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2011 International Conference on Electrical Engineering and Informatics 17-19 July 2011, Bandung, Indonesia
Design of Total Hip Replacement Digital Templating Software
Azrulhizam Shapi’i#1, Anton Satria Prabuwono#2, Mohammad Khatim Hasan#3 , Riza Sulaiman#4,
Abdul Yazid Mohd Kassim*5, Nor Hazla Mohamed Hafla*6
#Industrial Computing Research Group, Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi Malaysia
[email protected] [email protected]
[email protected] [email protected]
*Medical Center of Universiti Kebangsaan Malaysia, Bandar Tun Razak, 56000 Cheras, Kuala Lumpur, Malaysia
Abstract— In this study, by taking full advantage of digital X-ray and information technology, we have developed a semi-automated procedure to template hip implants, by making use of digital templating techniques. Using this approach, a software system called OrthoHipTM has been developed. The OrthoHipTM templating process uses a similar technique to that used by an orthopaedic surgeon, using manual templates over general X-ray films. From an image of patient’s X-ray, the OrthoHipTM template helps in quickly and easily selecting to the approximate template size needed. The visual templating features then allow the user to quickly review multiple template sizes against the X-ray and to thus obtain a nearly precise image of the implant size required. The system can assist by templating the patient’s image and generating database reports that can accompany the patient’s notes. The software system was implemented in Java programming, using object-oriented techniques to manage the graphics and objects. The approaches for image scaling used in this research also will be discussed. The study compared the results of the semi-automated (using digital templating) method to the conventional or observational method to demonstrate the accuracy and the utility of the system. Keywords—Digital templating, total hip replacement, implant, X-ray, sizing.
I. INTRODUCTION Digitalized images integrated with a computer system have become an important tool in the medical field, assisting diagnosis, surgery and therapy [1-5]. Orthopaedic surgery, the branch of medicine that deals with the musculoskeletal system, its repair, disease diagnosis and implantation, is no exception. X-ray films have played an important role in executing successful orthopaedic surgery. The common applications of X-rays include the preoperative determination or estimation of implant size, placement location and postoperative outcome analysis.
Over the last few years, the importance of preoperative implant templating has significantly increased since planning for surgery is now a mandatory and prudent part of the procedure for joint replacements. In addition, the current trend for minimal invasive surgery makes sizing at the operating table more difficult, which places an increased reliance on accurate preoperative implant templating. Conventional methods of implant templating require the surgeon to manually lay printed acetate templates of prosthesis of various sizes over general X-ray film. Once the optimal size and position has been established, the acetate is fixed in position with tape and used for visual reference during the operation. This conventional approach demands the time and labor of highly trained an orthopaedic surgeons, and can lead to high levels of intra and interobserver variability. Any errors generated from templating may increase the complexity of the operation as well as potentially compromising the success of the operation. This research is aimed at designing a semi-automated templating system using a digital templating method that can determine the size of hip implants to provide an improved orthopaedic templating method. This process involves matching the size and shape of an implant to the anatomical bone size.
II. RESEARCH BACKGROUND A. Total Hip Replacement
Total Hip Replacement (THR) or Total Hip Arthroplasty (THA) is a process in which the hip joints are replaced with artificial joints or implants. According to [6], THR is a surgical procedure which replaces the diseased cartilage and joint with artificial materials made of metal and plastic. The use of these implants is intended to help the patient lead a normal life without any interference or pain in their joints when walking and performing daily activities. In anatomy, the hip joint comprises of a ball and socket joint. The socket is
H1 - 3
978-1-4577-0752-0/11/$26.00 ©2011 IEEE
shaped like a cup of pelvic bone known as is connected to the end of the femur and The three main components involved in Tacetabular and ball. These components are that the metal will always rub against the gentle movement and minimum erosion [7]implants images used in THR and Fig. position of the implants after THR is perform
Fig. 1 Implants in THR (Zimmer, 2
Fig. 2 The position of the implants afte
acetabulum, which shaped like a ball.
THR are the stem, designed to ensure plastic, creating a
]. Fig. 1 shows the 2 show how the
med.
009)
er THR
B. THR Implants Template Template refers to a standard gframework of the bones. The othis template to match the X-rayoptimum size can be determinedsuppliers in accordance with Templates that are available frUniversiti of Kebangsaan, Malwith a magnification of 115% tby manually sticking it onto determine the appropriate size o3, Fig. 4 and Fig. 5 show theorthopaedic surgeon at PPUplanning.
Fig. 3 Acetabular
Fig. 4 Stem implant template
guidelines used in shaping the orthopaedic specialists will use y image of a patient so that the d. Templates are obtained from
each prosthetic design [7]. rom the Medical Center of the laysia (PPUKM) are Zimmers, to 120%. This template is used the AP view radiographs to
of the stem and asetabular. Fig. implant template used by an
UKM in THR preoperative
implant template
e (Versys Fiber Metal Taper)
Fig. 5 Stem implant template (CP
C. Preoperative Planning in THR Preoperative planning is recommended as apatient assessment, whereby the orthopaobtain an indication before the operatioimplant size. The normal procedure will bsurgeon to perform the templating process, the operating theater, and make the final deregarding the implant size. The use of theapplied to radiographs before surgery allodetermine the most appropriate size of implconventional, or manual templating, it is hithe technique used to take the preoperative bones. Any factor that alters the magnificathe image would affect the accuracy of temand Fig. 6(b) illustrates conventional templin order to plan the surgery at the preoperati
Fig. 6(a) Conventional stem templa
PT)
an important part of aedic surgeon will on of the optimal e for the operating have the results in
ecision at the table e implant templates ows the surgeon to lant to be used. For ighly dependent on radiographs of the
ation or rotation of mplating. Fig. 6(a) lating of the X-rays ive stage [8,9].
ating
Fig. 6(b) Conventional
III. MATERIALS
In the preoperative templattemplating utilize the X-ray diand provide measurement toolsfor orthopaedic surgery. Digitalthe surgeon to select from electronically overlay them on for radiographic magnification. the necessary measurements onstepwise preoperative plannenvironment. A. Image Scaling
In conventional templating, thewith two different magnificatioray film and the second is orepresenting implants at specifiimaging environment and the afilm is generated either in comThe conversion of the X-ray imsize of the anatomy is critical itemplating. The scaling factor of the X-ray film is obtained byon the side of the anatomical image, or by using the scalmagnification scale on the seriedefined by the manufacture. Usscales are not identical. In themake this adjustment manually,and labor-intensive. In the developed, by performing this pthe system addresses these limscaling conversion, the image issystem application. With the acan employ the stepwise methothe optimal template. The digitascale translation to convert
acetabular templating
S AND METHOD ting planning stage, digital gital images, manipulate them s, as well as implant templates l preoperative planning enables
a library of templates and an image, automatically scaled The surgeon can then perform
n the template and conduct the ning process in a digital
e operating surgeon has to deal n scales. The first is on the X-
on the various acetate images c magnifications. Based on the anatomical location, the X-ray mpressed or magnified mode. mage on the film to the actual in the preprocessing for digital
(magnification /compression) y either placing a scale marker joint when taking the X-ray le on the X-ray plate. The
es of acetate images are usually sually these two magnification e traditional method, surgeons , which is both time-consuming digitized templating method
procedure in an automated way mitations. After resolving the s digitized and displayed on the aid of the application, the user od and interactively determine al system requires an additional the on screen pixel density
measurement to the actual size of the tempis a measurement of the resolution of a related to the size of the display in inches anof pixels in the horizontal and verticameasurement is often referred to as dots pemeasurement more accurately refers to thcomputer printer. The scaling tasks werefollowing method [10]:
Fig. 7 Method for image scaling
B. Digital Implant Template
The library of templates has unique tempevery implant model stored in the systemplates were created using a CAD modeexample of the implant template created us(Autocad 2008). However to apply thesesoftware, the image format from CAD (.converted into a jpeg file format. Fig. 9 examples of the hip implant produced.
Fig. 8 Stem (CAD model)
plate. Pixel density computer display,
nd the total number al directions. This er inch, though that he resolution of a e expressed in the
g
plates for each and tem. The implant
el. Fig. 8, shows an sing CAD software e templates to the dwg file) must be and Fig. 10 show
Fig. 9 Stem
Fig. 10 Acetab
C. Zooming and Measurement
Zooming allows the surgeon to detail on both the original anbeing able to easily correlatemagnified and the original imagmagnification levels by selecmagnification (only allowing thlevels of magnification). For “command has been created magnification by a factor of 1/commands such as magnify 1/4and restrict the possible levelsthe level of magnification. Several types of measuremediagnosis process have been sapplication software as measurmathematic theorem and equaFor example, measurement usinthe applied length, the basic form
a2 + b
Thus, the square of a (a²) plus tthe square of c (c²). If we knowright angled triangle, a and b
m Implant
bular Implant
t Functions
simultaneously view the same nd magnified images, as well e measurements between the ges. “Zooming In” allows new cting from a fixed level of he user to specify certain fixed Zooming Out”, a magnify 1/2
to decrease the level of /2. Similarly, we have created , 1/8, 1/16/, 1/32 and full scale, to allow faster adjustment in
ents required in the orthopaedic tudied and were added to the rement tool features by using
ations, e.g. line, diameter, etc. ng Pythagoras’ Theorem to find mula of this theorem being:
2 = c2 the square of b (b²) is equal to
w the lengths of two sides of a b, then Pythagoras’ Theorem
allows us to find the length of the third side, c. This basic concept is applied to the system to find the length between two points, z, using two coordinates, x1,y1 (first point) and x2,y2, (second point) where;
(x2 – x1)2 + (y2 – y1)
2 = z2
D. Experiment To test the efficiency of the developed software, an experiment was conducted with assistance from an experienced orthopaedic surgeon using the conventional approach to determine the size of a hip implant. The results
from the conventional approach were compared to the results produced by our semi-automated method (a trial and error method). The same orthopaedic surgeon then also performed implant templating using the semi-automated software. The experiment recorded the implant size to be used and the time taken by both methods. Five randomly selected X-rays of unidentified patients were used for templating for both techniques. The graphical user interface developed for OrthoHipTM (see Fig 11) allows the user to easily visualize and manipulate the template over the X-ray image to select the optimal implant size.
Fig. 11 OrthoHipTM interface
Fig. 12 OrthoHipTM digital templating
IV. RESULTS AND DISCUSSIONS
Fig. 12 shows an example of digital implant templating using the OrthoHipTM software. For each X-ray sample, the best matching femoral stem implant sizes determined by both techniques were recorded. The difference between the two sizes was calculated and is shown in Fig. 13. It is evident that the computer system yielded very close results to those obtained by the conventional method in all five cases. The difference, if any, is within the error of clinically acceptable range (± one size). In addition, the study also qualitatively demonstrated that the average time taken for templating using the semi-automated technique was much less than using the conventional method. The decision support system showed promising results where the implants selected by using this method were within the acceptable range when compared to results from the conventional method. With the further studies on pixel density, this gave lack of human errors and variances. In addition, compared to the traditional templating method, it also saves the time and labor of a highly trained person. Other supporting features such as multi-level viewing allow the surgeon to accurately identify reference points for size determination. However, further tests are needed on usability and inter- and intra-variance with a larger sample population, including multiple users and digitized images. In another investigation, mapping methods in template matching to automatically enhance detection were investigated. It should be pointed out that the quality of the X-ray is important for accurate optimal matching.
Fig. 13 Results of comparative experiments between the conventional and semi-automatic method.
V. CONCLUSION This paper has presented a semi-automatic, decision support method for determining an implant size by making use of the digital templating method. Compared to the conventional templating method, it not only can save the time and labor of highly trained person, but also reduces human error and possibly inter- and intra-variances, especially in image scaling issues. Overall, this method can become an effective tool,
helping surgeons in the surgery planning and decision making processes. Although the current approach is a semi-automated technique, it could be extended to a fully-automated technique by employing more sophisticated noise removal and image analysis algorithms. Finally, the method developed can be applicable to other body joints such as knee and shoulder with small modifications in the programming, which will be another task in the future.
ACKNOWLEDGEMENT This research project was conducted in collaboration with Dr Abdul Yazid Mohd Kassim and Dr Nor Hazla Haflah from The Department Of Orthopaedic And Traumalogy and Dr Hamzaini Abd Hamid From The Department Of Radiology, Medical Centre Of University Kebangsaan Malaysia. This research was also funded by the University Grants UKM-OUP-ICT-35-179/2010 and UKM-GUP-TMK-07-01-035.
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