Radiological long-term follow-up up to 12 years of initially ultrasound unstable hip types D, III and IV after treatment with the Tübingen splint worn as a plaster

Developmental dysplasia of the hip (DDH) is the most common disease of hip joints in childhood and therefore a major clinical and scientific focus for pediatric orthopedists. DDH is characterized by a dysplastic maturation disorder of the lateral edge of the acetabulum and, associated with this, a lack of coverage of the acetabular roof over the femoral head [1]. During further development, the femoral head may dislocate resulting in an increase of pressure on the already dysplastic lateral edge and its growth area of the acetabulum leading to a further impairment of the acetabular development. Symptoms of DDH like pain and/ or limitation of the range of motion most often only occur with structural damage at a later time. Clinical signs and tests such as the Ortolani and Barlow tests are often unspecific (especially in borderline cases) or can only be properly performed by experienced examiners [2]. The implementation of the hip ultrasound examination in the 1980s by Graf and the introduction of a screening program in several countries led to a fundamental improvement for the children with a significant earlier diagnosis and less invasive as well as shorted treatment [3‐7].

Based on the ultrasound characteristics dysplastic hips can be classified into ultrasound stable and unstable hips. Ultrasound stable hips (hip type IIa, IIb and IIc according to Graf) are treated with so-called maturation orthoses such as the Tübingen splint or others; ultrasound unstable hips (hip type IID, III and IV) have to be securely reduced and after stabilization to be treated with retention devices such as the Fettweis plaster or Pavlik harness [8, 9]. In recent studies, the Tübingen splint is currently applied for the treatment of ultrasound unstable hips—especially in newborns up to the age of 6 to 8 weeks: it was shown that 92.3% to 98.0% of the unstable hips could be transferred into an ultrasound normal hip with the Tübingen splint [10‐12]. Advantages of the Tübingen splint are easy handling, easy adjustment in size and easy cleaning.

After successful therapy, the hips need radiological controls until cessation of growth in order to detect residual or recurrent dysplastic changes at an early stage and to reveal complications such as avascular necrosis of the femoral head (AVN). Therefore, an X-ray of the pelvis is an established method for follow-up examinations. By analyzing these radiographs, the bony development can be observed using several lines and angles, such as the acetabular index (ACI) and the center edge angle (CEA). In adolescents the ACI is no longer valid due to the closing of the triradiate epiphyseal plates. Here, the CEA is an established method to assess residual dysplasia.

Tönnis et al. analyzed and classified the development of the normal and abnormal hips. Based on these results, hips can be classified into normal findings, slightly or severely dysplastic pathologic findings [13]. The classification depends on the ACI, gender, affected side and age of the individual. Based on the classification therapy, recommendations can be made.

Until now, there are only limited data on the short- and mid-term radiological development of ultrasound unstable hips after treatment with the Tübingen splint [14]. Data on long-term outcome are not available yet.

Therefore, the aim of the present study is to evaluate the success of the treatment of ultrasound unstable hips with the Tübingen splint. Furthermore, the radiographic long-term development up to the age of 12 years will be analyzed.

The analysis after treatment of ultrasound unstable hips type D, III and IV with the Tübingen splint and start of treatment below the age of 6 weeks shows a good success rate of 95.5% with transfer into an ultrasound normal finding with an alpha-angle above 65°. The value 65° is used with respect to the maturation curve of Tschauner et al. that postulated a higher alpha-angle in the further development of the hip joints in the first few months [16].

The above-mentioned success rate of 95.5% is comparable with previous studies, which examined the therapy of ultrasound unstable hips with the Tübingen splint. Here, success rates of 92.3–98.0% were observed [10‐12, 17]. Seidl et al. found in their study with 52 ultrasound unstable hips a success rate of 98.0% [11]. Compared to our study they started treatment earlier—during the first week of life—and only one hip type IV was included. Pavone et al. were able to successfully treat 92.3% of ultrasound unstable hips with the Tübingen splint (n = 251) [12]. However, no specific information is provided about initial ultrasound hip type, average age at initiation of treatment and duration of treatment. Zhi et al. found in a meta-analysis a success rate for treatment with the Tübingen splint in hip type II (without precise differentiation of subtypes) of 98.0% and in type III hips of 96.0%. This is in accordance to our data with 98.9% success rate of type D and 95.3% success rate of type III hips. On the other hand, the success rate of 32.0% for type IV hips was very low (with statistically low heterogeneity in the study group) [17]. These data were significantly inferior to the results of the present study showing a success rate of 81.2% for type IV hips. This could be explained by the fact of inclusion of children younger than 6 weeks and without severe limitation of hip abduction in our study; the parents were also advised to wear the splint like a cast—meaning not to take off the splint at any time (24 h/d and 7d/w). A detailed comparison with the other studies is difficult because of the heterogenic of the different study population.

Compared to other treatment options for ultrasound unstable hips—such as the frequently used Fettweis plaster or the Pavlik harness—, the stated success rate is comparably good. The Fettweis plaster shows a success rate of 80 to 93% with a low AVN rate < 7.4% over time [18‐21]. However, the Fettweis plaster is applied under anesthesia associated with a higher burden for the patient and it is less comfortable for the parents in taking care for hygiene, etc. Another alternative is the widely used Pavlik harness with a success rate of 73 to 92% [22, 23]. Disadvantages compared to the Tübingen splint are the higher AVN rate of up to 16.1% and the more challenging application, handling and cleaning of the baby for the parents [23‐27]. Furthermore, the therapy duration up to six months is longer than with the Tübingen splint [28].

In the present study, the treatment failures with the Tübingen splint affected mainly hip types IV with 18.8% (4 of 22) compared to 1.1% (1 of 93) for hip type D and 4.7% (4 of 86) for hip type III. Therefore, treatment with the Tübingen splint should be carefully considered for the most severe type of hip dislocation. In favor for a therapeutic approach of hips, type IV with the Tübingen splint is the success rate of over 80%; in case of a failure to achieve a centered hip joint within the first 2 – 4 weeks after start of treatment, the modality will be converted to closed reduction and retention in a Fettweis plaster which then would be applied still timely within the first three months of life. The results show that finally all these cases could be successfully treated and transferred to an ultrasound hip type I. An open reduction was not required in any case. On the other hand, one might argue that the failed initial treatment would prolong the overall-treatment time, but in summary the over-all success-rate of 95.5% is promising and supports our initial approach.

The radiological follow-up until the age of 12 years showed a positive development of the hips with a rate of more than 80% normal findings and less than 20% slightly dysplastic hips at the latest follow-up X-ray (fourth radiograph). Most changes—predominantly improvements—were seen between the first and second radiographs taken at the time of 1–2 years and 2–4 years. Therefore, the question arises whether all hips require radiological controls at all time-points applied so far. However, the indication of radiological controls is supported by the fact that changes with improvements and deteriorations could be detected in all hip types at all time points. Especially type IV hips—due to the rather worse tendency—need regular controls which allow for less invasive surgical treatment during childhood in case of persistent or recurrent dysplasia. This can usually be performed by a single pelvic osteotomy while in adolescents or adults more complex types of surgery become necessary (triple pelvic osteotomy or periacetabular osteotomy). The concern of radiation exposure is diminished by the fact that modern X-ray technology with significant lower radiation exposure is used today after the introduction of digital radiography [29]. Here Vogel et al. showed a mean cumulative effective dose of 0.25 mSv of anterior–posterior pelvic radiographs. In comparison to that, the annual limit for healthcare workers is 20 mSv. The effective dose is classified as at very low risk [29]. In summary the current diagnostic and therapeutic approach shows a significant improvement in the detection and treatment of DDH: earlier and shorter treatment, less surgical interventions and less impairment of the physiological development of the affected child. The time points for X-ray examinations may better defined with more data of further studies with higher case numbers.

The rate of avascular necrosis of the femoral head (AVN) of 5.3% is similar to other treatment modalities such as Fettweis plaster with 2.1–7.4% and significantly lower compared to Pavlik harness with 2.4–16.1% [23‐27]. In addition, the AVN cases in our study only showed the lowest grade 1 according to Kalamchi and McEwen, which resolved in the further course. Other studies showed a more heterogeneous outcome with AVN levels of 1 to 3 [24, 25]. The comparisons with other outcome studies are problematic due to different study designs, different study populations and different study protocols.

Limitations of this study are the retrospective study design and the relative low number of patients in the long-term FU. But these are the data available at this time, showing the longest follow-up in this study population. We conclude that the modalities are supported by the results.

Treatment of ultrasound unstable hips type D, type III and type IV with the Tübingen splint which is worn like a plaster (no discontinuation at all) is a successful option especially for type D and III hips and—with a lower success rate—also for type IV hips. The treatment should start as early as possible, ideally before the age of 6 weeks and patients should not have any restrictions of range of motion specially of abduction. A favorable evolution could also be observed radiographically in the long-term follow-up to the age of 12 years. Nevertheless, regular radiological controls are recommended, since changes may occur and can be detected at the selected time point that then allows to indicate further treatment like corrective osteotomies in time.