One group of 70 patients underwent a posterolateral fusion without ins
truments and the other group of 69 patients underwent a posterolateral
instrumented fusion. The follow-up was in average 5.7 years resp. 4.6
years. The operations were divided in monosegmental, floating and pol
ysegmental fusions. In the total group, 10% of the non-instrumented an
d 28% of the instrumented patients had an osteoarthritis of the facet
joints, 10% resp. 23% were unstable and in 9% resp. 1% a disc resorpti
on occurred. There have been no statistical differences in the both po
lysegemental groups, but this was the case for all osteoarthrites and
instabilities in the monosegmental fusions. It is supposed that the ch
anges in kinematics together with material related alterations of elas
ticity led to higher stress concentration in case of instrumentation.