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C. Murphy, T. Aїt Si Selmi, M. Bonnin
204
Anatomical and biomechanical differences
exist between the medial and lateral
compartments of the knee, in particular
regarding slopes; marked discrepancies of up
to 27º between medial and lateral tibial slopes
have been reported in cadaveric studies [25],
while the Anteroposterior (AP) to Mediolateral
(ML) ratio is larger for the medial side than the
lateral, potentially leading to ML overhang in
order to achieve AP coverage [59]. This has
direct clinical relevance; an association has
been shown between early UKA failure and
those prostheses with a posterior tibial slope of
greater than 7º [23].
Kinematics of the knee are also different
between the medial and lateral compartments;
femoral rollback is more pronounced laterally
than medially, which may explain differing
patterns in cartilage wear pre-operatively (e.g.
early anterior wear formedial tibial gonarthrosis
[30], posterior wear for ACL-deficient knees
[64] and in polyethylene wear post-operatively
[1, 54, 63].
Obviously, implants and their manufacturers
have differing recommendations, with regard
to femoral bone preparation, and for optimizing
tibial slope; for example Accuris (Smith &
Nephew Memphis TN, USA) recommend a
neutral slope, while Oxford (Biomet, Warsaw
IN, USA) recommend a 7° slope. Each
prosthesis, medial or lateral, has specific
technical challenges associated with its
insertion. Surgery for lateral UKA has been
described as more technically challenging than
for medial joint replacement, with specific
technical considerations suggested;
i)
to avoid
excessive tibial slope,
ii)
to be very conservative
with tibial cuts to avoid the need for excessively
thick tibial components to restore alignment
and stability,
iii)
to err toward shifting the
femoral component laterally and the tibial
component medially to maximize ML
congruency, and
iv)
to carefully recess to
patella from impinging against the leading edge
of the femoral component [58]. Failure to
adhere to the principles of appropriate patient
selection,workupandtechnicallyaccomplished
surgery risk amplifying errors and early failure
necessitating revision surgery.
Perceived difficulty of revision and
technical considerations
Authors vary in their description of their
perception in the challenge posed by revising a
UKA to TKR. Certain authors consider revision
of UKA to TKA straightforward [17, 33, 35,
57], no more complex than a TKA [28], or
easier than revision of TKA [7, 34, 41]. Others
are more circumspect, citing complexity of
Table 1: Indication for Primary UKA for exclusively medial or lateral series.
1° OA
Osteonecrosis
Post Trauma
Lateral UKA
Odhera 2001 44
Argenson 2008 2
Sah 2007 54
Ashraf 2002 4
Lustig 2011 39
32/38
24/40
38/48
72/88
51/54
-
21/40
0
0
0
-
12/40
10/48
3/88
3/54
Medial UKA
Sierra 2013 60
Koskinen 2009 31
Bergeson 2013 9
147/175
42/46
825/839
12/175
2/46
7/839
8/175
2/46
4/839