Preclinical Bench Testing on a Novel Posterior Dynamic Deformity Correction Device for Scoliosis

Tissue response following implantation with the posterior dynamic distraction device (PDDD) in adolescent idiopathic scoliosis (AIS)

PURPOSE

The PDDD is a ratchet-based, unidirectional expandable rod to treat adolescent idiopathic scoliosis (AIS), primarily by correcting scoliotic deformity without full spinal fusion. We hypothesized that the device will be fully tolerated by the host and, if aseptic screw loosening occurs, it will be unrelated to wear particle formation.

METHODS

This study comprised tissue samples from seven patients from a prospective study (NCT04296903) to assess the PDDD's safety and benefits, reoperated due to complications. Host response was assessed from histological slides (four levels/implant) in accordance with GLP and ISO10993-6:2016. The elementary chemical composition of wear particles present in tissue sections was quantified by energy dispersive X-ray spectroscopy (EDX).

RESULTS

Host reaction was minor, characterized by low levels of diverse inflammatory cells, mild fibrosis, occasional small necrotic foci, neovascularization, hemorrhage, and, rarely, small bone fragments. Twenty-four of 28 tissue sections displayed varying degrees of wear particles (black discoloration), and most sections (17) were scored as 1 (< 25% of the sample). The discoloration observed corresponded to black-appearing, fine granular pigment. EDX analysis confirmed particles were composed of titanium, aluminum, and vanadium. Twenty-six of 28 samples were scored zero for necrosis and 2/28 were scored 1. Eleven samples were scored zero for fibrosis, 12 as 1, and five as 2. No aseptic screw loosening occurred.

CONCLUSION

The PDDD induced minimal host reaction with little or no degeneration, inflammation or fibrosis. No changes present could be expected to promote device failure. The PDDD implant for treating AIS is well-tolerated and locally safe.

Vertebral growth modulation by posterior dynamic deformity correction device in skeletally immature patients with moderate adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective, comparative, multicenter.

INTRODUCTION

Growth modulating spinal implants are used in the management of scoliosis such as anterior vertebral body tethering. A motion-sparing posterior device (PDDC) was recently approved for the treatment of moderate AIS. The purpose of this study was to determine if the PDDC can modulate growth in skeletally immature patients with AIS.

METHODS

From a database of patients treated with the PDDC over 4 years, we identified those who had a minimum of 2 years follow-up. Pre-operative and post-operative Cobb angles and coronal plane wedging of the apical vertebra were evaluated on standing full length radiographs. Independent sample t test and one-way ANOVA with post-hoc Tukey HSD analysis was used to compare three groups in varying skeletal maturity: Risser 0-1, Risser 2-3, and Risser 4-5.

RESULTS

45 patients (14.2-years old, 11-17) were evaluated with a mean pre-op curve of 46° (35°-66°). The average preoperative major curve magnitude, of either Lenke 1 or 5 curve type, was similar among the three groups 47.6°, 46° and 41.5°. Deformity correction was similar in the three groups, with reduction to 26.4°, 20.4° and 26.2°, respectively, at final follow-up [p < 0.05]. Pre-op wedging 7.4° (3.8°-15°) was reduced after surgery to 5.7° (1°-15°) (p < 0.05). Of those patients, Risser 0-1 (n = 16) had preoperative wedging of 9.5° (6°-14.5°) that was reduced to 5.4° (1°-8°) postoperatively (p < 0.05); Risser 2-3 (n = 15) had pre-op 7.7° (4°-15°) vs. post-op 7.0° (3°-15°); Risser 4-5 (n = 14) had pre-op 4.8° (3.8°-6.5°) vs. post-op 4.7° (3.7°-6.5°). Delta Wedging in Risser 0-1 stage was significantly different than for Risser 2-3 and for Risser 4-5.

CONCLUSION

The posterior dynamic deformity correction device was able to modulate vertebral body wedging in skeletally immature patients with AIS. This was most evident in patients who were Risser 0-1. In contrast, curve correction was similar among the three groups. This finding lends support to the device's ability to modulate growth.

Surgical management of moderate adolescent idiopathic scoliosis with a fusionless posterior dynamic deformity correction device: interim results with bridging 5-6 disc levels at 2 or more years of follow-up

OBJECTIVE

A posterior dynamic deformity correction (PDDC) system was used to correct adolescent idiopathic scoliosis (AIS) without fusion. The preliminary outcomes of bridging only 3-4 discs in patients with variable curve severity have previously been reported. This paper examines a subgroup of patients with the authors' proposed current indications for this device who were also treated with a longer construct.

METHODS

Inclusion criteria included a single AIS structural curve between 40° and 60°, curve flexibility ≤ 30°, PDDC spanning 5-6 levels, and minimum 2-year follow-up. A retrospective review was conducted and demographic and radiographic data were recorded. A successful outcome was defined as a curve magnitude of ≤ 30° at final follow-up. Any serious adverse events and reoperations were recorded.

RESULTS

Twenty-two patients who met the inclusion criteria were operated on with the PDDC in 5 medical centers. There were 19 girls and 3 boys, aged 13-17 years, with Risser grades ≥ 2. Thirteen had Lenke type 1 curves and 9 had type 5 curves. The mean preoperative curve was 47° (range 40°-55°). At a minimum of 2 years' follow-up, the mean major curve measured 25° (46% correction, p < 0.05). In 18 (82%) of 22 patients, the mean final Cobb angle measured ≤ 30° (range 15°-30°). Trunk shift was corrected by 1.5 cm (range 0.4-4.3 cm). The mean minor curve was reduced from 27° to 17° at final follow-up (35% correction, p < 0.05). For Lenke type 1 patterns, the mean 2D thoracic kyphosis was 24° preoperatively versus 27° at final follow-up (p < 0.05), and for Lenke type 5 curves, mean lumbar lordosis was 47° preoperatively versus 42° at final follow-up (p < 0.05). The mean preoperative Scoliosis Research Society-22 questionnaire score improved from 2.74 ± 0.3 at baseline to 4.31 ± 0.4 at 2 years after surgery (p < 0.0001). The mean preoperative self-image score and satisfaction scores improved from preoperative values, while other domain scores did not change significantly. Four patients (18%) underwent revision surgery because of nut loosening (n = 2), pedicle screw backup (n = 1), and ratchet malfunction (n = 1).

CONCLUSIONS

In AIS patients with a single flexible major curve up to 60°, the fusionless PDDC device achieved a satisfactory result as 82% had residual curves ≤ 30°. These findings suggest that the PDDC device may serve as an alternative to spinal fusion in select patients.