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P r o c e d i a E n g i n e e r i n g 6 0 ( 2 0 1 3 ) 3 0 0 – 3 0 6
1877-7058 © 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.
Selection and peer-review under responsibility of the School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University
Avai lab le on li ne at www.s cie nc edire ct .com
Asia-Pacific Congress on Sports Technology (APCST)
The effect of a knee-ankle restraint on ACL injury risk
reduction during jump-landing
Phillis S. P. Teng
*, K.F. Leong
, P.Y. Huang
, J. McLaren
Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Institute for Sports Research, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Received 20 March 2013; revised 6 May 2013; accepted 9 May 2013
Anterior cruciate ligament (ACL) is the most commonly injured ligament. It has a great impact on athletes causing
long absence from play and is linked with increased risks of osteoarthritis. Today, literature suggests that the knee
braces may not completely reduce ACL injury mechanism risks. Ankle braces, on the other hand, have shown
promising results in some of these aspects. Thus, the purpose of this research is to study the effectiveness of a knee-
ankle brace restraint in reducing ACL injury risks by increasing knee flexion and reducing knee valgus angles.
Eighteen healthy Asian male subjects performed a drop vertical jump maneuver from a 31cm platform. A motion
analysis capture was carried out to measure the knee flexion and knee valgus angles. Results show that the effect of a
knee-ankle brace restraint was insignificant in increasing knee flexion and in reducing knee valgus angles at initial
contact and at peak vertical ground reaction force (VGRF). While the ankle brace showed some trends of increasing
knee flexion angles at initial contact, the effect was insignificant. Similarly, the ankle brace did not show significant
effects on knee flexion angles at peak VGRF and on knee valgus angles at both instances. The knee brace had little
effect on knee flexion angles but showed significant effects on valgus angle increase. In conclusion, a knee-ankle
brace restraint was not found to have an effect on reducing ACL injury risks during jump-landing. Ankle brace use
did not adversely increase ACL injury risks but has shown weak effects in reducing the risks. The knee brace used in
this study was not found to be suitable for reducing valgus angles.
© 2013 Published by Elsevier Ltd. Selection and peer-review under responsibility of RMIT University
Keywords: Anterior cruciate ligament; knee brace; ankle brace
* Corresponding author. Tel.: +65-6790-4192 ; fax: +65-6792-4062.
E-mail address: email@example.com.
© 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.
Selection and peer-review under responsibility of the School of Aerospace, Mechanical and Manufacturing Engineering,
Phillis S.P. Teng et al. / Procedia Engineering 60 ( 2013 ) 300 – 306
Knee injuries are approximated to contribute up to 60% of all sport injuries . Ligament injuries are
the most common knee injuries (40%) and the anterior cruciate ligament (ACL) is the most frequently
injured ligament (46%) . Approximately 200 000 injuries take place in the United States yearly  and
surgery costs amounts to beyond $2 billion . For athletes, sustaining an ACL injury also has a
significant impact on their careers, resulting in long absence from play [5,6]. Mean time to return to
competitive play is almost 8 months after operation [5,6]. It also takes 5.2±3.6 years for athletes to reach
pre-injury performance . Injured athletes also have higher risks of developing osteoarthritis in the long-
An ACL injury frequently occurs under a non-contact condition  when there is no contact with other
players or objects . Video analyses have observed extended knees with less than 30º of knee flexion [9-
12] and knee valgus collapses just prior injury [11,12]. Low knee flexion angle  and high knee valgus
 are thus often associated with higher ACL injury risks. These injury mechanisms are often used to
study the effectiveness of preventive training programmes  and knee brace use [16,17]. They are also
used in this study to investigate the effectiveness of the knee-ankle restraint on ACL injury risks.
Knee braces have been used to prevent knee injuries  but the evidence of knee brace effect on the
ACL is still inconclusive . A large and well cited prospective, randomized study of 1396 cadets at the
U.S. Military Academy was conducted by Sitler et al. in 1990 . Although there were fewer ACL
injuries in the group that wore the prophylactic knee braces (PKBs) than in the control group, sample size
was not large enough for a statistical analysis . Severity of ACL injuries was also not significantly
reduced with the use of PKBs . One other study showed an increase in knee flexion angles during
stop-jump with brace use  but another study showed that brace use did not decrease ACL strain due to
valgus-varus moments . On the other hand, ankle restraints like ankle braces and foot orthotics have
shown some effect in reducing ACL injury risks despite not being designed for ACL prevention [20-22].
Ankle braces and foot orthotics were found to have an effect on the knee by increasing knee flexion 
and reducing knee valgus [21,22]. Thus, the purpose of this research is to study the effects of the knee and
ankle brace restraint on ACL injury risk reduction. The study is also conducted on an Asian sample to
study the effects of brace use on this group.
2. Experimental methods
Eighteen male subjects (age = 23.2 ± 2.8 years old, height = 1.76 ± 0.06m, weight = 71.6 ± 6.5kg)
volunteered for this study. Participants have no prior ACL injuries. The test protocol and the use of
human subjects were approved by the Institutional Review Board of the university. All participants also
signed a written consent form.
Retroreflective markers were placed on the sacrum, anterior superior iliac spine, greater trochanter,
mid thigh, medial and lateral knee epicondyles, tibial tuberosity, mid shank, medial and lateral malleoli,
heel, fifth metatarsal and toe (between second and third metatarsals) of the right leg. The anterior superior
iliac spine, greater trochanter, lateral knee epicondyle, medial and lateral malleoli, heel and toe (between
second and third metatarsals) were also placed on the left leg for comparison of data and for the
estimation of the hip joint location. A motion analysis system consisting of 7 digital cameras (Motion
302 Phillis S.P. Teng et al. / Procedia Engineering 60 ( 2013 ) 300 – 306
Analysis Corp, Santa Rosa, CA, USA) was used and sampled at 240Hz. Two force plates (AMTI, Boston,
MA, USA) collected the ground reaction force (GRF) and a sampling rate of 1200Hz was used. This was
time synchronized with the motion capture. Motion capture data was collected using Cortex (version
188.8.131.528, Motion Analysis Corp, Santa Rosa, CA, USA) and was imported into Visual 3D (version
4.96.8, C-Motion, Germantown, PA, USA) for data reduction.
A knee and an ankle brace were used to provide the restraint at the knee and at the ankle. The knee
brace used was the Donjoy Legend knee brace (Djo LLC, Vista, CA, USA) and the ankle brace used was
the ASO ankle brace (Medical Specialties Inc, Charlotte, NC, USA). The Donjoy Legend knee brace was
fitted with the default 10º extension stop.
2.3. Test protocol
Subjects performed a drop vertical jump (DVJ) from a platform (31 cm in height) with their feet 35 cm
apart. ACL injuries commonly occur in jump-landing and cutting/side-stepping during sports  and
DVJ is commonly used to simulate maneuvers such as jumping and landing in basketball . Subjects
were asked to drop off a platform and land with both feet on the ground, each on a force plate. They were
then asked to immediately jump to as high as possible. Each participant performed jumps under four
conditions, namely the no brace condition, knee brace condition, ankle brace condition and a knee-ankle
brace condition. Brace was only applied to the right dominant leg. Participants were first given 5min for a
warm-up and were allowed practice trials before the start of the study. A standing trial was first recorded.
Following that, motion capture data of 3 successful trials of each condition were collected and an average
data was taken from the 3 trials. The sequence of conditions was randomized for each participant to
prevent any noise due to fatigue or boredom.
2.4. Kinematic and kinetic analyses
Knee flexion-extension and valgus-varus angles were recorded for each participant. Force plate data
was also collected to detect the initial contact with the ground. Marker and force plate data was filtered
through a low-pass Butterworth digital filter at a cutoff frequency of 9Hz and 50Hz respectively. Knee
extension and varus angles were denoted as positive. Initial contact was defined as the first point that
vertical ground reaction force (VGRF) exceeded 10N. The first jump from the platform was used for the
analysis. Cardan/Euler rotation sequence was used for the knee joint angle calculation using Visual3D
(version 4.96.8, C-Motion, Germantown, PA, USA).
2.5. Statistical analysis
A 2-way analysis of variance was conducted (factors ‘ankle brace’ and ‘knee brace’ conditions) with
repeated measures on both factors. The level of significance was at 0.05. Statistical analyses were
conducted using Minitab (version 16, Minitab Inc., State College, Pa, USA).
Phillis S.P. Teng et al. / Procedia Engineering 60 ( 2013 ) 300 – 306
3. Results and Discussion
Knee-ankle brace restraint using the knee and ankle brace use did not have a significant effect on knee
flexion both at initial contact (p = 0.572; Table 1) and at peak VGRF (p =0.077; Table 1). Knee-ankle
brace restraint also did not have a significant effect on knee valgus angles at initial contact (p = 0.332;
Table 1) and at peak VGRF (p =0.277; Table 1). This shows that wearing both the knee and ankle brace
did not seem to help reduce or worsen ACL injury risks.
Table 1. Anova Results of Ankle and Knee Brace Factors for Each Variable
Variable F-Test p
Knee Extension/Flexion Angle Initial Contact
Ankle Brace 2.25 0.140
Knee Brace 2.11 0.152
Ankle-Knee Brace Combination 0.32 0.572
Knee Extension/Flexion Angle at Peak VGRF
Ankle Brace 2.33 0.133
Knee Brace 2.31 0.135
Ankle-Knee Brace Combination 3.26 0.077
Knee Varus/Valgus Angle Initial Contact
Ankle Brace 0.72 0.400
Knee Brace* 26.79 < 0.001
Ankle-Knee Brace Combination 0.96 0.332
Knee Varus/Valgus Angle at Peak VGRF
Ankle Brace 0.15 0.704
Knee Brace* 11.59 0.001
Ankle-Knee Brace Combination 1.21 0.277
* Significant at g = 0.05
The use of the ankle brace alone was not found to have a significant effect on knee flexion angle at
initial contact as well (p = 0.140; Table 1). By contrast, a study by DiStefano et al. found an increase in
knee flexion angle at initial landing also with the use of the ASO ankle brace (Medical Specialties Inc,
Charlotte, NC, USA) during a DVJ from a 30cm platform . DiStefano et al. also showed that ankle
movements in the sagittal plane were reduced with the use of the ankle brace . A separate study by
Cortes et al. showed that heel-first landing resulted in more knee flexion angles at initial landing than toe-
first landing . Thus, the ankle brace constraint might have resulted in less forefoot landing and in turn
could be one reason for more knee flexion angles to be observed during initial contact. Subjects in this
study were also found to have significant reduction of plantar flexion with the use of the ankle brace (p <
0.001; Table 2). The main effect plot in this study (Figure 1) also shows an increase in knee flexion angle
when the ankle brace was worn. However, this effect was not found to be large enough unlike the result
found in the study by DiStefano et al. . Ankle brace effect was also not significant for knee flexion
angles at peak VGRF (p = 0.133; Table 1). Furthermore, the ankle brace also did not have any significant
304 Phillis S.P. Teng et al. / Procedia Engineering 60 ( 2013 ) 300 – 306
effect on knee valgus angles both at initial contact (p = 0.400; Table 1) and at peak VGRF (p = 0.704;
Table 2. Anova Result of Ankle and Knee Brace Factors on Ankle Plantar Flexion
Variable F-Test p
Ankle Flexion Angle Initial Contact
Ankle Brace* 19.66 < 0.001
Knee Brace 0.01 0.924
Ankle-Knee Brace Combination 0.93 0.340
* Significant at g = 0.05
YqtpPqv" Yq tp
Fcv c" Og c pu
Fig. 1. Main Effect Plot of Knee Flexion Angles at Initial Contact
Ankle braces are generally designed to constrain the ankle from inversion and eversion motion 
and are not designed for reducing the ACL injury risks. While this result seemed to show some increase
in knee flexion angle trends, the insignificant effect is not completely unexpected. However, results also
further supported that ankle brace wearing did not have an adverse effect on the knee based on knee
flexion and valgus angle results used in this paper. Neither did the ankle brace give rise to increased
valgus angles that would potentially result in increased ACL injury risks.
The use of the knee brace was also not found to have a significant effect on knee flexion angles at
initial contact (p = 0.152; Table 1) and at maximum VGRF (p = 0.135; Table 1). The default extension
stop of 10º was used. The average knee flexion at initial contact was already exceeding 10º without any
use of brace (Table 3). Therefore, this could be the reason for the effect of the knee brace to be
insignificant for increasing knee flexion angles. On the other hand, the knee brace was found to result in
significant increase in valgus angles both at initial contact (p < 0.001; Table 1) and at peak VGRF (p =
Phillis S.P. Teng et al. / Procedia Engineering 60 ( 2013 ) 300 – 306
0.001; Table 1). In a study by Fleming et al., the ACL strain was also not decreased with the use of the
Donjoy Legend knee brace (Djo LLC, Vista, CA, USA) under varus-valgus moments . Together, this
could suggest that the knee brace used in this study might not be suitable for reducing ACL injury risks
due to increased knee valgus.
Table 3. Means (Standard Deviations) of Variables at Different Conditions
Variable No Brace Knee Brace Ankle Brace Knee and Ankle Brace
Knee flexion angle at initial contact -26.79 (5.38) -26.10 (5.59) -28.41 (4.66) -26.83 (6.29)
Knee flexion angle at maximum VGRF -53.03 (7.76) -53.43 (9.67) -53.42 (10.75) -48.85 (9.94)
Knee valgus angle at initial contact 0.04 (3.00) -1.23 (2.95) 0.60 (3.11) -1.27 (2.76)
Knee valgus angle at maximum VGRF 1.12 (4.26) -0.24 (2.75) 1.99 (4.20) -0.66 (2.77)
Results of this study showed that the knee-ankle brace restraint was not effective in further reducing
ACL injury risks. The ankle brace, on its own, showed an increasing knee flexion angle trend during
initial contact. However, this effect was not significant. The knee brace did not show an effect on
increasing knee flexion angles. This could be due to subjects having knee flexion angles that were already
more than the extension stop of 10º in the knee brace default installation. This knee brace was also found
to have a significant effect in increasing knee valgus angles both at initial contact and at peak VGRF.
Thus, this brace might not be suitable in reducing ACL injury risks due to knee valgus angles.
The authors would like to thank Judy Ong from the National Institute of Education Singapore, for the
software support during the data extraction phase of this study.
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