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centre of the knee. The anatomic femorotibial
angle (aFTA) describes the angle between the
anatomic axes of the femur and tibia, and is
usually around 6° of valgus. The mechanical
femorotibial angle (mFTA), formed by the
mechanical axes of the two bones, is usually 0°
or neutral. although variation exists in nature.
This is sometimes referred to as the hip-knee
ankle angle (HKA).
Care must be taken when performing stan
dardized radiographs for determination of
coronal plane alignment. Variance in limb
rotation and knee flexion may have significant
impact on the observed angles [3, 4].
Deformity affecting lower limb alignment may
occur at any level. In general, the closer an
extra-articular deformity to the knee, the greater
its importance [5].
Historical Evidence
Supporting Neutral
Alignment
In 1977, Lotke and Ecker first examined the
correlation between implant positioning and
functional outcome in 70 TKAs [6]. Alignment
and functional outcome were both evaluated
using the author’s own 100 point scales. Long
leg films were not used and component rotation
was not assessed. They noted a significant
correlation between good clinical results and
good alignment. In four of their five failures,
the tibial component was positioned in varus.
Denham and Bishop, in a 1978 study of
biomechanics in relation to knee reconstruction,
defined optimal positioning to be 7°±4° of
anatomic valgus for the femoral component
and 90°±4° to the anatomic axis for the tibia, to
ensure the weight bearing line passed through
the centre of the joint [7]. Hvid and Nielsen
reported an increased incidence of radiolucent
lines at two years surrounding tibial components
implanted with more than 4° tilt in any
direction, with the interesting exception of
varus angulation in osteoarthritic knees [8].
Interestingly, not all studies from this period
supported a neutral mechanical axis. Bargren
et
al.
reported a failure rate of 2.3% for the
Freeman Swanson (ICLH) knee when aligned
between 1-5° of anatomical valgus (1-5° varus
mechanical alignment), against an overall
failure rate of 27% [9].
In an important 1991 study, Jeffrey
et al.
published the results of 115 early Denham knee
arthroplasties with median 8 years follow-up
[10]. Using long leg radiographs to assess
coronal plane alignment, they found a significant
difference in the rate of loosening between
those aligned within ±3° of Maquet’s line (3%
loosening) and those outside these limits (27%
loosening) (p=0.001). This target range has
subsequently been supported by numerous
clinical and laboratory studies [11-18].
Recent Evidence
Challenging Neutral
Alignment
In the last few years, several reports have been
highlighted challenging the superiority of
neutral mechanical alignment.
Regarding survival, in 2007, Morgan and
colleagues reviewed the outcomes of 197
Kinemax TKAs at 9 years, and found no
difference in revision rate between those in
neutral, varus or valgus alignment [19]. In a
larger study, Parratte
et al.
published a
retrospective review of 398 cemented primary
knee arthroplasties performed at the Mayo
Clinic using three modern prostheses [20].
Long legalignment radiographswereperformed
for all patients pre- and post-operatively. The
outlier group comprised 106 knees with post-
operative mechanical alignment outside 0°±3°.
They found no difference in survivorship at
15 years between the well-aligned and outlier
groups, and concluded that describing
alignment as a dichotomous variable was of
little value for predicting durability. In a similar
study of 501 TKAs using a single prosthesis,