Biomedical Engineering Reference
In-Depth Information
All Cemented Implants
all diagnoses and all reasons
All Uncemented Implants
all diagnoses and all reasons
100
100
REOPERATION
1)
REOPERATION
1)
95
95
90
90
85
85
80
80
75
75
1979-1991, 26y = 73.6% (72.8-74.5), n = 93,868
1979-1991, 20y = 26.8% (23.7-30.3), n = 3,275
1992-2005, 14y = 87.9% (87.2-88.6), n = 139,283
1992-2005, 14y = 71.7% (68.6-74.8), n = 5,895
70
70
0
2
4
6
8 10 12 14 16 18 20 22 24 26
0 2 4 6 8 101214161820222426
years postoperatively
years postoperatively
Fig. 2.15
Not revised implants as function of years postop. Copy from the Internet site of the
Swedish National Hip Registry [73, p. 28]
And materials, are they not a part of the game? Why bother about further
improvements after the apparent absence of a negative story on materials in the
Register statistics?
From the register, we learn that most failures are provoked by patient-, design-
and surgery-related factors and the superior survival rate of cemented prostheses.
Here, however, we come closer to the role of materials in the business. Cements
were already mentioned and later on their chemistry and mechanics will receive a
closer look. A first class story about materials, however, cannot be skipped here!
At the end of 1980s, a new cement Boneloc was introduced: a butylmethacrylate,
where the methyl-group of conventional cement had been replaced by a butyl-group.
It was said to have a lower setting temperature and thus, potentially less necrotic for
bone. In the 1990s, it was commercialized, but soon it became clear it was a full
size disaster: in a 5-year period >50% of the stems were loosening, accompanied
by dramatic osteolysis [74-76]! Little sparks kindle great fires! Ringing the alarm
bell by the Swedish Register confined the disaster.
Further on, we find in the Register that stems perform better than cups and that
small changes in surface finish can result in major differences in revision risk.
The well-known example is the Exeter implant: the matt finish of the stem gave
far poorer results than the polished stem; in later chapters, we will discuss surface
modification and encounter other examples for the effect of surface finish. The main
properties of the classics stainless steels, cobalt-chrome and titanium alloys were
already discussed and polymers and ceramics follow later. A short separate chapter
will be devoted to a recently re-introduced metal zirconium (Chap. 5). The cup was
mentioned to perform less well. Work is going on to introduce a highly cross-linked
