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Head-at-risk signs in Legg-Calvé-Perthes disease: poor inter- and intra-observer reliability
Mark C Forster1, Senthil Kumar, Rohan A Rajan
1Department of Radiology, Lincoln County Hospital. Greetwell Road, Lincoln, LN2 5QY, UK. mcforster@doctors.org.uk
Background:
The head-at-risk signs are used as prognostic indicators in Legg-Calvé-Perthes disease. These signs have been assessed only once regarding inter-observer reliability, however. Intra-observer reliability seems not to have been studied to date.
Method:
76 anteroposterior pelvic radiographs of unilateral Legg-Calvé-Perthes disease were assessed by 5 observers on 2 occasions, in order to assess the inter- and intra-observer reliability in identifying head-at-risk signs. The observers included 1 consultant pediatric orthopaedic surgeon, 1 consultant radiologist, 2 specialist registrars and 1 senior house officer. Inter- and intra-observer reliabilities were assessed using the kappa coefficient.
Results:
The intra-observer reliability was good for lateral subluxation and metaphyseal cystic changes, moderate for lateral calcification, and fair for Gage's sign and horizontal growth plate. The inter-observer reliability was moderate for lateral subluxation, fair for lateral calcification and metaphyseal cystic changes, and slight for Gage's sign and horizontal growth plate.
Interpretation:
There was considerable variation in the diagnosis of the head-at-risk signs between observers. This makes the classification difficult to use in clinical practice.
