Correct identification of fusion levels in surgical planning for the management of adolescent idiopathic scoliosis is a complex task. Several classification systems and algorithms exist to assist surgeons in determining the appropriate levels to be instrumented. The Lenke classification is the benchmark system. Among the many factors and measurements that are taken into account when selecting the proper upper instrumented vertebra and lower instrumented vertebra are planning for selective fusion; preserving motion segments; preventing proximal and/or distal junctional kyphosis, shoulder imbalance, and neck pain; and maintaining short fusion lengths. Existing treatment algorithms do not account for every exception, and further research is required to improve long-term surgical outcomes.

/pdf/choosing-fusion-levels-in-adolescent-idiopathic-scoliosis-3eky9pammb.pdf

Choosing fusion levels in adolescent idiopathic scoliosis.

The frequency of disc degeneration (DD) in the distal mobile segments will increase over time following surgery for adolescent idiopathic scoliosis (AIS). Retrospective review of a prospective AIS registry. Durability of surgical outcomes is essential for maintenance of quality of life as well as for family decision making and for assessment of the value of a healthcare intervention. We assessed DD, its risk factors, and association with health-related quality of life 10 years after AIS surgery. Five radiographic indicators of DD, previously validated, were evaluated preoperatively and 1 month, 2, 5, and 10 years postoperatively by a radiologist in operative AIS patients. A composite radiographic score (CRS; range 0-10) was calculated using the sum of each of the DD indicators. The severity of CRS in relation to the time point after surgery and various risk factors were assessed using linear regression or Pearson χ2 test. CRS ≥3 was chosen to indicate significant DD. Association of CRS with SRS-22 outcome was evaluated by linear regression. 193 consecutive patients (mean age at surgery 14.4 years; 86% female) were assessed. Surgical approach included 102 posterior and 91 anterior fusions. Contributors to maximum CRS at 10 years were Schmorl’s nodes (7.3% of patients), osteophytes (40.4%), sclerosis (29%), and irregular endplate (8.3%). CRS ≥3 occurred in 1.6%, 0.54%, 3.7%, 6.8%, and 7.3% of patients at the various time points (r 2=0.83, p=.0313), respectively. More than 50% of DD occurred at the second (35.5%) and third (20%) disc caudal to the LIV. LIV of L4 compared with more cephalad LIV had the highest risk of developing significant DD (27.3%; p=.0267). It was found that disc wedging subjacent to the LIV (≥5°) and LIV translation (≥2 cm) lead to a sixfold increase in significant DD (odds ratio=6.71 and 6.13, respectively). Severity of DD was not associated with the number of levels fused (p=.2131), the surgical approach (p=.8245), or the construct type (p=.2922). No significant association was established between 10-year CRS and SRS-22 scores. In the first study of its kind, we found that only 7.3% of patients had significant DD 10 years after surgical correction of AIS. Rates of DD increased over time. Our data provide evidence to support recommendations to save as many caudal motion segments as possible, to avoid fusing to L4, and maintain the LIV tilt angle below 5° and LIV translation less than 2 cm.

Disc Degeneration in Unfused Caudal Motion Segments Ten Years Following Surgery for Adolescent Idiopathic Scoliosis.

STUDY DESIGN Prospective cohort study. OBJECTIVE To prospectively compare radiographic, perioperative, and functional outcomes between anterior spinal instrumentation and fusion (ASIF) and posterior spinal instrumentation and fusion (PSIF) in Lenke 5C curves. SUMMARY OF BACKGROUND DATA Historically, ASIF has been the treatment of choice for treatment of thoracolumbar adolescent idiopathic scoliosis. More recently, PSIF has gained popularity for its ease, versatility, and amount of correction achieved. Current literature lacks a prospective comparative analysis between these two approaches to better aid treating surgeons in decision making when treating Lenke 5C curves. METHODS A prospective, longitudinal multicenter adolescent idiopathic scoliosis database was used to identify 161 consecutive patients with Lenke 5C curves treated by ASIF with a dual rod system, or PSIF with a pedicle screw-rod construct. Pre- and 2-year postoperative radiographic data, Scoliosis Research Society outcome scores, and perioperative comparisons were made between the two approaches. RESULTS A total of 69 patients were treated with ASIF and 92 patients with PSIF. Curve extent, magnitude, stable, and end vertebrae distribution before surgery were similar between the two groups. At 2-year follow-up, there were no significant differences in percentage correction of the main curve (ASIF: 59.1%, PSIF: 59.6%), C7 decompensation (ASIF: -0.6 ± 1.2, PSIF: -0.3 ± 1.4 cm), length of hospital stay (ASIF: 5.6 days, PSIF: 5.7 days), postoperative day conversion to oral pain medication (ASIF: 3.2 days, PSIF: 3.2 days), and SRS outcome scores (P = 0.560) between the two groups. The number of levels fused was significantly lower in ASIF group (ASIF: 4.7, PSIF: 6.3; P < 0.001), but PSIF resulted in significantly less disc angulation below lowest instrumented vertebrae (ASIF: 3.4°, PSIF: 1.7°; P = 0.011), greater lumbar lordosis (P < 0.001), and greater % correction of lumbar prominence (P = 0.017). CONCLUSION The amount of correction achieved was similar between ASIF and PSIF. ASIF resulted in shorter fusions (average 1.6 levels) compared with PSIF. This was at the expense of increased disc angulation below the lowest instrumented vertebrae, less lumbar lordosis, and a lower % correction of the lumbar prominence than PSIF. LEVEL OF EVIDENCE 2.

A Detailed Comparative Analysis of Anterior Versus Posterior Approach to Lenke 5C Curves.

Effects of follower load and rib cage on intervertebral disc pressure and sagittal plane curvature in static tests of cadaveric thoracic spines

Study Design. Histological and ultrastructural evaluation of cell morphologies at the concave and convex side of apical intervertebral discs (IVD) of adolescent idiopathic scoliosis (AIS). Objective. To determine changes in cell morphology, viability, and cell death after asymmetric disc loading in AIS and to compare the findings with the tilt angles. Summary of Background Data. The reaction of cells to loading stimuli in the IVD seems to be specific. Although dynamic loads are more beneficial to the disc cells and maintain the matrix biosynthesis, static compressive loads suppress gene expression. Methods. Apical IVDs (Th8–Th9 to L1–L2) from 10 patients with AIS were studied histologically (including TUNEL [TdT-mediated dUTP-biotin nick end labeling] staining to identify disc cell death by apoptosis) and ultrastructurally for matrix evaluations and to quantify healthy, balloon, chondroptotic, apoptotic, and necrotic cells on the concave and convex sides. Patients' spines were classified according to the Lenke classification. Degeneration was assessed according to the Pfirrmann grading system. Two groups were established; group 1 (G1) with a tilt of 5° to 9° and group 2 (G2) with a tilt of 10° to 19°. Results. Balloon cells were found in significantly higher numbers at the concave side (G1—annulus fibrosus [AF]: mean 16%), with almost none found at the convex side. Mean numbers of healthy cells did not show differences comparing both sides. Significantly higher numbers of healthy cells were found with increasing tilt angle at the concave side. Necrosis (mean, 47%) increased toward the center of the disc but did not differ between the sides of the IVDs. The fibrils found in the outer AF on the convex side were 30% thinner. Conclusion. This study was able to show significant differences in cell morphologies in the AF on both sides and in correlation to the different tilt angles. The type and magnitude of load seem to influence disc cells. Further studies are required to provide more information on disc and cell changes in scoliosis.

Morphological differences in adolescent idiopathic scoliosis: a histological and ultrastructural investigation.

STUDY DESIGN In vitro cadaveric study. OBJECTIVE The purpose of this study was to quantify the relative biomechanical protection resulting from "saving a level" in long spinal fusions. SUMMARY OF BACKGROUND DATA "Saving levels" in spinal deformity surgery is desirable. Constructs with lowest instrumented vertebra (LIV) in the lumbar spine may increase loads on unfused lumbar intervertebral discs, leading to accelerated disc degeneration. No study to date has quantified the relative pressure changes that occur in the unfused caudal discs with progressively longer fusions. METHODS We used a validated in vitro cadaveric long fusion model to assess intradiscal pressures (IDPs) below simulated fusions. Eight fresh frozen T8-S1 specimens were instrumented from T8 to L5. A follower-type loading system and 7.5-N·m moments were applied in flexion and extension. IDP profiles were assessed with a pressure transducer. After acquiring IDP measurements at a given construct length, the rod was cut 1 level higher until LIV = T12. IDP data from each unfused disc were averaged and normalized to the mean value of the disc when immediately subjacent to the LIV. RESULTS In both flexion and extension, the mean normalized IDP of the unfused discs below the LIV increased with increasing fusion length. For each 1-level increase in construct length, pressure increased by 3.2% ± 4.8% in flexion and 4.3% ± 4.5% in extension for each unfused disc. Although the differences in pressure for a given unfused disc with differing LIV were not significant, there were significant differences between unfused discs at a given LIV. With shorter fusion lengths, pressure in the disc immediately subjacent to the fusion was consistently greater than for the caudal-most discs. CONCLUSION Unfused caudal lumbar discs experienced increased IDPs with increasing length of instrumentation, most notably at the subjacent discs closest to the LIV.

Quantification of intradiscal pressures below thoracolumbar spinal fusion constructs: is there evidence to support "saving a level"?

P84. Quantification of Intradiscal Pressures below Thoracolumbar Spinal Fusion Constructs: Is There Evidence to Support “Saving a Level?”

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Quantification of intradiscal pressures below thoracolumbar spinal fusion constructs: is there evidence to support "saving a level"?

P84. Quantification of Intradiscal Pressures below Thoracolumbar Spinal Fusion Constructs: Is There Evidence to Support “Saving a Level?”