Clinical Article The Korean Journal of Sports Medicine 2016;34(1):28-35 pissn 1226-3729 eissn 2288-6028 http://dx.doi.org/10.5763/kjsm.2016.34.1.28 한국프로야구투수들의극상근 - 건및이두박건장두에대한탄성초음파검사 서울대학교의과대학분당서울대병원정형외과 1, 서남대학교의과대학명지병원정형외과 2, 날개병원정형외과 3, 엘지트윈스프로야구단 4 오주한 1 ㆍ김준엽 2 ㆍ김도훈 3 ㆍ김용일 4 ㆍ조재호 2 Sonoelastography on Supraspinatus Muscle-Tendon and Long Head of Biceps Tendon in Korean Professional Baseball Pitchers Joo Han Oh 1, Joon Yub Kim 2, Do Hoon Kim 3, Yong Il Kim 4, Jae Ho Cho 2 1 Department of Orthopedic Surgery, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 2 Department of Orthopedic Surgery, Myongji Hospital, Seonam University College of Medicine, Goyang, 3 Department of Orthopedic Surgery, Nalgae Hospital, Seoul, 4 LG Twins Professional Baseball Club, Seoul, Korea The aim of this study was to evaluate the change of supraspinatus muscle and tendon as well as biceps tendon after in Korean professional baseball league pitchers by the application of sonoelastography. A total of 10 pitchers from Korean professional league were evaluated their supraspinatus muscle and tendon and long head of biceps tendon of dominant arm by sonoelastography at all-star break period. one month later, re-evaluations were performed after in the game. The strain ratio of supraspinatus muscle and tendon (red portion, soft; blue portion, hard), thickness of supraspinatus and long head of biceps tendons were evaluated. For the correlation analysis with, numbers of pitches, maximal velocity, maximal difference of velocity and ratio of breaking balls among pitches were investigated. The strain ratios of supraspinatus muscle, thickness of supraspinatus and long head of biceps tendon were decreased but not statistically significant. However, the strain ratio of red portion in supraspinatus tendon was significantly increased. There were no correlations between sonoelastograpic findings and pitches. Keywords: Baseball, Supraspinatus, Biceps, Sonoelastography Received: March 2, 2016 Revised: May 1, 2016 Accepted: May 2, 2016 Correspondence: Joon Yub Kim Department of Orthopedic Surgery, Myongji Hospital, Seonam University College of Medicine, 55 Hwasu-ro 14 beon-gil, Deokyang-gu, Goyang 10475, Korea Tel: +82-31-810-5114, Fax: +82-31-969-0500 E-mail: doctoryub@naver.com This study was supported by the Korean Orthopedic Ultrasound Society and Alpinion Medical Systems. Copyright 2016 The Korean Society of Sports Medicine CC This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 28 대한스포츠의학회지
오주한외. 한국프로야구투수들의극상근 - 건및이두박건장두에대한탄성초음파검사 서론탄성초음파 (Sonoelastography) 는초음파를통하여, 연부조직의기계적특징, 즉, 탄성도 (elasticity) 와경도 ( 단단한정도, stiffness) 를정성및정량적으로진단하는방법으로, 고전적으로외과영역에서간, 유방의암성병변을진단하는하나의방법이었다 1). 즉, 좀더부드러운연부조직에서는변형률 (strain ratio) 또는탄성도 (elasticity) 가증가하고, 좀더단단한연부조직에서는반대로변형률또는탄성도가감소하는물성특징을이용한진단적방법이라하겠다 2-4). 한편, 근골격계질환에서도탄성초음파가제한적으로진단에이용되어왔다 4). 근골격계탄성초음파의결과로근육부의병변은단단해지는경향이있으며, 건부위의병변은부드러워지는특징이있다 4-6). 또한, 이러한질환성병변외에도, 저항성운동후생기는근육의손상은근육의탄성도를떨어뜨린다는연구도있었다 7). 흔히행해지는일반적인탄성초음파 (conventional sonoelastography) 는압축탄성초음파 (compression sonoelastography) 로써, 초음파의탐촉자 (probe) 에압력을가하여, 연부조직의경도를검사하는방법으로, 술자에의존적이며, 탐촉자에가해지는다양한정도의압력이결과에영향을줄수있다 8-10). 따라서, 조직의변형 (strain) 의비 (ratio) 를측정하는것이비교분석하는방법으로연구에이용될수있다. Muraki 등 11) 에의하면, 탄성초음파가골격근의활성도를측정하는데유용하다고하였으며, Seo 등 12) 은회전근개건염환자에서건내국소병변을알수있는유용한방법이라고하였다. 프로야구투수들은대부분유소년시절 (9 12세) 부터오랜기간공을던지는반복적인행위를해온특별한상황에처해있으며, 일정한휴식기간을가지긴하지만, 긴시즌중의반복적인투구동작으로인해회전근개및관절와순손상이쉽게발생하는것으로알려져있다 13-16). 특히, 회전근개에서는견갑하건, 극상건손상이흔한것으로알려져있다 16,17). 또한, 이두박건장두의반복적인부하는투수들의상부관절와순전후병변 (superior labrum anterior to posterior lesion) 을유발하고, 이두박건장두에도산소포화도감소등의음성적영향을준다는보고도있다 18,19). 그러나, 투구의회전근개및이두박건에대한직접적인영향을영상학적으로분석을한연구는검사의접근제한성등으로인해이제껏충분히이루어지지않은측면이있다 16,20). 본연구에서저자들은투구가실제로극상근및극상건, 또한이두박건장두에즉각적인변화를유발하는것이탄성초음파로확인가능하며, 이러한근건의변화들이실제경기의 요소즉, 투구수, 투구속도및변화구비율등과연관관계가있을것으로가정하였다. 이에대하여프로야구투수들에서우세어깨에투구가극상근및극상건, 이두박건장두에미치는영향에대해탄성초음파를이용하여검사하고자하였다. 연구방법 1. 대상자 2015년도 LG 트윈스프로야구선수단에투수로등록된 34명의선수중, 7월올스타휴식기간 (2015.7.17 19) 에 1군에등록되어있으며, 연구에동의를한 16명의선수를대상으로실시간탄성초음파검사를시행하기로계획하였다. 이중 6명의선수들은데이터가충분히수집되지못하여연구에서제외하였으며, 최종 10명의투수들이이번연구에포함되었다. 10명의투수들의나이의중앙값은 29세 ( 범위, 24 35세 ), 키의중앙값은 185 cm ( 범위, 177 193 cm), 몸무게의중앙값은 89 kg ( 범위, 75 105 kg) 이었으며, 투구경력의중앙값은 18년 ( 범위, 14 25년 ) 이었다 (Table 1). 2. 탄성초음파검사법탄성초음파검사는한명의검사자 ( 정형외과전문의, 경력 8년 ) 에의해모두시행되었으며, 올스타휴식기간중 1회측정 ( 기저검사 ) 후, 약한달정도후에대상되는투수들의당일투구완료후재측정하는방법을사용하였다. 올스타휴식기간중에측정된 10명의투수들의투구휴지기는중앙값이 5일 ( 범위, 3 6일 ) 이었다. 투구후측정은투구완료후 30분내에측정하는것을원칙으로하였다. 탄성초음파는조직의변형도를 265 단계로표시하는색조지도영상으로그결과를표시하였으며, 적색부는부드러운부위, 청색부는단단한부위, 노란색과초록색부위는각각적색부와청색부에치우친경도를가진부위로정의되었다 21). 측정하려는값은투수들의극상근및극상건의변형률, 극상건의두께, 이두박건의두께였으며, 극상근및극상건의변형률은적색부 ( 부드러운부위, 탄성도가높은부위 ) 와청색부 ( 단단한부위, 탄성도가낮은부위 ) 로나누어측정하였다. 적색부와청색부는탄성초음파검사화면상가장명확하게적색, 청색으로표현되는부위를선택하였다. 탄성초음파는 Alpinion Medical Systems (Seoul, Korea) 의 E-CUBE 15 EX와 3.12 MHz의선형탐촉자를이용하였다. 제 34 권제 1 호 2016 29
JH Oh, et al. Sonoelastography on Supraspinatus Muscle-Tendon and Long Head of Biceps Tendon in Korean Professional Baseball Pitchers Table 1. Demographic characteristics of pitchers and basic data of the study Player Role Career (yr) Shoulder disease Age (yr) Height (cm) Weight (kg) Red portion of SSM Blue portion of SSM Red portion of SST Blue portion of SST Thickness of SST (mm) Thickness of long head of Bc (mm) Throw (n) Mesurement Proportion of breaking ball Highest of velocity (km/hr) Lowest of velocity (km/hr) 1 Starting 20 Bennett lesion, At resting 30 184 75 4.00 1.49 2.63 0.80 0.80 5.31 0 - - - 2.63 1.04 5.88 1.96 1.96 4.29 89 71.9 141 35 scapular dyskinesia 2 Starting 22 SLAP, partial rotator cuff tear, posterior instability At resting 32 190 105 6.25 3.57 4.55 1.69 1.69 5.06 0 - - - 8.33 1.27 5.88 1.05 1.05 4.29 106 54.7 149 35 3 Middle 14 Bennett lesion, At resting 24 183 77 8.33 1.12 7.14 2.08 2.08 6.75 0 - - - 5.26 1.47 5.00 0.88 0.88 5.81 10 70.0 149 29 internal impingement 4 Middle 22 SLAP At resting 32 193 100 4.55 1.72 1.69 0.63 0.63 4.45 0 - - - 10.00 2.08 4.55 1.67 1.67 4.29 72 52.8 144 22 5 Middle 17 SLAP, internal impingement 6 Starting 14 SLAP surgery (2008) 7 Middle 14 Subscapularis tendinitis, internal impingement 8 Middle 17 Internal impingement At resting 27 180 75 12.50 2.86 5.56 1.18 1.18 3.18 0 - - - 4.00 1.00 3.70 0.85 0.85 3.1 9 44.4 139 8 At resting 30 189 91 7.69 1.23 5.88 2.08 2.08 5.66 0 - - - 4.55 0.96 8.33 1.05 1.05 4.38 106 73.6 151 25 At resting 24 181 92 4.35 1.05 3.70 0.78 0.78 5.72 0 - - - 2.50 0.78 10.00 1.41 1.41 4.65 18 16.7 145 18 At resting 27 177 81 16.67 1.67 3.57 1.28 1.28 5.71 0 - - - 4.35 0.91 7.69 2.13 2.13 5.01 18 16.7 148 22 9 Starting 18 GIRD, SLAP At resting 30 186 95 6.67 1.59 4.35 1.45 1.45 4.61 0 - - - 4.76 2.22 7.69 1.96 1.96 4.97 104 44.2 158 33 10 Starting 25 SLAP surgery, supraspinatus repair (2014) At resting 35 190 98 12.50 3.85 2.94 1.06 1.06 3.57 0 - - - 10.00 2.63 4.17 1.19 1.19 5.16 19 57.9 146 21 SSM: supraspinatus muscle, SST: supraspinatus tendon, Bc: Biceps brachii, SLAP: superior labrum anterior to posterior, GIRD: glenohumeral internal rotation deficit. 30 대한스포츠의학회지
오주한 외. 한국 프로야구 투수들의 극상근-건 및 이두박건 장두에 대한 탄성초음파 검사 3. 극상근의 변형률 측정 자가 선택한 화면 전체로 한다. 변형률을 측정하기 위한 기준 부위로, 피하 지방 조직을 선택하였으며, 피하 지방의 두께를 측정 대상 선수들은 등받이가 없는 의자에 똑바로 앉은 넘지 않는 범위에서 참조 상자(reference box)를 위치시켜 기준 자세로 공을 던지는 팔(우세수)을 편안하게 측면에 위치 시키 으로 하고, 극상근내 적색으로 표시되는 탄성도가 높은 부위에 11,21,22) 도록 한다(Fig. 1). 어깨의 견갑골극(scapular spine) 중앙 참조상자를 위치시켜, 변형률(측정부위/기준부위)을 측정하 에서 손가락 하나 두께 정도의 전방부에 탐촉자를 위치시킨 고, 청색으로 표시되는 탄성도가 낮은 부위에서도 같은 방법으 후, 초음파의 일반검사 모드(B-mode, brightness mode)에서 극 로 변형률을 측정한다(Fig. 2). 상와(surpaspinatus fossa) 부위의 극상근을 관찰하고자 하는 목표를 가지고, 승모근과 극상근이 한 화면에 적절하게 위치한 다고 생각되면(연구 관심부위, area of interest), 탄성모드 (elastogram mode)를 작동시킨다. 탐촉자에 수직으로 압력을 4. 극상건의 변형률, 극상건 및 이두박건의 두께 측정 변형된 crass position을 선수들에게 취하도록 하고, 탐침자 가해 표시자가 나타내는 압력 지침자(pressure indicator)가 레 벨이 4 이상(레벨 1 6, 1이 가장 불안정한 압력, 6이 가장 안정적인 압력)이 되면, 안정적인 탄성초음파 검사가 이루어 질 수 있다고 판단하기로 하고, 탄성초음파의 관심범위를 검사 Fig. 1. The subject was on chair with his dominant arm at side during the examination. Fig. 2. Measurement of strain ratio of supraspinatus muscle. Reference box (rectangle box) was located at the subcutaneous fat layer (closed arrow) and the same size of target boxes were located at red portion of supraspinatus muscle (closed arrow with dashed line) and blue portion of supraspinatus muscle (open arrow). Fig. 3. Measurement of strain ratio of supraspinatus tendon (A), thickness of suprasinatus tendon (B) and biceps long head tendon (C). As in the manners with the measurement of strain ratio in supraspinatus muscle, reference box was located at subcutaneous fat layer (closed arrow), and target boxes were located at red (closed arrow with dashed line) and blue portion of supraspinatus tendon (open arrow) (A). The thickness of supraspinatus tendon (yellow dashed line) was measured with highest thickness at superior facet of greater tuberosity (B) and thickness of biceps long head tendon (yellow dashed line) was measured in the long axis view (C). 제34권 제1호 2016 31
JH Oh, et al. Sonoelastography on Supraspinatus Muscle-Tendon and Long Head of Biceps Tendon in Korean Professional Baseball Pitchers 의단축 (short axis) 으로극상건의전방부를 B-mode로관찰한다. 측정자가원하는극상건전방부가나온화면에서극상근에서변형률을측정했던동일한방법으로, 탄성모드를작동시킨후, 극상건의적색부와청색부의변형률을측정한다 (Fig. 3A). 그후, 극상건의가장두꺼운부위의건두께를측정한다 (Fig. 3B). 이후, 극상건전방부의이두박건을확인한후, 장축 (long axis) 으로탐촉자방향을전환하여, 이두박건장두의두께를측정한다 (Fig. 3C). 5. 투구정보모집투구와관련된데이터, 즉, 투구수, 구속, 구종에관한정보는 LG 트윈스전력분석팀의자료를이용하였다. 6. 통계통계학적분석은 SPSS ver. 18.0 (SPSS Inc., Chicago, IL, USA) 를이용하였다. 선수개개인의극상근및건의변형률의변화, 극상건및이두박건의두께변화는 Wilcoxon signed rank test로분석하였으며, 투구수와최고구속, 구속차및변화구비율등의투구관련요소와변형률, 건두께와의연관성은 Spearman correlation analysis를이용하여분석하였다. p값이 0.05 미만인경우만유의한것으로판단하였다. 결과올스타휴식기간중 10명의투수들을대상으로진행한검사의극상근의변형률 (strain ratio) 은적색부가평균 8.35 ( 범위, 4.00 16.67) 를나타냈으며, 청색부는 2.02 ( 범위, 1.05 3.85) 로적색부와청색부사이에유의한변형률차이를보였다 (p=0.001). 극상건의적색부변형률은 4.20 ( 범위, 1.69 7.14), 청색부는 1.30 ( 범위, 0.63 2.08) 으로건부위의변형률또한적색부와청색부사이에유의한차이를나타내었다 (p=0.000) (Table 2). 극상건의최대두께는 7.32 mm ( 범위, 5.48 9.84 mm), 이두박건장두의두께는 5.0 mm ( 범위, 3.18 6.75 mm) 를나타 내었다. 초기측정후한달정도의시간이흐른뒤경기에서공을던지고나서측정한극상근의적색부변형률은평균 5.64 ( 범위, 2.50 10.0), 청색부변형률은평균 1.43 ( 범위, 0.78 2.63) 의감소소견을보였으나, 유의미한변화는없었다 (p=0.116, p=0.092). 투구후에도근육부의적색부와청색부사이의변형률차는유의미하였다 (p=0.000). 투구후극상건의적색부변형률은 6.29 ( 범위, 3.70 10.00), 청색부의변형률은 1.42 ( 범위, 0.85 2.13) 로증가하는소견을보였으며, 적색부의변형률만이평균 2.01 (standard deviation, 2.59) 유의미한증가소견을보였다 (p=0.031) (Table 2, Fig. 4). 투구후건부위의적색부와청색부사이의차이는유의함을나타내었다 (p=0.000). 극상건의두께는 6.74 mm ( 범위, 6.23 7.34 mm), 이두박건의두께는 4.60 mm ( 범위, 3.10 5.81 mm) 로감소소견을나타내었다. 극상건및이두박건의두께도감소하였으나, 유의미한변화는없었다 (Fig. 5). 투구수와최고구속, 구속차이, 투구에서변화구의비율등은극상근및건의변형률및변형률의변화, 극상건의두께및이두박건의두께의변화와상관관계가없었다. 극상건의적색부와청색부의휴식기와투구후사이의변형률의변화는양의상관관계 (r=0.673, p=0.033) 가있었다. 고찰본연구결과에서프로야구투수들의투구후극상건의변형률은증가하는경향을보였으며, 특히적색부변형률은피칭후유의하게증가하였다. 또한, 극상근의변형률은투구후감소하는경향을보였으나, 유의한변화는보이지않았다. 이는투구후극상근은수축하고, 극상건의부드러웠던부위 ( 적색부, 악화되어있는부위 ) 는추가적인악화가야기됨을보여준다. 극상건및이두박건장두의두께는투구후감소하는소견을보였으나, 유의미한변화는없었다. Tudisco 등 23) 에의하면, 작은크기의극상건파열에서건의질을탄성초음파로평가한결과가실제임상점수와연관이 Table 2. Comparisons between strain ratios of supraspinatus muscle and tendon at red and blue portion at all-star break and after Variable Supraspinatus muscle (SD) Supraspinatus tendon (SD) p-value Red portion at all-star break 8.35 (4.23) 4.20 (1.65) 0.013 Blue portion at all-star break 2.02 (2.02) 1.30 (0.52) 0.090 Red portion after 5.64 (2.80) 6.29 (2.06) 0.644 Blue portion after 1.44 (0.65) 1.42 (0.48) 0.934 SD: standard deviation. 32 대한스포츠의학회지
오주한외. 한국프로야구투수들의극상근 - 건및이두박건장두에대한탄성초음파검사 Fig. 4. The change of strain ratio after compared to all-star break period at red and blue portion of supraspinatus muscle and tendon. SS: supraspinatus. Fig. 5. The change of thickness of supraspinatus tendon and biceps long head tendon after compared to all-star break period. SS: supraspinatus, Bc: biceps brachii. 있었다고하였다. 그러므로, 회전근개부분손상이상당수있을것으로추정되는프로야구투수들의투구후극상근및극상건의실제변화를탄성초음파로관찰한결과가투구기능과연관관계가있을가능성이있다. 근골격계병리에제한적으로사용되어온탄성초음파검사법은근육과건의질을이방성 (anisotropy) 에영향을받지않고, 색깔에의해측정할수있는장점과더불어높은관찰자간신뢰도로극상건내및극상건주변의변화감지에유용한검사임이밝혀져있다 12,21). 일반적으로건이근육에비해높은탄성도를나타내는것으로알려져있으나 11), 투수들의올스타휴식기에측정된결과에서는, 적색부의극상근의탄성도가적색부의극상건보다높은것으로확인되었다. 탄성초음파에서근육과건의변형률의의미가근육에서는이완, 건에서는건증및손상의의미로다르다는차이가있기도하겠지만 4), 이러한결과의차이는기존의연구는일반적인건강한성인을대상으로하였고, 저자들의연구에서는오랜기간투수로활동한프로스포츠선수를대상으로한연구로서, 그대상자가다르고, 기존의연구는적색부와청색부를혼합한근및건탄성도 ( 변형률 ) 를결과로보고하였고, 저자들의연구는적색부와청색부를구분하여변형률을보고했기때문에다른결과를나타낼수있다고생각한다. Muraki 등 11) 은극상근의등척성 (isometric) 수축의연구결과에서, 등척성수축의강도가심해짐에따라탄성초음파검사에서변형률이감소하였다고하였다. 대부분의근골격계질환에서, 또는격렬한운동후근육의탄성도는떨어지는것으로알려져있으며, 간혹, 피부근육염과근육의지방변성화될때탄성도가증가하는것으로알려져있다 4-7). 본연구대상인프로야구투수들은어깨근육이과사용되기는하나, 지방변성 을일으킬정도의손상은없으며, 투구는피로도를느낄정도의과도한운동이고, 반복되는등척성수축으로인하여, 근육의긴장도가증가하여변형률, 즉탄성도가떨어지는결과를본연구에서얻은것으로생각한다. 인대의변형률은자세에따라서많이변하며, 건파열의경우에는변형률이증가한다고하였다 4). 따라서, 본연구에서극상건의변형률이증가하는것은근육과달리오히려건내병변의증가로이해하는것이좋을듯하다. 특히, 이러한음성적인변화중유의한변화는부드러운조직부위 ( 적색부 ) 의건에서만확인되는것으로보아, 탄성도가상대적으로떨어지는부위가투구와관련된영향이더크다고생각할수있겠다. 그러나, 저자들의연구에서밝혀진건부위의적색부와청색부의휴식기와투구후사이변화율의양의상관관계로보아, 청색부의변화도적색부의변화가큰만큼어느정도영향을받을것이라고추측할수있다. 본연구의결과에서, 투구수와최고구속등과건탄성도의변화가연관성이없는결과가나온것은선수개개인의투수보직이다르며, 극상건에대한피로부하역치가다르기때문일것으로판단된다. 이번연구에는많은제한점이존재한다. 첫째, 표본의수가적어, 대표성을띈강력한결론을도출해낼수없었다. 둘째, 다양한경력및보직의투수들을포함하여, 투구수와구속차, 최고구속, 변화구비율등실제경기내용과영상학적결과와의관계를분석하는데제한점이있었으며, 셋째, 프로야구투수들의스케쥴로인하여, 일관된투구전후의관찰을할수없었으며, 넷째, 기능적점수와연관된분석을시행하지못했으며, 다섯째, 견갑하건, 극하건및이두박건에대한변형률을측정하지않는극상근및극상건에대한제한적인검사였 제 34 권제 1 호 2016 33
JH Oh, et al. Sonoelastography on Supraspinatus Muscle-Tendon and Long Head of Biceps Tendon in Korean Professional Baseball Pitchers 고, 여섯째, 탄성초음파가검사자간검사수치에차이를보일수있는검사임에도불구하고, 검사자간및검사자내신뢰도측정을시행하지않았다는점이있다. 그러나, 실제경기에참여하는프로야구 1군투수들을대상으로최초로탄성초음파를적용해본점, 투구후극상근및극상건의변형률및극상건의두께, 이두박건의두께를측정하여, 어깨근육에대한투구의즉각적인영향을탄성초음파로분석한첫번째연구라는점은본연구의강점이라하겠다. 반면, 건은적절한자극에는영구적변형없이회복이되나, 최대탄성률 (elastic modulus) 을넘어서는부하가가해지면, 비가역적인손상을입게되어탄성도를잃게된다 24,25). 따라서, 본연구와같은영상학적연구와투구피로도를연관시켜, 향후연구를진행하면, 투수들의건부위어깨부상을줄일수있으리라생각한다. 이번연구는탄성초음파로투수들의투구후극상근및건의탄성도변화를알아보는최초의시도였으며, 극상건의적색부 ( 부드러운부위 ) 의변형률이투구후유의하게감소하였으며, 극상건과이두박건의두께는감소하는양상이었다. Acknowledgements We thank to rest of field doctors of LG twins team 2016 Jae Yoon Chung, Se Kwan Oh, Byung Wook Song, Yeun Ho Kim, Yong Gon Na, Jeong Dong Lee) and LG twins athletic trainers (Hak Rim Cho, Se Hoon Oh, Yohan Bae, Yong Wan An, Jong Gon Park, Bon hak Koo, Yeob Kwon Lee) for the assistance to complete this study. Conflict of Interest No potential conflict of interest relevant to this article was reported. References 1. Klauser AS, Miyamoto H, Bellmann-Weiler R, Feuchtner GM, Wick MC, Jaschke WR. Sonoelastography: musculoskeletal applications. Radiology 2014;272:622-33. 2. Varghese T, Ophir J, Konofagou E, Kallel F, Righetti R. Tradeoffs in elastographic imaging. Ultrason Imaging 2001; 23:216-48. 3. Itoh A, Ueno E, Tohno E, et al. Breast disease: clinical application of US elastography for diagnosis. Radiology 2006; 239:341-50. 4. Lalitha P, Reddy MCB, Reddy KJ. Musculoskeletal applications of elastography: a pictorial essay of our initial experience. Korean J Radiol 2011;12:365-75. 5. De Zordo T, Chhem R, Smekal V, et al. Real-time sonoelastography: findings in patients with symptomatic achilles tendons and comparison to healthy volunteers. Ultraschall Med 2010;31:394-400. 6. Brandenburg JE, Eby SF, Song P, et al. Ultrasound elastography: the new frontier in direct measurement of muscle stiffness. Arch Phys Med Rehabil 2014;95:2207-19. 7. Yanagisawa O, Sakuma J, Kawakami Y, Suzuki K, Fukubayashi T. Effect of exercise-induced muscle damage on muscle hardness evaluated by ultrasound real-time tissue elastography. Springerplus 2015;4:308. 8. Moon WK, Chang SC, Huang CS, Chang RF. Breast tumor classification using fuzzy clustering for breast elastography. Ultrasound Med Biol 2011;37:700-8. 9. Park SH, Kim SJ, Kim EK, Kim MJ, Son EJ, Kwak JY. Interobserver agreement in assessing the sonographic and elastographic features of malignant thyroid nodules. AJR Am J Roentgenol 2009;193:W416-23. 10. Yoon JH, Kim MH, Kim EK, Moon HJ, Kwak JY, Kim MJ. Interobserver variability of ultrasound elastography: how it affects the diagnosis of breast lesions. AJR Am J Roentgenol 2011;196:730-6. 11. Muraki T, Ishikawa H, Morise S, et al. Ultrasound elastography-based assessment of the elasticity of the supraspinatus muscle and tendon during muscle contraction. J Shoulder Elbow Surg 2015;24:120-6. 12. Seo JB, Yoo JS, Ryu JW. Sonoelastography findings of supraspinatus tendon in rotator cuff tendinopathy without tear: comparison with magnetic resonance images and conventional ultrasonography. J Ultrasound 2015;18:143-9. 13. Kanematsu Y, Matsuura T, Kashiwaguchi S, et al. Epidemiology of shoulder injuries in young baseball players and grading of radiologic findings of Little Leaguer's shoulder. J Med Invest 2015;62:123-5. 14. Kinsella SD, Thomas SJ, Huffman GR, Kelly JD 4th. The thrower's shoulder. Orthop Clin North Am 2014;45:387-401. 15. Yang J, Mann BJ, Guettler JH, et al. Risk-prone activities and injuries in youth baseball: findings from a national sample. Am J Sports Med 2014;42:1456-63. 16. Yanagisawa O, Niitsu M, Takahashi H, Itai Y. Magnetic resonance imaging of the rotator cuff muscles after baseball. J Sports Med Phys Fitness 2003;43:493-9. 34 대한스포츠의학회지
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