利用高频超声评估正常胸锁乳突肌的内部精细结构及其变异，为胸锁乳突肌病变的诊断及肌瓣选择提供依据。

2022年5月至6月应用高频超声获取91名健康志愿者的双侧共182条胸锁乳突肌的长轴、短轴切面声像图，观察其全程形态、内部回声、解剖变异。测量乳突与胸锁关节连线中点处胸锁乳突肌总体厚度、各部分肌束厚度；锁骨上缘、胸骨上缘止点处肌肉肌腱整体宽度；距锁骨、胸骨止点上缘1 cm处内部腱膜宽度、厚度；锁骨头、胸骨头肌束内腱膜长度。采用独立样本t检验比较左侧与右侧、男性与女性的各测值的差异，采用方差分析比较胸锁乳突肌各部分厚度差异，并使用Pearson双变量相关分析检验胸锁乳突肌总厚度、各部分厚度与体质量指数是否相关。

高频超声可以清晰地显示胸锁乳突肌的头侧端止于上项线和乳突，足侧端止于胸骨和锁骨前上缘。动态扫查过程中，胸锁乳突肌的乳突锁骨束、乳突胸骨束、枕骨锁骨束、枕骨胸骨束彼此较易分辨，乳突与胸锁关节连线中点处胸锁乳突肌整体及4个部分厚度测量值分别为：（0.90±0.16）cm、（0.54±0.13）cm、（0.68±0.14）cm、（0.40±0.10）cm、（0.28±0.09）cm，双侧测值比较，差异均无统计学意义（P均＞0.05），男性与女性测值比较，差异均具有统计学意义（P均＜0.05），各部分厚度的测值两两比较，差异均有统计学意义（P均＜0.05）。91人中有7例（7.69%）可见锁骨止点变异，即存在2个锁骨头，均发生在单侧。乳突与胸锁关节连线中点处胸锁乳突肌总厚度、各肌束厚度，锁骨上缘、胸骨上缘止点处宽度，距锁骨、胸骨止点上缘1 cm处内部腱膜宽度、厚度，锁骨头、胸骨头肌束内腱膜长度的双侧测值差异均无统计学意义（P均＞0.05），上述测量项目中，除距锁骨、胸骨止点上缘1 cm处内部腱膜厚度及胸骨头肌束内腱膜长度外，男性、女性测值差异均具有统计学意义（P均＜0.05）。体质量指数与胸锁乳突肌总厚度及各部分厚度的Pearson相关系数为0.286~0.371（P＜0.01）。

高频超声能够准确评估胸锁乳突肌的内部精细结构、识别其变异，有助于胸锁乳突肌病变的诊断及为肌瓣的精准选择提供参考。

To explore the feasibility of using high-frequency ultrasound to observe the internal structure and composition of the sternocleidomastoid muscle, in order to provide a basis for the diagnosis of sternocleidomastoid myopathy and the selection of sternocleidomastoid muscle flaps.

High-frequency ultrasound was used to obtain long-axis and short-axis sonograms of 182 sternocleidomastoid muscles in 91 healthy volunteers from May to June 2022. The shape, internal echo, and anatomical variation were observed. The total thickness of the sternocleidomastoid muscle and the thickness of muscle bundles at the midpoint of the line connecting the mastoid and the sternoclavicular joint, the width at the upper edge of the clavicle and the insertion point of the upper edge of the sternum, the width and thickness of the internal aponeurosis 1 cm above the upper edge of the clavicle and the upper edge of the insertion of the sternum, the thickness of the tendon at the insertion point of the clavicle head and the upper border of the sternum, and the length of the aponeurosis within the muscle bundle of the clavicle head and the sternum head were measured. The t-test was used to compare the mean values and differences between the left side and right side and between males and females. The thickness difference of each part of the sternocleidomastoid muscle was compared by analysis of variance, and the correlation between the total thickness of the sternocleidomastoid muscle and the thickness of each part and BMI was analyzed by Pearson correlation.

High-frequency ultrasound can clearly display the whole course of the sternocleidomastoid muscle and its four-part structure, as well as the variations. The cephalic end of the sternocleidomastoid muscle inserts on the upper nuchal line and the mastoid process, and the foot end inserts on the sternum and the anterior superior border of the clavicle. During the dynamic scanning, it can be seen that the sternocleidomastoid muscle is composed of four parts, namely, the mastoid-clavicular bundle, the mastoid-sternal bundle, the occipital-clavicular bundle, and the occipital-sternal bundle. At the midpoint between the mastoid process and the sternocleidomastoid joint, the average thickness of the whole sternocleidomastoid muscle and its four parts was (0.90±0.16) cm, (0.54±0.13) cm, (0.68±0.14) cm, (0.40±0.10) cm, and (0.28±0.09) cm, respectively. There was no statistically significant difference in the muscle thickness between the two sides (P＞0.05), but there was a statistically significant difference between males and females (P＜0.05). There were statistically significant differences in the measured thickness of each part (P＜0.05). Pairwise comparisons of the measured values of these thicknesses showed that the differences were statistically significant (P＜0.01). Seven of the 91 cases (7.69%) showed the variation of the clavicle end, all of which occurred unilaterally, with two clavicle heads. The total thickness of the sternocleidomastoid muscle at the midpoint of the line between the mastoid and the sternoclavicular joint, the thickness of each muscle bundle, the width at the upper edge of the clavicle and the sternum, and the width of the internal aponeurosis 1 cm above the upper edge of the clavicle and the sternum showed no significant difference (P＞0.05). There was no significant difference in the bilateral measurement of the length of the aponeurosis within the clavicular head and the sternal head (P＞0.05). Among the above measurements, except for the thickness of the internal aponeurosis 1 cm above the upper border of the clavicle and sternum insertion, and the length of the aponeurosis wthin the muscle bundle of the sternum head, the difference between males and females was statistically significant (P＜0.05). The Pearson correlation coefficients between BMI and the total thickness of sternocleidomastoid muscle and the thickness of each part were 0.286-0.371 (P＜0.01).

High-frequency ultrasound is an effective imaging tool for evaluating the fine internal structure of the sternocleidomastoid muscle and identifying its variation, which provides a reference for the diagnosis of sternocleidomastoid myopathy and the precise selection of muscle flaps.