DOS BULLETIN - Dansk Ortopædisk Selskab

2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 117
A novel method for measuring the femoral
neck anteversion
Tommy Hemmert Olesen, Trine Torfing, Søren Overgaard
Department of Radiology & Department of Orthopaedics and
Traumatology, Odense University Hospital
Background: Several methods exist for measuring femoral neck anteversion
angle (FNAA) using CT-scans. A common problem is how to
realign femur prior to actual measurement. Proposed methods in the literature
are too complex for the clinical setting or differ widely in their
definition of FNAA. There is no consensus as to which method is best.
In this study a method is proposed, that is a modernization of Murphy et
al's original work on the subject.
Purpose: To compare two methods of measuring FNAA: The method
used at Odense University Hospital until recently (2D-OUH), and a new
method, 3D-OUH, which realigns femur prior to measurement.
Methods: 26 CT-scanned patients: 9 men and 17 women aged 12 to 64
with a mean age of 37 years. The right side FNAA was measured twice
with each method by one observer, measuring intraobserver variability.
Both methods are based on the following anatomy: Femoral head center,
center at level of lesser trochanter, posterior apex of the femoral
condyles. The 3D-OUH method measures FNAA relatively to anatomy
of femur itself, instead of the horizontal plane of the CT-scanner as with
the 2D-OUH method. The intercondylary notch center of the knee and
center at lesser trochanter is used in realignment.
Findings: 2DOUH significantly overestimated AV compared to
3DOUH by 4.2° (95 % CI: 2.8°;5.7°), P=0.00. The 3DOUH method had
a lower variability with a Limit of agreement (LOA) of -2.1° to 2.4°
against that of 2DOUH of -3.4° to 3.8°
Conclusion: Measurements made with the 3D-OUH method was significantly
lower than with 2D-OUH, implying systematic bias from the way
patients are positioned in the scanner. The 3D-OUH method had lower
intra-observer variability. Compared to the 2D-OUH method, it is more
precise, estimated by intra-observer variability alone.
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