Abstracts Posters SICOT-SOF meeting Gothenburg 2010 _2_

Poster
Topic: Trauma - Hip
Abstract number: 25783
INFLUENCES OF ROTATION ON FEMORAL NECK-SHAFT ANGLE
MEASUREMENTS IN THE ANATOMIC, VARUS MALREDUCED, AND
SHORTENED PERITROCHANTERIC FRACTURE.
Amir MATITYAHU, R. Trigg MCCLELLAN, Meir MARMOR
Orthopaedic Trauma Institute, San Francisco, CA (UNITED STATES)
Varus malreduction of peritrochanteric fractures causes failures. However,
measurements of the actual neck-shaft x-ray angle (NSA) are performed with the
femur internally rotated to compensate for proximal femoral antevesion. Frequently
patients have X-rays (XR) with an externally rotated femur. Therefore, we sought to
define the reliability of in-situ NSA measurements. Methods: We performed NSA
measurements of three proximal femurs with no malreduction (NM), 20° varus (VM),
and 10 mm shortening (SM). We measured the NSA rotating the femur relative to the
XR beam in 5° increments from 45° of internal to 50 ° of external rotation. Results:
NSA measurement varied less than 5° with the beam a ngle less than 30° but
exponentially increase with continued external or internal rotation for all groups. The
NSA of the NM femur was 128.0°, the VM femur was 10 7.5°, and 127.5° for the SM
femur. The femoral NSA graph for all the groups followed the following formula: NSA
= 90 + (tan-1[vertical height/(offset*Cos(Beam angle))]. At 50° of external rotation,
the average varus angle was 137.5° for the NM femur , 115.5° for the SM femur, and
140.5° for the VM femur. At 30° of internal rotatio n, the average varus angle was
143.5° for the NM femur, 131.5° for the SM femur, a nd 116.0° for the VM femur.
Conclusion: Measurements of proximal femoral NSA are accurate to within 5° when
rotation is less than 30° of the proximal femur rel ative to the XR beam.
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