Reliability of the severin classification in the assessment of developmental dysplasia of the hip

his study was undertaken to investigate the reliability Severin's classific ation at various ages, and to determine whether the reliability is improved by careful measurement rather than subjective assessment. The radiographs taken at ages 6, 10 and 16 years of 20 randomly selected patients treated f or developmental dysplasia of the hip were graded by six observers on two s eparate occasions using parameters measured according to Severin's criteria . In addition, four of these observers re-graded the same radiographs using subjective assessment without measurements being made on two other separat e occasions. Agreements between and within observers were evaluated using t he weighted Cohen's kappa statistic for each age group. Intraobserver relia bility was good, there being a close association between the measured and t he subjectively observed ratings. This accords with the subjective nature o f this classification. The interobserver reliability was found to be poor a lthough it improved when direct measurements were made. Overall agreement b etween observers improves as patient age increases. It is concluded that co mparisons between different observers using the Severin classification syst em are not reliable. However, a single investigator comparing treatment mod alities in the same study allowing for individual bias in assessing deformi ty and subluxation would produce reliable results.