Osteopathy Journals and Research by Darren Chandler

 

Dorsal ramus: anatomy and clinical presentation

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Anatomy

Spinal cord --> dorsal root (sensory) & ventral root (motor) --> spinal nerve (mixed sensory & motor) --> ventral rami (motor > sensory) & dorsal rami (sensory > motor). Dorsal rami --> medial branch of dorsal rami & lateral branch of dorsal rami.

Saito et al (2013) described the L2 spinal nerve and ventral rami as a 'continuous stem' . This is opposed to the dorsal rami that was described as a 'branch of the spinal nerve'. These authors did not specify if this was unique to L2.

There are numerous anastomoses between adjacent dorsal rami, medial branches and lateral branches. Shuang et al (2015) confirmed the existence of the middle [intermediate] branch of the dorsal rami which connects the lateral branch to the communicating plexus. These authors acknowledge some might recognize the middle [intermediate] branch as a muscular sub-branch of the lateral branch, and generally, it is acceptable to divide the dorsal rami into the medial and the lateral branches. 

The dorsal rami enters the back through a foramen bounded by the superior border of the transverse process, the anterior aspect of the superior articular facet joint and the intertransverse ligament (Zhou et al 2012).

It runs posteriorly on the medial aspect of the intertransversarri muscles (Shuang et al 2015).

The dorsal ramus then divides into the into medial and lateral branches at the junction of the facet joint and the proximal superior border of the transverse process (Zhou et al 2012). Bogduk and Long (1979) and Masini et al (2005) found the L1-L4 dorsal rami to divide into the medial and lateral branches within the intertransverse ligament.

Bogduk et al (1982) found different branching patterns for not just the medial and lateral branches of the dorsal rami but also the intermediate branches. The branching patterns varied depending on the spinal levels:

  • L1 & L2 dorsal rami: commonly double branching occurs. This includes a medial branch and a short common stem for the lateral and intermediate branches.
  • L4>L3 dorsal rami: commonly triple branching occurs. This includes the medial, intermediate and lateral branches.
  • L5 dorsal rami: gives rise to the medial and intermediate branches as it runs in the groove formed by the S1 superior articular process and the sacral ala. The L5 dorsal rami lacks a lateral branch as there is no attachment of the iliocostalis lumborum to L5 as it is replaced by the iliolumbar ligament.

Medial branch of the dorsal rami

As the medial branch of the dorsal rami passes through a groove formed between the root of the transverse process and root of the superior articular process Bogduk et al (1982) found it was bound to the periosteum by a layer of connective tissue which coated the superior articular process and transverse process.

The nerve then passes through a fibroosseous canal formed by the junction of the transverse process and the lateral aspect of the superior articular process. The roof of the canal is formed by the mammilloaccessory ligament. 

*: Mammilloaccessory ligament is a part of the medial side of the intertransverse ligament. It extends from the mammillary process to the accessory process. It gives origin to the intertransversarii, multifidus, longissimus and iliocostalis muscles.

The medial branch of the dorsal rami then penetrates the deep fascia near the median line to enter the subcutaneous tissue.

The medial branch of the dorsal rami innervates:

  • Facet joints: innervates the two to three adjacent facet joints e.g. the L4 facet joint is innervated by the L3 and L4 medial branches. To innervate the facet joint the proximal nerve runs between the intertransversarii and the most lateral fibres of multifidus; the distal nerve runs deep to the multifidus (Bogduk et al 1982).
  • Multifidus: Shuang et al (2015) found this innervation to be highly specific. They found each medial branch ran on the deep aspect of the multifidus and was solely innervated by this one branch without any communicating branches. This finding was disputed by Wu et al (1997) who found the multifidus to be polysegmentally innervated.
  • Interspinous ligament and muscle: the nerve weaves medially between the fascicles of the multifidus to reach the interspinous space (Bogduk et al 1982).
  • Supraspinous ligament.

Saito et al (2013) believed the intermediate branches are more widespread but have been regarded simply as muscular branches of the lateral branches. These authors described the anatomy of the dorsal rami as:

  • Medial branch: arises from the mammillary processes to enter the multifidus muscle.
  • Intermediate branch: arises from the accessory processes and enters the longissimus muscle.
  • Lateral branch: arises from the transverse processes and enters the iliocostalis.

Lateral branch of the dorsal rami

The lateral branch of dorsal rami lies in an osseous groove on the superior transverse process. It then sends branches to the iliocostalis and longissimus muscles.

After passing the iliocostalis muscle, the main lateral branch descends approximately two vertebral segments before it pierces the dorsal layer of the thoracolumbar fascia into the subcutaneous region and supplies the skin.

Distal anastomoses of the lateral branches have been noted < T11 and T12, T12 and L1, and L2 and L3.

The lateral branch innervates the tissues lateral to the facet joint line e.g:

  • Iliocostalis and Longissimus muscles. 
  • Cutaneous innervation of the back and pelvis.

Several authors regard the intermediate branch as a muscular branch of the lateral branch (Saito et al 2013). Those that classify the intermediate branch as a distinct branch of the dorsal rami found it to innervate the Longissimus (refer 'intermediate branch of the dorsal rami').

Bogduk et al (1982) found:

  • L1 and L2 lateral branches: cross the iliac crest in the subcutaneous tissue in parallel with the T12 cutaneous branch. T12 and L1 innervate the dermatome just below the lateral iliac crest and posterior to the ASIS.
  • L1-3 lateral branches: emerge from the posterolateral surface of the iliocostalis lumborum, pierce the posterior layer of the thoracolumbar fascia and become cutaneous. L3 is bound down to the iliac crest by a bridge of connective tissue just lateral to the origin of iliocostalis lumborum. L2 and L3 lateral branches innervate the skin over the buttocks.
  • L4-L5 lateral branches: there are no cutaneous branches of the L4 and L5 lateral branches. L4 lateral branch remains intramuscular. The L5 lateral branch typically communicates with the S1 dorsal ramus.

The lateral branch of the L5 dorsal ramus descends and merges into the S1 dorsal ramus (Zhou et al 2012).

Bogduk et al (1982) described the L5 dorsal ramus as lacking a lateral branch dividing the dorsal ramus at this level into the medial and intermediate branches. This was due to the absence of an attachment of the iliocostalis to L5 which is replaced by the iliolumbar ligament.

However both these authors also described the intermediate branch (Bogduk et al 1984) and lateral branch (Zhou et al 2012) of the L5 dorsal rami as innervating the longissimus thoracis as it attaches to the medial aspect of the dorsal segment of the iliac crest. Therefore both authors are probably describing the same nerve but under a different name.

Intermediate brach of the dorsal rami

The L3 and L4 dorsal rami (and sometimes L1 and L2) give off intermediate branches which supply the lumbar fibers of the longissimus thoracis (Zhou et al 2012) and mutifidus (L2 nerve, Saito et al 2013). 

This branch passed between the longissimus and iliocostalis muscles and extended to the skin.

Soft tissue relations to the dorsal rami

Zhou et al (2012) found the most commonly affected area from dorsal rami pain is around the thoracolumbar region and involving the L1 and L2 dorsal rami (Zhou et al 2012). This was opposed to facet joint pain that most commonly affected the L4-5 and L5-S1 levels.

Intertransversarii and intertransverse ligament

The L1-L4 dorsal rami to divide into the medial and lateral branches within the intertransverse ligament (Bogduk and Long 1979 &  Masini et al 2005).

The intertransverse ligament frequently blends with the intertransversarii muscle and has been described as looking more like a part of the thoracolumbar fascia rather than a true ligament (Hirsch et al 1963).

The intertransversarii muscle and intertransverse ligament relation to the medial branch of the dorsal rami is:

  • The dorsal rami runs on the medial aspect of the intertransversarii muscle.
  • The medial branch of the dorsal ramus innervates the facet joint. To innervate the facet joint the proximal nerve runs between the intertransversarii and the most lateral fibres of multifidus; the distal nerve runs deep to the multifidus (Bogduk et al 1982).
  • Medial branch of the dorsal rami lies in the fibrosseous canal formed from the mamilloaccessory ligament that is associated with the intertransverse ligament and intertransversarri muscle.

There are three distinct intertransversarii muscles (Gilchrist et al 2003):

  • Intertransversarii laterales ventrales: traverses proximally and distally between neighbouring transverse processes. Innervated by the ventral ramus.
  • Intertransversarii laterales dorsales: lies medial to the intertransversarii laterales ventrales. Inserts proximally to the accessory process and distally to the medial third of the adjacent transverse process below.
  • Intertransversarii mediales: attaches proximally to the accessory process, mamillary process, and mamillary-accessory ligament. Distally it inserts into the mamillary process of the vertebrae below. Innervated by the medial division of the dorsal rami.

Due to their small size and medial location, the intertransversarii muscles are weak posterior sagittal rotators and lateral flexors of the lumbar spine. These muscles primary function may more proprioceptive in nature providing positioning feedback to the larger muscles of the spine that react to maintain proper spinal alignment. 

The middle layer of the thoracolumbar fascia is the strongest layer of the thoracolumbar fascia and attaches to intertransverse ligaments. Hirsch et al (1963) described the intertransverse ligaments as being an extension of the thoracolumbar fascia rather than a ligament in its own right.

This continuity from the middle layer of the thoracolumbar fascia to the intertransverse ligament allows tension from the transversus abdominis, internal oblique and external oblique to be transmitted via the middle layer of the thoracolumbar fascia to the transverse processes and intertransverse ligaments (Barker et al 2007). Gilchrist et al (2003) also found the iliocostalis lumborum attaches on to the middle layer of the thoracolumbar fascia.

If the intertransversarii and intertransverse ligaments have a proprioceptive function then could this help explain how the lateral abdominal muscles influence segmental motion (Barker et al 2007)?

Multifidus

The multifidus relation to the medial branch of the dorsal rami includes:

  • Mammilloaccessory ligament is a point of attachment for the multifidus. This ligament forms the roof of the fibrosseous tunnel that the medial branch of the dorsal ramus runs through.
  • The medial branch of the dorsal ramus innervates the facet joint. To innervate the facet joint the proximal nerve runs between the intertransversarii and the most lateral fibres of multifidus; the distal nerve runs deep to the multifidus (Bogduk et al 1982).
  • The medial branch of the dorsal ramus weaves medially between the fascicles of the multifidus to reach the interspinous space (Bogduk et al 1982).

The multifidus arises from the spinous process of L5 to as low as the fourth sacral foramen, PSIS and dorsal sacroiliac ligament. The longest fibers of the multifidus run from the spinous processes of L1 and L2 to the dorsal segment of the iliac crest.

The multifidus is tightly adhered to the erector spinae aponeurosis at the lumbar (close to the midline) and sacral levels (Creze et al 2018). Johnson and Zang (2002) found the multifidus, longissimus thoracis and thoracolumbar fascia to be contributers to the supraspinous and interspinous ligaments. 

Paralleling the mutlifidus relation with the medial branch of the dorsal rami the sacral attachment of the multifidus is also tightly adhered to the medial branches of the sacral dorsal rami. To illustrate how tight this adherence is when the multifidus was removed piecemeal many of these nerves were removed along side with it (Cox & Fortin 2014).

Masaki et al (2019) paralled the work of Macintosh & Bogduk (1986) and found the lumbar multifidus is stretched effectively in trunk flexion. The addition of lateral flexion or ipsilateral rotation to flexion did not alter the effectiveness of the stretch. Flexion will also stretch the interspinous space.

References

The Anatomy of Dorsal Ramus Nerves and Its Implications in Lower Back Pain (2012) Linqiu Zhou, Carson D. Schneck, Zhenhai Shao.

Clinical Anatomy and Measurement of the Medial Branch of the Spinal Dorsal Ramus (2015). Feng Shuang, Shu-Xun HouJia-Liang Zhu, Yan LiuYing Zhou, Chun-Li Zhang, Jia-Guang Tang.

Muscular Control of the Lumbar Spine (2003). Russell V. Gilchrist, Michael E. Frey and Scott F. Nadler

An electrophysiological demonstration of polysegmental innervation in the lumbar medial paraspinal muscles (1997). P B WuW S KingeryM L FrazierE S Date

Analysis of the Posterior Ramus of the Lumbar Spinal Nerve: The Structure of the Posterior Ramus of the Spinal Nerve 2013). Toshiyuki Saito, Hanno Steinke, Takayoshi Miyaki,Shiro Nawa, Kanae Umemoto, Kunihisa Miyakawa, Norimitsu Wakao, Ken Asamoto, Takashi Nakano.

The human lumbar dorsal rami (1982)N BogdukA S Wilson, and W Tynan

The middle layer of lumbar fascia and attachments to lumbar transverse processes: implications for segmental control and fracture (2007). Priscilla J. Barker, Donna M. UrquhartIan H. StoryMarius Fahrer, and Christopher A. Briggs.

Effects of the trunk position on muscle stiffness that reflects elongation of the lumbar erector spinae and multifidus muscles: an ultrasonic shear wave elastography study (2019). Mitsuhiro MasakiXiang Ji, Taishi YamauchiHiroshige TateuchiNoriaki Ichihashi

Organization of the fascia and aponeurosis in the lumbar paraspinal compartment (2018). Creze M, Soubeyrand M, Nyangoh Timoh K, Gagey O.

Regional differences within the human supraspinous and interspinous ligaments: a sheet plastination study (2002). Gillian M Johnson and Ming Zhang

The anatomy of the lateral branches of the sacral dorsal rami: implications for radiofrequency ablation (2014). Cox R, Fortin  J.

The biomechanics of the lumbar multifidus (1986). J E MacintoshN Bogduk

The anatomy of the so-called "articular nerves" and their relationship to facet denervation in the treatment of low-back pain. N BogdukD M Long

Anatomical description of the facet joint innervation and its implication in the treatment of recurrent back pain (2005). M Masini, W S Paiva, A S Araújo Jr

THE ANATOMICAL BASIS FOR LOW BACK PAIN Studies on the presence of sensory nerve endings in ligamentous, capsular and intervertebral disc structures in the hurnnn lumbar spine (1963). CARL HIRSCH, Bo-ERIC INGELMARK and MALCOLME MILLER
 
The anatomy of the so-called “articular nerves” and their relationship to facet denervation in the treatment of low-back pain (1979).Nikolai Bogduk and Don M. Long

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