Original ResearchShoulder tendon characteristics in disabled swimmers in high functional classes – Preliminary report
Introduction
Swimmers are required to perform multi-faceted shoulder movements in 1 or more of 4 swim strokes; freestyle, butterfly, backstroke, and breaststroke. During each stroke, the shoulder is required to move through an arc of elevation with humeral rotation, and some degree of scapular protraction. For example, in the freestyle stroke during the pull-through phase, the scapula is protracted while the humerus is adducted and internally rotated (Johnson, Gauvin, & Fredericson, 2003). These scapular and humeral positions have been associated with rotator cuff tendon impingement, theoretically contributing to shoulder pain in swimmers (Struyf et al., 2017, Yanai and Hay, 2000, Yanai et al., 2000).
Epidemiologic studies have reported the incidence of shoulder injuries and pain in disabled swimmers (Weiler, Van Mechelen, Fuller, & Verhagen, 2016). During the Paralympic Games in London 2012, disabled swimmers had one of the highest incidence rates of injury (Willick et al., 2013). Moreover, it has been showed, that the shoulder was the most injured anatomical region of the body. Polish Paralympics swimmers had one of the highest injury rates in relation to other Polish athletes (Beijing 2008–13.1%; London 2012–9%) (Gawroński, Sobiecka, & Malesza, 2013). Disabled swimmers may be exposed to potentially higher shoulder overload, that may result in greater shoulder injuries (Ferrara and Peterson, 2000, Klenck and Gebke, 2007).
Findings from several studies suggest that intrinsic and extrinsic factors may affect shoulder biomechanics during swimming, leading to the development of shoulder pain (Struyf et al., 2017, Tovin, 2006). Yanai et al. (2000) investigated swimming stroke mechanics during freestyle swimming and reported that impingement occurred during 24,8% of the stroke time based on arm position. This finding suggests a high potential for impingement, without considering the supraspinatus tendon thickness and relationship to the subacromial space. Shoulder pain in swimmers is theorized to be commonly associated with impingement of the supraspinatus tendon in the subacromial space, called “swimmer's shoulder” (Bak, 2010, Struyf et al., 2017, Tovin, 2006).
Diagnostic ultrasound is a reliable technique used to investigate tendon characteristics (Del Baño-Aledo et al., 2017, Leong et al., 2012a, Michener et al., 2015). The measurement of the supraspinatus tendon thickness and acromiohumeral distance (AHD) was previously used to assess those with suspected impingement syndrome and rotator cuff tendinopathy (Braman et al., 2014, Leong et al., 2016, Leong et al., 2012b, Michener et al., 2015, Rodeo et al., 2016, Tucker et al., 2010) and rotator cuff tears (De Jesus et al., 2009, Naqvi et al., 2009). The relationship between the supraspinatus tendon thickness and subacromial space has not been investigated in swimmers, either with or without the presence of shoulder pain and disability. Michener et al. (2015) used the supraspinatus tendon occupation ratio to understand the mechanism of subacromial impingement of the tendon. Reduced subacromial space has been associated with improper scapular positioning (Silva, Hartmann, De Souza Laurino, & Biló, 2010), and alterations in abnormal shoulder kinematics (Blache et al., 2018, Kibler et al., 2013), and deficits in scapular muscle activation (Matzkin, Suslavich, & Wes, 2016).
The characteristics of supraspinatus tendon thickness and subacromial space may provide crucial foundational knowledge to enable the prevention and treatment of shoulder pain in disabled swimmers. The aim of this study was to compare disabled swimmers with upper and lower extremity disorders to an able-bodied swimmers group to characterize (1) supraspinatus tendon thickness, (2) subacromial space, and (3) supraspinatus tendon thickness as a percentage of subacromial space. We hypothesized that the supraspinatus tendon would be larger, the subacromial space would be smaller, and the tendon would occupy a greater proportion of the subacromial space in disabled swimmers with upper extremity disorders.
Section snippets
Participants
Subjects (n = 30) participated in this study were disabled swimmers with upper (DSw Upper) (n = 8) and lower (DSw-Lower) (n = 7) extremity disorders. The control group (CSw) consisted of 15 able-bodied swimmers. DSw-Upper and DSw-Lower were recruited from Para Swimming Polish Team and Para-Swimming section, while CSw from college swimming team. Two were elite Para-swimmers, including Summer Paralympic Games (Rio de Janeiro 2016) and international-level (World Cup, European Championship, World
Results
Intra-rater test-retest reliability of the supraspinatus-short axis [ICC(3.2) = 0.98; MDC90 = 0.4 mm; SEM = 0.05]; supraspinatus-long axis [ICC(3.2) = 0.97; MDC90 = 0.5 mm; SEM = 0.05]; AHD [ICC(3.2) = 0.99; MDC90 = 0.2 mm; SEM = 0.05] and occupation ratio [ICC(3.2) = 0.96; MDC90 = 0.6 mm; SEM = 0.08] revealed excellent reliability and acceptable measurement error in a pilot study of n = 15 participants.
Table 2 provides the mean values of the supraspinatus thickness and AHD parameters for the 3
Discussion
Two important findings were observed in this study. First, a 5.8% and 11.5% thicker supraspinatus tendon (in short and long axis respectively) was observed in the DSw-Upper group. Second, a 7.7% greater occupation ratio in the short axis was found in DSw-Upper as compared to DSw-Lower. The supraspinatus tendon thickness differences indicate an intrinsic change in the supraspinatus tendon. Tsui et al. (2007) showed increased supraspinatus tendon vascularity in those with tendinopathy. Moreover,
Conclusions
The present study showed for the first time that disabled paralympic swimmers, those with arm amputations and defects (e.g. phocomelia), have alterations in shoulder tendon characteristics and potential mechanism of impingement risk with a greater tendon occupation of the subacromial space (occupation ratio). Specifically, those swimmers had a thicker supraspinatus tendon and a greater occupation ratio, with the tendon occupying more of the subacromial space as compared to disabled swimmers
Funding statement
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. All authors disclose any financial and personal relationship with other people or organizations that could inappropriately influence their work.
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