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Introduction
Unicompartmental knee arthroplasty (UKA)
provides an alternative to total knee arthroplas
ty (TKR) in patients with monocompartmental
arthritis. The prerequisites cited in retrospective
studies for a UKA, include unicompartmental
disease, functioning anterior cruciate ligament
(ACL), tibiofemoral angles between physio
logical valgus and 10° varus and no subluxation
are largely accepted [17, 21], although the
boundaries continue to expand.
Failure is nevertheless increasing; the
inexorable consequence of increasing numbers
of procedures. Conversion of the failed UKA to
TKR shows favourable outcomes, but the
complexity of revision surgery remains
debatable, and the causes of failure different
between medial and lateral unicompartmental
arthroplasties. Not infrequently, papers
discussing ‘the failed UKA’ seem to be
synonymous with Medial UKA. Few studies
compare the differences between the revision
of these two types of prostheses to TKR. The
purpose of this paper is to examine the
differences between the revision of Medial and
Lateral UKAs to TKR.
Medialand Lateral
UKA; not synonymous
In considering revising medial and lateral
prostheses, it is important to remember that
they are different creatures, with different
indications, biomechanics, kinematics, and for
different patterns of wear.
In terms of frequency, Lateral UKAs are
performed between one in ten and one in fifteen
times less than medial UKAs, therefore make
up less than 1% of knee prostheses implanted
[58]. Indications are subtly different between
medial and lateral UKA [2, 4, 42, 50], as are the
diagnoses leading to unicompartmental
arthroplasty. Series for either medial or lateral
UKA where authors cite their respective
indication are shown in Table 1. For series
reporting indications for lateral UKA, primary
osteoarthritis by far themost common indication,
with sequalae of trauma next most common [2,
4, 39, 44, 54]. Argenson’s series aside, UKA for
osteonecrosis is not cited as an indication.
Medial UKA indications are performed
overwhelmingly for OA, with osteonecrosis
(0.8% to 6%) and sequalae of trauma (0.4% to
4.5%) much less common [9, 31, 60].
Revisions of UKAwith TKA;
Medial versus Lateral UKA
C.G. Murphy, T. Aїt Si Selmi, M. Bonnin