Total hip replacement in young adults with hip dysplasia.

Sir—It was with great interest that we read your article: “Total hip replacement in young adults with hip dysplasia: age at diagnosis, previous treatment, quality of life, and validation of diagnoses reported to the Norwegian Arthroplasty Register between 1987 and 2007” (Acta Orthop 2011; 82 (2): 149-54). We wish, however, to comment on the indiscriminate use of the term “dysplasia” for the whole spectrum of the deformity, which is not in agreement with the variety of underline pathology. In our opinion, in order to avoid confusion and diagnostic inaccuracies, the term ”dysplasia” should be reserved for the milder types of hip deformity.

It is clear, we still do not have an agreed terminology, covering the entire pathology of congenital deformities of the hip or a generally accepted classification that will improve our communication, our understanding of the natural history of the different types of the deformity, treatment planning and evaluation of results of various treatment.

We favor the use of the term ”Congenital Hip Disease”, for the whole spectrum of the deformity. Accordingly, it can be classified in infants as: dysplasia, subluxation, and dislocation (Wedge and Wasylenko 1979, Weinseine 1987), and in adults as: dysplasia, low dislocation and high dislocation (Hartofilakidis et al. 1988, 1996, 2000, Hartofilakidis and Karachalios 2000, Karachalios and Hartofilakidis 2010).

In one of our previous studies on the epidemiology, demographics, and natural history of congenital hip disease, based on 231 adult patients (356 hips), we confirmed that 170 hips (48%) were dysplastic, 85 (24%) had low dislocation, and 101 (28%) had high dislocation. 338 of the hips (95%) were in women. In the dysplastic hips, no history of hip disease in childhood was recorded. The disease had been undiagnosed until the onset of symptoms at a mean age of 35 (18–40) years. In patients with low and high dislocation, diagnosis was established since early childhood. Limping was present from infancy, with pain usually starting between the ages of 25 and 30.

Sir—First of all, we thank you for your interest in our article. The terminology of hip dysplasia is an essential topic and we agree on the importance of precise terms. The vocabulary has changed over time, and the wide spectre of severity of the condition and different ages at diagnosis may partly explain this conceptual dissatisfaction and confusion.

In your letter, you recommend the use of “Congenital Hip Disease” for the whole spectre of the deformity with a further sub-classification into 3 groups depending on the severity. You also refer to your interesting work on adult patients with osteoarthritis secondary to a congenital hip disease (Hartofilakidis et al. 2000). One of your findings is that patients with the mildest affection (dysplasia) had no history of hip disease in childhood. This supports the findings in our study (high age at diagnosis (median 7.8 years)), but also indicates that the term “congenital” can be misleading in this context. Americal Academy of Pediatrics, Academy of Orthopaedic Surgons (AAOS), and The Pediatric Orthopedic Society of North America (POSNA) have advocated the use of developmental dysplasia of the hip (DDH) as the terminology includes all cases that are clearly congenital and those that are developmental, incorporating subluxation, dislocation and dysplasia of the hip (Clinical practice guideline: early detection of developmental dysplasia of the hip. Committee on Quality Improvement, Subcommittee on Developmental Dysplasia of the Hip. American Academy of Pediatrics 2000). In our study we have used the DDH-term in combination with hip dysplasia, two terms also used interchangeably in the literature.

Your recommendation regarding the sub-classification of the condition is clearly useful. In our study, we had unfortunately no opportunity for such a classification, as the initial radiographs for a large proportion of the patients were missing. Another challenge would have been to define radiological measurements with corresponding cut-off values for the various subgroups.