Muscle:Semispinalis Thoracis

Semispinalis thoracis is classified anatomically as the outermost (most superficial) of the deep paraspinal muscles, but its pain patterns correspond to those of the longissimus fibres at the same segmental level. Although it is the most superficial of the deep group, it behaves clinically more like the superficial (erector spinae) group in its referral patterns. Its TrPs produce severe aching "bone" pain that is persistent, worrisome, and disabling. The semispinalis thoracis extends caudally only as far as T₁₀, overlying the multifidi.

TrPs in the semispinalis at any level will usually be associated with four to six segmental levels of articular dysfunction — the widest span of any muscle in the deep paraspinal group.

Anatomy

The semispinalis thoracis extends caudally as far as T₁₀, overlying the multifidi (Fig. 48.4). Its fibres cross at least five vertebrae. It is the most superficial of the deep paraspinal group and, although classified anatomically as a transversospinal muscle, its pain patterns correspond to those of the longissimus fibres at the same segmental level.

The deep group of paraspinal muscles are progressively shorter and more horizontal at successively deeper levels, increasingly rotating the spine rather than primarily extending it. The semispinalis, being the most superficial of this group, retains a more longitudinal orientation than the multifidi and rotatores.

Primary function: Acting bilaterally, extends the vertebral column. Acting unilaterally, rotates the vertebrae to the contralateral side. The semispinalis thoracis functions as part of the deep group for fine adjustments between vertebrae, rather than for gross spinal movements.

Innervation: Medial branches of the dorsal primary divisions of the spinal nerves.

Referred Pain Patterns

Although the semispinalis thoracis is classified anatomically as the outermost of the deep paraspinal muscles, its pain patterns correspond to those of the longissimus fibres at the same segmental level. This means its referral patterns are broadly caudal and similar to the superficial erector spinae group rather than the strictly midline pattern of the rotatores.

TrPs in the semispinalis thoracis at the midthoracic level produce pain patterns characteristic of that level. The severe aching "bone" pain from TrPs in any of the deep group of paraspinal muscles is persistent, worrisome, and disabling.

TrPs at any level of the semispinalis thoracis will usually be associated with four to six segmental levels of articular dysfunction — the widest span among the deep paraspinal muscles (compared to two to three levels for multifidus and single-level for rotatores).

Activation and Perpetuating Factors

• Sudden overload: A quick awkward movement combining bending and twisting of the back, especially when muscles are fatigued or chilled
• Sustained overload: Maintained in a fully shortened (hyperlordotic) position, or in stooped posture with prolonged muscle contraction
• Marked thoracic kyphosis: Deep thoracic paraspinal TrPs tend to occur in patients with marked thoracic kyphosis
• Structural asymmetries: Lower limb-length inequality and pelvic asymmetry perpetuate paraspinal TrPs at all levels
• Articular dysfunction: TrPs at any level of the semispinalis will usually be associated with four to six segmental levels of articular dysfunction, which can reciprocally perpetuate the TrPs
• Prolonged immobility: Sitting for hours in aircraft or automobile with the seat belt fastened

Clinical Examination

Deep Paraspinal Examination

Active TrPs in the deep paraspinal muscles cause guarded movements and restrict side bending, rotation, and hyperextension of the trunk.

During flexion, a hollow or flat area develops in the smooth curve formed by the spinous processes. The flattening usually spans one to three vertebrae. The apex segment is often exquisitely tender to palpation.

Examination technique:

1. Patient is recumbent or seated and leaning forward to flex the spine
2. The examiner taps or presses on the tips of successive spinous processes to elicit tenderness
3. When a spinous process in the flat area is hypersensitive, the deep musculature on each side is palpated by firm pressure in the groove between the process and the longissimus muscle
4. Deep finger pressure is directed along the side of the spinous process to exert pressure on the deep muscles against the underlying laminae
5. The semispinalis is the most superficial of the deep group and is thus reached at intermediate depth between the erector spinae and the rotatores

For the semispinalis thoracis specifically, four to six levels of spinous process tenderness (the widest span) are expected when this muscle is involved, in contrast to two to three levels for multifidus and a single level for rotatores.

Differential Diagnosis

Condition	Distinguishing features
Articular dysfunction	TrPs in the semispinalis at any level will usually be associated with four to six segmental levels of articular dysfunction — the widest span among the deep paraspinals; the most superficial and longest muscles (iliocostalis and longissimus) have TrPs associated with group dysfunctions
Longissimus thoracis TrPs	The semispinalis thoracis pain patterns correspond to those of the longissimus fibres at the same segmental level, making clinical distinction between the two sometimes difficult; depth of the TrP on palpation and the span of associated articular dysfunction help distinguish them
Visceral disease	Deep paraspinal pain may be referred anteriorly to the abdomen; always consider visceral causes when back pain is accompanied by gastrointestinal, urological, or gynaecological symptoms
Radiculopathy	When radiculopathy activates paraspinal TrPs, they may persist long after nerve root compression has been relieved, contributing to failed-back syndrome
Fibromyalgia	Any patient with chronic low back pain and additional widespread pain should be examined for fibromyalgia; each diagnosis requires its own therapeutic approach

Treatment

Trigger Point Release — Deep Paraspinal Muscles

To stretch the deep paraspinal muscles including the semispinalis thoracis, the seated patient's spine is flexed and simultaneously rotated, turning the chest toward the side of the involved muscle (Fig. 48.7):

1. After initial sweeps of vapocoolant spray, the operator takes up the slack and repeats the process several times to achieve full normal range of motion
2. To incorporate PIR, the patient looks first toward the contralateral side while the examiner resists any attempt to turn the torso; then the patient relaxes and turns toward the involved side
3. Release is augmented through reciprocal inhibition if the patient gently voluntarily assists rotation toward the involved side

Because the semispinalis is the most superficial of the deep group, it may also respond to the spray-and-stretch techniques used for the superficial erector spinae group, particularly the less strenuous seated flexion position (Fig. 48.6A).

Many manual release techniques directed toward spinal articular dysfunctions are as effective for releasing the tense deep spinal muscles as they are for releasing restricted joint movement.

Trigger Point Injection

The TrPs in the deep paraspinal thoracic muscles are injected by directing the needle caudally (not upward) and slightly medially (Fig. 48.8). For the semispinalis thoracis (as the most superficial of the deep group), slightly less needle depth is required than for the multifidus and rotatores. The needle must still be directed caudally to avoid the shingle-like overlap of the laminae.

The caudal slant of the needle eliminates the possibility of introducing the needle between the ribs into the pleural cavity or between the vertebrae into the epidural space. Penetration to a depth greater than the laminae is unnecessary and undesirable.

Corrective Actions

See Longissimus Thoracis — Corrective Actions for the full programme, including correction of structural inadequacies, modification of activities and environment, and exercises.

Satellite Trigger Points

• Multifidus — underlying layer; co-active; associated with two to three segmental levels of dysfunction
• Rotatores — deepest layer; co-active; associated with single-level dysfunction
• Longissimus Thoracis — superficial group at the same segmental level; pain patterns of semispinalis correspond to those of longissimus at the same level
• Iliocostalis Thoracis — superficial group; frequently co-involved at thoracic levels

Related Pages

• Muscle:Multifidus — intermediate layer of the deep paraspinal group
• Muscle:Rotatores — deepest layer of the deep paraspinal group
• Muscle:Longissimus_Thoracis — superficial group; pain patterns correspond at the same segmental level
• Muscle:Iliocostalis_Thoracis — superficial group; co-involved at thoracic levels
• Pain:Low_Back — diagnostic algorithm for back pain

References

• Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 2: The Lower Extremities. Baltimore: Williams & Wilkins; 1992. Chapter 48.