Abstract
A prospective clinical investigation to determine the optimum knee flexion angle for the ‘skyline’ patellofemoral joint radiograph.
Plain radiography of the patello-femoral joint includes the axial or ‘skyline’ radiograph. The optimum knee flexion angle for making this image remains unclear.
We therefore performed a prospective clinical study in which patients underwent three skyline radiographs with knee flexion angles of 30(or minimal flexion), 50 and 90 degrees. The patients were new patients, aged between 12 and 30, presenting to a knee clinic with anterior knee pain. Two observers evaluated the radiographs, making a standardised series of measurements. Blinding was organised so that the observers were unable to use any information other than the radiographic image alone. One observer evaluated all the films on two separate occasions to allow calculation of intra- and interassessor agreement.
There were 67 knees from 46 patients. There was a high level of intra- and inter-observer agreement. There were a number of patients in which the radiographic appearance of the patello-femoral varied markedly between the different views; in all cases the abnormality was best demonstrated by the 30-degree view. There were however a number of minimal flexion views in which the film contained incomplete information because part of the patello-femoral joint was missing from the image.
We conclude that whilst a minimal flexion skyline view is the most sensitive method for the detection of patellar tilt and subluxation, not all knees can be successfully imaged at the required position. A flexible approach is therefore needed, to obtain satisfactory images at minimal flexion.
The abstracts were prepared by Mr R. B. Smith. Correspondence should be addressed to him at the British Orthopaedic Association, Royal College of Surgeons, 35-43 Lincoln’s Inn Fields, London WC2A 3PN.
