Muscle:Pyramidalis

Pyramidalis is a small, variable, triangular muscle located within the anterior rectus sheath, just above the symphysis pubis. Its TrP refers pain close to the midline between the symphysis pubis and the umbilicus. The pyramidalis is absent bilaterally in approximately 17–20% of individuals and is absent unilaterally more commonly than bilaterally — its presence should never be assumed. It lies entirely within the anterior rectus sheath, and its TrP is closely associated with lower rectus abdominis TrPs and with pelvic floor dysfunction.

Anatomy

The pyramidalis attaches below to the anterior surface of the ramus of the pubis and above to the linea alba approximately mid-way between the symphysis pubis and the umbilicus. It lies entirely within the anterior rectus sheath.

Primary action: Tensing the linea alba.

Innervation: Branch of the twelfth thoracic nerve.

Frequency of absence:

• Absent bilaterally in approximately 3.3% of Japanese subjects
• Absent bilaterally in approximately 25% of Scottish subjects
• Absent bilaterally in 15–20% of bodies in general population studies
• In a study of 430 sides, absent in 17.7%
• Unilateral absence is more common than bilateral absence

Referred Pain Pattern

The pyramidalis refers pain close to the midline between the symphysis pubis and the umbilicus — a central lower abdominal pain that may be confused with pain from the lower rectus abdominis or from pelvic visceral structures. The pain is strictly midline and suprapubic, which helps distinguish it from lower rectus abdominis TrP pain which tends to be slightly more lateral and located above the pubic attachment.

Somatovisceral Effects

A TrP just above the pubis may cause spasm of the detrusor and urinary sphincter muscles. Given the pyramidalis' intimate anatomical relationship with the lower rectus abdominis TrPs and pelvic floor, these somatovisceral effects are difficult to attribute to the pyramidalis in isolation — they are more reliably attributed to the closely associated lower rectus abdominis.

Activation and Perpetuating Factors

Surgery

Lower abdominal and pelvic surgery (caesarean section, hysterectomy, prostatectomy, appendicectomy) places the pyramidalis directly in the surgical field; TrP activation from retractor stretch and ischaemia is probable.

Pelvic Visceral Disease

The same viscerosomatic cycle as for other abdominal muscles — pelvic visceral disease activates TrPs which may persist after the primary disease has resolved.

Related TrP Activity

TrP activity in the lower rectus abdominis — the pyramidalis' primary functional neighbour — likely activates pyramidalis TrPs as satellites.

Clinical Examination

The pyramidalis lies within the anterior rectus sheath just above the symphysis pubis and is palpated by flat palpation in the suprapubic region:

• The examiner presses down against the upper edge of the pubic arch — not on the flat anterior surface of the pubis
• These TrPs feel like small buttons or short bands at the region of attachment
• The midline location distinguishes pyramidalis TrPs from the slightly more lateral lower rectus abdominis attachment TrPs

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

Note for injection: Distinguish the pyramidalis TrP from the lower rectus abdominis attachment TrP by the strictly midline location and by the direction of needle injection — for the pyramidalis the needle is directed cephalad (away from the bone, toward the umbilicus), whereas for the lower rectus abdominis pubic attachment the needle is directed toward the pubic bone.

Differential Diagnosis

Condition	Distinguishing features
Lower rectus abdominis TrP	Pyramidalis TrP is strictly midline and suprapubic; lower rectus TrPs are located above the pubic attachment and slightly more lateral; both may coexist and are treated separately
Symphysis pubis dysfunction	Symphysis pubis pain reproduced by compression or distraction; pyramidalis TrP pain reproduced by direct TrP palpation; imaging may show symphysis changes in true symphysis pubis dysfunction
Cystitis / urethritis	Midline suprapubic TrP pain mimics bladder pain; urinalysis and culture differentiate
Gynaecological pathology	Central lower abdominal TrP pain may mimic dysmenorrhoea, endometriosis, or ovarian pathology — gynaecological examination and pelvic ultrasound differentiate
Detrusor instability	TrP just above the pubis may cause detrusor and sphincter spasm; distinguishing from primary detrusor instability may require urodynamic studies; TrP inactivation resolves symptoms in the myofascial case

Treatment

Trigger Point Injection

• The needle is directed cephalad, close to the midline, away from the pubis — rather than toward the bone
• This direction injects the pyramidalis muscle and distinguishes it from the lower rectus abdominis pubic attachment injection, where the needle is directed toward the pubic bone
• Injection proceeds as for other suprapubic attachment TrPs

Corrective Actions

• Direct pressure release on the suprapubic TrP, pressing toward the pubic arch; self-administration is valuable between menstrual periods
• Pelvic-tilt exercise (see Muscle:Rectus Abdominis — Corrective Actions)
• Abdominal (diaphragmatic) breathing
• Sit-back/Abdominal-curl exercise sequence when pain-free (see Muscle:Rectus Abdominis — Corrective Actions)

Satellite Trigger Points

• Rectus abdominis — primary functional partner; lower rectus TrPs commonly co-active
• Pelvic floor muscles — close anatomical relationship; commonly co-active in pelvic pain syndromes
• Internal oblique — conjoined tendon relationship at pubic arch

Related Pages

• Pain:Suprapubic — Pyramidalis and lower rectus as myofascial sources
• Pain:Dysmenorrhoea — Lower rectus and pyramidalis TrPs
• Muscle:Rectus Abdominis — Primary functional partner
• Muscle:Internal Oblique — Conjoined tendon partner at pubic arch

References

• Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 2: The Lower Extremities. Baltimore: Williams & Wilkins; 1992. Chapter 49.
• Beaton LE, Anson BJ. The pyramidalis muscle: its occurrence and size in American white and negroes. Am J Phys Anthropol 25:261–269, 1939.
• Anson BJ, Beaton LE, McVay CB. The pyramidalis muscle. Anatomical Record 72:405–411, 1938.