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Preoperative Planning. What I do Before a UKA
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upper weight limit is around 90kg [1, 31].
Others use the BMI metric to take into account
body habitus, with larger patients requiring
larger prostheses to tolerate the increased
mechanical loads; the upper limit using this
criteria is a BMI of 32-35 [6].
Gender
Females are disproportionatelywell represented
in the UKA registries on account of their lighter
body weight. The higher association of females
with osteoporosis can be considered
counterpoint to this. However, apart from the
weight-related arguments, gender does not
seem in itself to be an exclusion criteria.
Sporting Activity
Traditionally, patients who are engaged in
higher levels of sporting activity are directed
towards an osteotomy. The increasing
involvement of all age groups in sport, and the
feasibility of UKA for active patients has led to
this technique being offered to patients who are
involved in lower impact sports such a golf
(preferably for the trail leg), swimming, boules/
pétanque and tennis [8, 15]. It is imperative
these patients receive regular surveillance to
monitor polyethylene wear.
Discussion
The eligibility for a UKA is related to the
quality of the screening and can vary according
to the surgeon’s view [2]. The typical indication
for UKA is for a patient under 65 years old,
with Stage II or III OA, where pain is localised
to one compartment, the knee has a good range
of movement and where the weight of the
patient does not exceed 90kg. Reducibility of
the deformity must be verified clinically and
radiologically with stress-views. The views
confirm that the main deformity is intra-
articular. Goniometry should document the
femoro-tibial axis does not exceed 10° varus or
15° valgus. Axial views should show at most
some remodelling of the PFJ. Finally, the
presence of a healthy central pivot is checked
clinically, and confirmed radiologically by a
lack of spontaneous translation on the AP
weight-bearing views [9, 12, 23].
Due to the high prevalence of medial joint
wear, medial UKAs are far more common than
lateral UKAs. Recent studies though have
emphasised the benefits of the lateral UKA [3,
31]. Selection criteria are essentially the same,
but with two subtle differences. Firstly, valgus
deformity in the axial plane may be higher – up
to 7° – as opposed to 5° for the medial joint.
Secondly, PFJ involvement relates predomi
nantly to lateral femoro-patellar narrowing,
which is more acceptable, and easily treated
with a simple additional intra-operative
procedure. Lateral tibial plateau fractures
constitute a novel indication for lateral UKA.
For knees with advanced arthritis in whom the
deformity is only partially reducible, and which
are showing early changes in the other
compartments, but which still have a functional
ACL, use of a UKAcan be considered, but only
for patients that are very frail, elderly, with
significant cardio-vascular or thrombo-embolic
co-morbidities, or those patients whose axial
deformities exceed the recommended limit of
5°-8° (fig. 14 & 15). It is vital that clinical
history and examination correctly identifies the
cause of pain, and that clinical signs correlate
with the affected femoro-tibial compartment.
The aim of achieving “a forgotten knee
prosthesis” should be superseded by giving the
patient comfort, and allowing them regain their
autonomy [24]. Finally, Slower
et al.
highlight
the economic argument for offering these
patients a UKA [37].
Although a deficient or incompetent ACL is in
principle a strict contra-indication for UKA,
some success with ACL reconstruction
combined with UKA have been reported in the
short term [28, 38]. This seems reasonable, as
long as the arthritis is due to the ACL rupture
and there is no significant malalignment. This
is only feasible when there is no significant
tibial cupping, and when tibial translation is
still reducible. This saggital reducibility can be