The Knee 14 (2007) 2 – 8
Review
Psychometric properties of measurement tools for quantifying knee joint
position and movement: A systematic review
Pagamas Piriyaprasarth ⁎, Meg E. Morris
School of Physiotherapy, The University of Melbourne, Victoria, 3010, Australia
Received 26 June 2006; received in revised form 3 October 2006; accepted 15 October 2006
Abstract
This systematic review critically evaluates literature on the reliability and validity of measurement tools for quantifying knee joint angles
and knee movement. A search was conducted of seven medical databases and one biomedical engineering database, yielding 43 articles that
reported reliability or validity. Tools for quantifying knee joint angles included standard handheld goniometers, fluid-based goniometers,
gravity-based goniometers, photographs and two dimensional (2-D) motion analysis. Knee movement was measured with
electrogoniometers, 2-D and three dimensional (3-D) motion analysis. Intraclass correlation coefficients for testing knee angles ranged
from 0.51–1.00 for intratester reliability and 0.43–0.99 for intertester reliability. For quantifying knee position, sequential MRI and 2-D had
the least error of measurement, followed by hand held goniometers and photographs. For dynamic measurements, electrogoniometers and 3D motion analysis were most reliable and had low error of measurement. Strong concurrent validity was found between hand held
goniometers and radiographs, as well as between hand held goniometers and 3-D motion analysis.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Knee; Systematic review; Review; Reliability; Measurement
Contents
1.
2.
3.
Introduction . . . . . . . . . . . . . . . . . .
Methods . . . . . . . . . . . . . . . . . . . .
Results . . . . . . . . . . . . . . . . . . . . .
3.1. Search strategy yields . . . . . . . . . .
3.2. Quality of review articles . . . . . . . .
3.3. Participants . . . . . . . . . . . . . . .
3.4. Testers. . . . . . . . . . . . . . . . . .
3.5. Static knee joint angle measurements . .
3.6. Dynamic knee joint angle measurements
3.7. Statistical analysis . . . . . . . . . . . .
3.8. Validity of measurement tools. . . . . .
3.9. Reliability of measurement tools . . . .
4. Discussion . . . . . . . . . . . . . . . . . . .
5. Conclusion . . . . . . . . . . . . . . . . . . .
6. Potential conflict of interest . . . . . . . . . .
Acknowledgements . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . .
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⁎ Corresponding author. Tel.: +61 3 9265 1547.
E-mail address: [email protected] (P. Piriyaprasarth).
0968-0160/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.knee.2006.10.006
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P. Piriyaprasarth, M.E. Morris / The Knee 14 (2007) 2–8
1. Introduction
This systematic review critically evaluates the methods
used to quantify knee joint flexion and extension in both
static and dynamic conditions. The Cochrane Collaboration
guidelines for conducting a systematic review [1] were used
to generate protocols to address the research question: “How
reliable and valid are measurement tools for quantifying
sagittal plane knee joint angles and movements in humans?”
Several measurement tools have been used to quantify
knee joint angles and knee movements. The selection of a
measurement tool depends on the purpose of testing [2] and
psychometric properties such as reliability and validity [3].
To be valid, tools for quantifying knee position and movement need to produce minimal measurement error. Measurement error can arise from the tool, the tester or from
variability in the performance of the individual [4,5].
Static knee joint measurements include clinical tests of
passive and active range of motion [6]. Passive range of
motion tests are typically performed by an external force,
delivered by a human [3,7–9] or custom-built instrument to
position the knee [10,11]. Active range of motion tests are
performed by individuals who are instructed to move their
knee joint to a desired position. Both active and passive
range of motion are usually measured at the end range of
knee flexion [3,8,12,13] or extension [3,14–16]. This information assists clinicians and coaches to detect pathological knee joint conditions according to the degree of
extensibility and stiffness [2]. Active range of motion tests
can provide information about muscle function [2], whilst
passive range of motion tests are typically used to quantify
the integrity and function of non-contractile structures such
as the knee joint capsule, cartilages and ligaments [2]. This
review included all measurement tools used for quantifying
either active or passive knee joint motion.
Dynamic knee joint measurements are seldom performed in
the clinical setting due to the limitations of clinical measurement tools for quantifying motion [17]. Assessment of knee
joint movement is mostly performed in the laboratory where
accurate dynamic knee joint measurements are possible [18–
21]. Tools used include two dimensional (2-D) motion analysis,
three dimensional (3-D) motion analysis, electrogoniometers
and accelerometers for measuring walking [20,22], stair
climbing [23] and moving from sitting to standing [24].
2. Methods
One of the authors (PP) conducted an electronic search using seven
medical databases for articles published between 1966 and March 2006
(Cochrane Library, Medline@OVID (1966 to March Week 2 2006),
CINAHL (1982 to March Week 2 2006), Embase (1988 to 2006), Sport
Discus (1830 to March 2006), PsyInfo and Pubmed) and an engineering
database (IEEE Xplore). The keywords used in the search pertained to knee
joint measurement, validity and reliability. Reference lists from all papers
were hand searched to identify additional studies.
After completing the search, the total yields were retrieved. Two
reviewers (PP and MM) independently assessed the relevant articles from
titles and abstracts, applying pre-determined inclusion and exclusion
3
criteria. When a decision could not be made from titles and abstracts, the
full text was examined. To be included, studies needed to be published in
English and to measure knee position or movement in the sagittal plane.
Studies also had to report the psychometric properties of the measurement
tool or procedure. Articles that reported research conducted in animals,
cadavers or using mechanical models were excluded. Two reviewers compared the studies selected in a meeting and consensus was used to reach an
agreement when disagreement existed.
For the quality assessment, two reviewers (PP and EG) independently
appraised the methodologies used for each full text article. The key quality
checklist items were participant characteristics, testers, tool descriptions and
the selection of statistical methods used to analyze psychometric properties.
Participant characteristics documented included age and sex, methods of
participant recruitment and inclusion and exclusion criteria. The tester checklist
included descriptions of the testers, their experience and their training. The
authors (PP and MM) extracted and tabulated information on the participant
and tester numbers, the type of reliability and validity studies, measurement
protocols, statistical analyses, reliability coefficients and validity indices.
3. Results
3.1. Search strategy yields
Of the 921 articles yielded, 837 unsuitable articles were discarded. Eighty-four articles were identified as potentially relevant
and 42 of these met the inclusion criteria. Four further articles
[13,25–27] were obtained from a hand search through references of
the articles obtained. The full texts of the 46 articles were then
obtained and three more articles were discarded as they did not meet
the criteria. In total, 43 studies met the selection criteria and were
included for further analysis. There were 18 reliability studies and
nine which reported the validity of measurement tools. Sixteen
studies reported both reliability and validity. A summary of the key
studies is presented in Table 1.
3.2. Quality of review articles
The quality evaluation for the selected articles is summarized in
Table 2. Convenience sampling methods were generally used. The
number of testers and their experience in using the measurement
tools were usually reported [7,13,28,29] and standardized measurement procedures were used in most studies [8,10,13,16,25,30].
In some investigations, the testers used their own non-validated
techniques to quantify knee joint angles [3,7]. Statistical analysis
methods were reported for all studies.
3.3. Participants
The studies included were limited to healthy populations
[12,16,25,26,31] and some pathological knee conditions [11,29].
Most of the reliability and validity studies were conducted in healthy
adults and six studies used paediatric samples. Of these, two included
healthy children [9,32], two studies examined those with cerebral
palsy [33,34] and another two included both healthy children and
those with cerebral palsy [28,35]. Four investigations were on adults
with knee joint pathologies. These included studies of surgery to
correct lower limb alignment [29] or knee joint restrictions [11].
Participants who had knee joint range of motion measurements as a
part of their assessment were also included [3,7]. The number of
participants ranged from 15–60. Two studies tested a single participant to examine the variation of a measurement technique rather
than variations between participants [10,30]. Detailed justifications
for sample sizes were not provided in any study.
4
P. Piriyaprasarth, M.E. Morris / The Knee 14 (2007) 2–8
Table 1
Identified studies of psychometric properties of knee joint angle and movement measurement techniques
Measurement tools/techniques
Psychometric properties
Intertester
reliability
Static knee joint angle measurements
Visual estimation
–
Standard hand held goniometer
Studies
Intratester reliability Validity
SEM
ICC = 0.82–0.98
–
[7,11,38]
2.37°
[ 3 , 7 – 9 , 11 – 1 3 , 1 6 , 2 5 , 2 6 , 2 9 –
31,34,39,45]
–
–
[3,28]
–
–
[3]
[11,12]
[16,32,37,42]
r = 0.25 to 0.94
ICC = 0.82–0.98
r = 0.33–0.99
ICC = 0.98–0.99
Parallelogram goniometer
Gravity-based goniometer
CV = 13%–21%
r = 0.50–0.99
ICC = 0.62–0.99
r = 0.60–0.92
ICC = 0.61–0.92
r = 0.80–0.92
ICC = 0.71–0.99
ICC = 0.43–0.98
–
Fluid-based goniometer
Internet-based goniometer
r = 0.83
ICC = 0.96–1.00
CV = 10%–20%
r = 0.86–0.97
ICC = 0.85–0.99
r = 0.34–0.99
ICC = 0.97–0.99
r = 0.96–0.97
ICC = 0.96–0.97
ICC = 0.85–0.99
r = 0.99
CV = 0.5%–3.2%
ICC = 0.80–0.91
–
ICC = 1.00
Goniometer and photograph
Goniometer and videography
Sequential MRI
2-D motion analysis
–
ICC = 1.00
r = 0.96
–
ICC = 0.51–0.87
ICC = 1.00
r = 0.95–0.97
ICC = 0.69–1.00
–
–
r = 0.99
ICC = 1.00
–
[8]
LOA = − 1.9° to [10]
1.8°
1.65°–3.95°
[14,15]
–
[24]
1.05°–1.29°
[18]
0.84°–1.19°
[36]
–
r N 0.90
0.91°–2.3°
Small plastic goniometer
Metal goniometer
Dynamic knee joint angle measurements
Accelerometers, gyroscope and –
markers
Electrogoniometer
–
r = 0.33–0.99
r = − 0.33–0.79
–
–
r = 0.82–0.83
ICC = 0.99–1.00
Mean difference = 1°– 2.5°–3.0°
1.2°
–
ICC = 0.82–0.89
–
1.57°–1.70°
r = 0.99
CMD (r2 ) = 0.88– r = 0.99
3.5°
0.988
CMD (r2) = 0.91– CMC = 0.94–1.00
rms = 0.6°–1.6°
0.99
2-D motion analysis
3-D motion analysis
r = 0.93–0.95
[47]
[19,21,27,43,54]
[23,36]
[20,26,33,35,40,41,55,56]
r = reliability coefficient, ICC = intraclass correlation coefficient, CV = coefficient of variation, SEM = standard error of measurement, LOA = Limits of
agreement, CMD = coefficients of multiple determination, CMC = coefficient of multiple correlation, rms = root mean square.
3.4. Testers
Intratester reliability was usually evaluated by a single tester
[14,16,20,21,23,27,33,35–37]. There were 2–14 testers in studies of
intertester reliability. [3,7–13,16,24,26,28–31,34,38–42]. These
included physiotherapists [3,7,10,11,13,16,24,28,30,31,34,42],
physiotherapy students [8,9,12], physicians [42] and students of
biomedical engineering [18]. The experience of the testers was not
uniformly reported in the 43 studies. The use of paired testers in
some investigations [3,7,29] aimed to minimize bias in selecting
testers in intertester reliability studies.
3.5. Static knee joint angle measurements
Visual estimation techniques were used to quantify static knee
joint angles in three investigations [7,11,38]. Measurement tools for
Table 2
Methodological quality of the reviewed studies
Subject characteristics (n = 43)
Definition
Sampling
method
Inclusion criteria/
exclusion criteria
Adequate
(n = 31)
Partial
(n = 6)
Inadequate
(n = 6)
Not stated
(n = 23)
Convenience
(n = 19)
Populationbased (n = 1)
Stated (n = 26)
n = number of studies.
Limited (n = 12)
Not stated (n = 5)
Tester
Adequate
(n = 4)
Partial
(n = 17)
Inadequate
(n = 21)
Not stated
(n = 1)
Tool description
Described
(n = 42)
Limited
(n = 1)
Psychometric properties
Reliability
design (n = 33)
Protocol
description
Statistical
analysis
Validity design
(n = 26)
Statistical
analysis
Intratester (n = 6)
Stated
(n = 32)
Limited
(n = 1)
Adequate
(n = 33)
Construct
(n = 2)
Concurrent
(n = 24)
Adequate
(n = 24)
Inadequate
(n = 2)
Intertester (n = 5)
Intra- and
intertester (n = 15)
Test–retest
(n = 7)
P. Piriyaprasarth, M.E. Morris / The Knee 14 (2007) 2–8
the static measures included standard hand held goniometers
[3,7,8,11–13,16,25,26,29–31,34,37,39], gravity based tools such
as fluid based goniometers [8] or flexometers [42]. Reflective
markers coupled with photographs and parallelogram goniometers
[11,12] were also reported. Parallelogram goniometers are modified
goniometers with a movable arm elevated above a stationary arm.
The movable arm minimizes the difficulty in attaching the goniometer to knee joint segments. Two dimensional motion analysis
[24] and MRI [18] were also used for static knee joint angle
measurements.
3.6. Dynamic knee joint angle measurements
Measurement tools used for dynamic movements such as
walking [21] or moving from sitting to standing [24] included
electrogoniometers [19,21,27,43,44], 2-D [23,36] and 3-D motion
analysis [19,23,26,35,40].
3.7. Statistical analysis
Common methods used for statistical analysis were Pearson's
product correlation coefficients (r) and intraclass correlation coefficients (ICC). The r is an index of the degree of association
between two sets of continuous data whilst ICCs provide an index
of the mean change between two or more variables [5]. Different
ICC models were reported for the 43 studies [7,11,16,24,31], with
some reporting the use of ICCs without identifying the model
[3,10,12,14,15,28,36,38]. Using solely r or ICC values might not
be able to fully explain differences between measurement tools
because these correlation coefficients do not indicate the magnitude
of measurement error [4]. The standard error of measurement
(SEM) was used to provide information on measurement error in
the same unit of measurement for only a small number of investigations [14,18,36,45]. It is recommended that future studies
use the SEM in addition to ICCs or r to enable the error of
measurement to be estimated.
3.8. Validity of measurement tools
Twenty-six studies documented the validity of measurement
tools for quantifying sagittal knee joint angles or motion. Criterion
related validity in the form of concurrent validity was most often
reported [8,11,12,23,25,31,36,46]. Radiographs were used as the
criterion measurements in four concurrent validity studies, two of
which used standard plastic hand held goniometers [25,31] and two
which used parallelogram goniometers [11,12]. Standard hand held
goniometers were sometimes used as the criterion measure against
fluid-based goniometers [8], 3-D [26] and internet-based goniometers [10].
For the criterion related validity studies, there was a large range
of r values and variation in ICCs which may have been related to
differences in measurement tools and procedures. For the included
studies, r values ranged from 0.25 [11] to 0.99 [25,47], indicating
poor to excellent concurrent validity [5]. For the studies where ICCs
ranged from 0.82–1.00 [7,10], it could be assumed that measurement tools could be used interchangeably. The correlation
coefficients for goniometers and visual estimation against radiographs suggested that there was poor criterion related validity for
measuring knee extension [7].
Visual estimation was tested against standard plastic goniometers and photo images in three studies. Visual estimation of
5
knee extension was not as accurate as goniometric measurement
[11,12] or data taken from a photo image [38]. There was a strong
positive relationship between visual estimation techniques and
goniometric measurements (ICC or r N 0.80) [7,11] except for the
visual estimation of knee extension [11]. Measurements of knee
extension angles using visual estimation showed lower correlations
with goniometric measurements than for knee flexion.
Gravity-based goniometers and linear measurements of heel
distance in different knee positions were used in healthy children,
with a correlation r of 0.79 between these measures [32]. A high
Pearson's correlation coefficient does not always represent good
agreement between measurements taken from two different tools
[5]. Without reporting the SEM or the mean differences between
measurement tools, the actual agreement cannot be fully ascertained.
The magnitude of knee movement and the direction of
movement were found to influence concurrent validity. Brosseau
[12] tested the validity of a parallelogram goniometer against
radiographs in healthy participants and reported that measurements
of small range knee movements were less accurate than larger
movements. The criterion related validity of the range of motion
measurements in knee flexion was better than for knee extension
[11,12,25,31]. Brosseau [11] and Enwemeka [25] found that measurements of knee extension angles was less accurate than knee
flexion angles using goniometers, even though the participant
samples were different. Brosseau [11] tested participants with
limited knee joint range of motion whilst Enwemeka [25] used
healthy participants.
3.9. Reliability of measurement tools
Intertester reliability, intratester reliability, inter-device reliability and test-retest reliability were reported in 33 studies on sagittal
plane knee joint measurements. Several measurement tools were
found to be reliable for measuring knee angle in flexion and
extension [3,10,11,15,16]. These were standard hand held goniometers, fluid-based goniometers, gravity-based goniometers, 2-D
motion analysis and MRI. Most of the 33 studies used standardized
measurement protocols for quantifying knee joint angles or movements such as specified by the American Academy of Orthopaedic
Surgeons [48] and Norkin and White [49]. A standardized protocol
optimizes reliability because repeated measurements are similar and
the error of measurement arising from variation in measurement
protocols is minimized [3,7].
Although a standardized measurement protocol was followed,
variations between testers were greater than measurements taken by
the same person. This was shown by the finding that intratester
reliability of knee joint angle measurement was greater than
intertester reliability [3,7,11–13,29,30,39]. This was regardless of
the direction of movement and measurement techniques such as
passive or active tests.
The time between testing also affected reliability even though
the same person performed the tests in most studies [14,15,42]. The
period varied from separate tests on the same day [3,7] to 30 days
between tests [14,15]. Measurements performed on the same day
were more likely to have high reliability (ICC = 0.78–0.87) than the
measurements performed on different days (ICC = 0.53–0.75)
[14,15,28,42]. Presumably testers are more reliable at repeating
measurement procedures over short periods.
The number of measurements ranged from 1–20. If more than
one measurement was performed, the means of several trials were
usually used to estimate reliability. Averaging data can increase the
6
P. Piriyaprasarth, M.E. Morris / The Knee 14 (2007) 2–8
reliability coefficient by minimizing the magnitude of differences
between measurements, as shown in three studies [10,20,34].
Goniometers were used to measure knee joint angles in participants with conditions such as diplegia [28] and knee joint
restriction [11]. The reliability of measurements in diplegic children
was greater than for control participants for reasons that were not
easily explained. Likewise, Brosseau [11] found that measurements
of pathological knees were more reliable than for normal knees
although no explanation was given to account for this finding.
The direction of knee movement also influenced reliability.
Measurements of knee joint flexion were more reliable than for
knee extension [3,12,16]. This applied to standard goniometers
[3,7,16] and parallelogram goniometers [11]. Differences in measurement error for knee joint flexion and extension were not seen
for pendulum goniometers [37], photographs [15] or internet-based
goniometers [10].
From this systematic review, it is apparent that goniometric
measurements are more reliable than visual estimation for quantifying
knee position and movement [7,11]. Standard goniometers appear to
be able to be used interchangeably with parallelogram goniometers
[11,12], fluid-based goniometers [8] and internet-based goniometers
[10]. Sequential MRI [18] and 2-D motion analysis [36] had the least
error of measurement, being less than 1.3°.
For measurements of knee movement, 2-D analyses were used in
dynamic tasks in standing and during sit-to-stand with relatively
good intertester reliability (ICC = 0.69–0.92) [24,36]. There were
few reports of the error associated with measurements of knee joint
movement during gait [20,21,35,40]. High reliability (r N 0.90) was
found for both intratester reliability of 3-D analysis [20,26,33,35,41]
and the intratester reliability of electrogoniometers [27]. SEMs of
less than 3.5° were reported for repeated measurements using electrogoniometers or 3-D analysis [19,21,41]. Thus for quantifying
knee movement, either electrogoniometers or motion analysis systems appear reliable. Error of measurement from 3-D analysis arises
primarily from marker placement discrepancies [20,50]. For some
electrogoniometers, the propensity for the thigh attachment to slip
during movement can increase error [27].
4. Discussion
This systematic review found several tools to be reliable
and valid for quantifying knee position and movement. Hand
held goniometers, gravity-based goniometers, fluid-based
goniometers, internet-based goniometers, 2-D motion analysis
and measurements taken from sequential MRI can be used
with confidence for quantifying sagittal knee joint position.
For static knee joint angle measurements, defining the coordinate axes using MRI and 2-D motion analysis generated
low error of measurement, with high reliability coefficients. 2D motion analysis had less error than goniometric measurement and photographs. Static knee extension measures were
not as reliable as flexion measures. For dynamic measures of
knee motion, electrogoniometers and 3-D analysis had similar
levels of measurement error. Due to parallax error, 2-D
analysis appears to be less suitable for measuring knee motion
in all planes compared with 3-D analysis [51,52].
Parallel findings to previous literature reviews were found
for the extent of variability among testers and differences in
measurement protocols [2,37]. The reliability of measure-
ments was greatest when the measurements were performed
by the same tester and in a controlled environment using
standardized testing protocols. Within-session repeated
measurements were more consistent than between-session
measurements. Taking the mean of several measurements
also increased reliability, compared to taking a single measure. Lower reliability coefficients were reported when the
repeated measurements were performed by different testers
than by the same tester. The lowest ICCs were reported in
measurements using different testers with parallelogram
goniometers to measure knee extension angles [12]. Low
ICCs were also seen for measurements of both knee flexion
and extension angles using photographs by the same tester
within 30 day intervals [14]. Differing statistical analysis
methods were a contributing factor affecting the interpretation of reliability coefficients and validity indices [5,53].
The factors that affected the reliability of dynamic knee
joint angle measurements were different than for static
measures. The consistency of participant performance and
the ability of the tester to accurately position the measurement tools had a major influence on dynamic measures.
Errors from the measurement tool were minimized by careful
calibration and application [19–21].
5. Conclusion
To conclude, this systematic review found that several
reliable and valid methods are available to quantify knee
joint position and movement. Reliability and validity of
measurement were enhanced by using validated tools,
standardized measurement procedures and by minimizing
the number of testers. Knee joint flexion measurements were
found to be more reliable than knee joint extension measurements. Using the mean of several measurements
enhanced reliability. Adopting standardized measurement
protocols and trained testers were also effective strategies for
reducing measurement error.
6. Potential conflict of interest
There is no potential conflict of interest involved in this
review.
Acknowledgements
The authors would like to thank Erika Gosney for being
one of the independent reviewers in appraising the quality of
selected articles. Special thanks for Dr. Frances Huxham, Dr.
Jenny McGinley, Pamela Fok and Brook Galna for their
critical comments on the article.
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