What Extent a Higher Implants Density Gives More Correction? Correlation of Scoliosis Curve Correction with the Type and Density of Implants
Authors: Pedro Rubio , Teresa Bas , Bas Paloma , Perez Silvia 
Published: April 2016

Introduction Corrective Surgery for Adolescent Idiopathic Scoliosis (AIS) has evolved with the utilization of more sophisticated implants and higher implants density looking forward a better correction though a posterior approach. But, is this correction myth or reality? Our objective is to analyze the relationship between implant density and deformity correction, comparing two different instrumentations. Materials and Methods A retrospective cohort study was performed using patients from the database of our institution between 2009–2012. Inclusion criteria were diagnosis of AIS, age between 12–18 year-old, surgeries performed in our institution, complete radiological study and a minimum follow-up of two years. No curve restriction was considered. Analysis of radiology was done in three different moments for each patient: pre-op, first control after surgery and one year follow-up. Coronal and sagittal parameters were considered to evaluate deformity severity. Pre-op bending X-rays were analyzed for flexibility measurement. Post-operatively they were measured implant density for each group, fusion levels and deformity correction for both coronal and sagittal planes. Patients were classified following Lenke and divided in two groups: all pedicle screws instrumentation (APS) and hybrid instrumentation (HY). Statistical study was made using the T-Student test to analyze differences between cohorts and Pearson's Test for correlating variables. Results They were collected in total 82 cases, 67 of which were females. The mean age was 16 year-old. The 61% of total patients presented a Lenke type 1 curve. 35 patients were treated with APS instrumentation and 47 using a HY construction. Values for Cobb angle, flexibility and T5-T12 kyphosis pre-op were homogeneous between both groups. Post-operatively there were no significant statistical differences comparing fusion levels and percentage of coronal deformity correction between the two groups. Nevertheless, they were remarkable the 40% of implant density difference and the higher loss of kyphosis in APS group as compared with HY. Pearson's test evidenced that, in general, the only variable, which was statistically significant correlated with a higher coronal deformity correction, was pre-op flexibility; not implant density, fusion levels or type of instrumentation used. Significant differences were found comparing loss of thoracic kyphosis after surgery between groups, finding a significant correlation which indicated that using pedicle screws the higher implant density used, the bigger the loss of kyphosis. Loss of kyphosis was not statistically significant when correlated with percentage of coronal deformity correction. One-year follow-up X-ray did not show significant differences when values of Cobb angle and thoracic kyphosis were analyzed among groups. Conclusions Both hybrid and all pedicle screws instrumentations achieve equal coronal deformity correction operating on flexible curves, we do not obtain a bigger deformity correction with a higher implant density all pedicle screws instrumentation produce a higher loss of thoracic kyphosis.