AIP Conference Proceedings 2344, 020019 (2021); https://doi.org/10.1063/5.0047288 2344, 020019
© 2021 Author(s).
Design criteria for cementless total hip arthroplasty: A retrospective study from cadaver implantation
Cite as: AIP Conference Proceedings 2344, 020019 (2021); https://doi.org/10.1063/5.0047288 Published Online: 23 March 2021
Muhammad S. Utomo, Talitha Asmaria, Daniel P. Malau, Joko Triwardono, Ika Kartika, Ismail H. Dilogo, and Ahmad J.
Rahyussalim
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Design Criteria for Cementless Total Hip Arthroplasty: A Retrospective Study from Cadaver Implantation
Muhammad S Utomo
1,a), Talitha Asmaria
1, Daniel P Malau
1, Joko Triwardono
1, Ika Kartika
1, Ismail H Dilogo
2,3, Ahmad J Rahyussalim
2,31Research Center for Metallurgy and Materials, Indonesian Institute of Sciences, PUSPIPTEK Area, Building 470 South Tangerang, Banten 15314 Indonesia
2Faculty of Medicine, Universitas Indonesia, Jl. Salemba Raya No. 6, DKI Jakarta 10430 Indonesia
3Department of Orthopedics and Traumatology, RSUPN Cipto Mangunkusumo, Jl. Diponegoro No. 71, Salemba, Jakarta 10430 Indonesia
a)Corresponding author: [email protected]
Abstract. Total hip arthroplasty (THA) is the most frequent arthroplasty procedure performed worldwide including in Indonesia. To support Indonesian government initiative to establish a generic domestic THA implant, Research Center for Metallurgy and Materials - Indonesian Institute of Sciences in cooperation with Universitas Indonesia has designed and realized set of cementless titanium-based THA implant. Here we reported the result of first cadaver implantation for cementless titanium-based THA implant in Indonesia. There are three sets of cementless titanium-based THA implants implanted into the left leg of three cadavers. Implantation was performed simultaneously by three groups of orthopedic surgeons. There are three major aspects as evaluation from the cadaver implantation: design, material, and instrumentation. The current cementless titanium-based THA implant was designed based on the same template, material specification, process, and implanted using standard commercial instrumentation. As further directives, it is required to develop the cementless titanium-based THA implants with various shape and sizing in regard of Indonesia domestic requirement, appropriate coating for cementless implantation, refined material properties to facilitate the fabrication process, and customized instrumentation as a whole set of development within the development of the cementless titanium-based THA implant.
INTRODUCTION
With a population of 261.1 million in 2016, Indonesia is the fourth most populous country. Life expectancy in Indonesia has increased from year to year. It is estimated that in 2020, the life expectancy of Indonesian people would be at 71.7 years old with approximately 30 millions elderly persons [1]. The increased life expectancy shows an improvement in the quality of public health. On the other hand, increasing life expectancy requires better access to health services. Based on research by the Indonesian Osteoporosis Association in 2007, in Indonesia, as many as 32.3% of women and 28.8% of men aged 50 years old had osteoporosis [2]. It is estimated that the number will keep increasing align with the increasing population and life expectancy. One important medical technology in handling osteoporosis is bone implants. Through bone implants, the quality of life of people with osteoporosis can be improved.
On the other hand, the increasing population also increases the use of transportation as a cog for economic activity. The amount of traffic accidents with major injuries in Indonesia in 2014 is three times higher than in 2004 [3]. Until now the case of bone implantation due to an accident borne by the Social Security Organizing Agency of Health (BPJS) in recent years also reached 50,000 units annually. This fact is coupled with Indonesia's geographical condition, making it vulnerable to natural disasters such as earthquakes, landslides, tsunamis, and volcanic eruptions. Therefore, disaster preparedness emergency response, including bone provision implants, independently become essential and critical to be realized.
The need for THA implants is very high in Indonesia, faced with challenges in the form of high THA implant prices with a very high level of dependence on imported medical devices, reaching 92%. The circulation value of medical devices in Indonesia can reach 12 trillion rupiahs annually. Based on Presidential Instruction No. 6/2016 regarding the acceleration of the pharmaceutical and medical devices industry's development, the portion of medical devices circulating in Indonesia is targeted to reach 25 % from domestic industries in 2030. To overcome this, a new approach is needed in realizing national independence in health technology, especially in manufacturing THA implants. and its application in Indonesian medical technology. To develop THA implant technology, Indonesia requires interdisciplinary collaboration between researchers, engineers, and clinicians of various backgrounds in Indonesia.
METHODOLOGY
The current cementless total hip arthroplasty implants consist of five components: femoral stem, femoral head, femoral liner, acetabular bearing, and acetabular cup. The femoral stem, femoral head, and acetabular cup were made of Ti-6Al-4V which are standard Ti alloy for implants. Meanwhile, the femoral liner and acetabular bearing were made of polyethylene (PE). The metallic components were fabricated by investment casting in a partnering industry. Stock material in shape of solid cylinder was cut and remelted. The aluminum mold was machined to form the wax pattern. This wax pattern was used to create the silica mold which was then followed by heat treatment to harden the silica mold and melt the wax. The silica mold was used to cast the titanium alloy components. The casted products were then grinded and polished as finishing processes. The whole process took 2 months. Ideally, the titanium alloy components would be processed using CNC machining to produce essential geometrical features such as holes for screws and grooves for alignment. Unfortunately, none of the industries we contacted could perform titanium machining; thus, the components' essential geometrical features were not produced. Meanwhile, the polymeric components were fabricated by CNC machining from solid cylinder stock material.
Figure 1 shows the three sets of cementless, titanium-based THA implants. The metallic femoral stem, head, and acetabular cup were made of Ti-6Al-4V. The green polymeric bearing and liner were made of polyethylene (PE).
Before fabrication, the femoral head and stem's mechanical performance under various conditions such as walking and climbing have been analyzed using finite element analysis [4].
There are two approaches for total hip arthroplasty for the implantation method, which are posterolateral and anterior. We used the posterolateral approach in the current implantation test, where orthopedic surgeons approached the hip joint from the backside. The incision was along the side of the hip and upper thigh. Surgeons then opened the incision site, cut, and extract the femoral head using a bone saw. Surgeons then can choose whether to work on the acetabular cup side first or the proximal femur side. The acetabular cup is reamed using a reamer to clean the surface from damaged tissue and to prepare for cementless implantation. After that, the acetabular cup is positioned with assistance from a guiding instrument and secured with a screw. For the proximal femur, the cavity is prepared using a femoral broach. This step requires surgeons to use mallet and impactor to create the cavity. After the cavity is formed, the femoral stem was implanted, and since the current implant design is cementless, the fixation relies on fit tolerance between the cavity and femoral stem. After both sides were secured safely, the incision was closed.
FIGURE 1. Current set of cementless titanium-based THA implant
developed by Research Center for Metallurgy and Materials - Indonesian Institute of Sciences
RESULT AND DISCUSSION
The cadaveric implantation test was performed on February 2020 at Department of Anatomy, Faculty of Medicine, Universitas Indonesia. Three cadavers were involved: two males and one female. The orthopedic surgeons were divided into three groups and performed the implantation simultaneously. The instruments were provided by vendor. Three sets of total hip arthroplasty implants were implanted into the left leg of each cadaver.
Two implants on two male cadavers were successfully implanted into the cadavers and examined using a C-arm X- ray. One female cadaver implant was failed due to over-dimension of the femoral stem, causing a fracture in the proximal femur. The implantation lasted for two hours, and each surgeon were asked to evaluate the THA implant and overall experience on the implantation of the implant.
Design Aspect
The discussion on design covers the shape and sizing aspects. Both aspects depend on the hip anthropometry of the Indonesian people. Anthropometric is a study of measuring the human body. Several prior studies have been investigated in the decision of implant designing, particularly in total hip arthroplasty. A study from Mishra et al.
measured 25 pairs (50 bones) of cadaveric femora to evaluate the designed implant [5]. This study underwent morphologically and radiologically measurements of femoral head diameter, femoral neck diameter at sub-capital, transcervical, and basal, femoral shaft diameter just above and just below lesser trochanter and 7.5 below lesser trochanter using vernier caliper.
Another anthropometric measurement was done by Rawal et al. using computer-aided design techniques on computed tomography (CT) scanned images of 98 femurs (56 left and 42 right) [6]. The software used to convert the CT images into solid models was MIMICS® (Materialize, Inc., Leuven, Belgium). The geometrical parameters, viz., the femoral head offset, femoral head center (HC), femoral head diameter, femoral head relative position, position of shaft isthmus, neck-shaft angle, bow angle, femoral neck length, canal flare index, femoral length, and canal width at various locations, were chosen to design best-fit standard femoral stems for cementless insertion.
In India, research was conducted regarding total hip replacement on several parameters: vertical offset, horizontal offset, neck-shaft angle. The vertical offset is the perpendicular distance measured between the center of the femoral head and line drawn through the lesser trochanter's starting point. This is also referred to as a vertical drop in some studies. The horizontal offset is the perpendicular distance between center of the femoral head and femoral shaft axis. This is also known clinically as the lateral offset. The NSA is the angle measured between the neck shaft axis and the femoral shaft axis [7].
Figure 2 shows the radiological image of implanted THA into the cadaver. It shows how the long, straight femoral stem does not follow the femur interior's natural shape. Moreover, the sizing tolerance between the femoral stem and the femur interior wall is too close, making such implantation prone to failure if it was done for the actual patient.
The shape and sizing of current total hip arthroplasty implants refer to several commercial implants modified based on a bone model obtained from internet sources. Based on the implantation result, the current sizing could be considered large, and based on this reference, we could make the small and medium-size. This should not happen if only we can obtain access to anthropometrical data of Indonesian hip and femoral bone. Unfortunately, this kind of data is not yet available.
Material Aspect
Discussion on material consists of fabrication and surface aspects. For the fabrication aspect, the machinability of titanium alloys has become a primary issue. Here we used the Ti-6Al-4V, which is the standard biocompatible material for implant. The current implant products, especially the acetabular cup, were not finished due to our institution and domestic industries' incapability in processing the titanium alloys by machining. Features such as grooves for alignment and holes for screw fixation were not realized. To overcome this issue, we are currently working on the development of other titanium alloys, which have better machinability properties such as Ti-Al-Mo or Ti-Al-Nb [8-11]. It is also possible to develop substitution material for Ti alloys with higher machinability such as Ni-free stainless steel without sacrificing biocompatibility. Biocompatibility tests, including cytocompatibility, blood compatibility, and cell response, showed that the Ni-free stainless steel has better biocompatibility than nitinol alloy [12]. A Ni-free, high-nitrogen austenitic steel under brand name P2000 showed similar biocompatibility
properties to common biocompatible metals such as Ti6Al4V, 316L, and CoCrMo [13]. Moreover, the current total hip arthroplasty implant was fabricated by remelting and investment casting as the primary process and polishing as a secondary process. This is not an ideal method to fabricate THA since it involves phase changing and exposes the possibility for unwanted pore formation, which might alter titanium alloy's mechanical properties. Although due to limited budget and infrastructure availability, it is the most realistic way to realize the current total hip arthroplasty implant. Meanwhile, the ideal process would be a CNC machining, forging, or selective laser melting, which is a novel additive manufacturing method for titanium. Nevertheless, these methods are costly.
A critical aspect regarding the surface on cementless implant design is the osseointegration. Unlike the cemented implant, which relies on the cement for fixation, the cementless implant depends on the interaction between the implant surface and the surrounding bone tissue. There are several ways to enhance the osseointegration, including surface topology modification, coating treatment, or structural modification such as porous structure. The development of a porous structure for the hip stem component could also modify the hip stem's mechanical properties to fit specific cases such as implants for pediatric patients [14]. A comparative study between micro- grooved and smooth femoral stems showed that the stem taper surface morphology does not affect the fretting corrosion damage for both CoCr and Ti6Al4V alloys [15].
FIGURE 2. Cadaveric post-implantation radiological examination
Instrumentation Aspect
For the instrumentation aspect, the instrument for total hip arthroplasty can be divided into two groups, which are general and implant-specific instruments. The general instruments include a bone saw, bone drill, mallet, impactor, scalpel, forceps, and so on, while the implant-specific instruments include acetabular reamer and femoral broach. The reamer and broach should have various shapes and sizing which are related directly to the shape and sizing of the implant.
One important THA instrument is the femoral stem broach. It is related directly to the shape and sizing of the femoral stem. Broach is usually used together with a mallet. Mallet velocities should be optimized to obtain proper broaching impaction energy. Mallet velocity below the threshold would not push the broach into the femur, while over velocity might lead to failure [16].
Preutenborbeck et al. investigate the broaching process's mechanical aspect in an experimental setting [16]. The direct anterior approach requires more power and an amount of impaction than the posterior approach. This might encourage surgeons to exert more power, which increases the risk of intraoperative trochanter fracture. The posterior approach also showed dominant translational movement, while the anterior approach showed additional rotational movement.
Innovation can be done on developing dedicated instruments for minimally invasive surgery to reduce tissue damage and achieve better outcomes, such as thinner and curved broach handle, angled flanged retractors, and non- hemisphere reamers [17]. The issue arises due to poor anatomical visualization and landmarks that are exposed in the standard conventional approach. The femoral stem could also be designed for minimally invasive surgery to
preserve bone tissue. A short femoral stem could be implanted without wide dissection compared to classic straight stems with implication on different mechanical stress distribution.
Figure 3 shows the set of instrumentation used during the THA implantation test. A set of femoral stem broaches with holder was seen along with a set of acetabular reamers, a drill machine, and other instrumentations. They are usually made of stainless steel SS 316 L.
The uncemented femoral stem's primary stability is achieved by optimizing the degree between press-fit and the periprosthetic fracture risk. The cavity preparation for the uncemented femoral stem is achieved either by extraction or compaction broaching. Investigation of broaching types (compaction vs blunt extraction vs sharp extraction) and bone mineral density related to densification and contact condition at bone-implant interface provide various results.
Compaction broaching maximizes densification in higher bone density. Meanwhile, the sharp extraction broaching increases the bone-implant contact area. The blunt extraction broaching brings balance between increased contact area and bone densification. For lower quality bone (<115 mgHA/cm³), broach type is not significant to implant stability [18]. Different broach geometry and instrument design could affect the femoral alignment of the cementless femoral stem [19].
FIGURE 3. Instruments for THA implantation test on cadavers
CONCLUSION
Here we reported the result of the first cadaver implantation for cementless titanium-based THA implant in Indonesia. There are three major aspects as evaluation from the cadaver implantation: shape and sizing, material and surface, and instrumentation. As further directives, it is required to develop the cementless titanium-based THA implants with various shape and size in regard to Indonesia domestic requirement, coated or treated surfaces for cementless implantation, refined material properties to facilitate the fabrication process, and customized instrumentation as a whole set of development within the development of the cementless titanium-based THA implant. In order to develop THA implants with various shapes and sizing, it is suggested to build a systematic database of anthropometric data representing the Indonesian population.
ACKNOWLEDGMENTS
Authors would like to thank Indonesia Endowment Fund for Education (LPDP) and Research Center for Metallurgy and Materials – Indonesian Institute of Sciences for funding the whole research activity and providing facilities for designing and realizing the implants, respectively. Authors would also like to thank clinicians from the Department of Orthopaedics and Traumatology, Universitas Indonesia for conducting the cadaver implantation test, Dhyah Annur and Muhamad I. Amal for their contribution on designing and realizing the THA implants, and also Nurul T. Rochman, Andika Pramono, Fendy Rokhmanto, Franciska P. Lestari, Yudi N. Thaha, and Made D. Subekti who helped authors preparing the cadaver implantation test.
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