Effect of neck length on third-generation ceramic head failure; finite element and retrieval analysis.
BACKGROUND
Optimized design using finite element analysis (FEA) has considerably increased the longevity of ceramic implants in total hip arthroplasty. Unlike previous FEA studies, a 28-mm head with a short neck was found to be prone to failure, even with third-generation ceramic. We conducted a finite element analysis of the third-generation ceramic head failure according to neck lengths and a retrieval analysis of the four fractured ceramic heads.


METHODS
Models of real specimens were created for short-, medium-, and long-neck heads made of alumina, based on data given by the manufacturer and reverse engineering design. Static loading was simulated in a series of five steps to 46 kN, and fatigue loading consisting of 10(7) cycles was simulated in walking (4.3 kN) and high-impact (10 kN) conditions to determine the safety factor.


RESULTS
Although the maximum principal stress of the long-neck design was the greatest, consistent with a previous FEA study, the safety factor was the lowest at the inner corner between the roof and tapered bore of the ceramic head with the short-neck design in both fatigue-loading conditions. Furthermore, surface analysis of one head revealed that the fracture was propagated from the inner corner between the roof and tapered bore into the base of the ceramic head.


CONCLUSIONS
Our results suggest that the short-neck design with a 28-mm ceramic head has a greater potential risk of ceramic failure than other designs.
Department of Orthopedic Surgery, Seoul National University Bundnag Hospital, 82 Gumi-ro, 173 Beon-gil, Bundang-gu, Seongnam, Gyeonggi-do, 463-707, South Korea.
Young-Kyun
YK
Lee
Jae-Chul
JC
Lee
Yong-Chan
YC
Ha
Kyung-Hoi
KH
Koo
D000328:Adult; D002516:Ceramics; D019544:Equipment Failure Analysis; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure