Literature Review
Nilay Barde
Contents
Literature Review .......................................................................................................................................... 1
Factors that Cause ACL Injuries in Contact Sports .................................................................................... 2
Biology of the ACL ..................................................................................................................................... 3
Types of Braces ......................................................................................................................................... 5
Existing Injury Prevention Braces.............................................................................................................. 6
Applied Force and Angles Data ............................................................................................................... 10
Engineering Plan ......................................................................................................................................... 12
Engineering Problem............................................................................................................................... 12
Engineering Goal ..................................................................................................................................... 12
Procedure................................................................................................................................................ 12
References: ................................................................................................................................................. 13
Factors that Cause ACL Injuries in Contact Sports
The rate of anterior cruciate ligament (ACL) tears has been continuously increasing every
year in contact sports such as American football (LaBella, 2014). This injury occurs when the
knee hyperextends and pivots at the same time, for example, when someone changes direction
while their foot is planted (Wedro, 2016). The angle and force at which the athlete is hit can have
an effect on how severe the injury will be, as well as the type of field they are playing on and the
shoes they are wearing grass (Geier, 2013). In a study done by the National Football League,
found that the injury rate of ACL sprains were sixty-seven percent higher on FieldTurf than on
grass (Geier, 2013). A quick motion in the knee or the ankle while stuck in a hole can cause a
very severe injury. More than 70% of ACL injuries are caused by a non-contact blow to the knee
joint (Kiapour, 2014). Non-contact ACL injury processes are multi-planar, involving the
tibiofemoral joint (a joint positioned between the tibia and the femur) connected in all three
anatomical planes, sagittal, coronal, and the transverse (Kiapour, 2014). According to Kiapour,
there have been past studies that show that combined multi-planar loading including anterior
tibial shear, knee valgus and internal tibial rotation to be the primary mechanism for non-contact
ACL injuries. Figure 1 shows the rotations on the leg that would tear an ACL.
Figure 1: This is a diagram of the knee and the leg showing the rotations explained above that occur during most ACL tears.
(Kiapour, 2014)
Biology of the ACL
The bone structure of the knee joint is formed by the femur, tibia, and the patella. The
anterior cruciate ligament (ACL) connects the femur to the tibia. The knee is held together by the
medial collateral (MCL), lateral collateral (LCL), anterior cruciate
(ACL) and posterior cruciate (PCL) ligaments (Provencher, 2010) as shown in Figure 2 . The
ACL runs diagonally across the knee and provides rotational stability for the knee. When the
torque on this joint is too high, this ligament can tear. The ACL tends to be torn when the athlete
hyperextends the knee or twists the joint. The risk of injury is even greater when these motions
are combined. The ACL will not heal on its own, and surgery is necessary to repair the ligament
(Kiapour, 2014). Even with surgery, recovery takes on average 378 days (Olson, 2016). But even
then, these athletes may never be able to play at the same level as they did before. About eighty
percent of players who tear an ACL are able to return to play and most of the athletes that do are
only able to get up to eighty percent of their performance back from before the injury (Olson,
2016).
Figure 2: This is a diagram of the knee and the different ligaments that make up the knee (Knee Muscle Anatomy Diagram Leg
Knee Muscles Diagram System Anatomy Body Diagram, 2016)
The diagnosis of ACL injuries can be assessed by performing the Lachman test, where
the ACL is tested to see how it reacts to an anterior tibial translation in 20 to 30 degree flexion
while the knee is stabilized (Laskowski, 2014).
Figure 3: This is a diagram of the Lachman test being done on the knee. A hyperextended movement relative to the opposite
knee or a noticeable end point will determine a positive result (Medical Dictionary, 2009 Farlex and Partners)
Types of Braces
There are three main types of braces that are used for the knee, rehabilitation braces,
functional knee braces (FKB), and prophylactic knee braces (PKB). The FKB are designed to
provide stability in an unstable knee joint. Prophylactic knee braces (PKB) are designed to
prevent and reduce the severity of a knee injury. A Functional Knee Brace helps athletes with
ACL and PCL problems avoid further injuries in both non-weight-bearing and weight-bearing
situations (Jensen Maria, 2014). Prophylactic knee braces have an overall positive effect by
reducing the rate of knee injuries (Jensen Maria, 2014). Some PBK’s reduce forward speed and
agility. Off the shelf prophylactic braces provide 20 to 30% greater resistance to a lateral blow in
full extension (Jensen Maria, 2014). However, a prevention brace may slow down straight-ahead
sprinting speed, cause early fatigue, increase energy expenditure, etc (Jensen Maria, 2014). This
is the reason why many athletes do not like using these types of braces for in-game play.
Existing Injury Prevention Braces
Cable Knee System Brace:
The cable system brace acts very similarly to the natural motions of the ACL and MCL.
The cables are wrapped around the knee joint such that it resists the forces that cause
hyperextended joint movement and injury to the knee ligaments. As the leg travels through the
range of motion, the cables provide support to prevent the tibia bone from moving forward
(hyper extending) or twisting (lateral rotation) and or laterally bending with respect to the femur.
For a knee brace to be effective in resisting the hyperextended movements of the knee joint that
tear the ACL and or MCL, it must provide a differential force to the tibia relative to the femur
(Fleming, 2011). Because of the large amount of flesh surrounding the tibia bone and femur bone
the only way to prevent the leg from hyperextending or over rotating would be to have a firm
grip on these bones with some sort of mechanical instruments such as screws (Fleming, 2011).
This system can also be applied to other existing braces to increase their effectiveness.
Figure 4: This is a diagram of the Cable Knee Brace showing the main components of the brace (Fleming Darren, 2011)
Four-Point Anterior Cruciate Ligament Brace:
The four-point anterior cruciate ligament knee brace externally replaces the function of a
torn anterior cruciate ligament. The brace has femur and tibia levers hinged proximal to the knee
joint in order to help with the movement. In order for the brace to be effective, it needs to
embody a novel four-point leverage system that applies a force to the femur and tibia in such a
way that it is able to function like an ACL. (Mason B, 1987). According to the four-point
anterior cruciate ligament brace patent, one of the factors needed to establish leverage for a
working external replacement of an ACL is the use of a brace with bicentric and geared hinges
on both the lateral and medial sides of the knee. A bicentric hinge is a counterbalance hinge that
will eliminate pressure at the joint.
Figure 5: This is a diagram of Four-Point Anterior Cruciate Ligament Brace showing the main components of the brace (Mason
B, 1987)
Orthopedic Device for Dynamically Treating the Knee (PCL):
One of the inventors of this patent wrote that the Orthopedic device for dynamically
treating the knee is, a brace with a central axis and a frontal plane which intersects the central
axis to divide the brace. A knee brace that provides support to the back of the upper calf through
ranges of motion may be used to prevent harmful shifting. Many times PCL tears are not
surgically treated. A common form of treatment is to allow the PCL to heal on its own. When a
PCL is torn, the proximal end of the tibia usually shifts posteriorly which causes strain on the
healing PCL, and results in a healed PCL that is longer than it was before the injury. If a brace
could apply an external force to the posterior calf, in the correct amount, it would be able to have
the forces necessary to effectively co-locate the femur and tibia. Even for patients who have had
a previous PCL injury and experience joint laxity because they decided not to have surgery for
their knee, this brace may also provide enhanced stability and confidence to the knee. This
orthopedic device would allow for a stronger knee and an overall better body. (Ingimundarson,
2013)
Figure 6: This is a diagram of Orthopedic Device for Dynamically Treating the Knee showing the main components of the brace
(Ingimundarson Arni, 2013).
Low Profile Knee Brace:
The low profile knee brace is hinged and it provides support to the wearer who has
injuries to their ligaments. The brace has an upper component that is formed to fit around the
thigh of the person wearing the brace. The brace also has a lower component that is formed to
custom fit the calf of the user. Both the upper and lower components are connected by a
continuous liner. Between the upper and lower components are inflexible rigid members
constructed of a lightweight, yet durable material to provide strength and rigidity to the brace.
This brace is very low-profile so it can be worn underneath clothing. A multitude of straps on
this brace are used to create a maximum comfort for the wearer. The goal of this brace was to
lower the base profile while still making a formidable brace for ACL therapy.
Applied Force and Angles Data
A Quality Function Deployment study was done which found that the force needed to
cause an ACL tear is between 1700 N to 2200 N and is limited to a solid angle of about nine
degrees (Porumbescu, 2016). The ACL’s tensile force is about 38 N/ mm2, so in order for a brace
to be effective, it must be able to reduce an impact force to below this (Porumbescu, 2016). For a
brace to be successful in preventing an ACL tear it must be able to protect the knee from a force
of at least 2200 N of force.
In a brace designed by Porumbescu, two airbags are deployed (above and below the
knee) which will reduce the load on the wearer’s ACL to far below the ACL’s tensile strength of
38 N/ mm2. Also, the airbags will only deploy when the measured actual force exceeds the limit
only within a certain angle of motion. There are six accelerometers attached to the brace to detect
the forces acting on the knee joint and an electronic device to calculate the force applied to the
ACL and the direction of the applied force. When the force exceeds the limit, the airbags will
deploy and make the leg bones move in opposite directions which will prevent any twisting or
turning of the knee.
Engineering Plan
Engineering Problem
Anterior cruciate ligament tears occur about two-hundred thousand times per year and are
continuously increasing each year. Athletes that suffer this injury have a long recovery time
which forces them to be away from their respective sport. The injury may even force the athletes
to retire from their sport early.
Engineering Goal
The goal of my project is to engineer a brace that will prevent anterior cruciate ligament tears in
athletes more effectively than the current prevention techniques do. The brace will greatly reduce
the amount of stress on the knee.
Procedure
Development
A brace design was developed using published data about the forces and angles at which anterior
cruciate ligament tears occur. This design showed how the brace would fit on the knee and what
parts of the knee needed the most support in order to prevent ACL tears. Next, the brace was
created using neoprene, elastic material, Velcro, carbon fiber, and foam. Finally, the prototype
brace underwent numerous tests to see if it was strong enough to be effective. During this phase
the brace was improved using the data from the tests. This final phase was repeated in order to
fix new problems and optimize brace performance.
Design Criteria
The criteria that were important in this project were: lower ACL tear rates, high comfort, low
cost, and ease of use.
Testing
The brace was tested by putting applying force on the brace at different angles. The brace was
put on a model knee to simulate the motion of the knee during this process.
References:
Fleming Darren, inventorCable Knee Brace System. April 4, 2011.
Geier David. Ask dr. geier: Are ACL tears more common on grass or FieldTurf?. English
Journal. 2013. http://www.drdavidgeier.com/ask-dr-geier-acl-tears-on-natural-grass-orfieldturf/.
Ingimundarson Arni, Romo Harry, Omarsson Bjorn, Chetlapalli Janaki, inventorsOrthopedic
Device for Dynamically Treating the knee.
Jensen Maria, Kersting Uwe. Anterior cruciate ligament reconstruction. . 2014.
http://lib.myilibrary.com?ID=635343. doi: 10.1007/978-3-642-45349-6.
Kiapour AM, Murray MM. Basic science of anterior cruciate ligament injury and repair. Bone &
joint research. 2014;3(2):20-31. http://www.ncbi.nlm.nih.gov/pubmed/24497504. doi:
10.1302/2046-3758.32.2000241.
Knee Muscle Anatomy Diagram Leg Knee Muscles Diagram System Anatomy Body Diagram.
(2016, August 19). Retrieved November 21, 2016, from http://www.anatomydiagram.info/knee-muscle-anatomy-diagram/knee-muscle-anatomy-diagram-leg-kneemuscles-diagram-system-anatomy-body-diagram/
LaBella CR, Hennrikus W, Hewett TE. Anterior cruciate ligament injuries: Diagnosis, treatment,
and prevention. Pediatrics. 2014;133(5):e1450.
http://www.ncbi.nlm.nih.gov/pubmed/24777218. doi: 10.1542/peds.2014-0623.
Lachman test. (n.d.) Farlex Partner Medical Dictionary. (2012). Retrieved December 5 2016
from http://medical-dictionary.thefreedictionary.com/Lachman+test
Laskowski ER. ACL injury and rehabilitation. Current Physical Medicine and Rehabilitation
Reports. 2014;2(1):35-40.
Mason B, Mason J, Cawley P, inventorsFour-Point Anterior Cruciate Ligament Brace.
Olson Jeremy. NFL players with ACL injuries face uncertain recovery, shortened careers. TCA
Regional News. Aug 31, 2016. Available from:
http://search.proquest.com/docview/1815501908.
Porumbescu Aureliu. EBM resource center. . 2016.
Provencher M, Mologne TS, Bach B. ACL surgery. SLACK Incorporated; 2010. http://replaceme/ebraryid=10801944.
Seligman Scott, inventorLow profile knee brace and method of using same. Sept, 2006.
Wedro B. Source: http://www.medicinenet.com/script/main/art.asp?articlekey=121702. . 2016.