The Knee 21 (2014) 1191–1197
Contents lists available at ScienceDirect
The Knee
Lower extremity neuromuscular compensations during instrumented
single leg hop testing 2–10 years following ACL reconstruction
John Nyland ⁎, Jeff Wera, Scott Klein, David N.M. Caborn
Division of Sports Medicine, Department of Orthopaedic Surgery, University of Louisville, United States
Athletic Training Program, Spalding University, 901 South 4th Street, Louisville, KY 40203-2188, United States
a r t i c l e
i n f o
Article history:
Received 26 September 2013
Received in revised form 28 May 2014
Accepted 21 July 2014
Keywords:
Electromyography
Dynamic postural stability
Allograft
Perceived function
Knee
a b s t r a c t
Background: This study compared lower extremity EMG activation and sagittal plane kinematics of subjects at a
minimum of 2 years post-successful ACL reconstruction and rehabilitation during instrumented single leg hop
testing.
Methods: Comparisons were made based on subject responses to the following question, “compared to prior
to your knee injury how capable are you now in performing sports activities”? Group 1 = very capable, Group
2 = capable, and Group 3 = not capable. In addition to EMG (1000 Hz) and kinematic (60 Hz) data, subjective
knee function, internal health locus of control, sports activity characteristics (intensity, frequency) pre-knee
injury, and at follow-up were also compared.
Results: Group 3 had lower perceived knee function, decreased perceived sports intensity, and more subjects with
decreased sports activity intensity by two levels compared to pre-injury values. Perceived function scores, anterior laxity measurements and grades were similar between groups. During single leg hop propulsion and landing
Group 1 (very capable) had greater involved lower extremity gluteus maximus and medial hamstring activation
amplitudes than Group 3 (not capable). Perceived sports capability was related to better subjective knee
function, and higher perceived sports activity intensity.
Conclusion: Neuromuscular compensations suggesting a hip bias with increased gluteus maximus and medial
hamstring activation were identified at the involved lower extremity among most subjects who perceived
high perceived sports capability compared to pre-injury status. These compensations may be related to a
permanent neurosensory deficit, and its influence on afferent pathway changes that influence CNS sensorimotor
re-organization.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
No matter how well documented the functional deficits associated
with ACL deficiency are, the etiologic factors have not been clarified
[1]. There is growing evidence that supports the concept that in addition
to mechanical deficiency, ACL rupture represents a de-afferentation
injury that may lead to changes in ascending afferent pathway information leading to central nervous system (CNS) re-organization of sensorimotor programming [2–9]. The CNS has the capacity to adapt according
to the stimulus it receives from the ascending afferent pathways.
The ability of the brain to undergo any enduring morphological or functional cortical property re-organization is referred to as plasticity or
neuroplasticity [1,4]. Although mechanical function is largely restored
following surgical reconstruction, since neurosensory function is
not re-established, ACL injury may influence lower extremity neuromuscular activation long after successful surgical reconstruction and
rehabilitation [10–13].
⁎ Corresponding author. Tel.: +1 502 873 4224; fax: +1 502 585 7149.
E-mail address: jnyland@spalding.edu (J. Nyland).
http://dx.doi.org/10.1016/j.knee.2014.07.017
0968-0160/© 2014 Elsevier B.V. All rights reserved.
In studies of ACL deficient subjects and subjects following ACL injury
and reconstruction, Valeriani et al. [2,3] identified altered somatosensory evoked potentials in a number of patients suggesting that ACL
rupture lead to changes in ascending afferent pathway information
and CNS re-organization. They suggested that deafferentation from
ACL rupture could not be replaced by input from other knee joint somatosensory input or by the mechanical stability provided by reconstructive surgery [2]. In a study of 17 subjects with ACL deficiency,
Courtney et al. [5] suggested that reduced knee proprioception was related to CNS re-organization of sensorimotor programming that facilitated motor program modifications to produce more efficient lower
extremity neuromuscular activation synergies during gait. In a followup study they reported that ACL deficient subjects, who did not have impaired strength, resumed pre-injury function via altered lower extremity neuromuscular synergies and somatosensory evoked potentials [6].
In an electroencephalography study of 10 patients at N 1 year post-ACL
reconstruction, Baumeister et al. [7] reported greater cortical activation
in the parietal brain regions compared to healthy control subjects
during a knee angle re-production task suggesting a greater need for
focused attention to achieve effective task performance. In a later
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J. Nyland et al. / The Knee 21 (2014) 1191–1197
study comparing nine patients following ACL reconstruction with nine
health control subjects they reported that the ACL reconstruction
group required greater attentional control brain activation to reproduce
50% maximum voluntary quadriceps femoris isometric contraction
forces at 90° knee flexion [8]. In a functional MRI study comparing the
brain activation of 18 healthy volunteers with 17 subjects with chronic
ACL deficiency, Kapreli et al. [1] reported that the ACL deficient subject
group had diminished activation in several sensorimotor cortical areas
and increased activation in the contralateral pre-supplementary motor
area, contralateral posterior somatosensory area, and the ipsilateral posterior inferior temporal gyrus compared to the control group. They concluded that a likely explanation for this CNS re-organization of
sensorimotor programming was the establishment of neurophysiologic
changes in the ACL injury group [1].
Lower extremity neuromuscular extensor function, particularly at
the quadriceps femoris, is compromised following ACL injury and
reconstruction [14–17]. This impairs its ability to effectively attenuate
impact forces, increasing knee injury or re-injury risk [16–18]. Since
landing from a single leg hop for distance places high demands on the
lower extremity extensor musculature to absorb sudden impact forces,
this test is a widely-used clinical method for evaluating function following knee injury or surgery prior to release to sports [18–21]. The
purpose of this component of a larger study [11,22,23] was to compare
the involved and uninvolved lower extremity EMG activation amplitudes and sagittal plane kinematics of subjects at a minimum of two
years post-successful ACL reconstruction and rehabilitation, during instrumented single leg hop for distance testing, and compare these findings by subject perceived sports capability level. Subjective knee
function, internal health locus of control (IHLOC) and sports activity
characteristics (intensity, frequency) pre-knee injury, and at time of
follow-up were also compared. Based on previous work [11] and the
work of others [1–3,5–9,24,25], the hypothesis was that lower extremity neuromuscular activation during single leg hop for distance testing
would differ between the lower extremity that had undergone successful ACL reconstruction and rehabilitation and the uninvolved contralateral lower extremity between groups of differing perceived sports
capability compared to pre-injury status.
2. Methods
2.1. Experimental design
This was an evidence level IV therapeutic case series.
2.2. Subjects
From a group of 206 potential subjects who responded to the survey
portion of a larger study [11,22,23], 70 subjects (35 men, 35 women)
agreed to participate in this clinical phase. To control for the possible influence of knee laxity on lower extremity neuromuscular activation,
subjects who displayed a positive pivot shift glide [26] or a side-toside anterior translation knee laxity difference N4 mm were not included in this comparison decreasing the subject number to 65 (32 men, 33
women) subjects at 5.2 ± 2.9 years post-surgery. Subjects that participated in this clinical phase otherwise met the inclusion criteria of the
survey study [22]. Medical institutional research review board approval
was obtained, and subjects provided written informed consent. A minimum of two years had passed since subjects underwent unilateral primary ACL reconstruction with allograft tissue performed by the senior
author using transtibial tunnel drilling and bioabsorbable interference
screw fixation. Former patients who had undergone meniscal debridement, partial meniscectomy or meniscal repair (approximately 62%),
or who had grade I to III chondral injury at the medial or lateral femoral
condyle (approximately 10%) were allowed to participate. Patients who
had a posterior cruciate ligament injury, had undergone collateral ligament surgery, had an impaired contralateral knee, or who had not
adhered to the standardized progressive rehabilitation program were
excluded from study participation. Surgical intervention details and rehabilitation program functional milestone timetable information have
been previously reported [11]. Review of medical charts and physical
therapy records revealed that all subjects had complied with rehabilitation program recommendations and all had met or exceeded standard
accepted return-to-sports activity goals of a minimum 85% bilateral
equivalence with single leg hop for distance testing and 60°/s isokinetic
peak knee extensor and flexor torque testing prior to release from care
[12,19,27,28].
2.3. Data collection procedures
Clinical examination included knee joint palpation, passive knee
range-of-motion assessment using a handheld goniometer, and anterior
translational knee arthrometric testing at 133.4 N (KT-1000; MEDmetric,
San Diego, CA, USA). Electromyographic (4-channel, MyoSystem 1200;
Noraxon, Scottsdale, AZ, USA; 1000 Hz), and two-dimensional sagittal
plane kinematic (SIMI Motion 2D, Unterschleissheim, Germany; 60 Hz)
data were collected during single leg hop for distance testing. Gluteus
maximus, vastus medialis, medial hamstrings and medial head of gastrocnemius EMG activation amplitudes were standardized to levels
attained during single repetition, maximal volitional effort isometric
contractions (%MVIC). Additional details regarding EMG data collection
and analysis methods have been previously reported [11]. The primary
investigator performed the clinical evaluation and administered all
tests. Lower extremity test order was alternated between subjects to
control for potential order effects. Passive knee flexion range of motion
was evaluated with subjects in prone. Passive knee extension range of
motion was evaluated with subjects in supine. In both cases subjects actively flexed or extended their knee as far as possible. Following this the
primary investigator applied a slight pressure (approximately 22 N) to
assure that complete range of motion was achieved. Prior to single leg
hop for distance testing subjects performed two practice trials with
each lower extremity. Only two practice trials were performed prior to
data collection as all subjects had previous familiarity with test procedures. Testing was performed with unrestricted upper extremity movements using previously reported techniques [29]. Retro-reflective
markers were secured over the shoe of the test lower extremity to depict
the head of the fifth metatarsal, 2 cm distal to the protuberance of the lateral malleolus, over the joint line of the lateral knee, over gym shorts
depicting the greater trochanter of the femur, and over the spinous process of the third lumbar vertebrae. Following practice subjects performed
three test trials with each lower extremity (Fig. 1). A 3 m long by 2 m tall
calibration space was used for hip, knee, and ankle kinematic displacement measurement calculations at single leg hop for distance landing.
Following marker digitization and tracking, marker paths were
smoothed once using a low-pass digital filter. Peak displacement of
the hip, knee, and ankle was measured manually by the primary
investigator using a software curser function.
Sports activity participation level intensity and frequency prior to
ACL injury and at time of follow-up were measured using the Knee Outcome Survey Sports Activity Scale [11,22] and IHLOC was measured
using Multidimensional Health Locus of Control Survey Form C scores
[23,31,32]. The International Knee Documentation Committee (IKDC)
Subjective Knee Form was used to determine perceived knee function
[33].
2.4. Subject grouping
Subject group assignments were made based on how they responded
to the following question: “Compared to prior to your knee injury how
capable are you now in performing sports activities”, very capable
(group 1), capable (group 2), or not capable (group 3)? Most study subjects perceived that they had returned back to their preferred sport at
J. Nyland et al. / The Knee 21 (2014) 1191–1197
1193
Pilot testing of 6 subjects (3 men, 3 women) with similar demographics as study subjects (very capable = 2, capable = 2,
not capable = 2) revealed that surface EMG measurements had excellent test–retest reliability with intraclass correlation coefficients of
0.95–0.99 with comparable reliability noted for both single leg hop for
distance test propulsion and landing phases. Intra-rater test–retest reliability for passive knee range of motion measurements of the same subjects by the primary investigator using a handheld goniometer was 0.95
for knee extension and 0.97 for knee flexion. Two-dimensional sagittal
plane kinematic displacement measurements of the same subjects
displayed very good test–retest reliability with intraclass correlation
coefficients ranging from 0.92 to 0.96.
Minimal detectable differences were calculated (standard error of
the mean × 1.65 × √2) as described by Ries et al. [30]. The minimal
detectable side-to-side difference (90% confidence interval) for uninvolved and involved lower extremity gluteus maximus, vastus medialis,
medial hamstrings, and medial head of gastrocnemius standardized
surface EMG values (propulsion-landing) were 0.18–0.19, 0.16–0.17,
0.12–0.13, and 0.18–0.19 %MVIC, respectively.
2.6. Statistical analysis
Chi-square or Fisher's exact tests were used to determine categorical
group differences for gender distribution, the proportion of subjects in
each group whose perceived sports activity intensity or frequency differed from pre-injury values, allograft use frequency (bone-patellar
tendon-bone, hamstring, or tibialis anterior), anterior knee translation
laxity grade (A = ≤2 mm, B = N2–5 mm, C = N 5 mm), and IKDC Subjective Knee Survey grades (A = ≥ 90, B = 89–80, C = 79–70, D =
b70). A series of one-way ANOVA and Scheffe post-hoc tests were
used to evaluate continuous group demographic variables including
age at surgery, time post-surgery, height, weight, IKDC Subjective
Knee Form scores, IHLOC Survey scores, and sports activity participation
intensity and frequency differences (follow-up level–pre-injury level).
Group differences between lower extremities for standardized EMG
activation amplitudes, and peak lower extremity joint displacements
during single leg hop for distance testing were also evaluated using
one-way ANOVA and Scheffe post-hoc tests. An alpha level of P ≤ 0.05
was selected to indicate statistical significance. All statistical analysis
was performed using SPSS version 22.0 (IBM-SPSS, Armonk, NY, USA)
software.
Fig. 1. Instrumented single leg hop for distance test. Retro-reflective markers enabled twodimensional kinematic data analysis during landing phase. Surface EMG electrodes
positioned over the gluteus maximus, vastus medialis, medial hamstrings, and medial
head of gastrocnemius muscles enabled neuromuscular activation data analysis during
propulsion and landing phases.
pre-injury performance levels immediately following successful ACL
reconstruction and rehabilitation (Table 1).
2.5. Global question validation, measurement reliability, and EMG minimal
detectable differences
Pilot testing of the simple, global question regarding perceived sports
activity capability was performed among 30 subjects who only participated in the larger survey study [22] at a minimum of two years postACL reconstruction (group 1, n = 10, mean = 6.2 [95% CI = 3.4, 9]
years post-surgery, group 2, n = 8, mean = 7.3 [95% CI = 4.5, 10.1]
years post-surgery, and group 3, n = 9, mean = 5.1 [95% CI = 2.5, 7.7]
years post-surgery. Significant IKDC Subjective Knee Form score group
differences were observed between each group (96, 81.5, and 70.2,
respectively, P = 0.02).
3. Results
Knee palpation revealed that no subject had point tenderness or effusion at either
knee at the time of testing. Subject demographic information, IKDC Subjective Knee
Survey scores, IHLOC Survey scores, and perceived sports intensity and frequency changes
Table 1
Athletic activity at time of index knee injury and subjects who perceived recovery to preferred sport at pre-injury level following rehabilitation grouped by current perception of sports
activity capability compared to prior to knee injury. # = subject number.
Group 1 (very capable)
Athletic activity at
time of index knee
injury
American football
Soccer
Basketball
Volleyball
Skiing
Baseball or softball
Lacrosse
Horseback riding
Ice hockey
Tennis
#
5
4
3
2
1
1
1
1
1
1
20
Group 2 (capable)
Subjects who perceived
recovery to preferred sport
at pre-injury level (#)
Athletic activity at
time of index knee
injury
3
3
3
2
1
1
1
1
1
1
American football
Skiing
Basketball
Physical labor
Gymnastics/cheerleading
Rough play
Soccer
Field hockey
Rollerskating
17 (85%)
Group 3 (not capable)
#
5
5
3
3
2
2
1
1
1
23
Subjects who perceived
recovery to preferred sport
at pre-injury level (#)
Athletic activity at
time of index knee
injury
#
Subjects who perceived
recovery to preferred sport
at pre-injury level (#)
4
4
3
3
2
2
0
1
1
Basketball
American football
Motorcycle or ATV accident
Baseball or softball
Volleyball
Gymnastics/cheerleading
Skiing
Rough play
Physical labor
Running
Bowling
4
3
3
2
2
2
2
1
1
1
1
22
3
2
3
2
2
2
1
1
1
1
1
19 (86%)
20 (87%)
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J. Nyland et al. / The Knee 21 (2014) 1191–1197
are reported in Table 2. Subjects perceived themselves to be very capable of performing
sports activities (Group 1, n = 20); capable of performing sports activities (Group 2,
n = 23), or not capable of performing sports activities (Group 3, n = 22). Groups
displayed comparable demographic factors; however, Group 3 had significantly lower
mean IKDC Subjective Knee Form scores than Group 1 (P = 0.016) and had significantly
decreased perceived sports intensity level changes compared to Groups 1 and 2 (P =
0.004). Group 3 also had a higher than expected proportion of subjects that reduced
their sports activity intensity by two levels at time of follow-up compared to their preinjury status (Fisher's exact test statistic = 8.8, P = 0.01). Pre-injury and follow-up sports
activity frequency change differences did not display statistically significant group
differences.
Group comparisons for passive knee extension, passive knee flexion, anterior knee
laxity, and single leg hop for distance did not display significant differences (Table 3). Although groups with higher perceived sports capability displayed greater mean single leg
hop distances, significant group differences between the involved and uninvolved lower
extremities were not evident (P = 0.77). Groups also displayed comparable IKDC single
leg hop grade frequency distributions (Fisher's exact test = 8.0, P = 0.23), IKDC Subjective
Knee Survey grade distributions (Fisher's exact test = 7.7, P = 0.25), allograft type use
distributions (Fisher's exact test = 3.7, P = 0.46) and anterior knee laxity grade (Fisher's
exact test statistic = 1.6, P = 0.46). Peak hip flexion, knee flexion, and ankle dorsiflexion
displacements during instrumented single leg hop for distance landings also did not differ
between groups (P ≥ 0.42).
Involved–uninvolved lower extremity comparisons of standardized mean EMG activation amplitudes during single leg hop for distance propulsion and landing are reported
in Tables 4a and 5a, respectively. During both single leg hop for distance propulsion and
landing, Group 1 had increased involved lower extremity gluteus maximus and medial
hamstring standardized EMG activation amplitudes compared to Group 3. Chi-square
tests revealed that during both single leg hop propulsion and landing a significantly greater proportion of Group 1 subjects displayed increased involved lower extremity gluteus
maximus (Tables 4b, 5b) and hamstring (Table 4c, 5c) standardized EMG amplitudes
compared to Group 2 and Group 3. Post-priori statistical power calculations based on a
minimum of 20 subjects/group and an alpha level of 0.05 revealed ≥0.86 statistical
power (1 − β) for comparisons between Groups 1 and 3 for gluteus maximus and medial
hamstring standardized EMG activation amplitude side-to-side differences, with the exception of a statistical power of 0.66 for medial hamstring standardized EMG activation
amplitude during single leg hop for distance landing. Uninvolved and involved lower
extremity vastus medialis and medial head of gastrocnemius EMG activation amplitude
differences were comparable between groups.
4. Discussion
Subjects that perceived themselves to be very capable with current
sports activity function compared to prior to their knee injury had
increased involved lower extremity gluteus maximus and medial
hamstring muscle group neuromuscular activation during single leg
hop performance. IKDC subjective knee function grades, single leg hop
for distance test results and anterior knee laxity side-to-side differences
and grades were comparable between groups. These findings were evident at an overall mean of N 5 years after successful ACL reconstruction
and rehabilitation. These observations observed in subjects with higher
perceived sports capability suggest the use of compensatory involved
lower extremity neuromuscular activation to enhance single leg hop
for distance test performance [34]. These compensations following successful surgery, rehabilitation, and non-impaired knee laxity that lead to
most subjects being able to return to their preferred sport at their preinjury level immediately following rehabilitation may be related to a
permanent neurosensory deficit at the reconstructed ACL [1,2,5–8,11],
its influence on the afferent pathway and on CNS re-organization of
sensorimotor programming. With practice, patients who have undergone ACL reconstruction may become better at coping with higher
level sport movements through the development of compensatory
lower extremity neuromuscular activation patterns [1,2,5–8,11]. Improving our understanding of these strategies may improve the results
of post-surgical and non-surgical rehabilitation and help construct
new motor control learning criteria prior to advancing patients through
sport specific training and eventual release back to unrestricted sport
activities [4].
Perceived higher level sports capability compared to pre-knee injury status was associated with increased lower extremity neuromuscular compensations through hip muscle groups. Hip joint
afferent function remains non-impaired, decreasing dependence on
the sensory-impaired knee region. During maximum effort movements
such as a single leg hop for distance ipsilateral hip neuromuscular activation (gluteus maximus and medial hamstrings) may be up-regulated
to enable successful task performance while placing lesser dependence
on local knee extensor activation [34].
With greater understanding that ACL deficiency changes afferent
pathway information leading to CNS reorganization of sensorimotor
programming [1,4], and ACL reconstruction restores mechanical, but
not neurosensory function [2], rehabilitation should focus more on
CNS re-education rather than solely attempting to optimize peripheral
neuromuscular function. Rehabilitation clinicians should take greater advantage of adaptive CNS characteristics, identifying patient sports movement goals and providing guided rehabilitation exercise experiences that
stimulate motor learning thereby helping the re-programmed CNS find
effective solutions [1]. This may be especially important during the latter
stages of rehabilitation and during return to sport-specific training.
Criteria-based neuromuscular re-training programs directed at motivated patients may improve functional lower extremity extensor muscle
balance between the hip, knee and ankle joints at the involved lower extremity following ACL reconstruction [14,25,28]. However, given that
grafts used for ACL reconstruction (allograft or autograft) do not restore
native ACL neurosensory properties it is unlikely that a long-term restoration to premorbid sensorimotor relationships can be achieved [1,2,5–8,
11]. As patients learn to cope with progressively more challenging sports
movement tasks in the presence of modified afferent information during
rehabilitation and following return to play they may begin to develop
more effective use of compensatory lower extremity extensor neuromuscular activation through the hip.
5. Study limitations
This study has several important limitations. Asking subjects to
recall their perception of whether or not they successfully returned to
their preferred sport at their pre-injury level following surgery and
rehabilitation at approximately five years post-surgery may have led
to recall bias. Some subjects may have either over- or under-estimated
their true performance capability [35]. To minimize the potential influence of excessive anterior knee laxity on lower extremity neuromuscular activation amplitudes of the 70 subjects who agreed to participate,
Table 2
Subject demographic data, IKDC Subjective Knee Survey score, Internal Health Locus of Control Survey score, and perceived sports activity intensity and frequency change comparison by
perceived sports involvement level group. Mean [95% confidence interval]. * = P b 0.05.
Gender (#, % men)
Age at surgery (yrs)
Time post-surgery (yrs)
Height (cm)
Weight (kg)
IKDC subjective knee survey score
Internal health locus of control survey score
Perceived sports activity intensity change (current–pre-injury)
Perceived sports activity frequency change (current–pre-injury)
Group 1
Group 2
Group 3
P
20, 50%
26.5 [21.9, 31.8]
4.6 [2.8, 6.2]
176.5 [170.4, 180.1]
76.8 [67.4, 80.3]
91.0 [84.1, 94.6]
28.8 [25.0, 30.9]
−0.35 [−0.77, −0.10]
−0.30 [−0.77, −0.10]
23, 52.2%
29.3 [24.1, 34.4]
5.4 [4.2, 6.6]
172.8 [168.4, 177.3]
76.8 [68.3, 85.2]
87.2 [82.1, 92.4]
26.7 [24.1, 29.2]
−0.41 [−0.67, −0.15]
−0.54 [−0.90, −0.19]
22, 45.5%
33.6 [26.4, 39.1]
5.2 [3.8, 6.5]
172.1 [167.1, 177.1]
79.7 [68.0, 91.3]
78.6 [71.7, 85.5]
24.9 [22.0, 27.7]
−1.10 [−1.6, −0.65]
−0.60 [−1.0, −0.25]
0.95
0.20
0.56
0.38
0.86
0.016* (Groups 1 N 3)
0.44
0.004* Groups 1,2 N 3)
0.56
Table 3
Clinical examination results. Uninvolved–involved lower extremity for passive knee extension and flexion difference; involved–uninvolved lower extremity for knee laxity and single leg hop for distance differences. Mean [95% confidence interval].
UI = uninvolved lower extremity. I = involved lower extremity. Diff. = difference. Mean [95% confidence interval].
Group 1
Knee extension (°)
Knee flexion (°)
Knee laxity (mm)
Single-leg hop for distance (m)
Group 2
Group 3
UI
I
Diff.
UI
I
Diff.
UI
I
Diff.
P
1.9 [−0.1, 3.2]
143.6 [142, 147.4]
5.4 [4.6, 6.8]
1.27 [1.13, 1.51]
1.2 [−0.7, 2.2]
142.1 [140.1, 146.4]
6.7 [5.7, 7.9]
1.27 [1.14, 1.48]
0.7 [−0.5, 2.7]
1.5 [−0.4, 4.2]
1.3 [−0.2, 1.6]
0.0 [−0.9, 1.1]
1.8 [0.4, 3.1]
143.0 [138.9, 147]
5.4 [4.4, 6.5]
1.06 [0.85, 1.26]
0.9 [−0.6, 2.1]
139.0 [135.2, 142.8]
6.9 [5.9, 7.8]
1.10 [0.91, 1.29]
0.9 [−0.2, 1.0]
4.0 [1.0, 7.5]
1.5 [0.9, 2.4]
0.04 [−0.9, 1.0]
2.6 [1.2, 3.3]
139.7 [135.8, 143.8]
5.4 [4.3, 6.5]
0.95 [0.79, 1.11]
1.9 [0.5, 3.3]
137.3 [132.9, 142.4]
7. 0 [5.9, 8.2]
0.82 [0.67, 0.97]
0.7 [−0.7, 1.7]
2.4 [−1.0, 6.9]
1.6 [0.5, 2.4]
−0.13 [−0.8, 1.1]
0.78
0.82
0.25
0.77
Table 4a
Group 1
GM
VM
MH
G
Group 2
J. Nyland et al. / The Knee 21 (2014) 1191–1197
Table 4
Standardized EMG amplitudes during single leg hop for distance propulsion [%MVIC involved lower extremity − %MVIC uninvolved lower extremity]. GM = gluteus maximus, VM = vastus medialis, MH = medial hamstrings, G = gastrocnemius.
* = P b 0.05.
Group 3
UI
I
Difference
UI
I
Difference
UI
I
Difference
P
0.97 [0.87, 1.07]
1.31 [1.13, 1.48]
0.77 [0.62, 0.93]
1.32 [1.01, 1.42]
1.2 [1.02, 1.32]
1.21 [1.13, 1.46]
0.91 [0.76, 1.05]
1.38 [1.28, 1.48]
0.23 [0.07, 0.40]
−0.1 [−0.42, 0.21]
0.14 [−0.08, 0.36]
0.06 [−0.19, 0.30]
0.98 [0.90, 1.06]
1.36 [1.21, 1.51]
1.08 [0.79, 1.05]
1.20 [1.11, 1.28]
1.1 [1.07, 1.23]
1.16 [1.02, 1.3]
1.16 [1.04, 1.29]
1.29 [1.21, 1.37]
0.12 [−0.08, 0.26]
−0.2 [−0.60, 0.13]
0.08 [−0.17, 0.30]
0.09 [−0.08, 0.29]
1.09 [0.99, 1.19]
1.51 [1.34, 1.69]
1.27 [1.12, 1.43]
1.30 [1.2, 1.41]
1.00 [0.79, 1.15]
1.45 [1.28, 1.62]
0.97 [0.82, 1.12]
1.18 [1.09, 1.28]
−0.09 [−0.31, 0.11]
−0.06 [−0.33, 0.19]
−0.3 [−0.63, −0.07]
−0.12 [−0.30, 0.05]
Group 1 N 3, P = 0.036*
0.72
Group 1 N 3, P = 0.011*
0.20
Table 4b
Increased gluteus maximus activation amplitude at involved lower extremity
No change or decreased gluteus maximus activation amplitude at the involved lower extremity
Group 1
Group 2
Group 3
Total
16 [11.4]*
4 [8.6]
20
13 [13.1]
10 [9.9]
23
8 [12.5]
14 [9.5]
22
37 [37]
28 [28]
65 [65]
11 [7.7]*
9 [12.3]
20
10 [8.8]
13 [14.2]
23
4 [8.5]
18 [13.5]
22
25 [25]
40 [40]
65 [65]
Chi-Square = 8.1, P = 0.019*
Table 4c
Increased hamstring activation amplitude at involved lower extremity
No change or decreased hamstring activation amplitude at the involved lower extremity
1195
Chi-Square = 6.4, P = 0.041*
only those with a negative pivot shift test or ≤4 mm side-to-side anterior knee laxity difference were included in this analysis. Therefore, 5
subjects that demonstrated a positive pivot shift test were eliminated
from statistical analysis, leaving 65 subjects out of a pool of 206 subjects
who responded to the survey arm of the study [22]. The initial survey
study sample consisted of 335 consecutive former patients. Although
the subjects who participated in this study phase displayed similar
demographics to the overall subject pool the possibility of selection
and/or sampling bias exists [35,36]. Additionally, the post-test design
used in this prospective study relied on the opposite lower extremity
as a control. Ideally, a separate healthy, age-matched control group or
an otherwise healthy group of ACL deficient patients would have been
included in the study design. Clinical lower extremity functional
performance tests such as single leg hop for distance testing however
generally rely on comparisons with the contralateral, uninjured lower
extremity [19,27,29,37,38]. This study only evaluated the single leg
hop for distance. Other functional tests should be considered with future research in this area [21], using a longitudinal design and repeated
measures that evaluate changes throughout early and late rehabilitation, sport specific training, and return to sport phases. Thigh girth measurements were not performed in this study. Thigh girth measurements
may have provided additional insight regarding subject thigh muscle
mass and the magnitude of fast twitch muscle fiber atrophy. However,
without supporting cross-sectional magnetic resonance imaging to ascertain lean versus fat tissues it would have been difficult to accurately
delineate muscle volume. Additionally, this study represents a small
subject group consisting of former patients who had their ACL reconstructed by the same fellowship trained knee surgeon using exclusively
allograft tissue. Therefore these results may not generalize to other populations. Use of allograft tissue however negates the potential influence
of autogenous tendon harvest for ACL graft harvest on quadriceps
femoris or hamstring muscle group function and screening to ensure
the absence of a positive pivot shift test or excessive side-to-side anterior knee laxity differences minimized the influence of laxity on study
findings.
Another study limitation is use of two-dimensional sagittal kinematic analysis. Although three-dimensional kinematic analysis would have
provided more accurate depictions of lower extremity joint movements,
two-dimensional analysis remains useful and clinically practical as a
screening tool for primarily uniplanar movements such as single leg
hop for distance testing. Lastly, neither ground reaction force nor inverse dynamic moment analysis was performed. This addition would
have provided a more comprehensive representation of lower extremity joint contributions to single leg hop for distance test performance.
4 [8.5]
18 [13.5]
22 [22]
25 [25]
40 [40]
65 [65]
37 [37]
28 [28]
65 [65]
9 [8.8]
14 [14.2]
23 [23]
10 [12.5]
12 [9.5]
22 [22]
6. Conclusion
Lower extremity neuromuscular compensations suggesting a hip
bias with increased gluteus maximus and medial hamstring activation
was identified at the involved lower extremity among most subjects
who perceived high perceived sports capability compared to preinjury status. These compensations may be related to a permanent
neurosensory deficit, and its influence on afferent pathway changes
that influence CNS sensorimotor re-organization. Further prospective,
longitudinal research is needed.
Chi-square = 7.7, P = 0.021
12 [7.7]
8 [12.3]
20 [20]
Table 5c
Chi-square = 6.3, P = 0.048
Increased hamstring activation amplitude at involved lower extremity
No change or decreased hamstring activation amplitude at the involved lower extremity
11 [13.1]
12 [9.9]
23 [23]
16 [11.4]
4 [8.6]
20 [20]
Group 2
Group 1
Table 5b
1.61 [1.47, 1.89]
1.31 [1.20, 1.50]
1.50 [1.32, 1.69]
1.28 [1.17, 1.39]
Increased gluteus maximus activation amplitude at involved lower extremity
No change or decreased gluteus maximus activation amplitude at the involved lower extremity
Total
Group 1 N 3, P = 0.041*
0.80
Group 1 N 3, P = 0.023*
0.26
Group 3
P
Difference
1.14 [0.90, 1.39]
1.63 [1.45, 1.80]
1.23 [1.01, 1.44]
1.25 [1.12, 1.39]
UI
1.37 [1.18, 1.69]
1.58 [1.40, 1.77]
1.6 [1.51, 2.08]
1.32 [1.18, 1.46]
1.33 [1.06, 1.49]
1.46 [1.29, 1.60]
1.36 [1.17, 1.55]
1.26 [1.15, 1.38]
0.37 [−0.08, 0.82]
−0.13 [−.46, 0.21]
0.12 [−0.20, 0.44]
0.23 [−0.06, 0.53]
1.51 [1.36, 1.83]
1.39 [1.21, 1.55]
1.17 [0.97, 1.39]
1.23 [1.17, 1.54]
1.14 [0.88, 1.39]
1.52 [1.20, 1.57]
1.05 [0.84, 1.30]
1.00 [0.86, 1.14]
GM
VM
MH
G
I
UI
Group 1
0.28 [−0.18, 0.34]
−0.15 [−0.46, 0.16]
−0.16 [−0.51, 0.19]
0.02 [−0.27, 0.31]
Group 3
UI
Difference
Group 2
Difference
I
I
−0.23 [−0.42, 0.06]
0.05 [−0.28, 0.22]
−0.37 [−1.11, −0.17]
−0.07 [−0.44, 0.21]
J. Nyland et al. / The Knee 21 (2014) 1191–1197
Table 5a
Table 5
Standardized EMG amplitudes during single leg hop for distance landing [%MVIC involved lower extremity − %MVIC uninvolved lower extremity]. GM = gluteus maximus, VM = vastus medialis, MH = medial hamstrings, G = gastrocnemius.
Mean [95% confidence interval]. * = P b 0.05.
1196
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