Neonatal hip instability, developmental dysplasia of the acetabulum, and the risk of early osteoarthrosis

Acetabular dysplasia is a risk factor for the development of osteoarthrosis in young adulthood (Russell et al. 2006). Developmental dysplasia of the hip (DDH) is now the accepted term for NHI, but the term also includes those with dysplastic features of the acetabulum and femoral head who do not present with any degree of instability of the hip joint. The article by Engesæter et al. identifies patients with an established diagnosis of NHI, to see how many of these patients went on to develop osteoarthrosis of the hip that was severe enough to warrant total hip replacement (THR) in early adulthood. The authors found a 2.6‐fold increased risk compared to non‐NHI THR patients, yet with a low absolute risk of 57 per 100,000. It is apparent from their data, however, that the risk of NHI‐related severe osteoarthrosis increases quite dramatically with age after about 25 years of age (Engesæter at al., Figure 1). The register‐based study identified 95 young THR patients who had osteoarthrosis secondary to hip dysplasia, and only 8% of these had been treated for NHI. This is a clear indication that, generally speaking, hip dysplasia is not diagnosed in the neonatal period unless clinical instability is found, or—with supplementary selective ultrasound screening—there is a significant degree of static or inducible uncoverage of the femoral head. Recently, it was shown that certain findings from ultrasound (dynamic coverage index < 22%, α‐angle < 43 degrees, abnormal echogenicity of the acetabular roof) before treatment of NHI predict poor acetabular development later on (Alexiev et al. 2006). However, neonatal ultrasound measurement of the α‐angle does not appear to correlate with radiological measurement of the acetabular index later on (Castelein et al. 1992). It appears that the methods that are available to screen for acetabular dysplasia without NHI at an appropriate age (4–5 years of age would seem reasonable) are radiographs or MR scans of the pelvis. It remains to be seen whether these methods are risk‐effective or cost‐effective. A reasonable alternative to childhood detection and treatment of acetabular dysplasia other than late THR is treatment of symptomatic patients with acetabular dysplasia by periacetabular osteotomy in adolescence or later on.