The clinical implications of elevated blood metal ion concentrations in
asymptomatic patients with MoM hip resurfacings: a cohort study

David J Langton, Raghavendra P Sidaginamale, Thomas J Joyce, Shonali Natu,
Peter Blain, Robert Drysdale Jefferson, Stephen Rushton, Antoni V F Nargol

Full Study Here
10.1136/
bmjopen-2012-001541
January 31, 2014

Objective:
To determine whether elevated blood cobalt (Co) concentrations are associated
with early failure of metal-on-metal (MoM) hip resurfacings secondary to adverse
reaction to metal debris (ARMD).

Design:
Cohort study.

Setting:
Single centre orthopaedic unit.

Participants:
Following the identification of complications potentially related to metal wear
debris, a blood metal ion screening programme was instigated at our unit in 2007
for all patients with Articular Surface Replacement (ASR) and Birmingham MoM hip
resurfacings. Patients were followed annually unless symptoms presented earlier.
Symptomatic patients
were investigated with ultrasound scan and joint aspiration. The clinical course
of all 278 patients with ‘no pain’ or ‘slight/occasional’ pain and a Harris Hip
Score greater than or equal to 95 at the time of venesection were documented. A
retrospective analysis was subsequently conducted using mixed effect
modelling to investigate the temporal pattern of blood Co levels in the patients
and survival analysis to investigate the potential role of case demographics and
blood Co levels as risk factors for subsequent failure secondary to ARM

Results:
Blood Co concentration was a positive and significant risk factor (z=8.44,
p=2×10 – 16)  for joint failure, as was the device, where the Birmingham
Hip
Resurfacing posed a significantly reduced risk for revision by 89% (z= − 3.445,
p=0.00005 (95% CI on risk 62 to 97)). Analysis using Cox-proportional
hazards models indicated that men had a 66% lower risk of joint failure than
women (z= − 2.29419, p=0.0218, (95% CI on risk reduction 23 to 89)).

Conclusions:
The results suggest that elevated blood metal ion concentrations are associated
with early failure of MoM devices secondary to adverse reactions
to metal debris. Co concentrations greater than 20 μg/l are frequently
associated with metal staining of tissues and the development of osteolysis.
Development of
soft tissue damage appears to be more complex with females and patients with ASR
devices seemingly more at risk when exposed to equivalent doses of metal debri.