SEVERIN CLASSIFICATION-SYSTEM FOR EVALUATION OF THE RESULTS OF OPERATIVE TREATMENT OF CONGENITAL DISLOCATION OF THE HIP - A STUDY OF INTRAOBSERVER AND INTEROBSERVER RELIABILITY

The Severin classification system frequently is used to evaluate the r adiographic results of operations performed for the treatment of conge nital dislocation of the hip, However, the reliability of this classif ication scheme has not been established, to am knowledge, Ideally, a c lassification system should be validated before it is used to promote therapeutic guidelines or to compare results of treatment; the purpose of the present study was to establish the intraobserver and interobse rver reliability of the Severin classification system. Four blinded ra ters and the operating surgeon independently used the Severin system t o evaluate the most recent radiographs of thirty-seven children (fifty six hips) who had been managed, an average of nine years previously, w ith a medial open reduction for congenital dislocation of the hip. Thr ee of the raters evaluated the same radiographs again under similar te sting circumstances eight weeks later, Ten paired interobserver and th ree intraobserver comparisons then were analyzed with use of the Cohen kappa coefficient (kappa). The average kappa coefficient far the six pairwise comparisons between the four blinded raters was 0.15 (range, -0.05 to 0.42) when all Severin classes were analyzed iudependently. T he average kappa coefficient for the four pair,vise comparisons betwee n the blinded raters and the operating surgeon was even lower (0.02). The kappa coefficients for the three intraobserver comparisons were 0. 20, 0.38, and 0.44 (average, 0.34). Kappa analysis demonstrated variab le and low levels of agreement when the Severin system was used to rat e the results of operations performed for the treatment of congenital dislocation of the hip. We believe that the unadjusted kappa coefficie nt should indicate excellent agreement (kappa >0.75) for all compariso ns if this system is to be used for the evaluation of clinical results . The unacceptably low levels of intraobserver and interobserver relia bility call into question the clinical conclusions of reports in which the Severin system has been used as the basis of proof.