Effect of different surgical strategies on screw forces after correction of scoliosis with a VDS implant

Rohlmann, A.; Richter, M.; Zander, Thomas; Klöckner, C.; Bergmann, G.

doi:10.1007/s00586-005-0923-5

Cited by 22 publications

(12 citation statements)

References 14 publications

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“…[12]. A 2006 study by Rohlmann et al [14] used a 3D continuum model for the intervertebral discs (defined using isotropic linear elastic material properties), but the ligaments, facet joints, and ribcage were idealized using spring elements between adjacent vertebrae. The elastic beam/spring approach used in previous studies has the benefit of faster solution times and simplified prescription of SMS stiffness parameters, but the coarse anatomical representation does not allow investigation of how the load-bearing role of individual spinal structures and tissues would be altered by surgery.…”

Section: Discussionmentioning

confidence: 99%

Patient‐specific computational biomechanics for simulating adolescent scoliosis surgery: Predicted vs clinical correction for a preliminary series of six patients

Little

Adam

2010

Numer Methods Biomed Eng

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SUMMARYScoliosis is a spinal deformity that requires surgical correction in progressive cases. In order to optimize surgery outcomes, patient-specific finite element models are being developed by our group. In this paper, a single rod anterior correction procedure is simulated for a group of six scoliosis patients. For each patient, personalized model geometry was derived from low-dose CT scans, and clinically measured intra-operative corrective forces were applied. However, tissue material properties were not patient-specific, being derived from existing literature. Clinically, the patient group had a mean initial Cobb angle of 47.3 • , which was corrected to 17.5 • after surgery. The mean simulated post-operative Cobb angle for the group was 18.1 • . Although this represents good agreement between clinical and simulated corrections, the discrepancy between clinical and simulated Cobb angle for individual patients varied between −10.3 and +8.6 • , with only three of the six patients matching the clinical result to within accepted Cobb measurement error of ±5 • . The results of this study suggest that spinal tissue material properties play an important role in governing the correction obtained during surgery, and that patient-specific modelling approaches must address the question of how to prescribe patient-specific soft tissue properties for spine surgery simulation.

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Section: Discussionmentioning

confidence: 99%

Patient‐specific computational biomechanics for simulating adolescent scoliosis surgery: Predicted vs clinical correction for a preliminary series of six patients

Little

Adam

2010

Numer Methods Biomed Eng

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“…The transverse force may weaken the bone around the thread and lower the pullout resistance against the axial force. A strong correction at the cranial segment leads to high axial and transverse screw forces in the furthest cranial screw and thus to high risk of screw pullout [10]. The cranial end vertebra is also the vertebra where most screw pull-outs and subsequent lesions of adjacent structures have been observed.…”

Section: Discussionmentioning

confidence: 99%

Late Bronchus Perforation due to Spinal Implant Compression

Sokolović

Slobodnjak

Mažuranić

2016

JACCOA

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We report a rare case of perforation of the intermediate bronchus by a loosened osteosynthetic implant, 8 years after the patient had undergone surgery for right thoracic scoliosis with the VDS instrumentation. Due to chronic lung inflammatory alteration caused by bronchial obstruction, lower bi-lobectomy was performed. We believe that spinal growth and progression of idiopathic scoliosis can lead to implant failure, while the variance in intrathoracic topographic relations and respiratory excursion facilitate it's penetration into the bronchus. In order to impede foreign body perforation of mediastinal structures and to reduce its complications, preventive methods, along with timely diagnostics, are required. Atelectatic and chronic inflammatory alterations that compromise adequate lung ventilation could require a resection procedure.Keywords: Foreign body; Lobectomy; Thoracic scoliosis; VDS instrumentation of complications, such as: lethal outcome in less than 1%, neurological damage, irreversible loss of the normal active range of the movement in the vertebral column, strain on unfused vertebrae, post-surgery pain (19% of patients required re-operation within 2 to 8 years after surgery), deep wound infections (5-10%), bone deterioration due to inflammatory response to metallic implant, curvature progression due to failure of instrumentation, decompensation and increased sagittal deformity (˝flat back˝), torso deformity (˝flail chest˝) [1]. A choice of treatment for thoracic scoliosis is anterior instrumentation surgery because better correction can be obtained with shorter fusion levels [2]. However, anterior instrumentation carries a greater risk for penetration of vital structures by sprung fragment of inner vertebral fixator, as well as the effect of disrupted chest cage on pulmonary function.Spinal fusion surgery is recommended when the magnitude of curvature exceeds 45°, but it is expected for 1/3 of patients to lose all postoperative correction within 1-10 years post-surgery [3]. It has been noted that 1.5% of the screws inserted in the thoracic level were displaced, but they did not cause any adversely effect on long-term results [1]. We present a rare case of erosion of the intermediate bronchus caused by dislocated osteosynthetic material implanted for the treatment of thoracic scoliosis in 1995. To our knowledge, only one case of erosion of the bronchus after surgical treatment of scoliosis has been reported [4]. Both of patients presented with long-time history of cough, haemoptysis and dyspnoea. Case PresentationIn June of 1995 a 17-year-old patient underwent spinal instrumentation and fusion through placement of VDS implants for the treatment of idiopathic right thoracic scoliosis. The type of curve by Lenke classification system for scoliosis was 2AN (curve length from the 5th thoracic through the 1st lumbar vertebra), with measured Cobb's angle of 90°. The operation was performed through a right thoracotomy. The VDS implants were inserted laterally on the convex side of the vertebral bo...

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“…The longitudinal direction is defined by an axis which is perpendicular to the superior vertebral body endplate while the transverse plane is parallel to it. The Poisson's ratio for the disc was set at 0.45 which is common for lumbar annulus ground substance [12]. The major ligaments of the thoracic spine (anterior longitudinal ligament, interspinous ligaments and intertransverse ligaments) were also included in the model.…”

Section: Methodsmentioning

confidence: 99%

“…Studying the mechanical effect of a scoliosis correction system is very difficult since there is great variety in the shape and stiffness of scoliotic spines, and it is very difficult to obtain cadaveric scoliotic spine specimens for experimental studies. Finite element analyses have been performed to study scoliosis correction by orthotic [11] and by surgical treatment [2,3,6,7,12]. Mostly the CotrelDubousset instrumentation procedure was simulated with numerical analyses.…”

Section: Introductionmentioning

confidence: 99%

Flexible non-fusion scoliosis correction systems reduce intervertebral rotation less than rigid implants and allow growth of the spine: a finite element analysis of different features of orthobiom™

et al. 2007

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The orthobiom TM non-fusion scoliosis correction system consists of two longitudinal rods, polyaxial pedicle screws, mobile and fixed connectors and a crossconnector. The mobile connectors can move along and around the rod, thus allowing length adaptation during growth. The aim of this study was to determine the effects of different features of this novel implant on intervertebral rotations, to calculate the movement of the mobile connectors along the rods for different loading cases and to compare the results with those of a rigid implant construct. A finite element analysis was performed using six versions (M1-M6) of a three-dimensional, nonlinear model of a spine ranging from T3 to L2. The models were loaded with pure moments of 7.5 N m in the three main anatomical planes. First, the validated intact model (M1) was studied.

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Effect of different surgical strategies on screw forces after correction of scoliosis with a VDS implant

Cited by 22 publications

References 14 publications

Patient‐specific computational biomechanics for simulating adolescent scoliosis surgery: Predicted vs clinical correction for a preliminary series of six patients

Patient‐specific computational biomechanics for simulating adolescent scoliosis surgery: Predicted vs clinical correction for a preliminary series of six patients

Late Bronchus Perforation due to Spinal Implant Compression

Flexible non-fusion scoliosis correction systems reduce intervertebral rotation less than rigid implants and allow growth of the spine: a finite element analysis of different features of orthobiom™

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