BIOLOX-FORTE VS. BIOLOX-DELTA UNDER MICRO SEPARATION TEST MODE IN THE USA
Green, D. D., Williams, P. A., Donaldson, T. K. and Clarke I. C.
Department of Orthopaedic Surgery, Orthopaedic Research Center, Loma Linda Medical University, 11406 Loma Linda Dr. Suite 606, Loma Linda,
California, 92354 USA, Phone (909) 558-6490, Fax (909) 558-6018, [email protected]
compared to the delta (Fig: 2). Samples of wear debris from events 0.1
and 0.5Mc revealed sub-micron sized particulate ~5µm, with no
evidence suggesting any difference from Biolox-forte and delta.
Table 1 – Summary of wear rate data (volumetric) for
Biolox-Forte and Delta THR’s (linear regression analysis 0-1.01Mc)
Specimen
Forte
Ball (N=6)
Forte
Cup (N=6)
THR Forte
Forte
Ball (N=4)
Forte
Cup (N=4)
THR Forte
Delta
Ball (N=6)
Delta
Ball (N=6)
THR
Delta
Ave. Vol.
Wear-rate
(mm3/Mc)
95%CL
(mm3/Mc)
8.3
3.0
11.8
5.4
20.1
8.4
6.9
0.7
8.7
1.0
15.6
1.7
0.55
0.14
0.65
0.13
1.2
2.7
10
Cycles
0
0.E+00
2.E+05
4.E+05
6.E+05
8.E+05
1.E+06
1.E+06
-10
-20
-30
Forte THR's
Delta THR's
Weight (mg)
Introduction:
Many ceramic on ceramic wear studies have shown that these pairings
wear at extremely low rates and to a point where it becomes
undetectable [1-2]. A detailed retrieval study performed by Walters et al.
on modern alumina ceramic on ceramic components revealed a
phenomenon know as ‘stripe’ wear which was associated with a
maximum wear rate of 1.9mm3/year at only 2.5 years follow up. The
cause of such wear scars is associated with a ball-cup impingement
through micro-separation of the THR. Previous work by Stewart et al.
was the first laboratory study to mimic such phenomena which
correlated well with clinical outcomes.
In this study we compare a new composite Alumina to a 3rd
generation Alumina. Our goals are to study both materials under microseparation conditions to obtain stripe wear and to closely map the ‘runin’ wear of these materials to help better understand their tribological
behavior.
Materials and Methods:
36mm ceramic ball and liner of 3rd generation Alumina N=6, and new
Alumina Matrix Composite (AMC) N=6, were diametrically matched
over a range of tolerance, tested anatomically on a orbital hip simulator
(Shore Western) modified for micro-separation (MSX) with a cup angle
of 50 to the horizontal. Both materials were manufactured under trade
names Biolox-Forte™ and Delta™ (CeramTec Inc., Plochingen
Germany) respectively. Paul load curve (max. load 2Kn) was run at 1Hz
with a horizontal displacement (MSXH) set to 4mm. Alpha calf serum
(Hyclone®) was used as a lubricant (protein conc. 10mg/ml). Wear was
determined gravimetrically every 100,000 cycles. Wear scars ‘stripes’
were inspected every event and logged by macro-photography. Serum
was stored frozen for debris analysis under SEM. Post analysis of ball
and cup involved: SEM for topographical analysis and wear mode, Xray diffraction for determination of crystal structure of zirconia, surface
roughness and Raman spectroscopy for determining the residual stress
fields within the ceramic.
-40
15X decrease
-50
-60
run-in phase
steady state phase
-70
Figure: 1 – Wear stripe/scars after 1.01Mc (marked in ink) representing
a broad extended and deep stripe on the Biolox-forte ball (LHS) and a
less significant stripe on the Biolox-delta (RHS).
Results:
The wear rate for the forte balls over the range zero to 1.01Mc was
8.3mm3/Mc, this rate was made up of a run-in phase up to 0.4Mc (Table:
1, 10.7 mm3/Mc) and a steady state phase from 0.4 - 1.01Mc (7.3
mm3/Mc). This represented a ~30% reduction from run-in to steady
state. The forte cups had similar trend with average wear rate of
11.8mm3/Mc, this to showed a run-in phase and stead state phase of
14.1mm3/Mc and 8.6mm3/Mc respectively, representing a wear
reduction of ~40% between phases. The delta balls and cups showed
very low overall wear rates 0.55 and 0.65mm3/Mc respectively. These
demonstrated a biphasic wear trend, where run-in phase changed to
steady state phase at 0.4Mc.
Analysis of the weight loss trends of the individual Bioloxforte balls and cups revealed two outliers one that consistently under
performed and another that represented excessive wear. Excluding both
these samples from each set changed the average wear rate for the balls
(N=4) to 6.9mm3/Mc and cups (N=4) to 8.7mm3/Mc, representing a
THR rate of 15.6mm3/Mc. Comparing the THR’s wear rate for both
materials we obtained a ~15 fold reduction from Biolox-forte to delta
(Fig: 2). Comparison of the wear stripe/scar at the end of 1.01Mc,
clearly illustrating the greater magnitude of wear on the Biolox-forte ball
Figure: 2 – Average weight loss trends for Biolox-forte and delta THR
over the 1.01Mc, showing the 15-fold reduction in weight loss of
Biolox-delta over forte.
Discussion/Conclusion:
With any new total joint orthopaedic material (Biolox-delta), validation
of its tribiological performance is critical in assessing its longevity in
vivo. Our model demonstrated severe run-in wear rates for ceramic on
ceramic bearings up to 12 fold greater, compared to other studies [5].
We have also been able to discriminate between two ceramics under
these conditions. Biolox-delta clearly revealed greater resistance to
stripe wear phenomenon compared to forte (Fig: 1 and 2). The wear scar
for Biolox-forte was broader and deeper compared to delta. Thus the
Biolox-delta clearly demonstrated a resistant to ‘stripe’ wear through the
crucial ‘run-in’ phase.
References:
1.
2.
3.
4.
5.
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Saikko, V and Pfaff, H. G., (1997), Wear of alumina-alumina total replacement hip joints
studied with a hip joint simulator, in Proc. 2nd Symp on Performance of the wear couple
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Walter, W. L., Insley, G., Walter, W. K. and Tuke, M. (2003), The mechanics of stripe
wear formation in a modern ceramic on ceramic bearing., in 70th Annual Meeting AAOS,
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Acknowledgements: The authors wish to thank CeramTec, Plochingen
Germany for donation of implants and financial support.
51st Annual Meeting of the Orthopaedic Research Society
Paper No: 0239