Hip dysplasia in young adults
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According to data held by the Medical Birth Registry of Norway, approximately 1% of all newborns in Norway are diagnosed annually with hip instability at birth. Abduction treatment (Frejka pillow) for 6-12 weeks is the standard treatment in Norway, with which the majority will develop normal hips. Additionally to those detected by the neonatal screening program, some are late-diagnosed cases (diagnosis >1 month of age). For this group, the treatment is usually more demanding and prolonged. The older the child is at start of treatment, the poorer is the prognosis. A dysplastic hip causes altered mechanical conditions, predisposing for increased wear of the cartilage and development of osteoarthritis of the hip in young adult age. The final treatment option for this condition could be a total hip replacement.
In Paper I, we linked two national registries, the Norwegian Arthroplasty Register and the Medical Birth Registry of Norway, using the unique national identification number. The Birth Registry contains information on all newborns in Norway from 1967 and the Arthroplasty Register includes all total hip replacements inserted in Norway from 1987. The study found a 2.6 times increased risk for a total hip replacement in young adulthood for patients reported with hip instability in the newborn period. The absolute risk was however low at only 57 in 105 for patients with hip instability compared to 20 in 105 for those with stable hips. Only 8% of those who underwent a total hip replacement due to hip dysplasia were reported to have had instable hips at birth.
In Paper II, we validated the dysplasia diagnosis reported to the Norwegian Arthroplasty Register for subjects born after 1967. Medical records were reviewed and we also investigated age at dysplasia diagnosis, previous treatment and quality of life. We found the dysplasia diagnosis reported to the Arthroplasty Register to be correct in 88% of the hips. Median age at time of diagnosis was as high as 7.8 years: 4.4 years for females and 22 years for males. 75% of the patients had undergone different hip-preserving treatments before their prosthesis, and the dysplasia patients scored poorer in quality of life (EQ-5D) compared to the age-matched general population in Sweden and the UK.
In Paper III, we aimed to validate a digital measurement programme for hip dysplasia at skeletal maturity. Ninety-five radiographs were measured by three independent observers in both a newly developed digital measurement programme and manually in AgfaWeb1000. Eleven radiological measurements, all relevant for hip dysplasia at skeletal maturity, were evaluated. We found acceptable inter- and intra-observer reproducibility for most measurements, but with poorer accuracy for measurements with small absolute values. The reproducibility was relatively similar for the two methods used, but the digital measurements were performed much faster.
In Paper IV, we used data from the 1989 Hip Project and reported on the prevalence of hip dysplasia in 2081 19-year old Norwegians. The prevalence of hip dysplasia in the cohort varied from 1.7% to 20% depending on the radiological measurement used. A Wiberg’s angle <20° was seen in 3.3% of the cohort: 4.3% in women and 2.4% in men. We found no association between subjects with radiological signs indicating hip dysplasia and body mass index (BMI), Beighton hypermobility score, EQ-5D score or WOMAC score.
The overall conclusions of this thesis are as follows: About 25% of all total hip replacements in young adults (< 40 years) are performed due to an underlying hip dysplasia. The dysplasia diagnosis is in general detected late, indicating that clinical testing for hip instability in newborns is an insufficient screening method to detect hips that require a total hip replacement in young adulthood. Several radiographic measurements for hip dysplasia are proposed in the literature. The reproducibility for these measurements varies, but with acceptable results for the more common measurements such as Wiberg’s centre-edge and Sharp’s acetabular angle. The prevalence of hip dysplasia is highly dependent on the radiographic measurements used, but a high prevalence for some of the measurements is found in skeletally mature Norwegians as compared to other studies on Caucasians in the literature.