It is best done on both AP and true lateral projections. On the AP view of a normal hip, the Klein line intersects a small portion of the lateral capital epiphysis.
In typical posterior displacement of the capital epiphysis, the line intersects a smaller portion of the epiphysis or does not intersect it at all - the positiveTrethowan sign.
It is one of the signs that may help in the initial phase (mild slip) with typical posterior displacement, where AP radiographic findings are known to be subtle.
- 1. KLEIN A, JOPLIN RJ, REIDY JA et-al. Roentgenographic features of slipped capital femoral epiphysis. Am J Roentgenol Radium Ther. 2004;66 (3): 361-74. Pubmed citation
- 2. Richard J. Montgomery, Slipped upper femoral epiphysis, Orthopaedics and Trauma, 2009-06-01, Volume 23, Issue 3, Pages 169-174