Clinical Anatomy 26:228–235 (2013)
ORIGINAL COMMUNICATION
Musculotendinous Architecture of Pathological Supraspinatus: A Pilot In Vivo Ultrasonography Study SOO Y. KIM,1* ROBERT R. BLEAKNEY,2 TIM RINDLISBACHER,3 KAJEANDRA RAVICHANDIRAN,4 BENJAMIN W.C. ROSSER,5 AND ERIN BOYNTON6 1
School of Physical Therapy, University of Saskatchewan, Saskatoon, Canada Musculoskeletal Division, Joint Department of Medical Imaging, University Health Network, Mount Sinai Hospital and Women’s College Hospital, University of Toronto, Toronto, Canada 3 Cleveland Clinic Canada and Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada 4 Faculty of Medicine, University of Toronto, Toronto, Canada 5 Department of Anatomy and Cell Biology, University of Saskatchewan, Saskatoon, Canada 6 Graduate Department of Rehabilitation Sciences, University of Toronto, Toronto, Canada 2
Architectural changes associated with tendon tears of the supraspinatus muscle (SP) have not been thoroughly investigated in vivo with the muscle in relaxed and contracted states. The purpose of this study was to quantify the geometric properties within the distinct regions of SP in subjects with fullthickness tendon tears using an ultrasound protocol previously developed in our laboratory, and to compare findings with age/gender matched normal controls. Twelve SP from eight participants (6 male/2 female), mean age 57 6 6.0 years, were investigated. Muscle geometric properties of the anterior region (middle and deep parts) and posterior region (deep part) were measured using image analysis software. Along with whole muscle thickness, fiber bundle length (FBL) and pennation angle (PA) were computed for architecturally distinct regions and/or parts. Pathologic SP was categorized according to the extent of the tear in the tendon (with or without retraction). In the anterior region, mean FBL of the pathologic SP was similar with normal controls; however, mean PA was significantly smaller in pathologic SP with retraction compared with normal controls, in the contracted state (P < 0.05). Mean FBL in the posterior region in both relaxed and contracted states was significantly shorter in the pathologic SP with retraction compared with normal controls (P < 0.05). Findings suggest FBL changes associated with tendon pathology vary between the distinct regions, and PA changes are related to whether there is retraction of the tendon. The ultrasound protocol may provide important information on architectural changes that may assist in decision making and surgical planning. Clin. Anat. 26:228–235, 2013. V 2012 Wiley Periodicals, Inc. C
Key words: rotator cuff; muscle; tendon; fiber bundles; pennation angle; sonography; imaging; ultrasound
INTRODUCTION Tears of the supraspinatus muscle are commonly seen in the clinic (Codman, 1990). This painful injury can inhibit and compromise normal shoulder function. To optimally treat supraspinatus tendon tears C 2012 V
Wiley Periodicals, Inc.
*Correspondence to: Soo Kim, School of Physical Therapy, University of Saskatchewan, 1121 College Drive, Saskatoon, Saskatchewan, Canada S7N 0W3. E-mail:
[email protected] Received 30 March 2011; Revised 7 February 2012; Accepted 14 February 2012 Published online 19 March 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ca.22065
Investigation of Pathological Supraspinatus an accurate understanding of its musculotendinous architecture and sequence of change in relation to tendon pathology is needed. We have previously shown the architecture of supraspinatus is complex having architecturally distinct regions: anterior and posterior, each of which is further subdivided into superficial, middle and deep parts (Kim et al., 2007). Biomechanical testing has demonstrated a distinct functional difference between the anterior and posterior regions of the supraspinatus muscle with respect to humeral rotation (Gates et al., 2010). Ultrasonography (US) can be used to measure changes in architectural parameters of human skeletal muscles in vivo. Parameters such as muscle thickness (MT), fiber bundle length (FBL), and pennation angle (PA) can be quantified in healthy and pathological muscle (Narici et al., 1996; Chow et al., 2000; Bleakney et al., 2002; de Boer et al., 2008). To date, in vivo assessment of the morphological changes of supraspinatus associated with rotator cuff tears has focused on muscle atrophy and fat infiltration (Shimizu et al., 2002; Strobel et al., 2005; Khoury et al., 2008). These parameters have been found to be important prognostic factors for the anatomical and functional results following surgical repair of the rotator cuff (Goutallier et al., 2003). The musculotendinous architecture is frequently overlooked despite important insights that can be gained on the functional changes associated with tendon tear (Ward et al., 2006; Be ´nard et al., 2009). Large full-thickness supraspinatus tendon tears can cause the musculotendinous unit to retract and FBLs, muscle volume and cross sectional area can be altered (Meyer et al., 2004; Melis et al., 2010). These architectural changes can limit muscle function which is directly influenced by musculotendinous architecture (Lieber et al., 2000). Cadaveric studies of supraspinatus with full-thickness tendon tears reported FBL changes with full-thickness tendon tears but were not related to architecturally distinct regions and PA was not measured (Itoi et al., 1995, Tomioka et al., 2009). Data of FBL and PA of the torn supraspinatus could enhance clinical decision-making and guide rehabilitative treatments (Ward et al., 2006, 2010). Even so, in vivo US quantification of the muscle geometric properties of the distinct regions of the supraspinatus muscle in participants with tendon pathology has not yet been thoroughly investigated. A valid and reliable US protocol to quantify the dynamic musculotendinous architecture of supraspinatus was developed in our lab and reported in one of our recent publications (Kim et al., 2010). The US protocol allowed for in vivo images of fiber bundles within anterior and posterior regions to be captured and quantified in vivo during relaxed and contracted states and with different positions of the glenohumeral joint in subjects with healthy rotator cuffs. The purpose of this study is to use this US protocol to quantify architectural parameters within the distinct regions of supraspinatus in subjects with a full-thickness tendon tear, and to compare findings with age and gender matched normal controls. We hypothesize this US protocol can be reliably performed
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Fig. 1. Ultrasound probe positioning. Right shoulder in contracted position. Acr, acromion; (. . .. . ...) white dotted line indicating approximate division between anterior and posterior regions of supraspinatus; (----------) black dashed line demonstrating the position of the intramuscular tendon extending medially within the anterior region. A: Starting position of ultrasound probe to image fiber bundles within the anterior region. B: Position of ultrasound probe to image fiber bundles of the posterior region. Inset demonstrating probe in position A.
on patients with a pathologic supraspinatus and that significant architectural differences will be found between pathologic and normal control supraspinatus.
MATERIALS AND METHODS Participants The supraspinatus muscles of eight study participants (6 male/2 female) each with at least one suspected full-thickness tendon tear of the supraspinatus tendon were scanned bilaterally. To be included in the study, a full-thickness tendon tear had to be confirmed with US imaging. Those with previous shoulder surgery, neuromuscular disease, acute shoulder pain that prevented active abduction, and reported shoulder symptoms greater than 12 months in duration were excluded. Mean age of eligible subjects was 57 6 6 years (range, 52–69). Participants were categorized into one of three groups: (1) tears with retraction of tendon; (2) tears without retraction; and (3) normal intact tendon. A tear was defined as having retraction when the tear involved the entire extent of the supraspinatus tendon from anterior to posterior. Data of normal controls that were gender and age matched (63 years) were obtained from an existing database. Mean age of normal controls was 55 years (range, 49–66). All participants were recruited from the Cleveland Clinic,
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Fig. 2. Anterior region: Longitudinal ultrasound scans of the left supraspinatus. A single fiber bundle from each scan has been demarcated by a white line (). Left column: Relaxed state. Arm resting by the subjects’ side and the palm of the hand at the side of the chair; (a) normal controls; (c) tear without retraction; (e) tear with retraction of tendon. Right column: Contracted state. Arm abducted to 608 with neutral gle-
nohumeral rotation; (b) normal controls; (d) tear without retraction; (f) tear with retraction of tendon. SK, skin; SC, subcutaneous tissue; TP, trapezius muscle; SF, supraspinous fossa; AS, superficial part of anterior region; AM, middle part of anterior region; AD, deep part of anterior region; llllll, intramuscular tendon; * pennation angle. Note: individual ultrasound scans are of different scaling.
Toronto, Canada. This study was approved by the Mount Sinai Hospital (05-0235-E) and University of Toronto and Saskatchewan (#15513, #11-53), Research Ethics Boards. Each participant gave written informed consent in accordance with standard ethical procedures.
this, the shoulder was positioned adducted and internally rotated behind each subject’s back. Second, the US protocol described by Kim et al. (2010) was performed on each participant. The supraspinatus was scanned in the relaxed state and one contracted state. For the relaxed state, the muscle was scanned with the arm resting by the subjects’ side and the palm of hand at the side of the chair. For the contracted state, the muscle was scanned with the subject holding their arm in 608 of shoulder abduction against gravity with neutral glenohumeral rotation (Fig. 1). A goniometer was used to measure shoulder position. Panoramic longitudinal US images were taken by aligning the probe along the length of supraspinatus and used to capture fiber bundles of the middle and deep parts of the anterior region, and the deep part of the posterior region (Fig. 1). To minimize measurement errors associated with the orientation of the probe, the tilt angle was kept perpendicular to the plane of the fiber bundles being captured (Be ´nard et al., 2009). Sagittal US images were taken by placing the probe perpendicular to the muscle and used to assess the thickness of the muscle. Care was taken not to deform the underlying tissues by using minimum pressure required to
Ultrasound Examination Ultrasound examinations were performed by one musculoskeletal radiologist (R.R.B) with 10 years of experience in shoulder US. An HDI 5000, Advanced Technology Laboratories (Bothell, WA) real-time US scanner with a linear (38 mm) 12 MHz transducer (resolution, 0.3mm) was used. Information was processed with eFilm Merge PACS system (Milwaukee, WI). The US examination was standardized according to previously published techniques (Kim et al., 2010). During the entire testing session, each participant was seated with his/her back supported in a chair with adjustable height. First, the muscles and tendons of the rotator cuff were scanned to verify the presence of a full-thickness tear of the supraspinatus tendon and to document dimensions. For
Investigation of Pathological Supraspinatus
Fig. 3. Posterior region: Longitudinal ultrasound scan of left supraspinatus with tear and retraction. SK, skin; SC, subcutaneous tissue; TP, trapezius muscle; SF, supraspinous fossa; PR, posterior region; Acr, acromion; AS, superficial part of anterior region; AM, middle part of anterior region; AD, deep part of anterior region; llllll, intramuscular tendon; fiber bundle length ().
take a clear image. All data were saved as Tagged Image File Format and transferred to a computer for subsequent analyses.
Quantitative Measurement of Architectural Parameters from US scans All quantitative measurements were made by the principal investigator (S.Y.K.), trained previously by a musculoskeletal radiologist and proficient in quantitative measurement from US images of supraspinatus. Three architectural parameters were computed from US scans: FBL, PA, and MT. Initially, clearly visible fiber bundles within the middle and deep parts of the anterior region and deep part of the posterior region were identified. To ensure the plane of the ultrasound image was parallel to that of the fiber bundles, for quantitative analysis we used only fiber bundles that could be seen for most of their length and at both their medial and lateral attachment sites. Next, using image analysis software developed in our laboratory, the architectural parameters identified were computed. The software was calibrated for each US image to account for rotation and scaling using linear transformation. Fiber bundle lengths were computed as a linear distance between the medial and lateral attachment sites (Fig. 2), as outlined by Kim et al. (2010). Pennation angle was defined as the angle between the fiber bundle and its attachment to the intramuscular tendon (Fig. 2). Pennation angle of the posterior region could not be measured due to shadowing of the acromion (Fig. 3). Muscle thickness was measured at the midpoint of the scannable muscle belly, between the medial border of the acromion and the most medial point of attachment of the muscle belly
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Fig. 4. Muscle thickness measurement. Sagittal ultrasound scan of right supraspinatus at the midpoint of muscle belly. MT, muscle thickness; SC, subcutaneous tissue; TP trapezius muscle; SF, supraspinous fossa.
in the suprascapular fossa. Muscle thickness was computed as the distance between the superficial surface of the muscle belly and the supraspinous fossa (Fig. 4). To determine intrarater reliability of measurements, FBL and PA measurements on all scans of five participants were repeated eight weeks later by the principal investigator. To test interrater reliability of this quantitative measurement technique a second randomly chosen blinded investigator independently measured FBL and PA of five study participants. The blinded rater had completed four 2-hr training sessions of US measurements to allow for sufficient background and familiarity.
Data Analysis FBL, PA, and MT data were imported into SPSS (Version 15.0, SPSS, Chicago, USA). Each architectural parameter was characterized with descriptive statistics (mean, standard deviation, and range) for the relaxed and contracted states. Paired-samples ttests were carried out to compare means between relaxed and contracted states and One-way Between-groups ANOVA followed by Tukey’s Post Hoc Test for comparison between the pathologic subject groups and normal controls. Independent-samples t-tests were used to compare middle and deep parts. Reliability of measurement was tested by Paired-samples t-tests and the Spearman Rank Order Correlations were calculated. Statistical significance was set at P < 0.05.
RESULTS Ultrasonograms of 12 supraspinatus muscles from eight subjects were found to have full-thickness tears, satisfying the main criterion for inclusion in this study. Within the final study sample, the supraspinatus tendon was retracted in four cases with infraspinatus also partially torn in one case. The
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TABLE 1. Anterior and Posterior Regions of Supraspinatus: Architectural Parametersa FBL (cm) n Anterior region Tear and retraction
4
Tear and no retraction
8
Normal controls
12
Posterior region Tear and retraction
4
Tear and no retraction
8
Normal controls
10
PA (degrees)
Relaxed
Contracted
Relaxed
Contracted
5.321a 6 0.83 (4.03–6.70) 5.521a 6 1.18 (4.34–7.86) 5.591a 6 1.00 (3.88–7.21)
4.032a 6 0.55 (3.14–4.76) 4.492a 6 1.02 (3.20–6.90) 4.182a 6 0.54 (2.75–4.93)
10.381a 6 3.45 (6.57–15.85) 12.431a 6 2.56 (8.49–18.66) 13.241a 6 3.34 (8.02–22.13)
14.552a 6 3.26 (9.24–19.79) 16.642ab 6 3.68 (10.34–23.32) 19.032b 6 2.84 (14.10–24.23)
2.721a 6 0.52 (2.20–3.24) 2.871ab 6 0.62 (1.98–3.79) 3.641b 6 0.45 (3.04–4.42)
2.472a 6 0.41 (2.12–3.05) 2.542a 6 0.21 (2.16–2.81) 3.441b 6 0.46 (2.89–4.21)
–
–
–
–
–
–
a Measurements for the anterior region were derived from two measurements: one from the middle part and one from the deep part. Values in the parentheses indicate ranges. The superscript numbers are used to indicate the presence or absence of statistical significance between the relaxed and contracted state and superscript letters to indicate the significance between the pathological groups and normal controls (P < 0.05). 6 standard deviation.
TABLE 2. Anterior Region of Supraspinatus: Architectural Parameters of the Middle and Deep Partsa FBL (cm)
Relaxed Middle Deep Contracted Middle Deep
PA (degrees)
Tear and retraction
Tear and no retraction
Normal controls
Tear and retraction
Tear and no retraction
Normal controls
5.791a 6 0.68 (5.09–6.70) 4.701a 6 0.60 (4.03–5.20)
5.611a 6 1.30 (4.34–7.56) 5.401a 6 1.13 (4.55–7.86)
5.521a 6 0.91 (3.88–6.72) 5.651a 6 1.14 (4.07–7.21)
8.481a 6 1.46 (6.57–9.79) 12.911a 6 3.96 (8.41–15.85)
11.871b 6 2.13 (8.49–15.19) 13.001a 6 2.81 (10.04–18.66)
12.071b 6 2.13 (8.75–15.51) 14.601a 6 4.10 (8.02–22.13)
3.971a 6 0.31 (3.59–4.36) 4.111a 6 0.86 (3.14–4.76)
4.291a 6 0.63 (3.20–5.23) 4.691a 6 1.32 (3.40–6.90)
4.021a 6 0.60 (2.75–4.93) 4.341a 6 0.43 (3.30–4.82)
12.731a 6 2.63 (9.24–15.44) 16.981a 6 2.45 (15.27–19.79)
15.451ab 6 3.50 (10.34–20.85) 17.831a 6 3.68 (12.37–23.32)
17.951b 6 2.07 (14.10–20.09) 20.221a 6 3.18 (15.85–24.23)
a Values in the parentheses indicate ranges. The superscript numbers are used to indicate the presence or absence of statistical significance between the middle and deep parts of the anterior region and superscript letters to indicate the significance between the pathological groups and normal controls (P < 0.05). 6 standard deviation.
mean length of retraction measured from the greater tuberosity for these four participants was 2.9 cm (range, 2.5–3.0 cm). The tendon tear in participants without retraction had a mean area of 2.78 cm2 ranging from 0.35–8.4 cm2. The intramuscular portion of the anterior tendon was observed extending medially from the acromion in all of the pathologic muscles.
Reliability Intrarater measurements of FBL (r ¼ 0.87) and PA (r ¼ 0.84) were strongly correlated with no significant difference between measurements (P < 0.001). Inter-rater reliability of FBL and PA measurements were also strongly correlated (FBL: r ¼ 0.87; PA: r ¼ 0.89), between the two independent raters (P < 0.001) and not significantly different (P < 0.001).
Architecture of Supraspinatus Anterior region. Fiber bundles of the middle and deep parts of the anterior region could be identified in all pathologic muscles examined extending from the supraspinatus fossa to the deep surface of the intramuscular tendon. Fiber bundles within the superficial part of the anterior region, a very thin layer of the muscle, could not be seen as single fiber bundles. US scans of the relaxed and contracted states for both the pathologic participants and normal controls are presented in Figure 2 and mean FBL and PA in Tables 1 and 2. Mean FBL did not vary significantly between the pathologic participants and normal controls. In the contracted state, mean FBL was significantly shorter compared with the relaxed state in the pathologic participants and normal controls (P < 0.05). Among the three study groups, mean FBL did not vary significantly in the middle and deep parts of the
Investigation of Pathological Supraspinatus
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TABLE 3. Mean Muscle Thicknessa MT (mm) n Tear and retraction Tear and no retraction Normal controls a
4 8 12
Relaxed 1ab
21.6 6 1.90 (19.1–23.4) 22.81a 6 4.13 (15.70–29.5) 18.41b 6 3.26 (13.0–22.3)
Contracted 1a
23.7 6 2.52 (21.0–26.2) 24.61a 6 2.34 (21.0–28.2) 21.32a 6 3.44 (15.0–25.0)
Values and analyses expressed as in Table 1.
anterior region. For both relaxed and contracted states, mean FBL between middle and deep parts of the anterior region did not differ significantly in any of the groups (Table 2). In the pathologic participants, mean PA was smaller compared with normal controls. The difference was significant between the normal controls and patients with tears with retraction in the contracted state (P < 0.05). In the contracted state, mean PA was significantly larger compared with the relaxed state (P < 0.05). Within the anterior region, mean PA of the middle part was significantly smaller in patients with tears with retraction compared with normal controls and to patients with tears and no retraction in the relaxed state (P < 0.05). In the contracted state, mean PA of the middle part was also significantly smaller in participants with tears with retraction compared with normal controls but not between subjects with tears with no retraction. Mean PA of the middle part did not vary significantly from the deep part in any of the three study groups. Posterior region. Fiber bundles of the deep part of posterior region could be visualized in all of the pathological muscles. In two normal controls, fiber bundles of the deep part could not be delineated. In all specimens, the lateral attachment of fiber bundles was obscured by the acromion and thus PA could not be measured. Mean FBL of the posterior region are presented in Table 1. In participants with a torn and retracted tendon, mean FBL was significantly shorter (P < 0.05) compared with normal controls in both relaxed and contracted states. Muscle thickness. Mean MT is presented in Table 3. The MT of supraspinatus increased significantly from the relaxed to contracted state in normal controls but not in the pathologic participants (P < 0.05). In the relaxed state, mean MT of patients with tears and no retraction was significantly larger compared to normal controls (P > 0.05).
DISCUSSION This novel study piloted in vivo US to quantify musculotendinous architectural changes associated with tendon tears of the supraspinatus muscle. The principal findings of this study are (1) in vivo geometric measurements of the pathologic supraspinatus muscle with real-time US is reliable and feasible and (2) changes in supraspinatus muscle geometry associated with full-thickness rotator cuff tendon tear impact the regions of the muscle differently. Our findings confirm and contrast existing literature
and provide interesting directions for further study and for clinical practice. The real-time US protocol we developed previously (Kim et al., 2010) can be reliably performed on patients with a full-thickness supraspinatus tendon tear and whose initial onset of shoulder pain and/or dysfunction are less than 12 months. The correlation coefficients for intra- and inter-rater reliability found in this study are consistent with the values for normal supraspinatus presented in our previous article (Kim et al., 2010), adding credence to the reliability of the protocol. Although cadaveric studies have found fiber bundles of supraspinatus to be shorter in length in specimens with a full-thickness tendon tear, this could not be verified statistically for both the anterior and posterior regions of the muscle in this study (Itoi et al., 1995, Tomioka et al., 2009). The results in our study demonstrate FBL changes vary between the distinct regions of the muscle. Mean FBL of the posterior region, but not the anterior region, was significantly shorter in cuff tear groups compared with the normal. Since the supraspinatus has the shortest muscle fibers among the rotator cuff muscles, it is highly sensitive to length changes (Ward et al., 2006). Therefore, a change of fiber bundle length in the posterior region in patients with full-thickness tendon tears will impact the contraction velocity and excursion, ultimately compromising its force generating capacity (Ward et al., 2010). Fiber bundle length changes in the posterior region may also be related to the extent of the tendon tear. A trend toward shorter fiber bundles in the relaxed state in participants with larger tears can be seen in this study, a finding warranting further investigation with a larger number of participants. To our knowledge, pennation angle changes of the torn supraspinatus in humans have not been reported previously. In this study, pennation angles were smaller in participants with a tear compared to normal controls, and the difference was significant in the contracted state between those with a tear and retraction and normal controls. A decrease in muscle fiber diameter associated with atrophy may explain this decrease in pennation angle (Huijing, 1998). Studies of the infraspinatus muscle in sheep have shown PA is significantly larger in a torn and retraced muscle (Meyer et al., 2004, Gerber et al., 2009). There are several reasons that may account for differences between our findings and those from animal studies. First, the muscle architecture of supraspinatus and infraspinatus are quite different and likely to respond to tendon tears differently. Second, the
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studies by Meyer et al. (2004) and Gerber et al. (2009) examined retracted tears much more chronic in nature than experienced by the participants in our study. The mean symptomatic period reported by our participants was 24 weeks whereas in the study by Meyer et al. (2004), the infraspinatus tendon was released for 35 weeks and architectural measurements made on the 75th week. Our data suggests there is good potential for functional recovery of the anterior region following tendon repair of a full-thickness tendon tear, within the first year of onset since a decrease in PA with very little changes in FBL will likely not cause large changes to the force generating capacity of the anterior region (Ravichandiran et al., 2009). Further investigation of PA changes within the distinct parts of the anterior region revealed mean PA was significantly smaller in the middle part between subjects with tears with retraction and controls, but not in the deep. This suggests the middle part undergoes greater architectural change compared with the deep part when there is a tear with retraction. Muscle atrophy and a net loss of muscle volume are common changes found with chronic rotator cuff tendon tears (Thomazeau et al., 1997; Hata et al., 2005). Although muscle volume was not measured directly, muscle thickness was measured on sagittal scans. A significant increase was found in participants with tendon tears and no retraction compared with normal controls in the relaxed state, indicating larger cross sectional area. This change may be reflective of medial excursion of the torn tendon and/ or muscle recoil. These findings also suggest the supraspinatus muscle does not undergo muscle atrophy when the tear is 12 months or less in age. Further study is needed to better define timelines when significant changes do occur.
CONCLUSIONS The musculotendinous architecture of the supraspinatus is complex with fiber bundles oriented in different planes attaching onto distinct parts of the tendon (Vahlensieck et al., 1994; Roh et al., 2000; Volk et al., 2001; Kim et al., 2007). With a thorough understanding of its architecture, real-time US can reliably capture and quantify the dynamic geometric properties within the distinct regions of the supraspinatus muscle not only in healthy individuals but also those with tendon pathology. Delineating fiber bundles in the distinct regions of the supraspinatus muscle and measuring muscle geometric properties in relaxed and contracted states using other imaging modalities such as magnetic resonance imaging is technically challenging and more costly. The results of this pilot study serve as a platform to pursue a larger clinical study with an increased number of participants. They also compel future studies of muscle architecture in other positions of abduction, with different types of contraction and at various stages of tendon pathology. Such subsequent studies will further our understanding about the functions of the distinct regions and parts of the muscle and determine the time course of musculotendinous changes of supraspinatus preceding or resulting from tendon pathology. This knowledge is critical for progressive clinical advancements in tear prevention, rehabilitation, and surgical procedures.
ACKNOWLEDGMENT The authors are grateful for Dae Jong Lee’s assistance with reliability testing.
REFERENCES Clinical Relevance Rotator cuff tears can be treated conservatively or surgically. We know extensive changes in muscle geometry are associated with a high rate of tendon repair failure and inferior clinical outcomes (Fuchs et al., 2006). The US protocol used in this study can serve as a useful clinical assessment tool to examine changes in muscle geometry and screen for patients with extensive fiber bundle changes; in turn, knowledge of these clinical measures can aid in improving treatment decisions and rehabilitation planning. The results from this study imply rehabilitation protocols for patients with full-thickness rotator cuff tears, treated conservatively or operatively, may need to focus on restoring functional impairments associated with the posterior region. According to a recent study by Gates et al. (2010), the posterior region acts as an external rotator and is not involved in internal rotation regardless of the position of the humerus. Fiber bundle length changes found in this study suggest the posterior region contribution to external rotation of the glenohumeral joint is likely impaired with rotator cuff tears.
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