A new X-ray calibration/reconstruction system for 3D clinical assessment of spinal deformities.

The main objective of this study was to develop a 3D X-ray reconstruction system of the spine and rib cage for an accurate clinical assessment of spinal deformities. The proposed system uses an explicit calibration technique and a new calibration object composed of: (1) a set of radiopaque markers embedded in a jacket worn by the patient during the X-ray exposures; (2) six control markers to define a reference vertical plane. Computer simulations were performed to evaluate the accuracy of the 3D reconstruction procedure when different kind of displacements were applied on a reference model. Clinical indices computed from the 3D X-ray reconstruction of the spine for 24 scoliotic subjects were compared to those obtained with the DLT method. The results of the evaluation study showed that the new system allows the patient to adopt a normal attitude without any constraint, compensating for its displacement between exposures.

Evaluation of the efficiency of patient stabilization devices for 3D X-ray reconstruction of the spine and rib cage.

Four devices designed to stabilize the patient's position and/or posture between X-ray exposures were investigated in order to obtain accurate 3-D reconstruction of their spine: a pelvis support, two elbow supports with handlebars, a back neck contact system and a device with three divergent laser beams pointing on subject body targets. Stability and the bearing of natural posture on a group of 10 adults without scoliosis was evaluated for the different devices using a statistical experimental design (Plackett-Burman plan of resolution IV). Small displacements of subjects were obtained by an Optotrak system with 11 infrared diodes placed on the subject's back. Results showed that the elbow supports with handlebars and pelvis support improved the subject's stability while the pelvis support was the device that produces more changes in the subject's natural posture. The elbow and back neck supports were retained for further evaluation.

[In vitro evaluation of computer-assisted pedicle screw system]. / Evaluation in vitro d'un système informatique de forage pédiculaire.

GOAL: The goal of this study is to evaluate influence on the accuracy of pedicle hole positions when a surgeon uses a computer assisted system. STUDY DESIGN: This comparative study was undertaken using dry thoraco-lumbar specimens in order to measure the position of drilled holes with and without computer assistance in the hands of an experienced surgeon as well as with a resident in training. METHODS: Pedicle holes were drilled from D1 to L5 in identical dry thoraco- lumbar specimens. For half of the specimens a computer assisted pedicle screw installation system was used. Holes having been drilled for all specimens, we then measured the maximum distance between the axis of the drilled holes and the pedicle cortices All distances less or equal to 2 mm were classified as safe while all bigger distances were classified as unsafe for pedicle screw installation. RESULTS: Nine specimens were drilled for a total of 306 holes, 170 of them with computer assistance. We have observed a 95% success rate with the computer assisted holes compared to a 62% success rate using conventional methods (p < 0.001). No difference was found between the results of an experienced surgeon and the results of a resident in training while using the computer assistance system. All holes drilled from D12 to L5 were found to be in optimal position, completely within the pedicles. CONCLUSION: These results suggest that this computer assisted pedicle screw installation system could improve the accuracy of pedicle screw placement and enhance the safety of the procedure. Moreover, the computer system could become a valuable teaching tool for the training spine surgeons.

[Computer assisted pedicle screw installation. Our first 3 cases]. / Installation de vis pédiculaires par ordinateur. Nos trois premiers cas.

Pedicle screw fixation is sometimes a difficult surgical procedure relying on anatomical landmarks that may be modified by vertebral asymmetries. A significant incidence of cortex penetration and neuro-vascular complications have been documented. Our study evaluates the usefulness of a computer-aided pedicle installation system and analyses the results for our first 3 clinical cases. The system was used for 3 adolescent patients with idiopathic scoliosis undergoing surgical correction and instrumentation. In all cases, selected vertebrae were reconstructed in 3D pre-operatively. At surgery, the surgeon compared the computer-suggested pedicle location to his own opinion. After pedicular hole drilling was done in the usual fashion, hole positions were confirmed per-operatively with the computer software. Post-operatively, software hole positions were measured and compared to the actual screw axis using CT-Scans. Three dimensional models produced for all selected vertebrae allowed visualization of asymmetrical deformations of the scoliotic vertebrae. All pedicles were correctly detected by the software. Pedicular hole measurements agreed with the actual screws positions on post-op CT-Scans. The computerized surgical assistant can be of value in a clinical situation. These initial results warrant a large scale trial in order to establish accuracy and reliability.

Three-dimensional effect of the Boston brace on the thoracic spine and rib cage.

STUDY DESIGN: Three-dimensional reconstructions of the spine and rib cage were done and compared just before and 1 month after initiation of treatment with a Boston brace in a group of adolescents with idiopathic scoliosis. OBJECTIVES: To document the immediate changes in shape of the thoracic spine and rib cage induced by the original Boston brace design. SUMMARY OF BACKGROUND DATA: The effect of the Boston brace has been well documented in the frontal plane but is poorly understood in the other planes of deformity. METHODS: Three-dimensional reconstructions were obtained with and without the brace using a stereoradiographic technique in a group of 40 adolescents with idiopathic scoliosis. Several geometric indices of the spine and rib cage were compared using Student t tests. RESULTS: The brace produced significant curve correction of the spinal deformity in the frontal plane at the expense of a significant reduction of thoracic kyphosis in the sagittal plane, as well as in the plane of minimum deformity. No significant effect on rotation of the thoracic apical vertebra, on the rib hump, or on frontal balance could be documented, but changes were noted in the sagittal orientation of the rib cage and in the sagittal balance of the spine. CONCLUSIONS: The original Boston brace does not completely correct the three-dimensional deformities associated with thoracic idiopathic scoliosis, although it reduces Cobb angles in the frontal plane.

Comparison between preoperative and postoperative three-dimensional reconstructions of idiopathic scoliosis with the Cotrel-Dubousset procedure.

STUDY DESIGN: Pre- and postoperative three-dimensional reconstructions of the spine and rib cage were done and compared in a group of adolescents with idiopathic scoliosis. OBJECTIVE: Changes in the shape of the thoracic spine and rib cage induced by the Cotrel-Dubousset instrumentation and procedure were documented. SUMMARY OF BACKGROUND DATA: Although many authors have reported significant curve improvement in the frontal plane, attempts to document derotation of the spine have shown only limited correction of apical vertebral rotation. METHODS: Three-dimensional reconstructions were obtained pre- and postoperatively using a stereoradiographic technique in a group of 37 adolescents with idiopathic scoliosis. Several geometrical indices of the spine and rib cage were compared using Student t tests. RESULTS: The curve correction averaged 50% in the frontal plane and 24% in the plane of maximum curvature, while normal thoracic kyphosis was maintained in the sagittal plane. The orientation of the plane of maximum curvature was shifted very significantly toward the sagittal plane, indicating en bloc movement of the thoracic spine and three-dimensional correction of the deformity. A small but significant change in vertebral axial rotation and rib hump was found and improvement in the overall orientation of the ribs was documented. CONCLUSIONS: The Cotrel-Dubousset instrumentation and procedure are effective in producing three-dimensional improvement of the thoracic spine by en bloc relocation of the instrumented spine rather than by vertebral axial derotation.

Peroperative three-dimensional correction of idiopathic scoliosis with the Cotrel-Dubousset procedure.

STUDY DESIGN: A peroperative measurement technique based on magnetic fields was used to document the thoracic and lumbar vertebral changes induced by derotation of the concave rod during corrective surgery of idiopathic scoliotic deformities with Cotrel-Dubousset instrumentation. OBJECTIVES: Objective was to accurately document the immediate changes induced by the derotation maneuver to gain a better understanding of its effect on curve correction during a surgical procedure. SUMMARY OF BACKGROUND DATA: Accurate peroperative documentation of these three-dimensional changes was very limited, and the exact contribution of the derotation maneuver in the entire process of correction of a scoliotic deformity was still poorly understood. METHODS: A digitizer using magnetic fields was used to record the three-dimensional orientation and x, y, and z coordinates of the tip of every spinous process exposed at surgery before and after derotation of the concave rod in a group of 22 female patients with idiopathic scoliosis. RESULTS: A significant improvement of the scoliotic deformity was noted in the frontal plane, and improvement of thoracic hypokyphosis and lumbar hypolordosis in the sagittal plane was seen. Vertebral axial rotation remained unchanged. CONCLUSIONS: The derotation maneuver is effective in achieving three-dimensional correction of idiopathic scoliosis, but vertebral axial derotation is not an important component of this correction.

Variability of geometric measurements from three-dimensional reconstructions of scoliotic spines and rib cages.

Three-dimensional (3-D) reconstructions of the spine are being used with increasing frequency to describe scoliotic deformities, but the reproducibility of most of these techniques and the implication for the reliability of measurements made on the reconstructions has not been reported. How reliable are these reconstructions, and can a clinician interpret with confidence the results of studies based on such mathematical models? A reproducibility study of various computerised measurements obtained from 3-D reconstructions of the spine and rib cage for five subjects with adolescent idiopathic scoliosis was done to evaluate the errors associated with repeated measurements and compare them with inter- and intraobserver errors reported for similar commonly used clinical measurements. The mean variation for the Cobb angle differed according to the plane of computation from 0.6 degrees in the frontal plane to 6.7 degrees in the sagittal plane; vertebral axial rotation varied from 2.3 degrees to 5.9 degrees according to the vertebral level, and rib hump measurements displayed an average variation of 1.4 degrees. All these variations are below or within the error levels reported for equivalent 2-D measurements used by clinicians, which suggests that this 3-D model of idiopathic scoliosis may be used with confidence for clinical evaluations.

[Intraoperative three-dimensional evaluation of Cotrel-Dubousset's procedure for the treatment of idiopathic scoliosis]. / Evaluation tridimensionnelle per-opératoire de la procédure Cotrel-Dubousset pour le traitement de la scoliose idiopathique.

In order to evaluate with accuracy the tridimensional (3D) vertebral correction induced by the surgical correction of idiopathic scoliosis with Cotrel-Dubousset instrumentation and technique, we have developed a new per operative measurement system based on 3D digitization with magnetic fields. This method has been used on 23 adolescent patients treated with surgical correction. A statistically significant change in vertebral 3D orientation of 11.4 degrees +/- 5.6 degrees has been found. The measurement repeatability was +/- 2.5 degrees. We conclude that the Cotrel-Dubousset technique truly realizes a 3D correction of the thoracic and lumbar spine of adolescent idiopathic scoliosis.

[3-D study of the immediate effect of the Boston brace on the scoliotic lumbar spine]. / Etude 3-D de l'effet immédiat du corset de Boston sur la colonne lombaire scoliotique.

In order to study the immediate 3-D effect of the Boston brace on lumbar scoliosis, 31 adolescents with idiopathic scoliosis King type I or II had a 3-D computerised reconstruction of their deformity with and without the brace. Results demonstrate that the brace produces a distraction of the lumbar spine similar to that produced by the Harrington instrumentation by correcting the frontal deformity at the expense of a significant reduction of the physiological lumbar lordosis. No significant effect on rotation of the apical vertebra or "detorsion" of the spine could be measured. We feel that a orthosis that provides a real 3-D correction of the deformity has yet to be developed.