Pelvis: structure, diameters, static Ákos Lukáts MD. Ph.D (lukats@ana2.sote.hu) 2015. 11. 17.

os coxae (pelvic bone) 2x! Osseous pelvis Sacroiliac joint sacrum os coxae (pelvic bone) 2x! coccyx (tail bone) Ring, composed of 3 (+1) bones Limited movements, great forces and shear stress Coccyx has no major mechanical role Pubic symphysis

Os coxae ilium pubic bone ischium

Iliac crest ant. sup. iliac spine post. sup. Iliac spine ant. inf. iliac spine post. Inf. Iliac spine Acetabulum Symphyseal surface Ischiac spine Obturator foramen Tuber ishiadicum.

Importance of palpation: intramuscular injection Triangular technique (trochanter major, anterior superior iliac spine, iliac crest) NOT to hit: superior gluteal a., v., n. Sobota - Atlas of Human Anatomy

Lesser sciatic foramen : They enter the ischiorectal fossa! Gluteal region Suprapiriform hiatus : superior gluteal a., v., n. Infrapiriform hiatus: inferior gluteal a., v., n. sciatic n. posterior femoral cut. n. internal pudendal a., v. pudendal n. Lesser sciatic foramen : internal pudendal a., v. pudendal n. They enter the ischiorectal fossa! Sobota - Atlas of Human Anatomy

3 bones ossify together near puberty to form an 8-shaped structure Firs centers of ossifications already visible at 3rd fetal month Common body of the bones forms the acetabulum – extremely strong Force acting from proper direction in utero is inevitable for the normal development of acetabulum. (hip dysplasia) pecten Symphyseal surface

Hip dysplasia, hip dislocation Causes: intrauterine developmental defect of acetabular fossa, not deep enough, can dislocate to relatively small forces. (twins, oligohydramnion, ??) Screening (physical examination, ultrasound)

Hip dysplasia, hip dislocation Therapy: proper positioning of femur after birth: Pavlik harness (anteflexion, abduction) Forces acting on the head of femur deppen the acetabular fossa! Operations rarely needed today. http://uuhsc.utah.edu/healthinfo/pediatric/orthopaedics/ddh.htm Greater degrees in small children!

Sacrum, coccyx 5 sacral and 2-4 coccygeal vertebrae ossify together (synostosis). Coccyx fairly rudimental, can ossify together with sacrum. Problems at birth. Auricular surface (fibrous cartilage)

Sacroiliac joint, pubic symphysis Structures holding osseous ring together: Sacroiliac joint (plane joint) great shear stress: fibrous cartilage symphysis (synchondrosis – almost proper joint) Sacroiliac joint Pubic symphysis

Ligaments of Sacroiliac joint Sacro-iliac ligaments dorsal inerosseal ventral Functionally belong to here: Ileolumbal lig. , Sacrospinous lig. Sacrotuberous lig. (two-armed lever)

Pubic symphysis

Bones and ligaments Greater schiatic foramen Obturator canal Subinguinal hiatus Sacrospinous lig. Sacrotuberous lig. Inguinal lig. Lesser schiatic foramen Obturator membrane (+ m. obt. Ext, int.)

Pelvis minor Superior aperture : 60-65º - inclinatio pelvis Terminal line (linea terminalis): Promontory Lateral mass Arcuate line Pecten ossis pubis Symphysis, upper border Inferior aperture: 10-15º Coccyx Sacrotuberous lig. Rami of pubic and schiatic bones Symphysis, inf. border

Diameters of the lesser pelvis a: superior aperture b: cavity (amplitudo pelvis) (greatest diameter) c: angustia pelvis (smallest diameter) d: inferior aperture a b HOUR-GLASS FORM c d

distantia spinarum (25-26 cm) distantia cristarum (28-29 cm) Diameters: superior aperture Greatest: transverse diameter Median diameter 11 cm Oblique diameter 12 cm Transverse diameter 13,5 cm distantia spinarum (25-26 cm) distantia cristarum (28-29 cm)

Conjugates a b c a: conjugata anatomica vera anatomical conjugate 12 cm b: conjugata anatomica obstetrica obstetric conjugate 11.5 cm c: conjugata diagonalis diagonal conjugate 13 cm Diagonal conjugate can be measured by intravaginal examination. a b c

Diameters: amplitudo pelvis Almost circular Greatest diameter: oblique (approx.14 cm) All diameters >13cm

Diameters: angustia pelvis Almost circular Smallest diameters of pelvis Greatest diameter: oblique (approx.10 cm)

Diameters: inferior aperture 11,5-12 cm Coccyx bends away: 2 cm

Greatest diameters Superior aperture: transverse: 13-13.5 cm Amplitudo pelvis: oblique: 14 cm Inferior aperture: sagittal: 9.5-11.5 cm

A bit of gynecology oblique transverse sagittal At birth, the head of the baby must always fit to the greatest diameters: rotates 90 degrees!

Axis pelvis Bent tube

Sexual differences Arcus pubis Angulus pubis Female Male

Female Male

Static of pelvis: center of gravity Passing through the following structures: atlantooccipital joint lower lumbar vertebrae, anterior to promontory head of femur - acetabulum talus (highest point of longitudinal lantar arch) Weight and support in the same plane! – Can stay in equilibrium without continuous muscle work. It is only possible if the superior aperture of pelvis is bent 60-65 degrees! – Pelvic inclination

Pelvic inclination Approximately 60-65 degree. (male – 60, female – 65) Ant. Sup iliac Spine and symphysis lies approximately in the same frontal plane. Position of sacrum: almost horizontal.

Leonardo da Vinci 1452-1519 Vesalius (1538)

Flexible support, energy absorption Two-armed lever F1 x d1 = F2 x d2 F1 F2 d1 d2 Flexible support, energy absorption

Double arch

Aqueduct, Pont du Gard, France

Sitting position Force/weight is transferred to tuber ischiadicum. „Sitting tubercule”!

Normal AP. X-ray.

Fracture with dislocation (open book)

Post-partum pubic diastasis

Always to think about pelvic deformity Trauma (car accidents) Vertebral deformity Vit D deficiency (rachitis) Any disease requiring long-term inbed therapy in children Some genetic diseases (fetal size)

Dog: pelvic fracture

Literature Szentagothai J, Réthelyi M: Funkcionális anatómia, Medicina, 1989 Sobota - Atlas of Human Anatomy, 20th edition, Urban and Schwarzenberger, 1993 Renner Antal: Traumatológia, 2nd edition, Medicina, Budapest, 2003 Vízkelety Tibor: Az ortopédia tankönyve, 2nd edition, Semmelweis Kiadó, 1999 Radiologic images: http://rad.usuhs.mil/medpix/index.html