A tribological study of retrieved hip prostheses

Area of Science:

• Orthopedic surgery
• Biomaterials science
• Failure analysis

Background:

• Charnley cemented acetabular cups are widely used in total hip arthroplasty.
• Revision surgery provides insights into implant failure modes and longevity.
• Understanding wear mechanisms is critical for improving prosthetic joint performance.

Purpose of the Study:

• To investigate the failure modes of explanted Charnley cemented acetabular cups and femoral stems.
• To quantify the wear rate and its correlation with implant service life.
• To identify factors contributing to the failure of cemented hip prostheses.

Main Methods:

• Analysis of 100 explanted Charnley acetabular cups and 78 femoral stems from revision surgeries.
• Review of patient records and radiographic assessments to determine failure causes.
• Categorization of damage to acetabular cups and femoral stems, including wear measurement.

Main Results:

• Component loosening was the most frequent cause of failure.
• Observed acetabular cup damage included erosion, rim wear, cement ingress, cratering, discoloration, and scoring.
• Femoral stem damage included fracture and roughening of the femoral head, often due to contrast medium.
• Mean femoral head penetration into the acetabular cup was 1.69 mm, with a mean rate of 0.21 mm/year.
• A high penetration rate was associated with a shorter implant service life.

Conclusions:

• Component loosening is the predominant failure mode in Charnley cemented hip implants.
• Wear, particularly high penetration rates, significantly impacts implant longevity.
• Reducing wear rates holds potential for enhancing the performance and durability of artificial hip joints.