The femoral neck-shaft angle (NSA) is an important measure for the assessment of the anatomy of the hip and planning of operations. Despite its common use, there remains disagreement concerning the method of measurement and the correction of hip rotation and femoral version of the projected NSA on conventional radiographs. We addressed the following questions: (1) What are the reported values for NSA in normal adult subjects and in osteoarthritis? (2) Is there a difference between non-corrected and rotation-corrected measurements? (3) Which methods are used for measuring the NSA on plain radiographs? (4) What could be learned from an analysis of the intra- and interobserver reliability?
A systematic literature search was performed including 26 publications reporting the measurement of the NSA on conventional radiographs.
The mean NSA of healthy adults (5,089 hips) was 128.8° (98-180°) and 131.5° (115-155°) in patients with osteoarthritis (1230 hips). The mean NSA was 128.5° (127-130.5°) for the rotation-corrected and 129.5° (119.6-151°) for the non-corrected measurements.
Our data showed a high variance of the reported neck-shaft angles. Notably, we identified the inconsistency of the published methods of measurement as a central issue. The reported effect of rotation-correction cannot be reliably verified.