Running Head: PROPRIOCEPTION POST-ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION 1

Proprioception Post-Anterior Cruciate Ligament Reconstruction

Sarah Weatherford

Colorado State University

EDRM 600

Dr. Tobin Lopes

Proprioception Post-Anterior Cruciate Ligament Reconstruction 2

Abstract

An injury to the anterior cruciate ligament (ACL) within the knee is thought to have a

negative impact on joint proprioception, even after the extensive rehabilitation process is

complete. The purpose of this research was to determine if there is a deficit in proprioception

following anterior cruciate ligament (ACL) reconstruction. Using a quantitative, correlational

study research method, twenty-six current and former Colorado State University student-

athletes were chosen for this study. Each of these participants was chosen due to the fact that

they had one or more previous ACL tear in one knee. At the time this data was collected, they

ranged in age from 17 23, although their age at the time of their ACL tear ranged from 13 to 20.

The participants’ time from reconstruction to when this data was collaged ranged from six years

to nine months. SWAY Balance was used as a method to measure proprioception through single

leg balance. Results of the study showed no significant difference between single leg balance

scores on the previously injured leg versus the contralateral leg.

Key Words: anterior cruciate ligament (ACL) reconstruction, proprioception

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Area of Focus

Tears of the anterior cruciate ligament (ACL) are some of the most traumatic for an

athlete, given the recovery time and perceptions that their mechanics are forever changed.

During four years competing at the collegiate level, 3.2% of male athletes and 3.5% of female

athletes will tear their ACL at least once. Given the fact that the recovery process for this injury

is at least six months long, it is important that the rehabilitation process be taken seriously.

Mechanoreptors within the knee can both affect and be affected by injuries to the joint.

In terms of the ACL, these mechanoreceptors play a protective role and initiate a reflex that

stabilizes the knee to prevent injury. When the knee is injured, so are the mechanoreceptors,

which ultimately leads to a decrease in proprioception at the joint (Reider et al, 2003).

Proprioception is a necessary, functional sensory sensation that allows for proper joint

functionality (Lephart et al, 1992). Whether in the knee, shoulder, ankle, or any other joint,

proprioception is how individuals know where their body is within space.

Previous research has shown that what athletes perceive as a "successful" ACL

reconstruction correlates more with restored proprioception instead of stability of the graft

(Reider et al, 2003). If this is truly the case, it is important to place more emphasis on

proprioception rehabilitation exercises instead of strength training exercises. Ultimately,

athletes need to feel comfortable with their knee before returning to sports.

Purpose Statement: The purpose of this research is to investigate the relationship between

athletes’ proprioception and reconstruction of the anterior cruciate ligament.

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Research Question: Does tearing the ACL predispose an individual to lasting proprioception

deficits, even after the ligament is repaired? If so, what can the athlete do to decrease, and

ultimately prevent, these deficits?

Background and Rationale

The anterior cruciate ligament (ACL) makes up about 50% of all ligament injuries within

athletics (Bonfim et al, 2003). Surgery is almost always needed to repair the ligament, especially

if it is completely torn. Anatomical changes are well known post-reconstruction, but the

functional changes are only now beginning to be researched. Although physicians will base

return-to-play decisions on the stability of the knee joint post-anterior cruciate ligament (ACL)

reconstruction, recent research has shown that “proprioceptive feedback might be an

important factor relating to functional outcomes” (Dhillon et al, 2011, p. 295).

The main purpose of the anterior cruciate ligament (ACL) is to prevent any “excessive

anterior tibial translation in various degrees of flexion” (Dhillon et al, 2011, p. 296). Research

has shown that it may take as few as 1725 Newtons of force to completely tear the ACL (Dhillon

et al, 2011), although that number may increase or decrease due to age, physical activity,

muscle strength, or any other number of factors. Loads on the knee joint can quickly exceed

this estimate during strenuous activities. During physical activity, the knee cannot rely simply

on the strength of the ligaments to maintain stability. The muscle contractions must be aided

by the sensations transmitted through mechanoreceptors in the ligaments to the brain (Dhillon

et al, 2011).
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Proprioception is a specific sense of touch that combines joint movement and joint

positioning that has three components: static awareness of joint position, detection of

movement and acceleration, and efferent activity that starts reflex responses and regulates

muscle activity (Dhillon et al, 2011). There are two types of proprioception – conscious and

unconscious. Conscious proprioception involves joint function, while unconscious

proprioception initiates reflex stabilization (Lephart et al, 1992). Mechanoreceptors are the

sensory cells that respond to touch stimuli, and are closely related to proprioception. Studies

have shown that there are a significant number of mechanoreceptors within the ACL; these

mechanoreceptors play a protective role for the ACL. When the mechanoreceptors are excited

by activity, they initiate a reflex that then leads to stabilizing contractions of the surrounding

muscles (Reider et al, 2003). Because the proprioception of the knee is compromised, the brain

interprets that feedback as saying that the mechanical stability of the knee is also

compromised. Thus, proprioception can be severely affected when those mechanoreceptors

are damaged.

It is important to understand any proprioception deficits that occur within the knee joint

as the result of injury to the ACL because of lasting effects on the athlete. Studies have shown

that in knees with damage to the ACL, even after reconstruction of the ligament, there are

altered gait patterns, generally due to the change in proprioceptive feedback at the joint, not

any mechanical instability (Dhillon et al, 2011). Rehabilitation post-reconstruction of the ACL is

a lengthy process, a minimum of six months, but generally between nine and twelve months of

rehabilitation is needed before the athlete can be cleared for full return to activity. Research
Proprioception Post-Anterior Cruciate Ligament Reconstruction 6

has shown that an athlete’s perception of a successful surgery correlates more with “restored

proprioception than with mechanical stability” (Reider et al, 2003).

Research Methods

This study consists of 26 current and former Colorado State University student-athletes

ages 18-23, with a previous history of anterior cruciate ligament (ACL) tears. Each of these

athletes has been cleared to fully participate in sports following six to twelve months of

rigorous rehabilitation. Individuals were excluded from this study if they had bilateral ACL tears

or any history of knee surgeries on the knee opposite of their ACL tear. The participants’ time

from reconstruction to when this data was collaged ranged from six years to nine months.

The SWAY Balance System is a mobile phone application used to assess sway as an

indicator of balance. While generally used to test an individual’s balance after sustaining a

concussion, it can also be used to look at proprioception bilaterally. When used for testing an

individual, it measures double leg balance, single leg balance on both legs, and tandem stance

balance on both legs; each test is performed with the individual's eyes closed. Scores are

calculated out of 100, with a higher score indicating better balance as a measure of

proprioception. See Figures 1-5 for visual explanations of how the SWAY Balance test is

completed.
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Figure 1. SWAY Balance Figure 2. Double Leg Stance Figure 3. Tandem Stance

Figure 4. Single Leg Stance Figure 5. Graph of Balance Scores

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Participants in this study performed the SWAY Balance Assessment just as they would if

they were performing the test as a concussion screening tool. The test was performed on a

laminate floor, with the participants barefoot. The environment was quiet, allowing the

participants to focus on their balance and body awareness. All five tests were performed:

double leg stance, single leg stance bilaterally, and tandem stance bilaterally. Scores were

calculated by the SWAY Balance mobile application.

Participants completed the SWAY Balance test a total of three times, giving them three

measurements for double leg stance, tandem stance with left leg forward, tandem stance with

right leg forward, single leg stance on left foot, and single leg stance on right foot. Only data for

the single leg stances of the left and right leg were used for this research, due to the ability to

isolate the injured and uninjured knees of the participants.

For data analysis, the participants’ three trials for the single leg stance on the left leg

and their three trials for the single leg stance on the right leg were averaged to get two

numbers for each student-athlete – one average for the leg with the previous ACL and

subsequent reconstruction, and another average for the healthy leg. The healthy leg served as

an intrinsic control for each participant.

When gathering data, it was necessary to know whether the left or right knee of the

participant was previously injured. For analysis, however, the data was compiled into “Injured”

and “Uninjured” instead of “Left” and “Right”, as the side of injury was not being studied in this

research. A paired t test was used to analyze the data of the injured and uninjured single leg

balance scores.
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Results

There were an equal number of males and females that participated in this research

study (Table 1), with eleven football players reporting a previous ACL tear (see Table 2), the

most of any varsity sport at Colorado State University. Track and field had six student-athletes

meet the inclusion criteria for this study – two males and four females. Cheer and dance and

women’s basketball followed with three student-athletes, then women’s soccer with two, and

women’s volleyball with one.

Table 1. Number of Athletes by Gender

Male 13
Female 13

Table 2. ACL Tears by Sport

Football 11
Men’s Track and Field 2
Women’s Track and Field 4
Cheer and Dance 3
Women’s Soccer 2
Women’s Basketball 3
Women’s Volleyball 1

There was a slight difference in the single leg balance score means of the two groups,

with injured having a lower score than uninjured by 2.3 percentage points, although this

difference was not significant. The P value of a one-tail t test was 0.0985, while the P value of a

two-tail t test was 0.197. The critical t value for a one-tail test was 1.708, while the critical t

value for a two-tail test was 2.060 (see Table 4). These results are not significant under the

alpha value of 0.05.

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The data has a Pearson Correlation Efficient of 0.745 (see Table 4), which shows a

positive correlation between the single leg stance balance scores of the injured and uninjured

sides.

Table 3. Injured vs Uninjured Single Leg Balance Scores

Male vs Female Injured Average Uninjured Average
male 77.09333 63.89667
female 81.10333 80.40333
female 74.99 76.15
female 93.69667 97.03333
male 89.54 85.86
female 88.73667 87.83
male 89.16667 87.848
female 87.35333 91.05667
female 79.86333 87.96
male 77.78333 75.09333
male 63.65333 76.39
female 79.31 89.09667
male 73.11 91.79667
female 85.19333 84.44667
female 47.735 34.72
male 59.89 69.15
female 87.03 98.05
male 85.05667 82.21
male 75.55667 75.06333
male 90.32333 85.15333
female 96.68 94.65
male 49.12 75.33
male 84.01 94.37333
female 84.08333 87.58
male 81.04 78.27667
female 79.65667 72.36333
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Table 4. t-Test: Paired Two Sample for Means

Variable 1 Variable 2
(Injured) (Uninjured)
Mean 79.2605769 81.6069744
Variance 150.926075 169.212865
Observations 26 26
Pearson Correlation 0.74663842
Hypothesized Mean Difference 0
df 25
t Stat -1.3252759
P(T<=t) one-tail 0.09853235
t Critical one-tail 1.70814076
P(T<=t) two-tail 0.1970647
t Critical two-tail 2.05953855

Discussion

Proprioception is a key sensation in the human body that is necessary for body and

movement awareness. Without it, sports, activities of daily living, occupational tasks, and even

muscle function and reflex stabilization can be compromised or made to be extremely difficult

(Lephart et al, 1992). While previous researchers have used the threshold to detection of

passive motion (TTDPM or TDPM) to measure for any proprioception deficits, this research was

the first to use balance as a measure of proprioception. Previous research has found significant

differences in TTDPM between ACL reconstructed knees and the uninvolved knee (Lephart et al,

1992). While this research did find a difference in the mean balance scores between injured

and uninjured legs, the results were not significant.

Threshold to Detection of Passive Motion (TTDPM) is widely considered to be the gold

standard for measuring proprioception; balance is another measure of proprioception,

although in a less controlled environment. Single leg balance is one of many other ways to

determine the proprioceptive feedback of a joint. The single leg balance test brings in more
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variables for which to be accountable, such as the ankle and hip joints. This research did not

exclude participants with a history of hip, ankle, foot, or other lower extremity injuries, which

brings up a significant limitation of the study. Injuries to any joint in the body will cause a

decrease in proprioceptive feedback at the joint if it is not properly rehabilitated. SWAY Balance

results could very easily be affected if the participant had any number of injuries to the lower

extremity, regardless of the severity.

Results of this research also showed a higher proportion of football student-athletes

represented than other sports; football players made up 42% (11 of 26) of all participants in this

study. While football is one of the sports with the highest rates of ACL tears in athletics,

women’s soccer has been widely shown to have the highest rate of ACL tears (Joseph et al,

2013). Women’s soccer only made up 7.7% (2 out of 26) of the participants in this study, which

can be explained by the fact that there are significantly fewer women’s soccer players in a

single NCAA Division 1 athletics program than there are football players. Football rosters

generally have anywhere from 100 to 140 males on their teams, while women’s soccer rosters

are usually capped around 30. These roster numbers explain why there are a higher number of

football student-athlete participants in this study.

Other limitations of this research come from the small sample size of participants. With

only 26 participants, it is hard to generalize data results to the general population. Additionally,

all of the participants are also NCAA Division 1 athletes in their respective sports, but the ACL

tears they sustained occurred before they came to the collegiate level. This leads the

researcher to conclude that their rehabilitation protocol was outstanding and they were highly
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motivated. If these athletes had not recovered from their ACL reconstructive surgery, it is safe

to assume that they would not be competing at a NCAA Division 1 level.

There are many ways to increase proprioception in the knees following an injury or

reconstruction of the ACL. Although there is much research on the deficits in proprioception

after injury, little is known about the timeline for proprioceptive feedback to return. Future

research on this topic should be done to investigate the potential timelines for the return of

proprioception. Additional future research includes studies of the differences between males

and females and the ACL rehabilitation process, as well as the rehabilitation process for

different types of ACL grafts.

A significant number of studies have shown that females are much more likely to suffer

an injury to their ACL than males (Arendt, Agel, & Dick, 1999). There are numerous theories as

to why this is, but no research has been done on females and males after they have completed

the rehabilitation process following ACL reconstruction. More research should be done to

investigate if females are more likely to re-tear their ACL grafts, as well as if there is a significant

difference in time it takes to recover from ACL reconstructive surgery.

There is also conflicting research on what type of ACL graft is the best – hamstring

tendon, patellar tendon, or cadaver. Cadaver is widely accepted to be the lowest quality, but

hamstring tendon and patellar tendon each have their benefits. Research should be done to

determine if the type of graft used in an ACL reconstructive surgery has an effect on the

recovery time or return of proprioception.

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Conclusions

In this study, single leg balance tests did not show a significant difference in

proprioception between knees with a previously injured ACL when compared to the

contralateral side. Previous research demonstrates a deficit in proprioception in both injured

and uninjured knees following ACL reconstruction, but this research was unable to definitively

replicate that. Despite this research not showing significant deficits, it is still important to

address proprioceptive changes in both knees following an injury to the ACL and subsequent

reconstruction. In order to perform at a high level, athletes must feel comfortable in the

structural stability of their knee, as well as the proprioceptive feedback they are able to receive

from their body. Implications of this research topic are applicable to athletes of all genders,

ages, and sports.

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References

Arendt, EA, Agel, J, & Dick, R (1999). Anterior Cruciate Ligament Patterns Among Collegiate Men

and Women. Journal of Athletic Training, 34(2):82-92.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1322895/pdf/jathtrain00006-0014.pdf

Barrett, DS (1991). Proprioception and Function After Anterior Cruciate Reconstruction. Journal

of Bone and Joint Surgery, 73-B(5): 833-837.

http://www.bjj.boneandjoint.org.uk/content/jbjsbr/73-B/5/833.full.pdf

Bonfim, TR et al (2003). Proprioceptive and Behavior Impairments in Individuals with Anterior

Cruciate Ligament Reconstructed Knees. Archives of Physical Medicine and

Rehabilitation, 84, 1217-1223. http://ac.els-cdn.com/S0003999303001473/1-s2.0-

S0003999303001473-main.pdf?_tid=677f3f08-080e-11e7-9241-

00000aab0f26&acdnat=1489424541_137f9427dd50b5ea7895f4a26faacdc0.

Dhillon, MS, Bali, K, & Prabhakar, S (2011). Proprioception in anterior cruciate ligament

deficient knees and its relevance in anterior cruciate ligament reconstruction. Indian

Journal of Orthopaedics, 45(4), 294-300.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3134012/?report=printable.

Fremerey, RW et al (2000). Proprioception after rehabilitation and reconstruction in knees with

deficiency of the anterior cruciate ligament. The Journal of Bone and Joint Surgery, 82-

B(6): 801-806.

Joseph, AM et al (2013). A Multisport Epidemiologic Comparison of Anterior Cruciate Ligament

Injuries in High School Athletics. Journal of Athletic Training, 48(6): 810-817.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3867093/
Proprioception Post-Anterior Cruciate Ligament Reconstruction 16

Kruse, LM, Gray, B, and Wright, RW (2012). Rehabilitation After Anterior Cruciate Ligament

Reconstruction: A Systematic Review. The Journal of Bone and Joint Surgery. American

Volume, 94(19): 1737-1748. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3448301/

Lephart, SM et al (1992). Proprioception Following Anterior Cruciate Ligament Reconstruction.

Journal of Sports Rehabilitation, 1, 188-196.

http://journals.humankinetics.com/doi/pdf/10.1123/jsr.1.3.188.

Liu-Ambrose, T et al (2003). The effects of proprioceptive or strength training on the

neuromuscular function of the ACL reconstructed knee: a randomized clinical trial.

Scandinavian Journal of Medicine & Science in Sports, 13: 115-123.

Reider, B et al (2003). Proprioception of the Knee Before and After Anterior Cruciate Ligament

Reconstruction. The Journal of Arthroscopic and Related Surgery, 19(1), 2-12.

http://ac.els-cdn.com/S0749806303500081/1-s2.0-S0749806303500081-

main.pdf?_tid=df9a9822-080c-11e7-b240-

00000aacb362&acdnat=1489423884_4dbb418a81b3861a164ae5b451afb80f