CONTRIBUTION OF NITROGEN-ION IMPLANTED TITANIUM HEADS IN ASEPTIC LOOSENINGS OF TOTAL HIP ARTHOPLASTIES

Abstract

Purpose: Use of nitrogen-ion implanted titanium heads appeared to us as an essential factor in the development of aseptic acetabular and femoral loosenings.

Material and methods: Our series included 62 implanted titanium heads reviewed at a mean follow-up of 84.4 months. Nine patients had died and one was lost to follow-up. The heads were combined with a titanium-sanded elastic pressfix cup in 40 cases, and with the same cup with hydroxyapatite surfacing in 12 cases. Titanium femoral stems were cemented in 16 cases and non-cemented in 36 with a titanium-sanded metaphyseal support.

Results: At mean follow-up of 84.4 months, there was a lucent line in three zones on the AP view, including 9 that were complete, in 11 cups. Acetabular osteolysis was observed around five cups and femoral osteolysis around eight stems. Mean wear was 0.18 mm per year. Considering the entire series (61 heads), there were 11 cups requiring revision for aseptic loosening at a mean 74.2 months; four stems (all without cement) that had to be replaced for aseptic loosening at 74.5 months. Polyethylene wear on the removed implants was more pronounced than for the non-revised implants (0.34 mm/year versus 0.14 mm/year, p < 0.05). Metallosis was associated in eight cases. Macroscopic analysis of the heads revealed evidence of delamination on the entire contact surface with the polyethylene. The femoral and acetabular implants did not appear to be the cause of these loosenings because associated with other types of heads (stainless steel, chromium-cobalt, alumine, zircone, niturate titanium) they did not lead to loosening except in one case (stainless steel head) out of 118.

Discussion: Titanium is known to be have poor friction properties. To improve performance, ionic implantation has been proposed. The layer of nitrogen ions projected onto the surface of the head only cover a thickness to the order of one micron. Once this protective film is rapidly dissipated by abrasion, the titanium comes in direct contact with the polyethylene, leading to important release of titanium and polyethylene particles that can cause osteolytis and aseptic loosening.

Conclusion: Close surveillance of patients with these heads is necessary to recognise wear early and propose synovectomy and head replacement in case of implant loosening.