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Journal of Orthopaedic Sports Physical Therapy
2OOl;3l(ll):655-66O
n
Proprioceptive Training and Prevention of
Anterior Cruciate Ligament injuries
G.
Cerulli
MD s
D.
I Benoit
MScl
A.
Caraffa
MD1s2
Ponteggia
MD3
--- - --,,- 7 *-. , ..-.
-*.,-. .
This commentary describes a program developed to help reduce the incidence of anterior
cruciate ligament injuries in soccer players The basic principles underlying the injury
prevention protocol are described with respect to the proprioceptive control mechanisms at
the knee joint This is followed by a detailed description of the program Orthop Sports
Phys Ther .?OOl;3 :655 660.
ey
Words: injury prevention knee joint proprioception
n our experience, the anterior cruciate ligament (ACL) injury
rate of soccer players not trained in injury prevention is 1.15 per
team per season compared to players trained with a propriocep
tive training program (0.15; < 0.001) in groups matched for
practice and game exposure over 3 years.' Not surprisingly, the
ACL injury causes the greatest financial expense and highest number of
player days missed in the sport.'*JJ s in most sports, ACL injuries in
soccer occur from both contact and noncontact situations. Most ACL
injuries occur between 0 and 30 knee flexion,SzJ primarily in noncon-
tact situations during running and jumping. In running, the move-
ments associated with the injury include change of direction, rapid de-
celeration, spontaneous stopping, and torsional movements. In j u m p
ing, the movements include landing with varus and internal rotation
stress or valgus and external rotation stress.
Currently there is little research that identifies the critical phases of
these movements that cause injury. However, recent advances with in
vivo ACL strain measurement during rapid deceleration have confirmed
that the rapid deceleration movement, such as when a player unexpect-
Let People Move Biomechanics Laboratory Perugia Italy.
Department of Orthopaedic Surgery University Hospital of Perugia Italy.
Lecturer Physical Medicine and Rehabilitation University of Florence Italy.
Send correspondence to Daniel Benoit Let People Move Via G.B. Pontani
9
Perugia Umbria
06
128
Italy. E-mail: [email protected]
edly stops, causes a high level of
strain on the ACL, which initiates
at foot contact when the leg is
most e~ te nd ed .~lthough this
study confirms that the ACL will
be
in high stress situations during
sports, the point at which injury
may occur is still unknown. The
injury mechanism is triggered
through an interaction of kine-
matic and kinetic variables that, by
definition, can only be altered by
changing either the external or
internal forces acting on the body.
In a noncontact injury situation,
the external forces may be altered
by shoe-playing surface interface,
as this is the only point at which
an external force may act on the
body. The internal forces are gov-
erned by bone on bone forces, lig-
ament and soft tissue, and mus-
cles. Muscle contractions generate
the forces acting on the bones,
which alters the position of body
segments and also greatly affects
joint stiffness. When referring to
alterations of postural control or
body position, it thus implies an
associated alteration in neuromus-
cular control.
C o p y r i g h t © 2 0 0 1 J o u r n a l o f O r t h o p a e d i c & S
p o r t s P h y s i c a l T h e r a p y ® . A l l r i g h t s r e s e r v e d .
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PROPRIOCEPTION ND THE KNEE JOINT
In ord er to describe the proprioceptive system, we
must first discuss the issue of proprioception. A pro-
prioceptor may be described as a sensory receptor
that can detect stimuli generated by the system it-
self. Many authors have demonstrated the existence
of mechanoreceptors and free nerve endings in sev-
eral parts of the knee joint. These receptors provide
the basis for the proprioceptive feedback system that
would allow adaptive changes to occur during pre-
ventive training programs, thus helping in the pre-
vention of knee injuries during sports. For a proprio-
ceptive training program to function, the premise is
that adaptations will take place based on the stimuli
the proprioceptors receive during or prior to initia-
tion of the deleterious movement. This information
will alter the possibly programmed response in a
manner that modifies the mechanical conditions act-
ing on the ACL. For this to occur, the injury mecha-
nism, or pattern of movement, must be recognized
by the sensory control system as deleterious. A cor-
rective response must then be initiated to modify the
movement of the involved limbs in a way that reduc-
es or alters the stresses applied to the ACL by apply-
ing a different movement strategy. This implies an al-
tered neuromuscular response, as the only way to al-
ter a movement pattern is to modify the internal
forces applied to the system, that is, by changing
muscle activation patterns.
Currently in the literature, the evidence supports 2
main views of where the corrective response may be
initiated:
(1)
via peripheral feedback from sensory
receptors or (2) based on preplanning through the
central nervous system.Vt is beyond the scope of
this commentary to discuss these views; however, a
theme common to both views is that training may al-
ter the neuromuscular response to unexpected per-
turbations. This indicates that, in some way, the feed-
back derived from sensory input may be modified to
alter neuromuscular response. It is possible that the
structures within the ACL9.'R.242H.x'nd soft tissues
within and around the knee jointl.H.10.1W. .2(i.27.21) may
provide sensory information that could contribute to
the proprioceptive system.
PROPRIOCEPTION ND THE NKLE JOINT
Along with the knee, the ankle is an important
joint to consider in the prevention of ACL injuries,
as it will have a direct influence on tibial orientation
and, thus, the position of the ACL. Freeman and
Wyke14 found type I, 11, and receptors in ankle
joint capsules and type I, 111, and receptors in an-
kle ligaments in cats. Lynch et al tested 10 unin-
jured subjects with a tilt platform to reproduce quick
ankle inversion and plantar flexion by recording
muscle contraction latency with surface electromyog-
raphy. The results showed that increasing the range
of motion of plantar flexion-inversion augments the
latency response of the peroneus muscles, while in-
creasing inversion velocity reduces the latency time
in these same muscles. Sheth et alJ1used surface
electromyography to investigate the effect of proprio-
ceptive training on the activation pattern of ankle
muscles during simulated ankle sprains in nonim-
paired subjects. They concluded that 8 weeks of exer-
cises on an ankle disk (15 minutes per day) led to
selective modulations in the sequence of muscle con-
traction. The pretrained athletes showed simulta-
neous activation of anterior and posterior tibialis,
peroneus longus, and flexor digitorum longus mus-
cles, whereas in posttraining there was delayed activa-
tion of the inversion muscles, thus allowing the pero-
neals to counteract the sprain.
These studies demonstrate the importance of using
ankle disk exercises in an injury prevention training
program. Exercises on a disk cause quick ankle
movements that may be similar to those occurring
prior to or at the time of injury. This sensory input
may lead to improved kinesthesia (sense of move-
ment) and proprioception (sense of position), fac-
tors that may be important for injury prevention.
Based on the information described here, we de-
fine a preventive proprioceptive training program as
a series of exercises o r situations that will elicit a re-
sponse from the nervous system in order to counter-
act external stimuli. The program must be progres-
sive and include both situations controlled by the
athlete and those that change based on extrinsic fac-
tors. For example, directional changes elicited by
coaching instructions or bases of support disturbed
at random intervals are both situations that necessi-
tate a neuromuscular response to effectively counter
the stimuli.
TR INING ND PREVENTION
Knee joint alignment is directly affected by the
kinematics of the hip and ankle joints. For example,
sensory feedback and motion control at the foot and
ankle will directly affect tibial loading and orienta-
tion, thereby predetermining the condition in which
the ACL will be loaded. It is, thus, possible for knee
injury prevention to be initiated not at the knee but
at the ankle. The same situation is present with re-
spect to the hip and femoral loading and orienta-
tion. Postural control following a perturbation or in
preparation for movement of a nonrelated segment
is not limited to the lower limb; instead, it is con-
trolled by a complex interaction of anticipatory and
preparatory contractions also seen in the arms and
trunk muscle^ ^^^ Horak and Nashner17 have found
that altering the base of support from a normal sur-
face to one that is short in relation to foot length
will cause the control strategy to shift from the ankle
C o p y r i g h t © 2 0 0 1 J o u r n a l o f O r t h o p a e d i c & S
p o r t s
P h y s i c a l T h e r a p y ® . A l l r i g h t s r e s e r v e d .
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TABLE
Proposed training program.
Training
level lmtructiom Frequency
Level 1 Balance training without a 2.5 min 41d 3lwk
board 1-legged stance on the
ground)
Level
2
Balance training on a rectangu- 2.5 min 41d 3lwk
lar balance board each leg
alternately)
Level 3
Training on
a
round board 2.5 min 4/d 3lwk
Level 4 Training on a combined round 2.5 min 4ld 3/wk
and a rectangular board
Level 5 Training on a multiplanar board 2 5 min 4ld 3lwk
to the hip, respectively, as well as the base of s u p
port. Therefore, any training for the prevention of
knee injuries must take into consideration these oth-
er links in the kinetic chain of the lower limb, s
well
s
upper body postural control mechanisms.
Muscle fatigue seems to induce proprioceptive de-
teriorat i~n.~. ' ~herefore, the training program
must also include enough exercise sequences to elicit
fatigue and train these responses. Hamstring activity
appears to help reduce anterior tibia1 displacement
at certain joint angles and should also be stressed
during the training program. Further evidence of the
important role of the hamstrings may be deduced
from the fact that there is a greater latency of muscle
contraction in ACMeficient knees compared not
only with control groups of nonimpaired subjects,
but also with the uninjured contralateral side in the
same patient. The correlation between latency and
functional instability (frequency of giving way) in pa-
tients with ACL deficiencyJ insinuates that this func-
tion could play a protective role. Evidence that the
reflex hamstring contraction latency time can be re-
duced by performing proprioceptive exercises with
the aim of improving speed and facility of hamstring
contractions further supports the principles of injury
prevention training. A training program including
weight-bearing exercises and a progressive reduction
in stability (wobble board, eyes open and then
closed) with increasing repetitions and rate of con-
tractions appears better than a traditional program
of muscle strengthening (non-weight-bearing and
graduated weight-resisted exercises) in improving re-
flex hamstring contraction latency and dynamic joint
stability2 A functional exercise program (training of
leg muscles while bearing weight and of trunk mus-
cles to improve coordination, postural reactions, and
endurance) also appears to improve standing balance
in patients with ACL deficiency.%
Proprioceptive training must be performed
throughout the range of joint motion; this is impor-
tant because the mechanoreceptors seem to be acti-
vated selectively at specific angles.20Muscle receptors
play a primary role in the intermediate range of mo-
tion, while joint receptors and muscle receptors are
FIGURE
1. Step-downs off of the training board.
more important in the extreme ranges of motion.
Muscle training focused on building endurance,
strength, and power is important along with the pro-
prioceptive programs. Hewett et all demonstrated
the importance of plyometric training in preventing
knee injuries in female athletes, reducing the injury
rate from 0.43 per 1000 exposures to 0.12 P
0.05), following a &week jump training program. A
Swedish study by Tropp et al,3%owever, demonstrat-
ed that coordination training might help to prevent
functional instability, reducing the frequency of ankle
sprains in athletes with previous ankle injury. The
training program was composed of exercises per-
formed on a disk with a spherical undersurface, with
one leg straight and the other raised and flexed at
the knee while the arms were placed over the chest.
The training time was 10 minutes
5
times weekly for
10 weeks, then 5 minutes 3 times weekly; the length
of the study was 6 months. Comparing proprio cep
tively trained and control groups, both composed of
players with previous ankle problems, the difference
in reinjury was significantly lower in the trained
group (5% vs. 25%;
P
0.01).
Following these same principles, our group applied
similar methods to determine if it is possible to re-
duce the incidence of ACL lesions in soccer players
by adding proprioceptive exercises to traditional train-
ing programs. In a prospective controlled study by
Caraffa et a17 of 600 soccer players (semiprofessional
or amateur teams), we evaluated the possible preven-
tive effect of gradually increased proprioceptive train-
ing during 3 soccer seasons. A control group of 300
J Orthop Sports Phys Ther Volume
3
.Number l .November 2 1
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FIGURE
2. Example of the proprioceptive neuromuscular facilitation ex
ercises.
players w s trained traditionally, without specific bal-
ance exercises, while the experimental group of 300
players followed a proprioceptive training program.
During 3 soccer seasons, 10 arthroscopically verified
CL
lesions occurred in the proprioceptively trained
group , while 70 were recorded in the traditionally
trained group P 0.001). The training program
used in this study, and today, is described below.
The experimental gro up was instructed to train 20
minutes per day, with 5 levels of difficulty (Table).
Each phase of training was performed for 3 to
6
training days, depending on proficiency, and all
FIGURE 4.
Use of multiplanar board along the oblique axis.
training sessions lasted for a t least 30 days. The ath-
letes had to demonstrate proficiency in each phase
before progressing to the next level. This was selfde-
termined based on the instruction that they could
perform the exercises without the need for addition-
al support (the other foot or hand) in a consistent
manner and without fear of falling.
In addition, the subjects were instructed to per-
form anterior and posterior u ps te p exercises while
standing on the training board. F this exercise, the
subjects used the free leg to step off of the board,
barely touching the floor with the free foot, and
then returned to the standing position (Figure
1 .
This was repeated in a controlled manner and forced
the subject to maintain balance over a wide range of
knee joint angles. All subjects also took part in p r e
prioceptive neuromuscular facilitation exercises for
the lower limb, assisted by a trained technician (Fig-
ure
2).
These proprioceptive neuromuscular facilita-
tion exercises were performed as part of the regular
FIGURE 3.
Multiplanar board configuration.
stretching routine during practice sessions. The tech-
nician performed these knee and hip exercises on
J Orthop Sports Phys Ther-Volume 3 Number -November 2 1
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FIGURE 5 Increased training difficulty with 2 boards.
the subjects with the subjects in a supine position,
and the exercises included passive movements of
flexionextension, internal-external rotation, abduc-
tion-adduction movements, and combinations there-
of. The subjects were then asked to reproduce these
same movement patterns unassisted active move-
ments). These exercises were meant to increase sub-
ject awareness of limb position; however, this effect
was not measured or quantified.
The subjects were also instructed to follow a modi-
fied version of the neuromuscular facilitation pro-
gram described by Hervkou and Mksskan.I5 This con-
sisted of using both a circular and a rectangular
board. The rectangular board, with
spheres placed
obliquely o r along its longitudinal axis, allowed for
movement along 3 axes Figure 3) , depending on
the patient starting position and sphere placement.
The subject was instructed to perform forward lung-
es with deep knee bends using the rectangular board
along all 3 axes. The subject had to maintain the po-
sitional alignment of the knee above the foot no in-
ternal or external rotation of the hip and control of
foot pronation and supination) Figure
4).
The de-
gree of difficulty was increased by stepping off of a
raised height eg, a stair) ont o the board and per-
forming the lunge to maximal knee bend. The sub-
ject would then perform the exercise by stepping off
of the circular board, keeping the trailing leg on it,
ont o the rectangular board, or vice-versa Figure
5).
Although not part of the original prevention pro-
gram, additional tests may be added to further in-
crease the degree of difficulty. These movements
could place the athlete in safe but unstable situations
that mimic the movement patterns known to cause
injury, such as hopping onto the training board, thus
training the athlete to adapt to unexpected situations
Figure
6).
FIGURE 6 Increased difficulty by hopping onto the training board.
CONCLUSIONS
Our previous results have indicated the potential
to reduce the incidence of CL injuries in soccer
players; however, more work is necessary to optimize
these prevention protocols. multifaceted approach
should be applied and customized based on the
needs of the athlete. The goal is to provide an inter-
esting and challenging routine that puts the athlete
in situations that force a reaction to expected and
unexpected changes in the environment. Using the
techniques described, along with other innovative a p
proaches, we believe that the incidence of CL inju-
ries in soccer players can be reduced.
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