Download THE PASSIVE CONTRIBUTIONS OF THE VASTUS MEDIALIS AND

THE PASSIVE CONTRIBUTIONS OF THE VASTUS MEDIALIS AND VASTUS LATERALIS
TO KNEE EXTENSION AND HIP FLEXION
1,2
David B. Lipps, 2Emma Baillargeon, 2Thomas G. Sandercock and 1,2Eric J. Perreault
1
Rehabilitation Institute of Chicago, Chicago, IL USA
2
Northwestern University, Chicago, IL, USA
email: [email protected]
INTRODUCTION
METHODS
Muscles primarily transmit forces through tendon,
but also transmit forces to neighboring muscles
through myofascial connections. These adhesions
strengthen following surgery as scar tissue, which
produces greater myofascial force transmission and
less tendon force transmission [1]. Musculoskeletal
injuries may lead to greater intermuscular fibrosis
[2], strengthening these myofascial connections.
Since vastus medialis tendon elongation is reduced
in patellofemoral pain [3], we seek to explore if
patellofemoral forces are altered by the myofascia.
First, we need to understand how healthy
myofascial connections affect the vastus lateralis
(VL) and vastus medialis (VM). The VL and VM
articulate the knee, but are adjacent to hip flexor
muscles (rectus femoris, tensor fasciae latae). The
VL and VM will be isometric during passive hip
flexion if the myofascial connections are irrelevant.
Therefore, we investigated whether the healthy VL
and VM will shorten during passive knee extension
and remain isometric during passive hip flexion.
Three healthy adults (2 F, 1 M; 2 R, 1 L leg; mean
age: 29 yrs, height: 175 cm, weight: 68 kg) had one
leg moved within a Lokomat driven gait orthosis
(Homoca, Inc.). The Lokomat was attached with
three leg cuffs and a pad over the greater trochanter
to prevent pelvic motion (Fig. 1). The Lokomat
repeatedly moved the limb with a gait profile of 1
km/h. This profile was customized so the knee joint
(10°–73° flexion) was passively moved with the hip
fixed (0° flexion), or the hip joint (-16°–37° flexion)
was passively moved with the knee fixed (8°
flexion). The subjects were provided 50% bodyweight support while standing on the contralateral
limb.
Muscle activity recorded with surface
electromyography (EMG) of the VL, VM, rectus
femoris (RF), biceps femoris (BF) and
semitendinosus (ST) (Motion Lab Systems) was
normalized to a maximum voluntary contraction
and rectified. Data were sampled at 2 kHz.
Peak Knee Flexion Peak Knee Extension
Vastus Lateralis
Superficial
Proximal
Distal
Deep
Vastus Medialis
EMG
US Probe
Image Probe
Probe Average
Figure 1: (left) Lokomat schematic. (right) Sample VL
and VM ultrasound images with measurement probes
tracked from peak knee flexion to peak knee extension.
A Siemens ACUSON Antares ultrasound system
(B-mode, 13 MHz transducer, 38 mm width, 75 µm
pixel resolution) was synchronized to the Lokomat
and recorded motion of the VL and VM (40 Hz).
The transducer was aligned to each muscle fiber
orientation with a custom holder secured around the
thigh to minimize movement. The transducer was
distally located at ~20% femur length between the
epicondyle and greater trochanter (Fig. 1). An
automated Lucas-Kanade-Tomasi algorithm [4]
tracked the spatial and temporal gradients between
ultrasound images over one cycle of knee extensionflexion or hip flexion-extension. The displacement
of two sets of four measurement probes (initially 30
mm apart) was tracked and averaged along the
superficial and deep surface of the fascicle region
(Fig. 1). Paired t-tests compared peak proximal
displacement during hip flexion of the superficial
The present study shows that even in healthy
subjects, the vasti muscles shorten during passive
hip flexion, even though they do not articulate the
hip. Similar results have been shown between the
soleus and gastrocnemius [5]. It is known that
myofascial connections can alter the relative motion
of the quadriceps muscle following rectus femoris
tendon transfer [6]. We posit that myofascial
connections between the vasti and neighboring hip
flexors contribute to these results. However, future
work is needed to confirm this hypothesis and to
determine if the length changes shown here result in
significant intermuscular force transmission in both
healthy and pathologic populations.
The study was limited by a small sample size and
the lack of measurements of fascicle length, the
distal rectus femoris (due to the thigh cuff), femoral
internal rotation, and myofascial force transmission.
The Lokomat also had a shorter knee cycle than hip
cycle. Future work will address these concerns.
REFERENCES
1. Maas H, et al. J Biomech 45, 289-96, 2012.
2. Williams, PE, et al. J Anat, 158, 109-14, 1988.
3. Wilson N, et al. J Appl Physiol 107, 422-8, 2009.
4. Darby J, et al. J Appl Physiol 112, 313-27, 2012.
5. Bojsen-Moller J, et al. J Appl Physiol 109, 160818, 2010.
6. Asakawa DS, et al. J Biomech 35, 1029-37, 2002.
ACKNOWLEDGEMENTS
Dr. Yasin Dhaher, Dr. Wendy Murray, Tim
Haswell, Andrew Tan, and Despina Kotsapouikis.
Proximal
Tissue
Joint Angle Displacement
(deg)
(mm)
Exemplar trials of VL during one cycle of passive
knee and hip motion show tissue displacement was
greater during knee extension than hip flexion, and
greater deep than superficial (Fig. 2). The VL
shortening during hip flexion is a novel finding
since this muscle does not articulate the hip.
Similar results were found for the VM (Fig. 3).
EMG recordings confirm the muscles remained
passive since all muscle activity was less than 1%
MVC. The joint angles indicate only a single joint
was moved during the experiment. During passive
hip flexion, the proximal displacement of VL and
VM indicates the muscles were not isometric,
regardless if the measurement were superficial or
deep (all 4 p-values < 0.001). There was a
significant interaction between the measurement
surface and the joint moved (VL & VM: p < 0.001).
Post-hoc comparisons are provided in Fig. 3.
Displacement of the deep and superficial borders of
the VL and VM indicates local shortening during
passive hip flexion, even though these muscles do
not articulate the hip. Future work will address if
myofascial connections are responsible.
Rectified
EMG
(%MVC)
RESULTS AND DISCUSSION
CONCLUSIONS
Knee Extension-Flexion
15
10
Super
5
Deep
0
0
1
2
3
80
Knee
Hip
40
0
5
0
1
2
RF
BF
0
0
VM
3
VL
Hip Flexion-Extension
15
10
5
0
0
2.5
5
40
10
−20
5
0
2.5
5
0
2.5
Time (sec)
5
ST
1
2
Time (sec)
3
0
Figure 2: Exemplar trials of passive knee extension
(left) and hip flexion (right) of the vastus lateralis.
20
Proximal Tissue
Displacement (mm)
and deep surfaces of the VL and VM to zero (i.e.
isometric). Peak displacement of the VL and VM
was analyzed with a 2x2 ANOVA (fixed:
measurement surface (superficial/deep), joint
moved (hip/knee); random: subject) with Tukey
post-hoc tests (alpha: p = 0.01).
15
Vastus Medialis Oblique
*
*
Vastus Lateralis
*
*
*
*
*
10
5
0
Superficial, Hip Flexion
Deep, Hip Flexion
Superficial, Knee Extension
Deep, Knee Extension
Figure 3: Peak muscle shortening of the superficial and
deep borders of the vasti muscles during passive knee
extension and hip flexion. * - significant post-hoc
comparison (p < 0.01)