Introduction MRI basics patient is positioned in a large magnetic field protons in body align with the magnetic field external radiofrequency current pulses through patient and stimulates protons, causing to spin out of equilibrium once external radiofrequency current is discontinued energy is released by protons sensors detect the energy released by the protons and the time it takes the protons to return to equilibrium Fourier transformation is used to convert sensor data at each location into image data relaxation time time required for protons to align with external magnetic field corresponds to T1 and T2 login to view 2 more bullets gadolinium contrast paramagnetic agent (contains heavy metal) shortens T1 interval login to view 1 more bullet direct hip arthrography login to view 1 more bullet indirect hip arthrography login to view 3 more bullets magnetic strength 1.5 T login to view 2 more bullets 3.0 T login to view 6 more bullets Tissue Appearance on MRI Tissue T1 T2 Synovial fluid Dark Bright Blood Dark Bright Fat Bright Dark Inflammation Dark Bright Muscles Gray Dark Gray Paramagnetic substances (Iron, hemosiderin, gadolinium, etc.) Bright Dark Normal Anatomy Osteology Pelvis innominate bone login to view 3 more bullets fuse together at the triradiate cartilage acetabulum login to view 4 more bullets Femur strongest bone in the body femoral head login to view 2 more bullets greater trochanter login to view 5 more bullets Labrum rim of fibrocartilage that surrounds the acetabulm triangular in shape on cross section horseshoe shaped surrounding acetabulum increases congruity and depth of the femoroacetabular joint adds to the suction cup stability of the acetabulofemoral joint originates from the transverse acetabular ligament small percentage of patients do not have a labrum approximately 3% Ligaments ligamentum teres ligamentous connection between femoral head and acetabulum login to view 2 more bullets in patients with developmental hip dysplasia the ligamentum teres can be hypertrophied and elongated iliofemoral ligament also referred to as ligament of Bigelow or Y-ligament anterior to femoroacetabular joint and is major ligamentous stabilizer of the femoroacetabular joint Muscles Muscle on MRI Muscle MRI Iliopsoas Pectineus Sartorius Rectus femoris Vastus lateralis Gluetus maximus Gluteus medius Gluteus minimus Tensor fascia lata Semitendinosus Semimembranosus Biceps femoris Quadratus femoris Piriformis Nerves Nerves on MRI Nerve MRI Femoral nerve Sciatic nerve Obturator nerve Blood vessels Blood vessels on MRI Blood vessel MRI Femoral artery Femoral vein Anatomic Variants Labral variants sublabral sulci present in up to 25% of patients login to view 3 more bullets can be mistaken for a labral tear login to view 7 more bullets transverse acetabular ligament labral junction sulcus can appear in the anterior an posterior intersection of the transverse acetabular ligament and the labrum login to view 3 more bullets can occur in conjunction with a periligamentous recess anteromedial to the ligamentum teres perilabral sulcus anatomic space between the joint capsule and labrum login to view 1 more bullet can be mistaken for a perilabral cyst MRI arthrogram with joint distension can differentiate between perilabral cyst and perilabral sulcus anterosuperior cleft partial extension of fluid into the anterosuperior labrum on sagittal and coronal images login to view 1 more bullet Nonlabral variants synovial herniation pits also known as Pitt pits predominantly found on the anterosuperior femoral neck login to view 1 more bullet found in up to 33% of patients with femoroacetabular impingement login to view 1 more bullet os acetabuli ossicle adjacent to the superior acetabular rim due to perisistent secondary ossification center that remains unfused to the acetabulum login to view 1 more bullet accessory iliacus tendon seperated iliacus tendon from the iliopsoas tendon present in up to 66% of patients undergoing hip arthrograms can be mistaken for a longitudinal tear of the iliopsoas tendon login to view 2 more bullets plicae synovial folds that are embyronic remnants and are located at the interface of the articular surface mostly are asymptomatic login to view 1 more bullet pectinofoveal fold also known as the middle retinaculum of Weitbrecht extends from lesser trochanter to fovea capitis contains the posteroinferior retinacular arteries and branches of the medial femoral circumflex artery found in 95% of hip MRI arthrograms almost never becomes symptomatic supraacetabular fossa typically located at the 12 O'clock position of the acetabulum can be filled with synovial fluid or cartilage login to view 1 more bullet can be mistaken for an acetabular cartilage defect login to view 1 more bullet does not communicate with the acetabular fossa stellate crease area of the acetabulum that is bare of hyaline cartilage usually medial to where supraacetabular fossa would be located in continuity with the acetabular fossa Pathology Femoroacetabular impingement impingement between the acetabulum and femoral neck most often the anterolateral femoral neck and anterosuperior acetabulum two types of impingement: cam impingement login to view 1 more bullet pincer impingement login to view 1 more bullet high association with labral tears radiographic assessment head-neck offset login to view 2 more bullets alpha angle login to view 7 more bullets acetabular version login to view 3 more bullets Labral tears intrasubstance tear or detachment of the labrum from the acetabulum occurs most commonly in the anterosuperior quadrant login to view 1 more bullet freuqently occurs in conjunction with femoroacetabular impingement and developmental hip dysplasia radiographic assessment: MRI arthrogram is the most sensitive study for diagnosing labral tears login to view 1 more bullet Hip avascular necrosis necrosis of the bone involving the femoral head occurs in the epiphysis idiopathic etiology is most common radiographic assessment usually presents with hypointense signal on T1 weighted imaging localized to the epiphysis modified Kerboul combined necrotic angle login to view 2 more bullets Modified Kerboul Combined Necrotic Angle Risk group Combined Angle Low-risk <190° Medium-risk between 190° and 240° High-risk >240° Transient osteoporosis of the hip localized hyperemia of the proximal femur with decreased venous return and increase marrow pressure radiographic assessment: hypointense signal on T1 and hyperintense singal on T2 that spans the metaphysis and epiphsysis login to view 1 more bullet Trochanteric bursitis inflammation involving the greater trochanteric bursa can be classified based on location of inflammation on MRI imaging sub-gluteus maximus (most common) sub-gluteus medius sub-gluteus minimis radiographic assessment high signal present in the trochanteric bursa on T2 sequences login to view 1 more bullet Osteomyelitis bacterial of fungal infection of bone most often due to hematogenous spread frequently involves the metaphysis in pediatric patients login to view 1 more bullet radiographic assessment: login to view 5 more bullets Ischiofemoral impingement impingement of soft tissue beween the lesser trochanter and the ischial tuberosity radiographic assessment: axial T1 weighted images can be used to calculate distance between lesser trochanter and ischial tuberosity login to view 3 more bullets axial T2 weighted images login to view 2 more bullets treatment: nonoperative login to view 1 more bullet operative login to view 3 more bullets Osteoarthritis degenerative changes of the femoroacetabular joint that leads to cartilage loss radiographic assessment: diagnosis predominantly made with plain radiographs MRI has low utility in diagnosis and treatment modification login to view 8 more bullets Metastic disease most common cause for detructive bone lesions in adults proximal femur is the most common site for metastasis next to the spine 50% femoral neck 20% pertrochanteric region 30% subtrochanteric radiographic assessment most surgical decision making is done with standard AP and lateral hip and full-length femur radiographs magnetic resonance imaging login to view 2 more bullets