ARTHROPLASTY ROUNDS
RADIOLOGY OF THE HIP
Chris DowdingDec 8, 2011
Prev. by: Sebastian Rodriguez-Elizalde, Gill Bayley
OVERVIEW
Approach to ImagingScreening for DeformitiesHip DysplasiaFemoral Acetabular
Impingement
APPROACH TO IMAGING
1. Screening Imaging2. Specific XR Views - quantify deformity
3. CT – helps with operative planning
4. MR(A) – Soft tissues
SCREENING – AP RADIOGRAPH
SCREENING – AP RADIOGRAPH- 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 25-40 mm for men, 40-55 mm for women
- Pelvic Symmetry Assessment: Symmetry of obturator foramina Relationship of sacral midpoint and the
pubic symphysis
SCREENING IMAGING
Femoral Angle - 120-135 degrees
SCREENING IMAGING
Femoral Angle
Femoral Head - Cam deformity - AVN - Sclerosis, lesions
SCREENING IMAGING
Femoral Angle
Femoral Head
Shenton’s Line Continuous line from neck of femur to superior pubic ramus
SCREENING IMAGING
Femoral Angle
Femoral Head
Shenton’s Line
Acetabulum - Sclerosis, osteophytes - Coxa profunda, protrusio - Pincer - Widening
SCREENING IMAGING
Femoral Angle
Femoral Head
Shenton’s Line
Acetabulum
Acetabular Retroversion
Coxa Profunda
Leunig M et al. Radiology 2005;236:237-246
©2005 by Radiological Society of North America
HIP DYSPLASIA
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
V E
C
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
HIP DYSPLASIA:
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
75-100% Subluxation
GRADE 4 Insufficient acetabular development > 100% Subluxation
FALSE PROFILE VIEW
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 degrees
C
VINV
E
VENTRAL INCLINATION ANGLE
Carlisle et al, The Iowa Orthopaedic Journal, 2011
HIP ABDUCTION VIEW
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?
FEMORAL ACETABULAR IMPINGEMENT (FAI)
• 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
ALPHA ANGLE
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
CA
DUNN VIEW
- 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 junction
A
C
TYPE I - CAM IMPINGEMENT
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
EIJER’S OFFSET RATIO
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 OffsetHead Diameter
Normal Ratio > 0.15
TYPE 2 - PINCER IMPINGEMENT
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
MRA ASSESSMENT
Triad of Type 1 FAI on MRA
1. Abnormal alpha angle2. Anterior superior labral tear3. 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
ACETABULAR RETROVERSION
CROSSOVER SIGN - the Anterior lip of the acetabulum should never cross lateral to the posterior wall on the APPOSTERIOR WALL SIGN - the center of the femoral head should not be lateral to the posterior wall
MR ALPHA ANGLE
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
LABRAL TEARS
CORONAL OBLIQUE
TORN SUPERIORLABRUM
Recent Developments
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
Recent Developments
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
Recent Developments
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