Povijest i čimbenici preživljavanja umjetnog zgloba kuka

Biomechanical factors
The level of physical activity and body mass
index influence the forces that affect the endoprothesis,
thus they are considered as biomechanical
factors. Another potentially important
factor would be the constructional one that is,
the biomechanical features of the endoprothesis
(26). A large number of endoprothetic models are
available, that differ significantly with respect to
constructional details. There is no data based on
which one could conclude about potential differences
in aseptic instability occurrence that would
be attributable to the constructional features.
There is also no data that would indicate that the
surgical procedures that are sometimes necessary
in addition to the endoprothesis implantation
(acetabuloplasty or trochanter osteotomy),
and which change the biomechanical situation
of the hip joint, affect the occurrence of aseptic
instability. On the other hand, the inclination angle
of the acetabulum achieved at endoprothesis
implantation significantly influences the occurrence
of aseptic instability. Namely, the goal
is to achieve an angle of 45 degrees, whereby a
discrepancy of +/- 5 degrees is tolerated. Unfavorable
inclination angle of the acetablumum
due to a bad biomechanics of the joint itself, and
consequently larger friction between the constituting
part of the endoprothesis, increases the
risk of aseptic instability (27, 28). Unfortunately,
it has been shown that aseptic instability occurs
also with a favorable inclination angle (40-50
degrees) (19).
Exceeding body mass (body mass index, BMI,
>25 and particularly >30) is a classical factor
that contributes to (over)burdening of the skeletal-muscular
system, and also of the hip endoprothesis.
However, the research of the influence
of BMI on the occurrence of aseptic instability
is related with certain problems. Namely, in this
kind of research the outcome of interest is time
elapsed until the occurrence of event (instability)
and patients are followed-up for a long period
of time (e.g., 10 years or longer). Data are
typically analyzed with the assumption of the
“constant hazard” - it is assumed that the risk
associated with a certain factor is constant over
time (for example, age at the time of surgery,
type of endoprothesis, gender, disease leading
to the need for endoprothesis, etc.). Body mass
index can change significantly over time. In the
literature, there is practically no study in which
BMI has been considered as a time-dependent
variable. It is therefore difficult to realistically
assess the influence of this factor on the occurrence
of aseptic instability. In a study conducted
over a shorter period of time, body mass
index >30 at the time of the implantation of endoprothesis
was identified as a negative factor
for the endoprothesis survival (29). It should be
noted, however, that aseptic instability occurs
also in patients with a permanent physiological
body mass index.
Other factors
Kolundžić et al Total hip atroplasty
Based on the analysis of around 54,000 endoprotheses
from the Norwegian THA registry (30), the
risk of aseptic instability is higher in patients
with developmental hip anomalies than in those
in which THA was indicated for other reasons
(e.g., primary osteoarthritis, aseptic necrosis of
the femoral head, injuries etc).
Based on the analysis of around 32,000 endoprotheses
(cemented and non-cemented) from
the Norwegian THA registry (31, 32), more
experienced surgeons (measured by a number of
procedures annually) need less time for the implantation
of endoprothesis than less experienced
surgeons. Independent of the age and gender of a
patient, the type of endoprohesis or disease that
led to the need for endoprothesis, the risk of aseptic
instability is higher in patients treated by less
experienced surgeons. The risk of aseptic instability
is greater if the operations last longer than the
average of 90 minutes. Also, the risk is greater if
the operation lasts shorter than 50 minutes.
For quite some time, it has been a common opinion
that there are “patient-dependent factors”,
which are not demographic, (co)morbidity or biomechanical,
that significantly determine the individual
„inclination“ towards the development of
aseptic instability of THA (33-35). Namely, large
interindividual differences have been noticed in
the intensity of the inflammatory process which
results in aseptic instability for a given type of
prothesis, for the amount of loose particles, demographic,
(co)morbidity and biomechanical
features and the „skill of the surgeon“. During
the last 7-8 years, the concept has arisen which
assumes that this „unexplained part of the indivi-
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