Pelvic Tilt
Intratester Reliability of Measuring the Standing Position and Range
of Motion
RICHARD GAJDOSIK,
RALPH SIMPSON,
RICHARD SMITH,
and RICHARD L. DONTIGNY
The purpose of this study was to examine intratester reliability of a test designed
to measure the standing pelvic-tilt angle, active posterior and anterior pelvic-tilt
angles and ranges of motion, and the total pelvic-tilt range of motion (ROM). After
an instruction session, the pelvic-tilt angles of the right side of 20 men were
calculated using trigonometric functions. Ranges of motion were determined from
the pelvic-tilt angles. Intratester reliability coefficients (Pearson r) for test and
retest measurements were .88 for the standing pelvic-tilt angle, .88 for the
posterior pelvic-tilt angle, .92 for the anterior pelvic-tilt angle, .62 for the posterior
pelvic-tilt ROM, .92 for the anterior pelvic-tilt ROM, and .87 for the total ROM. We
discuss the factors that may have influenced the reliability of the measurements
and the clinical implications and limitations of the test. We suggest additional
research to examine intratester reliability of measuring the posterior pelvic-tilt
ROM, intertester reliability of measuring all angles and ROM, and the pelvic tilt of
many types of subjects.
Key Words: Pelvis, Range of motion, Reliability tests, Physical therapy.
Physical therapists (PTs) routinely administer therapeutic
procedures that either directly or indirectly affect the standing
position and active range of motion (ROM) of the pelvic tilt
in the sagittal plane. The effects of the procedures are rarely
quantified, however, because noninvasive clinical tests that
isolate pelvic motion as an independent functional movement
are unavailable. Physical therapists should consider clinical
tests designed to provide objective and reliable pelvic-tilt data
because such tests would permit documenting change in the
pelvic tilt after a specific physical therapy regimen. The effects
of therapeutic procedures could then be quantified and
changes in the procedures could be made accordingly.
Numerous techniques for measuring trunk motions in the
sagittal plane have been reported in the literature. The techniques include using radiography,1-4 photography,3, 5, 6 spondylometry,7, 8 flexible rules that conform to trunk curves,9, 10
tape measures to record the change in centimeters between
skin marks11-14 or bony landmarks,15 and variations of
goniometry.6,1 0 , 1 4 ,6-18 Although interest has been widespread
in measuring trunk movements, none of these published
papers reported measuring active ROM of the pelvic tilt as an
Mr. Gajdosik is Associate Professor, Physical Therapy Program, University
of Montana, Missoula, MT 59811. He is currently doing graduate work at the
University of North Carolina at Chapel Hill, Chapel Hill, NC. Address correspondence to 612 Hibbard Dr, Chapel Hill, NC 27514 (USA).
Mr. Simpson was a senior physical therapy student when this study was
conducted. He is currently Staff Physical Therapist, The Sports Medicine Clinic,
Seattle, WA.
Mr. Smith is Visiting Assistant Professor, Physical Therapy Program, University of Montana, Missoula, MT.
Mr. DonTigny is a physical therapist at the Havre Clinic, Havre, MT.
This paper was adapted from a presentation at the Spring Meeting of the
Montana Chapter of the American Physical Therapy Association, Missoula,
MT, May 21, 1983.
This article was submitted January 12, 1984; was with the authors for
revision 11 weeks; and was accepted August 16, 1984.
Volume 65 / Number 2, February 1985
isolated movement. Radiographic methods for measuring the
standing pelvic-tilt (SPT) position have been reported,2, 3 and
these methods could be used to measure ROM, but radiographic examination is generally regarded as expensive, potentially harmful, and not always available to PTs. We found
one study that reported measuring the SPT angle, the posterior
pelvic-tilt (PPT) angle, and the anterior pelvic-tilt (APT) angle
with a noninvasive computerized method, the Iowa Anatomical Position System (IAPS).19 Even so, the IAPS, as with
radiography, is not readily available to PTs.
Recently, Sanders and Stavrakas suggested a noninvasive
clinical technique for measuring the SPT angle relative to the
horizontal plane.20 The reliability of the technique, however,
was not reported. We postulated that the test suggested by the
authors could be used reliably to measure the SPT angle, and
by modifying the test and standardizing testing procedures,
the test could also be used reliably to measure the PPT and
APT angles after active movement. These angles could then
be compared with the SPT angle to determine the PPT-ROM
and the APT-ROM. The total pelvic tilt (TPT) ROM could
be calculated as the difference between the PPT and APT
angles. The purpose of this study was to investigate intratester
reliability of measuring the angles of SPT, PPT, APT, and the
active ROM of pelvic tilting in the sagittal plane.
METHOD
Subjects and Instructions
Twenty healthy men ranging in age from 19 to 34 years,
with a mean age of 25.2 years, volunteered to participate in
this study. Their mean weight was 75 kg (range, 61-91 kg),
and their mean height was 179 cm (range, 170-195 cm).
Subjects were limited to men who had Normal muscle
strength and normal ROM of the back and lower extremities
169
and who had no history of orthopedic or neurologic disorders.
All subjects were instructed to restrict excessive physical activity on the day of testing, such as recreational running and
bicycling, and to wear gym trunks for the tests.
On the day of testing, all subjects reviewed and signed
informed consent forms for the study that had been approved
by the University of Montana Institutional Review Board for
Use of Human Subjects in Research. We then taught the
subjects how to perform the PPT and the APT. After learning
the movements, they were required to perform the movements for approval by the researchers. In addition, we encouraged all subjects to relax and told them that the movements would not be judged as "good" or "bad." We believed
these verbal cues decreased subjects' anxiety and, therefore,
helped to standardize the testing.
Testing
Fig. 1. Examiner measuring distance between ASIS and PSIS by
compressing depth caliper over adhesive-backed stars.
Fig. 2. Standing pelvic tilt: Showing position of examiner measuring
distance between PSIS and floor. Note distance from ASIS to floor.
170
We conducted a pilot study to refine instrument placements
and testing procedures. As a result, we found that in some
subjects the pelvis moved under the skin during active movement. Consequently, when the posterior superior iliac spines
(PSISs) and the anterior superior iliac spines (ASISs) were
marked with a felt-tip pen as suggested by Sanders and Stavrakas,20 the pelvis moved under the skin and yielded invalid
measurements. To ensure that the test was clinically valid,
the PSIS and ASIS were palpated and marked with removable,
small adhesive-backed stars when the end points of PPT and
APT were reached.
The actual test session for collecting data included both a
test and a retest on the same day between 2 PM and 5 PM.
Three subjects were tested each afternoon. After the initial
tests, the subjects relaxed supine on beds for 30 minutes
before the retests, but neither physical activity nor sleep were
allowed during the rest periods. One of us (R. Simpson)
administered each test and retest by using bony landmarks
on the right side of the subjects. The time required to conduct
one complete test of all angles was less than 10 minutes.
Standing pelvic tilt. Each subject stood erect with his feet
approximating a designated line on a tile floor. The right
ASIS and right PSIS were palpated and marked with the
adhesive-backed stars. We then placed a depth caliper over
the stars, which were compressed to "firm resistance," and
observed and recorded the distance between the spines to the
nearest millimeter (Fig. 1). This point to point measurement
on one innominate bone should remain constant with any
change in position of that bone. The measurement was,
therefore, used to calculate the PPT and APT angles.
After measuring the distance from the right ASIS to the
right PSIS, we used a sliding pointer on a meter stick mounted
on a wood base to measure the distances from the floor to the
right ASIS and from the floor to the right PSIS (Fig. 2). We
then recorded the measurements to the nearest millimeter
and removed the stars.
Posterior pelvic tilt. While the subject stood erect as in the
SPT measurements, we instructed him to keep his knees
straight, to tighten the abdominal and gluteal muscles, and to
move the top of the pelvis back to initial resistance without
causing pain or discomfort (Fig. 3). The subject held this
position while the right PSIS was palpated, marked, and the
distance to the floor measured, and the right ASIS was palpated, marked, and the distance from the star to the floor
measured. The subject then relaxed to the SPT position, and
we removed the stars.
Anterior pelvic tilt. From the SPT position, the subject was
reminded to stand erect and instructed to arch the low back
PHYSICAL THERAPY
RESEARCH
and move the top of the pelvis forward to initial resistance
without causing pain or discomfort (Fig. 4). Again, the iliac
spines were palpated, marked, and the distances from the
stars to the floor measured. The subject relaxed to the SPT
position, and we removed the stars for the last time.
Data Analysis
We calculated SPT, PPT, and APT angles from the raw
data by using a trigonometric calculator to determine angle
theta (θ) using the formula:
(1)
where the side opposite was the height difference between the
PSIS and the floor and the ASIS and the floor, and the
hypotenuse was the distance between the ASIS and PSIS (Fig.
5).20 Pelvic-tilt angles with the PSIS above the horizontal were
assigned positive degree values and those with the PSIS below
the horizontal were assigned negative degree values.
The PPT-ROM was calculated as the difference between
the PPT angle and the SPT angle, and the APT-ROM was
calculated as the difference between the APT angle and the
SPT angle. We determined the TPT-ROM as the difference
between the PPT and APT angles. To check for systematic
variation of the pelvic-tilt angles and ROM, paired t-ests were
conducted on the test-retest data. The level of significance
was set at p ≤ .05.
We used the Pearson product-moment correlation coeffi­
cient to determine intratester reliability. To interpret the
reliability coefficients, we chose to designate reliability of .90
to .99 as high; .80 to .89 as good; .70 to .79 as fair; and those
TABLE
Pelvic-Tilt Angles, Pelvic-Tilt Range of Motion, and Reliability
Fig. 3. Posterior pelvic tilt: Showing a) contracted abdominal mus­
cles, b) contracted gluteal muscles, and c) extended knees. Note
distance from PSIS to floor (A) and distance from ASIS to floor (B).
Degrees
Tests (N = 20)
r
s
Standing tilt
angle
Test
Retest
Posterior tilt
angle
Test
Retest
Anterior tilt
angle
Test
Retest
Posterior tilt
ROM
Test
Retest
Anterior tilt
ROM
Test
Retest
Total ROM
Test
Retest
Range
less than .69 as poor.21 Tests of significance were calculated
for each correlation coefficient to determine if they were
significantly different from zero.
8.35
8.53
4.17
4.08
1.99-15.72
1.33-18.57
.88a
-0.53
0.19
4.49
4.02
- 6 . 9 7 - 7.55
- 5 . 6 7 - 7.64
.86a
21.21
21.10
5.10
4.84
13.37-29.37
14.02-30.43
.92a
8.88
8.34
3.93
2.32
0.34-14.96
2.43-14.55
.62b
RESULTS
The pelvic-tilt angles, ROM, and reliability for the tests and
retests are reported in the Table. No significant difference was
found between the test and retest angles or the test and retest
ROM measurements. The most reliable measurements were
the APT angle (r = .92) and the APT-ROM (r = .92). The
SPT angle (r = .88), the PPT angle (r = .86), and the TPTROM (r = .87) were all measured with good reliability. Poor
reliability was demonstrated for the PPT-ROM (r = .62). The
correlation coefficients were statistically significant (p < .05).
DISCUSSION
12.86
12.57
5.47
5.79
5.85-26.45
5.81-25.28
.92a
21.74
20.91
6.69
6.39
12.34-35.22
10.53-35.94
.87a
a
p < .001.
b p < .005.
Volume 65 / Number 2, February 1985
We believe that obtaining high reliability for the APT angle
and good reliability for the SPT and PPT angles depended on
instruction sessions and testing procedures that were consist­
ently applied to each subject. Before testing, we confirmed
that each subject could perform the PPT and the APT.
Because the subjects knew the actions, the influence that
learning the actions could have had between tests and retests
171
Fig. 5. Schematic diagram of pelvic-tilt measurement. A-B = side
opposite and C = hypotenuse. Reprinted with permission from Sanders and Stavrakas.
Fig. 4. Anterior pelvic tilt: Showing arched low back and distance
from PSIS to floor (A) and distance from ASIS to floor (B).
on reliability was decreased. Practicing the movements probably contributed to the stability of the test and retest measurements by decreasing the effect that repeated measurements
could have had on the PPT and APT angles. Atha and
Wheatley reported that the act of measuring hip flexion
increases the ROM of hipflexion,and that most changes take
place over the first four trials when testing without a practice
motion.22 In our study, the lack of systematic variation between the tests and retests indicates that practicing the movements before testing served as a warm-up and lessened the
potential for increases in ROM from early repeated measurements.
Consistently applying the same action commands ensured
that all subjects performed the same movements and reached
similar end points of each motion for both tests and retests.
Telling the subjects to stand erect during the actions isolated
the motion to the pelvis and limited anterior and posterior
leaning that could have affected the pelvic angles. Also, the
correlation coefficients indicate no need to use stabilizing
devices to prevent swaying movements that may distort the
172
measurements from the iliac spines to the floor by a parallelogram effect.
Accurately palpating the iliac spines and accurately placing
the adhesive-backed stars over the spines also could have
contributed to reliable measurements. Furthermore, the stars
provided a precise reference point for placing the depth caliper
and the sliding pointer.
The depth caliper used in this study provided a relatively
large surface area for placing the caliper firmly over the iliac
spines. As a result, slipping off the spines was easily prevented.
The large surface area also permitted compressing the caliper
to "firm resistance" without causing pain. For these reasons,
using a caliper with a large surface area may be more reliable
than using a bowleg caliper as Sanders and Stavrakas suggested.20
Although measuring the distance between the ASIS and the
PSIS yielded reliable measurements of pelvic-tilt angles, the
raw measurements do not represent a "true" bone to bone
distance because the intervening skin and subcutaneous connective tissue are compressed. We addressed this problem by
compressing the caliper to firm resistance in an effort to
standardize the force of compression. Even though our results
were reliable, measuring this distance on people who are obese
or whose body weight changes over time may not be as reliable
as reported on the subjects in this study. Variations in subcutaneous connective tissue thickness should be considered
because patients may vary in body build from lean to obese;
all subjects in our study were lean to medium body build.
Moreover, palpating the iliac spines may be difficult in some
patients because of obesity or bony variations of the ilium. If
the spines cannot be palpated, the test cannot be used.
The APT-ROM was determined with high reliability and
the TPT-ROM was determined with good reliability, but the
PPT-ROM demonstrated poor reliability. The fact that the
reliability for the PPT-ROM deviates from that of the PPT
angle is likely to be a result of increased noise (fluctuations)
PHYSICAL THERAPY
RESEARCH
because the motion computations involved twice as many
raw measurements as for the angle. The noise was apparently
much less significant in the APT-ROM and the TPT-ROM.
Additional studies should be conducted to examine the reliability of measuring the PPT-ROM. Furthermore, if more than
one examiner measures the same person, then the intertester
reliability for measuring all angles and ROMs should be
studied before the test is used with confidence.
Clinical Implications
The clinical implications of the test may be far-reaching.
Measurements of the APT and the PPT may represent the
standing ROM of lumbar trunk extension and flexion, respectively. In a study of the effect of pelvic tilt on standing
posture, Day et al documented increased depth of the lumbar
curve (extension) with the APT and decreased depth (flexion)
of the lumbar curve with the PPT.19 We also observed this
relationship of pelvic tilting to lumbar trunk motion (Figs. 3,
4). If the test is used to examine ROM of the lumbar trunk,
the possibility that motion or lack of motion in the sacroiliac
joints (SIJs) could affect the pelvic-tilt measurements should
not be overlooked. Lavignolle et al demonstrated movement
in the SIJs with active flexion and extension of the lower
limbs.23 Other studies have documented that movement occurs in the SIJs in conjunction with trunk motions in the
sagittal plane.2. 24. 25 Accordingly, the SIJs may move during
anterior and posterior pelvic tilting and cause either bilateral
or unilateral movement of the pelvis in addition to movement
of the lumbar spine. Clinical evidence indicates that both
bilateral and unilateral SIJ dysfunction can alter the positions
and ROM of the pelvis, thus affecting the bilateral symmetry
of the pelvic tilt.26, 27 In addition to the possibility of pelvic
tilt asymmetry from SIJ dysfunction, asymmetry may result
from disorders of the trunk, such as scoliosis or unilateral
muscle spasms, and from problems affecting the lower limbs,
such as diseases of the hips or leg-length discrepancies. Trunk
and pelvic girdle muscle strength-flexibility imbalances and
bony anomalies may also contribute to bilateral asymmetry
of the pelvic tilt. Although we measured the right side only,
we encourage therapists to measure and compare both sides
and to conduct further research to examine the effects of
therapeutic procedures on the pelvic tilt.
Physical therapists should realize that the test is limited to
measuring pelvic-tilt angles and ROM in the sagittal plane.
We do not imply, however, that the pelvis moves only in the
sagittal plane. Gait studies have demonstrated that the pelvis
also moves in the transverse plane.28-30 The relationship of
pelvic tilting, as measured in our study, to pelvic tilting and
transverse pelvic rotation during walking, however, is undetermined and warrants further study.
Physical therapists should also consider that the test is
limited to persons who can actively tilt the pelvis and hold
the end point of each motion while standing. Instruction
sessions before testing should, therefore, be considered. Because the PPT is the most complex action, special training
may be needed before the action is adequately performed.
CONCLUSION
Within the limitations of this study, we conclude that the
technique suggested by Sanders and Stavrakas20 for measuring
the SPT angle is reliable, and that by modifying the test, one
examiner can reliably measure the PPT angle, APT angle,
APT-ROM, and TPT-ROM. The PPT-ROM was measured
with poor reliability. If the test is conducted as described in
this article, the test should provide both clinicians and researchers with an objective, reliable, and quick method of
measuring pelvic-tilt angles and ROM. Reliable measurements will permit documenting these angles and ROM, and
any change in the angles and ROM after a specific physical
therapy regimen. The effects of therapeutic procedures can
then be quantified and changes in the procedures can be made
accordingly. Additional studies are suggested to examine the
1) intratester reliability of measuring the PPT-ROM, 2) intertester reliability of measuring all angles and ROM, and 3)
the pelvic tilt of people with normal muscle strength and
ROM and of patients with problems affecting the pelvic tilt.
Acknowledgments. We thank Kathleen Miller, PhD, the
University of Montana; and Phil Witt and Barney LeVeau,
PhD, of the University of North Carolina, for their assistance
with the statistical analysis. Also, special thanks to Carrie
Gajdosik for her editorial suggestions and Betty Stewart for
typing the manuscript.
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