PHASE TRANSFORMATION OF ZIRCONE HEADS AFTER TOTAL HIP ARTHROPLASTY: MYTH OR REALITY ?

Abstract

Purpose: From 1985 to 2001, nearly 400,000 Zircone heads were implanted for total hip arthroplasty. In France, following an abnormally high rate of ruptures in two lots of heat-treated heads, production of Zircone heads was interrupted in 2001. Following work by Allain et al., another controversy developed concerning abnormal secondary wear of Zircone heads. According to certain authors, head roughness was increased by pitting phase transformation. This hypothesis was corroborated by Haraguchi (2001) who reported three explanted heads. We wanted to check the hypothesis.

Material and methods: In 2002, we explanted three Prozyr 22.2 Zircone heads for recurrent dislocation. We compared the explanted heads with a new Zircone head, a 28-mm alumina head explanted after prosthesis loosening and a new alumina head, using the same protocol as Haraguchi.

Results: On the explanted heads, the percentage of monoclinic Zircone was always less than 10% (3–10%). Roughness was also very minimal (Ra=0.01μm) for Zircone and ceramic heads, whether new or explanted, with no pitting and no notable structural change. The mean size of femoral head grains remained within the ISO 13 356 standard (1997).

Discussion: In 2003, Clark who studied three Zircone heads removed 2.8 to 10 years after implantation selected among 23 explanted heads, was unable to demonstrate any phase transformation or surface alterations. On one head explanted at eight years, Clark found significant monoclinic phase transformation. In our study, the three explanted heads did not exhibit significant monoclinic phase transformation since it remained less than 10% without pitting nor increased roughness. The behaviour of 22.2 Zircone heads may be different from 28 Zircone heads in terms of fracture (since no fractures have been observed after high-temperature furnace treatment of 22.2 heads) and in terms of monoclinic phase transformation.

Conclusion: This point is crucial for patients with a Zircone head total hip arthroplasty. Surveillance must be continued. At the present time and for mid term, we can conclude that the rate of monoclinic phase transformation of explanted Zircone heads is minimal and that production quality is good, particularly for 22.225 mm heads.