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Revisions of UKA with TKA; Medial versus Lateral UKA
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surgery in the frequent presence of bone loss
[43, 47]. Some authors are more relativistic in
their descriptions; “relatively simple procedure
if planned thoroughly” [57], others consider
the revision of UKAtoTKA“requires precision,
but not is technically difficult” [13], and a
procedure whose “complexity and compli
cations compare favourably with those of TKR
revision” [55]. These cases can and do present
specific challenges to the surgeon.
Indications for revision for Medial
UKA and Lateral UKA
Table 2 highlights the reasons for failure of
UKA in the various published series. Low
numbers in the studies addressing only revision
of lateral UKA makes interpretation difficult,
but the larger series addressing revision of both
medial UKA and lateral UKA, including those
from the various joint registers demonstrate
that the indications for revision are broadly
similar. For series that describe reasons for
failure in Medial only UKAs, aseptic loosening
is the number one most common indication
cited in five papers [9, 52, 55, 57, 60] and
progression of OA the number one in two
papers [31, 43], with failure of poly insert,
pain, component failure or periprosthetic
fracture, and sepsis the other reasons cited. For
Lateral only UKAs, progression of OA is the
most commonly cited indication for revision,
with aseptic loosening and component failure/
periprosthetic fracture the next most common
[2, 4, 39, 44, 50, 54]. In the heterogeneous
larger series, which include the joint registers,
where both medial and lateral UKAs are
discussed, aseptic loosening and progression of
OA are cited as first and second respectively
most common indications in four papers, with
progression of OA and aseptic loosening
respectively most common in two papers. Pain
is cited as number one cause in two papers, and
second most common in two more papers.
Malalignment, sepsis, and poly wear make up
the lesser cited reasons in each group.
Results and Outcomes
UKA to TKA Vs Primary TKA – are
the results comparable?
Comparisons between UKA to TKA and a
primary TKA are variable, and use differing
yardsticks, including clinical scores, radio
logical data, retrospective reviews and registry
data. Several authors have reported results for
UKA to TKR equivalent to primary TKA [28,
35, 41, 55]. Larger series however find that the
results are inferior [7, 10, 12, 27, 47, 49]. Given
the high rate of usage of revision TKR
prostheses (stem, augments) and presence of
bone loss requiring grafts in a sizeable pro
portion of UKA to TKA cases (Table 3), it is
reasonable to state that UKAtoTKAprocedures
are on balance more complex than a primary
TKR.
Inhomogeneous series
The nature of the publications on revision of
UKA to TKA is extremely inhomogeneous.
Most series are retrospective, although not all
[20]. The outcomes are frequently blurred by
inclusion of multiple modes of revision for the
conversion of failed UKA (including
polyethylene change, conversion of UKA to
UKA, UKA to Bilateral UKA and UKA to
PFA), differing patient cohorts (older or
younger), differing prosthesis type, and for
variable timeframes. However, one message
seems to be emerging, especially from more
recent publications; when a UKA requires
revision, the best results are achieved when it is
converted to TKA [22, 32, 36, 53]. Other
variables in outcome include the type of
prosthesis used, and in some cases, but not all
[32] volume of procedures performed by the
unit, with a figure of 13 cases per year suggested
as a minimum “to achieve results comparable
with the high-volume operators” [5]. Two are
of the Nordic joint registries have previously
noted the effect on volume on outcome; a