Jihui Li

Jim X Chen

Mark M Theiss

Qi Xing

Wenzhen Yang

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1
INTRODUCTION 
Lower extremity deformity can cause joint pain and malfunction. 
Patients with severe deformity usually need a correction surgery or total 
knee replacement (TKR) surgery to realign the orientation of the femur 
and tibia. Lower extremity deformity needs to be accurately assessed 
before any clinical decision can be made. In practice, physicians and 
radiologists rely mainly on X-ray images to evaluate the deformity, and 
CT is used in complex cases only. Manual assessment on X-rays is 
tedious, time consuming and inaccurate [1]. Computer aided diagnosis 
was proved efficient to understand patients’ anatomy, analyze lower 
limb deformity and plan the possible surgery [2]. However, notable 
interactive works were required during the identification of the 
anatomic features, and the accuracy was unguaranteed when the 
physician is not familiar with the diagnosis software. In this study we 
developed an automatic assessment system to identify patients’ 
anatomic features and quantify lower extremity deformity.  
 
MATERIALS AND METHODS 
Six computer models of lower limb (from femoral head to foot) were 
developed from patients’ CT images. The lower extremity deformity 
assessment system was a customized program that sets up a virtual 
environment for physicians to browse the computer models, identify 3D 
anatomic features, and analyze lower extremity deformities. 
Sophisticated computer graphics and visualization techniques were 
used to identify articulate centers, mechanical/transverse axes, and 
planes automatically [3]. For example, a mesh partition technique was 
employed to extract the surface of a femoral head from the femoral 
neck, and a sphere fitting method was applied to calculate the center of 
the femoral head (Cfh). Then we used a skeletonization method to find 
the center of a knee joint (Ckj), center of an ankle joint (Caj), center of a 
proximal/distal femur or tibia (Cfp, Cfd, and Ctp, Ctd) (Fig. 1). By 
connecting the proximal and distal articulate centers, we were able to 
achieve the mechanical axes of the femur and tibia (AXfm and AXtm) 
(Fig. 2). We could also determine the femur/tibia/ankle transverse axes 
(AXft, AXtt and AXat) by connecting the corresponding extremity 
points lying on the convexities or concaves of the bones. Through the 
feature points and axes we could further define planes, such as femur 
anatomic plane (PLfa), femur mechanical plane (PLfm), tibia 
mechanical plane (PLtm), and Tibia anatomic plane (PLta) (Fig. 3). 
Based on the above anatomic features physicians were able to 
calculate the critical spatial angles, such as hip-knee-ankle angle θHKA, 
condylar-hip angle θCH, and plateau
level of lower extremity deformit
definition and description of these p
the anatomic features and the comp
were automatic. During the proce
inform the system the interested fe
compared our results with the traditi
based on the 2D radiographic images
 
RESULTS AND DISCUSSION 
Based on the six lower limb comput
ankle angle θHKA is -1.4° ± 1.6°, whiin a large cohort survey (-1.3° ±
showed the mean value of the cond
which were also close to the value re
 
The major limitation of this study w
ray images for physician’s assessm
compare the lower extremity defo
traditional diagnosis method relied o
anatomic features and parameters 
system were distinguished by th
automatically, its accuracy was 
AUTOMATIC ASSESSMENT OF LOWER EXTREMITY DEFORMITY BASED ON PATIENT 
SPECIFIC COMPUTER MODELS  
Qi Xing (1,2), Mark M. Theiss, MD (3),  
Wenzhen Yang, Ph. D (4), Jim X. Chen, Ph. D (2,1), Jihui Li, Ph. D (3) 
(1) Southwest Jiaotong University 
Chengdu, China 
(2) George Mason University 
Fairfax, U.S.A 
(3) Inova Fairfax Hospital 
Fairfax, U.S.A 
(4) Zhejiang Sci-Tech University 
Hangzhou, China 
 
Proceedings of the ASME 2011 Summer Bioengineering Conference 
SBC2011 
June 22-25, 2011, Farmington, Pennsylvania, USA 
SBC2011-53808 
Downloaded From: https://proceedings.asmedigitalcollection.asme.org on 06/28/2019 Terms of Use: http://www.asme.org/about-asme/terms-of-u-ankle angle θPA, and evaluate the 
y. Table 1 listed the geometric 
arameters. The identification of all Copyright © 2011 by ASME 
utation of the related parameters 
dure physicians only needed to 
atures or parameters. Finally we 
onal physicians’ diagnosis method 
 in the frontal plane.  
er models, we found the hip-knee-
ch is close to Cooke’s observation 
 2.0°) [4]. Similarly, our results 
ylar-hip angle θCH is 85.3° ± 5.4°, ported by Paley (85.1° ± 2.9° )[5].  
as that we do not have patients’ X-
ent. As a result we could not 
rmity assessment system to the 
n X-ray only. However, since the 
achieved by the new assessment 
e computer graphics technique 
expected to be better than the 
se
Copyright © 2011 by ASME 2
traditional diagnosis method that is lack of 3D information and more 
subjective. Nevertheless, significant error might occur in the new 
assessment method when the patient has extreme local deformities or 
damages. This would distort the automatic localization of the nearby 
feature points and influence the final results. Future study will focus 
on validating of the new assessment system, and further collaborating 
with experienced orthopedic physicians to optimize the strategy of 
anatomic feature identification.  
 
CONCLUSIONS 
In the present study, we developed a fully automatic patient-specific 
assessment system that can identify the 3D anatomic features (articulate 
centers, mechanical axes, transverse axes, and planes) of lower limb 
and diagnose the severity of its deformity. The proposed system had a 
potential to reduce diagnostic errors and tedious work related to the 
traditional X-ray diagnosis method. The technique might help 
orthopedic physicians in lower extremity deformity patient evaluation, 
surgery planning, and computer aided surgeries.  
 
ACKNOWLEDGEMENT 
This study was financially supported by the George Mason University 
& Inova Fairfax Hospital Research Fund, the Excellent Young Team 
of Zhejiang Province, China (No.R107725), and the Zhejiang Science 
Technology Plan Project, China (No. 2009C31021). 
 
REFERENCES 
1. Iseki Y, Takahashi T, Takeda H, Tsuboi I, Imai H, Mashima N, 
Watanabe S, Yamamoto H., 2009. Defining the load bearing axis 
of the lower extremity obtained from anterior-posterior digital 
radiographs of the whole limb in stance. Osteoarthritis and 
Cartilage 17, 586-91. 
2. Kim YH., 2003. Computer simulation of multi-dimensional bone 
deformity correction and lengthening by unilateral external fixator. 
Proc of 2003 International Conference on Computational Science 
771-8. 
3. Xing Q, Yang WZ, Theiss MM, Li JH, P Q, Chen JX., 2010. 3D 
automatic feature construction system for lower limb alignment. 
2010 International Conference on Cyberworlds Oct. 2010. 
4. Cooke TDV, Sled EA, Scudamore RA., 2007. Frontal plane knee 
alignment: a call for standardized measurement. Journal of 
Rheumatology 34, 1796-801. 
5. Paley D, Herzenberg JE, Tetsworth K, Mckie J, Bhave A., 1994. 
Deformity planning for frontal and sagittal plane corrective 
osteotomies. Orthop Clin North Am 25, 425-65. 
 
Table 1 Parameters definition and description 
Parameter Definition Description 
HKAθ  Hip-knee-ankle 
angle 
Angle between PLfm 
and PLtm 
CHθ  Condylar-hip 
angle 
Angle between PLfm 
and PLft 
PAθ  Plateau-ankle 
angle 
Angle between PLtm 
and PLtt 
 
Figure 1. The articulate centers identified: (A) center of femoral head (Cfh) 
(B) center of proximal and distal femur/Tibia (Cfp and Cfd, Ctp and Ctd); 
(C) center of ankle joint (Caj) in 2D and 3D images. 
 
fhC
ajC
kjC
ajC
fhC
kjC
kjC kjC
kjC
a jC
 
 
Figure 2. Mechanical and transverse axes identified: (A) Femur 
mechanical axis (AXfm); (B) Tibia mechanical axis (AXtm); (C) Lower limb 
mechanical axis (AXllm); (D) Femur transverse axis (AXft) in 2D and 3D 
images; (E) Tibia transverse axis (AXtt); (F) Ankle transverse axis (AXat). 
 
 
 
Figure 3. The feature planes identified: (A) Femur anatomic plane (PLfa); 
(B) Femur mechanical plane (PLfm); (C) Tibia anatomic plane (PLta). 
Downloaded From: https://proceedings.asmedigitalcollection.asme.org on 06/28/2019 Terms of Use: http://www.asme.org/about-asme/terms-of-use


Automatic Assessment of Lower Extremity Deformity Based on Patient Specific Computer Models

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Automatic Assessment of Lower Extremity Deformity Based on Patient Specific Computer Models

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