Influence of implant rod curvature on sagittal correction of scoliosis deformity

Abstract

PURPOSE:To analyze the changes of implant rod angle of curvature during surgery and establish its influence on sagittal correction of scoliosis deformity. STUDY DESIGN:A retrospective analysis of the preoperative and postoperative implant rod geometry and angle of curvature was conducted.PATIENT SAMPLE: Twenty adolescent idiopathic scoliosis patients underwent surgical operation. Average age at the time of operation was 14 years. OUTCOME MEASURES:The preoperative and postoperative implant rod angle of curvature expressed in degrees was obtained for each patient. METHODS:Two implant rods were attached to the concave and convex side of the spinal deformity. The preoperative implant rod geometry was measured before surgical implantation.The postoperative implant rod geometry after surgery was measured by Computed Tomography scanner. The implant rod angle of curvature at the sagittal plane was obtained from the implant rod geometry. The angle of curvature between the implant rod extreme ends was measured before implantation and after surgery. The sagittal curvature between the corresponding spinal levels of healthy adolescents obtained by previous studies was compared to the implant rod angle of curvature to evaluate the sagittal curve correction. The difference between the postoperative implant rod angle of curvature and normal spine sagittal curvature of the corresponding instrumented level was used to evaluate over or under correction of the sagittal deformity.Page | 3 RESULTS:The implant rods at the concave side of deformity of all patients were significantly deformed after surgery. The average degree of rod deformation Δθ at the concave and convex side was 15.8 deg. and 1.6 deg., respectively. The average preoperative and postoperative implant rod angle of curvature at the concave side was 33.6 deg. and 17.8 degrees, respectively. The average preoperative and postoperative implant rod angle of curvature at the convex side was 25.5 degrees and 23.9 degrees, respectively. A significant relationship was found between the degree of rod deformation and preoperative implant rod angle of curvature (r = 0.60, p < 0.005). The implant rods at the convex side of all patients did not have significant deformation. The results indicate that the postoperative sagittal outcome could be predicted from the initial rod shape. CONCLUSIONS:Changes in implant rod angle of curvature may lead to over or under correction of the sagittal curve. Rod deformation at the concave side suggests that corrective forces acting on that side are higher than the convex side.

Effects of Multilevel Facetectomy and Screw Density on Postoperative Changes in Spinal Rod Contour in Thoracic Adolescent Idiopathic Scoliosis Surgery

“…Careful investigation of the changes in implant rod geometry is important to fully understand the biomechanics of scoliosis correction [16]. However, there have been few studies examining the relationship between rod deformation and sagittal alignment of the thoracic spine [15,16,18].…”

“…However, there have been few studies examining the relationship between rod deformation and sagittal alignment of the thoracic spine [15,16,18]. Cidambi et al [15] documented that a significant difference was observed between pre- and postoperative rod contour, particularly for concave rods, and that the resulting deformations were likely associated with substantial in vivo deforming forces.…”

“…The initial shape of the rod could lead to a certain sagittal outcome. However, it has been recognized that rods bent by surgeons prior to implantation tend to flatten after surgery [15,16]. The postoperative implant rod deformation as a “spring-back” effect can alter the sagittal alignment of the spine and consequently the clinical outcome [17].…”

Surgical treatment of double thoracic adolescent idiopathic scoliosis with a rigid proximal thoracic curve

“…Salmingo et al [19] also recently analyzed changes in the implant rod curvature angle during rod rotation maneuvers and established its influence on sagittal curve correction using SDRRT. The results indicated that implant rod curvature greatly influences sagittal curve correction [19,22] Here, TK and apical vertebral rotation improved significantly after surgery, and this improvement was maintained, suggesting that the present technique provides 3D correction of Lenke 2 AIS. In addition, in our study, no significant difference was observed between the pre-and postoperative values of the sagittal vertical axis.…”

“…Radiographs and Scoliosis Research Society (SRS) outcome instrument scores (SRS-22) were evaluated for all patients. The average age and Risser sign at surgery were 15.8 (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) years and 3.7 (0-5), respectively. The minimum follow-up period was 2 years (mean, 2.7 years).…”