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Knee Cap
This means the more or less spontaneous recurrent dislocation
of the knee cap which is slipping out of the femoral groove during
the very early phase of knee flexion. Whereas the first episodes
of acute dislocation are very painful and need medical treatment
in chronic stages the displacement of the patella is no longer
too much painful and the patients generally are able to reduce
the patella themselves. The main cause of these instabilities
is congenital. Usually a flat femoral groove is combined with
a high-riding patella, axial malalignement and external rotation
of the tibia. Normal individuals have a well developed concave
proximal femoral groove, but these patients have a flat or even
convex femoral groove (trochlea). In combination with other pathological
factors, this leads to a late centering of the knee cap in the
trochlea with lateral displacement or even complete lateral dislocation.
This happens usually in the first 15 to 20° of knee flexion.
For diagnosis a thorough clinical examination, multiple x-rays
on different levels between hip joint, knee joint and ankle joint
are necessary.
The patients should wear a soft knee brace with lateral
support of the knee cap, whereas for the sessions during
an intensive physiotherapy program lateral taping is most
helpful. Unfortunately the majority of cases cannot compensate
for this type of instability by conservative treatment alone
and operative treatment is needed.
The approach is to correct each individual pathological
factor. For example a high riding patella is put in a more
distal position by transferring the anterior tibial tubercle.
After solid fixation with 2 screws, functional treatment
and partial weight bearing is possible. Another important
step is the transfer of the musculus vastus medialis obliquus
(VMO) more distally. As a consequence, the patella is pulled
more medially. In cases with a convex proximal trochlea
the proximal hypertrophic part of this “tongue”
is resected and a more anatomical femoral groove is shaped.
Very severe instabilities with axial and rotational malalignement
may require osteotomies in 1, 2 or even 3 plains. Depending
on the severity of the instability, the outcome of most
of the procedures is satisfactory and the incidence of recurrence
is low. The patients have to be hospitalised for only a
couple of days and the intervention is followed by immediate
functional treatment.
Continuous passive motion (CPM) is started immediately after
the intervention and combined with one or two sessions of
physiotherapy with active assisted exercises at one or two
sessions daily. Sometimes straight leg raising against gravity
may be prohibited for the time of bone healing due to the
tubercle-transfer. After transfer of the VMO knee flexion
should not exceed 80° during the first four weeks. Full
weight bearing is allowed not before complete healing of
the inner structures, i.e. 6 to 8 weeks. The period of physiotherapy
should last for three months as a minimum.
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distal transfer
of patella tendon (red arrow)
distal transfer of medial quadriceps tendon insertion
at patella (yellow arrow)
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shaping of flat gliding truff which
helps balancing the patella (red)
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physiotherapy as important integral
part of surgical and conservative treatment of patella
dislocation
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