A radiological assessment of osteoarthrosis of the knee: experiments in observer error.

In a trial to determine the best palliative physiotherapy for the painful osteoarthrosic knee, radiological assessment was suggested as a measure for testing homogeneity of treatment groups. Preliminary observer error experiments showed that an accepted standard grading scheme was unsatisfactory. A different system was designed in which all three knee compartments were graded separately (medial, lateral and patello femoral), based on a comparison of supine and erect films. The two systems have been compared in use on the same set of radiographs, and the observer error results are presented. The advantages of grading each compartment separately are discussed.