Surgical and Radiologic Anatomy

, Volume 28, Issue 3, pp 228–234

The medial branch of the lateral branch of the posterior ramus of the spinal nerve

Authors

    • Department of AnatomyNippon Medical School
  • Masami Yoshimoto
    • Department of AnatomyNippon Medical School
  • Yoshiyuki Yamamoto
    • Department of AnatomyNippon Medical School
  • Takayoshi Miyaki
    • Department of AnatomyTokyo Medical University
  • Masahiro Itoh
    • Department of AnatomyTokyo Medical University
  • Shogo Shimizu
    • Department of Anesthesia, School of DentistryNihon University
  • Yoshiyuki Oi
    • Department of Anesthesia, School of DentistryNihon University
  • Wolfgang Schmidt
    • Institute of AnatomyUniversity of Leipzig
  • Hanno Steinke
    • Institute of AnatomyUniversity of Leipzig
Original Article

DOI: 10.1007/s00276-006-0090-3

Cite this article as:
Saito, T., Yoshimoto, M., Yamamoto, Y. et al. Surg Radiol Anat (2006) 28: 228. doi:10.1007/s00276-006-0090-3
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Abstract

In the needle insertion of epidural anesthesia with the paramedian approach, the needle can pass through the longissimus muscle in the dorsum of the patients. When the needle touches a nerve in the muscles, the patients may experience pain in the back. Obviously, the needle should avoid the nerve tract. To provide better anesthetic service, analysis of the structure and where the concerned nerves lie in that region is inevitable. Material and method: We studied five cadavers in this study. Two cadavers were fixed with Thiel’s method. With these cadavers, we studied the nerve running of the posterior rami of the spinal nerve from the nerve root to the distal portion. Three of them were used for the study of transparent specimen, with which we studied the course and size of the nerve inside the longissimus muscle. Results: We observed there were three branches at the stem of the posterior rami of the spinal nerves between the body segment T3 and L5, i.e. medial branch, medial branch of the lateral branch and lateral branch of the lateral branch. The medial branch of the lateral branch supplied to the longissimus muscle. With the transparent specimen, we found that there were different nerve layouts between the upper thoracic, lower thoracic, upper lumbar, and lower lumbar segments in the medial branch of the lateral branch in the longissimus muscle. In the lower thoracic and upper lumbar segments, the medial branch of the lateral branch of the upper lumbar segments produced layers nerve network in the longissimus muscle. L1 and L2 nerves were large in size in the muscle. Conclusion: In the upper lumbar segments the medial branch of the lateral branch of the posterior rami of the spinal nerve produced dense network in the longissimus muscle, where the epidural needle has high possibility to touch the nerve. Anesthetists have to consider the existence of the medial branch of the lateral branch of the posterior rami of the spinal nerve when they insert the needle in the paramedical approach to the spinal column.

Keywords

Spinal nervePosterior ramusMedial branchTransparent specimenLongissimus muscleAnesthesia

Introduction

After Cathelin FM started caudal anesthesia in 1901 and Dogliotti AM tried lumbar epidural anesthesia in 1933, epidural anesthesia has become very popular in the management of surgical interventions. During the needle insertion in the epidural anesthesia, patients sometimes complain of pain in the back at the needle insertion. This is because the needle touches or pierces a nerve in the longissimus and spinous muscles. Although the textbooks require topical anesthesia in advance of the insertion of the needle, they do not describe even where to anesthetize [1,2,5,9].

In the paramedian approach in the epidural anesthesia where the needle can aim the epidural space through the narrow spatium intervertebrale independent from the shape of spinous process, the needle may pass through the longissimus muscle. Therefore, we think that it is worthwhile examining the nerve layout in the longissimus muscle.

Materials and methods

We studied five cadavers in this study (Table 1).
Table 1

Demographic data of the cadavers

 

Sample No.

Sex

Age

Cadavers for transparent specimens

1

M

76

2

F

71

3

M

89

Cadavers fixed with Thiel’s method

1

M

93

2

M

79

The cadavers with cancer in the posterior chest wall were excluded from the subject in this study

Step 1: study of the posterior rami of the spinal nerve with fixed cadavers

The first step in this study was to investigate the proximal portion of the posterior rami. Two cadavers were allocated to this study. The cadavers were fixed by Thiel’s methods [12,13]. After performing the Thiel’s methods, their vertebral columns between T3 and L5 with dorsal muscles were taken from the rest of the cadaver body. The limit of the specimen was decided by the range of the actual epidural anesthesia. We had enclosed both sides of the latissimus dorsi and the dorsal muscles. We had cut out the ribs bilaterally at the lateral border of the latissimus dorsi correspondingly. To take out the specimen from the cadavers the quadrates lumborum and the psoas muscles were dissected. The aorta, the heart and the lungs were removed from the specimen. The corpus vertebrae, spinal cord and the processus transverses were removed. On these blocks, we studied the tract of the posterior rami of the spinal nerve from the anterior region toward the posterior, i.e. from the proximal region toward the distal. This study enabled us to examine the branching pattern of the posterior rami near the stem to the rami.

Step 2: study with transparent specimens

Three cadavers contributed to this study. We took the musculus longissimus between T2 and L5 to use for the study. This muscle bloc was processed to make a transparent specimen with the modified Spalteholz’s technique [8,11]. With the transparent specimens, we studied the course and the size of the posterior branches in the longissimus muscle.

For the first specimen, we removed the back muscle of a 76-year-old male together with the skin from the posterior surface of the vertebras and the ribs. That is, the longissimus and a part of the spinous muscles were dissected at the posterior surface of the rib, of the intercostal muscles, of the transverse process, of the intertransversal ligament, of the arcus vertebrae, of the ligamentum flavum, of the spinous process, and of the interspinous ligament. The skin, subcutaneous tissue and the iliocostalis muscle were removed from the specimen. The specimen was made of the longissimus and the part of the spinous muscles. To stain the nerves we used toluidine blue [6]. After that we bleached the specimen and performed a freeze substitution [10]. However, this specimen was not used for further anatomical analysis because the staining was not satisfactory. Toluidine caused rapid browning of the whole specimen, which let us abandon the specimen.

The second specimen was a longissimus muscle of a 71-year-old female. For the second specimen, we adopted iron alum for staining. We bleached and dehydrated the specimen to obtain bright tissue [11]. In the process of impregnation, we cut the muscle block into about four segments, so that each block can get the maximum effect of benzyl benzoate. The transparent specimens were mounted in glass cubes, and we examined the nerve running inside the specimen without any traumatic damage to the specimen.

The last specimen was sectioned from the backside of an 89-year-old male. We used the Thiel nerve fermentation methods [12,13] combined with bleaching and dehydration [7] and tanning with iron alum and made the specimen transparent, thereafter [8].

Results

Step 1

Figure 1 shows branching of the posterior ramus at the proximal region at the T4 segment. To examine the branching pattern at the stem of the posterior ramus, the processes transverses were removed. We could see one medial branch and one lateral branch in the posterior ramus. The lateral branch divided into two divisions at a more lateral point. The medial branch passed just above and posterior to the processes transverses of the one lower vertebra and turned around its arcus vertebrae. One of the two lateral branches supplied the iliocostalis muscle. The other branch supplied to the longissimus muscle.
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Fig. 1

The branch of the posterior rami of the spinal nerve at T4. Two branches were observed in the dissection, the medial branch (T4M) and the lateral branch. The lateral branch divides into to branches. One of the two branches supplies to the iliocostalis muscle (T4L). The other branch supplies to the longissimus muscle (simple arrow). Because the longissimus muscle is distant from the midline at this segment, the lateral branch is free from the needle insertion for the induction of regional anesthesia. T4A: ventral branch of the T4 spinal segment

Figure 2 shows branching of the posterior ramus at the proximal region at the T5 segment. The processes transverses were also removed. We also could see one medial branch and one lateral branch in the posterior ramus. The lateral branch divided into two divisions. The medial branch passed just above and posterior to the processes transverses of the one lower vertebra and turned around its arcus vertebrae. One lateral branch supplied to the iliocostalis muscle. The other branch supplied to the longissimus muscle.
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Fig. 2

The branches of the posterior ramus of the spinal nerve at T5. One medial branch and one lateral branch with branching are seen. The region behind the arcus vertebrae is thought to be supplied by the medial branch. Abbreviation, T5M: the medial branch, T5L: the lateral branch, T5A: the ventral ramus of the spinal nerve at T5

Figure 3 shows branching of the posterior ramus at the proximal region at T6 segment. At this segment, we could not find any lateral branch. We could only find the medial branch of the posterior ramus and the ventral ramus. The medial branch at T6 passed down the posterior surface of the processes transverses of T7 vertebra. We found that the medial nerve later turned along the arcus vertebrae. We could not follow the nerve further in this study.
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Fig. 3

The branches of the posterior ramus of the spinal nerve at T6. At this segment, we could not find any lateral branch of the posterior ramus at this segment. The medial branch turned along the arcus vertebrae and supplied the region behind the spinal column. Abbreviation, T6M: the medial branch, T6A: the ventral ramus of the spinal nerve at T6

Figure 4 shows branching at the posterior ramus at the T7 segment. We found one medial branch and one lateral branch, which branched again very near its stem. The medial branch as it went in the upper segments, passed down posterior to the processes transverses of the one caudal vertebra, and went along the posterior surface of the arcus vertebrae. The branch of the medial side of the lateral branch went to the lateral border of the longissimus muscle. The other branch (lateral side) of the lateral branch supplied iliocostalis muscle.
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Fig. 4

The branches of the posterior ramus of the spinal nerve at T7. We found one comparatively small medial branch in diameter, and two also small lateral branches. Abbreviation, T7M: the medial branch T6L and simple arrow: the lateral branches, T7A: the ventral ramus of the spinal nerve at T7

Figure 5 shows branching of the posterior ramus at T9. We could find one medial branch and two branches in the lateral branch as we saw in the all segments examined except for the T6 segment. In this segment, branching of the lateral branch was located very close to the branching of the medial and lateral branch. Therefore, the branch of the medial side of the lateral branch was like an intermediate branch in the posterior ramus. The medial branch ran along the posterior surface of the arcus vertebrae and supplied to the spinous muscles. The intermediate branch (which is the medial branch of the lateral branch) turned at the tip of the processes transverses, changed its direction rather medially and went posteriorly to supply to the longissimus muscle. The lateral branch went in the direction of the iliocostalis muscle.
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Fig. 5

Branching of the posterior ramus of the spinal nerve at T9. The medial branch and the intermediate branch went into the region posterior to the arcus vertebrae. The intermediate branch turned posterior to the tip of the processus transversus, and later supplied to the longissimus muscle. Abbreviations, T9M: the medial branch, T9L: the lateral branch, simple arrow: the intermediate branch of the posterior ramus, and T9A: the ventral branch of the spinal nerve at T9

Figure 6 shows branching of the posterior ramus at T11 segment in the third cadaver on the right side. At this segment, as at T9 and T10 and down to L2, there were three branches. The intermediate should be the same branch of the medial branch of the lateral branch of the posterior rami at the segments between T3 and T8, and between L3 and L5. But the branching point from the lateral branch is very near to the point of branching of the medial and the lateral branch, that the medial branch, the medial branch of the lateral branch (medial–lateral branch) and the lateral branch of the lateral branch (lateral–lateral branch) of the posterior ramus seemingly produced a triple branching pattern. The medial branch ran very close to the arcus vertebrae. The intermediate branch turned around the tip of the processes transverses of one lower vertebra, and ran toward the region behind the spinal column, probably to the longissimus muscle. We found that the medial branch and the intermediate branch supplied the region behind the spinal column. We could not identify the exact target in this study.
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Fig. 6

Branching of the posterior ramus of the spinal nerve at T11. Three branches were seen at this segment. The medial branch went medially. The intermediate branch went down posterior to the processus transversus. Both these branches supplied the posterior region of the spinal column. We could not follow further in this study

Figure 7 shows branching of the posterior ramus of the spinal nerve at L2. We saw three branches at this segment as well as T11, T12, and L1, the medial, intermediate and lateral branches. At these segments, the medial and the intermediate branch ran very close to the arcus vertebrae. The lateral branch supplied to the iliocostalis muscle.
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Fig. 7

Branching of the posterior ramus of the spinal nerve at L2. Three branches were still seen after we first found at T9 segment. The medial and intermediate branches supplied the region behind the spinal column. The lateral branch supplied to the iliocostalis muscle

Figure 8 shows branching of the posterior ramus of the spinal nerve at L3. While the medial branch went close to the posterior surface of arcus vertebrae, the lateral branches both went laterally. Like in the segments of the upper thoracic region, the branches of the lateral branch of the posterior ramus went deep laterally. At the segments of L3, L4, and L5, the medial branch and the lateral branch of the posterior ramus shrank in diameter. The patterns of branching below L3 were like that at L3. The pattern of branching in the lower lumbar segments was like those at T4, T5 segments.
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Fig. 8

Branching of the posterior ramus of the spinal nerve at L3. We saw one medial branch and one lateral branch. The medial branch went medially as it did at every segment. The lateral branch divided soon, into the what we call “intermediate” branch and “lateral” branch. However, the medial branch did not go close to the spinal column. The intermediate and the lateral branches supplied the regions lateral to the spinal column

Step 2

Figure 9 shows the transparent longissimus muscle taken from one cadaver. The nerves of T3, T4, and T5 ran from the medial side to lateral on the internal surface of the longissimus to supply the muscle. The fact that the nerves supply to the muscle from the medial side coincides with our previous observation with the fixed cadavers that the medial branch of the lateral branch of the posterior rami entered into the muscle from the medial side (Figs. 1, 2).
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Fig. 9

The transparent specimen of the longissimus muscle with a part of the spinous muscle in one cadaver at upper thoracic region. Three supplying nerves between T3 and T5 are seen. They supply the longissimus muscle from its the medial side. White arrow shows the medial side of the longissimus muscle

Figure 10 shows the transparent longissimus muscle in the lower thoracic region in the third cadaver in the study of transparent specimen. We could not find any trace of the nerves between T6 and T9, the medial branch of the lateral branch of the posterior ramus. At the segments between T10 and T12, the nerves are shown to enter the muscle from the lateral side and run medially and caudally toward the middle line. Therefore, in the thoracic region, the medial branch of the lateral branch of the posterior rami that entered the longissimus muscle from the medial side at the upper thoracic segments, could not be seen in the transparent muscle at the middle thoracic segments, entering from the lateral side at the lower thoracic segments.
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Fig. 10

The transparent specimen of the longissimus muscle in the other cadaver at the middle and lower thoracic region. The red arrow shows the mid line. While nerves supplying the longissimus muscle in the upper segment come from the medial side, the nerve in the lower segments comes from the lateral side to supply the muscle. The nerve to the longissimus muscle between the T6 and T9 was not seen in the transparent specimen

Figure 11 shows the transparent longissimus muscle of the more caudal region in the same cadaver. At the lower thoracic and the upper lumbar segments, the medial branch of the lateral branch of the posterior rami enter into the longissimus muscle from the lateral side. The nerves ran caudad and medially. They stratified in the longissimus muscle. The nerve at L2 was the biggest in diameter in the segments between T3 and L5. The nerve at L3 was the second biggest in diameter. At the lower lumbar segments of L4 and L5, the medial branch of the lateral branch could not be seen in the transparent longissimus muscle as they were between T6 and T9.
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Fig. 11

The transparent specimen of the longissimus muscle in the second cadaver at the lower thoracic and lumbar regions. All supplying nerves come from the lateral side of the muscle. The red arrow shows the mid line. Although the nerves enter into the muscle from the lateral border, they finally come close to the medial border within the muscle

Discussion

The longissimus muscle covers the spinous muscle and the vertebral column. The needle for anesthesia may pass through the longissimus muscle before the needle enters into the spinous muscles. When the needle touches any nerve, it is anticipated that the nerve is damaged to some extent. There is a recent report of the nerve damage of the medial branch of the posterior rami of the spinal nerve. Boelderl et al. reported the danger of damaging the medial branch of the posterior rami of spinal nerve during orthopedic surgical intervention [3]. But there is no report as yet about the structural analysis and the possibility of the nerve damage in the longissimus muscle.

The longissimus muscle is supplied by the medial branch of the lateral branch of the posterior rami. After we extensively examined the branching pattern of the posterior rami of the spinal nerve and the layout of the medial branch of the lateral branch, these factors were found different according to each body segment. Between T3 and T5, the medial branch of the lateral branch originated from the lateral branch of the posterior rami at a point distant from the branching point of the posterior rami of the spinal nerve. The medial branch of the lateral branch went farther lateral to enter into the longissimus muscle from the medial side of the muscle. The size of the nerve in diameter was almost the same for both. At these body segments, the longissimus muscle is located the most laterally, farthest from the vertebral column. Therefore, it is quite natural that the nerve enters into the longissimus muscle from the medial side. In the anesthetic practice, because the longissimus muscle is located very laterally and relatively far from the vertebral column, it is not likely that the needle punctures the longissimus muscle and touches the nerves inside.

At T6, we did not identify (see) the lateral branch of the posterior ramus in any cadaver studied regardless of either for the study with fixed cadaver or that with transparent specimen. We do not know the reason of the non-existence of the lateral branch at T6. Future investigations are necessary.

In the lower thoracic and the upper lumbar regions between T7 and L2, we found that branching pattern of the posterior rami was more like triple branches, which supplied to the posterolateral region of the trunk, i.e. the medial branch, the medial branch of the lateral branch, which is more like an intermediate branch, and the lateral branch of the lateral branch. Branching points of the medial branch from the lateral branch were very close to the point where the posterior rami divides into the medial branch and lateral branch. Carlson reported this branching pattern as three branches in the posterior rami in the lumbar region in cats [4]. He reported that the lateral, intermediate and medial branches are specifically distributed to the iliocostalis, longissimus, and multifidus, respectively. Our finding between T7 and L2 coincides with his report. In the study with transparent specimen, the medial branch of the lateral branch of the posterior rami did not show their trace at these segments. We think that this is because the nerve enters the longissimus muscle from the anterior edge and branches extensively after the nerve enters into the muscle. Between the T10 and L2 segments, the medial branch of the lateral branch was shown to have entered into the muscle from the lateral side. This is because the longissimus muscle changed its position. The muscle came close to the midline as the body segment came caudal. Therefore, it is very natural that the nerve entered into the muscle from the lateral side after it originated at the upper edge of the tip of the transverse process.

Between T10 and L2 segment, the medial branch of the lateral branch descends in the longissimus muscle for about three segments within the longissimus muscle. Therefore, the nerve of the upper, middle, and lower segments produce layers within the muscle. At L1 and L2 body segments, the medial branch of the lateral branch of the posterior rami is the biggest in size, which goes medially. Therefore, the needle for epidural anesthesia may pierce or touch the nerve at L1 and L2 body segments. The layout of the nerve of this region should be better examined to avoid pain caused by the nerve damage by needles. The layout of the nerve in this region is thought to be complicated by the medial branches of the lateral branch and the medial branch of the posterior rami of the spinal nerve.

We feel a three dimensional study about the relation of the layout of the medial branch of the lateral branch of the posterior rami in the longissimus muscle and needle path is necessary to know the exact possibility of the nerve damage in the longissimus muscle.

Copyright information

© Springer-Verlag 2006