Acetabular cavity:
Hemispherical with elevated bone rim. This rim is absent inferiorly called acetabular notch.
Lunate surface is seen between notch and acetabular fossa and may be devoid of cartilage; seen in the medial aspect of acetabular roof and called superior acetabular notch
Transverse acetabular ligament:
Covers the deficient portion of the acetabulum, i.e., inferomedially
Lunate:
Horse shoe shaped acetabular cartilage lines acetabulum, except centrally (acetabular fossa) which is filled with fibrofatty tissue lined by synovium
Femoral head:
Completely covered by cartilage except fovea capitus, which is central depression
Ligamentum teres:
From fovea, runs inferiorly, inserts to transverse ligament
Joint capsule:
Attched to acetabular rim - anteriorly and posteriorly attached to the base of labrum creating a small perilabral recess; superiorly attched few mm above labrum creating a larger perilabral recess
Extends anteriorly up to intertrochonteric line; posteriorly covers only half of the neck
Acetabular labrum:
Fibrocartilagenous tissue
Attached to bony acetabular rim, and transverse acetabular ligament anteriorly and posteriorly at acetabular notch. Cleft is formed at the junction of labrum and T ligament (not be confused for tear)
Thick posteorsuperiorly, thin anteroinferiorly
Triangular in cross section (seen as triangle on axial and coronal MR)
Ligaments (thickening of capsule):
Superficial: longitudinally oriented pubofemoral ligament, iliofemoral ligament, Ischiofemoral ligament
Deep: circular oriented zona orbicularis at neck base
Recesses:
Perilabral recess (sulcus): Between labrum and joint capsule
Sublabral sulcus (recess): Between labrum and articular surface (the same site where labrum blends with transverse acetabular ligament)
Iliopsoas bursa:
communication in 10-15%
MR appearance:
Triangular in 70%; but may be round, flat, irregular or absent normally
References:
1.Resnick et al. Internal dergangements of joints. 2nd edition. Saunders Elsevier. 2007
2. http://radiographics.rsnajnls.org/cgi/content/abstract/20/suppl_1/S3
