Wear and performance of a tripolar total hip replacement

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Medical Device Engineering

Background:

• The tripolar hip replacement is an unconstrained prosthesis combining a large-capacity acetabular component with a bipolar prosthesis.
• It aims to prevent dislocation and maintain a near-normal range of motion (ROM), differing from newer dual mobility designs.
• Limited data exists on the long-term wear and performance of tripolar hip replacements.

Purpose of the Study:

• To evaluate the wear, performance, and mechanical function of retrieved tripolar hip prostheses.
• To compare the tripolar prosthesis to conventional and dual mobility designs in high-demand patients.

Main Methods:

• Twenty-four tripolar prostheses were retrieved from 23 patients after a mean of 14 years (range, 5-21 years).
• Implants were from high-demand patients (adventure sports, high-risk occupations, revisions).
• Key design features included a large-diameter, highly cross-linked polyethylene acetabular component, a titanium nitride-coated bipolar, and positive eccentricity.

Main Results:

• Total volumetric wear was 24 mm³/yr, significantly lower than dual mobility (54 mm³/yr) and conventional (38 mm³/yr) prostheses.
• Increased jump distance (16 mm vs. 12 mm) and range of motion (145° vs. 119°) were observed.
• No osteolysis was found, and radiographs indicated continued articulation between components.

Conclusions:

• Tripolar hip prosthesis wear is below the osteolytic threshold, indicating long-term viability.
• Enhanced ROM and jump distance offer superior stability for an unconstrained hip replacement.
• The technology demonstrates safety advantages over dual mobility prostheses, with no intraprosthetic dislocation or adverse metal reactions observed.