Fabrizio Giudici1, Fabio Galbusera2, Antonino Zagra1, Hans-Joachim Wilke3, Marino Archetti1, Laura Scaramuzzo4. 1. Spinal Division I, I.R. C.C. S. Galeazzi Orthopedic Institute, Via R. Galeazzi 4, 20161, Milan, Italy. 2. I. R. C.C. S. Galeazzi Orthopedic Institute, Milan, Italy. 3. Institute of Orthopaedic Research and Biomechanics, Centre for Trauma Research Ulm (ZTF), Ulm University, Ulm, Germany. 4. Spinal Division I, I.R. C.C. S. Galeazzi Orthopedic Institute, Via R. Galeazzi 4, 20161, Milan, Italy. scaramuzzolaura@gmail.com.
Abstract
PURPOSE: Aim of the study was to evaluate the role of the mechanical properties of the rod and of the characteristics of the patients (age, skeletal maturity, BMI, and Lenke type) in determining the deformity correction, its maintenance over time and the risk of mechanical failure of the instrumentation. METHODS: From March 2011 to December 2014 120 patients affected by AIS underwent posterior instrumented fusion. Two 5.5-mm CoCr rods were implanted in all patients. For every patient, age, sex, Risser grade, Lenke type curve, flexibility of the main curve, body mass index (BMI), and percentage of correction were recorded. In all patients, the Cobb angle value and rod curvature angle (RC) were evaluated. RC changes were registered and correlated to each factor to establish a possible statistically significance in a multivariate analysis. A biomechanical model was constructed to study the influence of rod diameter and material as well as the density of the anchoring implants in determining stress and deformation of rods after contouring and implantation. RESULTS: Radiographic and biomechanical analysis showed a different mean rod deformation for concave and convex side: 7.8° and 3.9°, respectively. RC mean value at immediate follow-up was 21.8° for the concave side and 14.6° for the convex. At 2-year minimum follow-up, RC value increases 1.5° only for the concave side. At 3.5-year mean follow-up, RC value increases 2.7°, p = 0.003, for the concave side and 1.3° for the convex, p = 0.06. The use of the stiffest material as well as of the lowest diameter resulted in higher stresses in the rods. The use of either a low or a high instrumentation density resulted only in minor differences in the loss of correction. CONCLUSIONS: Rod diameter and material as well as patient characteristics such as BMI, age, and Risser grade play an important role in deformity correction and its maintenance over time.
PURPOSE: Aim of the study was to evaluate the role of the mechanical properties of the rod and of the characteristics of the patients (age, skeletal maturity, BMI, and Lenke type) in determining the deformity correction, its maintenance over time and the risk of mechanical failure of the instrumentation. METHODS: From March 2011 to December 2014 120 patients affected by AIS underwent posterior instrumented fusion. Two 5.5-mm CoCr rods were implanted in all patients. For every patient, age, sex, Risser grade, Lenke type curve, flexibility of the main curve, body mass index (BMI), and percentage of correction were recorded. In all patients, the Cobb angle value and rod curvature angle (RC) were evaluated. RC changes were registered and correlated to each factor to establish a possible statistically significance in a multivariate analysis. A biomechanical model was constructed to study the influence of rod diameter and material as well as the density of the anchoring implants in determining stress and deformation of rods after contouring and implantation. RESULTS: Radiographic and biomechanical analysis showed a different mean rod deformation for concave and convex side: 7.8° and 3.9°, respectively. RC mean value at immediate follow-up was 21.8° for the concave side and 14.6° for the convex. At 2-year minimum follow-up, RC value increases 1.5° only for the concave side. At 3.5-year mean follow-up, RC value increases 2.7°, p = 0.003, for the concave side and 1.3° for the convex, p = 0.06. The use of the stiffest material as well as of the lowest diameter resulted in higher stresses in the rods. The use of either a low or a high instrumentation density resulted only in minor differences in the loss of correction. CONCLUSIONS: Rod diameter and material as well as patient characteristics such as BMI, age, and Risser grade play an important role in deformity correction and its maintenance over time.
Entities:
Keywords:
Adolescent scoliosis; Biomechanical properties; CoCr rod; Rod deformation
Authors: H Mehta; E Santos; C Ledonio; J Sembrano; A Ellingson; P Pare; B Murrell; D J Nuckley Journal: Clin Biomech (Bristol, Avon) Date: 2011-11-08 Impact factor: 2.063
Authors: Odysseas Paxinos; Parmenion P Tsitsopoulos; Michael R Zindrick; Leonard I Voronov; Mark A Lorenz; Robert M Havey; Avinash G Patwardhan Journal: J Neurosurg Spine Date: 2010-10