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Patellofemoral arthritis is a pathology which
can be caused by several factors. Depending on
the interplay of the structures involved in the
patellofemoral joint there is a difference between
the direct and indirect development of the PFA.
The group of direct causes includes direct blunt
trauma, fracture of the patella, traumatic patellar
dislocation, chronic overloading by profession,
sports or overweight and rarely osteochondritis
dissecans. Malalignment, a poor tracking and
positioning of the patella, is the cause for the
indirect development of PFA. It is mainly
induced by trochlear dysplasia, valgus deformity
and femoral anteversion. Regarding successful
therapy of PFA the precise clinical and
radiological diagnostics of the underlying
causes is a necessary precondition.
Since biological treatment options in the PFJ
are limited in their success, and anterior transfer
of the tuberosity can only be carried out by
accepting a medial or lateral increase of the PF
loading, which may be not sufficient in some
cases, especially with an underlying trochlear
dysplasia, the indication for an isolated
patellofemoral replacement may be given.
For a long time, reputation of these partial
arthroplasties have been not very promising (in
comparisonwith theUKR i.e.), since the outcome
was no as satisfying due to a symmetrical, non-
physiological V-shape of the systems.
However, actual products respect the given
anatomy and can be separated in traditional
onlay and recent inlay systems.
The main difference in between those two
systems is the surgical technique and the
postoperative joint volume: in onlay systems,
the arthroplasty is cemented onto a bony plain,
flattened by an anterior femoral osteotomie,
where the degenerative cartilage and the
underlying bone has been removed (fig. 1).
While some rotational malalignments and even
valgus mismatches can be influenced positively
by an anterior osteotomie, the only technique
comprises the risk of a postoperative bone-
volume augmentation: in cases of small knees,
where the anterior osteotomie is limited by
given anatomical facts to avoid a weak spot of
the distal femur and the risk of a postoperative
fracture, an anteriorisation of the femoral joint
line and an therefore an augmentation of the
patellofemoral joint pressure with ongoing pain
can occur.
Other then that, in inlay systems, the defect
area is reamed only down to the demanded
depth of the trochlea, respecting the supero-
inferior curvature of the given joint. Therewith
it is possible to recreate the given trochlea
shape or to change a before dysplastic into a
physiological
trochlea,
respecting
the
surrounding bone shape and curvature. In these
Inlay or Onlay PFA
P.B. Schoettle