Muscle:Rectus Abdominis

Rectus abdominis is the primary medial abdominal muscle, running vertically between the pubic symphysis and the anterior rib cage. Its TrPs produce some of the most clinically confusing pain patterns in the body: bilateral horizontal back pain at the thoracolumbar level, deep epigastric pain mimicking peptic ulcer, periumbilical cramping indistinguishable from intestinal colic, dysmenorrhoea, pseudo-appendicitis at McBurney's point, and precordial pain. Because the muscle is divided into functional segments by tendinous inscriptions, TrPs in different segments produce distinctly different referred patterns. Understanding the rectus abdominis is essential for the differential diagnosis of chest pain, abdominal pain, and low back pain.

The symptoms caused by TrPs in this muscle are largely dependent on the location of the TrP and are considered in three groups: upper rectus (above umbilicus), periumbilical, and lower rectus (below umbilicus).

Anatomy

The rectus abdominis attaches below along the crest of the pubic bone; the paired muscle fibres interdigitate across the symphysis. Above, the muscle attaches to the cartilages of the fifth, sixth, and seventh ribs.

The fibres are usually interrupted by three or four transverse tendinous inscriptions — one near the xiphoid process, one close to the level of the umbilicus, and one midway between them. Sometimes one or two partial inscriptions are also present below the umbilicus. In 115 cadavers, the total number of inscriptions per muscle ranged from one to four.

The rectus abdominis lies within the rectus sheath formed by the aponeuroses of the three lateral wall muscles. Below the arcuate line (a short distance below the navel) there is no posterior sheath — this is a critical anatomical point for injection technique.

The abdominal section of the pectoralis major may overlap fibres of the upper rectus abdominis, accounting for the occasional reference of pain to the anterior chest from TrPs in this region.

Primary action: Prime mover for spinal flexion, especially of the lower thoracic and lumbar spine; tenses the anterior abdominal wall to increase intra-abdominal pressure. Antagonistic to the paraspinal group (especially the longissimus thoracis) during flexion/extension; synergistic with the psoas muscle if the lumbosacral spine is flexed.

Innervation: Seventh through twelfth intercostal nerves derived from the corresponding spinal nerves; different segmental nerves innervate fibres between different tendinous inscriptions.

Referred Pain Patterns

Upper Rectus Abdominis — Bilateral Back Pain and Epigastric Pain

An active TrP high in the rectus abdominis on either side refers pain bilaterally to the mid-back, described by the patient as running horizontally across the back on both sides at the thoracolumbar level. The patient demonstrates this with a crosswise motion of the hand — this crosswise pattern is characteristic of the rectus abdominis and distinguishes it from the up-and-down pain pattern of the iliocostalis thoracis and other more superficial paraspinal muscles.

TrPs high in the rectus abdominis also refer pain to the region of the xiphoid process, and cause symptoms of abdominal fullness, "heartburn," indigestion, and sometimes nausea and vomiting. Nausea and epigastric distress occur more often when these TrPs are on the left rather than the right side.

Bilateral mid-back pain from upper rectus TrPs is usually aggravated by taking a deep breath, especially when the back is arched in marked lumbar lordosis. Back pain from paraspinal TrPs is not usually influenced by respiration — this is a useful distinguishing feature.

Periumbilical Rectus Abdominis — Colic and Cramping

Periumbilical TrPs at the lateral border are likely to produce sensations of abdominal cramping or colic. The patient often bends forward for relief. Infants, especially neonates, who burp and cry persistently with colic may be suffering from periumbilical TrPs — their symptoms can be relieved by vapocoolant spray applied to the abdomen.

Lewis and Kellgren demonstrated experimentally that injection of hypertonic saline into the normal rectus abdominis induced a familiar colic-like pain, much stronger anteriorly than toward the back, extending diffusely over several segments in front — indistinguishable from the pain of intestinal colic.

Lateral TrPs near the umbilicus may also evoke diffuse abdominal pain accentuated by movement.

Lower Rectus Abdominis — Pseudo-appendicitis, Dysmenorrhoea, and Bladder Spasm

Pseudo-appendicitis: A TrP in the lateral border of the right rectus abdominis in the region of McBurney's point (halfway between the anterior superior iliac spine and the umbilicus) produces symptoms closely simulating acute appendicitis — marked local tenderness and rigidity. The muscle shows a palpable nodule and ropiness, differing from the more generalised board-like rigidity of all abdominal musculature found in acute appendicitis. Nearly 40% of appendices removed in one large series were normal; a more recent study found normal appendices in 12.4% of "appendicitis" patients — active TrPs contributed to symptoms in many of these cases.

Dysmenorrhoea: Inactivation of TrPs in the lower rectus abdominis, about half-way between the umbilicus and the symphysis pubis (or in the overlying skin), may relieve dysmenorrhoea. Theobald demonstrated this by stimulating the endometrium to produce abdominal wall pain centrally over the rectus abdominis, and showed that visceral-referred uterine pain was eliminated by procaine infiltration of the reference zone — suggesting a convergence-facilitation mechanism. Self-treatment of TrPs in this region is especially valuable between menstrual periods.

Bladder spasm: A TrP just above the pubis may cause spasm of the detrusor and urinary sphincter muscles.

Sacroiliac and low back pain: In the lowest part of the rectus abdominis, TrPs may refer pain bilaterally to the sacroiliac and low back regions.

Somatovisceral and Viscerosomatic Effects

Active TrPs in the rectus abdominis can generate diarrhoea, vomiting, food intolerance, colic, and dysmenorrhoea indistinguishable from primary visceral disease. TrPs may cause a lax, distended abdomen with excessive flatus — contraction of the abdominal muscles is inhibited by the TrPs so that the patient cannot "pull the stomach in." This apparent distension is readily distinguished from that due to ascites by physical examination.

Conversely, visceral disease activates and perpetuates rectus abdominis TrPs; the pain-generation can persist long after the visceral disease has resolved.

Activation and Perpetuating Factors

Visceral Disease

Peptic ulcer, intestinal parasites, dysentery, ulcerative colitis, diverticulosis, and cholelithiasis are important activating factors.

Surgery and Trauma

Rectus abdominis TrPs may be initiated in conjunction with abdominal surgery and perpetuated by paradoxical breathing that develops as the result of postoperative abdominal soreness. TrPs also discourage abdominal muscle activity, which further contributes to paradoxical breathing.

Exercise and Postural Overload

• Excessive sit-ups or heavy "curl-type" resistance exercises
• Prolonged vigorous activity requiring forceful abdominal breathing
• Slumped sitting or forward-head posture, which shortens the upper rectus abdominis
• Sitting leaning forward for hours with the abdominal muscles shortened and tense and the back unsupported
• Structural inadequacies — short leg or small hemipelvis add unnecessary overload

Other Factors

Emotional tension and stress; cold exposure; viral infections.

Clinical Examination

Pendulous Abdomen in Standing

When the patient with active TrPs in the rectus abdominis stands, the abdomen is likely to sag and become pendulous. TrPs inhibit the muscle's supportive function. The tense palpable band associated with an active TrP shortens only the segment between inscriptions in which it lies; however, TrP activity apparently inhibits contraction of adjacent segments, causing lengthening of the muscle as a whole rather than shortening.

Paradoxical Breathing

Patients with active rectus abdominis TrPs are likely to exhibit paradoxical breathing. The threat of pain from stretching the involved rectus apparently subconsciously inhibits normal diaphragmatic contraction on inspiration — when the patient inhales deeply, protruding the abdomen, referred pain from rectus abdominis TrPs may be exacerbated. This may be a rectus abdominis–diaphragmatic reflex inhibition.

If asked to take a deep breath, these patients are likely to exhibit paradoxical respiration. Back pain from upper rectus TrPs is usually aggravated by deep breathing, especially when the back is arched in marked lumbar lordosis. Back pain from paraspinal TrPs is not usually influenced by respiration.

Trigger Point Examination

Active TrPs are commonly found:

• In the angle between the costal arch and the xiphoid process
• Between the xiphoid process and the umbilicus
• In the middle or lower portions, especially along the lateral border
• At or near the attachment to the pubic bone (these feel like small buttons at the insertion)

In thin supine subjects, the needle can be inserted horizontally into the lateral border of the rectus abdominis by depressing the abdominal wall lateral to the rectus sheath.

The Abdominal Tension Test is essential and is performed as described for all abdominal muscles.

Differential Diagnosis

Condition	Distinguishing features
Peptic ulcer	Upper rectus TrPs producing epigastric heartburn and nausea; TrP pain reproduced and relieved by TrP examination; upper GI series and endoscopy differentiate
Intestinal colic	Periumbilical TrPs produce colic experimentally indistinguishable from true colic; absence of systemic features (fever, abnormal bloods) favours TrP
Appendicitis	McBurney's point TrP in right rectus lateral border produces pseudo-appendicitis; palpable nodule and ropiness rather than board-like diffuse rigidity; Abdominal Tension Test positive; Rovsing's sign and rebound tenderness absent; normal ESR and WBC
Cholecystitis / cholelithiasis	Upper right quadrant TrPs mimic gallbladder pain; ultrasound and liver function tests differentiate
Dysmenorrhoea	Lower rectus TrPs may greatly intensify dysmenorrhoea or produce pain indistinguishable from it; TrP inactivation may relieve dysmenorrhoea
Sacroiliac joint dysfunction	Lowest rectus TrPs refer pain bilaterally to sacroiliac and low back regions with crosswise pattern; Abdominal Tension Test positive; articular provocation tests differentiate
Chest pain / precordial pain	Left-sided upper rectus TrP may produce precordial pain mimicking cardiac pain — once cardiac and pectoralis/sternalis sources are excluded, rectus is easily overlooked
Renal colic	Right lower rectus TrPs may simulate renal colic; urinalysis and imaging differentiate
Fibromyalgia	Widespread pain ≥3 months; fibromyalgia and TrPs are different diseases requiring different treatments; more than half of fibromyalgia patients also have TrPs

Treatment

Trigger Point Release — Spray and Stretch

• Patient lies supine on a firm support with legs extending over the end, arms positioned upward over the head; one foot initially supported on a stool so that the thighs are not extended at the hips
• Vapocoolant spray applied in sweeps in the caudal direction (down-sweep pattern — more effective than up-sweep pattern)
• Patient allows the lower limb on the treatment side to hang free and takes a very deep breath, allowing the diaphragm to strongly protrude the relaxed abdominal musculature — this is the critical stretch step
• Sweeps of spray continue in the caudal direction as the patient begins slowly to exhale
• Both right and left rectus abdominis muscles must always be treated — they function as a team
• After release, patient assumes bilateral knee-to-chest position to unload the lumbosacral spine; moist heat applied promptly

Trigger Point Injection

Most TrPs can be reached with a 3.8-cm (1½-inch) needle. Inserting the needle at a shallow angle (rather than nearly perpendicular to the skin) aligns the shaft with the muscle fibres and allows changes in consistency of fat, fascia, and muscle to be felt as the needle penetrates successive layers.

Critical anatomical consideration: There is no posterior sheath to the rectus abdominis below the arcuate line (a short distance below the navel). Penetration beyond the second layer of epimysium (the posterior rectus sheath) must be avoided below the umbilicus to prevent peritoneal puncture.

Injection of upper rectus TrPs in the space between the costal margin and the xiphoid process requires careful attention to the depth of needle penetration to avoid entering the abdominal cavity. Postinjection soreness and stiffness for 6–12 hours should be anticipated.

Active full range of motion with repetition of vapocoolant spray is performed slowly after injection, then followed by moist heat.

Corrective Actions and Exercises

Abdominal (diaphragmatic) breathing — the most effective active stretch exercise for the abdominal musculature, especially performed in the prone position (which also stretches the lateral wall muscles).

Pelvic-tilt exercise:

• A gentle and effective strengthening movement for the lower rectus abdominis
• Patient lies supine; contracts the lower abdominal muscles (not the gluteal muscles) to rock the symphysis pubis toward the xiphoid process, bringing the ASIS closer to the rib cage
• This flattens the lumbar spine on the bed and rocks the coccyx upward
• Hold for several seconds breathing normally; relax; repeat several times

Sit-back/Abdominal-curl/Sit-up exercise sequence:

• A progressive combination of three exercises; always begin with the Sit-back
• The Sit-back is a lengthening (eccentric) contraction that places relatively less load on the involved musculature — the patient pushes to sitting position, then does a slow curl-down, smoothly and without jerks
• Only when the Sit-back goal of 10 repetitions is reached comfortably does the patient progress to the Abdominal-curl (partial sit-up from supine), then to the full Sit-up
• The pause between each cycle is as important as the movement — the muscle has time to recharge with blood and wash out metabolic waste products
• The Sit-up should never be performed unless it is pain-free

Self-pressure release: While lying in a tub of warm bath water, the patient locates a tender spot, protrudes the abdomen, and applies steady increasing pressure until the spot is no longer sensitive.

Skin-rolling of panniculosis over affected muscles may also be performed by the patient while relaxing in a warm bath.

Laughter — a vigorous isometric exercise for all abdominal muscles; "pleasant medicine."

Satellite Trigger Points

• External oblique — lateral synergist; commonly co-active
• Internal oblique — lateral synergist
• Transversus abdominis — deep synergist
• Pyramidalis — inferior functional partner; pubic attachment shared
• Paraspinal muscles (thoracolumbar) — bilateral back pain from upper rectus may coexist with paraspinal TrPs; rectus TrPs are frequently overlooked as the primary source
• Pelvic floor muscles — lower rectus and pelvic floor TrPs frequently co-active in pelvic pain syndromes

Related Pages

• Pain:Abdominal — Diagnostic algorithm
• Pain:Low Back — Bilateral Horizontal — Upper rectus as source
• Pain:Epigastric — Upper rectus referral pattern
• Pain:Dysmenorrhoea — Lower rectus as myofascial source
• Pain:Right Lower Quadrant — Pseudo-appendicitis from lower rectus lateral border TrP
• Muscle:Pyramidalis — Inferior partner
• Muscle:External Oblique — Lateral synergist

References

• Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 2: The Lower Extremities. Baltimore: Williams & Wilkins; 1992. Chapter 49.