Anatomy: A Tale of a Bone called Coccyx

Breaking News… the coccyx is no longer a bone that only Women’s Health Specialists are concerned about.  As physical therapists, we spend a significant amount of time treating the spine and dysfunctions of the pelvis, pelvic floor and lower extremities.  What these areas all have in common is this one little bone that we don’t think too much about… the coccyx.

Normalization of a dysfunctional coccyx enhances objective signs in other lumbopelvic girdle structures.  Conversely, when related structures (sacrum, innominate, lumbars spine and hips) are treated, coccygeal dysfunctions rarely improve. – Gregg Johnson (Wise 2015)

Inner Body’s Graphic

The Coccyx

  • Many consider it to be the key structure for the lumbopelvic girdle (Wise 2015)
  • has important muscle attachments that influence the body beyond the pelvic floor
    • Gluteus Maximus
    • Levator Ani
    • Coccygeus
  • Has important ligamentous attachments:
    • The anococcygel ligament helps with the functioning of the anus by holding the external anal sphincter in place. (Taylor 2017)
  • is the anchor for the inferior part of the spinal cord & meninges within the spinal canal
    • Serves as the distal attachment of the filum terminal (extension of the meninges) (Moore 2014).
  • Is involved in functional activities:
    • when we are sitting, the body weight rests on the coccyx posteriorly (Taylor 2017)
    • in women, the coccyx extends to create more space for the child in the birthing process (Taylor 2017)
  • Anatomical differences in males & females (Taylor 2017)
    • males:  aligned more anteriorly
    • women: aligned more inferiorly

The Dirty Details from Moore’s Clinically Oriented Anatomy (2014).

The Pelvic Girdle: This is the ring of bones that essentially connects the spine to the femurs, bears the weight of the upper body in sitting, and provides many attachments for the muscles used for locomotion and posture.  The girdle also houses the pelvic viscera and inferior abdominal viscera. And in women, this area supports the growing fetus.

  • specifically, the coccyx makes up the pelvic outlet which is the inferior pelvic aperture.  This ring consists of the pubic arch, ischial tuberosities, inferior margins of the sacrotuberous ligament and the tip of the coccyx.
  • It also makes up the lesser pelvis which includes the pelvic cavity and the deep pars of the the pelvic floor.
    • Pelvic Floor (pelvic diaphragm): separates the pelvic cavity form the perineum

Ligamentous Attachments

  • Sacrotuberous ligament: a massive ligament that connects the posterior margin of the ilium along the scarum & coccyx to the ischiums, which helps to form to the sciatic foramen.
  • Sacrospinous ligament: this ligament further divides the sciatic foramen into the greater and lesser sciatic foramina.
    • the piriformis muscle passes through the greater sciatic foramen
    • The Inferior gluteal a. (supplies muscles and skins of the buttocks and posterior surface of the thigh) and superior gluteal a.(gluteal mm) runs through the greater sciatic foramen
    • pudendal nerve leaves the pelvis through the greater sciatic forament
    • Superior glutetal nerve: supplies motor to the mm in the gluteal region
    • Inferior gluteal nerve: glut max

These two ligaments together help to counterbalance the weight of the body when the vertebral body sustains a sudden increase in force or weight (while jumping, running, lifting weights etc.).  The superior end of the sacrum is pushed inferiorly and anteriorly, while the ligament prevents the superior and posterior rotation of the sacrum anchoring the sacrum to the ischium (Moore 2014).

  • Sacrococcygeal ligament: reinforces the sacrococcygeal joint

Muscles that attach to the coccyx:

  • Coccygeus muscles (Ischiococcygeus):
    • forms a small part to the pelvic diaphragm that supports pelvic viscera
    • flexes the coccyx
    • origin: inferior sacrum and coccyx
    • insertion: sacrospinous ligament
  • Levator ani (puborectalis, pubococcygeus and iliococcygeus)
    • forms most of the pelvic diaphragm that supports the pelvic viscera
    • resists intra-abdominal pressure
  • Pubococcygeus
    • origin: posterior aspect of the pubis and anterior tendinous arch
    • insertion: coccyx and anococcygeal body (ligament between the anus and coccyx (aka Levator plate))
  • iliococcygeus: 
    • origin: arch and ischial spine
    • insertion: blends with anococcygeal body posterior

Arteries

  • Median Sacral a: blood supply for the inferior lumbar vertebrae, sacrum and coccyx

Adjacent Nerves:

  • Coccygeal plexus: formed by the rami of S4 and S5 plus the coccygeal nerves.
    • supplies: coccygeus, levator ani, sacrococcygeal joint
  • Anococcygeal nerves: pierces coccygeus and anococcygeal ligament to supply the small area of skin between the coccyx and the anus.
  • Ganglion impar (sympathetic chain) lies on the anterior aspect of the coccyx
  • Filum Terminale: the caudal part of the spinal cord that serves as an anchor of the inferior end of the spinal cord and the spinal meninges.

Positional Faults of a dysfunctional Coccyx

– From Gregg Johnson’s Functional Mobilization Approach (Wise 2014)
  • Sacrococcygeal Junction
    • Compression
    • Rotation
    • Posterior Shear: often seen after childbirth
    • Anterior Shear: result of a direct fall.
    • Lateral Translation: can be right or left
  • Dysfunctions of the Coccyx body
    • Deviation
    • Extension
    • Flexion

There are treatment strategies outlined in Wise’s book.  For more information, I recommend looking into courses by the Institute of Physical Art, specially Functional Mobilization I. (See their Schedule here.)

Resources:

  1. Wise, Christopher H. Orthopaedic Manual Physical Therapy: from Art to Evidence. Philadelphia, PA, F.A. Davis Company, 2015.
  2. Taylor, Tim. “Coccyx.” InnerBody, www.innerbody.com/image_skelfov/skel38_new.html. Accessed 2 Sept. 2017.
  3. Moore, Keith L., et al. Clinically Oriented Anatomy. Philadelphia, Wolters Kluwer, 2014.

 

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