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Study Design: Prospective evaluation of a new suspension test to determine curve flexibility in adolescent idiopathic scoliosis (AIS) in comparison with erect side-bending., Objective: To verify whether the suspension is a better method than side-bending to estimate curve reducibility and to assess spine flexibility., Summary of Background Data: Spinal flexibility is a decisive biomechanical parameter for the planning of AIS surgery. Side-bending is often referred as the gold standard, but it has a low reproducibility and there is no agreement amongst surgeons about the most advantageous method to use. Even more, every technique evaluates reducibility instead of flexibility since the forces involved in the change in shape of the spine are not considered., Methods: Eighteen patients scheduled for AIS surgery were studied. Preoperative radiological evaluation consisted of 4 radiographs: standing posteroanterior, left and right erect side-bending, and suspension. The side-bending and the suspension tests were compared on the basis of the apical vertebrae derotation and the scoliosis curve reduction. Frontal and axial flexibility indices, expressed as the ratio between the moment induced by the body weight and the reduction, were calculated from the suspension data., Results: The average scoliosis curve reduction and apical vertebra derotation were 21 degrees (37%) and 3 degrees (12%), respectively for erect side-bending and 26 degrees (39%) and 7 degrees (28%), respectively for suspension. The erect side-bending test generated a larger curve reduction (P = 0.05) when considering the moderate curves only and the suspension test (P = 0.02) when considering the severe curves. The suspension test produced a larger axial derotation (P = 0.007) when considering all the curves. The average traction force during suspension was 306 N (187 N-377 N). The average estimation for the frontal flexibility index was 1.64 degrees/Nm (0.84-2.82) and 0.51 degrees/Nm (0.01-1.39) for the axial flexibility index., Conclusion: Results of this study demonstrate the feasibility to really evaluate the spine flexibility with the suspension test. The estimated flexibility values are realistic and similar to those reported in vitro. Suspension should be used in the future for spine flexibility assessment.

The lateral bending test is routinely used by clinicians for the preoperative assessment of spinal mobility. The evaluation of bending motion is usually based on the qualitative analysis of a two-dimensional (2-D) antero-posterior X-ray image. The aim of this paper is to introduce a novel three-dimensional (3-D) reconstruction technique that is a prerequisite for the quantitative 3-D analysis of lateral bending motion. An algorithm was developed for the 3-D reconstruction of the spine from a single X-ray image. The X-ray is calibrated using a small calibration object and an explicit calibration algorithm. The information contained in the single X-ray is completed by registering a priori 3-D geometric models of individual vertebrae. Part of the error yielded by the 3-D/2-D registration is corrected by a vertebral alignment constraint that aims to minimize intervertebral dislocations. Three-dimensional models of 15 different scoliosis patients, obtained from a standard stereo-radiographic 3-D reconstruction, were used in simulation and validation experiments. Experimental results show that the new method is robust and accurate. With pessimistic levels of simulated noise, the average root mean square reconstruction error is 2.89 mm, which is appropriate for common clinical applications.

This paper reports the changes in spinal shape resulting from scoliotic spine surgical instrumentation expressed as intervertebral rotations and centers of rotation. The objective is to test the hypothesis that the type of spinal instrumentation system (Cotrel-Dubousset versus Colorado) does not influence these motion parameters. Intervertebral rotations and centers of rotation of the scoliotic spines were computed from the pre- and post-operative radiographs of 82 patients undergoing spinal correction. The three-dimensional (3D) reconstruction of six anatomical landmarks was achieved for each of the thoracic and lumbar vertebrae. A least-squares approach based on singular value decomposition was used to calculate the rigid body transformation parameters. Average centers of rotation for all intervertebral levels are located in the neural canal at the mid-sagittal plane and approximately at the superior endplate level of the inferior vertebra. Intervertebral rotations have components in all planes: 6.7 degrees (frontal), 5.5 degrees (sagittal) and 4.5 degrees (transverse) RMS for all intervertebral levels. Nearly all intervertebral rotations and centers of rotation are not significantly different for the two instrumentation systems. Various intervertebral rotations and 3D reconstruction errors were simulated on a theoretical model of a lumbar functional unit to assess the proposed method. Intervertebral rotation errors were 1.7 degrees when simulating 3D errors of 3mm on the position of the landmarks. Maximum errors for the position of centers of rotation were below 1cm in the case of intervertebral rotations larger than 2.5 degrees (most cases), but were larger (38 mm) for small intervertebral rotations (<1 degrees ). The type of instrumentation system did not influence intervertebral rotations and centers of rotation. These results provide valuable data for the development and validation of simulation models for surgical instrumentation of idiopathic scoliosis.

Study Design: Prospective study to evaluate the association between strap tension and brace interface forces in the treatment of adolescent idiopathic scoliosis using the Boston brace system., Objectives: To determine the strap tension associated with optimal brace interface forces., Summary of Background Data: Trim lines, pad placement, and areas of relief for the brace are guided by radiographic studies. However, optimal adjustment of strap tension is unclear and remains mostly empirical., Methods: Brace interface forces in all regions of the trunk were measured for 41 patients with adolescent idiopathic scoliosis at three standardized strap tensions (20 N, 40 N, and 60 N). The brace interface forces were assessed using a mat made of force-sensing transducers. Equivalent interface pressure for each trunk region was also calculated to estimate the distribution of the interface forces., Results: The brace interface forces and the corresponding effective areas increased along with the strap tension for all patients. For patients with a single right thoracic curve, the interface pressure tended to increase with increasing strap tension. This increase was significant in the left axillary, right thoracic, right pelvic, and sternal regions. For double right thoracic-left lumbar curves, the increase in interface pressure was significant in the left axillary, right pelvic, and sternal regions. However, most of this increase occurred between 20 N and 40 N of strap tension, with only slight increase or even a decrease in interface pressures between 40 N and 60 N., Conclusions: The strap tension should be set as high as possible (up to 60 N) for right thoracic curves. For right thoracic-left lumbar curves, the optimal strap tension was approximately 40 N. However, clinicians should ensure that the prescribed strap tension does not cause excessive skin pressure or affect the compliance with the brace. A side opening in the right lumbar area may improve the effectiveness of the brace for double right thoracic-left lumbar curves, but care must be taken to avoid skin problems at the opening.

Study Design: To analyze Boston brace biomechanics, pressure measurements and finite element simulations were done on 12 adolescent idiopathic scoliosis patients., Objectives: The aim was to analyze the Boston brace effectiveness using a finite element model and experimental measurements., Summary of Background Data: There are not very many biomechanical studies of Boston brace effectiveness, and its biomechanical action is not completely understood., Methods: This study was performed on 12 girls with scoliosis treated with the Boston brace system. The experimental protocol was composed of the acquisition of two sets of multiplanar radiographs with and without brace followed by the pressure acquisition at the brace-torso interface. A personalized finite element modeling of the trunk was generated from the 3D reconstruction of the patient's geometry. The brace treatment was simulated by the application of equivalent forces calculated from the pressure measurements., Results: Two Boston brace force patterns were defined from the pressure measurements. The first one consisted of high right thoracic forces of 31-113 N, lumbar forces less than 47 N, and included a left thoracic extension working as a counter pad. The second one consisted of low thoracic forces less than 20 N, lumbar forces up to 70 N, without left thoracic extension. The simulations showed that the passive forces only produced a coronal Cobb angle correction up to 9 degrees, whereas real correction was up to 16 degrees., Conclusion: High thoracic pads reduced more effectively both thoracic and lumbar scoliotic curves than lumbar pads only. The study suggests that mechanisms other than brace pads produce correction and contribute to the force equilibrium within the brace.

The prone operative position affects the geometry of the scoliotic spine. However, the literature provides little information concerning the effect of operative position on the scoliotic trunk geometry. This study compared the trunk deformity of 31 adolescent idiopathic scoliosis patients in two standardized positions: standing and prone on a Relton-Hall frame. The geometry of the trunk was assessed using 11 magnetic sensors placed on anatomical landmarks. Eight geometric indices of the trunk were compared using paired Student t-tests (alpha=0.01). The transverse rotation of shoulders, the coronal rotation of shoulders, the lateral shift of C7 with respect to S1, and the thoracic and lumbar angles of trunk rotation assessed in the operative position did not show any significant change compared to the standing position. Therefore, operative positioning using the Relton-Hall frame did not lead to an overall reduction in the scoliotic trunk deformity. Modifications to the Relton-Hall frame are required for optimal presurgical correction of the scoliotic trunk deformity.

Scoliosis is not simply a lateral deviation of the spine but is a complex deformity of the entire trunk. Recent advances in 3-dimensional (3-D) imaging have improved our understanding of the 3-D nature of adolescent idiopathic scoliosis (AIS) and have resulted in the development of a new generation of spinal instrumentation. Stereophotogrammetry, computed tomography, magnetic resonance imaging and surface topography all have their specific 3-D applications and relevance in the clinical management of AIS. In the near future, novel 3-D imaging applications will provide tools to guide the surgeon in the planning, performance and evaluation of increasingly sophisticated and less invasive surgical procedures, thus improving the outcome of surgical treatment for AIS.

The Boston brace has been shown to efficiently prevent scoliosis curve progression. However, it rarely achieves complete 3-D correction; its adjustment being often empirical and its biomechanical modes of action still remaining poorly understood. This study investigates the in-brace spinal shape (correction) in relationship with the patient's out-of-brace deformation, and the adjustment parameters of the brace, namely the strap tensions and the equivalent forces calculated at the patient-brace interface. Many of the observed relationships illustrate the fact that the in-brace spinal shape is strongly related to the characteristics of the patient's out-of-brace deformation. The pattern of pressure distribution as described by the equivalent forces computed in the thoracic, lumbar, pelvic and sternal regions has important effect on the in-brace Cobb angles, lumbar lordosis, frontal and sagittal imbalances and the apical axial rotations. The complex role of the strap tension on the correction has not been explained and needs further investigation. This project has the potential to give insight into the biomechanical effects of brace treatment by providing a statistical model leading to more rational and personalized brace adjustments.