Subcutaneous Rod Research Articles

Biomechanical characteristics of fixation methods for floating pubic symphysis

BackgroundFloating pubic symphysis (FPS) is a relatively rare injury caused by high-energy mechanisms. There are several fixation methods used to treat FPS, including external fixation, subcutaneous fixation, internal fixation, and percutaneous cannulated screw fixation. To choose the appropriate fixation, it is necessary to study the biomechanical performance of these different methods. The goal of this study was to compare the biomechanical characteristics of six methods by finite element analysis.MethodsA three-dimensional finite element model of FPS was simulated. Six methods were used in the FPS model, including external fixation (Ext), subcutaneous rod fixation (Sub-rod), subcutaneous plate fixation (Sub-plate), superior pectineal plate fixation (Int-sup), infrapectineal plate fixation (Int-ifa), and cannulated screw fixation (Int-scr). Compressive and rotational loads were then applied in all models. Biomechanical characteristics that were recorded and analyzed included construct stiffness, micromotion of the fracture gaps, von Mises stress, and stress distribution.ResultsThe construct stiffness of the anterior pelvic ring was decreased dramatically when FPS occurred. Compressive stiffness was restored by the three internal fixation and Sub-rod methods. Unfortunately, rotational stiffness was not restored satisfactorily by the six methods. For micromotion of the fracture gaps, the displacement was reduced significantly by the Int-sup and Int-ifa methods under compression. The internal fixation methods and Sub-plate method performed well under rotation. The maximum von Mises stress of the implants was not large. For the plate-screw system, the maximum von Mises stress occurred over the region of the fracture and plate-screw joints. The maximum von Mises stress appeared on the rod-screw and screw-bone interfaces for the rod-screw system.ConclusionsThe present study showed the biomechanical advantages of internal fixation methods for FPS from a finite element view. Superior stabilization of the anterior pelvic ring and fracture gaps was obtained by internal fixation. Subcutaneous fixation had satisfactory outcomes as well. Sub-rod fixation offered good anti-compression, while the Sub-plate fixation provided favorable anti-rotational capacity.

“Anterior subcutaneous pelvic internal fixator (INFIX), Is it safe?” A cadaveric study

IntroductionAnterior pelvic internal fixator (INFIX) is used to treat unstable pelvic ring injuries. Nerve injury complications with this procedure have been reported. ObjectivesThis anatomic study attempted to identify structures at risk after application of INFIX. Materials and methodsINFIX was applied in fifteen fresh, frozen, anatomical specimens using polyaxial pedicular screws and subcutaneous rods. Surgical dissection was done to identify the structures at risk including the femoral nerve (FN), femoral artery (FA), femoral vein (FV) and the lateral femoral cutaneous nerve (LFCN) related to which are potentially affected by the implant. ResultsAll structures at risk were closer to the rod than to the pedicular screw. Measurements were made between the rod and the structures at risk. The LFCN was an average of 13.49±1.65mm (95% CI 12.871–14.103) from the lateral end of the rod. The FN was an average of 12.43±3.42mm (95% CI 11.151–13.709), the FA was an average of 12.80±3.67 (95% CI 11.430–14.173) and the FV was an average of 13.48±3.73 (95% CI 12.082–14.871) below the rod. No direct compression of the rod to the structure at risk was observed. ConclusionsThe femoral nerve is the structure most at risk of compression by the INFIX rod. Careful surgical technique is required in every step of this surgery. We suggest using polyaxial screws and recommend that during screw insertion the surgeon should leave some space between the screw and rectus fascia. The the rod should be trimmed as short as possible to reduce LFCN irritation.

Ethylene vinyl acetate (EVA) as a new drug carrier for 3D printed medical drug delivery devices

The main purpose of this work was to investigate the printability of different grades of ethylene vinyl acetate (EVA) copolymers as new feedstock material for fused-deposition modeling (FDM™)-based 3D printing technology in fabrication of custom-made T-shaped intrauterine systems (IUS) and subcutaneous rods (SR). The goal was to select an EVA grade with optimal properties, namely vinyl acetate content, melting index, flexural modulus, for 3D printing of implantable prototypes with the drug incorporated within the entire matrix of the medical devices. Indomethacin was used as a model drug in this study. Out of the twelve tested grades of the EVA five were printable. One of them showed superior print quality and was further investigated by printing drug-loaded filaments, containing 5% and 15% indomethacin. The feedstock filaments were fabricated by hot-melt extrusion (HME) below the melting point of the drug substance and the IUS and SR were successfully printed at the temperature above the melting point of the drug. As a result, the drug substance in the printed prototypes showed to be at least partly amorphous, while the drug in the corresponding HME filaments was crystalline. This difference affected the drug release profiles from the filaments and printed prototype products: faster release from the prototypes over 30days in the in vitro tests. To conclude, this study indicates that certain grades of EVA were applicable feedstock material for 3D printing to produce drug-loaded implantable prototypes.

Late Onset Infections after Surgical Treatment of Spinal Deformities in Children

Study design: Retrospective review of monocentric database. Objective: To determine the rate of late infection (LI) after surgical treatment for spinal deformities in children, to assess the risk factors and to follow them after treatment. Summary of background data: Late infection is not very well documented. They are described as less frequent than early infection (EI) with a relatively good prognosis after implants removal. Review of a monocentric database with a long follow-up will address the questions. Methods: We went through our database to look for any septic problem and compared the population with LI, without infection and with EI. Every spine deformity in children or adolescent treated between 1983 and 2010 were included with at least two years of follow up. Results: During the study period, 1091 surgeries were performed. Nine EI occurred (8-33 days postoperatively) and sixteen LI (8 months-22 years). If we compare LI surgeries versus no infection the risk factors we found are posterior instrumentation (0.05) especially subcutaneous rod insertion (0.0003), the type of implants we used, with more infection with stainless steel than titanium (0.013) and diamond-shape rod than smooth rod (0.013). If we compare LI surgeries versus EI surgeries, fever, discharge, raised CRP are not seen frequently. Cultures were positive in fourteen of the sixteen cases, frequently with low virulence organisms than in EI (0.003). Removal of the implants and antibiotics were used as treatment. Infection resolved in all the cases after initial surgery more frequently than in EI (0.0002). In six cases we observed a loss of correction after implant removal. Conclusion: LI are frequent. They may be due to low-virulence organisms. Smooth and titanium rods should be preferred. If removal of implants is the treatment of choice, reinstrumentation must be considered later. LI could be underestimated if the follow up is too short. Risk factor analysis could be done only if data are collected prospectively. This was done in our study.

Complications of Growing-Rod Treatment for Early-Onset Scoliosis

Previous reports have indicated high complication rates associated with non-fusion surgery in patients with early-onset scoliosis. This study was performed to evaluate the clinical and radiographic complications associated with growing-rod treatment. Data from the multicenter Growing Spine Study Group database were evaluated. Inclusion criteria were growing-rod treatment for early-onset scoliosis and a minimum of two years of follow-up. Patients were divided into treatment groups according to rod type (single or dual) and rod location (subcutaneous or submuscular). Complications were categorized as wound, implant, alignment, and general (surgical or medical). Surgical procedures were classified as planned and unplanned. Between 1987 and 2005, 140 patients met the inclusion criteria and underwent a total of 897 growing-rod procedures. The mean age at the initial surgery was six years, and the mean duration of follow-up was five years. Eighty-one (58%) of the 140 patients had a minimum of one complication. Nineteen (27%) of the seventy-one patients with a single rod had unplanned procedures because of implant complications, compared with seven (10%) of the sixty-nine patients with dual rods (p ≤ 0.05). Thirteen (26%) of the fifty-one patients with subcutaneous rod placement had wound complications compared with nine of the eighty-eight patients (10%) with submuscular rod placement (p ≤ 0.05). The patients with subcutaneous dual rods had more wound complications, more prominent implants, and more unplanned surgical procedures than did those with submuscular dual rods (p ≤ 0.05). The risk of complications occurring during the treatment period decreased by 13% for each year of increased patient age at the initiation of treatment. The complication risk increased by 24% for each additional surgical procedure performed. Regardless of treatment modality, the management of early-onset scoliosis is prolonged; therefore, complications are frequent and should be expected. Complications can be reduced by delaying initial implantation of the growing rods if possible, using dual rods, and limiting the number of lengthening procedures. Submuscular placement reduces wound and implant-prominence complications and reduces the number of unplanned operations.

Three-Dimensional Evolution of Scoliotic Curve During Instrumentation Without Fusion in Young Children

This study respectively evaluated 12 young children with progressive curves who underwent subcutaneous rod instrumentation (SCRI) without fusion and were followed until definitive surgery. The mean curve Cobb angle was 58 degrees at the time of SCRI. The mean apical vertebral rotation at the time of presentation was 20 degrees. Curves were observed to have progressed to an average of 59 degrees before definitive surgery and were corrected to 34 degrees with instrumentation. The average apical vertebral rotation was found to be 34 degrees before the definitive treatment. This value was significantly larger than the pre-SCRI value (P = 0.002). The average number of lengthening operations per patient was 4.6, and the number of all operations per patient was 7. Six patients developed complications. The average time spent in hospital was 101 days. The findings demonstrate that the curves were essentially unchanged in the frontal plane during the period of lengthening. The sagittal curves remained mostly within normal limits, but there was an alarming increase in rotation.

Subcutaneous Rodding for Progressive Spinal Curvatures: Early Results

This study retrospectively reviewed the clinical records and radiographs of 11 patients with progressive early-onset scoliosis who failed to respond to nonoperative management and who underwent consecutive distraction of subcutaneous rods. Eleven children were treated by consecutive distraction of subcutaneous rods, and in two patients with rodding and anterior apical fusion. At surgery, the average patient age was 5.66 years, with a mean Cobb angle of 74 degrees and an average Pedriole angle of 39 degrees. The etiology of the scoliosis included four syndromic and one each congenital, post-rib resection, post-spinal tumor resection, neurofibromatosis, myelomeningocele, infantile idiopathic, and juvenile idiopathic. Subcutaneous rodding halted curve progression in all patients. At an average of 5.1 years after surgery, one patient showed no deterioration of the curve and nine patients showed an improvement of > or =40% in the magnitude of the original curvature. Eight of these patients had already had definitive surgery performed with segmental spinal instrumentation and fusion. Spinal growth occurred in all 11 patients and ranged from 0.5 to 4.5 cm (mean 2.0). Early results from these patients show that subcutaneous rodding with consecutive distraction allows correction of progressive early-onset scoliosis that failed to respond to nonsurgical management, preserving the individual growth potential of the spinal column and delaying definitive surgical treatment. Rotational deformity did not deteriorate radiographically, but clinical deformity increased subjectively. The amount of growth achieved and the number of procedures required to obtain these results raises the question of whether patients would be better served by a single anterior, posterior fusion and instrumentation at a young age.

Spontaneous Fusion in Scoliosis After Instrumentation Without Arthrodesis

The technique of subcutaneous rod insertion without exposure of the curve has been proposed as a method of controlling the progression of scoliosis while allowing the spine to grow. We review the literature and present three patients whose spines spontaneously fused unexpectedly while undergoing this form of treatment. The fusion occurred posteriorly, and continued anterior growth led to increased deformity from the crankshaft phenomenon. Based on this experience, the authors recommend careful follow-up and early anterior fusion when the crankshaft phenomenon is observed.