Bones of the pelvis
The pelvis consists of the sacrum, the coccyx, the ischium, the ilium, and the pubis.[1][2] The structure of the pelvis supports the contents of the abdomen while also helping to transfer the weight from the spine to the lower limbs.[3] During gait, the joints within the pelvis work together to decrease the amount of force transferred from the ground and lower extremities to the spine and upper extremities.[3]


Innominate bone.jpg
  • Sacrum
  • Coccyx
  • Two innominate bones, which consist of the:
    • Ischium
    • Ilium
    • Pubis[1]

Joint Articulations

There are three articulations within the pelvis:

  • Inferiorly between the sacrum and the coccyx
  • Posteriorly between the sacrum and each ilium (sacroiliac (SI) joint)
  • Anteriorly between the pubic bodies (pubic symphysis).[2]

Other articulations:

The pelvis and femur articulate via the acetabulum[1]



Ligaments of the Pelvis

Sacroiliac Ligaments

  • Ventral/Anterior sacroiliac ligament
  • Dorsal/Posterior sacroiliac ligament
  • Interosseous sacroiliac ligament

Sacrococcygeal Ligaments

  • Ventral/Anterio sacrococcygeal ligament
  • Dorsal sacrococcygeal ligament
  • Lateral sacrococcygeal ligament

Pubic Symphysis Ligaments

  • Superior pubic ligament
  • Inferior pubic ligament
  • Anterior pubic ligament
  • Posterior pubic ligament


There are 36 muscles that attach to the sacrum or innominates. The purpose of these muscles is primarily to provide stability to the joint not to produce movement.[5]

Muscles that attach to the sacrum or innominates are:

Adductor brevis Adductor longus Adductor magnus Biceps femoris - long head Coccygeus
Erector Spinae External oblique Gluteus maxiumus Gluteus medius Gluteus minimus
Gracilis Iliacus Inferior gemellus Internal oblique Latissimus dorsi
Levator ani Multifidus Obturator internus Obturator externus Pectineus
Levator ani Piriformis Psoas minor Pyramidalis Quadratus femoris
Quadratus lumborum Rectus abdominis Rectus femoris Sartorius Semimembranosus
Semitendonosus Sphincter urethrae Superficial transverse perineal ischiocavernous Superior gemellus Tensor fascia lata
Transversus abdominus

Sex-specific differences

The female pelvis consists of a wider sacrum and a wider subpubic angle when compared to males. The female pelvis’ ischial spines are also less prominent than the male’s ischial spines.[6][7][8] The male pelvis’ sacrum is generally longer and more curved with a narrower sub-pubic arch.[8] In females a wider pelvic aperture is needed as it functions as the birth canal during labour.[6][7][9][10][11]

Clinical Examination


Prior to the assessment of the sacroiliac joint both the lumbar spine and hip should be assessed and any underlying pathology should be ruled out.

Special Tests

SI Joint stress tests

Leg Length tests

  • Prone test
  • Standing leg length test
  • Functional leg length test

Other Special Tests

Outcome Measures



  1. 1.0 1.1 1.2 White TD, Black MT, Folkens PA. Human osteology. Academic press; 2011.
  2. 2.0 2.1 Lewis CL, Laudicina NM, Khuu A, Loverro KL. The human pelvis: Variation in structure and function during gait. The Anatomical Record 2017;300(4):633-42.
  3. 3.0 3.1 Magee DJ. Orthopedic physical assessment. Elsevier Health Sciences; 2013.
  4. Anatomy Zone. Bones of the Pelvis. Available from: [last accessed 27/01/2020]
  5. Calvillo O, Skaribas I, Turnipseed J. Anatomy and pathophysiology of the sacroiliac joint. Current review of pain 2000;4(5):356-61.
  6. 6.0 6.1 Kurki HK. Pelvic dimorphism in relation to body size and body size dimorphism in humans. Journal of Human Evolution 2011;61(6):631-43.
  7. 7.0 7.1 Meindl RS, Lovejoy CO, Mensforth RP, Carlos LD. Accuracy and direction of error in the sexing of the skeleton: implications for paleodemography. American Journal of Physical Anthropology 1985;68(1):79-85.
  8. 8.0 8.1 Tague RG. Sexual dimorphism in the human bony pelvis, with a consideration of the Neandertal pelvis from Kebara Cave, Israel. American Journal of Physical Anthropology 1992;88(1):1-21.
  9. Rosenberg KR. The evolution of modern human childbirth. American Journal of Physical Anthropology.1992;35(S15):89-124.
  10. Lovejoy CO. The natural history of human gait and posture: part 2. Hip and thigh. Gait & posture 2005;21(1):113-24.
  11. Abitbol MM. The shapes of the female pelvis. Contributing factors. The Journal of reproductive medicine 1996;41(4):242-50.