In this study we found, that there are multiple risk factors affecting on the recovery rate in DDH in first three months. Some of the known risk factors were associated in slower recovery rate (positive family history and girl sex) and some did not have an effect on the recovery rate (birth weight, pregnancy duration, first born birth) and some were associated with faster recovery rate (breech presentation). In the 6th months follow-up, all the differences were leveled. We also found, that first clinical status of the hip did not have an effect on the recovery rate and in mild DDH watchful waiting strategy seems effective.
It was clear that improvement in our data happened most effectively during the first three months. This is likely due to the fact, that after birth, acetabular and femoral head remodeling is most rapid during the first weeks of life 1. It`s noted that positive Ortolani test indicates more severe form of DDH when comparing to Barlow positive or mildly loose hips 1–3. In our data it seemed, that first clinical status of the hip did not have an effect on the recovery rate. Immediate abduction treatment was effective, however, group of children in watchful waiting had the fastest recovery since almost 90% of these children had normal hips in the 2nd months follow-up. We believe that this is due to excellent remodellation capacity in the first weeks of life combined with successful selection of these children by the pediatric surgeons in our center. According to our data, watchful waiting strategy seems to work in mild DDH, however, it forms a risk of later recovery. Delayed abduction treatment was associated with delayed recovery rate in the 3rd months follow-up, which however does not indicate that delayed abduction treatment would be ineffective in treatment of DDH. Later initiated treatment inevitably leads to delayed improvement. Immediate Pavlik harness treatment in infants with mild DDH (Ortolani negative) is controversial because majority of the infants will improve without treatment, and it seems that it is safe to wait with the initiation of the treatment 27,28. Our results give new information as it seems that in mild DDH recovery might delay because of the watchful waiting period. Even if waiting is safe, it is mandatory to inform families of the possibility of more rapid recovery with the immediate abduction treatment. However, further studies are needed to evaluate the effectiveness of the watchful waiting strategy in mild DDH.
Clinical status of the hip and ultrasound appearance are not always congruent, and with ultrasound dysplasia can be detected also in the hips clinically tested as normal 29,30. However, ultrasound used in screening does not seem to prevent the late cases of DDH and is not associated with improved outcomes when comparing to programs based on clinical appearance of the hip 12,15,31,32. Radiological classification at birth according to the Graf method has been associated with median age of normalization. Median age of normalization was linear with radiological grade of the hip (Type IIa – Type IV) as more severe forms of DDH gained recovery later 33. Result of the study are partly in contradiction to our study, which can be partly explained by the fact that treatment initiation indication and treatment method were different from ours.
Female sex is a known risk factor of DDH 10,11. In our study female sex was associated with lower recovery rate compared to male sex (p<0.001) in the 1st, the 2nd and the 3rd -months’ follow-up. Sex remained statistically significant in multivariable design. In previous studies, inconsistent with our finding, male gender has been associated with Pavlik harness treatment failure and slower rate of recovery 34–37. Our findings however indicate, that in addition of being a risk factor of DDH, female gender might also be a risk factor of slower recovery of DDH.
Positive family history is a well-known risk factor of DDH (10,11). We found that positive family history is associated with slower recovery in first three months. This finding remained statistically significant in multivariable design, however, in the 6th months follow-up, the differentiation was no more statistically significant. This finding gives new information of the effect of positive family history as a risk factor of DDH. Earlier we found, that positive family history could also predispose to failure of the Pavlik harness treatment (unpublished manuscript). These findings underline the importance of close follow up of these patients during the abduction treatment. It seems that genetic factors predispose to severity of DDH and in addition of adding the risk of DDH itself, adding the risk of late recovery and failure of the treatment.
Intrauterine breech presentation was associated with faster recovery rate in the first 3 months of age. However, in multivariable design, it seemed that the found association was explained with other variables. Association was only barely statistically significant in multivariable design in the 3rd months control. We believe, that this is due to two reasons. Earlier we found (unpublished manuscript) that breech presentation might predispose to Ortolani positive dislocation, which means, that initial abduction treatment is started. We also believe, that clinicians might start abduction treatment initially more easily in breech born infants, even if the hips are only mildly loose (Ortolani negative) compared to those children without this risk factor. The initial abduction treatment, however, seems to explain the faster recovery rate of breech born children. Our finding indicates, that breech born children are to recover well with correct treatment and do not have a risk of delayed recovery. We think that this is due to breech presentation being purely mechanical risk factor of DDH, without any additional genetic or hormonal factors affecting on the condition.
For other risk factors assessed in this study (parity, birth weight and gestation age) no associations with the rate of improvement of alpha angles were found.
Our study has some limitations that should be addressed. The data was collected retrospectively, and the earliest cases dated back over 20 years. Although the sample size was substantial, data was not inclusive for all patients. Data of parity was missing for most of the patients and data of family history was also inadequate. Due to this factor, our results considering these risk factors might not be adequate. However, we still found that positive family history might predispose to delayed improvement, despite the incomplete data of this part. In our center, ultrasound evaluation includes measurements of alpha angles (according to Graf’s criteria) and bony coverage of acetabulum (according to Terjesen method) as well as dynamic evaluation of hip stability during provocation. Our radiologists have not reported beta angles, and due to that we could not classify hips further according to Graf’s criteria. However, normal hips were considered to have alpha angles over 60 degrees (at any age), which is comparable to Graf’s criteria, and we still found clear associations of risk factors and recovery rate of DDH. Despite of the differences to Graf’s ultrasound evaluation, our center had only 48 (5.1%) children needing casting or operation, which of 14 were late diagnosed cases and 3 were teratological dislocations leaving only 31 (3.3%) children failing the initial treatment in 20 years of time. Even though the concept of confounding factor was taken in account in the multivariable analysis, the multivariable analysis itself was not perfectly fit for our data because of the incomplete data of family history, leaving some of the patients out of the multivariable analysis. However, our findings still were in line with the first found associations in the univariate designs. In Tampere University hospital, where the study data originates, Pavlik harness is used for abduction treatment. Previously Frejka pillow was also used. Our results on the treatment should be considered with precautions, keeping in mind that abduction treatment methods vary according to location.