THE PATELLOFEMORAL JOINT - A CRITICAL-APPRAISAL OF ITS GEOMETRIC ASSESSMENT UTILIZING CONVENTIONAL AXIAL RADIOGRAPHY AND COMPUTED ARTHRO-TOMOGRAPHY

In the quest for treatable causes of anterior knee pain, plain film sk yline views of the patello-femoral joint are requested, often in 30-de grees, 60-degrees and 90-degrees of flexion, to assess the functional relationships of the joint. Patello-femoral malalignment predisposes t o recurrent subluxation and dislocation, articular cartilage damage an d premature degenerative change. The aim of this study is to evaluate critically, by comparative assessment, the information provided by sky line views and axial computed arthro-tomography (CTA). Measurements of the patello-femoral angle (assesses patellar tilt), the congruence an gle (assesses patellar lateralization) and the trochlear depth were ma de on Merchant's skyline views and on axial CTA on each of 50 symptoma tic knees. Results are presented in graphic form with visual examples indicating a poor correlation between the two imaging methods. We conc lude that skyline views are inaccurate and unsuitable primarily becaus e they cannot be obtained in less than 30-degrees of flexion. We sugge st that skyline views have no role to play in screening for maltrackin g as even florid examples must be missed, and would strongly urge that no surgery be performed on their basis alone as this would result in inappropriate operations. Although computed tomography is the preferre d mode of assessing patello-femoral geometry, difficulties are still e ncountered and the ways of circumventing them are discussed.