Elevated Serum Titanium Levels in Children With Early Onset Scoliosis Treated With Growth-friendly Instrumentation

Is posterior vertebral arthrodesis at the end of the electromagnetic rod lengthening program necessary for all patients? Comparative analysis of sixty six patients who underwent definitive spinal arthrodesis and twenty four patients with in situ lengthening rods

PURPOSE

Magnetically controlled growing rods (MCGR) should be removed or changed at most two years after their implantation in the treatment of patients with early-onset scoliosis (EOS) (Safety notice July 2021). However, in the face of patients at high risk of intraoperative complications and relying on the principle of auto-fusion of the spine, some surgeons would prefer a more wait-and-see attitude. The aim of this study was to report on patients who did not undergo final fusion at the end of the lengthening program with MCGR and to compare them with those who did.

METHODS

This was a multicenter study with ten centres. We collected all graduate patients with EOS who had received MCGR between 2011 and 2022.

RESULTS

A total of 66 patients had final fusion at the end of the lengthening program and 24 patients kept MCGRs in situ. The mean total follow-up time was 66 months (range, 25.3-109), and the mean follow-up time after final lengthening was 24.9 months (range, 3-67.7). Regarding the main curve and thoracic height, there was no significant difference in the percentage of correction over the whole follow-up between the two groups (p = 0.099, p = 0.176) although there was a significant difference between the end of lengthening and the last follow-up (p < 0.001). After completion of the lengthening program, 18 patients who had final fusion developed 24 of the 26 recorded complications (92.3%).

CONCLUSION

Contrary to the manufacturer's published safety notice, not all patients systematically benefited from the removal of the MCGRs. Although arthrodesis significantly improved the scoliotic deformity, no significant difference was found in terms of radiographic outcome between patients who underwent spinal fusion and those who kept the MCGRs in situ.

Serum Titanium Levels Remain Elevated But Urine Titanium is Undetectable in Children With Early Onset Scoliosis Undergoing Growth-Friendly Surgical Treatment: A Prospective Study

BACKGROUND

Elevated serum titanium levels have been found in patients with early onset scoliosis (EOS) treated with traditional growing rods (TGR), magnetically controlled growing rods (MCGR), and vertical expandable prosthetic titanium rib (VEPTR). No studies have investigated whether serum titanium remains persistently elevated and if titanium is excreted. Our purpose was to compare serum titanium levels in patients with EOS with growth-friendly instrumentation to age-matched controls and evaluate urine titanium and serial serum titanium levels in patients with EOS.

METHODS

This was a prospective case-control study. Patients with EOS with TGR, MCGR, or VEPTR underwent urine titanium and serial serum titanium collection at a minimum 6-month interval. Control patients did not have a history of metal implant insertion and underwent serum titanium collection before fracture fixation.

RESULTS

Twenty patients with EOS (6 TGR, 8 MCGR, and 6 VEPTR) and 12 controls were analyzed. The control group had no detectable serum titanium (0 ng/mL), whereas the patients with EOS had a median serum titanium of 4.0 ng/mL ( P < 0.001). Analysis of variance showed significantly higher median serum titanium levels in the MCGR and VEPTR groups than the TGR group at time point 1 (5.5 vs 6.0 vs 2.0 ng/mL, P = 0.01) and time point 2 (6.5 vs 7.5 vs 2.0 ng/mL, P < 0.001). Binary comparisons showed a significant difference in serum titanium level between TGR and MCGR (time point 1: P = 0.026, time point 2: P = 0.011) and TGR and VEPTR (time point 1: P = 0.035, time point 2: P = 0.003). However, there was no difference between MCGR and VEPTR (time point 1: P = 0.399, time point 2: P = 0.492) even though the VEPTR group had a longer duration of follow-up ( P = 0.001) and a greater number of lengthenings per patient at the first serum collection ( P = 0.016). No patients with EOS had detectable urine titanium.

CONCLUSIONS

Patients with EOS treated with titanium alloy growth-friendly instrumentation had elevated serum titanium levels compared with age-matched controls that persisted over time with no evidence of renal excretion. Additional studies are necessary to assess for local and systemic accumulation of titanium and the significance of long-term exposure to titanium in growing children.

LEVEL OF EVIDENCE

Level III, therapeutic.

The Evaluation of Serum Metal Ion Levels and Metallosis in Graduated Patients With Magnetically Controlled Growing Rods

BACKGROUND

Magnetically controlled growing rods (MCGR) aim to control curve progression while limiting surgical burden in children with early-onset scoliosis. Systemic and local distribution of metal debris has been documented in children with spinal implants. The aim of the study was to assess serum metal ion levels and local metal debris-related changes at the conclusion of MCGR treatment.

METHODS

Between February 2019 and September 2022, all patients who had a conversion to definitive fusion at the completion of MCGR treatment in our institution were invited to participate in this study. Consenting patients had serum metal ion levels drawn (titanium, cobalt, and chromium) and histologic analyses of peri-implant tissue samples.

RESULTS

We enrolled 24 children who underwent definitive fusion post-MCGR treatment for early-onset scoliosis. The average age at definitive fusion was 13.3 years (range: 11 to 17 y). The average length of MCGR treatment was 4.8 years (range: 1.5 to 6.8 y). At the end of the MCGR treatment, 23 (96%) patients had elevated serum metal ion levels. Mean serum titanium levels were 165.4 nmol/L (range: 30 to 390 nmol/L), mean serum cobalt levels were 4.6 nmol/L (range: 1.2 to 14 nmol/L), and mean serum chromium levels were 14 nmol/L (range: 2.4 to 30 nmol/L). Peri-implant soft tissue histologic analysis demonstrated local metal debris and foreign body reactions in all patients.

CONCLUSIONS

At the completion of MCGR treatment, the majority of patients demonstrate elevated serum metal ion levels and local metal debris-related peri-implant soft tissue changes. Although there is no current literature to suggest these findings are harmful, further research as to the clinical significance is required.

LEVEL OF EVIDENCE

Level IV.

Inter-screw index as a novel diagnostic indicator of tether breakage

PURPOSE

Tether breakage is the most common complication of Vertebral Body Tethering (VBT) occurring in up to 52% of Adolescent Idiopathic Scoliosis (AIS) patients and risks continued progression and revision. Radiographical diagnosis of tether breakage is commonly defined by a 5° increase in inter-screw angle and associates breakage with loss of correction. However, the sensitivity of this method was 56% only, suggesting that tethers can break without an increase in angulation, which was supported by other studies. To our knowledge, current literature lacks a method merely focusing on the diagnosis of tether breakage radiographically that does not associate the breakages with loss of correction.

METHODS

This was a retrospective review of prospectively collected data of AIS patients who underwent VBT. The "inter-screw index" is defined as the percentage increase in inter-screw distance since post-op, with ≥ 13% increase defined as tether breakage as suggested by our mechanical tests. CTs were reviewed to identify the breakages and compared with inter-screw angle and inter-screw index.

RESULTS

94 segments from 13 CTs were reviewed, and 15 tether breakages were identified. Use of inter-screw index correctly identified 14 breakages (93%), whereas ≥ 5° increase in inter-screw angle only identified 12 breakages (80%).

CONCLUSION

Use of inter-screw index is proven to be more sensitive than inter-screw angle in identifying tether breakages. Therefore, we propose the use of inter-screw index to diagnose tether breakages radiographically. Tether breakages were not necessarily accompanied by a loss of segmental correction leading to an increase in inter-screw angle, especially after skeletal maturity.

LEVEL OF EVIDENCE

Level 3.

Blood titanium levels in patients with large and sliding titanium implants

Background

Titanium, which is known to be a highly biologically inert element, is one of the most commonly used metals in orthopaedic implants. While cobalt and chromium blood metal ion testing is routinely used in the clinical monitoring of patients with metal-on-metal hip implants, much less is known about the levels of titanium in patients with other implant types. The aim of this study was to better understand the normal ranges of blood titanium levels in patients implanted with large and sliding titanium constructs by comparison with reference levels from conventional titanium hips.

Methods

This study examined data collected from 136 patients. Over a period of 24 months, whole blood samples were collected from 41 patients implanted with large titanium implants: long (range 15 to 30 cm) spine rods with a sliding mechanism (“spine rods”, n = 18), long bone tumour implants (“tumour implants”, n = 13) and 3D-printed customised massive acetabular defect implants (“massive acetabular implants”, n = 10). This data was compared with standard, uncemented primary titanium hip implants (“standard hips”, 15 cm long) (n = 95). Clinical, imaging and blood titanium levels data were collected for all patients and compared statistically between the different groups.

Results

The median (range) of blood titanium levels of the standard hip, spine rods, femoral tumour implants and massive acetabular implants were 1.2 ppb (0.6–4.9), 9.7 ppb (4.0–25.4), 2.6 ppb (0.4–104.4) and 5.7 ppb (1.6–31.5) respectively. Spine rods and massive acetabular implants had significantly greater blood titanium levels compared to the standard hips group (p < 0.001).

Conclusion

This study showed that titanium orthopaedic implants that are large and/or have a sliding mechanism have higher blood titanium levels compared to well-functioning, conventionally sized titanium hips. Reassuringly, the increased levels did not appear to induce adverse metal reactions. This study provides useful baseline data for future studies aimed at assessing blood titanium levels as a biomarker for implant function.

Titanium wear from magnetically controlled growing rods (MCGRs) for the treatment of spinal deformities in children

Magnetically controlled growing rods (MCGRs) are an effective treatment method for early-onset scoliosis (EOS). In recent years, increasing titanium wear was observed in tissue adjacent to implants and in blood samples of these patients. This study aims to investigate the potential correlation between amount of metal loss and titanium levels in blood during MCGR treatment as well as influencing factors for metal wear. In total, 44 MCGRs (n = 23 patients) were retrieved after an average of 2.6 years of implantation and analyzed using a tactile measurement instrument and subsequent metal loss calculation. Titanium plasma levels (n = 23) were obtained using inductively coupled plasma-mass spectrometry (ICP-MS). The correlation of both parameters as well as influencing factors were analyzed. Titanium abrasion on MCGRs was observed in the majority of implants. There was no correlation of metal implant wear or titanium plasma values to the duration of MCGR implantation time, number of external lengthening procedures, patient’s ambulatory status, gender, weight or height. Material loss on the MCGRs showed a positive correlation to titanium blood plasma values. The present study is one of the first studies to analyze retrieved MCGRs using high-precision metrological techniques and compare these results with ICP-MS analyses determining blood titanium values.

Are Serum Ion Levels Elevated in Pediatric Patients With Metal Implants?

BACKGROUND

Previous studies report elevated serum titanium (Ti) levels in children with spinal implants. To provide additional data on this topic, we sought to assess serum ion levels at multiple timepoints in pediatric patients with growing spine devices, spinal fusion instrumentation, and extremity implants placed for fracture treatment. We hypothesized that serum Ti, cobalt (Co), and chromium (Cr) levels would be elevated in pediatric patients with growing spine devices compared with patients with extremity implants.

METHODS

Pediatric patients undergoing any primary spine implant placement, those with spine implant revision or removal surgery and patients with other appendicular implant removal had serum Ti, Co, and Cr ion levels drawn at the time of surgery. Fifty-one patients (12 growing spine devices, 13 fusions, and 26 extremity implants) had one set of labs, 31 of whom had labs drawn both preoperatively and postoperatively. Biopsies obtained from tissue specimens at the time of implant revision were analyzed histologically for the presence of metal debris and macrophage activity.

RESULTS

Patients with growing spine implants had elevated serum Ti (3.3 vs. 1.9 ng/mL, P=0.01) and Cr levels (1.2 vs. 0.27 ng/mL, P=0.01) in comparison to patients with fusion rods or extremity implants. With respect to patients with extremity implants, patients with growing spine devices had elevated serum Ti (3.3 vs. 0.98 ng/mL, P=0.013), Co (0.63 vs. 0.26 ng/mL, P=0.017), and Cr levels (1.18 vs. 0.26 ng/mL, P=0.005). On matched pairs analysis, patients who had labs drawn before and after spine implantation had significant increase in serum Ti levels (0.57 vs. 3.3 ng/mL, P=0.02). Histology of tissue biopsies adjacent to growing spine implants showed presence of metal debris and increased macrophage activity compared with patients with extremity implants.

CONCLUSION

Serum Ti, Co, and Cr levels are elevated in children with spinal implants compared with those with extremity implants, particularly in those with growing spine devices. However, the clinical significance of these findings remains to be determined.

LEVEL OF EVIDENCE

Level II-prospective comparative study.

When Is a Growth-friendly Strategy Warranted? A Matched Comparison of Growing Rods Versus Primary Posterior Spinal Fusion in Juveniles With Early-onset Scoliosis

BACKGROUND

In 7 to 11-year-old juveniles with severe early-onset scoliosis (EOS) the optimal surgical option remains uncertain. This study compares growing rods (GRs) followed by definitive posterior spinal fusion (PSF) versus primary PSF in this population. We hypothesized that the thoracic height afforded by GRs would be offset by increased rigidity, more complications, and more operations.

METHODS

This retrospective comparative study included EOS patients aged 7.0 to 11.9 years at index surgery treated with GR→PSF or primary PSF during 2013 to 2020. Primary outcomes were thoracic height gain (ΔT1-12H), major curve, complications, and total operations. Primary PSFs were matched with replacement 1-to-n to GR→PSFs by age at index, etiology, and major curve.

RESULTS

Twenty-eight GR→PSFs met criteria: 19 magnetically controlled GRs and 9 traditional GRs. Three magnetically controlled GRs were definitively explanted without PSF due to complications. The remaining 25 GR→PSFs were matched to 17 primary PSFs with 100% etiology match, mean Δ major curve 1 degree, and mean Δ age at index 0.5 years (PSFs older). Median ΔT1-12H pre-GR to post-PSF was 4.7 cm with median deformity correction of 37%. Median ΔT1-12H among primary PSFs was 1.9 cm with median deformity correction of 62%. GR→PSFs had mean 1.8 complications and 3.4 operations. Primary PSFs had mean 0.5 complications and 1.3 operations. Matched analysis showed adjusted mean differences of 2.3 cm greater ΔT1-12H among GR→PSFs than their matched primary PSFs, with 25% less overall coronal deformity correction, 1.2 additional complications, and 2.2 additional operations per patient.

CONCLUSIONS

In juveniles aged 7 to 11 with EOS, on average GRs afford 2 cm of thoracic height over primary PSF at the cost of poorer deformity correction and additional complications and operations. Primary PSF affords an average of 2 cm of thoracic height gain; if an additional 2 cm will be impactful then GRs should be considered. However, in most juveniles the height gained may not warrant the iatrogenic stiffness, complications, and additional operations. Surgeons and families should weigh these benefits and harms when choosing a treatment plan.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Focal osteolysis and corrosion at the junction of Precice Stryde intramedullary lengthening device : preliminary clinical, radiological, and metallurgic analysis of 57 lengthened segments

Aims

This study aims to enhance understanding of clinical and radiological consequences and involved mechanisms that led to corrosion of the Precice Stryde (Stryde) intramedullary lengthening nail in the post market surveillance era of the device. Between 2018 and 2021 more than 2,000 Stryde nails have been implanted worldwide. However, the outcome of treatment with the Stryde system is insufficiently reported.

Methods

This is a retrospective single-centre study analyzing outcome of 57 consecutive lengthening procedures performed with the Stryde nail at the authors’ institution from February 2019 until November 2020. Macro- and microscopic metallographic analysis of four retrieved nails was conducted. To investigate observed corrosion at telescoping junction, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) were performed.

Results

Adjacent to the nail’s telescoping junction, osteolytic changes were observed in bi-planar radiographs of 20/57 segments (35%) after a mean of 9.5 months (95% confidence interval 7.2 to 11.9) after surgery. A total of 8/20 patients with osseous alterations (40%) reported rest and ambulation pain of the lengthened segment during consolidation.

So far, 24 Stryde nails were retrieved and in 20 (83%) macroscopic corrosion was observed at the nail’s telescoping junction. Before implant removal 11/20 radiographs (55%) of lengthened segments with these 20 nails revealed osteolysis. Implant retrieval analysis by means of SEM showed pitting and crevice corrosion. EDX detected chromium as the main metallic element of corrosion.

Conclusion

Patients are exposed to the risk of implant-related osteolysis of unclear short- and long-term clinical consequences. The authors advocate in favour of an early implant removal after osseous consolidation.

Cite this article: Bone Joint Res 2021;10(7):425–436.

Complications, Reoperations, and Mid-Term Outcomes Following Anterior Vertebral Body Tethering Versus Posterior Spinal Fusion: A Meta-Analysis

Background

Anterior vertebral body tethering (AVBT) is a growth-modulation technique theorized to correct adolescent idiopathic scoliosis (AIS) without the postoperative stiffness imposed by posterior spinal fusion. However, data are limited to small series examining short-term outcomes. To assess AVBT's potential as a viable alternative to posterior spinal fusion (PSF), a comprehensive comparison is warranted. The purpose of this meta-analysis was to compare postoperative outcomes between patients with AIS undergoing PSF and AVBT. Our primary objective was to compare complication and reoperation rates at available follow-up times. Secondary objectives included comparing mid-term Scoliosis Research Society (SRS)-22 scores, and coronal and sagittal-plane Cobb angle corrections.

Methods

We performed a systematic review of outcome studies following AVBT and/or PSF procedures. The inclusion criteria included the following: AVBT and/or PSF procedures; Lenke 1 or 2 curves; an age of 10 to 18 years for >90% of the patient population; <10% non-AIS scoliosis etiology; and follow-up of ≥1 year. A single-arm, random-effects meta-analysis was performed. Deformity corrections, complication and reoperation rates, and postoperative SRS-22 scores were recorded.

Results

Ten AVBT studies (211 patients) and 14 PSF studies (1,069 patients) were included. The mean follow-up durations were similar for both groups. Pooled complication rates were 26% for AVBT versus 2% for PSF, and reoperation rates were 14.1% for AVBT versus 0.6% for PSF with nonoverlapping confidence intervals (CIs). The pooled reoperation rate among studies with follow-up times of ≥36 months was 24.7% in AVBT versus 1.8% in PSF. Deformity correction, clinical outcomes, and mid-term SRS-22 scores were similar.

Conclusions

Our study showed greater rates of complications and reoperations with AVBT compared with PSF. Reoperation rates were significantly greater in AVBT studies with longer follow-up (≥36 months). Deformity correction, clinical outcomes, and mid-term SRS-22 scores were similar. While a potential fusionless treatment for AIS merits excitement, clinicians should consider AVBT with caution. Future long-term randomized prospective studies are needed.

Level of Evidence

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