THR loosening

Most common cause of THR failure
Acetabular loosening incereases with time
Improvement in technque have reduced femoral lossening

Radiography:
Lucency between cement and bone more than 2 mm
Prosthetic migration
Cement fracture
Peristeal reaction

Arthrography:
Acetabular loosening: 90% sensitive, 70% specific
Contrast in all zones, I & II, II & III, or I & III with pseudocapsule or bursa (there are 3 zones divided by 2 perpendicular lines drawn from the centre of the acetabulur line; the lateral is zone I, middle zone II and medial zone III)
Contrast more than 2 mm thick in any zone
Femoral lossening: 90% sensitive and specific
Contrast below intertrochontric line

References:
Resnick et al, Bone and joint imaging, 3rd edition, Elsevier Saunders publications

THR: radiographic appearance

Component position:
1. Acetabular inclination: Angle between horizonatl base line and actabular orifice is usually 40-50 degrees. More angle = verticle inclination, less angle = horizaontal inclination
2. Acetabular anteversion: on true lateral view, angle between axis of acetabulum and a line perpendicular to the base line
2. Verticle position of the femur: Perpendicluar distance between centre of hip and interteardrop line
3. Mediolateral position of the femur: Distance between centre of hip and interteardrop line
4. Femoral stem: should be within the centre of medullar canal or slightly medially.
5. Length: Distance between proximal edge of lesser trochonter and base of ischial tuberosity

Component fixation:
Lucent lines between cement and bone usually stabilise in 2 years, measuring 0.1 to 1.5 mm. More 2 mm indicates loosening.

References:
Resnick et al, Bone and joint imaging, 3rd edition, Elsevier Saunders publications