RADIOLOGY OF THE HIP Chris Dowding Dec 8, 2011 Prev. by: Sebastian Rodriguez-Elizalde, Gill Bayley

 Approach to Imaging  Screening for Deformities  Hip Dysplasia  Femoral Acetabular Impingement

1. Screening Imaging 2. Specific XR Views - quantify deformity 3. CT – helps with operative planning 4. MR(A) – Soft tissues

- Tube to film distance of 120 cm - Central beam directed to midpoint between upper border of symphysis and a horizontal line connecting both ASISs - Pubic symphysis distance to sacrococcygeal joint should be mm for men, mm for women - Pelvic Symmetry Assessment:  Symmetry of obturator foramina  Relationship of sacral midpoint and the pubic symphysis

Femoral Angle degrees

Femoral Angle Femoral Head - Cam deformity - AVN - Sclerosis, lesions

Femoral Angle Femoral Head Shenton’s Line Continuous line from neck of femur to superior pubic ramus

Femoral Angle Femoral Head Shenton’s Line Acetabulum - Sclerosis, osteophytes - Coxa profunda, protrusio - Pincer - Widening

Femoral Angle Femoral Head Shenton’s Line Acetabulum Acetabular Retroversion

Coxa Profunda Leunig M et al. Radiology 2005;236: ©2005 by Radiological Society of North America

 PLAIN RADIOGRAPHS  AP Pelvis (Standing) ▪ Shenton’s Line ▪ Center-Edge Angle ▪ Tonnis Angle (Roof Angle) ▪ Extrusion Distance ▪ Severity of subluxation (Crowe Classification) ▪ Acetabular Retroversion (30%)  False Profile  Abduction View

 SHENTON’S LINE  Continuous line from neck of femur to superior pubic ramus

 CENTER EDGE ANGLE (of Wiberg) Angle between... - Vertical Line from “C” (Center of Femoral Head) to - Line between “E” (Edge of Acetabulum) to C Normal is > 25 degrees CEA VEC

 TONNIS ANGLE Measures inclination of Weight Bearing zone of acetabulum - Horizontal line from medial edge WB zone - Line from medial to lateral edge WB zone Normal < 10 °  TONNIS ANGLE Measures inclination of Weight Bearing zone of acetabulum - Horizontal line from medial edge WB zone - Line from medial to lateral edge WB zone Normal < 10 ° TA

 EXTRUSION DISTANCE  Lateral part of the femoral head not covered by acetabulum (A)  Divided by total width of the head (B)  Expressed as a percentage ▪ NORMAL > 80% A B

 Classification: Crowe, Mani & Ranawat (JBJS Am Jan 1979)  Classifies degree of dysplasia  Based on severity of subluxation on AP pelvis GRADE 1< 50% Subluxation GRADE 2 May have false acetabulum overlapping true acetablulum 50-75% Subluxation GRADE 3 Absence of acetabular roof, false acetabular development % Subluxation GRADE 4 Insufficient acetabular development > 100% Subluxation

 Standing - Affected hip against cassette - Pelvis rotated 65° from plane of cassette

 FALSE PROFILE VIEW  Assess anterior coverage of femoral head  (Lequesne) VENTRAL INCLINATION ANGLE: ▪ Similar to CEA ▪ Normal > 25 degreesCVIN V E

Carlisle et al, The Iowa Orthopaedic Journal, 2011

 AP Hip in maximum ABDuction  Useful to assess if patient is candidate for periacetabular osteotomy  Does hip reduce?  Is femoral head covered?  Is joint congruent?  Is there a good joint space?

PLAIN RADIOGRAPHS  TYPE I - CAM Impingement ▪ AP, DUNN, Lateral  TYPE 2 - PINCER Impingement ▪ AP

- Cam-type impingement is characterized by an insufficient femoral head neck offset ratio - Aspheric femoral head - Gives the appearance of a “Pistol Grip” deformity

 Point A is the femoral head/neck junction  ALPHA ANGLE < 55 degrees used as a cut off for FAI Notzli et al The Contour of the Femoral Head-Neck Junction as a Predictor for the Risk of Anterior Impingement JBJS-Br C A

- Dunn view in 45° hip flexion, neutral rotation, 20° abduction - ALPHA ANGLE < 55 degrees used as a cut off for FAI - Also Assess the sphercity of the head-neck junctionA C

 LATERAL OF FEMUR  Taken at 15 degrees of internal rotation for a true lateral of anterior femur  Eijer’s Offset Ratio can be calculated from the lateral

O N D Diameter (D) taken at maximal head width at perpendicular to neck shaft (N) Offset (O) taken from anterior neck cortex to anterior head Anterior Offset Head Diameter Normal Ratio > 0.15

 PRIMARY  Due to the contact between the femoral head-neck junction and the acetabular rim  Either from acetabular retroversion or coxa profunda  SECONDARY  Anterior pelvic tilt (lateral)  Osteophytosis

 Triad of Type 1 FAI on MRA 1. Abnormal alpha angle 2. Anterior superior labral tear 3. Anterior superior cartilage abnormality Kassarjiam A, Yoon LS, Belzile E, et al. Triad of MR arthrographic findings in patients withCam-type femoroacetabular impingement. Radiology 2005;236:588–92.

NORMALNORMAL ABNORMALABNORMAL CROSSOVER SIGN - the Anterior lip of the acetabulum should never cross lateral to the posterior wall on the AP POSTERIOR WALL SIGN - the center of the femoral head should not be lateral to the posterior wall

 APLHA ANGLE  Draw best fit circle over the femoral head  Draw a line through centre of femoral neck to centre of femoral head  Angle between that line and a line drawn to the femoral head neck junction, just beyond the circle Loss of concavity of antero-superior head-neck junction NORMAL < 50.5

 CORONAL OBLIQUE TORN SUPERIOR LABRUM

 Standard for MRI of hip pathology is MRA  Standard MRI cannot get good enough resolution with current technology  Gadnolinium injected into hip prior to MRI  Infiltrates labral tears and boney defects, allowing visulaization  dGEMRIC  MRI protocol  Delayed Gadolinium Enhanced MRI of Cartilage  Uses fact that cartilage has negative charge due to glyclosaminoglycans, analyzes penetration rates to estimate cartalige depths

 B. Bittersohl et al., 2011, Italy Orthopedic Reviews  dGEMRIC was developed using IV gadnolinium ▪ Low penetration into joint, not enough resolution to be very useful  Combined the protocol with MRA ▪ Significant difference in uptake comparing patients with and without OA

 Efforts to develop software for analysis of radiological images  Active shape modeling  Rebecca J. Barr et al., Rheumatology, 2011  Able to grade OA and predict risk of progression to THR with significance