European multidisciplinary consensus statement on the use and monitoring of metal-on-metal bearings for total hip replacement and hip resurfacing.

INTRODUCTION: There is an ongoing debate about the optimal use of metal-on-metal (MoM) bearings in total hip replacement, since there are uncertainties about local and systemic adverse effects due to wear and corrosion of these bearings. Despite various national recommendations, efforts to achieve international harmonization of specific evidence-based recommendations for best practice are still lacking. HYPOTHESIS: An international consensus study group should be able to develop recommendations on the use and monitoring of MoM bearings, preferably at the European level, through a multidisciplinary approach, by integrating the perspectives of various stakeholders. MATERIALS AND METHODS: Twenty-one experts representing three stakeholder groups and eight countries participated in this European consensus study, which consisted of a consensus meeting, subsequent structured discussion, and consensus voting. RESULTS: The current statement defines first of all benefits, local and systemic risks, as well as uncertain issues related to MoM bearings. Safety assessment after implantation of MoM comprises all patients. A closer follow-up is recommended for large head MoM (≥36mm) and resurfacing. In these implants basic follow-up should consist of x-rays and metal ion measurement of cobalt in whole blood, performed with GF-AAS or ICP-MS. Clinical and/or radiographic abnormality as well as elevated ion levels needs additional imaging (ultrasound, CT-scan and/or MARS-MRI). Cobalt values less than 2 µg/L are probably devoid of clinical concern, the threshold value for clinical concern is expected to be within the range of 2-7 µg/L. DISCUSSION: This is the first multinational, interdisciplinary, and multiprofessional approach for developing a recommendation for the use and monitoring of MoM bearings in total hip replacement. The current recommendations are in partial agreement with previous statements regarding the extent of follow-up and imaging techniques. They however differ from previous communications regarding measurement of metal ions and especially the investigated medium, technique, and eventual threshold levels. LEVEL OF EVIDENCE: Level V, expert opinion/agreement conference.

Survivorship of rough-surfaced threaded acetabular cups. 382 consecutive primary Zweymüller cups followed for 0.2-12 years.

We studied prospectively 382 cementless (Zweymüller stem) and hybrid (cemented stem) primary total hip replacements and used a cementless grit-blasted titanium alloy threaded cup. After a median 5 (0.2-12) year follow-up, 1 cup was exchanged, 2 cups were removed for deep sepsis, and 3 cups showed definite loosening; of these, 2 subsequently required revision. Actuarial calculation methods indicated a 10-year survivorship of 99% with cup retrieval for any cause (clinical failure), definite cup-loosening (radiographic failure), and revision for aseptic cup-loosening as endpoints. These intermediate results exceed those from smooth-surfaced screw rings and compare favorably with those from cemented cups and cementless, press-fit, metal-backed cups.

Acetabular screw rings and surface treatment.

The Zweymüller truncated self tapered threaded ring is forged in pure titanium with a 3- to 5-mu grit blasted surface roughness. Among 167 consecutive primary total hip arthroplasties prospectively studied, two threaded components failed to achieve initial stability, with one requiring almost immediate revision. One hundred twenty-six hips have been fully documented with a 5-year minimum followup. The mean modified Harris hip score improved from 44.4 points preoperatively to 91 points at 7 years average followup (range, 60-121 months). Bone to implant gap rate decreased from 54.7% after surgery to 2.4% at last review, with only one detectable early migration that had secondary stable osseointegration. Annual linear wear of more than 0.2 mm per year could be detected in only one ceramic on polyethylene bearing surface with one corresponding femoral osteolysis granuloma. At the 9- to 10-year interval, the survivorship with definite loosening as a failure was 98.7%. Delayed loosening by failure of an initially stable reconstruction, progressive lucencies, liner disassociation, or worrisome osteolysis have not been observed. These midterm results are much better than those of former screw rings with smooth surface finishes. The main reason for the general failure and justified abandonment of threaded polished components may not be the screw in mechanism of their primary fixation, but the lack of an appropriate surface for bone ingrowth and osseointegration.

Primary total hip arthroplasty with the Karl Zweymüller first-generation cementless prosthesis. A 5- to 9-year retrospective study.

A consecutive series of 72 primary total hip arthroplasties were performed in 70 patients using the first-generation Zweymüller cementless titanium press-fit femoral and threaded acetabular components (AlloPro, Baar, Switzerland). Twelve hips were excluded from the study because of insufficient follow-up evaluation, including one patient who underwent a socket revision within the first 2 weeks. Sixty total hip arthroplasties with an average follow-up period of 80 months (range, 60-108 months) were retrospectively reviewed. Clinical results were graded excellent or good in 54 cases (90%), fair in 3 (5%), and poor in 3 (5%) with 2 early implant failures (1 acetabular cup and 1 femoral stem in 2 hips). Cumulative survival rates at the 6- to 7-year interval, with failure defined as revision and/or loosening are 98.47% (SD, 2.0%) for the femoral component (1 single septic and loose stem, revised at 5 years), 97.08% (SD, 2.72%) for the screw ring (2 unstable but only 1 revised), and 95.56% (SD, 3.36%) for both components. This encouraging experience with the first-generation prosthesis supports the rationale for continued use of the new Zweymüller Alloclassic stem and open-back screw ring available since 1988.