Reliability of Hamstring Flexibility Measurements in Children with Cerebral Palsy and Typically Developing Children using a Biodex Dynamometer
Stacey DeJong, PT, MS, PCS1, Wayne Stuberg, PhD, PT, PCS1, Susan Puumala, MS2, Julie Stoner, PhD2
Munroe-Meyer Institute Motion Analysis Laboratory1 and Dept. of Preventive and Societal Medicine2, University of Nebraska Medical Center, Omaha, NE
Figure 6a: Torque-Angle Curve
Introduction
Methods
Methods
Children and adults with cerebral palsy frequently have decreased flexibility of muscle and
tendon, which contributes to movement impairment and activity limitation. Physical therapy
intervention may include therapeutic exercise, positioning, and/or use of orthoses to improve
flexibility. Accurate objective measurement of muscle and tendon length is essential to
quantify severity, guide intervention, and assess outcomes.
Testing Protocol
Variables
• The positioning chair of the Biodex System 3 dynamometer5 was modified to provide firm
stabilization of the pelvis and thigh, with a hip angle of 115 degrees.
• Ao: knee angle when minimal
corrected torque (0.5 Nm) was
recorded
In this study, we developed a method to measure hamstring flexibility objectively using a
Biodex dynamometer to generate torque-angle curves. We then examined intra-session and
inter-session reliability in children with spastic cerebral palsy, as well as intra-session
reliability in children with typical development.
Subjects
1. Eleven children with spastic cerebral palsy (CP)
• Ages 5 to 12 Years (Mean 9.2, SD 2.5)
• 6 males, 5 females
• 6 with spastic diplegia, 5 with spastic quadriplegia
• Gross Motor Function Classification Scale Levels 1 through 4
• 3 subjects in Level 1
• 1 subject in Level 2
• 4 subjects in Level 3
• 3 subjects in Level 4
• No lower extremity surgery within the previous year, or Botox in the previous 6 months
• Tmax: torque at Amax
• Stiffness: slope of the line from
Amax to Ao on the torque-angle
curve
Figure 1
Custom back support to
anteriorly tilt the pelvis
Figure 2
Pelvic straps to prevent pelvis
from sliding forward (rear view)
Figure 3
Strap to stabilize
distal femur
• Passive mode was used to extend the subject’s knee very slowly (2 degrees per second),
from 95 deg. of flexion toward extension.
• The subject was instructed to relax and to ‘Let it go as far as you can, then say stop’.
• The knee was immediately returned to the starting position.
• Each test included at least 5 repetitions.
• Surface electromyography (EMG)6 was used to monitor the medial and lateral hamstrings
and the vastus lateralis. Muscle activity was defined as present if the EMG signal of any
muscle remained 3 standard deviations above its baseline level for greater than 500 msec.
Children with CP were also measured again on a separate day within two weeks of the
first session, for inter-session reliability.
1.
2.
3.
4.
Stuberg, WA, et al, Dev Med Child Neurol, 30:657-665, 1988
Kilgour, G, et al, Dev Med Child Neurol, 45:391-399, 2003
Tardieu C, et al, Arch Phys Med Rehabil, 63(3):97-102,1982
Holt S, et al, Dev Med Child Neurol, 42:541-544, 2000
Ao-Amax
10
Torque (Nm)
9
Slope = ΔTorque/ ΔAngle
= Stiffness in Nm/Deg.
8
7
6
5
4
3
2
1
0
-1
0
15
30
45
Position (deg.)
Amax
-2
Figure 6b
75
90
Ao
Figure 6c
14
14
Test 1
12
10
8
8
6
6
4
4
2
2
0
30
60
Test 2
12
10
0
60
90
0
0
-2
A-HCT
30
60
90
A-HCT
Statistical Analysis
Descriptive statistics were calculated. Intra-class correlations were used to assess reliability
based on a single randomly selected leg for each subject. Differences between the paired
groups (CP vs TD) were examined using a Wilcoxon signed rank test.
Results
Table: Results
Intra-Session
TD Group
Intra-Session
CP Group
Inter-Session
CP Group
Ao
0.90
0.84
0.80
80.42 ± 2.68
81.15 ± 3.03
0.9
• Repetitions were eliminated from analysis if muscle activity was present, except at the
end of the movement.
Amax
0.99
0.87
0.61
38.62 ± 3.82
42.54 ± 2.85
0.9
Tmax
0.99
0.92
0.85
9.82 ± 2.23
8.89 ± 1.43
0.8
• Remaining repetitions were averaged. Torque due to gravity was subtracted, and gravitycorrected torque in Newton-meters was plotted against knee angle in degrees. Curve
fitting was done using XLFit4 software8 and a reciprocal exponential model. (Figure 6a-c).
Amax-Ao
0.96
0.94
0.81
41.80 ± 3.57
38.62 ± 4.23
0.6
A-HCT
0.96
0.75
0.74
39.77 ± 4.01
46.82 ± 2.26
0.4
Stiffness
0.97
0.95
0.98
0.20 ± 0.04
0.23 ± 0.05
0.6
• Biodex torque, position, and velocity analog signals and electromyography signals were
recorded and processed with RUN Technologies7 A-D board and Datapac 2K2 software.
(Figure 5)
Figure 5 - DataPac data acquisition.
Variable
TD Group
Mean ± SE
CP Group
Mean ± SE
TD vs. CP
Wilcoxon
p-value
Conclusions: Intra-session reliability was high, with all ICCs above 0.75 for the CP and TD
groups. The TD group demonstrated higher reliability for each measure than the CP group.
Inter-session reliability for the CP group was generally lower but still high, with most ICC
values greater than 0.75. For inter-session reliability in the CP group, reliability of the position
at maximum subject tolerance (Amax) was lower than reliability of the position at a given
torque level (A-HCT).
Clinical Relevance: This study demonstrates a reliable method of measuring hamstring
flexibility using a Biodex dynamometer. The advantage of using the Biodex rather than a
goniometer is to allow measurement of musculotendinous characteristics, including angle at
initial resistance, angle at a given torque load, angle at maximum tolerance, and the amount
of resistive torque tolerated.
Testing Schedule:
•
13
11
-2
Methods
All children were measured twice within one session for intra-session reliability.
• A-HCT: angle at the highest
common torque level achieved
across all tests for each subject
14
12
To=0.5
• Amax-Ao: difference between
Amax and Ao
2. Eleven children with history of typical development (TD)
• Age and gender matched to the subjects with cerebral palsy
• Ages 5 to 12 Years (Mean 9.2, SD 2.5)
• No history of musculoskeletal or neurological condition
•
Tmax
• Amax: knee angle when
maximum subject tolerance was
reached
Flexibility is typically assessed clinically using goniometric measurement of passive range of
motion. The maximum angle of joint excursion is measured, while an unknown amount of
torque is applied by the examiner. Many investigators have reported high intra-rater reliability
of goniometry for single joint muscles in adult subjects without neurological impairment.
Reliability coefficients have been shown to decrease, however, with multiple testers, multijoint muscles, and subjects who have spasticity. In studies of inter-session reliability of
goniometric hamstring flexibility measurements in children with cerebral palsy, mean
differences of 5 to 10 degrees have been reported, with 95% confidence intervals up to 16
degrees.1,2 This limits the usefulness of goniometry in clinical settings as well as in outcomes
research.
Complete description of muscle and tendon flexibility requires additional information that is
not typically obtained with goniometry. Tardieu,3 Holt,4 and others have used custom made
laboratory equipment to measure the relationship between joint angle and torque applied
during passive muscle/tendon stretch. Analysis of the torque-angle curve provides a more
complete description of muscle and tendon flexibility.
15
Figure 4
Positioning for testing
5.
6.
7.
8.
Biodex Medical Systems, Inc. 20 Ramsay Road, Shirley, New York 11967-4704
Motion Lab Systems, Inc., 15045 Old Hammond Hwy, Baton Rouge, LA 70816
RUN Technologies, 22702 Via Santa Maria, Mission Viejo, CA 92691
idbs, 215 1st Street, Cambridge, MA 02142
Funding for this study was provided by the Foundation for Physical Therapy Clinical Research Grant 2003,
the Watt Foundation in Omaha, NE, in part by Project #8188 from the Maternal Child Bureau (Title V, Social Security Act),
Health Resources and Services Administration, Department of Health and Human Services (DHHS), and in part by grant
90DD0533 from the Administration on Developmental Disabilities, Administration for Children and Families, DHHS.