Medial femoral head border is a reliable and reproducible reference for axis determination for femoral component of unicompartmental knee arthroplasty.
OBJECTIVE
The femoral component should be implanted parallel to the mechanical axis in unicompartmental knee arthroplasty. It was hypothesised that a line between medial femoral condyle centres and medial border of femoral head will be parallel to the mechanical axis; this study set out to examine this hypothesis.


METHODS
One hundred X-rays in fifty patients were included for this study. Long-leg standing X-rays including hip and ankle with patellae facing forwards were obtained. On these films, we measured the angle, α, between mechanical axis and the line between the femoral head centre and knee centre (medial mechanical axis), and the angle, β, between the medial mechanical axis and a line between medial femoral condyle and femoral head centre.


RESULTS
The average value of α was 0.1 ± 0.5° and the average value of β 3.0° ± 0.3°. These data indicate that mechanical axis and medial mechanical axis are virtually parallel to each other.


CONCLUSIONS
As medial femoral head border is easily identified fluoroscopically, it is a reliable landmark for orientating the femoral component of medial UKA.
Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences (NDORMS), University of Oxford, Windmill Road, Headington, Oxfordshire, Oxford, OX3 7HE, UK, takafumi.hiranaka@gmail.com.
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T
Hiranaka
H
H
Pandit
H S
HS
Gill
Y
Y
Hida
H
H
Uemoto
M
M
Doita
M
M
Tsuji
D W
DW
Murray
D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging* / Q000601:surgery; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D014057:Tomography, X-Ray Computed