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