with the traditional GR, tandem GR can achieve better curve correction, better shoulder balance, and retains more capacity for longitudinal spine growth.

Rod Fracture in Magnetically Controlled Growing Spine Rods

BACKGROUND

The mechanisms of fracture in magnetically controlled growing rods (MCGRs) and the risk factors associated with this are poorly understood. This retrospective analysis of explanted MCGRs aimed to add understanding to this subject.

METHODS

From our cohort of over 120 retrieved MCGRs, we identified 7 rods that had fractured; all were single-rod constructs, retrieved from 6 patients. These were examined and compared with 15 intact single-rod constructs. Retrieval and fractographic analyses were used to determine the failure mode at the fracture site and the implant's functionality. Cobb angle, degree of rod contouring, and the distance between anchoring points were computed on anteroposterior and lateral radiographs.

RESULTS

5/7 versus 3/15 rods had been inserted after the removal of a previously inserted rod, in the fractured versus control groups. All fractured rods failed due to bending fatigue. Fractured rods had greater rod contouring angles in the frontal plane ( P = 0.0407) and lateral plane ( P = 0.0306), and greater distances between anchoring points in both anteroposterior and lateral planes ( P = 0.0061 and P = 0.0074, respectively).

CONCLUSIONS

We found all failed due to a fatigue fracture and were virtually all single rod configurations. Fracture initiation points corresponded with mechanical indentation marks induced by the intraoperative rod contouring tool. Fractured rods had undergone greater rod contouring and had greater distances between anchoring points, suggesting that it is preferable to implant double rod constructs in patients with sufficient spinal maturity to avoid this complication.

CLINICAL RELEVANCE

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.

How much does depth matter? Magnetically controlled growing rod distraction directly influenced by rod tissue depth

PURPOSE

Magnetically controlled growing rod (MCGR) for the treatment of early-onset scoliosis (EOS) is a relatively innovative technique. MCGR benefits over traditional growing rods are known but limitations and complications are being revealed. The purpose of this study was to examine the importance of tissue depth on rod lengthening.

METHODS

A single-institution retrospective review of 72 MCGR patients was performed. Ultrasound measured rod distraction. Differences in programmed and actual distraction, and complications were recorded. Tissue depths and achieved length were averaged and used to construct a regression to account for variability.

RESULTS

Percentage of std and offset orientation rod lengthening relative to the programmed distraction was inversely proportional to rod depth (std R = 0.50, p = 0.002) (offset R = 0.60, p < 0.001). Expected std rod lengthening achieved decreased by 1.46%/mm depth. Expected offset rod lengthening achieved decreased by 1.68%/mm depth. 28 pts (38.9%) sustained complications. Age, sex, BMI, standard tissue depth, and/or offset tissue depth had no predictive ability with respect to complications sustained (overall model R = 0.31, p = 0.36).

CONCLUSION

In a series of EOS surgical patients treated with MCGRs, the relationship between percentage of programmed lengthening achieved as well as total lengthening was inversely proportional to tissue depth of the rod. There was a trend towards increasing frequency of complications recorded with decreasing tissue depth though this was not significant. These data can help with surgical planning during MCGR placement.

Minimally Invasive Surgery for Neuromuscular Scoliosis: Results and Complications at a Minimal Follow-up of 5 Years

STUDY DESIGN

A prospective study.

OBJECTIVE

The aim of this study was to report the results of an alternative technique to growing rods (GR) for neuromuscular scoliosis using a minimally invasive fusionless surgery with a minimum of 5 years' follow-up.

SUMMARY OF BACKGROUND DATA

Conservative treatment is not effective in progressive neuromuscular scoliosis. Early surgery using GR is increasingly advocated to control the deformity while preserving spinal and thoracic growth before arthrodesis. These techniques still provide a high rate of complications.

METHODS

The technique relies on a bilateral double rod sliding instrumentation anchored proximally by four hooks claws and distally to the pelvis by iliosacral screws through a minimally invasive approach. The clinical and radiological outcomes of 100 consecutive patients with neuromuscular scoliosis who underwent this fusionless surgery with a minimum follow-up of 5 years were reviewed.

RESULTS

6.5 ± 0.7 years after initial surgery, six patients were lost of follow-up and 11 died of unrelated raison. Of the 83 remaining patients at latest follow-up, mean Cobb angle was stable to 35.0° which correspond to 61% correction of the initial deformation. Mean pelvic obliquity was 29.6° (0.3°-80.0°) preoperatively and 7.2 (0.2°-23.5°) at latest follow-up. Correction of the hyper kyphosis remained stable. Skeletal maturitywas reached in 42 of 83 patients (50.6%). None of these patients has required spinal fusion. The global complication rate was 31.3%.

CONCLUSION

The outcomes of this minimally invasive fusionless technique at 5 years follow-up showed a stable correction of spinal deformities and pelvic obliquity over time, with a reduced rate of complication. The arthrodesis was not required for all patients at skeletal maturity. This technique could be a good alternative to arthrodesis for neuromuscular scoliosis.Level of Evidence: 3.

Is rod diameter associated with the rate of rod fracture in patients treated with magnetically controlled growing rods?

INTRODUCTION

Few risk factors for fracture in magnetically controlled growing rods (MCGR) have been identified. We hypothesize an increased rate of rod fracture in small diameter rods compared to large diameter rods in patients with early-onset scoliosis (EOS). The purpose of this study was to determine the association between the diameter of MCGR constructs and the rate of rod fracture.

METHODS

Patients with EOS who underwent MCGR implantation-primary or conversion-from 2013 to 2018 were identified from two registries including 40 centers. Rod diameter sizes greater than 5.0 mm or less than or equal to 5.0 mm were defined as "Large" and "Small" rods, respectively. Only dual-rod constructs were included. The primary outcome measure collected was rod fracture at any point in treatment up to the most recent follow-up. Cox regression was utilized for unequal follow-up to compare rate of breakage at the last follow-up between cohorts.

RESULTS

527 patients with 1,054 rods were included. 552 (52.4%) rods had a diameter of less than or equal to 5.0 mm and 461 (43.7%) rods had a diameter of greater than 5.0 mm. 41 (3.9%) rods were missing a recorded rod diameter and were not included in the analysis to determine the association between the rate of fracture and rod diameter. 20 (1.9%) total rod fractures occurred: 9 (1.6%) rods with diameters of ≤ 5.0 mm, 10 (2.2%) rods with diameters of > 5.0 mm, and 1 uncategorized rod (p = 0.529). No difference in the rate of rod fracture or survival distribution was found between rod diameters of > 5.0 mm and ≤ 5.0 mm even after stratification by ambulatory status, major coronal curve, weight, or location of anchors.

DISCUSSION

Rod fracture appears to be a rare event in dual MCGR constructs and rod diameter does not seem to be associated with the incidence or rate of rod fracture. Surgeons may consider other criteria for selecting rod diameter in their patients such as patient size, amount of surgical correction, single vs. dual constructs, and risk of hardware prominence.

Lengthening Less Than 7 Months Leads to Greater Spinal Height Gain With Rib-based Distraction

BACKGROUND

Severe early-onset scoliosis (EOS) has been associated with a multitude of comorbidities, chief among them being deficient thoracic spine growth and pulmonary complications. EOS management with rib-based instrumentation involves repeated lengthening. Despite expansion practice patterns, there is limited literature and no evidence-based guidelines for optimal expansion intervals. Our study evaluates clinical outcomes in relation to lengthening intervals with the aim of optimizing the timing of surgical expansion in EOS patients.

METHODS

A single-institution retrospective review of 60 EOS patients treated with rib-based growth instrumentation with a minimum of 3-year follow-up and 3 expansion/revision surgeries. Patients were separated into 2 expansion cohorts: (1) more frequent lengthening [MFL group (≤7 mo)] and (2) less frequent lengthening [LFL group (>7 mo)]. Demographic information and clinical factors were recorded. Univariate and bivariate analyses were performed.

RESULTS

Both the MFL group (35 patients) and LFL group (25 patients) were similar in sex distribution, diagnosis, preoperative parameters of interest, and treatment duration. The mean follow-up was 6.0 years. There was an increase in postoperative T1-S1 spine height gained in the MFL group (P=0.006) as well as a higher percent expected spine growth based on normative values (P=0.03) when compared with the LFL group. The MFL group had more expansion/revision surgeries (P=0.003) but no increase in the number of complications (P=0.86).

CONCLUSIONS

More frequent lengthenings were associated with statistically significant overall spinal height gain and percent expected growth without a significant increase in complication rates. It was shown that change in major curve and space available for the lungs was not associated with the lengthening intervals.

LEVEL OF EVIDENCE

Level III-a comparative retrospective study.

Prospectively collected surgeon indications for discontinuation of a lengthening program for early-onset scoliosis

INTRODUCTION

At some point after children with early-onset scoliosis (EOS) undergo implantation of a distraction construct to control deformity and promote growth, a decision is made to discontinue lengthening. The purpose of this study was to evaluate surgeon indications for discontinuation of a lengthening program and to evaluate patient outcomes.

METHODS

As a part of a multicenter database, surgeons prospectively completed a questionnaire at the completion of growth-friendly treatment. Surgeon indications for discontinuation included patient age, pain/functional status, implant status, and spinal deformity parameters. Patient demographics, scoliosis type, deformity parameters, and length of time in a growing program were queried. Patients were treated with a final fusion or observation, and rate of secondary surgeries was analyzed.

RESULTS

Questionnaires were completed on 121 patients (61% female). EOS etiology was 31% neuromuscular, 43% congenital, 16% idiopathic, and 10% syndromic. Average age at initiation of growing program was 6.8 ± 3.1 years, and average age at discontinuation was 12.7 ± 2.5 years. The most commonly cited indications for discontinuation of a lengthening program included bone age/skeletal maturity (n = 46), patient age (n = 33), and diminishing returns with expansions (n = 33). A larger coronal Cobb angle was found in patients who underwent definitive fusion (65°) when compared with continued observation (55°, p = 0.001). Twenty-nine (24%) patients were initially treated with observation after completion of a growing construct. In this subgroup, at a minimum of 2 years' (average 3.8 years') follow-up, 26/29 (90%) patients remained stable with observation alone; whereas, three (10%) underwent delayed final fusion surgery.

CONCLUSIONS

The most common surgeon-cited indications for discontinuation of a lengthening program in EOS patients are skeletal maturity and patient age. The majority of patients (76%) underwent definitive spinal fusion after discontinuation of a lengthening program; whereas, those treated with observation alone had a survivorship of 90% at a minimum follow-up of two years.

Outcomes at Skeletal Maturity of 34 Children With Scoliosis Treated With a Traditional Single Growing Rod

STUDY DESIGN

Retrospective case series.

OBJECTIVES

To analyze the outcomes at skeletal maturity of patients treated with a single traditional growing rod (GR). To compare results of patients according to whether posterior spinal fusion (PSF) was performed at treatment completion.

SUMMARY OF BACKGROUND DATA

Few studies examined the end results of GRs at skeletal maturity. There is no agreement on requirement of PSF at GR treatment completion.

METHODS

Clinical and radiological analysis of consecutive patients with severe and/or progressive scoliosis treated initially with traditional single GR. Group comparisons of patients with PSF and without fusion surgery at treatment completion.

RESULTS

Thirty-four patients underwent traditional single GR implantation at a median age of 11.7 years. Median follow-up was 6.5 years. At last follow-up, T1-S1 distance was increased by a median 116 mm (P < 0.001) and median major curve Cobb angle was changed from 55° preoperatively to 30° (P < 0.001). Complications included 26 rod fractures, 1 implant prominence, 4 proximal junctional kyphosis, 2 proximal hook dislodgments, and 2 wound infections. At the beginning our experience, PSF was performed systematically in 17 patients. Relying on spinal ankylosis, 17 patients were subsequently not fused at GR treatment completion (single GR removed N = 2, single GR retained N = 7, dual GR surgery N = 8). There were no statistical differences between groups in improvements of radiological parameters from preoperative GR insertion to last follow-up. No GR fracture occurred after dual GR surgery.

CONCLUSION

Single GR allows curve control and promotes spinal growth. Dual GR is, however, recommended for rod fracture prevention and better correction maintenance. In patients with satisfactory deformity correction at skeletal maturity, one may consider retaining dual GR instead of performing PSF.

LEVEL OF EVIDENCE

4.

Device-Related Complications Associated with Magec Rod Usage for Distraction-Based Correction of Scoliosis

Introduction

Recent literature identifies similar failure rates such as anchor pull-out and rod breakage, but a higher unplanned revision surgery with MAGEC rods than with traditional growth rods. Besides known failure modes such as rod fracture, infection, etc., failure to noninvasively distract the rods was cited as the main cause of such unplanned surgeries. The source of these data ranges from multicenter cohort studies to singular case series. These studies included explanted implants that had undergone failure in distraction mechanism, rod fracture, or infection, or had reached their maximum length. Nevertheless, in addition to identifying the overall mode of failure, it is equally important to identify the large-scale incidence of exclusive failures in comparison with standard instrumentation failure modes in spine surgery.

Methods

The US Food and Drug Administration (FDA) Manufacturer and User Facility Device Experience (MAUDE) databases were searched for reports on MAGEC rods, and on standard instrumentation used for spinal fusion. The adverse events were recorded, tabulated, and analyzed.

Results

A search of the US FDA MAUDE database yielded reports of 163 device-related adverse events. These included distraction mechanism failure (n=129), rod fracture (n=24), and minor voluntary reports of infection and tissue discoloration (n=10). For standard instrumentation usage in spine surgery, pedicle screw breakage post surgery (n=336), set screw damage during surgery (n=257), rod breakage post surgery (n=175), interbody cage breakage during surgery (n=118), and pedicle screw breakage during surgery (n=75) were identified as the top 5 failure modes.

Conclusions

The study identified the distraction mechanism failure as the most common and growing complication associated with MAGEC rod usage in children with scoliosis, leading to unplanned invasive revision surgeries.

Early Onset Scoliosis: Is there an Improvement in Quality of Life With Conversion From Traditional Growing Rods to Magnetically Controlled Growing Rods?

BACKGROUND

Modern treatment of early onset scoliosis (EOS) includes implantation of traditional growing rods (TGR) or magnetically controlled growing rods (MCGR) for posterior-based distraction if nonoperative treatment plans failed. The recent MCGR innovation has largely been expected to improve patient and family burden by avoiding frequent return to the operating room. At least one study has shown no HRQoL difference between TGR and MCGR, but none have specifically investigated a cohort of conversion patients whose families have experienced both.

METHODS

An EOS database was queried for all patients treated with TGR, MCGR, and those converted from TGR to MCGR who had at least 1 pretreatment and 1 posttreatment HRQoL assessment (EOSQ-24). Data on demographics, diagnoses, and major curve size, as well as EOSQ-24 domain scores were studied.

RESULTS

There were 156 TGR, 114 MCGR, and 32 conversion patients, with an average of 2.0 years between first and final EOSQ-24 surveys. There was no significant difference in outcome in any EOSQ-24 domain between the converts and the other 2 treatment groups. There was a significant post-op improvement in MCGR versus TGR in transfers and energy level (P=0.01; P=0.01).

CONCLUSIONS

Although patient families and their surgeons may subjectively report improved HRQoL after conversion from TGR lengthenings to in-office MCGR lengthenings, these improvements were seen in transfer and fatigue domains, not burden or satisfaction. Although the EOSQ-24 is a well-validated EOS metric, it may not be sensitive enough to overcome the QoL floor-effect associated with the diagnosis itself, or perhaps the improvement in QoL must be assessed over a longer interval to assess meaningful change.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.