A multibody simulation of the spine for objectification of biomechanical quantities after VBT: a proof of concept and description of baseline data.

PURPOSE: Vertebral Body Tethering (VBT), an alternative treatment for adolescent idiopathic scoliosis, shows satisfactory post-operative results. However, the biomechanical quantities and consequences after VBT surgery remain largely unknown. Therefore, the aim of this study is to analyze the spinal biomechanics during different motions using a multibody simulation approach. METHODS: The tether and intervertebral compression forces were simulated in a validated spine model during different physiological movements at different pre-tensions and screw positions, while considering the anatomical muscle and ligament properties. RESULTS: The simulations showed that an augmentation of the pre-tension and an alteration of the screw position have both significant impact on the intervertebral compression and tether forces. The forces also vary depending on the movement performed, with the highest tether forces measured during lateral bending. In the upright position, with a pre-tension of 200 N, the maximum compression force increases by up to 157% compared to the untethered maximum compression force. The screw position can lead to large differences in the distribution of forces in the spine. CONCLUSION: The biomechanical data provide a first impression of the forces that occur along the spine during various physiological movements and are consistent with published clinical data. Forces are not evenly distributed along the spine, with higher lumbar forces. The tether forces reach values during lateral bending that can potentially destroy the tether´s integrity and thus may explain the common post-operative complication, namely tether breakage. The results of the model can therefore have an impact on future directions for improved surgical VBT treatment.

The effects of vertebral body tethering on sagittal parameters: evaluations from a 2-years follow-up.

INTRODUCTION: While the effects of VBT on coronal parameters have been investigated in various studies, this has not yet been the case for sagittal parameters. This is of particular relevance considering that VBT does not allow direct correction of the sagittal profile. Thus, we investigated the effects of VBT on sagittal parameters in patients with adolescent idiopathic scoliosis. MATERIALS AND METHODS: Retrospective, 2-Center study. Patients who underwent VBT and presented a 2-years follow-up were included. The differences in sagittal parameters were evaluated, along with modifications of sagittal profile following Abelin-Genevois' classification. RESULTS: Data from 86 patients were obtained. Mean Cobb angle was 52.4 ± 13.9° at thoracic level and 47.6 ± 14.3° at lumbar level before surgery, and 28.5 ± 13.6 and 26.6 ± 12.7° at the 2-year follow-up, respectively. Mean thoracic kyphosis increased from 28.3 ± 13.8 to 33 ± 13°, the lumbar lordosis (LL) was unvaried (from 47.5 ± 13.1 to 48.4 ± 13.5°), PT decreased from 9.4 ± 8.5 to 7.4 ± 6.1°, the sagittal vertical axis SVA decreased from 4.5 ± 31.4 to - 3.6 ± 27.9 mm. No kyphotic effect on LL in patients who underwent lumbar instrumentation was observed. Before surgery, 39 patients had a type 1 sagittal profile, 18 were type 2a, 14 type 2b and 15 type 3. Postoperatively, 54 were type 1, 8 were 2a, 13 were 2b and 11 were type 3. CONCLUSIONS: VBT positively influences sagittal parameters and does not have a kyphotic effect on LL.

Preliminary outcomes after vertebral body tethering (VBT) for lumbar curves and subanalysis of a 1- versus 2-tether construct.

INTRODUCTION: Aim of this study was to analyze the rate of tether breakages after lumbar vertebral body tethering (VBT) and to study the effects and possible benefits of the use of a 2-tether construct. Tether breakage is a known mechanical complication after VBT. However, the literature only refers to thoracic VBT, and no data on the breakage rate or 2-tether construct after lumbar VBT are available. MATERIALS AND METHODS: Patients who underwent lumbar VBT with lowest instrumented vertebra at L3 or L4 and had a 1-year follow-up were included. Radiologic data were obtained preoperatively, at the 1st standing X-ray and at the 1-year follow-up to study breakage rate, loss of correction and lumbar lordosis in 1- and 2-tether constructs. RESULTS: Data from 30 patients (mean age 14.7 ± 1.8) were available, 12 with double tether. Double tether did not decrease lumbar lordosis. The breakage rate was 24% in segments instrumented with a single tether and 16% in segments instrumented with a double tether (OR 1.6, p = 0.4). Lumbar loss of correction was 10° ± 6.8° in the entire cohort and 12.1° ± 5.4° in patients with a breakage (p = 0.2). Revision rate was 10%, due to tether breakage and loss of correction. CONCLUSION: Breakage rate after lumbar VBT is high, but was improved with the use of a 2-tether construct. Despite tether breakage, loss of correction was limited and the revision rate low. The use of a double tether does not have a kyphotic effect on the lumbar spine.

Return to sport and daily life activities after vertebral body tethering for AIS: analysis of the sport activity questionnaire.

PURPOSE: Vertebral body tethering (VBT) is an alternative to fusion for selected scoliosis patients. As VBT does not limit spine mobility, it has been propagated that this technique allows a quicker return to physical activity than fusion. However, no data are available to support this statement. Aim of this study was to quantify how much time patients required to resume preoperative activity level and to seek possible associations between return to physical activity and demographic, radiographic and surgical data. METHODS: One year postoperatively, the validated sport activity questionnaire (SAQ) was administered to all skeletally immature patients who underwent VBT at our institution. SAQ data were analyzed and a multivariate analysis was conducted to investigate associations between SAQ and demographic, radiographic and surgical data. RESULTS: Thirty-one patients aged 14.5 years completed the SAQ. Within 3 months from VBT, 97% returned to school, 61% resumed physical education, 97% carried a backpack, 68% run, and 82% rode a bike; 70% bent within a month from VBT. Ninety-four percent of patients returned to their preoperative athletic level. Within 3 months, 63% of responders resumed noncontact, 61% contact and 53% collision sports. No relevant associations were observed between the SAQ and demographic, radiographic and surgical data. In particular, number of instrumented vertebrae, level of the lowest instrumented vertebra and postoperative Cobb angle did not influence patients' return to preoperative activities. CONCLUSION: VBT allows patients to quickly return to their preoperative activity level, irrespectively of the postoperative Cobb angle or type of instrumentation.

Choosing fusion levels in adolescent idiopathic scoliosis.

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.

Radiographic Results after Vertebral Body Tethering. / Radiologische Ergebnisse nach Vertebral Body Tethering.

Vertebral body tethering (VBT), otherwise known as fusion-less anterior scoliosis correction (ASC), is a new and increasingly interesting therapeutic option for selected scoliosis patients. The available data on this surgical technique are still limited and guidelines on patient selection or surgical timing are not available. The aim of this study was to conduct a systematic review of the available literature on VBT. The analysis was performed in accordance with the PRISMA Statement. Nine studies with data from 175 patients were available. On average, 7.3 vertebrae were instrumented. Surgical time was 230 min and the estimated blood loss 153 ml. The mean correction on the coronal plane was 52%, and there was no significant change in sagittal parameters. The revision rate was 18.9%. The methodological quality assessment with the Coleman score gave unsatisfactory results, so that available data are not sufficient to propose general indications or guidelines to perform VBT.

Learning curve for vertebral body tethering: analysis on 90 consecutive patients.

STUDY DESIGN: Retrospective study. OBJECTIVES: Vertebral body tethering (VBT) is raising interest for the treatment of adolescent idiopathic scoliosis (AIS), but many scoliosis surgeons have not been trained in anterior surgical approaches. We analyzed data of our first patients to define the learning curve for VBT. VBT has shown encouraging results in the treatment of growing AIS patients, but there is a paucity of data and long-term results are not yet available. To our best knowledge, there is no published data regarding the learning curve for VBT. METHODS: A retrospective analysis was performed, of all consecutive patients who underwent VBT at our Institution. Outcomes of interest were intubation time, surgical duration and estimated blood loss per screw and hospitalization length. For the statistical analysis, we referred to a linear model regression diagnostic and we used the Pearson product-moment correlation (r) for pairwise correlation. The final effect ranked between + 1 and - 1. RESULTS: Data of 90 patients were analyzed, age 14.6 ± 1.8 years. On average, 9.4 ± 2.6 levels were instrumented. Per screw, mean intubation time was 33.1 ± 7.6 min (r = - 0.57; p > 0.0001), mean surgical duration 21.3 ± 5.7 min (r = - 0.55; p > 0.0001), mean estimated blood loss 21.3 ± 18.2 ml (r = - 0.66; p > 0.0001). Mean hospitalization length was 8.3 ± 3.1 days (r = - 0.32; p = 0.002). No intraoperative complications were reported. CONCLUSION: VBT has a rapid learning curve: the estimated blood loss per screw is expected to decrease by 60%, intubation time and surgical duration by over 50%, and hospitalization length by 32% for each treated patient. LEVEL OF EVIDENCE: III.

Correlation between age, coronal and sagittal parameters and spine flexibility in patients with adolescent idiopathic scoliosis.

PURPOSE: To investigate the correlation between spine flexibility and age, skeletal maturity, coronal and sagittal parameters for adolescent idiopathic scoliosis (AIS). METHODS: All AIS patients evaluated for surgery were included. Following parameters were obtained: age, gender, skeletal maturity (Risser and Sanders), Cobb angle at high thoracic (HT), mean thoracic (MT) and thoracolumbar/lumbar (TL/L) level, flexibility of HT, MT and TL/L curves, coronal and sagittal parameters. A multivariate diagnostic through the Pearson Product-Moment Correlation Coefficient ([Formula: see text]) was performed. RESULTS: Data from 200 patients were obtained (30 males, age 15 ± 1.9 years). No significant correlation was found between curve flexibility and age or gender. A negative correlation was observed between flexibility of MT curves and magnitude of HT ([Formula: see text] = - 0.4) and MT curves ([Formula: see text] = - 0.4). A weak correlation among curve flexibility at different levels was observed: the flexibility of HT curves correlated with the flexibility of MT and TL/L curves, and the flexibility of MT curves correlated with flexibility TL/L curves. A negative correlation between flexibility of MT curves and AVT-T (thoracic apical vertebral translation) ([Formula: see text] = - 0.2) was evidenced. No correlations between flexibility and sagittal parameters were observed. CONCLUSIONS: No strong correlation were observed between curve flexibility and age or skeletal maturity. A negative correlation between curve magnitude and flexibility at thoracic level was demonstrated. Furthermore, a weak positive correlation between flexibility of PT, MT and TL/L curves was observed.

Histologic analysis of ruptured quadriceps tendons.

Quadriceps tendon ruptures are uncommon injuries. Degenerative changes in the tendon are felt to be an important precondition for rupture. We retrospectively reviewed 45 quadriceps tendon ruptures in 42 patients. Quadriceps tendon ruptures occurred most often in the sixth and seventh decade of life. Men were affected six times as often as women. A tissue sample from the rupture-zone was obtained in 22 cases and histologic analysis was performed. Degenerative changes were present in only 14 (64%) of the 22 samples. We observed an increasing ratio of degenerative to nondegenerative tendons with increasing patient age. Our data suggests that quadriceps tendon rupture, especially in younger patients, can occur in the absence of pathologic tendon degeneration.

Dynamic Scoliosis Correction as Alternative Treatment for Patients with Adolescent Idiopathic Scoliosis: a Non-Fusion Surgical Technique. / Die dynamische Skoliosekorrektur als Therapieoption bei adoleszenter idiopathischer Skoliose.

Anterior dynamic scoliosis correction is an innovative non-fusion option in the treatment of patients with severe adolescent scoliosis. Growth modulation and sometimes intraoperative curve correction is achieved by convex insertion of segmental screws and a flexible polyethylene cord. The present review analyses and discusses the current literature and proposes a new treatment algorithm that is based on our own experience. Short term results are published for approximately 100 patients from different institutions. Fusion could be prevented in the vast majority of patients. Perioperative complication rate is very low but a few cases of cord rupture and overcorrection are reported. Anterior dynamic scoliosis correction has promising short term results but there is a paucity of literature and optimal criteria for the best candidate has yet to be defined.