Novel Design of an Anterior Cruciate Ligament (ACL) Injury Prevention
Brace
Authors: Rachel Porter, Justin Killewald, Dan Greenshields
December 18, 2013
Biomedical Engineering Program, Lawrence Technological University, MI 48075
ABSTRACT
Anterior cruciate ligament (ACL) injuries are serious and fairly frequent sports injuries.
In the United States alone 200,000 to 300,000 ACL injuries occur annually. More often than not,
ACL injuries occur with no contact from another athlete. Common ACL injury mechanisms
include: hyperextension, valgus bending, internal rotation of the tibia, anterior shear of the tibia,
and axial loading. While there are current knee braces on the market that are worn by athletes to
reduce their risk of ACL injury, these knee braces are designed primarily to prevent
hyperextension and valgus bending. Another type of knee brace commonly worn is an
osteoarthritis (OA) brace. These braces are worn by older patients with OA in one side of the
knee. The brace is classified as a unicompartmental offloading brace that reduces the
compressive load on the medial compartment of the knee. The goal of our project is to redesign
the hinge mechanism currently used in the unicompartmental offloading brace, which is
Donjoy’s FourcePoint hinge, so that our redesigned knee brace will protect not only against
compressive loading on the lateral compartment of the knee, but it will protect against
hyperextension and valgus bending. We also plan on filing a patent application related to the
brace’s lateral compartment offloading function, so as to protect the intellectual property of our
brace. We will be doing human subject testing without a brace, with Donjoy’s OA Defiance
brace, and with our redesigned knee brace to determine if our brace is successful in reducing
compressive load forces. The human subjects will be participating in trials where they will be
jumping off of a low platform onto force plates while wearing motion capture markers. We will
be measuring the ground reaction force, segment acceleration, knee angles and kinematics; those
values will be used to calculate the joint reaction force and moment about the knee.
Keywords
Knee brace, ACL, osteoarthritis, valgus bending, hyperextension, compression, unicompartmental
BACKGROUND
Knee anatomy
The human knee joint is regarded as the largest and most complex knee joint in the body.
The knee is comprised of four bones – the femur, tibia, fibula and patella. The distal end of the
femur is shaped by the medial and lateral condyles. These condyles contact the medial and
lateral plateau of the tibia. The femur and tibia act like a hinge joint, designating flexion and
extension as the primary ranges of motion. In addition to the bone structure, the knee is
comprised of many ligaments and soft tissue. The function of a ligament is to connect bone to
bone, for stabilization purposes and support. The medial collateral ligament and the lateral
collateral ligament are located on the exterior portion of the joint. The anterior cruciate ligament
and the posterior cruciate ligament are located in the synovial capsule of the knee. The medial
meniscus and the lateral meniscus act as shock absorbers for the joint and help disperse forces on
the knee. Each anatomical feature of the knee joint is essential to an effectively functioning
knee.
Knee Injuries
The knee joint is one of the most injured structures in the body, with an increased chance
of injury when sports are involved. Knee injuries account for nearly 60% of all sports related
injuries. Continuing, ligaments are the most commonly injured constructs (40%) and, of those
injuries, 46% of those injuries are to the ACL [3]. Knee joint injuries account for roughly 19-
23% of all joint related injuries. The medial meniscus, medial collateral ligament, and the
anterior cruciate ligament are the most frequently injured components of the knee [10]. Among
those structures injured, the anterior cruciate ligament is the most commonly injured construct.
ACL Injuries
The ACL is responsible for approximately 200,000 – 300,000 injuries annually in the
United States [2]. Such a great amount of injuries comes with a price beyond two billion dollars
in healthcare related costs [3]. The ACL can be injured in many different ways. Possible
mechanisms for injury include: internal rotation of the tibia, valgus bending, anterior shear of the
tibia, hyperextension, and axial loading. Internal rotation injuries result when the foot is planted
firmly on the ground while the rest of the body twists. Valgus bending injuries typically occur
when the foot is planted on the ground and the knee is hit from the lateral side. Anterior shear of
the tibia result from a force being applied to the knee from the front. Hyperextension causes
ACL tearing due to the extreme amount of tension that is put on the ligament when it’s stretched
beyond the normal anatomical range of motion. Axial loading of the knee joint has also been
shown to produce injuries to the ACL. In this case, the compressive load of an axial force causes
the tibia to slip forward. As described, it is understood that many ACL injuries occur without
contact. With the help of video analyses, it is observed that ACL injuries occur most commonly
in low flexion angle and high knee valgus conditions.
Epidemiology of ACL
Injury to the anterior cruciate ligament can be sustained from contact, yet injury can also
occur in non-contact conditions. In fact, one study found that 70% of ACL injuries occur
without contact. The same study examined injuries from high school soccer, basketball, and
volleyball players and found that 75% of ACL injuries occurred without contact [4]. In addition,
gender plays a vital role in the incidence of ACL injuries. One study found that women
competing in jumping or cutting sports are four to six times more likely to injure their ACL
compared to their male counterparts [5].
Existing ACL Braces
There are two classes of knee braces currently on the market – prophylactic and
functional knee braces. Prophylactic knee braces are used to prevent an injury from occurring.
On the other hand, functional braces are used in post-injury circumstances. Functional knee
braces are designed to substitute for damaged ligaments by providing additional support to the
knee joint. A study that reviewed the efficacy of prophylactic knee braces reports decreased
peak tension magnitudes and impulse responses on knee ligaments when wearing the brace [6].
The only clinically proven knee brace shown to reduce ACL strain is Donjoy’s Defiance brace.
The brace is a prophylactic brace, but can also be used post-injury as well. The brace protects
against valgus bending and hyperextension. The main component of the brace is the hinge
mechanism. The FourcePoint hinge which is located on the lateral and medial side of the knee
joint incorporates a series of resistance arms in the design. The resistance arms engage in the last
25° of extension and essentially make it more difficult to straighten the leg. The most ‘at-risk’
position for ACL tears is 0°-25° of flexion, so this brace reduces the time spent in the vulnerable
position, while also allowing other muscles and tendons to help stabilize the knee.
Existing OA Braces
Osteoarthritis is an articular disorder that affects tens of millions of United States
citizens. More specifically, approximately 9.7 million people have symptomatic osteoarthritis in
the knee joint [7]. Typically, the medial compartment of the knee joint degenerates before the
lateral compartment. This occurs as a progressive varus leg axis develops due to cartilage loss in
the knee [8]. To relieve pain in this type of circumstance, the medial compartment needs to be
offloaded. Fortunately, knee braces have been developed for people with this type of disorder.
Osteoarthritis braces act to distribute loads more evenly across the knee joint. The knee brace
performs this by creating a slightly valgus moment on the knee, reducing the pressure on the
medial compartment. This even distribution is known as unicompartmental loading.
Unicompartmental loading offloads the medial compartment and loads the lateral compartment
to a greater extent in osteoarthritis braces.
IMPLICATIONS
This knee brace design is novel in its field and has the potential to reduce the number of
ACL injured athletes. The brace will protect against three mechanisms that have been proven to
cause ACL injuries, whereas previous braces can only account for two components. The three
injury mechanisms that will be protected are valgus bending, hyperextension, and reduced
compressive forces during axial loading. Additionally, the benefits of this brace will reduce
healthcare costs related to ACL knee injuries and will decrease the amount of reconstructive
surgeries. Likewise, many professional and recreational athletes can have career ending ACL
injuries, so this will aim to increase the length of athletic careers.
DELIVERABLE
The deliverable of our project is to have developed a knee brace aimed for use in the
athletic industry. The knee brace will act to prevent ACL injuries caused from valgus bending,
hyperextension, and axial loading.
RESEARCH PLAN
IRB Application
The application for approval to conduct research with human participants was submitted
to the Institutional Review Board (IRB) for approval, along with a participant information sheet
and informed consent form. The participant information sheet is necessary because it gathers
information on previous or current injuries. It also includes information needed to use Vicon
Nexus for marker recording. Once IRB approval is obtained, subjects can sign the informed
consent forms and fill out the participant information sheet so that human subject testing can
commence.
Testing Parameters
A previous study that was done on one of Donjoy’s knee braces had 20 participants, 10
male and 10 female. All participants were recreational athletes. They performed a stop-jump
task with and without the knee brace they were testing. Three dimensional videography and
force plate data was collected. Upon landing, they determined the knee flexion angle, maximum
knee flexion angle, and the peak ground reaction forces [11].
The participants in this study will consist of one male and one female athlete who are
healthy and not injured. Athletes with previous or current lower extremity injuries, along with
athletes under the age of 18, will be excluded.
The first step in the data collection process with the participants is to attach markers and
input the measurements for weight, height, knee width, ankle width, and total leg length, as
mentioned in the Methods section of this report. Participants will then be fitted for the knee
brace they will be wearing for testing. This will take approximately 30 minutes and will be
completed in the Experimental Biomechanics Laboratory.
For each test we will be running five trials which will also take place in the Experimental
Biomechanics Laboratory. The first test will consist of our subjects doing stop-jump and jump
landing trials onto a force plate with and without a knee brace. We expect these trials to take
approximately an hour of our subject’s time. The knee brace used for these trials is an existing
knee brace already on the market. This will allow for comparison with the data from our
redesigned knee brace. The last test we will be doing is with our redesigned knee brace. Just
like in the previous trials, the subjects will be doing five stop-jump and jump landing trials off of
a low platform and onto force plates while wearing motion capture system markers. We may
repeat these trials weekly to test changes made in the knee brace.
The data that will be measured includes the ground reaction force and segment
acceleration. Those values can be used to calculate the joint reaction force and moment about the
knee. The data from the three different trials—jump landings without a knee brace, with an
existing knee brace, and with our redesigned knee brace will be used to determine if our brace is
successful in lessening the load to the lateral side of the knee during a jump landing. We will be
analyzing the data using Vicon Nexus and Polygon. From the five trials, the averages and
standard deviations will be taken to perform a t-test to determine if our data is statistically
significant.
While undergoing testing there will be possible risks to the participants because the
testing involves jump landings. Minor negative effects include fatigue, and major negative
effects include potential risk of injury. To minimize risks to the participants the testing will be of
short duration and will not be strenuous or outside of the normal ranges of motion for the body.
If at any time the subject feels pain or discomfort they are strongly encouraged to stop testing
immediately. They will be jumping from a low height and landing in a self-selected body
position.
Testing Setup & Procedure
There are many steps that must be taken in order to record motion in three dimensions.
The software program Vicon Nexus is the key program for making this recording. After data is
collected from Nexus, it will then be exported to Polygon for analysis and model representation.
The following steps illustrate the process for recording a “Plug-in Gait” experiment with an
additional forceplate.
Preparing Cameras and Nexus
1. Position eight cameras pointed toward the rectangular calibration area.
a. Connect each camera, using an Ethernet cable, to the Vicon MX-Giganet
controller.
2. Place the calibration wand and six individual markers in the center of the cameras,
designating the appropriate test area.
3. Begin Nexus and calibrate the program using the calibration wand. Adjust the cameras
so the calibration wand is visible in each camera’s field of view.
a. Remove the six individual markers from the floor after calibration is complete.
4. Mask out any unwanted reflections by clicking on the ‘System Preparation’ button
located in the Tools pane. Next, select ‘Create Camera Masks’ and click start. After it
has completed creating masks, click stop. The masked out area will be represented by
gray areas.
5. Recalibrate the entire test area using the ‘Calibrate Cameras’ section. Select the number
of frames to record to 1000 frames to ensure a large capture volume.
a. Move the wand around in front of each camera until each camera shows 1000
recorded frames. Refer to the ‘Calibration Feedback’ section for frame values for
each camera.
6. Refer to the Tools System Preparation pane and locate ‘Set Volume Origin’ tab. Click
‘start’ to begin; after a few seconds select the ‘Set Origin’ tab.
Experimental Procedure
1. Using Nexus, create an initial trial by selecting the ‘Data Management’ button. Select the
‘New Database’ button and select and create the template of choice.
2. Measure dimensions of the leg including:
a. Hip to knee length
b. Knee to ankle length
c. Knee width
d. Ankle width
e. Total leg length
3. Place reflective markers on the test subject and label the markers according to the setup
guide.
4. Insert general body measurement values for weight, height, knee width, ankle width, and
total leg length.
5. Complete a static calibration for the “Plug-in Gait” pipeline.
6. Record data for jump landings off of a low platform onto two force plates, located on the
ground in front of the platform.
7.
Export the data to Polygon for further analysis and model representation
Hinge Design
Shown below in Figure 1 is a polycentric hinge design that aims to prevent valgus
bending and hyperextension. This design is used in a majority of the knee braces on the market.
All knee braces researched have shown to include two identical hinges on the lateral and medial
sides, respectively. Our design will focus on two different hinges. The lateral component of the
knee brace will continue to use a polycentric hinge. This hinge will still perform its function in
the prevention of valgus bending and hyperextension. The medial component will incorporate a
new design that has yet to be used in current braces. A spider gear hinge will take the place of a
polycentric hinge on the medial side. This is shown in Figure 2 below. The reason for choosing
a spider gear setup is because it will still protect against valgus bending and hyperextension, and
we hypothesize that it will also reduce compressive loading forces on the lateral compartment of
the knee joint.
Spider gears have a lot of useful characteristics and are typically used in the automotive industry.
They have the ability to work in parallel with another spider gear and they can also function in a
perpendicular manner. This multiple axis feature of the gears inspired its use our knee brace. To
incorporate the hinge into a knee brace we would orient it on the medial side with the gears
facing the medial side of the knee brace. Therefore, when an axial load is applied to the knee, a
varus moment will be created in the brace. This varus moment occurs due to the spider gears
beveled edges. The varus moment created will then refocus the force, shifting more of the
weight to the medial compartment, which is much stronger than the lateral compartment.
Predictably, the brace will then prevent against three injury mechanisms of the ACL –
hyperextension, valgus bending, and axial loading.
Figure 1. Polycentric Hinge
Figure 2. Spider Gear Hinge
Patent Search
Table 1. Matrix of Relevant Patents
Patent
Number
8,343,083
OA
Brace
6,471,664
Hinge
Special Attributes
Why important to project
Figure #
X
No hinge but spring connects top and
bottom cuffs
1
X
Hinge has torsion spring to provide
resistance
Configuration to alleviate medial
and lateral compartmental
osteoarthritis of a knee
Restrain pivotal movement of upper
and lower members between an
extension and a flexion position
Laterally & medial selectively and
retainable positioning in angular
relationship to the lower member
OA brace is rigid frame and corrects
compartmental loading
Restricting anterior tibial movement
prevent some ACL tears
Adjustable hinge could be versatile
in its use
Adjustable second hinge could
change the project design
Adjustable second hinge could
change the project design
6
6,875,187
X
Knee brace with a slidable engager
(adjuster)
7,311,687
X
Knee brace with a rigid embodiment
RE37,297 X
5,807,294
X
5,766,140
X
7,306,572
X
Creates a force counteractive to
abnormal anterior movement of the
tibia.
Adjustable hinge assembly for an
osteoarthritic knee brace
Second hinge to correct knee bending
varus/valgus
Second hinge assembly allows
medial/lateral articulation
2
3
4
5
7
8
Although there are 100s of patents on knee braces and their components, finding relevant
patents for our project has been time consuming. A matrix of some of the relevant patents to our
redesign are shown above in Table 1. This is a small sampling of the existing braces and hinge
designs already patented. A knee brace that protects against hyperextension, valgus bending and
shifts axial loading to the medial compartment has not been found in the patent search. The
osteoarthritis (OA) knee brace market is saturated with braces. Various designs of the braces are
being taken into consideration to help improve the function of our brace. Many patents for OA
braces use angle arm adjustment to equal out the loading in the knee between the medial and
lateral compartments. Most are adjustable by the user and would work for the ideal OA stricken
patient, above 50 years old. We are targeting athletes because of the occurrence of ACL injuries
caused from sports.
A patent is a legal document that is granted to somebody, or group of people, that have
designed a product that is unique to any other invention. Obtaining a patent would exclude
others from making, using or selling our product for twenty years (from the date of the filed
patent application). A patent should be submitted to protect the intellectual property (IP) of the
product.
The process of filing a patent is very complicated and most people use an attorney to get
it done. The steps for filing a patent are listed below.
Step 1: Search the patent databases to see if our idea has been done and patented.
Step 2: Decide what type of patent we would be filing for. Our knee brace falls under the utility
patent which is the most common and consists of useful process, machine, and article of
manufacture and composition of matter.
Step 3: Determine where to file the patent. International protection is harder to get and is a longer
process. We plan to file in the United States.
Step 4: Choosing which type of utility patent application to file: provisional or nonprovisional.
Provisional patents are good for 12 months and then expire if not converted to a nonprovisional
patent, or a nonprovisional patent is filed in reference to the provisional patent.
Step 5: Expedited examination is when an applicant opts to have prioritized examination. The
application will be attributed special status during prosecution before the patent examiner. The
goal is to provide a final disposition within twelve months.
Step 6: Who will file the patent for the invention. File yourself (Pro Se) or use a registered
attorney or agent (Recommended).
Step 7: Prepare for electronic filing of the patent and pay the processing fees and apply for a
customer number and digital certificate to file.
Step 8: Apply for patent using electronic filing system as a registered e-Filer
Step 9: USPTO examines application
Step 10: Applicant pays the issue fee and the publication fee. USPTO grants patent
Step 11: Maintenance fees due at the 3.5, 7.5, and 12.5 year time points, after the patent is
granted.
The application and patent search can be very time consuming and could delay the
approval of a patent if done incorrectly, providing reason to use an attorney. Having a patented
knee brace allows us to control the rights of the intellectual property, who we choose to sell it to
(if anybody), and the means for its production and manufacture. For our particular case, we
would sell the patent to a marketable company that has prior experience in knee braces and their
applications.
TEAM MEMBERS & RESPONSIBILITIES
The team members for this novel design of an ACL prevention brace are Justin
Killewald, Daniel Greenshields, and Rachel Porter. Thus far, Dan has been working on the
patent research to ensure that the intellectual property of our new ACL brace will be protected.
This has included looking through existing patents and determining what makes our design
different, meeting with a patent attorney, and determining what needs to be done to file a patent.
We plan on filing a patent application on the “lateral-unloading” function of our brace. Justin
has been researching the hinge design. He has been studying Donjoy’s FourcePoint hinge and
looking at how we’re going to redesign it to meet our needs. Rachel has been working on the
human participant section; this includes obtaining IRB approval and figuring out our
experimental methods for our human subject testing. In the future, Justin and Rachel will be our
human subjects that we will be testing our redesigned brace on. Once we have our proposed
prototype design, Dan will be working on the fabrication. All three of us will be working on the
testing and data analysis because this will determine the effectiveness of our brace and what
changes, if any, we need to make to it. For the final report, Justin will be the main report writer,
Rachel will work on the tables and appendices, and Dan will work on the figures and references.
These roles are not set in stone, and we plan on readjusting our roles as necessary when we see
what areas of our project need more attention.
COST ANALYSIS
For this project we plan on purchasing two knee braces: one male and one female. We
would like to do this so that we can test them on our human subjects and use this as a reference
point to see if our redesigned knee brace better protects the ACL and also so that we can take one
of them apart and analyze the hinge design. We believe this will help us to gain a better
understanding in exactly how it works and what we can do to improve it. The brace that we were
looking at buying is the Donjoy OA Defiance brace and it is roughly $550, so we’re budgeting
$1100 for braces. We also need materials for the hinge redesign such as springs, bands, screws,
bolts, washers, riveting tools, and whatever metal we decide to use. In addition to materials for
the hinge design, we will need testing supplies such as velcro and double sided tape. We
budgeted $500 for the hinge redesign material and $300 for the testing supplies to come to a total
budget of $1800 for this project.
ANTICIPATED CHALLENGES
For any project with an extensive amount of work and detail, complications can
essentially be expected. We have developed a series of anticipated challenges that would inhibit
our project in one way or another. A challenge we may face is that our brace doesn’t show a
significant reduction in the compressive load forces. This is the most severe of our challenges
because if we don’t show that our brace can reduce the compressive forces in the knee then the
project will have not reached the expected outcome. Furthermore, another challenge we face is
time restrictions. We expect multiple design and redesign phases throughout our design process,
each phase accounting for a substantial amount of time. Additionally, we have filed for IRB
approval through Lawrence Technological University, however if we don’t get approval we will
not be able to do human subject testing. This is a trivial challenge due to our expectations of
being granted approval. Lastly, the patent filing process will most likely provide challenges to
our group. No group member has a great deal of knowledge in the patent filing process,
therefore this portion of the project will require additional assistance, most likely from Ken
Cook.
FUTURE DIRECTIONS
This project has great potential to carry over into future BME Senior Projects classes.
Our proposed hinge design will need years of improvements after we finish the project, as all
products do after their initial invention. Aside from academia, the knee brace could be sent to a
certified lab testing center to ensure its efficacy and reliability. Following certified approval of
the brace it can then be marketed to any company for manufacture and production.
REFERENCES
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[9] www.djoglobal.com/education/patient-education/acl-bracing
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