Aseptic loosening is considered relatively common complication of hip joint replacements. It is usually considered a long-term complication and is often considered as the most common complication ³.

Pathology

Aseptic loosening can occur as a result of inadequate initial fixation, mechanical loss of fixation over time, or a biological loss of fixation caused by particle-induced osteolysis surrounding the implant.

The causes of particle accumulation vary from implant interface wear, micromotion occurring in response to corrosion, oxidative reactions, and minor pathogen contamination. The initial response to particulate debris can include a subtle inflammatory response, which becomes more pronounced as osteolysis progresses. This inflammatory environment provokes a cellular response that is characterised by elevated levels of secreted factors such as TNF, RANKL, IL-6, IL-1, and IL-11.

Radiographic features

Plain radiograph

A peri-implant lucency of greater than 2 mm or progressive change is considered a concerning feature.

• <1 mm in thickness are usually clinically insignificant

• 1-2 mm in thickness probably indicates membrane formation with pseudo-stable implants

• >2 mm in thickness (especially if new or progressive) are likely indicative of aseptic loosening of hip joint replacements

Stress views may show an interval change in position. The loosening is not lined by sclerosis. The features may include:

• medial migration of cement and cup mass

• change in inclination of the cup

See also

• DeLee & Charnley and Gruen zones