http://informahealthcare.com/ptp ISSN: 0959-3985 (print), 1532-5040 (electronic) Physiother Theory Pract, 2014; 30(5): 360–366 ! 2014 Informa Healthcare USA, Inc. DOI: 10.3109/09593985.2013.876693
DESCRIPTIVE REPORT
Ultrasonographic measurements of lower trapezius muscle thickness at rest and during isometric contraction: a reliability study Nancy R. Talbott, PhD, MS, PT, and Dexter W. Witt, DHS, DPT, OCS, FAAOMPT
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Department of Rehabilitation Sciences, College of Allied Health Sciences, University of Cincinnati, Cincinnati, OH, USA
Abstract
Keywords
Objective: The purpose of this study was to determine the intra-rater reliability and inter-rater reliability of ultrasound imaging (USI) thickness measurements of the lower trapezius (LT) at rest and during active contractions when the transverse process and the lamina were used as reference sites for the measurement process. Participants: Twenty healthy individuals between the ages of 22 and 32 years volunteered. Methods: With the subject prone and the shoulder in 145 of abduction, images of the LT were taken bilaterally by one examiner as the subject: (1) rested; (2) actively held the test position; and (3) actively held the test position while holding a weight. Ten subjects returned and testing was repeated by the same examiner and by a second examiner. LT thickness measurements were recorded at the level of the transverse process and at the level of the lamina. Results: Intra-class correlation coefficients (ICC) for within session intra-rater reliability (ICC3,3) ranged from 0.951 to 0.986 for both measurement sites while between session intra-rater reliability (ICC3,2) ranged from 0.935 to 0.962. Within session inter-rater reliability (ICC2,2) ranged from 0.934 to 0.973. Conclusions: USI can be used to reliably measure LT thickness at rest, during active contraction and during active contraction when holding a weight. The described protocol can be utilized during shoulder examinations to provide an additional assessment tool for monitoring changes in LT thickness.
Lower trapezius, reliability, ultrasound imaging
Introduction Optimal position and control of the scapula is critical for upper limb function (Ebaugh, McClure, and Karduna, 2005). The scapula, as it moves and maintains its position, contributes to both the movement and control of the glenohumeral joint (Cools et al, 2007; Ludewig and Reynolds, 2009; Mottram, 1997). Through upward rotation, posterior tilting and external rotation, the scapula orients the glenoid to enhance congruity with the humeral head and maintains the subacromial space to allow for overhead motion of the arm without impingement (Endo, Ikata, Katoh, and Takeda, 2001; Lin et al, 2005; Ludewig and Cook, 2000; McClure, Michener, and Karduna, 2006). Appropriate scapular motion and scapular stability is therefore essential to the prevention and rehabilitation of rotator cuff tears, bursitis and other shoulder pathologies. Scapular stabilization and movement, however, is highly dependent on the activity of the trapezius and serratus anterior muscles (Cools et al, 2003, 2007; Mottram, 1997). Although all three parts of the trapezius (the upper, middle and lower) and the serratus anterior have a role in the stabilization of the scapula, the lower trapezius (LT) has been more consistently associated with shoulder pathologies (Cools et al, 2002, 2003, 2007; Lin, Wu, Wang, and Chen, 2005; Ludewig and Cook, 2000). The LT activity has been found to be decreased in patients with frozen shoulder syndromes and in patients with impingement and has delayed activation in patients with shoulder instability
Address correspondence to Nancy R. Talbott, PhD, MS, PT, Department of Rehabilitation Sciences, College of Allied Health Sciences, University of Cincinnati, Cincinnati, OH, USA. E-mail: [email protected]
History Received 6 December 2012 Revised 26 November 2013 Accepted 30 November 2013 Published online 10 January 2014
(Cools et al, 2003; Lin, Wu, Wang, and Chen, 2005; Matias and Pascoal, 2006). Multiple exercise programs have been proposed to specifically enhance and normalize LT activation and to correct abnormal scapular mechanics (Cools et al, 2007; Kibler and Sciascia, 2010; Kibler et al, 2008; Ludewig and Braman, 2011; McClure, Greenberg, and Kareha, 2012). Clinical tools, therefore, are needed to assess the function and activation of the LT. Currently, clinical assessment of scapular function relies on observation of static and dynamic scapular position, manual muscle tests (MMT) of the scapular muscles and a selection of special tests (Magee, 2008; McClure, Greenberg, and Kareha, 2012; Wright, 2013). Use of these techniques may have limited value in a patient examination due to low reliability, poor validity and weak association with clinical symptoms (Hickey, Milosavljevic, Bell, and Milburn, 2007; McClure, Greenberg, and Kareha, 2012; Michener, Boardman, Pidcoe, and Frith, 2005; Odom, Taylor, Hurd, and Denegar, 2001; Shadmehr, Bagheri, Ansari, and Sarafraz, 2010; Wright, 2013). Although electromyography (EMG) and three dimensional motion analysis have also been employed to assess scapular motion and muscle activity in a research context (Lin et al, 2005; Ludewig and Cook, 2000; Matias and Pascoal, 2006; McClure, Michener, and Karduna, 2006; Mell et al, 2005), these methods of examination of the scapula can be expensive, time consuming to use and traditionally require extensive post testing analysis (Ebaugh, McClure, and Karduna, 2005; Ludewig, Cook, and Nawoczenski, 1996). A viable adjunct to current scapular muscle assessment is the use of ultrasound imaging (USI). USI is portable, requires less time for testing and needs little processing of collected data
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DOI: 10.3109/09593985.2013.876693
(Bembem, 2002; O’Sullivan et al, 2009; Whittaker et al, 2007). At the same time, individual muscles can be imaged permitting visualization of muscle boundaries, architecture and changes with active movement. Reliability and validity of USI has been established for multiple muscles (Hides et al, 2007; Kiesel et al, 2007; Nestorova et al, 2012; Raney, Teyhen, and Childs, 2007; Riddiford-Harland, Steel, and Baur, 2007; Wallwork, Hides, and Stanton, 2007; Yim and Corrado, 2012) and USI has been used for visual feedback during exercises (Ariail, Sears, and Hampton, 2008; Henry and Westervelt, 2005; Hides et al, 2006; Lee et al, 2011). In the scapular area, USI of the LT muscle has been shown to be valid and reliable at rest when the arm is at the side (O’Sullivan, Bentman, Bennett, and Stokes, 2007; O’Sullivan et al, 2009). However, reliability of LT USI has not been explored in a contracted state, a condition important to the clinical assessment and rehabilitation of that muscle. As the LT function is one of mobility and stability, reliable procedures that isolate its activity or changes during active contraction with and without resistance are needed. The purpose of this study was to develop a clinically applicable method to reliably measure LT thickness both at rest and during states of contraction using USI. Specifically, the aims of the study were to: (1) describe a method to measure LT thickness using USI; (2) determine within session intra-rater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight; (3) determine between session intra-rater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight; and (4) determine within session interrater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight.
Methods To determine the intra-rater and inter-rater reliability of using USI to measure LT muscle thickness at two different image sites (the transverse process and the lamina), a single group repeated measures design was employed. The study received institutional review board approval and all study participants signed a written informed consent prior to their participation in the study. Participants
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corresponding level (Neumann, 2002). The level of the spinous process was further confirmed by palpating the spinous processes in the lower cervical spine, extending the neck to identify the less palpable spinous process of the sixth cervical vertebrae, palpating the seventh cervical spinous process just inferior and counting down to the seventh thoracic process. Although the LT could be measured at various sites, this location was selected because it was easily located and was similar to the levels in which USI measurements of the LT have been reported as being valid (O’Sullivan et al, 2009). Following the location of the landmarks, the subject was placed prone on a treatment table with the shoulder in 145 of abduction. This shoulder position was confirmed through the use of a goniometer and was chosen because it is the position commonly suggested for MMT of the LT (Hislop and Montgomery, 2007). The arm was supported on an adjoining electronically adjustable high low table. The midline of the transducer was placed horizontally over the marked seventh thoracic vertebrae resulting in an image of both the right and the left LT muscle at that vertebral level. The probe was then moved laterally toward the dominant side until the examiner could visualize the dominant side LT, the concavity of the dominant side lamina and the convexity of the dominant side transverse process (Figure 1). After a clear image of the LT, transverse process and lamina could be seen on the ultrasound screen, the subject was instructed to rest the arm on the table in the test position (Figure 2A). The image was frozen and stored for off line measurement. No synchronization with inspiration was attempted as previous researchers reported no changes in LT thickness during respiration (O’Sullivan, Bentman, Bennett, and Stokes, 2007). Following capture of the rest image, the subject was instructed to maintain the test position while the high low table under the test arm was lowered until the table was no longer in contact with the test side arm (Figure 2B). The examiner monitored the on screen image and ensured that the lamina, transverse process and LT borders were visible before the image was frozen and stored. The table was then raised until the test side arm was once again supported in the appropriate test position. After 30 s of rest, a two pound weight was placed in the subject’s hand and the subject instructed to maintain the position while the high low table was
Participants were recruited from a population of convenience at a large urban University. To be enrolled in the study, individuals were required to meet the following criteria: (1) no trauma, pain or surgery involving the neck, shoulder or arm; (2) no history of neuromuscular or musculoskeletal disorders; (3) full active pain free range of motion of the cervical spine and shoulders; and (4) between the ages of 18 and 65 years. Individuals were excluded if they reported that they were pregnant, had any metal implants, or were involved in specific activities aimed at increasing the strength of the scapular muscles. If all criteria requirements were satisfied, height and weight were measured. Individuals with a body mass index of greater than 30 kg/m2 were excluded due to the potential difficulty obtaining clear ultrasound images. Procedures A Biosound MyLab 25 Gold USI system (Esaote, Indianapolis, IN) with a 40 mm linear transducer was used in the B-mode at a frequency of 18MHz. Calibration was performed using a phantom prior to the initiation of the study. Before initiation of the USI, the subject was seated with the thoracic spine exposed. The spinous process of the seventh thoracic vertebrae was identified by palpating the inferior angle of the respective scapula and marking the spinous process at the
Figure 1. Measurement of left lower trapezius thickness. (A) Measurement at the transverse process site. At a location perpendicular to the transverse process (arrow on the left), measurement of lower trapezius thickness was taken between the hyperechoic borders of the muscle (dotted line on the left). (B) Measurement at the lamina site. At a location perpendicular to the lamina, measurement of the lower trapezius thickness was taken between the hyperechoic borders of the muscle (dotted line on the right).
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Physiother Theory Pract, 2014; 30(5): 360–366
Microsoft Excel (Microsoft Inc., Redmond, WA) spreadsheet for later analyses.
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Data analysis
Figure 2. Test positions for USI of the lower trapezius.
again lowered until the table was no longer in contact with test side arm (Figure 2C). The landmarks were monitored to keep the same area of the LT on the screen. The image was frozen and then stored. The ultrasound probe was removed, the subject was given a 30-s rest and the process was repeated two additional times. After a 30-s rest, the imaging was repeated three times on the nondominant arm. To determine intra-rater reliability between sessions, ten of the subjects returned within seven days and the same testing procedure was repeated by the original examiner. On their return, these 10 subjects also had the same testing procedure repeated by a second examiner. The two examiners performing the USI procedures were physical therapists who had been performing USI of the scapular muscles for 4 years. Both had at least 50 h of hands on training in musculoskeletal ultrasound including over 30 h with a registered sonographer. Measurements All linear measurements of LT muscle thickness on the captured ultrasound images were completed off-line utilizing ImageJ (Abramoff, Magalhaes, and Ram, 2004). Measurements were completed by the single investigator who participated in both days of imaging. ImageJ was selected because it directly records the numerical value of a measurement onto a spreadsheet that can be minimized on a computer screen. The measurer, therefore, cannot see previously recorded values while measuring a subsequent image, a procedure which mitigates measurement bias. Using ImageJ, the actual thickness measurements of the LT in this study were taken at two locations: (1) the lamina; and (2) transverse process. The LT thickness measurement taken at the lamina was completed by first locating the lamina deep to the LT. At the deepest aspect of the concavity of the lamina, a vertical line was extended from the concavity through the LT. The portion of this line that was located between the inside margin of the inferior echogenic fascial line of the LT and the inside border of the superior echogenic facial line of the LT was measured (Figure 1). The second measurement taken using the transverse process as a landmark was completed in a similar manner. A perpendicular line was drawn from the superior part of the convexity on the transverse process and the portion of that line located between the inside margins of the LT was measured (Figure 1). The linear measurements were transferred from the ImageJ software to a
Data was transferred from a Microsoft Excel spreadsheet to IBM SPSS Statistics 20 (IBM, Armonk, NY) for statistical analysis. Descriptive statistics (mean ± SD) were completed for age, height (cm), weight (kg) and body mass index (kg/m2). A one-way analysis of variance (ANOVA) was used to analyze any variability in LT thickness measurements associated with hand dominance and with body mass index. Additional ANOVAs were constructed to analyze variability in LT thickness measurements associated with: (1) repetition; (2) day of testing; and (3) examiner. Intra-rater reliability and inter-rater reliability were assessed using intra-class correlation coefficients (ICCs) with ICC3,3 the model for intra-examiner reliability within a day; ICC3,2 the model for intra-examiner reliability between days; and ICC2,2 the model for inter-examiner reliability on the same day. Coefficients above 0.75 were interpreted as indicating good agreement, coefficients between 0.50 and 0.75 reflected moderate agreement, and coefficients below 0.50 represented poor agreement (Portney and Watkins, 2000). The standard error of measurement pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi(SEM) was calculated using the formula SEM ¼ S 1 ICC where S ¼ the pooled standard deviation and ICC is the reliability coefficient. Confidence intervals for each of the ICC values were calculated. Reliability was further evaluated by using Bland and Altman plots. These plots offer an easy to interpret visual representation of the degree of agreement, allow for prompt identification of outliers and potential bias and have been promoted as the preferred statistical methodology for studies of reliability (Rankin and Stokes, 1998). All analyses were completed separately for LT thickness measurements taken at the lamina site and measurements taken at the transverse process site.
Results Twenty subjects participated in the study. Demographic information can be found in Table 1. Variations in LT thickness measurements were not found to be significantly associated with body mass index (p40.05), eliminating the need for thickness measurements to be adjusted for height and weight. In addition, LT thickness measurements were not significantly associated with arm dominance (p40.05) supporting the pooling of LT thickness measurements for the dominant and nondominant arm in all subsequent analyses. LT measurements taken on day 1 by examiner 1 are reported in Table 2. Mean LT thickness measurements when measured at the lamina and at the transverse process site were not significantly different between repetitions (p40.05). Reliability was good within a session with all ICCs greater than 0.95 (Table 2). LT measurements taken on day 1 and day 2 by examiner 1 are listed in Table 3. Mean LT thickness measurements when measured at the lamina and at the transverse process site were not significantly different between days (p40.05). Reliability between days was good with all ICCs greater than 0.93 (Table 3). LT measurements taken on day 2 by examiner 1 and LT thickness measurements taken on day 2 by examiner 2 are presented in Table 4. Mean measurements taken in the rest position by Examiner 1 were less than 0.2 mm different from those of Examiner 2 and were not significantly different (p40.05). Reliability between examiners was high with ICCs greater than 0.93 (Table 4). Figures 3 and 4 depict sample Bland–Altman plots examining the agreement between days and between examiners.
USI thickness measurements of the lower trapezius
DOI: 10.3109/09593985.2013.876693
The differences between the measurements taken by examiner 1 on day and on day 2 are shown in Figure 3. The mean differences between LT thickness measured on day 1 and those measured on day 2 were close to zero (50.10 mm). All differences fell within
two standard deviations of the mean difference illustrating the consistency of the measurements between days. The differences between the measurements taken by examiner 1 and 2 are shown in Figure 4. The mean differences between LT thickness measured by examiner 1 and those measured by examiner 2 were50.02 mm. All differences between measurements fell within two standard deviations (0.152 mm) of the mean difference with the exception of one outlier which was within 0.16 mm of the mean difference.
Table 1. Participant characteristics.
Characteristic Age (y) Height (cm) Weight (kg) Body mass index (kg/m2)
All subjects Mean (SD)
Men (n ¼ 7) Mean (SD)
25 172.7 79.2 26.4
26 182.0 87.3 26.3
(2) (10.2) (17.6) (4.7)
(3) (6.3) (8.7) (2.1)
Women (n ¼ 13) Mean (SD) 24 167.8 74.8 26.4
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(1) (8.2) (19.9) (5.7)
Discussion The results of this study demonstrate that LT thickness can be reliably measured at rest, during an active contraction and during an active contraction with a weight. When the traditional MMT
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Table 2. Intra-rater reliability within a session: Lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Repetition 1 Mean (SD) (mm)
Repetition 2 Mean (SD) (mm)
Repetition 3 Mean (SD) (mm)
Pooled Mean (SD) (mm)
ICC3,3 (95% CI)
SEM (mm)
3.4 (1.0) 3.6 (1.3)
3.3 (1.1) 3.7 (1.2)
3.5 (1.1) 3.6 (1.2)
3.4 (1.1) 3.6 (1.2)
0.951 (0.917–0.972) 0.961 (0.935–0.978)
0.2 0.2
5.3 (2.0) 5.6 (2.4)
5.2 (2.0) 5.4 (2.4)
5.0 (2.0) 5.1 (2.4)
5.2 (1.9) 5.4 (2.3)
0.984 (0.973–0.991) 0.982 (0.969–0.990)
0.2 0.3
6.0 (2.2) 6.2 (2.6)
5.8 (2.2) 6.0 (2.7)
5.7 (2.3) 5.7 (2.8)
5.8 (2.2) 6.0 (2.6)
0.978 (0.963–0.988) 0.986 (0.976–0.992)
0.3 0.3
The mean and SD for each repetition and the pooled means (the mean for all three repetitions) are listed. ICCs and SEM values for intra-tester reliability on Day 1 are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
Table 3. Intra-rater reliability between sessions: lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Day 1 Mean (SD) (mm)
Day 2 Mean (SD) (mm)
Pooled Mean (SD) (mm)
ICC3,2 (95% CI)
SEM (mm)
3.8 (1.3) 3.8 (1.6)
3.1 (1.2) 3.4 (1.4)
3.5 (1.3) 3.6 (1.5)
0.956 (0.893–0.987) 0.935 (0.844–0.981)
0.3 0.4
4.9 (1.6) 4.9 (1.9)
4.4 (1.3) 4.8 (1.9)
4.7 (1.5) 4.8 (1.9)
0.961 (0.907–0.989) 0.944 (0.865–0.984)
0.3 0.4
5.6 (1.8) 5.3 (2.2)
5.1 (1.6) 5.3 (2.1)
5.3 (1.6) 5.3 (2.1)
0.956 (0.895–0.987) 0.962 (0.909–0.989)
0.3 0.4
The mean and SD for the three scans taken on Day 1, the means and SD for the three scans taken on Day 2 and the pooled means (the mean for all scans on both days) are listed. ICCs and SEM values for intra-tester reliability between days are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
Table 4. Inter-rater reliability within a session: lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Examiner 1 Mean (SD) (mm)
Examiner 2 Mean (SD) (mm)
Pooled Mean (SD) (mm)
3.1 (1.2) 3.4 (1.4)
3.3 (1.1) 3.4 (1.4)
3.2 (1.1) 3.4 (1.4)
0.962 (0.908–0.989) 0.957 (0.896–0.988)
0.2 0.3
4.4 (1.3) 4.8 (1.1)
4.7 (1.7) 4.8 (2.0)
4.5 (1.5) 4.8 (1.9)
0.934 (0.840–.981) 0.966 (0.917–0.990)
0.4 0.4
5.1 (1.6) 5.3 (2.1)
5.3 (1.9) 5.3 (2.3)
5.2 (1.7) 5.3 (2.1)
0.945 (0.868–0.984) 0.973 (0.934–0.992)
0.4 0.4
ICC2,
2
(95% CI)
SEM (mm)
The mean and SD for the three scans taken by examiner 1, the means and SD for the three scans taken by examiner 2 and the pooled means (the mean for all scans by both examiners) are listed. ICCs and SEM values for inter-tester reliability are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
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Physiother Theory Pract, 2014; 30(5): 360–366
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Figure 3. Bland and Altman plots showing differences in lower trapezius thickness measurements when measured at the lamina site on different days by one examiner. (A) Differences when measured at rest. (B) Differences when measured while holding a weight.
Figure 4. Bland and Altman plots showing differences in lower trapezius thickness measurements when measured at the lamina site on the same day by different examiners. (A) Differences when measured at rest. (B) Differences when measured while holding a weight.
test position was used and when measurements on the LT ultrasound image were taken at the site of the lamina and the transverse process, values were consistent between days and between examiners.
The findings in this study that LT thickness measurements are reliable at rest are consistent with a study by O’Sullivan, Bentman, Bennett, and Stokes (2007) in which LT ICC values were reported as 0.90–0.96 for intra-rater reliability within a
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DOI: 10.3109/09593985.2013.876693
session; 0.89–0.91 for intra-rater reliability between sessions; and 0.88 for inter-rater reliability within a session, respectively. Although both the current and the previous study demonstrated good reliability, the ICC values for inter-rater reliability in the current study were slightly higher than the previous study. In addition, mean values of the two examiners varied by 0.2 mm or less in the current study compared to the maximum difference of 1.0 mm between two of the examiners in the previous study. Although the clinical implications of differences in sizes of LT muscles have not been established, minimizing error between measurers would be a factor in a research or clinical setting in which interventions aimed at increasing LT thickness are employed. As LT thickness is relatively small (ranging between 3.1 mm to 6.2 mm at rest in the current study), larger inconsistencies between measurers reflects a much higher percentage of the total LT muscle thickness. The increased consistency between measurers that was found in the current study may be attributable to a measurement process which differed from the 2007 study by O’Sullivan, Bentman, Bennett, and Stokes. The measurement process described in the O’Sullivan, Bentman, Bennett, and Stokes (2007) study involved identifying the lateral border of the spinous process, measuring from that landmark a standard distance and then measuring LT thickness at that site. In the current study, measurements were taken perpendicular to the lamina and perpendicular to the transverse process eliminating the need to measure from the spinous process to the measurement site. The hyperechogenicity of the lamina and the transverse process were easily visible when images were being taken facilitating the consistent placement of the ultrasound transducer by different examiners and by the same examiner on different days. This visual acuity also facilitated the exactness of the site for off line measurement as the hyperechoic lines of the bony landmarks clearly delineated where, within the LT, the thickness measurements were to be taken. In addition, the distance from the spinous process to the measurement site in the current study varied with body size. If the individual was larger, the lamina and transverse process were farther away from the spinous process, while if the individual was smaller, the lamina and transverse process were closer to the spinous process. While this might have had little effect on reliability, the use of the landmarks in the current study may be more adaptable to measuring LT thickness in individuals of varying sizes. To the authors’ knowledge, this is the first study to document LT reliability values during LT active contraction and during LT contraction against resistance with the arm in the MMT position. LT thickness was measured during active contraction with the shoulder in 90 and 120 of abduction in a 2012 study by O’Sullivan et al., however, there was no documentation of the reliability of their LT thickness measurements in the contracted state. The LT measurement process used in the 2012 study has been found, in a previous study (O’Sullivan, Bentman, Bennett, and Stokes, 2007), to be reliable when the arm was at rest and positioned at the side. It is unclear, however, if a method that reliably measures LT thickness at rest translates to equivalent reliability during activation and similar reliability when the arm is placed in different positions. Clearly, the LT must be assessed in a contracted state and a reliable method for that active assessment is needed for the method to add value to the examination. Clinically, the findings of this study that USI can be used reliably to measure LT thickness at rest, during contraction and during contraction with resistance have implications for examining and treating impairments of the shoulder. The current study utilized the common manual muscle testing position for scanning to provide a reliable method of isolating LT muscle changes during at least part of a MMT of the LT. This protocol simulates three of the manual muscle testing grades routinely assigned
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during MMT: (1) zero; (2) fair; and (3) good. The rest condition of this protocol involved no palpable contractile activity and would simulate the 0/5 grade, the active hold condition mimics the fair or 3/5 grade as it involves an active hold in the muscle testing position without additional resistance, and the weight condition is comparable to a good or 4/5 grade as moderate resistance is supplied by the small weight. The advantage of using USI during this MMT is to allow the examiner to focus specifically on the behavior of the LT during the test. Previous studies have found that multiple scapular muscles are active during the MMT of the LT including the upper trapezius, middle trapezius, rhomboid, and serratus anterior muscles (Ekstrom, Donatelli, and Soderberg, 2003; Ekstrom, Soderberg, and Donatelli, 2005; Michener, Boardman, Pidcoe, and Frith, 2005). If the LT is weak, MMT results may appear as normal if substitution by other stronger scapular muscles is occurring. USI allows direct visualization of the specific changes the LT muscle undergoes during testing regardless of the activity in surrounding scapular stabilizers. Limitations Limitations of the study include the selection of the study population and the number of subjects involved in between session and inter-rater reliability testing. A healthy younger population participated in the study preventing results from being generalized to individuals with pathology. It is possible that USI of LT thickness in individuals with LT dysfunction may not be as reliable as in asymptomatic individuals, especially if pain or other symptoms limit active control or effort. In addition, the number of subjects returning for a second session of testing was 10. While this number may be small, the confidence intervals for the correlation coefficients were narrow supporting the reliability of the LT measurement values. Future studies, however, should consider a larger population of participants with a variety of LT dysfunctions to further establish the reliability of USI when measuring LT thickness.
Conclusions In summary, the described USI protocol can be used to reliably measure LT thickness in healthy adults at rest, during active contraction and during active contraction when holding a weight. The novel procedure described provides researchers and clinicians with an additional assessment or outcome tool for monitoring changes in LT thickness in a clinical rehabilitation setting. Future studies are needed to expand reliability testing of this method to subjects with upper extremity dysfunction, to correlate LT thickness with clinical symptoms and to determine if patterns of thickness changes with active contraction reflect dysfunction.
Declaration of interest The authors have nothing to disclose regarding this research and declare that they have no competing interests.
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DESCRIPTIVE REPORT
Ultrasonographic measurements of lower trapezius muscle thickness at rest and during isometric contraction: a reliability study Nancy R. Talbott, PhD, MS, PT, and Dexter W. Witt, DHS, DPT, OCS, FAAOMPT
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Department of Rehabilitation Sciences, College of Allied Health Sciences, University of Cincinnati, Cincinnati, OH, USA
Abstract
Keywords
Objective: The purpose of this study was to determine the intra-rater reliability and inter-rater reliability of ultrasound imaging (USI) thickness measurements of the lower trapezius (LT) at rest and during active contractions when the transverse process and the lamina were used as reference sites for the measurement process. Participants: Twenty healthy individuals between the ages of 22 and 32 years volunteered. Methods: With the subject prone and the shoulder in 145 of abduction, images of the LT were taken bilaterally by one examiner as the subject: (1) rested; (2) actively held the test position; and (3) actively held the test position while holding a weight. Ten subjects returned and testing was repeated by the same examiner and by a second examiner. LT thickness measurements were recorded at the level of the transverse process and at the level of the lamina. Results: Intra-class correlation coefficients (ICC) for within session intra-rater reliability (ICC3,3) ranged from 0.951 to 0.986 for both measurement sites while between session intra-rater reliability (ICC3,2) ranged from 0.935 to 0.962. Within session inter-rater reliability (ICC2,2) ranged from 0.934 to 0.973. Conclusions: USI can be used to reliably measure LT thickness at rest, during active contraction and during active contraction when holding a weight. The described protocol can be utilized during shoulder examinations to provide an additional assessment tool for monitoring changes in LT thickness.
Lower trapezius, reliability, ultrasound imaging
Introduction Optimal position and control of the scapula is critical for upper limb function (Ebaugh, McClure, and Karduna, 2005). The scapula, as it moves and maintains its position, contributes to both the movement and control of the glenohumeral joint (Cools et al, 2007; Ludewig and Reynolds, 2009; Mottram, 1997). Through upward rotation, posterior tilting and external rotation, the scapula orients the glenoid to enhance congruity with the humeral head and maintains the subacromial space to allow for overhead motion of the arm without impingement (Endo, Ikata, Katoh, and Takeda, 2001; Lin et al, 2005; Ludewig and Cook, 2000; McClure, Michener, and Karduna, 2006). Appropriate scapular motion and scapular stability is therefore essential to the prevention and rehabilitation of rotator cuff tears, bursitis and other shoulder pathologies. Scapular stabilization and movement, however, is highly dependent on the activity of the trapezius and serratus anterior muscles (Cools et al, 2003, 2007; Mottram, 1997). Although all three parts of the trapezius (the upper, middle and lower) and the serratus anterior have a role in the stabilization of the scapula, the lower trapezius (LT) has been more consistently associated with shoulder pathologies (Cools et al, 2002, 2003, 2007; Lin, Wu, Wang, and Chen, 2005; Ludewig and Cook, 2000). The LT activity has been found to be decreased in patients with frozen shoulder syndromes and in patients with impingement and has delayed activation in patients with shoulder instability
Address correspondence to Nancy R. Talbott, PhD, MS, PT, Department of Rehabilitation Sciences, College of Allied Health Sciences, University of Cincinnati, Cincinnati, OH, USA. E-mail: [email protected]
History Received 6 December 2012 Revised 26 November 2013 Accepted 30 November 2013 Published online 10 January 2014
(Cools et al, 2003; Lin, Wu, Wang, and Chen, 2005; Matias and Pascoal, 2006). Multiple exercise programs have been proposed to specifically enhance and normalize LT activation and to correct abnormal scapular mechanics (Cools et al, 2007; Kibler and Sciascia, 2010; Kibler et al, 2008; Ludewig and Braman, 2011; McClure, Greenberg, and Kareha, 2012). Clinical tools, therefore, are needed to assess the function and activation of the LT. Currently, clinical assessment of scapular function relies on observation of static and dynamic scapular position, manual muscle tests (MMT) of the scapular muscles and a selection of special tests (Magee, 2008; McClure, Greenberg, and Kareha, 2012; Wright, 2013). Use of these techniques may have limited value in a patient examination due to low reliability, poor validity and weak association with clinical symptoms (Hickey, Milosavljevic, Bell, and Milburn, 2007; McClure, Greenberg, and Kareha, 2012; Michener, Boardman, Pidcoe, and Frith, 2005; Odom, Taylor, Hurd, and Denegar, 2001; Shadmehr, Bagheri, Ansari, and Sarafraz, 2010; Wright, 2013). Although electromyography (EMG) and three dimensional motion analysis have also been employed to assess scapular motion and muscle activity in a research context (Lin et al, 2005; Ludewig and Cook, 2000; Matias and Pascoal, 2006; McClure, Michener, and Karduna, 2006; Mell et al, 2005), these methods of examination of the scapula can be expensive, time consuming to use and traditionally require extensive post testing analysis (Ebaugh, McClure, and Karduna, 2005; Ludewig, Cook, and Nawoczenski, 1996). A viable adjunct to current scapular muscle assessment is the use of ultrasound imaging (USI). USI is portable, requires less time for testing and needs little processing of collected data
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DOI: 10.3109/09593985.2013.876693
(Bembem, 2002; O’Sullivan et al, 2009; Whittaker et al, 2007). At the same time, individual muscles can be imaged permitting visualization of muscle boundaries, architecture and changes with active movement. Reliability and validity of USI has been established for multiple muscles (Hides et al, 2007; Kiesel et al, 2007; Nestorova et al, 2012; Raney, Teyhen, and Childs, 2007; Riddiford-Harland, Steel, and Baur, 2007; Wallwork, Hides, and Stanton, 2007; Yim and Corrado, 2012) and USI has been used for visual feedback during exercises (Ariail, Sears, and Hampton, 2008; Henry and Westervelt, 2005; Hides et al, 2006; Lee et al, 2011). In the scapular area, USI of the LT muscle has been shown to be valid and reliable at rest when the arm is at the side (O’Sullivan, Bentman, Bennett, and Stokes, 2007; O’Sullivan et al, 2009). However, reliability of LT USI has not been explored in a contracted state, a condition important to the clinical assessment and rehabilitation of that muscle. As the LT function is one of mobility and stability, reliable procedures that isolate its activity or changes during active contraction with and without resistance are needed. The purpose of this study was to develop a clinically applicable method to reliably measure LT thickness both at rest and during states of contraction using USI. Specifically, the aims of the study were to: (1) describe a method to measure LT thickness using USI; (2) determine within session intra-rater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight; (3) determine between session intra-rater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight; and (4) determine within session interrater reliability of USI thickness measurements at rest, during active contraction and during active contraction with a weight.
Methods To determine the intra-rater and inter-rater reliability of using USI to measure LT muscle thickness at two different image sites (the transverse process and the lamina), a single group repeated measures design was employed. The study received institutional review board approval and all study participants signed a written informed consent prior to their participation in the study. Participants
USI thickness measurements of the lower trapezius
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corresponding level (Neumann, 2002). The level of the spinous process was further confirmed by palpating the spinous processes in the lower cervical spine, extending the neck to identify the less palpable spinous process of the sixth cervical vertebrae, palpating the seventh cervical spinous process just inferior and counting down to the seventh thoracic process. Although the LT could be measured at various sites, this location was selected because it was easily located and was similar to the levels in which USI measurements of the LT have been reported as being valid (O’Sullivan et al, 2009). Following the location of the landmarks, the subject was placed prone on a treatment table with the shoulder in 145 of abduction. This shoulder position was confirmed through the use of a goniometer and was chosen because it is the position commonly suggested for MMT of the LT (Hislop and Montgomery, 2007). The arm was supported on an adjoining electronically adjustable high low table. The midline of the transducer was placed horizontally over the marked seventh thoracic vertebrae resulting in an image of both the right and the left LT muscle at that vertebral level. The probe was then moved laterally toward the dominant side until the examiner could visualize the dominant side LT, the concavity of the dominant side lamina and the convexity of the dominant side transverse process (Figure 1). After a clear image of the LT, transverse process and lamina could be seen on the ultrasound screen, the subject was instructed to rest the arm on the table in the test position (Figure 2A). The image was frozen and stored for off line measurement. No synchronization with inspiration was attempted as previous researchers reported no changes in LT thickness during respiration (O’Sullivan, Bentman, Bennett, and Stokes, 2007). Following capture of the rest image, the subject was instructed to maintain the test position while the high low table under the test arm was lowered until the table was no longer in contact with the test side arm (Figure 2B). The examiner monitored the on screen image and ensured that the lamina, transverse process and LT borders were visible before the image was frozen and stored. The table was then raised until the test side arm was once again supported in the appropriate test position. After 30 s of rest, a two pound weight was placed in the subject’s hand and the subject instructed to maintain the position while the high low table was
Participants were recruited from a population of convenience at a large urban University. To be enrolled in the study, individuals were required to meet the following criteria: (1) no trauma, pain or surgery involving the neck, shoulder or arm; (2) no history of neuromuscular or musculoskeletal disorders; (3) full active pain free range of motion of the cervical spine and shoulders; and (4) between the ages of 18 and 65 years. Individuals were excluded if they reported that they were pregnant, had any metal implants, or were involved in specific activities aimed at increasing the strength of the scapular muscles. If all criteria requirements were satisfied, height and weight were measured. Individuals with a body mass index of greater than 30 kg/m2 were excluded due to the potential difficulty obtaining clear ultrasound images. Procedures A Biosound MyLab 25 Gold USI system (Esaote, Indianapolis, IN) with a 40 mm linear transducer was used in the B-mode at a frequency of 18MHz. Calibration was performed using a phantom prior to the initiation of the study. Before initiation of the USI, the subject was seated with the thoracic spine exposed. The spinous process of the seventh thoracic vertebrae was identified by palpating the inferior angle of the respective scapula and marking the spinous process at the
Figure 1. Measurement of left lower trapezius thickness. (A) Measurement at the transverse process site. At a location perpendicular to the transverse process (arrow on the left), measurement of lower trapezius thickness was taken between the hyperechoic borders of the muscle (dotted line on the left). (B) Measurement at the lamina site. At a location perpendicular to the lamina, measurement of the lower trapezius thickness was taken between the hyperechoic borders of the muscle (dotted line on the right).
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Physiother Theory Pract, 2014; 30(5): 360–366
Microsoft Excel (Microsoft Inc., Redmond, WA) spreadsheet for later analyses.
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Data analysis
Figure 2. Test positions for USI of the lower trapezius.
again lowered until the table was no longer in contact with test side arm (Figure 2C). The landmarks were monitored to keep the same area of the LT on the screen. The image was frozen and then stored. The ultrasound probe was removed, the subject was given a 30-s rest and the process was repeated two additional times. After a 30-s rest, the imaging was repeated three times on the nondominant arm. To determine intra-rater reliability between sessions, ten of the subjects returned within seven days and the same testing procedure was repeated by the original examiner. On their return, these 10 subjects also had the same testing procedure repeated by a second examiner. The two examiners performing the USI procedures were physical therapists who had been performing USI of the scapular muscles for 4 years. Both had at least 50 h of hands on training in musculoskeletal ultrasound including over 30 h with a registered sonographer. Measurements All linear measurements of LT muscle thickness on the captured ultrasound images were completed off-line utilizing ImageJ (Abramoff, Magalhaes, and Ram, 2004). Measurements were completed by the single investigator who participated in both days of imaging. ImageJ was selected because it directly records the numerical value of a measurement onto a spreadsheet that can be minimized on a computer screen. The measurer, therefore, cannot see previously recorded values while measuring a subsequent image, a procedure which mitigates measurement bias. Using ImageJ, the actual thickness measurements of the LT in this study were taken at two locations: (1) the lamina; and (2) transverse process. The LT thickness measurement taken at the lamina was completed by first locating the lamina deep to the LT. At the deepest aspect of the concavity of the lamina, a vertical line was extended from the concavity through the LT. The portion of this line that was located between the inside margin of the inferior echogenic fascial line of the LT and the inside border of the superior echogenic facial line of the LT was measured (Figure 1). The second measurement taken using the transverse process as a landmark was completed in a similar manner. A perpendicular line was drawn from the superior part of the convexity on the transverse process and the portion of that line located between the inside margins of the LT was measured (Figure 1). The linear measurements were transferred from the ImageJ software to a
Data was transferred from a Microsoft Excel spreadsheet to IBM SPSS Statistics 20 (IBM, Armonk, NY) for statistical analysis. Descriptive statistics (mean ± SD) were completed for age, height (cm), weight (kg) and body mass index (kg/m2). A one-way analysis of variance (ANOVA) was used to analyze any variability in LT thickness measurements associated with hand dominance and with body mass index. Additional ANOVAs were constructed to analyze variability in LT thickness measurements associated with: (1) repetition; (2) day of testing; and (3) examiner. Intra-rater reliability and inter-rater reliability were assessed using intra-class correlation coefficients (ICCs) with ICC3,3 the model for intra-examiner reliability within a day; ICC3,2 the model for intra-examiner reliability between days; and ICC2,2 the model for inter-examiner reliability on the same day. Coefficients above 0.75 were interpreted as indicating good agreement, coefficients between 0.50 and 0.75 reflected moderate agreement, and coefficients below 0.50 represented poor agreement (Portney and Watkins, 2000). The standard error of measurement pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi(SEM) was calculated using the formula SEM ¼ S 1 ICC where S ¼ the pooled standard deviation and ICC is the reliability coefficient. Confidence intervals for each of the ICC values were calculated. Reliability was further evaluated by using Bland and Altman plots. These plots offer an easy to interpret visual representation of the degree of agreement, allow for prompt identification of outliers and potential bias and have been promoted as the preferred statistical methodology for studies of reliability (Rankin and Stokes, 1998). All analyses were completed separately for LT thickness measurements taken at the lamina site and measurements taken at the transverse process site.
Results Twenty subjects participated in the study. Demographic information can be found in Table 1. Variations in LT thickness measurements were not found to be significantly associated with body mass index (p40.05), eliminating the need for thickness measurements to be adjusted for height and weight. In addition, LT thickness measurements were not significantly associated with arm dominance (p40.05) supporting the pooling of LT thickness measurements for the dominant and nondominant arm in all subsequent analyses. LT measurements taken on day 1 by examiner 1 are reported in Table 2. Mean LT thickness measurements when measured at the lamina and at the transverse process site were not significantly different between repetitions (p40.05). Reliability was good within a session with all ICCs greater than 0.95 (Table 2). LT measurements taken on day 1 and day 2 by examiner 1 are listed in Table 3. Mean LT thickness measurements when measured at the lamina and at the transverse process site were not significantly different between days (p40.05). Reliability between days was good with all ICCs greater than 0.93 (Table 3). LT measurements taken on day 2 by examiner 1 and LT thickness measurements taken on day 2 by examiner 2 are presented in Table 4. Mean measurements taken in the rest position by Examiner 1 were less than 0.2 mm different from those of Examiner 2 and were not significantly different (p40.05). Reliability between examiners was high with ICCs greater than 0.93 (Table 4). Figures 3 and 4 depict sample Bland–Altman plots examining the agreement between days and between examiners.
USI thickness measurements of the lower trapezius
DOI: 10.3109/09593985.2013.876693
The differences between the measurements taken by examiner 1 on day and on day 2 are shown in Figure 3. The mean differences between LT thickness measured on day 1 and those measured on day 2 were close to zero (50.10 mm). All differences fell within
two standard deviations of the mean difference illustrating the consistency of the measurements between days. The differences between the measurements taken by examiner 1 and 2 are shown in Figure 4. The mean differences between LT thickness measured by examiner 1 and those measured by examiner 2 were50.02 mm. All differences between measurements fell within two standard deviations (0.152 mm) of the mean difference with the exception of one outlier which was within 0.16 mm of the mean difference.
Table 1. Participant characteristics.
Characteristic Age (y) Height (cm) Weight (kg) Body mass index (kg/m2)
All subjects Mean (SD)
Men (n ¼ 7) Mean (SD)
25 172.7 79.2 26.4
26 182.0 87.3 26.3
(2) (10.2) (17.6) (4.7)
(3) (6.3) (8.7) (2.1)
Women (n ¼ 13) Mean (SD) 24 167.8 74.8 26.4
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(1) (8.2) (19.9) (5.7)
Discussion The results of this study demonstrate that LT thickness can be reliably measured at rest, during an active contraction and during an active contraction with a weight. When the traditional MMT
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Table 2. Intra-rater reliability within a session: Lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Repetition 1 Mean (SD) (mm)
Repetition 2 Mean (SD) (mm)
Repetition 3 Mean (SD) (mm)
Pooled Mean (SD) (mm)
ICC3,3 (95% CI)
SEM (mm)
3.4 (1.0) 3.6 (1.3)
3.3 (1.1) 3.7 (1.2)
3.5 (1.1) 3.6 (1.2)
3.4 (1.1) 3.6 (1.2)
0.951 (0.917–0.972) 0.961 (0.935–0.978)
0.2 0.2
5.3 (2.0) 5.6 (2.4)
5.2 (2.0) 5.4 (2.4)
5.0 (2.0) 5.1 (2.4)
5.2 (1.9) 5.4 (2.3)
0.984 (0.973–0.991) 0.982 (0.969–0.990)
0.2 0.3
6.0 (2.2) 6.2 (2.6)
5.8 (2.2) 6.0 (2.7)
5.7 (2.3) 5.7 (2.8)
5.8 (2.2) 6.0 (2.6)
0.978 (0.963–0.988) 0.986 (0.976–0.992)
0.3 0.3
The mean and SD for each repetition and the pooled means (the mean for all three repetitions) are listed. ICCs and SEM values for intra-tester reliability on Day 1 are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
Table 3. Intra-rater reliability between sessions: lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Day 1 Mean (SD) (mm)
Day 2 Mean (SD) (mm)
Pooled Mean (SD) (mm)
ICC3,2 (95% CI)
SEM (mm)
3.8 (1.3) 3.8 (1.6)
3.1 (1.2) 3.4 (1.4)
3.5 (1.3) 3.6 (1.5)
0.956 (0.893–0.987) 0.935 (0.844–0.981)
0.3 0.4
4.9 (1.6) 4.9 (1.9)
4.4 (1.3) 4.8 (1.9)
4.7 (1.5) 4.8 (1.9)
0.961 (0.907–0.989) 0.944 (0.865–0.984)
0.3 0.4
5.6 (1.8) 5.3 (2.2)
5.1 (1.6) 5.3 (2.1)
5.3 (1.6) 5.3 (2.1)
0.956 (0.895–0.987) 0.962 (0.909–0.989)
0.3 0.4
The mean and SD for the three scans taken on Day 1, the means and SD for the three scans taken on Day 2 and the pooled means (the mean for all scans on both days) are listed. ICCs and SEM values for intra-tester reliability between days are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
Table 4. Inter-rater reliability within a session: lower trapezius thickness at lamina and transverse process measurement sites.
Condition site Rest Lamina Transverse process Contraction Lamina Transverse process Contraction with weight Lamina Transverse process
Examiner 1 Mean (SD) (mm)
Examiner 2 Mean (SD) (mm)
Pooled Mean (SD) (mm)
3.1 (1.2) 3.4 (1.4)
3.3 (1.1) 3.4 (1.4)
3.2 (1.1) 3.4 (1.4)
0.962 (0.908–0.989) 0.957 (0.896–0.988)
0.2 0.3
4.4 (1.3) 4.8 (1.1)
4.7 (1.7) 4.8 (2.0)
4.5 (1.5) 4.8 (1.9)
0.934 (0.840–.981) 0.966 (0.917–0.990)
0.4 0.4
5.1 (1.6) 5.3 (2.1)
5.3 (1.9) 5.3 (2.3)
5.2 (1.7) 5.3 (2.1)
0.945 (0.868–0.984) 0.973 (0.934–0.992)
0.4 0.4
ICC2,
2
(95% CI)
SEM (mm)
The mean and SD for the three scans taken by examiner 1, the means and SD for the three scans taken by examiner 2 and the pooled means (the mean for all scans by both examiners) are listed. ICCs and SEM values for inter-tester reliability are provided. mm, millimeters; SD, standard deviation; ICC, intra-class correlation coefficient; CI, confidence interval; SEM, standard error of the measurement.
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Figure 3. Bland and Altman plots showing differences in lower trapezius thickness measurements when measured at the lamina site on different days by one examiner. (A) Differences when measured at rest. (B) Differences when measured while holding a weight.
Figure 4. Bland and Altman plots showing differences in lower trapezius thickness measurements when measured at the lamina site on the same day by different examiners. (A) Differences when measured at rest. (B) Differences when measured while holding a weight.
test position was used and when measurements on the LT ultrasound image were taken at the site of the lamina and the transverse process, values were consistent between days and between examiners.
The findings in this study that LT thickness measurements are reliable at rest are consistent with a study by O’Sullivan, Bentman, Bennett, and Stokes (2007) in which LT ICC values were reported as 0.90–0.96 for intra-rater reliability within a
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DOI: 10.3109/09593985.2013.876693
session; 0.89–0.91 for intra-rater reliability between sessions; and 0.88 for inter-rater reliability within a session, respectively. Although both the current and the previous study demonstrated good reliability, the ICC values for inter-rater reliability in the current study were slightly higher than the previous study. In addition, mean values of the two examiners varied by 0.2 mm or less in the current study compared to the maximum difference of 1.0 mm between two of the examiners in the previous study. Although the clinical implications of differences in sizes of LT muscles have not been established, minimizing error between measurers would be a factor in a research or clinical setting in which interventions aimed at increasing LT thickness are employed. As LT thickness is relatively small (ranging between 3.1 mm to 6.2 mm at rest in the current study), larger inconsistencies between measurers reflects a much higher percentage of the total LT muscle thickness. The increased consistency between measurers that was found in the current study may be attributable to a measurement process which differed from the 2007 study by O’Sullivan, Bentman, Bennett, and Stokes. The measurement process described in the O’Sullivan, Bentman, Bennett, and Stokes (2007) study involved identifying the lateral border of the spinous process, measuring from that landmark a standard distance and then measuring LT thickness at that site. In the current study, measurements were taken perpendicular to the lamina and perpendicular to the transverse process eliminating the need to measure from the spinous process to the measurement site. The hyperechogenicity of the lamina and the transverse process were easily visible when images were being taken facilitating the consistent placement of the ultrasound transducer by different examiners and by the same examiner on different days. This visual acuity also facilitated the exactness of the site for off line measurement as the hyperechoic lines of the bony landmarks clearly delineated where, within the LT, the thickness measurements were to be taken. In addition, the distance from the spinous process to the measurement site in the current study varied with body size. If the individual was larger, the lamina and transverse process were farther away from the spinous process, while if the individual was smaller, the lamina and transverse process were closer to the spinous process. While this might have had little effect on reliability, the use of the landmarks in the current study may be more adaptable to measuring LT thickness in individuals of varying sizes. To the authors’ knowledge, this is the first study to document LT reliability values during LT active contraction and during LT contraction against resistance with the arm in the MMT position. LT thickness was measured during active contraction with the shoulder in 90 and 120 of abduction in a 2012 study by O’Sullivan et al., however, there was no documentation of the reliability of their LT thickness measurements in the contracted state. The LT measurement process used in the 2012 study has been found, in a previous study (O’Sullivan, Bentman, Bennett, and Stokes, 2007), to be reliable when the arm was at rest and positioned at the side. It is unclear, however, if a method that reliably measures LT thickness at rest translates to equivalent reliability during activation and similar reliability when the arm is placed in different positions. Clearly, the LT must be assessed in a contracted state and a reliable method for that active assessment is needed for the method to add value to the examination. Clinically, the findings of this study that USI can be used reliably to measure LT thickness at rest, during contraction and during contraction with resistance have implications for examining and treating impairments of the shoulder. The current study utilized the common manual muscle testing position for scanning to provide a reliable method of isolating LT muscle changes during at least part of a MMT of the LT. This protocol simulates three of the manual muscle testing grades routinely assigned
USI thickness measurements of the lower trapezius
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during MMT: (1) zero; (2) fair; and (3) good. The rest condition of this protocol involved no palpable contractile activity and would simulate the 0/5 grade, the active hold condition mimics the fair or 3/5 grade as it involves an active hold in the muscle testing position without additional resistance, and the weight condition is comparable to a good or 4/5 grade as moderate resistance is supplied by the small weight. The advantage of using USI during this MMT is to allow the examiner to focus specifically on the behavior of the LT during the test. Previous studies have found that multiple scapular muscles are active during the MMT of the LT including the upper trapezius, middle trapezius, rhomboid, and serratus anterior muscles (Ekstrom, Donatelli, and Soderberg, 2003; Ekstrom, Soderberg, and Donatelli, 2005; Michener, Boardman, Pidcoe, and Frith, 2005). If the LT is weak, MMT results may appear as normal if substitution by other stronger scapular muscles is occurring. USI allows direct visualization of the specific changes the LT muscle undergoes during testing regardless of the activity in surrounding scapular stabilizers. Limitations Limitations of the study include the selection of the study population and the number of subjects involved in between session and inter-rater reliability testing. A healthy younger population participated in the study preventing results from being generalized to individuals with pathology. It is possible that USI of LT thickness in individuals with LT dysfunction may not be as reliable as in asymptomatic individuals, especially if pain or other symptoms limit active control or effort. In addition, the number of subjects returning for a second session of testing was 10. While this number may be small, the confidence intervals for the correlation coefficients were narrow supporting the reliability of the LT measurement values. Future studies, however, should consider a larger population of participants with a variety of LT dysfunctions to further establish the reliability of USI when measuring LT thickness.
Conclusions In summary, the described USI protocol can be used to reliably measure LT thickness in healthy adults at rest, during active contraction and during active contraction when holding a weight. The novel procedure described provides researchers and clinicians with an additional assessment or outcome tool for monitoring changes in LT thickness in a clinical rehabilitation setting. Future studies are needed to expand reliability testing of this method to subjects with upper extremity dysfunction, to correlate LT thickness with clinical symptoms and to determine if patterns of thickness changes with active contraction reflect dysfunction.
Declaration of interest The authors have nothing to disclose regarding this research and declare that they have no competing interests.
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