In-Vivo Validation of a Self-Adaptive Growing Rod System for Early Onset Scoliosis
Date Issued
2015
Date
2015
Author(s)
Chen, Zong-Xing
Abstract
Background. Early onset scoliosis (EOS) is a disabling condition commonly defined as the development of an abnormal spinal curve occurred in children before the age of 10. The deformity of spinal column restricts the development of cardiopulmonary function, and leads to the impairment of body growth. Invasive corrective spinal surgeries are often required for the children who ineffectively respond to conservative treatment. Surgical implantation such as spinal growing rod is used to constrain spine deformity and, at the same time, allow spine to growth. Two types of growing rod system were developed: the forced growing rod system and the growth guidance system. The forced growing rod systems constrain the spinal posture by the resistance of rigid rods. It requires periodical revision surgery as the children grow. The revision surgery increases the risk of complications such as wound infection, and causes significant impact on patients’ psychological stresses. Recently, the magnetically controlled growing rod was developed to avoid the revision surgery. However, the mechanism of this system is complicated and the complications are still found clinically. The revision surgery is not necessary for the growth guidance system. However, clinical complications such as insufficient spinal stability, spinal growth, and implant failure are frequently reported. Given the shortcomings and the disadvantages of the current systems, this study designed a novel self-adaptive growing rod system. Purpose. The aim of current study is to validate a novel self-adaptive growing rods system, which is able to maintain the spinal posture and to grow with spinal column without the revision surgery. Material and Method. The self-adaptive growing rod system allows a unidirectional extension. The growing rod is composed of an external tube, an inner cylindrical sleeve, a triangular ratcheted pawl, and a spring. The rod is able to be extended freely, but at the same time, to provide resistance against axial force. The minimally required force for the extension of the self-adaptive growing rods was determined before the in-vivo test. The growing rod is connected to the commercially available bone rod, crosslinks and screws, hence surgeons can follow the tradition surgical protocol for EOS. This study completed three in-vivo experiments. The self-adaptive growing rod system, manufactured with medical grade stainless steel material, was implanted and then followed for 12 weeks. After the implementation, the pigs were closely monitored for general well-being and x-rays were taken. Cobb angle, the elongation of rods, vertebral unit height (VUH), disc height and vertebral body height were measured via the radiographs. The integrity of the device and the blood biochemical and histology analysis were then examined after the sacrifice of pigs. Result. In the first test, the pig was sacrificed due to wound infection and the implants were retrieved after one week. The retrieved growing rods system revealed that the growing rods were slightly extended on both sides, connective rods were deformed, pedicle screws were loosen in both cranial and caudal sides. Observable gunk was found within the sleeve of the device causing slight clogging. Nevertheless, the integrity of the device was satisfactory without signs of implant failure and remained functional. In the second and the third tests, the modified versions were used. The tensile tests of modified rods showed a pull force of 15.9 and 12.6 N, respectively. The radiographs showed the elongation of growing rods is similar to the total VUH augmentation among the instrumented levels. In terms of the integrity of the device, the screw loosening was observed at the caudal connective rod in the right side during the second test. The other part of the device remained intact throughout the experiment. Observable gunk was found within the sleeve of the device. No significant lesions were found in the blood biochemical and histology analysis. Conclusion. The current study successfully implanted the self-adaptive growing rod system into pigs, and validated its functionality and feasibility with the in-vivo study. After 12 weeks follow-up, the self-adaptive growing rod system could be lengthened with spinal growth, and implantation of the self-adaptive growing rods system would not restrict spinal growth. It is acknowledged that the device in its current design may not meet the requirement of medical device regulation. Designs based on the experiences of this study can further be improved.
Subjects
Early Onset Scoliosis
growing rod
spinal implant
fusionless instrumentation
in-vivo test
Type
thesis
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