Brudvig, Howard 1
EFFECT OF HAMSTRING TENDON VS PATELLAR TENDON ON KNEE STABILTY
FOLLOWING ACL RECONSTRUCTION
Adrien Brudvig and Sha’ Howard
ESS 265 A Research Methods in Athletic Training / Spring 2014
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Chapter 1 - Introduction
Anterior cruciate ligament (ACL) tears are common knee injuries occurring most often in
individuals who participate in high-risk sports, such as basketball, football, skiing, and soccer.
These injuries occur from indirect trauma related to cutting, twisting, jumping, and sudden
deceleration movements. 1 Damage to the ACL ligament prevents athletes from returning to sport
participation due to loss of knee stability and leads to lower activity levels, increased joint laxity
and loss of muscular strength.2 For athletes wishing to return to their initial level of activity,
reconstructive surgery is required to improve knee stability and limit the risk of subsequent
injuries.2,3 It is important to determine which graft; the patella tendon or the hamstring tendon,
for athletes and non-athletes will be most effective in improving overall mobility and strength in
the affected joint. The best choice will result in greater knee stability, meeting the individuals’
overall expectations and minimal post-operative complications which will result in the individual
returning to their pre-injury state.
Purpose statement:
The purpose of this study is to investigate which anterior cruciate ligament (ACL) graft is
superior in providing knee stability post ACL reconstruction for athletes and non-athletes.
Research question:
Which ACL graft, patellar tendon or hamstring tendon, will provide better outcome results for
knee stability?
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Hypothesis:
The hypothesis of this study is that the patellar tendon graph will have better outcome results on
knee stability than the hamstring tendon grafts.
Operational Definitions:
Surgical reconstruction- involves replacing the torn anterior cruciate ligament. ACL
reconstructions aim to restore normal knee stability, movement, strength, knee function
and improve quality of life.
Anterior Cruciate Ligament- is an internal band of tough tissue that runs diagonally
between the back of the femur and the tibia plateau.
Patellar tendon graph- is obtained from the middle third of the patellar tendon which
originates on the distal apex of the patella and inserts on the tibial tuberosity.
Hamstring tendons graphs- hamstring tendons cross the knee joint and connect on each
side of the tibia just below the joint. The graft is taken from the tendon along the inside
part of the thigh and knee.
Knee stability- is when the tibia maintains position limiting the forward movement off
the femur and maintains rotational movement. It is the supporting factor for knee
movements.
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Delimitations:
The delimitations in this study include individuals with ACL reconstruction with either the
patellar tendon graft or hamstring tendon graft. The subject focus included both athletes and nonathletes with no other knee ligament injury involvement.
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Chapter 2 – Review of Literature
This chapter addresses two different approaches to ACL reconstruction and describes the
literature relevant to the research purpose of this study. It is organized into four sections: 1)
patellar tendon graft (2) hamstring tendon graft, (3) advantages of each tendon graft, (4) and
disadvantages of each tendon graft. This study will provide comparative information reflecting
which ACL tendon graph effectively influences greater knee stability results.
Patellar Tendon
The patellar tendon graft is a safe and effective option for ACL reconstruction. Most
orthopedic surgeons are familiar with this technique. Bone-patellar tendon-bone grafts (BTB)
remain the gold standard for ACL reconstruction since the 1980’s.4 The reconstruction involves
removing the middle 1/3 of the individuals patellar tendon accompanied by a bony piece of the
patella and a bony piece of the tibial tuberosity.5 The surgeon attaches the block of bone in the
bone tunnel rather than attaching it to soft tissue producing a strong bond between the bonetendon intersection.
Patellar Tendon Advantages
The patellar tendon graft has many advantages. The patellar tendon graft heals bone-tobone in approximately 6-8 weeks, which appears to be quicker than the healing process of soft
tissue-to-bone grafts.6 Rapid healing is an important part of ACL reconstruction as it allows for a
prompt rehabilitation and return to physical activity. For this reason, patellar tendon grafts are
often suggested to younger and more active patients.7 Patellar tendon grafts have demonstrated
excellent surgical outcomes resulting in 90-95% success rate of athletes returning to pre-injury
level of play .6 Individuals with patellar tendon grafts also return to sport participation sooner.8
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This type of graft produces greater knee stability, less pivot shift and less anterior laxity.8 Patella
tendon grafts also maintain tension better which results in decreased laxity measurements.9 It has
a successful track record revealing excellent results with stability at different levels of athletic
participation.
Patellar Tendon Disadvantages
Orthopedists are switching from patellar tendon grafts to alternative grafts due to increased
rates of anterior knee pain when patients resume athletic activities. An increased rate of
patellofemoral pain or patellar tendonitis is seen with stair usage, jumping, skiing and other
activities that are hard on the knees 6-12 months post-surgery.6 These conditions are treatable
with continued strengthening exercises and rest. There is a large incision site and has been
known to cause greater post-operative pain such as increased tenderness when kneeling on the
donor incision site. Patellar tendon grafts are known to be associated with donor site morbidity
such as anterior knee pain, patellar injuries with BTB grafts, postoperative neuroma, additional
scarring, extensor strength deficit, and patellofemoral osteoarthritis.3,7,10 An increased potential
for patellar fractures, quadriceps muscle weakness and infrapatellar contracture is also
documented.11,12 In addition, the harvest site has been known to rupture within the 6-8 weeks of
surgery with overuse and increased tension on the site.
Patellar tendon grafts have a stronger fixation after surgery therefore allowing for more
aggressive rehabilitation. It also has a lower rate of graft failure and produces better knee
stability. The pivot shift test has revealed greater outcomes on stability.8 Overall, the patellar
tendon graft is a suitable choice for ACL reconstruction for active individuals seeking return to
same level of sport participation.
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Hamstring Tendon
The hamstring graft is a soft tissue to bone fixation instead of bone to bone.1 Hamstring
tendon grafts involve the semitendinosus and gracilis tendon in a single or double band for
reconstruction. This construct increases the graft strength. The graft ends are inserted into
predrilled holes in the femur and tibia. Once positioned, the ends are either screwed or stapled
into position.
Hamstring Tendon Advantages
The use of hamstring grafts has become more prevalent due to its lower rate of donor site
morbidity.7 This ACL reconstruction option utilizes a smaller incision site producing less
recovery pain. The hamstring tendon graft is also ideal due to the ease in harvesting it. Hamstring
tendon repairs heal more quickly at the harvest site, usually in three months.5 The hamstring graft
is less stiff producing greater knee extension abilities.10 Individuals with this type of ACL graft
experience minimal patellar pain when they return to sport participation. Also, patients are able
to kneel on the affected site with little discomfort.11 Additionally, hamstring tendon grafts have
been associated with knee flexion strength and internal tibial rotation strength. This procedure is
associated with higher patient reported outcome scores and less evidences of arthritis.4
Hamstring Tendon Disadvantages
A disadvantage of hamstring tendon grafts is that harvesting requires surgical
experience. Many surgeons are less familiar with this procedure which requires a longer
operative time due to increased opportunities to injure the saphenous nerve, blood supply and
other tendons while harvesting.10 Also, this procedure requires a different technique for
tensioning the hamstring tendon in the knee.1 Since the surgeon has to fixate soft tissue to bone it
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creates a longer healing process which affects rehabilitation and recovery length. Hamstring
recovery requires a slower rehabilitation time with a focus on strengthening exercises in order to
regain loss of muscle power.8 This graft option has an increased chance for significant functional
loss and can lead to greater laxity diminishing the stability of the knee.2 This graft is also
associated with nearly twice the risk of revision than those who received patellar tendon
grafts.7,10,13
There are also disadvantages for individuals with increased joint flexibility, prior
hamstring harvest, or recurrent hamstring tears and they are advised on alternative graft choices.
One of the major drawbacks to the hamstring tendon graft is the lengthy healing timeframe. To
enhance the healing, osteoconductive materials, shock waves and hyperbaric treatments are
being utilized to increase vascularity to improve bone growth. 9 Individuals can experience less
stable knees and require additional strengthening exercises meaning a slower recovery delaying
return to sport participation.
The study is investigating which tendon graft produces greater outcomes on knee stability
after having ACL reconstructive surgery. Individuals need to weigh the advantages and
disadvantages of all available graft options taking into consideration recovery time, rehabilitation
time, the surgeon’s preference and experience, and post-operative complications. The best choice
will result in overall improved knee stability, meeting the individuals overall expectations, and
long term outcome of the surgical procedure. Patellar tendon grafts have greater influence on
knee stability after ACL reconstruction than the hamstring tendon option. A sense of greater
knee stability will reduce the fear of re-injury allowing athletes to be confident during sport
participation. The patellar tendon graft will return the patient to their pre-injury state with less
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complication and maintain their level of physical activity; therefore this graft is the optimal
choice in ACL reconstruction.
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Chapter 3 – Methodology
Participants
Participants for the study will consist of both males and females ranging from 18 to 50
years of age. These individuals will have a ruptured ACL with no other structural damage. This
also means that no prior injuries have been sustained on the knee being tested. These participants
will be found through the help of orthopedic surgeons who have scheduled patients for ACL
reconstruction using a hamstring or patellar tendon.
Instrumentation
Pivot Shift Test: This will test tibio-femoral internal rotation and anterior tibial translation when
the ACL is insufficient.14 The participant will begin with the knee in full extension and the
researcher will grasp the leg with two hands and put the patient's ankle underneath the arm. The
researcher will then internally rotate the leg while applying a combination of axial load and
valgus stress. The participant’s leg will be flexed while maintaining these forces. As the knee is
flexed the tibia shifts from a subluxed to a reduced position in those with an ACL injury. In an
uninjured knee, there will be no shifting. This test will be graded on a scale form 0-3. Grade 0:
no detectable shift; Grad I: tibia moves in a smooth glide during reduction; Grade II: tibia
abruptly reduces or jerks; Grade III: tibia clunks or momentarily locks in a subluxed position
before reducing.
Tegner Activity Scale: Each participant will be asked to identify knee stability using the Tegner
Activity Scale. This rating scale is used to determine the activity levels in those with an ACL
rupture.10,13 It incorporates sport and work related activities.
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Single Leg Hop: Participants will also be asked to perform a Single Leg Hop which will be used
to measure functional performance following ACL reconstruction.15 To perform this test
participant will begin with toes immediately behind a starting line, jump off one leg, and landing
on two. The hop is measured in centimeters from the starting line to the end of the toes after
completion of the hop. The participant is allowed one trial hop for each leg. The measurements
from the uninjured knee are compared to the injured knee.2
KT-1000 Arthrometer: This is a more accurate way to determine knee stability in those who have
undergone ACL reconstruction. This provides direct measurements of side-to-side knee laxity as
well as provides objective measurements of anterior tibial displacement.13 The researcher will
instruct the patient to lie supine, a thigh support will be attached to keep both knees at the same
flexion of 20-25 degrees. This is the angle where measured laxity is greatest. A foot support will
be attached to limit external tibial rotation equally on both sides. The arthrometer sits with the
calibration arrow above the joint line, and is held on the anterior aspect of the leg by two velcro
straps. One sensor pad is placed on the tibial tubercle and one on the patella. When an upward
force is applied an audio tone is signaled. The displacement at these forces will be measured in
millimeters from the dial indicator. Greater than 3 mm on side-to-side measurements is a
determinant of increased laxity suggesting failure or stretching of the graft.
Kinesthetic Ability Trainer (KAT 2000): This will also be used for the evaluation of balance
ability in those with ligament injuries pre-operatively, post-operatively and during the
rehabilitation period. This test consists of a movable platform which is supported by a small
pivot. The stability of the platform is controlled by pressure in a circular cushion that rests
between the platform and the base of the unit. When the cushion is inflated, the platform is
stabilized and when it is deflated the platform is extremely unstable. The pressure in the cushion
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is based on the person's weight and on the type of test being performed. A tilt sensor on the front
of the platform is connected to a computer which registers the deviation of the platform from the
reference position throughout the test period. The distance from the center of the platform to the
reference position is measured at every registration. These calculate the BI (Balance index) score
which is determined by the person's ability to keep the platform near the reference position. A
low BI indicates a good ability to maintain the balance.
Procedures
After receiving approval from the IRB, medical records will be obtained from orthopedic
surgeons at various hospitals. This information will be used to find 100 participants for the
research study who have a ruptured ACL but have not sustained any other structural injuries.
These patients will also be scheduled to have ACL reconstruction performed with either a
hamstring or patellar tendon. All participants will be contacted using a mass email giving a brief
description of the study. Individuals will also be contacted face-to-face to encourage
participation in the study.
After getting all participants, a mass meeting will be held with all participants giving
thorough details of the study and having consent forms signed. Pretesting will begin immediately
to get baseline values for knee stability prior to surgery. Post-operative testing will begin one day
after surgery once a week for up to six months. Each participant will be doing the same
rehabilitation protocol throughout the research study. Pre and post testing will consist of five
different stability tests for both the hamstring tendon and patellar tendon groups containing 50
participants in each group.
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Each participant will identify individual knee stability using the Tegner Activity Scale.
This rating scale is used to determine the activity levels in those with an ACL rupture and will
incorporate sport and work related activities. Participants will then be asked to perform a Single
Leg Hop which will be used to measure functional performance. The measurements from the
pre-operative values will be compared to the post-operative values.
The Pivot Shift Test will then be performed to test tibio-femoral internal rotation and
anterior tibial translation. This test will be graded on a scale from grades 0 to 3. Following these
tests, knee stability will be determined using the KT-1000 Arthrometer. This will be used to
provide objective measurements of anterior tibial displacement. Displacement will be measured
in millimeters.
Lastly, the Kinesthetic Ability Trainer (KAT 2000) will be used for the evaluation of balance
ability in those with ligament injuries pre-operatively, post-operatively and during the
rehabilitation period. This test consists of a movable platform which is supported by a small
pivot. These tests will be performed once a week for up to six months following reconstructive
surgery. Following the six months of testing, all data will be gathered from both the hamstring
and patellar groups and results will be compared from all tests determining if it has proven the
hypothesis.
Data Analysis
Upon completion of this study, data will be analyzed using an Analysis of Variance
(ANOVA). This will allow variances to be seen for multiple tests over an extended length of
time. Data will include results from each participant from the hamstring graft group and the
patellar graft group for the Pivot Sift Test, Tegner Activity Scale, Single Leg Hop, KT-1000
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Arthrometer, and Kinesthetic Ability Trainer. This analysis will assess results from said tests
performed prior to reconstructive surgery and once a week following surgery for the duration of
six months.
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