Localization of the Center of the Intramuscular Nerve Dense Region of the Suboccipital Muscles: An Anatomical Study

Abstract

Purpose: This study aimed to determine the body surface puncture position and depth of the center of the intramuscular nerve dense region in the suboccipital muscle to provide morphological guidance for accurate botulinum toxin A injection to treat headaches caused by increased suboccipital muscle tension.

Methods: Twenty-four cadavers aged 66.5 ± 5.3 years were studied. The curve line connecting occipital eminence or mastoid process and spinous process of the 7th cervical vertebrae was considered the longitudinal reference line (L) and horizontal reference line (H), respectively. Sihler's staining, barium sulfate labeling, and CT were employed. The body surface projection point of the center of the intramuscular nerve dense region was designated as P. The projection of the center of the intramuscular nerve dense region was in the opposite direction across the transverse plane and was recorded as P'. The intersections of the vertical line through point P and lines L and H were designated as P_L and P_H. The percentage position of the P_H and P_L points on the H and L lines and the depths of the center of intramuscular nerve dense regions were identified.

Results: Sihler's staining showed one intramuscular nerve-dense region in each suboccipital muscle. The P_H of the center of the intramuscular nerve dense region was located at 51.40, 45.55, 20.55, and 43.50%. The P_L was located at 31.38, 30.08, 16.91, and 52.94%. The depth of the center of the intramuscular nerve dense region was at 22.26, 22.54, 13.14, and 27.30%. These percentage values are all the means.

Conclusion: Accurately defining the body surface position and depth of the center of intramuscular nerve dense region in suboccipital muscles will help to improve botulinum toxin A to target localization efficiency for treating tension-type headache.

Keywords: botulinum toxin A; center of intramuscular nerve dense region; suboccipital muscle; target localization; tension-type headaches.

Figure 1

Common types of right suboccipital nerve entry points. 1, Rectus capitis posterior minor muscle. 2, Rectus capitis posterior major muscle. 3, Obliquus capitis superior muscle. 4, Obliquus capitis inferior muscle. 5, Greater occipital nerve. The red, green, blue, and white dots represent the nerve entry points of the rectus capitis posterior minor, rectus capitis posterior major, obliquus capitis superior, and obliquus capitis inferior muscles, respectively.

Figure 2

Overall distribution pattern of intramuscular nerves and position of nerve-dense region of the suboccipital muscle. (A–D) Showing the Sihler's staining of the rectus capitis posterior minor muscle, rectus capitis posterior major muscle, obliquus capitis superior, and obliquus capitis inferior muscles, respectively. The red boxes showing the intramuscular nerve dense regions, and the red points represent the center of the intramuscular nerve dense regions. Scale: cm. (E) A schematic drawing showing the intramuscular position of INDRs and CINDRs.

Figure 3

CT images of the center of intramuscular nerve dense region (CINDR₁) of left rectus capitis posterior minor. (A) Spiral CT three-dimensional reconstruction image shows the body surface projection position and design reference line of the CINDR. Point a is the external occipital protuberance, point b is the mastoid process, and point c is the spinous process of the 7th cervical spine. P₁ is the body surface projection point of CINDR₁ of rectus capitis posterior minor. ac line = L reference line, a-P_1L = L₁'; bc = H reference line, and b-P_1H = H₁'. (B) The length of the L reference line and L₁' line on the sagittal section through the ac line. (C) The length of the H reference line and H₁' line on the cross-section passing through the bc line. (D) The depth of CINDR₁, measured on the cross-section through P₁.