Anaesthesiologists rarely focus on the relationship between the omohyoid muscle and the internal jugular vein. In 1988, early literature suggested that the omohyoid muscle was related to the blood flow of the internal jugular vein [6, 7]. There were few reports of further study, which might be due to various reasons. For example, early ultrasound-guided technology was rarely used in internal jugular vein catherization. Locating and studying the omohyoid muscle was technically challenging. In addition, the omohyoid muscle is easily ignored in a clinical setting. The literature reports that, in the clinical setting, omohyoid muscles are more often used as the hypoglossal muscle valve for surgical repair after floor of the mouth cancer[8]. At the same time, omohyoid muscle syndrome is rare. The disease is primarily caused by genetic factors[9], which may explain the lack of focus on the relationship between the omohyoid muscle and the internal jugular vein. However, through the research of some scholars, we can still see a close anatomical relationship between the two [7]. In addition, we can still find a close relationship between the two in clinical work (see Fig. 8). In addition, we have observed in clinical work that in some cases, obvious neck discomfort (including the pharynx and shoulder) will appear after internal jugular vein catheterization. In some cases, it is more apparent when swallowing. After ultrasonic examination, it was suspected that the discomfort might be related to the catheter penetrating and connecting the omohyoid muscle during internal jugular vein catherization[10] (see Fig. 9).
Our study mainly observed the anatomical relationship between the omohyoid muscle and the internal jugular vein in two planes under ultrasound guidance. The selection of the two planes corresponds to the punctured plane of the traditional middle method and posterior method for internal jugular vein puncture. The main results included the overlap of the IJV and OM at the corresponding head angle for each plane and the anatomical angle α of the IJV under ultrasound with OM. We found that the lower the punctured plane was, the more significant the overlap and α of the IJV and OM.
The overlapping relationship between OM and IJV has not been previously documented. Our results showed that there was no significant difference in the overlap of the IJV and OM at different head angles on the same plane. Then, the number of overlapping cases, OWOI, and the OR of PST planes in different planes with the same angle are smaller than those of the PSL plane. This also indicates a greater likelihood of injury to the omohyoid muscle by a puncture at a relatively low level.
The results show that for the α angle in the PST plane, the median values of the three individual bit angles were 14.17°, 14.97°, and 12.89°, indicating that the OM is mainly located on the upper medial side of the IJV in the PST plane. The α angle in the PSL plane was larger, and the median values of the three individual bit angles were 62.75°, 45.68°, and 107.33°, indicating that the right OM was mainly located on the medial and lateral surfaces of the right IJV. The PST plane was the insertion point for our middle puncture. Generally, the puncture needle was oriented towards the posterolateral during middle puncture, which also suggested that the probability of injury to omohyoid muscle during middle puncture was lower. However, the PSL plane corresponds to the posterior puncture point, and the OM below the PSL plane is mainly located on the upper and lateral sides of the IJV, and the needle insertion direction of posterior puncture is generally towards the posterior and medial sides, which also indicates that the probability of passing through the omohyoid muscle during puncture is higher.
The levels of PST and PSL correspond to the puncture planes of the traditional middle method and posterior method for internal jugular vein puncture. Based on the results of this study, it can be seen that the traditional middle approach, if the insertion point plane is too low or the traditional posterior approach is chosen, is more likely to damage the omohyoid muscle and cause discomfort to the patients. At present, in many hospitals, it is impossible to perform internal jugular vein catheterization under ultrasound guidance. The traditional middle route puncture point was selected at the top of the triangle, where the sternal head at the lower end of the sternocleidomastoid muscle and the clavicle meet, which could effectively avoid injury to the omohyoid muscle, to an extent. Even ultrasound-guided catheterization of the internal jugular vein can cause damage to the omohyoid muscle if it is not well recognised. Therefore, it is crucial for clinicians to popularize the anatomical relationship between the omohyoid muscle and the internal jugular vein.