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Soft-tissue
impingement after TKA:
What is it?
In TKAs’, residual pain and poor functional
results can be due to soft tissues impingements
with the prosthetic components [5, 8, 9].
Several structures can be involved such as the
Popliteus Tendon (PT), the Patellar tendon
(PaT), the Quadriceps tendon (QT) the Medial
Collateral Ligament (MCL), the Patellofemoral
Ligaments and generally speaking all the knee
joint capsule. Very few reports are available in
the literature about that topic and they focus
mostly on the relationships between PT and the
lateral condyle [1, 2, 7].
Soft-tissue impingement are mainly due to a
prosthetic overhang [3, 4, 6, 8] but they can
also be observed after apparently well-sized
implants, without real prosthetic overhang [7].
In a previous work we reported better pain
scores, better functional scores and better ROM
in patients with “undersized components”,
where the implants did not cover the all bone
cut area, than in patients with “normosized
implants”, where bone implant fit was
apparently optimal [3].
In our hypothesis soft tissues-implant impin
gement is not only due to prosthetic overhang
(technical mistake) but also to design factors –
the non-anatomic shape of knee components –
and therefore may occur in apparently well
sized implants.
The Popliteus Tendon in
TKA: Whya
theoretically
“normosized” tibial
plateau is in fact
“oversized”?
In a normal knee the Popliteus Tendon (PT) is
in close contact with the posterolateral aspect
of the lateral tibial plateau, which can easily
be visualized during anatomic dissections or
during MRI (fig. 1). At the jointline level, the
PT crosses the Lateral Meniscus through the
Politeus Hiatus and is stabilized by the
popliteomeniscal ligament. During TKA, the
surgeon aims at preserving the native thickness
of the tibial plateau, as measured on the
healthy side – generally at the top of the
convexity of the lateral tibial plateau. However,
prosthetic tibial components do not reproduce
the shape of the posterolateral tibial plateau –
concave rather than convex – and this can lead
to a Popliteus Tendon impingement with the
tibial plateau (fig. 2). The potential tendon
instability, due to the lateral meniscectomy
and the resection of the popliteomenical
ligaments, probably increases also the risk of
impingement.
Soft tissues and TKA
M. Bonnin, T. Van Hoof, A. De Kok, M. Verstraete,
C. Van der Straten, T. Aït Si Selmi and J. Victor