sonographic measures of the gluteus medius, gluteus minimus, and vastus medialis muscles

journal of orthopaedic & sports physical therapy | volume 44 | number 8 | august 2014 | 627

[ brief report ]

The clinical use of ultrasound imaging (USI) by physiotherapists to measure muscle morphology during static and dynamic conditions falls within the scope of rehabilitative ultrasound imaging.17 Specifically, rehabilitative USI refers to the USI

procedures used by physiotherapists to evaluate the morphology and behavior of muscle and its related soft tissues, to provide biofeedback about muscle behavior during restoration of function,

and to carry out research aimed at in-forming clinical practice.17

To date, USI has been used to investi-gate a variety of muscles and to address a diversity of research questions. Sonogra-phy has been shown to be a valid method (primarily in healthy adults under rest-ing conditions) to measure the morphol-ogy of the trunk (abdominal and lumbar multifidus),2,3 as well as a range of other muscles,5,8,10,11 through comparison to magnetic resonance imaging. Further, there are numerous investigations that have assessed the reproducibility of so-nographic measures of the trunk mus-cles.1,6,7,18 In general, these investigations report moderate to excellent reliability for repeated resting measures, and poor to good reliability for measures of mor-phological change during a task in both healthy and patient samples.

A large number of investigations consider sonographic measures of the morphology of the trunk muscles; however, there is a paucity of informa-tion regarding other muscles that may be amenable to USI. Of particular in-terest, and the topic of this report, are the muscles of the lateral hip (gluteus medius [GMd] and gluteus minimus [GMn]) and knee (vastus medialis [VM]), which play an important role

TT STUDY DESIGN: Intrarater, repeated-measures, within-session reliability study.

TT OBJECTIVE: To describe a standardized method and preliminary reliability estimates for sonographic measures of resting and contracted gluteus medius (GMd), gluteus minimus (GMn), and resting vastus medialis (VM) muscles.

TT BACKGROUND: Sonography has been used to assess the morphology of a diversity of muscles in relation to a variety of musculoskeletal dysfunc-tions. Although the GMd, GMn, and VM muscles are associated with dysfunctions such as patel-lofemoral pain and osteoarthritis, there is a paucity of information regarding protocols for sonographic measurements of these muscles.

TT METHODS: A standardized method was devel-oped and used to gather sonographic measures of resting and contracted (sidelying hip abduc-tion task) GMd and GMn thickness and resting VM cross-sectional area during 1 measurement session in 29 female soccer players 14 to 17 years of age.

TT RESULTS: Intrarater reliability values for ultrasound imaging measurements of resting,

contracted, and change during contraction (intra-class correlation coefficient model 3,3 [ICC3,3]) of the GMd were 0.98 (95% confidence interval [CI]: 0.97, 0.99), 0.98 (95% CI: 0.96, 0.99), and 0.84 (95% CI: 0.71, 0.92), respectively, and of the GMn were 0.98 (95% CI: 0.97, 0.99), 0.94 (95% CI: 0.88, 0.97), and 0.53 (95% CI: 0.21, 0.76), respectively. Reliability (ICC3,3) for resting VM cross-sectional area was 0.99 (95% CI: 0.99, 0.99). Standard error of measurement for GMd, GMn, and VM varied between 0.5 and 1.6 mm, 0.3 and 1.4 mm, and 0.4 cm2, respectively, and 95% minimal detectable change ranged from 0.8 to 4.5 mm for the gluteals and 0.4 to 0.5 cm2 for the VM.

TT CONCLUSION: Reliable sonographic measure-ments of the lateral hip and knee musculature at rest and during contraction are feasible. Further investigation is required to establish the generalizability and reproducibility of the protocols presented in this report. J Orthop Sports Phys Ther 2014;44(8):627-632. Epub 16 July 2014. doi:10.2519/jospt.2014.5315

TT KEY WORDS: gluteal muscles, quadriceps, reliability, ultrasonography

1Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada. 2The Alberta Children’s Hospital Research Institute for Child and Maternal Health, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Ethics approval was granted from the Conjoint Health Research Ethics Board at the University of Calgary, Calgary, Alberta, Canada. The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article. Address correspondence to Dr Jackie L. Whittaker, Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4. E-mail: [email protected] T Copyright ©2014 Journal of Orthopaedic & Sports Physical Therapy®

JACKIE L. WHITTAKER, PT, PhD, FCAMPT1,2 • CAROLYN A. EMERY, PT, PhD1,2

Sonographic Measures of the Gluteus Medius, Gluteus Minimus,

and Vastus Medialis Muscles

44-08 Whittaker.indd 627 7/16/2014 3:46:32 PM

628 | august 2014 | volume 44 | number 8 | journal of orthopaedic & sports physical therapy

[ brief report ]

in the control of the hip, knee, and patellofemoral joints during gait, run-ning, and sporting activities.16 Although there has been preliminary work pub-lished with respect to sonographic assessment of these muscles, the meth-ods presented are difficult to replicate in clinical research due to insufficient reporting4 and the need for advanced imaging techniques and analyses.9 If methods amenable to clinical research

could be established, they would en-able the assessment and comparison of the morphology of these muscles with respect to a variety of populations (eg, healthy, sporting, and injured), dys-functions (patellofemoral pain, osteo-arthritis, etc), and interventions (eg, strengthening, balance, and injury-prevention programs). Consequently, the primary purpose of this report was to present a sonographic methodology

for investigating the morphology of the GMd, GMn, and VM that is amenable to clinical research and practice, and, if adopted by other investigative teams, will facilitate the synthesis of data from future investigations. A secondary pur-pose was to assess the feasibility of this methodology by presenting preliminary estimates of within-session intrarater reliability.

METHODS

Participants

Participants included 29 healthy, consenting female ado-lescent (aged 14 to 17 years) soc-

cer players recruited from 2 teams (n = 36) that participated in a random-ized controlled trial investigating the implementation of a neuromuscular injury-prevention program across 29 teams (n = 226) during the 2011 sea-son. Information regarding partici-pant recruitment and eligibility for the implementation trial is detailed else-where.14 Ethics approval was granted from the Conjoint Health Research Ethics Board at the University of Cal-gary, Calgary, Alberta, Canada.

USI ProtocolAll sonographic images were collected by a single experienced sonographic operator (J.W.), an experienced phys-iotherapist with 12 years of USI experi-ence. A USI system (MyLab 25; Esaote North America, Inc, Indianapolis, IN) with a 5.0-MHz curvilinear trans-ducer (40-mm footprint; lateral and axial resolution of 1.0 and 0.93 mm, respectively) was used to collect bilat-eral anonymized resting B-mode ul-trasound images of the GMd and GMn (FIGURE 1) from a sidelying position, and of the VM (FIGURE 2) from a supine position. Additionally, images of the GMd and GMn during muscular con-traction were obtained during a stan-dardized sidelying hip abduction task (20-mmHg reduction in a pressure biofeedback cuff ). Precise descriptions

FIGURE 1. (A) Lateral hip muscle imaging site (gray oval). (B) GMd and GMn thickness measurements (dashed circle represents the superior lip of the acetabulum). (C) Sidelying hip abduction task. Abbreviations: GMd, gluteus medius; GMn, gluteus minimus.

FIGURE 2. (A) VM imaging site (gray oval). (B) VM cross-sectional area measurement. Abbreviation: VM, vastus medialis.



of participant position, imaging site, and hip abduction task are provided in TABLE 1. These procedures were chosen after review of cadaveric specimens, thorough review of previous imaging studies,4,9 and extensive pilot testing in both clinical and laboratory settings. Three images were acquired at each imaging site for both resting and con-tracted (GMd and GMn) conditions (ie, 3 trials). The transducer was removed and repositioned between trials, which provided the participant with a 10- to 20-second rest. To avoid an order or fatigue effect, the order in which the muscles and maneuvers were imaged was randomized. Testing of all partici-pants occurred over a 3-day period.

Images were measured offline using custom-written measurement codes in MATLAB Version 7.1 software (The MathWorks, Inc, Natick, MA). The measurement codes had 2 unique fea-tures relevant to this investigation. First, they prompted the operator to plot a reference line, which ensured that measurements could be made at the same location in the resting and contracted images. Second, the codes concealed measurements from the op-

erator by directly exporting them into an Excel (Microsoft Corporation, Red-mond, WA) worksheet. This ensured blinding of the examiner throughout the measurement process.

Measurements of GMd and GMn thickness (FIGURE 1) and VM (FIGURE 2) cross-sectional area were made and the mean of the 3 repetitions used for analyses. All measurements ex-cluded the perimuscular connective tissue (thickness was defined as the distance between the inside edges of each muscle border), as this tissue has been shown to differ in thickness be-tween case and healthy populations.18 Information from 2 previous studies regarding the influence of transducer motion on measurements of muscle thickness,19 as well as the pattern of transducer motion that occurs during leg-lifting maneuvers,20 was taken into consideration during data collection. Namely, the operator made every at-tempt to keep the angular and inward/outward motion of the transducer to a minimum, and paid specific attention to countering transducer motion at the point of initiation of the leg lift during the hip abduction task.

Data AnalysisStatistical analyses were performed

using the statistical software Stata Ver-sion 12.1 (StataCorp LP, College Station, TX). The mean and 95% confidence in-terval (CI) values for resting GMd and GMn thickness and VM cross-sectional area, as well as for the contracted GMd and GMn during hip abduction, were calculated. Intraclass correlation coeffi-cients (ICCs) with 95% CIs were calcu-lated to assess within-session intrarater reliability (model 3,3).13 To assess mea-surement precision, standard error of measurement (SEM) was calculated as SD × √1 – ICC.12 The 95% minimal de-tectable change (MDC95), which repre-sents the minimal change in thickness that must occur to be 95% confident that a true change has occurred, was calcu-lated as 1.96 × SEM × √2.15 To assess ab-solute agreement, the mean difference between measurements 1 and 3, as well as the 95% limits of agreement (mean difference between measurements ±2 SD), were calculated. Bland-Altman plots were used to look for any system-atic bias, outliers, and relationships be-tween the difference in values between images and their magnitudes.

TABLE 1Summary of Techniques for Ultrasound Imaging of the Gluteus Medius, Gluteus Minimus, and Vastus Medialis

Abbreviations: ASIS, anterior superior iliac spine; CSA, cross-sectional area; NA, not applicable; PBU, pressure biofeedback unit (Chattanooga Stabilizer; DJO Global Inc, Vista, CA); PSIS, posterior superior iliac spine.

Muscle Participant Position Transducer Location Contraction Technique

Gluteus medius and minimus

Sidelying with the test leg up. The test-leg hip is in neutral flexion/extension, neutral rotation, and 20° of adduction (inclinometer confirmed). The test-leg knee is in full extension, with a PBU placed under the ankle and foot.

Place the transducer on the lateral aspect of the hip on the lower half of a coronal line located between the top of the greater trochanter and a point 25% of the distance between the ASIS and PSIS. Adjust the cranial-caudal position of the transducer until the superior lip of the acetabulum (dashed circle in FIGURE 1) is one third of the distance from the right border of the image.

To standardize across participants, inflate the PBU so that the starting position is 20° of hip adduction from the horizontal. Instruct participants to gently lift their leg toward the ceiling, keeping their toes pointing forward, until the reading on the PBU decreases by 20 mmHg.

Vastus medialis Supine with the hips of both legs in neutral flexion/extension, rotation, abduction/adduction, and the knee in full extension.

Place the transducer in a transverse orientation just superior to the patella. Slide the transducer down until it butts up against the top of the patella, then move it medially (with care given not to adjust the cranial-caudal position and to maintain a tangential orientation to the surface of the knee) until entire CSA of the muscle is within the field of view (FIGURE 2).

NA



[ brief report ]

RESULTS

Participants ranged in age from 14 to 17 years (mean ± SD age, 15.2 ± 0.79 years; 95% CI: 14.9, 15.5) and

had a mean ± SD body mass index of 21.3 ± 2.2 kg/m2 (95% CI: 20.4, 22.1). Resting and contracted values (mean ± SD with 95% CI), intrarater ICC3,3 with 95% CI, SEM, and MDC95 values are summarized in TABLE 2. The mean change in thick-ness of the GMd during the hip abduction task was 2.1 mm, whereas the correspond-ing value for GMn was less than 1 mm (0.4-0.9 mm). The reliability estimates (ICC3,3) for the resting, contracted, and change during contraction of the GMd were 0.98 (95% CI: 0.97, 0.99), 0.98 (95% CI: 0.96, 0.99), and 0.84 (95% CI: 0.71, 0.92), respectively, and of the GMn were 0.98 (95% CI: 0.97, 0.99), 0.94 (95% CI: 0.88, 0.97), and 0.53 (95% CI: 0.21, 0.76), respectively. The reliability estimate for resting VM cross-sectional area was 0.99

(95% CI: 0.99, 0.99). In regard to mea-surement precision, SEM values for rest-ing and contracted conditions were less than or equal to 1.6 mm for the gluteal muscles and 0.2 cm2 for the VM muscles. The SEM values for change in thickness during contraction were 0.6 mm and 1.6 mm for GMd and 0.7 mm and 1.4 mm for GMn, with the error values for GMn exceeding the observed mean change in thickness. Finally, values for MDC95 ranged from 0.8 to 4.5 mm for the gluteals and 0.4 to 0.5 cm2 for the VM.

The mean absolute differences be-tween measurements 1 and 3, as well as 95% limits of agreement, for all param-eters and muscle states are summarized in TABLE 2. Difference values for the gluteal muscles ranged from an absolute value of 0.002 mm (right GMn thickness change with contraction) to –0.13 mm (left GMn thickness change with contraction), whereas differences between measure-ments 1 and 3 for the VM ranged between 0.06 and 0.08 cm2. Bland-Altman plots

did not reveal any significant systematic bias or relationships between the differ-ence in measurements 1 and 3 and their magnitudes. Further, none of the mean differences were greater than the MDC95, suggesting that they did not represent a true difference.

DISCUSSION

This report demonstrated a fea-sible and potentially reliable method-ology for measuring the morphology

of the GMd, GMn, and VM in an athletic, adolescent female population at rest and, in the case of the hip parameters, during a dynamic task. Although only preliminary, a comparison of all sonographic measures during resting and contracted conditions showed promising within-session intra-rater reliability (ICC point estimates of 0.83 or greater, with lower bounds of the 95% CI greater than or equal to 0.70). In contrast, the reliability estimates as-sociated with measurements of absolute

TABLE 2Descriptive Data and Within-Day Intrarater ICC, SEM, MDC, Bias, and Limits-of-Agreement Values

Abbreviations: GMd, gluteus medius; GMn, gluteus minimus; ICC, intraclass correlation coefficient; MDC, minimal detectable change; SEM, standard error of measurement; VM, vastus medialis.*Values in parentheses are 95% confidence interval.†Values in parentheses are 95% limits of agreement.

Muscle/State Mean ± SD* ICC3,3* SEM MDC95 Difference (Measures 1 and 3)†

GMd right, mm

Rest 20.5 ± 3.9 (19.0, 22.0) 0.98 (0.97, 0.99) 0.5 1.4 0.05 (–0.23, 0.32)

Contracted 22.6 ± 3.8 (21.1, 24.0) 0.98 (0.96, 0.99) 0.6 1.5 0.02 (–0.24, 0.29)

Change 2.1 ± 1.5 (1.5, 2.7) 0.84 (0.71, 0.92) 0.6 1.6 –0.03 (–0.34, 0.29)

GMd left, mm

Rest 20.2 ± 4.0 (18.7, 21.7) 0.96 (0.92, 0.98) 0.8 2.3 0.05 (–0.68, 0.77)

Contracted 22.5 ± 4.0 (20.9, 24.0) 0.91 (0.83, 0.95) 1.2 3.4 0.03 (–0.19, 0.25)

Change 2.1 ± 2.4 (1.1, 3.0) 0.54 (0.22, 0.77) 1.6 4.5 –0.09 (–1.02, 0.85)

GMn right, mm

Rest 12.2 ± 2.2 (11.3, 13.0) 0.98 (0.97, 0.99) 0.3 0.8 –0.03 (–0.19, 0.14)

Contracted 12.6 ± 2.1 (11.8, 13.4) 0.94 (0.88, 0.97) 0.5 1.5 –0.03 (–0.33, 0.27)

Change 0.4 ± 1.0 (0.07, 0.08) 0.53 (0.21, 0.76) 0.7 1.9 0.01 (–0.37, 0.38)

GMn left, mm

Rest 11.9 ± 2.4 (11.0, 12.8) 0.96 (0.92, 0.98) 0.5 1.4 –0.02 (–0.30, 0.27)

Contracted 12.8 ± 2.5 (11.8, 13.8) 0.83 (0.70, 0.92) 1.0 2.8 –0.05 (–0.34, 0.24)

Change 0.9 ± 2.0 (0.1, 1.6) 0.50 (0.19, 0.75) 1.4 3.9 –0.13 (–0.97, 0.70)

VM right at rest, cm2 12.7 ± 2.9 (11.6, 13.8) 0.99 (0.99, 0.99) 0.2 0.4 0.08 (–0.69, 0.86)

VM left at rest, cm2 12.5 ± 2.5 (11.6, 13.5) 0.99 (0.99, 0.99) 0.2 0.5 0.06 (–0.68, 0.81)



thickness change of GMd and GMn dur-ing the hip abduction task were lower and associated with wide 95% CIs (ICC point estimates of 0.50 or greater, with lower bounds of the 95% CI of 0.19 or greater). This likely reflects the fact that these mea-sures incorporate the measurement error from both the resting and contracted measures from which they are calculated (contracted thickness – resting thickness = change in thickness), and the small ab-solute change in thickness seen in these muscles with the hip abduction task (less than 1 mm). In general, these findings suggest that sonographic measurements of the lateral hip and knee musculature are feasible; however, additional research is required to establish between-session and interrater reliability. Further, these data can assist future investigators with study design and, in particular, sample-size calculation.

LimitationsThere are several limitations to this study. First, the sample size was small and all participants were young, active girls. As such, the generalizability of the findings may be questioned. Second, as only intra-rater, within-session estimates of relative and absolute reliability were calculated, further work is required to establish the reproducibility of these methods. Finally, although every attempt was made to stan-dardize all aspects of data collection, it is important to acknowledge that the re-sponses being measured, particularly as they relate to change in muscle thickness with contraction, are inherently unstable. However, as the goal of this investiga-tion was to present a clinically amenable methodology, it was expected that some sources of error would not be controlled for. It is likely that the inherent instabil-ity of the parameters being measured and the clinical test employed led to this vari-ability. Based on the size and exclusivity of the sample, and the limited conclusions regarding reliability that can be made from within-session, intrarater estimates of reproducibility, further investigation of these methods and their reproducibility is

required in larger and more diverse popu-lations before widespread use.

CONCLUSION

This report presents a methodol-ogy for investigating the morphology of the GMd, GMn, and VM muscles

with sonography that is amenable to the clinical setting. Having demonstrated feasibility and preliminary reliability (within-session measurements of resting and contracted conditions), these meth-ods could be adopted by other investiga-tive teams interested in the morphology of these muscles to facilitate future data synthesis. t

ACKNOWLEDGEMENTS: This report was based on a randomized controlled trial funded by the FIFA Medical Assessment and Research Centre and the Sport Injury Prevention Re-search Centre at the University of Calgary, and supported by the International Olympic Committee Research Centre Award, the Al-berta Children’s Hospital Research Institute for Child and Maternal Health Professorship in Pediatric Rehabilitation (Alberta Children’s Hospital Foundation), and Alberta Team Os-teoarthritis (supported by Alberta Innovates-Health Solutions). The authors would also like to acknowledge the assistance of Maria Romiti, Tracy Blake, Catriona Peggie, and Kim Lee-Knight and the participation of youth soccer players.

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sonographic measures of the gluteus medius, gluteus minimus, and vastus medialis muscles

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