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The lateral tibiofemoral joint does not have the
same geometry as the medial. The shape and
geometry of the femoral and tibial condyles are
different compared to the medial tibiofemoral
joint [1-3] (Table 1) and challenge our current
practice to use a medial left off-the-shelf
implant for the right lateral side and vice versa.
The lateral femoral condyle is wider and flatter
compared to the medial condyle. The anterior
radius of the lateral J-curve is almost twice the
anterior radius of the medial condyle (fig. 1)
[1]. The width of the lateral condyle is much
wider in extension but narrower posteriorly
(fig. 2). The lateral condyle is not as curved as
the medial condyle and is shorter (fig. 3). Most
current off-the-shelf (OTS) UKA are
asymmetric and narrower compared to femoral
condylar widths allowing the surgeon to place
the component more medial or lateral [3] to
improve central tracking on the tibial
component. However, a symmetric straight
femoral component would fit better on the
lateral condyle. The challenge of lateral UKA
using off-the-shelf (OTS) UKA is to place an
implant shaped more to the medial condyle on
the lateral condyle.
The same challenge exist for the tibial compo
nent. The medial condyle is more D-shaped
and not as round as the lateral tibial plateau
(fig. 4).
Doing a lateral UKA through a mini-invasive
medial approach is impossible. Amini invasive
lateral approach is more difficult and requires
attention to certain details. Exposure is limited
due to the patellar tendon and the more lateral
sitting patella. In order to subluxate the patella
medially a longer arthrotomy is necessary in
most cases. Surgeons place the not wide enough
femoral component as lateral as possible on the
femoral condyle and move the tibial component
moremedial to compensate for the shortcomings
of implant design (not wide enough). Placement
of the tibial component in 10 to 20 degrees of
internal rotation is also recommended to allow
centerline articulation [4] but may require to
perform the vertical “L” cut through the patella
tendon (fig. 5). It remains unclear whether
posteromedial tibial coverage of the lateral tibia
plateau is sufficient to allow for lateral rollback
in deep flexion. Custom implants not only
restore the geometry of the lateral tibiofemoral
joint, but also simplify the surgical technique
and may open this satisfying procedure to more
patients with isolated lateral tibiofemoral
osteoarthritis with the potential to improve
mixed results reported in the literature [4-7].
Custom Lateral UKA
W. Fitz