June 6, 2023

Modified Thomas Test is Not a Valid Indicator of Hip Extension unless Pelvic Tilt is Controlled

This article explores how the Modified Thomas Test may not accurately measure hip extension if pelvic tilt is not accounted for. Learn why controlling for this factor is crucial for accurate results.

Brent Brookbush

DPT, PT, MS, CPT, HMS, IMT

Research Review: Modified Thomas Test is Not a Valid Indicator of Hip Extension unless Pelvic Tilt is Controlled

By Nicholas Rolnick SPT, MS, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Vigotosky AD, Lehman GJ, Beardsley C, et al. (2016). The modified Thomas test is not a valid measure of hip extension unless pelvic tilt is controlled. PeerJ. 4:e2325; DOI 10.7717/peerj.2325. ARTICLE.

Why is this relevant?: The Modified Thomas Test (MTT) is a commonly used assessment to determine hip extension range of motion. In the MTT, the client is positioned supine at the edge of the table, maximally flexing one leg while allowing the tested leg to passively hang off the table. A positive MTT occurs when the femur/leg cannot reach parallel with the table, indicating the presence of a restriction in hip flexion. Despite the common use of this assessment, not much research has been done to determine the assessments validity. The authors of the current study sought to determine the criterion validity of the MTT using two-dimensional sagittal plane motion capture.

Caption: Modified Thomas Test as performed in the current study

Modified Thomas Test as performed in the current study - laurentlebosse.wordpress.com

Study Summary

Study Design	Observational Study
Level of Evidence	IIA: Evidence from at least one controlled study without randomization
Subject Demographics	Age (± standard deviation) and Gender: 11 Males - 22.18 ± 4.14 years old 18 Females - 21.80 ± 3.68 years old Other Subject Information: Height (in m) (± standard deviation) Males - 1.79 ± 0.06 m Females - 1.65 ± 0.06 m Body mass (in kg) (± standard deviation) Males - 85.00 ± 10.00 kg Females - 60.71 ± 10.02 kg Characteristics of the Study: Protocol: A ten minute standardized warm-up was performed for each subject. The warm-up consisted of five minutes on an Airdyne bike, two sets of 20 bodyweight squats, two sets of 10 leg swings in both the frontal and sagittal planes, and two sets of 10 of bodyweight lunges. Reflective markers were placed on the subject's skin or tight-fitted clothing. One marker was placed on the iliac crest Another marker was placed in line with the anterior superior iliac spine and the posterior superior iliac spine, placed 10 cm apart. Another marker was placed on the lateral femoral epicondyle. The last marker was placed on the greater trochanter of the femur. Measurements Hip extension range of motion was calculated by subtracting the four-point angle made by the markers from 90°. Pelvic tilt angle was measured as the angle between the intercristal line (which is a line created by the anterior superior iliac spine to the posterior superior iliac spine) and the horizontal plane, offset by 90°. Sagittal plane motion capture was obtained with a camera set to 30 Hz using motion capture technology. The current study measured hip extension angle relative to the pelvis, and NOT the plinth, which is an important consideration to be made as previous studies have not done this. The authors referred to this as the "true hip extension angle." This measurement modification reduced the chance that confounding variables such as lumbar hyperextension, decreased hip flexion ability, waist circumference, and thigh girth. Procedure for the Modified Thomas Test (MTT) The subject was instructed to lie supine on the edge of the table with the non-tested leg to his/her chest while letting the tested leg passively hang off the table. Each leg measurement was performed three times for each subject, with the subject getting up from the plinth, sitting down, and standing up between each trial. The average hip extension value between the three trials was used for data analysis. Statistical Analyses Bland-Altman plots with 95% limits of agreement and 95% confidence intervals for those limits of agreement were created to determine the variability of the differences between "true hip extension angle" and the MTT (using the plinth as a measuring surface and not the pelvis as traditionally performed). Pearson correlation coefficients were used to investigate discrepancies between the two different measurement protocols (MTT and "true hip extension angle") with hip flexion range of motion prior to pelvic tilt or thigh-waist contact, the sum of waist and thigh circumferences, and pelvic tilt during MTT. Validity of the MTT was calculated using traditional Pass/Fail criteria of the thigh reaching the table or not, and comparing this with "true hip extension angles." Sensitivity, specificity, and 95% confidence intervals were determined from this comparison. A "+" test was when the tested leg did not contact the table and a "-" test was when the tested leg contacted the table. Inclusion Criteria: N/A Exclusion Criteria: Subjects were excluded if they had current symptoms of back, lower extremity musculoskeletal, or neuromuscular injury or pain.
Outcome Measures	Bland-Altman Plot of true hip extension angle and the MTT Differences between true hip extension angle and the MTT Differences between the MTT and true hip extension angle versus pelvic tilt during the MTT Validity of MTT
Results	Bland-Altman Plot and correlations Mean difference of 0.7°, with 95% limits of agreement of -18.3° - 19.7° was found between the MTT and true hip extension Angle of the thigh relative to the horizontal (the traditional measurement standard) was moderately correlated (0.50) with true hip extension angle. These differences between the true hip extension angle and the traditional measurement could not be explained solely by hip flexion range of motion (r - 0.11) or waist/thigh circumference (r = -0.12). The degree of pelvic tilt was strongly associated with the difference between true hip extension angle and the MTT (r = 0.98). Validity MTT displayed a sensitivity of 31.82% (95% confidence interval ) and a specificity of 57.14% (95% confidence interval ).
Conclusions	The MTT is not a valid measurement of hip extension unless lumbopelvic motion is controlled, as the test exhibits poor sensitivity (31.82%), specificity (57.14%), and criterion reference validity (using sagittal plane motion capture).
Conclusions of the Researchers	The MTT can be a reliable assessment tool for assessment of hip extension range of motion if pelvic tilt is controlled. Pelvic motion can be accounted for by application of a blood pressure cuff underneath the low back inflated to 60 mm Hg.

Caption: hip extension, modified thomas test, thomas test, flexibility, assessment

The Modified Thomas Test, as performed by the Brookbush Institute. Note: the patient is cued to pull the leg toward the chest until the lumbar spine is "flat" in an attempt to control the amount of pelvic rotation.

Commentary:

The current study exhibited several strengths in its methodology. Criterion validity of the Modified Thomas Test (MTT) has not been previously explored in the literature. The authors devised a novel way to measure hip extension angle, ensuring the thigh was measured relative to the hip, rather than the thigh relative to the plinth which as has been used in previous studies. This modification minimized the influence of other factors (such as thigh girth or excessive waist circumference) on true hip extension angle. Further, the authors were thorough in their analysis of the data. After the data was analyzed for validity, the authors ran the data again accounting for pelvic motion. In doing so, the authors concluded that pelvic motion alone could explain the variance observed between the test results and the participant's "true" hip extension range of motion. This implies that if the practitioner can control the degree of pelvic motion during the assessment, hip extension range of motion could be reliably determined. The authors suggested simple techniques to minimize pelvic motion during assessment, including placement of a blood pressure cuff underneath the small of the back or use of palpation to control the degree of pelvic tilt. Future studies are needed to assess technique validity.

The study also had a few weaknesses that should be mentioned prior to application in practice. The participant position used for MTT in this study does not necessarily depict true hip extension range of motion (as described above). Further, factors including muscle guarding, the ability of a client/patient to comfortably get into the test position, and even restrictive clothing can affect test outcomes, and were not mentioned in this study. Caution should be taken when using the MTT as the sole assessment tool to determine hip extension range of motion. Other useful assessment techniques include Ober's test , Ely's test and hip extension goniometry . Additionally, as the participants in the current study were healthy, asymptomatic individuals, care must be taken in applying study findings to injured or "at risk" populations.

Why is this study important?

The movement toward evidence-based practice and emphasis on research, has highlighted the rather poor validity and reliability of some of the commonly used assessments in rehab, performance and fitness settings. It is important that research is continued to examine the reliability and validity of commonly used assessments so that assessment techniques may be optimized. The MTT is designed to determine hip extension range of motion, but limited research has been published about its validity (assessment results match the variable measured). The current study concluded that the MTT exhibits poor sensitivity, specificity, and criterion reference validity, unless pelvic tilt is controlled. Future studies should seek to validate protocols for controlling pelvic motion (such as a blood pressure cuff underneath the low back).

How does it affect practice?

The current study suggests that the Modified Thomas Test (MTT) is not a valid assessment of hip extension range of motion unless lumbopelvic motion is controlled. Practitioners should make an effort to control lumbopelvic motion when performing MMT (as is performed by the Brookbush Institute - Modified Thomas Test ), and cluster results with additional hip extension assessments, for example inclusion of the Ober's test , Ely's test and hip extension goniometry .

How does it relate to Brookbush Institute Content?

Overhead squat assessment (OHSA) compensations "excessive forward lean " and "anterior pelvic tilt " indicate potential over-activity of the hip flexor musculature (iliacus and psoas ). The MTT is indicated to determine the relative contribution of these muscles to the postural dysfunctions observed in the OHSA. The Brookbush Institute performs the MTT differently than described in the current study, with the client supine and the tested leg resting on the table (rather than hanging off of it). To control lumbopelvic motion, the practitioner places one hand underneath the curve of the lower back, and instructs the client to pull the knee towards the chest to induce a posterior pelvic tilt until the lumbar spine is "flat". If iliacus and psoas are at optimal length, the other leg should remain on the table with toes pointing up. If any change occurs in the resting position of the tested leg, the implies that the psoas and/or iliacus are short/over-active.

In accordance with the approach of the Brookbush Institute in addressing signs of movement dysfunction/impairment, over-active psoas and iliacus may be released (by a licensed manual therapist, as self-administered release is contraindicated) and stretched , followed by activation and integration of the transverse abdominis , gluteus maximus , and gluteus medius . Other interventions to improve hip extension range of motion include hip mobilizations and kinesiotape application to facilitate gluteus maximus activation .

The following videos include the Modified Thomas Test (MTT) assessment (as performed by the Brookbush Institute), as well as common approaches to improving hip extension flexibility deficits.

Brookbush Institute Videos

Modified Thomas Test Assessment

Psoas and Iliacus Manual Release

Static Hip Flexor Stretch

Transverse Abdominis Isolated Activation

Gluteus Medius Isolated Activation

Gluteus Maximus Isolated Activation

SA Banded Hip Mobilizations

Gluteus Maximus Activation Taping

Questions, comments, and criticisms are welcomed and encouraged -

Modified Thomas Test is Not a Valid Indicator of Hip Extension unless Pelvic Tilt is Controlled

Research Review: Modified Thomas Test is Not a Valid Indicator of Hip Extension unless Pelvic Tilt is Controlled

Brookbush Institute Videos

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