Journal of Robotics, Networking and Artificial Life, Vol. 3, No. 2 (September 2016), 69-73

Knee Android Model Reproducing Internal-External Rotationwith Screw-Home Movement of the Human Knee
Daichi Yamauchi, Sho Takei, Noritaka Sato, Yoshifumi Morita

Department of Computer Science and Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan
E-mail: d.yamauchi.170@nitech.ac.jp

Abstract
This paper proposes a knee android model (Knee-AM) that can reproduce the internal-external rotation with screwhome movement (SHM) of the human knee. This rotation of the Knee-AM was realized by changing the number,
lengths, and fixing points of the nylon-cords of our previous Knee-AM. Moreover, when the anterior cruciate
ligament (ACL) was removed from the Knee-AM to imitate ligament injury, SHM did not occur during knee
extension. The results show the important role played by the ACL in SHM.
Keywords: Android model, Knee model, Human knee joint, Screw-home movement, Joint mechanism.

1. Introduction
In the recent times, the time available for rehabilitation
treatment is limited and the number of patients,
particularly elderly patients, is increasing. Against thisbackground, efficient and effective treatments are social
needs in the field of rehabilitation. As a solution forthese needs, we earlier proposed a knee android model(Knee-AM) for supporting treatment planning1.
An android model of the human joint was developedby Sanaka to improve the medical technology in thefield of rehabilitation2. Android models are anatomical
models composed of the minimum number of parts
required for reproducing the corresponding human
movement. They can reproduce the three elements ofmovement (“slide,” “roll,” and “leave”) that occurbetween two articulating bones. Sanaka2 found that thekinematic mechanisms of an android model of the index
finger had some different properties from those of theactual movement of the index finger. Moreover,rehabilitation based on the knowledge gained from
android models has contributed to improving the rangeof motion, which was reduced upon tenorrhaphy.
Consequently, Sanaka’s study confirmed that theknowledge obtained using android models is beneficial
for medical treatment.
The internal-external (IE) rotation during knee
extension in humans can be classified into three types3,
namely, “External rotation type,” “Internal rotation atthe end type,” and “Internal rotation type”. In ourprevious study, we proposed a Knee-AM consisting of atibial model, a femoral model, and 10 nylon-cords
imitating the ligaments. The IE rotation of the KneeAM was similar to the internal rotation at the end type.
This type did not occur commonly, and often occurredin humans with joint laxity3.
In this study, we aimed to develop a Knee-AM thatcan reproduce the IE rotation of the external rotation
type. Since most of the human knee motion belongs tothis type, reproducing this type in the Knee-AM isimportant for using the model on a wider scale.
Additionally, since external rotation at the end ofextension, that is, the screw-home movement (SHM), in
this type, we investigated the mechanism of the SHM
using the Knee-AM. Furthermore, we also aimed to gain
knowledge of a ligament injury by simulating the injury
in the Knee-AM.

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Daichi Yamauchi, Sho Takei, Noritaka Sato, Yoshifumi Morita

2. Knee Android Model (Knee-AM)
The Knee-AM is shown in Fig. 1. It imitates the rightknee joint and consists of a tibial model, a femoral
model, and five nylon-cords. To allow the Knee-AM
extend automatically, we used a drive unit.
2.1. Bone models
We used the same bone models as those in our previous
study1. The tibial and the femoral models, imitating thetibia and the femur, were made of a smooth nylon-basedmaterial by using a 3D printer. The femoral model wascut near the knee joint to about one-fifth of its fulllength. An aluminum rod was attached to the cut surface
along the long-axis of the femoral model to fix thefemoral model to the drive unit. A lightweight squareplate (length of side: 150 mm) also was attached to thetibial model for attaching measurement markers.
2.2. Nylon-cords
We used five inextensible nylon-cords to imitate theligaments of the knee on the basis of the motion and theanatomy of the human knee4, as shown in Fig. 2. The
nylon-cords were attached to the bone models by copper
nails. When measuring the lengths of the nylon-cords,
we measured the lengths between the centers of two
copper nail heads. The correspondences of the fivenylon-cords to the ligaments of the human knee, and thelengths of these cords are listed in Table 1. We used
fewer nylon-cords than in our previous Knee-AM1 toinvestigate knee motion in a simple structure; we also
rearranged the positions and the lengths of the nyloncords to reproduce the human knee motion precisely.
The tibial collateral ligament (TCL) was imitated byone nylon-cord (Cord T). One end of Cord T wasattached near the center of the medial femoral condyle(MFC) so that Cord T did not become loose when theflexion angle changed from 90° to 0°. The other end
was attached to the posterior of the insert part of the pes
anserinus.
The fibular collateral ligament (FCL) was imitatedby one nylon-cord (Cord F). One end of Cord F wasalso attached near the center of lateral femoral condyle(LFC) so that Cord F did not become loose when theflexion angle changed from 90° to 0°. The other end inthe actual knee is attached to the fibular head. However,since the Knee-AM did not include the fibular model,
the other end was attached to the insert part of theposterior ligament of the fibular head.
The anterior cruciate ligament (ACL) was imitatedby two nylon-cords (Cords A1 and A2, collectively
referred to as Cord A). Two nylon-cords were usedbecause the ACL and the PCL consist of many fibers ofdifferent lengths4. One end of Cord A1 was attached tothe distal posterior of the LFC. The other end wasattached near the insert part of the medial meniscus.
Similarly, one end of Cord A2 was attached to theproximal posterior of the LFC. The other end wasattached at the medial posterior 9 mm from the end ofCord A1 on the tibial model.
The posterior cruciate ligament (PCL) was imitatedby one nylon-cord (Cord P). In order to reproduce themotion between a flexion angle of 90° and fullextension, we imitated the PCL, which tightens at 90° offlexion4, with one nylon-cord. One end of Cord P wasattached to the distal anterior of the MFC. The other endwas attached to the center posterior of the tibial plateau.

Table 1. Lengths and correspondences of the five nylon-cords
used in the model to the ligaments of the human knee (TCL:Tibial collateral ligament, FCL: Fibular collateral ligament,
ACL: Anterior cruciate ligament, PCL: Posterior cruciateligament)

Fig. 1. Knee android model (Knee-AM)

Name of cord

Ligament

Cord T
Cord F
Cord A1
Cord A2
Cord P

TCL
FCL
ACL
ACL
PCL

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Length [mm]
58.5
39.3
34.2
37.3
31.1

Knee Android Model Reproducing

2.3. Drive unit

3. Experiment

The drive unit and the Knee-AM are shown in Fig. 3.
The drive unit comprised a motor, a reel fixed on themotor shaft, a pulley, a wire, and a frame. The drive unit
extended the joint of the Knee-AM by pulling a wire
connected to the tibial tuberosity. The wire was run
through the pulleys and wound onto the reel. The motor
was placed above the long-axis of the femoral model sothat the wire made an angle of 0° horizontally withrespect to the long-axis of the femoral model. Thepulley was placed at a position corresponding to thehuman patella at full extension. The femoral model was
fixed on the frame by clamping the aluminum rod andthe proximal part of the femoral model. This fixing
method is an improvement of that used in our previous
study1 to fix the Knee-AM on the drive unit firmly.

We conducted two experiments to confirm the utility ofthe Knee-AM. In the experiments, we measured themotions of the bone models with a motion capturesystem VICON (Vicon Movement Systems Ltd.) andcalculated the flexion angle and IE rotation angle byusing the same calculation methods as in our previous
study1.
3.1. Experiment method
First, we tested the reproducibility of the Knee-AM for
the IE rotation of the human knee. In this test, the KneeAM was extended from 90° of extension angle to full
extension by the drive unit. To evaluate thereproducibility, we compared the IE rotation of KneeAM with that of the human knee.
Second, we investigated the knee motion of an ACL
injury by using the Knee-AM. In this simulation, Cords
A1 and A2 were removed, as shown in Fig. 4. The
Knee-AM simulating an ACL injury is referred to as theinjured Knee-AM. The experimental procedure was thesame as that of the first experiment.
The measured data included small vibrations causedby the mechanical resonance of the Knee-AM. In order
to eliminate these vibrations, we used a low-pass filter
with a cutoff frequency of 5Hz.
3.2. Results(a) Tibial collateral
ligament (TCL)(b) Fibular collateral
ligament (FCL)(c) Anterior cruciate
ligament (ACL)(d) Posterior cruciate
ligament (PCL)The IE rotations of the Knee-AM and the injured KneeAM are shown in Fig. 5. In order to compare the IE
rotations of these two types of Knee-AMs with those of
the human knee, we used the human knee movement
data obtained from Ref. 3.

Fig. 2. Nylon-cords imitating the ligaments in the human knee

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Fig. 3. Drive unit and Knee-AM

Daichi Yamauchi, Sho Takei, Noritaka Sato, Yoshifumi Morita

3.3. Discussion
We considered the mechanism causing SHM.
Comparison of the waveforms of the Knee-AM and theinjured Knee-AM in Fig. 5 show differences inmovements between flexion angles of -20° and 0°.
Accordingly, it was assumed that Cord A started totighten from -20° and that the SHM was caused by CordA.
In order to clarify the mechanism causing the SHM,
we observed the motions of the lateral and the medialplateaus with respect to the femoral model and thetensions of the nylon-cords of the two types of Knee-AMs; these data are listed in Table 2. In the case of theKnee-AM, Cords T, F, and P were weakly stretched at aflexion angle of -90°. When the Knee-AM started toextend, the lateral and the medial plateaus rolled from aflexion angle of -90° to -60°, and then these plateaus
started to slide toward the anterior. In addition, thetension in Cord T increased until full extension, andCord P became loose. Around a flexion angle of -20°,
Cord A started to tighten, and the lateral plateau ceased
to slide and began to roll. In contrast, the medial plateau
kept sliding toward the anterior. The differences in themotions of the lateral and the medial plateaus cause
SHM4. Additionally, Cord F tightened with the roll of
the lateral plateau. At full extension, Cords T, F, and A
tightened strongly, and the tibial model became fixed on
the femoral model. This means that the phenomenon inwhich the knee was locked occurred in the Knee-AM.
The above-described motion of the Knee-AM was inagreement with that described in Ref. 4 with regard thefollowing points:(i) the lateral plateau rolls to a greater extent than themedial plateau,(ii) the TCL and the FCL tighten during extension, and(iii) the ACL tightens at the extended position, and thePCL tightens at the flexed position.
This agreement implies that the knowledge gained using
the Knee-AM is valid.

Rotation angle [deg]External
Internal

In the graph in Fig. 5, the horizontal axis is theflexion angle, with extension denoted in the positivedirection. The vertical axis is the IE rotation angle, withinternal rotation denoted in the positive direction. The
rotation angle is set to be zero at a flexion angle of -90°.
The markers show the maximum absolute value of therotation angle between flexion angles of -90° and 0°.
Ishii and Yamamoto3 classified IE rotation of 30
subjects into three types. “Type 1” corresponded to theexternal rotation at the end of extension, namely, SHM.
“Type 2” corresponded to external rotation occurring at
the beginning of extension, and internal rotation
occurring in the second half of extension. “Type 3”
corresponded to internal rotation occurring over theentire extension.
As seen from the figure, in the case of Knee-AM,
the round marker corresponded to Type 1; that is, SHMoccurred. Therefore, the Knee-AM can reproduce the IErotation with SHM of the human knee. On the other
hand, in the injured Knee-AM, the round marker
corresponded to Type 1, though SHM did not occur.
Thus, it is inferred that the ACL is a necessarycomponent for SHM.

20151050-5-10-15-140-120

Flexion-100-80-60-40

Flexion angle [deg]-20020Extension

Type 1
Type 2Type 3Knee-AM
Injured Knee-AM

Fig. 4. Injured Knee-AM

Fig. 5. Comparison of internal-external rotations duringextension of Knee-AM and thirty human subjects3.

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72Knee Android Model Reproducing

On the other hand, in the case of the injured KneeAM, the motion of lateral plateau and the tension in
Cord F were different from those of the Knee-AM
between flexion angles of -20° and 0°. The lateralplateau continued sliding toward the anterior until thefull extension, but Cord F did not strongly tighten.
Therefore, SHM did not occur, and the tibial model did
not become fixed on the femoral model at full extension.
This means that the phenomenon which the knee waslocked did not occur in the injured Knee-AM.

Table 2. Time chart of the tension in the nylon-cords and themotion of the medial and lateral plateaus (WT: Weakly Tight,T: Tight, ST, Strongly Tight, L: Loose, S: Slide, R: Roll)

Flexion angle [°]

-90
WT
WT
L
WT
R
R

-20
T
WT
L
L
S
S

↗
→→
↘
S
S

0↗
↗
↗
→
S
R

ST
ST
ST
L
R
R

(b) Injured Knee-AM
Flexion angle [°]-90

Tension of Cord T
Tension of Cord F
Tension of Cord A
Tension of Cord P
Motion of medial plateau
Motion of lateral plateau

WTWT↗
→WTRR↘
SS

In this paper, we proposed a Knee-AM that canreproduce the IE rotation of external rotation type byrearranging the nylon-cords of our previous Knee-AM.
Our investigation of the mechanism of SHM by using
the Knee-AM revealed that the roll of the lateral plateau
tightens Cord F and that strong tightening of Cords T, F,
and A fixes the tibial model on the femoral model. In
addition, our simulation results of the ACL injury in theKnee-AM showed that in the absence of the ACL, SHM
and the knee-locking phenomenon did not occur.
In future studies, we will experimentally investigate
the roles of other ligaments. We also plan to discuss ourfindings with medical personnel with regard the medicaltreatments, the improvement in medical technology, andother applications of the Knee-AM.
References(a) Knee-AM
Tension of Cord T
Tension of Cord F
Tension of Cord A
Tension of Cord P
Motion of medial plateau
Motion of lateral plateau

4. Conclusion-20
T
WTNoneLSS0↗
→TWT→SSLSS

1. D. Yamauchi, N. Sato, and Y. Morita, An ExperimentalStudy on the Relationship between the Components andMovement of the Human Knee Using an Android Model- Measurement of Internal-External Rotation andAnterior-Posterior Tibial Translation -, in Procs. of Int.
Conf. on Control, Automation and Systems 2015
(BEXCO, Busan, 2015), pp. 811–815.
2. K. Sanaka, Android with Biological Structure for
Supporting Medical Technology, in Tokai-Section Joint
Conference on Electrical, Electronics, and Related
Engineering (Shizuoka Univ., Hamamatsu, 2013), S2-5.
(in Japanese)
3. S. Ishii and S. Yamamoto, Kinematic Analysis of Screw
Home Motion with Active Knee Extension in the NonWeight Bearing Position, in Rigakuryoho Kagaku, 23(1)(2008), pp. 11–16. (in Japanese)
4. I. A. Kapandji and E. Shiota (trasl.), Physiology of theJoints: Volume 2 Lower Limb, 6th edn. (Ishiyaku
Publishers, Inc., Tokyo, 2010), pp. 108–129. (inJapanese)

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