AIP Conference Proceedings 2092, 020025 (2019); https://doi.org/10.1063/1.5096693 2092, 020025
© 2019 Author(s).
Concept design and possibility study
interpedicular locking screw implant fixation for osteoporosis spine bone
Cite as: AIP Conference Proceedings 2092, 020025 (2019); https://doi.org/10.1063/1.5096693 Published Online: 09 April 2019
Radhi Maladzi, Sugeng Supriadi, Ahmad Jabir Rahyussalim, and Yudan Whulanza
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Concept Design and Possibility Study Interpedicular Locking Screw Implant Fixation for Osteoporosis Spine
Bone
Radhi Maladzi
1, Sugeng Supriadi
2,a), Ahmad Jabir Rahyussalim
3, Yudan Whulanza
21Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia.
2Research Center for Biomedical Engineering, Universitas Indonesia
3Department of Orthopaedics and Traumatology, Faculty of Medicine, Universitas Indonesia, Dr. Cipto Mangunkusumo General Hospital, Jakarta 10320, Indonesia
Corresponding author: a)[email protected]
Abstract. Osteoporosis is a condition which bone become fragile. Osteoporosis vertebrae bone causes fracture easily and also decreases fixation strength between pedicle screw implant and spine bone. Lack of fixation strength between pedicle screw implant and osteoporotic vertebrae bone lead to implant failure such as pedicle screw pull out. Therefore the purpose of this research is to develop intrapedicular locking screw concept of pedicle screw implant system which can resist pull out failure on osteoporotic bones. The main objective of this study is to know the possibility of intrapedicular locking screw for vertebral segments. The method of this study is by simulation of the position of intrapedicular locking screw design for each vertebral segment using Solidworks. Vertebral segments CT Scan sample is taken from one of the patients. After each pedicle screw is positioned correctly to the vertebral segments, pedicle screw position angle is measured. The result from measuring the position angle from pedicle screw it obtains the angle between 40°-70° for each vertebral segments sample. After this study is done, it concludes if the intrapedicular concept can be applied almost every vertebral segments.
Keywords: fixation, implant, osteoporosis, pedicle screw, pull out, vertebral
INTRODUCTION
Osteoporosis is a condition where whole bones become fragile, so it decreases bone’s strength and leads to bone fracture easily, it happened because of aging that makes bone mineral density become low. Osteoporosis is one of the causes of backbone fracture. The most necessary vertebral segment is lumbar because it supports body movement at most [1,2]. Medical treatment to overcome vertebral bone fracture need some instrumentations to maintain the vertebral bone, one of the instrumentation to fixate the bone is using pedicle screw. Pedicle screw fixation instrumentation system for vertebral bone is firstly introduced by Harrington and Tulos at 1969. This system becomes the primary instrumentation for spinal surgery until now [3]. Pedicle screw insertion technique also becomes an important part of spinal surgery because it takes much consideration which could injure spinal nerves that lead to complication risk [4].
However, pedicle screw ability to maintain on osteoporotic bones condition become questionable because it makes the vertebral bones become fragile and weaken the bond between pedicle screw and the bones. Decreased excessive fixation strength on pedicle screw can cause loosening and pull out failure easily [5-7].
Various studies have been conducted to increase the fixation strength of pedicle screw on osteoporotic bones, one of the studies is modifying the geometry to increasing pull out force on pedicle screw [8]. Although the geometry of pedicle screw has been modified but pull out failure still can happen on severe osteoporosis condition. Another technique to strengthen fixation bond between pedicle screw and the bone is using bone cement. On Stadelman et al research, explained using biocompatibility material such as calcium phosphate (CaP) as bone cement then injected to the vertebral bone by cannulated pedicle screw to prevent pull out failure, using biocompatibility is important thing when it relates to the implant [9-10]. Even though bone cement able to increase a lot pull out force on pedicle screw, bone cement utilization still has some deficiencies such as leakage that leads to spine nerves injury [11].
Therefore a new concept has to be developed such as both of pedicle screw connected each other with a new system. Tt means that both of them will mutually reinforce each other and increase the pull out force on osteoporosis bone without using bone cement. Using modern technology such as additive manufacturing concept can help to realize the concept design of product [12,13].
METHODS Pedicle Screw Modeling
Pedicle screw design process uses the reverse engineering method. Reverse engineering process is to obtain geometric CAD model from physical or existing product. Digital microscope dinolite which can be seen in Figure 1 could see and measure small detail geometry of pedicle screw. Pedicle screw consists of 3 different geometries which are head, body, and tip. First, commercial pedicle screw is put on the digital microscope dinolite for initial setup and do the calibration process. Each geometry using various magnification scale which is adjusted to the accuracy of dinolite.
FIGURE 1. Digital Microscope Dinolite
Pedicle screw measurement process is done 3 times, and the result value will be calculated to get the average. After all pedicle screw geometry dimensions are obtained, CAD model of pedicle screw can be sketched with CAD software.
CAD model from commercial pedicle screw will be modified for the initial concept design.
Concept Design Interpedicular Locking Screw
Interpedicular locking screw concept is a modification from common and commercial pedicle screw. The purpose of the development concept pedicle screw is to increase fixation strength so it can prevent pedicle screw from pull out failure under osteoporosis bone condition without using bone cement material. A design concept of interpedicular locking screw consists of 2 parts which are a wire and a pair of the pedicle screw. The pedicle screw has hollow shaped along the body and its function as wire path. The wire will enter into the pedicle screw through a hole from head to tip of pedicle screw and also get into another pedicle screw. The wire will bind both of pedicle screw so it will be connected and also locked each other. The different between interpedicular locking screw and common pedicle screw is both of pedicle screw in interpedicular locking screw system could lock each other while common pedicle screw did not.
Along with this initial concept, pedicle screw will increase fixation strength because it could strengthen one and another pedicle screw is expected. For the last, there is one condition to implemented this interpedicular locking screw concept which is both of pedicle screw tip should meet in one point (locking point) which can be seen in figure 2.
Therefore, this study aims to simulate if both of pedicle screw tip could meet in one point according to vertebral bone segment structure or not.
Wire
Body
Tip
Head
FIGURE 2. 3D Model Concept Design Interpedicular Locking Screw
Segmentation Process Vertebral Bone
In this segmentation process, CT scan data with dicom format is obtained from one of the patients who suffer kyphotic as can be seen in figure 3. In the human body, there are 33 vertebral bone segments. Each possible vertebral bone segment will be sliced one by one. The benefit of using this software is to facilitate the illustration of the bone with the real size and structure according to CT scan condition. The first step in this process, dicom data is opened with slicer software to see the whole bone structure which already scanned. After that, setup the volume rendering to gain more focus picture of whole vertebral bone. Segmentation process in slicer software is a process to get a vertebral bone segment which is desired from the total segment in CT scan data. The purpose of this process is to get specific bone such as vertebral bone segments in this study and it will be evaluated. Next step, the vertebral bone segment that already obtained will be refined with the software feature to eliminate the roughness in vertebral bone segments structure.
FIGURE 3. CT-Scan Dicom Data in Software Display
After the vertebral bone is ready to be evaluated, the bone will be saved as stl format and later it will be converted to iges format. With iges format vertebral bone segment is ready be simulated in CAD software.
Assembling Process Pedicle Screw CAD Model and Vertebral Bone Segment
In this process, the pedicle screw CAD model and vertebral model are readily simulated in CAD software both of them will be assembled. This process using CAD software to manipulate pedicle screw position according to vertebral bone segment structure. Pedicle screw CAD model position is moved and adjusted to every vertebral bone segment that already sliced from the previous process. Pedicle screw entrance and path in vertebral bone segment simulation based on the vertebral bone surgery process. Another important condition for implemented initial design interlocking pedicle screw is both of pedicle screw tip should meet in one point (locking point). After both of pedicle screw installed in the vertebral bone segment, the position of pedicle screw will be evaluated according to the vertebral bone segment structure is it possible implemented interpedicular locking screw or not.
RESULTS AND DISCUSSION Design Possibility Study
After every step has been done, pedicle screw and vertebral bone are ready to be assembled with CAD software.
Because of vertebral bone from dicom data is in bad condition therefor total vertebral bone segments that success to be sliced is 12 bone segments from total 33 human body vertebral bone segments. Total 12 vertebral segments that success to be sliced which are lumbar segment (L4, L5,); thoracic segment (T1, T2, T3, T4, T5, and T7); and cervical segment (C5, C6, and C7). Every vertebral bone segment have different size and structure such as lumbar have ticker bone structure compared with thoracic and cervical bone segments.
Assembly
Pedicle Screw CAD Model
Vertebral Bone CAD Model
FIGURE 4. Assembly Result of Pedicle Screw CAD Model and Vertebral Bone Model
Pedicle screw model on figure 4 installed inside the vertebral bone model with the condition both of pedicle screw tip should meet in one point (locking point) to realize design concept of the interpedicular locking screw. Every pedicle screw CAD model is installed inside vertebral bone and the position are adjusted according to the vertebral bone segments structure.
After every pedicle screw installed in vertebral bone segments in CAD software, the pedicle screw position adjusted to the vertebral bone structure. When both of pedicle screw planted in the vertebral bone model, it formed an angle against the horizontal line. On figure 5, the section view of pedicle screw assembled in the vertebral bone model could seem both of pedicle screw tip meet in one point with the angle which has been formed.
Pedicle Screw 1 Angle
Pedicle Screw 2 Angle
Locking Point
FIGURE 5. The angle which Formed by Pedicle Screws
The angle which formed by pedicle screw is measured. The results are shown in table1 which exhibit the variation of the angles. Pedicle screw installing simulation in vertebral bone segments possible in almost every vertebral segment except on cervical segment (C5). It is not possible because the pedicle screw implant size is too big than the cervical segment (C5) itself. The other vertebral bone segment shows both of pedicle screw could meet at one point.
So, it means that it is applicable to the design concept interpedicular locking screw. However, pedicle screw still possible installed in other vertebral bone segments under the interpedicular locking screw concept condition, but when it planted in vertebral segment cervical and thoracic the pedicle screw size seems too big according to the bone size.
TABLE 1. Pedicle Screw Angle on Vertebral Bone Segment
Vertebral Bone Segment Pedicle screw 1 angle Pedicle screw 2 angle
Lumbar L5 56.61° 57.31°
Lumbar L4 52.04° 67.57°
Thoracic T7 56.26° 67.02°
Thoracic T6 60.14° 68.64°
Thoracic T5 61.31° 61.14°
Thoracic T4 56.80° 68.38°
Thoracic T3 61.16° 67.43°
Thoracic T2 56.71° 59.00°
Thoracic T1 49.50° 55.90°
Cervical C7 50.61° 54.41°
Cervical C6 48.10° 55.42°
Cervical C5 Not possible Not possible
The angle that formed within both pedicle screw can be seen on table 1. it can be seen the angle value is between 40°-70°. Although the angle is determined with this study, the result value is uncommon so it is difficult to make entry pedicle screw with those angle value during the real surgery process.
CONCLUSION
Based on this study, design concept of intrapedicular locking screw can be applied almost every obtained vertebral bone segment because both of pedicle screw could meet in one point except on cervical segment (C5). Pedicle screw variations need to be done because of varied size vertebral bone segment since in some vertebral segment pedicle screw almost touch spine nerve. To implement this concept, in actual surgery, need some instrument tools for establishing pedicle screw path and angle, because as can be seen in figure. The angle is provided uncommonly between 40°-70°. In this initial study from design concept of interpedicular pedicle screw need other test or study to realize and manufacture the product.
ACKNOWLEDGMENT
The authors would like to thank the Direktorat Riset dan Pengabdian Masyarakat (DRPM) Universitas Indonesia for funding this research under PITTA grant no.2563/UN2.R3.1/HKP.05.00/2018
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