冈下肌肌筋膜疼痛综合征的特点
王娟 译
目的
探讨冈下肌MTrP的特点，评估MTrP注射的治疗效果。
方法
本研究对297名患者（221名女性；年龄，53.9 /-11.3岁）的冈下肌MTrP的医疗记录进行回顾分析。 对总共380例冈下肌存在MTrP的病人都进行了研究（214例在单侧，83例双侧都有）。收集的具体特征包括主诉区、牵涉痛模式、局部抽搐反应的数量和肌肉中MTrP的分布。统计分析用配对t检验比较第一次注射前和注射后两周的视觉模拟量表。
结果
冈下肌上的MTrP最常见出现在肩胛区。牵涉痛最常见的地方是手臂的前外侧（肘部上方）。冈下肌中活化的MTrP多见多个出现，单一的比较少见，并且经常出现在肌肉的中心。
在冈下肌MTrP注射可以显著地降低疼痛强度。与基线相比，第一次注射后视觉模拟量表评分明显下降（7.11与3.74；p＜0.001）。
结论
评估MTrP的特点及注射疗效。这些发现可以为临床医生诊断和治疗冈下肌肌筋膜疼痛综合征提供有用的信息。
关键词
冈下肌，肌筋膜疼痛综合征，MTrP，疼痛，注射
介绍
肩胛骨附近的非特异性的疼痛非常常见，可能是由颈椎或肩关节紊乱引起的。但是有时候肩胛骨附近的疼痛似乎与颈椎或肩关节没有任何关系，这时候就需要用临床研究来揭示可能的疼痛原因并找到有效的治疗方法。
激痛点(MTrPs)可以为肩胛疼痛的病理生理机制提供另一种解释。虽然激痛点很少是疼痛的主要来源[1,2]，但有证据表明激痛点是由另一种软组织的病变引起的或与之有关，如脊柱紊乱或肩袖疾病[2,3]。激痛点是对压力高度敏感的局部点。
激痛点的触诊可以产生疼痛、肌肉功能紊乱和交感亢进等相关特征。激痛点分为活化的和失活的两种。活化的激痛点表现为临床疼痛，伴有或不伴有紧绷带的压痛，而失活的激痛点在临床上是不活动的，只有在触诊时才会疼痛。
根据我们的临床经验，许多有脊椎或肩袖疾病或者没有这些疾病的患者也有冈下肌产生的肩胛痛。冈下肌是一种厚三角肌，占据了下凹窝的主要部分，并协助手臂的外旋和肱骨在手臂运动时的稳定[7]。这块肌肉中活化的激痛点会引起局部和肩区相关疼痛，并向下到手臂的前面和外侧[5]。
冈下肌上经常出现激痛点。在一项对126名患者进行的研究中，在31%的病例中，肩胛下肌引起相关肩区疼痛的频率仅次于肩胛提肌(55%)[8]。另一项研究也报告了类似的结果[9]。在年轻、无疼痛的成人中，冈下肌是紧随肩胛提肌(20%)和上斜方肌(35%)[10]的第三大广泛存在失活激痛点的肌肉(18%)，。
通过详细的病史和体格检查评估，我们最近观察到许多患者符合在冈下肌中存在激痛点的标准。在治疗这些病人的过程中，我们发现了一些与之前的研究[11]的差异：主诉区域，牵涉痛模式，激痛点的分布，以及触发点注射的治疗效果。本研究的目的是报告冈下肌上的激痛点的特点。
材料和方法
参与者
在机构审查委员会批准后，我们回顾分析了在2013年3月至2015年11月期间访问西富兰斯医院门诊部的446名疑似冈下肌上存在激痛点的患者的医疗记录，以确定所有符合条件的病人(4 -2015- 1049)。诊断活化的激痛点是根据之前的标准,包括冈下肌的痛处，按压痛处引起相应疼痛的兼容模式,限制范围的肩膀的运动，和在紧绷的最敏感的地方明显的或可见的局部抽搐反应(LTRs)。在触发点注射过程中，LTRs被诱导和评估。由于针刺在识别LTRs时比手动触诊更加敏感，因此选择针刺方法来确认激痛点的存在。
在冈下肌有激痛点的患者中，符合下列标准的包括:肌肉和筋膜的激痛点，独有的肌腱病;在0-10的数值范围的视觉模拟量表(血管)测量的疼痛分数大于2(≥3);并且有一个触发点注射。排除有以下情况的患者:(1)在干预前2周接受治疗，并通过随访期，有可能影响到结果(如止痛药、物理治疗或其他注射治疗);(2)存在一些其他可能出现相同症状的全身疾病(如:纤维肌痛);(3)有神经学肩/肩胛痛(如:，颈椎病或周围神经损伤;(4)既往使用过利多卡因或类固醇，或者在注射过程中可能使病人有重大风险的状况或情况。
然而，如果患者符合在冈下肌有激痛点的标准，即使他们有肩袖和/或颈椎疾病的病史，也不会被排除在外。冈下肌筋膜疼痛综合征的特点。
MTrP注射
所有注射均在超声(US)引导下进行。然而，这项研究的回顾性设计并不是评估超声指导下的冈下肌注射的有用性。考虑到本研究的冈下肌的激痛点，我们对先前报告的超声指导的下背部肌肉、深骨盆肌肉和臂肌触发点注射方法进行了改良(12 - 14)。我们使用一台Accuvix V10 超声机器(麦迪逊,首尔,韩国)在无菌环境、目标肌肉周围的一个5到12 mhz的线性阵列传感器上进行了b模式的实时超声。一名有8年以上肌肉骨骼超声经验的物理治疗师执行了所有超声指导的注射手术。
病人俯卧于检查床,患臂做延伸、内旋、内收动作并尽力够到胸椎,也就是在类似于手术“折臂固定”的位置进行注射手术(图1)。这个位置,我们可以通过分离肩胛骨周围组织简单而又安全地到达冈下肌。
我们通过对肌群的超声扫描将三角肌、斜方肌、大圆肌、小圆肌、背阔肌和冈下肌区分开来，并通过触诊肌肉在皮肤上标记压痛点。通过对标记点的探头定位，将探头转向最佳视角，可以看到目标区域的图像(图1、2)。使用彩色多普勒图像来避开神经血管束。在超声指导下连接一根25尺、2.6厘米的针头与一个含有4毫升0.5%利多卡因与1毫升40毫克去炎松的5毫升注射器，在触到压痛点的冈下肌上进行注射。在一个肌肉有多个压痛点的情况时，所有的压痛点都要重复注射。
在每次治疗期间，注射部位的顺序都是根据触诊压痛点时疼痛严重程度的下降顺序确定的。每个压痛点的注射量为0.5 mL，如果准备好的5毫升溶液全部用完(最多每次治疗10个注射点)或触诊没有发现有压痛点，就不再进行注射。利用离面法，我们可以看到针穿过皮肤和脂肪组织进入肌肉。物理治疗师超声下观察LTRs并进行触发点注射。重复针刺来引出尽可能多的LTRs。如果尝试10次后没有观察到LTR，就停止针刺，并注射混合溶液。按压注射部位以确保术后止血。所有肌肉的触发点注射都在2周的间隔内进行。如果病人对减少不适或疼痛程度的效果感到满意，或者不想再次注射，则不考虑额外注射。教导病人做拉伸运动(每天重复10到20次)，避免任何可能会加重症状的不良姿势。
数据收集
收集年龄、性别、患侧及症状持续时间等人口统计学和临床数据。记录疼痛强度、症状持续时间、主诉区、牵涉痛模式、注射次数、LTRs的数量，肌肉上激痛点的分布建立在超声指导下注射的LTRs那侧(图3)。
疼痛强度用10厘米水平的从0(没有疼痛)到10(最难以想象的疼痛)视觉模拟评分法测量。在每次注射的基线和2周后用视觉模拟评分法进行评估。
系统分析
我们对病人信息和冈下肌上激痛点的特点进行了描述性分析。
对于双侧冈下肌均存在激痛点的患者，每一侧的疼痛强度，症状持续时间，主诉区域，牵涉痛模式，注射次数，以及LTRs的数量都进行了评估。触发点注射效果的评估使用了在基线和第一次注射的2周后获得的视觉评分模拟数据的夏皮罗-威尔克检验，以查明该分布是否正常。使用夏皮罗-威尔克检验显示这些参数的正态分布的同时，采用配对t 检验来比较第一次触发点注射前与注射两周后的参数。统计学意义为p值< 0.05。SPSS版本21.0软件(IBM,Armonk,NY,USA)用于所有统计分析。
结果
在2013年3月至2015年11月期间，我们回顾了446例疑似冈下肌上有激痛点的患者的医疗记录。其中297名患者(221名女性和76名男性)符合参加这项研究的条件。
因为有83例患者在双侧冈下肌中存在激痛点，有380例冈上肌存在激痛点的符合纳入标准。
在83例双侧冈下肌存在激痛点的患者中，双侧肌肉都在持续时间、疼痛严重程度、主诉区域和牵涉痛模式上分别进行评估。表1总结了297例患者的人口统计学和临床数据，并总结了380例有激痛点的冈下肌的临床特征。
297名患者中有103名患者有肩部疾病的病史，包括肩袖疾病(n = 103,34.7%)，运动伤或工伤而没有肩部和劲椎疾病(n = 89,30.3%)，颈椎疾病(n = 61,20.5%)，肩病合并颈椎病(n = 44,14.8%)。在工伤患者中，我们发现17人(5.7%)在照顾孩子。
在380例冈下肌存在激痛点患者中，最常见的主诉区域为肩胛区;其次是在肩膀的前面深处(表1)。有一百三十一例病人提到除了主要的主诉区域外的疼痛;最常见的区域是手臂的前外侧(肘部上方)(表2).
根据所有380例冈下肌确定了对诊断激痛点必须的LTRs 。然而，在医学图表中，LTRs的数量只有153例。其中38例(24.8%)少于5个LTRs。6 - 10、11 - 15、16 - 20和> 10 LTRs分 别为45(29.4%)、46(30.1%)、24(15.7%)和70(45.8%)。
图3总结了297例患者肩胛骨下肌筋膜的分布情况。在一共380例患者中，发现了1468个激痛点，平均每块肌肉有4.9个激痛点。
在380例病例中，对135例进行了触发点注射的治疗。这135例患者，有16例(11.9%)注射1针，2周内注射2次，88例(65.2%)，31例患者每2周注射3例(23.0%)。与基线相比，第一次注射后两周VAS有明显的下降(p < 0.001)。在第一次治疗后，平均值从7.11(SD = 1.45)预处理到3.74(SD = 1.53)。
讨论
这项研究有三个重要的发现。首先，冈下肌激痛点的主要症状之一是产生肩胛骨疼痛。第二，活化的激痛点几乎总是多个出现的，而非在患侧冈下肌单独出现。第三，冈下肌的活化激痛点的失活会明显降低疼痛强度。
在早期的研究[9,15 - 18]中，冈下肌激痛点的主要症状是在肩前深部的疼痛，包括前三角肌区。虽然激痛点的疼痛经常发生在肩前的深部，但在这项研究中肩关节部位的疼痛更加普遍。这些发现可能取决于激痛点定义的差别，病人的数量，以及在体检中询问病人的问题的正确性。
首先，激痛点可以存在于骨骼肌组织，肌肉的腱膜(筋膜)，或肌腱，但这项研究仅限于冈下肌组织和/或肌筋膜内的激痛点，即最普遍形式的激痛点[19]。
其次，我们并没有排除那些符合冈下肌存在激痛点的标准但有颈椎病史或肩损伤病史的患者。第三，由于患者可能不能区分肩胛骨疼痛和肩痛，理疗师在体检时提出了一些问题，来确认疼痛是出现在肩胛骨区域。如果理疗师并没有特别询问肩胛疼痛，病人就可能会认为这个问题是关于肩痛的。
牵涉痛是一种疼痛感，并不是真正的原发部位[20]。在本研究中，来自冈下肌的激痛点所提到的疼痛位置在频率上依次是手臂的前外侧(肘部以上)，外侧前臂，上后颈，和手的放射状区域(包括一个手指)。我们的结果与对193例患者的研究结果相似，其中手臂的前外侧部分(46%)是最常出现的疼痛部位，其次是前臂外侧(21%)，后颈(14%)，手的桡侧(13%)[9,11,15,16,18,21,22]。如果牵涉痛在手部的放射状区域时，将其区别于颈椎病尤为重要，主要是C5或C6级[23]。
牵涉痛的范围和部位取决于冈下肌激痛点的位置和强度，以及需要进一步的研究。冈下肌和小圆肌的激痛点经常会一起出现，而且经常被错误地评估为肩袖损伤或颈椎间盘源性疼痛。另外，冈下肌的激痛点经常被错误地评估为肩关节炎，肩胛上神经的压迫或者肱二头肌肌腱炎[19]。还有，冈下肌激痛点应与大圆肌、冈上肌、、前三角肌、肩胛下肌和胸肌[19]区别开来。
这项研究的主要贡献之一是发现了在疼痛侧的冈上肌上有多个活化的激痛点，而不仅仅是单个。此外，每块冈下肌上有多个LTRs，我们已经观测到很多有十多个LTRs的例子(45.8%)。如果在注射过程中诱导出LTRs，尤其使用快进快出手法后，疼痛经常可以得到迅速的缓解[24,25]。反之如果在触发点注射时没有引起LTRs，病人就不能体验到迅速完全的疼痛缓解。
注射了一个反应点后，其他的LTRs可以被激发出来。重复这些步骤，直到所有(或尽可能多)反应点被注入[26]。据我们所知，LTRs的数量之前没有报告过。因此，这些结果强调了在冈下肌肌筋膜疼痛综合征患者的一块肌肉中寻找多个活化的激痛点区域和LTRs的重要性。在同一块肌肉中的多个激痛点每一个都可能导致整体的牵涉痛模式。
冈下肌的触发点注射治疗效果非常好，并且治疗后VAS评分也降低了。我们建议，对于冈下肌上有激痛点的病人，如果怀疑他的肩胛骨疼痛是由冈下肌引起的，对其进行冈下肌触发点的注射则对于诊断和治疗都会有效。
冈下肌的激痛点通常是由急性压力或多次负荷过多的压力激活的。这些激痛点可能会在特定的持续因素的影响下变得活化然后诱发疼痛，例如重复性和持续的肩部活动[27,28]。这可能是那17名没有肩膀损伤但是照顾孩子的病人患病的原因。当肩膀外展和弯曲时，冈下肌显示的活动比冈上肌的少[29]。然而，在外展超过140°以后冈下肌活动显著增加。因此，当病人长时间肩带超过肩峰水平的负重时，，就会损伤冈下肌。这些机制可以解释那些没有潜在疾病但是经常参与照顾孩子的妇女案例。不同于冈上肌，冈下肌更容易在不寻常和短暂的运动中被激活，而且急性负荷可能比持续负荷的任务更容易产生激痛点[11]。
肌肉的不平衡也会使激痛点活跃,并引起复发性疼痛。既然激痛点可以诱导正常的肌肉活化模式和后续的运动功能障碍的改变，那么识别和灭活激痛点应该能够改善运动功能,缓解肌肉僵硬,恢复肩部的正常生物力学[30]。
了解在冈下肌中激痛点的常见部位很重要，以便为这块肌肉的激痛点的临床识别提供指导。仔细触诊可以容易发现冈下肌的多个痛点，也被认为是多个病变。在以往的研究中，最常见的激痛点区域是在肩胛骨脊柱缘最内侧和邻近区域四分之一长的交界处(上内侧病变)[11]。第二个最常见的激痛点区域为肩胛骨脊柱缘中点尾部[11]。在本研究中，常见的激痛点区域与Travel发现的相似，但定位更广泛，且肩胛骨的下角更为常见。因为在体检过程中，冈下肌面积广泛，全部触诊可能会很耗时，本研究可以为识别冈下肌的激痛点提供有用的指导。
超声指导注射对检测肌肉中位置深的LTRs和在注射时对更不容易接触的肌肉深度进行控制很有用。超声指导也可以减少因针头放置不当造成的意外伤害。但在冈下肌触发点注射时没有必要使用超声引导，因为冈下肌位置表浅，而且针头不太可能在不经意间伤害周围的组织，比如肺。然而，通过使用超声引导的注射，我们可以观察到更多的LTRs来提高注射的效果并且区分邻近的大圆肌,三角肌和斜方肌，以便更准确地诊断，并通过记录内置视频来提供治疗反馈。这些优势可能值得关注。
我们的研究有一些局限性。首先，因为这项研究是回顾性的，我们可能错过准确分析所需的信息。
其次，我们总结的触发点注射的疗效没有对照组比较。不过，在短期治疗中，我们不能忽视视觉评分模拟量表注射量的显著减少(超过3分)。
第三，每个案例我们只研究了一种牵涉痛模式。如果存在多个痛点，则可能会有许多不同的疼痛模式，这些都取决于痛点的位置、数目和疼痛的严重程度。这也是一个回顾性研究的局限性，可以通过进一步的前瞻性研究来补充。
第四，触发点注射治疗效果的随访时间相对较短。虽然没有长期随访，但对冈下肌内激痛点的触发点注射的长期效果与其他肌肉并不会有什么区别。如果不能消除潜在的病原病灶，一个触发点注射的效果通常会持续2周[13]。然而，活化的激痛点的失活对某些情况是必要的，包括出现严重的、无法忍受的疼痛、干扰功能活动的疼痛和不适，以及持续的疼痛和紧张。同样的原理可以应用于冈下肌。
第五，选择组的患者不均匀。特别是一些有肩或颈椎损伤的患者参与了这项研究。激痛点可继发于病理状态，如慢性重复小肌肉拉伤、不良坐姿、全身疾病、肌肉骨骼损伤(如应变、扭伤、神经炎、粘液囊炎、关节炎、椎间盘损伤)[2,3]。但对于我们研究中有肩部或颈椎损伤病史的患者，其病变并不是其就诊的主要原因。此外，他们的症状符合了激痛点标准，具有讽刺意味的是，他们的激痛点并不比没有肩部或颈椎损伤病史的患者更少[1]。
综上所述，冈下肌激痛点的发现和触发点注射的疗效，可以为临床医生诊断和治疗冈下肌肌筋膜疼痛综合征提供有用的信息。
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原文链接：
http://www./journal/viewJournal.html?year=2017&vol=041&page=573
Characteristics of Myofascial Pain Syndrome
of the Infraspinatus Muscle
Objective
To report the characteristics of myofascial trigger points (MTrPs) in the infraspinatus muscle and evaluate the therapeutic effect of trigger-point injections.
Methods
Medical records of 297 patients (221 women; age, 53.9±11.3 years) with MTrPs in the infraspinatus muscle were reviewed retrospectively. Because there were 83 patients with MTrPs in both infraspinatus muscles, the characteristics of total 380 infraspinatus muscles with MTrPs (214 one side, 83 both sides) were investigated. Specific characteristics collected included chief complaint area, referred pain pattern, the number of local twitch responses, and distribution of MTrPs in the muscle. For statistical analysis, the paired t-test was used to compare a
visual analogue scale (VAS) before and 2 weeks after the first injection.
Results
The most common chief complaint area of MTrPs in the infraspinatus muscle was the scapular area. The most common pattern of referred pain was the anterolateral aspect of the arm (above the elbow). Active MTrPs were multiple rather than single in the infraspinatus muscle. MTrPs were frequently in the center of the muscle.
Trigger-point injection of the infraspinatus muscle significantly decreased the pain intensity. Mean VAS score decreased significantly after the first injection compared to the baseline (7.11 vs. 3.74; p<0.001).
Conclusion
Characteristics of MTrPs and the therapeutic effects of trigger-point injections of the infraspinatus muscle were assessed. These findings could provide clinicians with useful information in diagnosing and treating myofascial pain syndrome of the infraspinatus muscle.
Keywords
Infraspinatus, Myofascial pain syndromes, Trigger points, Pain, Injections
INTRODUCTION
Nonspecific complaints of pain near the scapula are commonly encountered, and may originate from any disorder of the cervical spine or shoulder joint. In some cases, however, pain near the scapula appears without any relation to the cervical spine or shoulder, and additional clinical studies are required to reveal possible causes of pain and to find the effective treatments.
Myofascial trigger points (MTrPs) may offer an alternative explanation for the pathophysiological mechanism of scapular pain. Although MTrPs are rarely a primary origin of pain [1,2], evidence suggests that MTrPs are caused by or related to a lesion in another soft tissue, such as spine disorder or rotator cuff disease [2,3]. MTrPs are local points that are highly sensitive to pressure.
Their palpation causes characteristic referred sensations, including pain, muscle dysfunction, and sympathetic hyperactivity [4-6]. MTrPs are classified into active and latent. Active MTrPs present clinical pain with or without activity associated with tenderness in a taut band, whereas latent MTrPs are clinically quiescent and are painful only when palpated.
Based on our clinical experiences, many patients with or without spine or rotator cuff diseases also have scapular pains that originate in the infraspinatus muscle. The infraspinatus muscle, a thick and triangular muscle, occupies the chief part of the infraspinatus fossa and assists external rotation of the arm and stabilization of the humerus head during an arm movement [7]. Active MTrPs in this muscle cause both local pain and referred pain in the shoulder region and down to the frontal and lateral side of the arm [5].
The infraspinatus muscle frequently harbors MTrPs. In one study with 126 patients, referred pain to the shoulder region arose from the infraspinatus muscle in 31% of the cases, a frequency second only to that of the levator scapulae (55%) [8]. Another study reported similar results [9]. Among young, pain-free adults, the infraspinatus muscle was the third (18%) in the prevalence of latent MTrPs, following the levator scapulae (20%) and the upper trapezius (35%) [10].
We recently observed many patients who were compatible with the criteria of MTrPs in the infraspinatus muscle, as assessed by careful history taking and physical examination. In treating these patients, we found some differences from previous studies [11] in the chief complaint area, referred pain pattern, distribution of MTrPs, and therapeutic effect of trigger-point injection.The objectives of this study were to report on the characteristics of MTrPs in the infraspinatus muscle.
MATERIALS AND METHODS
Participants
After Institutional Review Board approval, we retrospectively reviewed the medical records of 446 patients with suspected MTrPs in the infraspinatus muscle who had visited the outpatient clinic of Severance Hospital between March 2013 and November 2015 in order to identify all eligible patients (4-2015-1049).Diagnosis of active MTrPs was based on prior criteria, including tender spots in the infraspinatus muscle, a compatible pattern of referred pain elicited when tender spots were compressed, restricted range of motion of the shoulder, and palpable or visible local twitch responses (LTRs) at the most sensitive spot in the taut band. LTRs were elicited and assessed during trigger-point injections. Since needling is more sensitive than manual palpation in identifying LTRs, the needling method was chosen to confirm the presence of MTrPs.
Among patients with MTrPs in the infraspinatus muscle, those who met the following criteria were included in this study: MTrPs of muscle and fascia, exclusive of enthesopathy; pain score measured by a visual analog scale (VAS) greater than 2 (≥3) on a numeric scale of 0−10; and
having a trigger-point injection. Patients were excluded if they had: (1) received treatment that could affect the result (such as pain killers, physical therapy, or other injection therapy) from 2 weeks before intervention and through the follow-up period; (2) some other systemic disease that could present the same symptom (e.g., fibromyalgia); (3) neurologic shoulder/scapular pain (e.g., cervical radiculopathy or peripheral nerve injury); and (4) previous history of an adverse effect of lidocaine or steroid, or any conditions or situations that might place the patient at significant risk during the injection.
However, if the patient met the criteria of MTrPs in the infraspinatus muscle, they were not excluded even if they had a history of the rotator cuff and/or cervical spine disease.Characteristics of Myofascial Pain Syndrome of the Infraspinatus Muscle.
Trigger-point injection
All injections were performed under ultrasound (US)-guided injection. However, this retrospective design of the sdeep pelvic muscles, and the brachialis muscles was modified for MTrPs in the infraspinatus muscles [12-14]. We performed B-mode, real-time US in a sterile environment using an Accuvix V10 US machine (Medison, Seoul, Korea) interfaced with a 5- to 12-MHz linear array transducer around the target muscle. A physiatrist with more than 8 years of experience in the musculoskeletal US carried out all the US-guided injection procedures.
The patients lay prone on an examination bed with the affected arm extended, internally rotated, and adducted, and try to reach the thoracic spine—that is, in a position similar to the surgical “chicken wing” position for injection procedures (Fig. 1). With this position, we could easily and safely approach the infraspinatus muscle by separating the scapular bone from the surrounding tissues.
We differentiated the infraspinatus muscle from the deltoid, trapezius, teres major, teres minor, and latissimus dorsi muscles by US scanning and marked the tender points on the skin by palpating the muscle. By positioning the probe on the marked points and turning the probe for the best view, we obtained the image of the target area (Figs. 1, 2). Color Doppler images were used to avoid the neurovascular bundle. Under US guidance, a 25-gauge, 2.6-cm needle connected to a 5-mL syringe containing a mixture of 4 mL of 0.5% lidocaine and 1 mL of 40 mg of triamcinolone was inserted into the infraspinatus muscle at the region where the tender spot was palpated. In the case of multiple tender spots in one muscle, the injections were repeated for all tender spots.
The sequence of the injection sites was determined at each treatment period in terms of the decreasing order of pain severity in the tender points when palpated. The injection volume per tender point was 0.5 mL. No more injections were done once all the prepared solution of 5 mL had been used up (at most, there could be 10 injections per treatment session) or when no more palpated tender point were found. With the use of an out-of-plane method, we could see the needle passing through the skin and adipose tissue to penetrate the muscle. The physiatrist observed the LTRs on the US while performing the trigger-point injections. The needling was repeated to elicit as many LTRs as possible. If no LTR was observed after 10 attempts, the needling was stopped and a mixture solution was injected. The injection site was pressed to ensure proper hemostasis after the procedure. Trigger point injections were carried out in all MTrPs of the muscle at 2-week intervals. Additional injections were not considered if patients were satisfied with the reduction in discomfort or pain severity, or if patients did not want another injection for some reason. The patients were taught to do stretching exercise (repeated 10−20 times daily) and to avoid any posture that might aggravate the symptoms.
Data collection
Demographic and clinical data including age, gender, affected side, and the duration of symptoms were collected. Pain intensity, duration of symptoms, chief complaint area, referred pain pattern, the number of injections, and the number of LTRs were recorded, and the distribution of MTrPs in the muscle was established in terms of the sites of LTRs that were given US-guided injections (Fig. 3).
Pain intensity was measured by using a 10-cm horizontal VAS, which ranged from 0 (no pain) to 10 (worst imaginable pain). VAS was assessed at baseline and at 2 weeks after each injection.
Statistical analyses
We carried out descriptive analyses of patient informa-tion and characteristics of MTrPs in the infraspinatus muscle. For patients with MTrPs in both infraspinatus muscles, pain intensity, duration of symptoms, chief complaint area, referred pain pattern, the number of injections, and the number of LTRs were evaluated on each side. Evaluation of the effect of the trigger-point injections used the Shapiro-Wilk test of the VAS data acquired at baseline and at 2 weeks after the first injection to find out whether the distribution was normal. When the Shapiro-Wilk test showed a normal distribution for these parameters, a paired t-test was used to compare parameters before and 2 weeks after the first injection. Statistical significance was set at a p-value of <0.05. SPSS ver. 21.0 software (IBM, Armonk, NY, USA) was used for all statistical analyses.
RESULTS
We reviewed the medical records of 446 patients with suspected MTrPs in the infraspinatus muscles between March 2013 and November 2015. Of these, 297 patients (221 females and 76 males) were eligible for this study.
Because there were 83 patients with MTrPs in both infraspinatus muscles, there were 380 cases of infraspinatus muscles with MTrPs that satisfied the inclusion criteria.
In 83 patients with MTrPs in both infraspinatus muscles, both muscles were evaluated separately for the duration, pain severity, chief complaint area, and pattern of referred pain. The demographic and clinical characteristics of 297 patients and the clinical characteristics of the 380 infraspinatus muscles with MTrPs are summarized in Table 1.
Among the 297 patients, there were 103 with a medical history of shoulder disease, including rotator cuff disease (n=103, 34.7%), sports or work-related injury without shoulder and cervical spine disease (n=89, 30.3%). cervical spine disease (n=61, 20.5%), and shoulder disease combined with cervical spine disease (n=44, 14.8%). Among the patients with work-related injury, we found that 17 (5.7%) took care of the children.
In the 380 infraspinatus muscles with MTrPs, the most common chief complaint area was the scapular area; the next most common was deep in the front of the shoulder (Table 1). One hundred thirty-one cases had referred pain except in the areas of chief complaint; the most common area was the anterolateral aspect of the arm (above the elbow) (Table 2).
The LTRs necessary for diagnosing MTrPs were identified in all 380 infraspinatus muscles. However, the number of LTRs was recorded in the medical charts for only 153 cases. Of these, 38 cases (24.8%) had fewer than 5 LTRs. Cases with 6–10, 11–15, 16–20, and >10 LTRs were 45 (29.4%), 46 (30.1%), 24 (15.7%), and 70 (45.8%), respectively.
Fig. 3 summarizes the distribution of MTrPs in the infraspinatus muscles based on the scapular bone in 297 patients. For all 380 cases, 1,468 MTrPs were found, averaging 4.9 MTrPs per muscle.
Among the 380 cases, the effect of the trigger-point injections was assessed for 135 cases. One injection was given to 16 (11.9%) of the 135 patients, 2 injections at an interval of 2 weeks for 88 patients (65.2%), and 3 injections every 2 weeks for 31 patients (23.0%). There was a significant decrease in the VAS at 2 weeks after the first injection compared to the baseline (p<0.001). The mean value decreased significantly from 7.11 (SD=1.45) pretreatment to 3.74 (SD=1.53) after the first treatment.
DISCUSSION
There are three important findings in this study. First, one of the main symptoms of MTrPs in the infraspinatus muscle is scapular pain. Second, active MTrPs were almost always multiple rather than single in the infraspinatus muscle on the painful side. Third, inactivation of active MTrPs in the infraspinatus muscle significantly decreased pain intensity.
The main symptom of MTrPs in the infraspinatus muscle was pain deep in the front of the shoulder, including the anterior deltoid area, in previous studies [9,15-18]. Although the pain from MTrPs was frequent deep in the front of the shoulder, pain in the scapular area was more
common in this study. These findings may depend on the differences in the definition of the MTrPs, the patient population, and the exactitude of the questions asked to patients during the medical examination.
First, MTrPs can exist within skeletal muscle tissue, aponeurosis (fascia) of the muscle, or the tendon, but this study was restricted to MTrPs within the infraspinatus muscle tissue and/or fascia of the muscle, which is the most common type of MTrPs [19].
Second, we did not exclude patients who had a history of cervical spine disease or shoulder lesion if the patients met the criteria of MTrPs in the infraspinatus muscle. Third, because patients may not be able to distinguish scapular pain from shoulder pain, the physiatrist asked questions to find out if the pain presented exactly around the scapular area during the medical examination. If the physiatrist did not ask specifically about scapular pain, a patient could have thought the question was about shoulder pain.
Referred pain is a pain felt in other than the true site of origin [20]. In this study, the locations of referred pain from MTrPs in the infraspinatus muscle were, in order of frequency, the anterolateral aspect of the arm (above the elbow), the lateral forearm, the upper posterior neck, and the radial aspect of the hand (including a finger). Our
results were similar to those of a study of 193 patients, in which the anterolateral aspect of the arm (46%) was the most frequent site of the referred pain, followed by the lateral forearm (21%), the posterior neck (14%), and the radial aspect of the hand (13%) [9,11,15,16,18,21,22].
When the referred pain is on the radial aspect of the hand, it was especially important to differentiate it from cervical radiculopathy, mainly at the C5 or C6 level [23].
The range and site of the referred pain can depend on the location and intensity of the MTrPs in the infraspinatus muscle, and further study is required. MTrPs in the infraspinatus and teres minor muscles often occur together and are often incorrectly assessed as rotator cuff lesions or cervical discogenic pain. In addition, MTrPs in the infraspinatus muscle are often incorrectly assessed as osteoarthritis of the shoulder joint, entrapment of the suprascapular nerve, or bicipital tendinitis [19]. Also, MTrPs in the infraspinatus muscle should be differentiated from those in the teres major, supraspinatus, anterior deltoid, subscapularis, and pectoralis major muscles [19].
One of the main contributions of our study is the finding that there were multiple, not just single, active MTrPs in the infraspinatus muscle on the painful side. Furthermore, there are many LTRs per infraspinatus muscle, and cases of more than 10 LTRs were frequently observed (45.8%). If LTRs are elicited during injection, especially if the fast-in–fast-out technique was used, immediate pain relief could be achieved more often [24,25]. Patients can fail to experience immediate and complete pain relief if the LTRs are not elicited during a trigger-point injection.
After injection into one responsive locus, other LTRs can be elicited. These procedures should be repeated until all (or as many as possible) responsive loci are injected [26]. To our knowledge, the number of LTRs has not been reported previously. Therefore, these results highlight the importance of searching for multiple active MTrPs regions and LTRs within one muscle in patients with myofascial pain syndrome in the infraspinatus muscle. Multiple MTrPs in the same muscle can each contribute to the overall referred pain pattern.
Trigger-point injection of the infraspinatus muscle resulted in excellent outcomes, and VAS scores decreased after treatment. We suggest that, in a patient with MTrPs in the infraspinatus muscle, trigger-point injection of the infraspinatus is effective for both diagnosis and treatment when the scapular pain is suspected to originate from the
infraspinatus muscle.
MTrPs in the infraspinatus are usually activated by an acute stress or by multiple overload stresses. These MTrPs may become active and induce pain under the influence of certain perpetuating factors, such as repetitive and sustained shoulder activities [27,28]. This could be the explanation for the 17 patients without shoulder lesion who took care of children. When the shoulder is abducted and flexed, the infraspinatus muscle shows less activity than the supraspinatus muscle [29]. However,
there is a marked increase of infraspinatus activity at over 140°of abduction. Therefore, when the patient carries heavy loads for a long time with the shoulder abducted above the acromion level, the infraspinatus muscle could be damaged. These mechanisms could explain the cases of MPS in women without underlying disease who were actively involved in child care. Since the infraspinatus muscle, unlike the supraspinatus muscle, is likely to be strongly activated in movements that are unusual and transient, acute overload could be much more likely to develop MTrPs than tasks that impose a sustained overload [11].
The muscle imbalance may also keep the MTrPs active and induce recurrent pain. Since MTrPs can induce changes in normal muscle-activation patterns and subsequent motor dysfunction, identifying and inactivating MTrPs should improve motor function, release muscle stiffness, and restore normal biomechanics of the shoulder [30].
It is important to know the common sites of MTrPs in the infraspinatus muscle in order to provide guidance on the clinical identification of MTrPs in this muscle. Careful palpation frequently discloses multiple tender spots in the infraspinatus muscle as indicated by the multiple lesions. In previous studies, the most common MTrPs region was caudal to the junction of the most medial and adjacent quarter of the length of the scapular spine (upper medial lesion) [11]. The next most common MTrPs region was caudal to the midpoint of the scapular spine (lateral upper lesion) [11]. In this study, the common MTrPs region was similar to that found by Travel, but was more broadly positioned, and the inferior angle of the scapula was more frequently observed. Because the infraspinatus muscle is quite broad and palpating all of it during the physical examination could be time-consuming, this study could provide a helpful guideline for identifying MTrPs in the infraspinatus muscle.
US-guided injection is useful for detecting LTRs in deeply located muscles and for controlling the depth during injection for even less-accessible muscles. US guidance can also reduce inadvertent injuries that could be caused by improper needle placement. It might seem unnecessary to use US-guided injection, because the infraspinatus muscle is located superficially, and the needle is less likely to injure surrounding tissues, such as the lung, inadvertently. However, by using US-guided injection, we could observe more LTRs to improve the effects of injection, differentiate the neighboring teres major, deltoid, and trapezius muscles in order to diagnose more accurately, and provide feedback for the treatment by recording with built-in video. These strengths could be worthy of attention.
There are some limitations to be considered in our study. First, because the study was retrospective, we could have missed information required for accurate analysis.
Second, we conclude the therapeutic effects of trigger point injections without comparison to a control group. Nevertheless, we could not ignore the significant decrease in the VAS scale (more than 3 points) from injections during short-term treatment.
Third, we investigated only one referred pain pattern per case. If multiple tender points exist, there could be many different referred pain patterns depending on the location, number, and pain severity of the tender points. This is also a limitation of a retrospective study, which could be complemented by further prospective studies. Fourth, the follow-up period of the therapeutic effect of the trigger-point injections was relatively short. Although there was no long-term follow-up, the long-term effects of trigger-point injections for MPS in the infraspinatus
muscle would not differ from those for other muscles. If the underlying etiologic lesion cannot be eliminated, the effect of one trigger-point injection usually lasts about 2 weeks [13]. Inactivation of active MTrPs, however, is necessary for some situations, including the presence of severe and intolerable pain, pain or discomfort that interferes with functional activities, and persistent pain and tightness. The same principle can be applied to the infraspinatus muscle.
Fifth, the selected group of patients was not homogeneous. In particular, some patients with shoulder or cervical spine lesions were included in this study. MTrPs could be secondary to pathologic conditions such as chronic repetitive minor muscle strain, poor posture, systemic diseases, and musculoskeletal lesions (such as strain, sprain, enthesopathy, bursitis, arthritis, and spinal disc lesion) [2,3]. But for the patients with a history of shoulder or cervical spine lesion in our study, their lesions were not their main reason for visiting a clinic. In addition, their symptoms satisfied MTrPs criteria and, ironically, their MTrPs were less frequent than for patients without a history of shoulder or cervical spine lesion [1].
In conclusion, our findings of MTrPs in the infraspinatus muscle and the therapeutic effect of trigger-point injections in that muscle may provide clinicians with useful information in diagnosing and treating myofascial pain syndrome of the infraspinatus muscle.
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
