Positive predictive values in clinical screening for developmental dysplasia of the hip

Background: The Danish selective screening programme for developmental dysplasia of the hip (DDH) is based on clinical examinations and screening for risk factors of all newborns. Studies have shown a low positive predictive value (PPV) of clinical hip examinations performed by a heterogenic group of screeners in the United Kingdom. As no true definition of DDH exists, the PPV is difficult to assess.
Aim: To establish the positive predictive value (PPV) of clinical hip examinations performed by referrers in the Danish screening programme for Developmental Dysplasia of the Hip (DDH) utilising three definitions of true positive DDH diagnosis.
Materials and Methods: We retrospectively identified 290 children (169 female) referred during a four-year period to the orthopaedic outpatient clinic at our institution with a positive clinical hip examination. We calculated PPV for clinical hip examinations across three definitions of a true positive clinical hip examination for all referrers and subgroups consisting of general practitioners, midwives and paediatricians. The PPV for clinical hip examinations was calculated for paediatric orthopaedic surgeons, who were blinded to the results of ultrasound examination, using one of the three definitions.
Results: PPV of clinical hip examinations for all referrers were 5.4%, 3.6% and 1.8% with the definition of a true positive DDH diagnosis defined as clinical instability found by orthopaedic surgeon, ultrasound classification = Graf IIc or both definitions combined, respectively. PPV of clinical hip examinations performed by orthopaedic surgeons was 33.3% with a true positive clinical examination defined as an ultrasound classification = Graf IIc.
Interpretation / Conclusion: In this first review of results from the Danish screening programme for DDH, we conclude that the positive predictive value of clinical hip examinations made by referrers in the Danish screening programme for DDH is low. As clinical examinations are a critical part of the selective screening for DDH, this study demonstrates a need for focused training of screeners in clinical hip examinations to improve the screening of DDH in Denmark.