1 Introduction

Developmental dysplasia of the hip (DDH) is a condition where either due to a shape, alignment, or size abnormality, an infant's acetabulum does not cover their femoral head properly from birth. This structural abnormality results in an inability to support the hip bone and can range from stable mild dysplasia to severe dysplastic dislocated hips. There seems to be some play between genetics, and family history as well as how the baby presents during birth, but the exact cause remains unknown. It also appears more commonly in females, affecting 1 in every 600 girls but only 1 in every 3000 boys.¹ The overall incidence is estimated at 11.5/1000 births, presenting as one of the most common orthopedic hip conditions in infants.² In terms of Graf grade, it is a technique for classifying hip dysplasia using ultrasound. This is done by checking the alpha angle (type), and beta angle (subtype). The alpha angle is the angle between the roof of the acetabulum and the vertical cortex of the ilium, while the beta angle is between the triangular labral fibrocartilage and the vertical cortex.³ A normal hip has an alpha angle of around >60° and a beta angle of <55°. The smaller the alpha angle gets and the larger the beta angle gets, the worse the Graf grade (Fig. 1A and B). DDH treatment typically consists of starting with conservative treatment such as a brace or spica cast, and if that fails, then moving to closed reduction followed by open reduction. This also varies depending on the age of the patient, as conservative treatments are typically reserved for younger cases, while more severe treatment options are for older.⁴ If untreated, DDH poses many problems for infants as they age, including disability, early osteoarthritis, avascular necrosis of the femoral head, and hip pain. This is why early intervention is key in terms of reducing future complications.

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Fig. 1 Hip Graf α & β Angle Measurements. A: ultrasound image; B: illustration figure.

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In terms of early intervention, bracing has the most common use, with the current standard being the Pavlik harness (Fig. 2A–B) in the US, but there are other options available as well. One which is gaining more traction is called the Tubingen splint (Fig. 3A–B). Being newer and coming out in Germany originally during 1990, the Tubingen splint has been increasing in prevalence due to its reported ability as an alternative to the Pavlik harness.^5,6 There is currently no true comparison study on the outcomes between the two done directly, which one is better or worse, pros and cons, especially for each Graf grade. This is why this study is a systematic review that is conducted to directly contrast these two braces in order to determine which one should be preferably used and is most effective in order to treat DDH for different hip grades in infants.

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Fig. 2 Pavlik harness. A: Image of this brace; B: Brace function image.

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Fig. 3 Tubingen splint. A: Image of this brace; B: Brace function image.

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The main questions of this review addressed were: “For each Graf grade, in terms of success and failure rates, which brace fared better?”, “Is there a significant difference in how long the brace is worn and for how many hours per day between the two braces?”, “Which brace between the two is less likely to cause avascular necrosis (AVN)?”, and “Is there a significant difference between the braces for the age that the braces are initiated/given to the infants?”

2 Methods

Three main databases were used: PubMed, Google Scholar, and Embase. The original search was “Tubingen versus Pavlik DDH”, which resulted in very few studies. The search was expanded by searching “DDH Pavlik” and “DDH Tubingen” separately, yielding more results. Then the terms “Pavlik Orthotic/Brace” and “Tubingen Orthotic/Brace” were used, and those papers were also included as well. Studies were looked over by the authors independently and then cross-analyzed together to ensure that they would be applicable to the review. If a disagreement occurred, the authors reviewed and examined the paper together to determine whether it should be included. Through the various papers, studies were included if they provided information on conservative treatment, the Tubingen splint, and the Pavlik harness, as well as what the outcomes were in terms of the studies' goals. The excluded studies were ones that focused on the diagnosis of DDH rather than treatment, ones that discussed surgical treatments, papers that focused on the mechanism of DDH, and studies that weren't in English.

From these papers, the criteria that were extracted specifically were the success rate, failure rate, general outcomes, number of patients, age at treatment initiation, which brace was received, rates of AVN, and how long the brace was put. This was done and reviewed by the authors individually. The success rates were calculated based on the number of successfully reduced hips over the total number of hips, and the number of failed hips with brace treatment over the total number of hips gave the failure rate. Studies were not used if they did not provide the total number of hips. For the duration, studies were used if they gave a good, estimated range of how long the brace was used for, and if this information was vague or did not give an exact length of time, the study was not used for this calculation. This is the same for time per day, which had to be given in hours, and only studies that gave exact ranges or specific values of hours per day were included in that calculation. Finally, for age of initiation, studies where a specific age was given for when the treatment was started were used in the data set. If age was not fully specified or the paper just stated the time of diagnosis rather than the time treatment was started, then that study was not included in the data used.

For success and failure rates, each Graf grade was assessed using a Chi-squared test to determine if a difference was seen. A Chi-squared test was also used to compare the AVN rates. For the duration that each brace is worn and how many hours per day, a Student's t-test was employed to compare the values between the braces to see if a difference is seen. For the age at which the brace is initiated, a two-tailed t-test was used to compare the data in order to see if there is a difference between the two braces. For each of these tests, a level of significance of p ≤ 0.05 was used.

3 Results

Through this process, a total of 77 articles were identified, 45 were removed due to the factors discussed, and 32 papers were further evaluated. 7 more were excluded after this. Finally, 5 more papers were removed due to either not enough information, or not having pertinent information. This left 20 papers: 7 Tubingen papers, 10 Pavlik papers, and 3 papers that talked about both (Fig. 4, Table 1^5–24). This resulted in a total of 1243 Tubingen hips and 420 Pavlik hip samples. Graf 1 hips were not included due to the fact that they are considered normal at an alpha angle>60°.³ The average success rates using successfully reduced hips over total hips for Tubingen for Graf 2, D, 3, 4: 95.94 %, 80.05 %, 88.33 %, and 43.69 %. Pavlik had success rates of 79 %, 69 %, 72.38 %, 55.89 %. There was a general trend of a decreasing success rate and higher failure rate with increasing Graf grade. The mean duration for Tubingen was 9.76 ± 4.91 weeks for 21.2 ± 0.89 h/day, while Pavlik was 11.14 ± 6.76 weeks for 23.5 ± 0.46 h/day. The AVN incidence was 0.60 % for Tubingen and 4.97 % for Pavlik. The AVN rates for the studies didn't include the Graf grade specification on which hips underwent necrosis. The mean age of initiation was 9.96 ± 6.26 weeks for Tubingen and 8.87 ± 7.05 weeks for Pavlik.

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Fig. 4 Flow chart.

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For Graf 2, Tubingen splint was shown to have a significantly greater success rate and lower failure rate compared to Pavlik (p < 0.001). For Graf D, the Tubingen splint also was shown to have a greater success rate and lower failure rate compared to Pavlik (p < 0.05). For Graf 3, Tubingen again had a higher success rate and lower failure rate that was significantly different from Pavlik (p < 0.001). This points to the Tubingen splint being the better choice for Graf 2, D, and 3 hips. Both braces had a low success rate for Graf 4 (less than 60 %). The literature and the results indicate that Graf 4 is hard to treat with bracing. To not delay healing, surgery might be offered as an alternative option for these patients.

For duration, there was no significant difference in the amount of time each brace was used (p > 0.05). For the number of hours per day, just like duration, there was no statistically significant difference seen between the two braces (p > 0.05). These results indicate both braces are used very similarly to each other in terms of duration and hours per day, and using either one will not result in any significant disadvantages in terms of this factor.

The Tubingen splint had a much lower average incidence of AVN compared to Pavlik (p < 0.001). This is possibly due to the fact that the Tubingen splint lowers the angle of abduction to around 40° compared to the Pavlik harness around 60°, reducing the stress on the femoral vessels and nerves. The Tubingen splint restricts adduction more than Pavlik, which prevents hip dislocation. It positions the child that has the hips less abducted in order to put less pressure on the vessels and nerves, thereby posing potentially less risk for AVN compared to the Pavlik.

There was no significant difference between the average age that the brace was initiated between the Tubingen group and the Pavlik group (p > 0.05). Both braces are generally recommended for DDH of infants below 6 months old. The results point to a similar conclusion that both braces are used for similar age ranges.

4 Discussion

DDH is one of the most common orthopedic hip conditions in pediatrics, presenting in 11.5/1000 births and being more common in females.² It is a condition where the hip socket does not provide proper coverage of the femoral head, which if not corrected, could result in long-term complications. This is why it is crucial to diagnose and treat the condition as early as possible. The first line of conservative treatment for infants is braces, the most common being the Pavlik^10,7. An alternative brace that has shown promising results though is the Tubingen.^7,12 Currently, there has been only one retrospective comparison study done between the two braces, resulting in a lack of knowledge of which brace is preferred for early intervention for infants with different Graf grades. This is why this review was conducted, as it aimed to provide information on which brace should be given to infants to treat early DDH for each hip grade. This review found that the Tubingen splint performs very similarly to the Pavlik harness, even performing better in terms of Graf 2, D, and 3 hips, and also has a lower incidence of AVN. For Graf 4, both braces had poor outcomes. Due to this, surgery might be offered more frequently as an option for Graf 4 and more serious hip grades compared to lower grades.

In terms of limitations, due to the relatively newer nature of the Tubingen splint, the amount of information and use is lower than the Pavlik harness, especially in North America.^5,6 It is unknown whether the better results of the Tubingen are due to it being a better brace, or if procedures and techniques for using braces for DDH have become better with increased knowledge over the years. Also, due to Pavlik being used more broadly for every Graf grade, in order to get a comparison for the different grades, fewer samples were available for Pavlik compared to Tubingen for the success and failure rates. This can be seen as for each of the four Graf grades analyzed, the Tubingen splint had a greater number of articles used to gain the average success and failure rate than the Pavlik harness, which could've affected the results. The reason Graf grade was used rather than clinical reducibility/irreducibility is because it provides a more quantitative measurement, which makes the comparison more specific and accurate. Due to the Graf classification being a newer system, only 10 studies were available for the numerical calculations using Graf grade, with Pavlik having only 4 studies. The majority of them also weren't randomized control studies. This makes it harder to pool the data and do a meta-analysis. Also, for the AVN, the majority of the studies did not state which Graf grades or types of hips underwent AVN, which makes it difficult to determine whether the cause was the actual braces or whether the hips that became necrotic were just a higher grade. Also, 12 of the studies chosen were retrospective case-control studies, meaning that there is a chance some data or potential confounding variables were missing from some studies.^{5,6,8,11–13,18,20,22–24} Also, due to the lack of previous direct comparison studies between the two braces, the current review was forced to use mostly individual brace studies and group them together into Pavlik or Tubingen in order to compare the braces against each other, resulting in a potential variable population for each of the braces individually.^25–27 This also leads to potentially confounding variables such as genetic etiology and mechanical etiology (such as breech presentation). In the future, random controlled studies on this subject are encouraged.

In terms of the results, for Graf 2, D, and 3 hips, the Tubingen splint had an overall higher success rate and lower failure rate than the Pavlik harness, while both braces struggled with Graf 4. The Tubingen splint also had a much lower incidence of AVN compared to the Pavlik, 0.60 % versus 4.97 %. Besides this, the braces had similar ages of initiation and duration of treatment. This makes sense as both braces are typically used for infants less than 6 months old with DDH.^5,7,9,17 This leads to the deduction that the braces can be used and recommended for the same population, and neither brace will result in a delayed or faster outcome compared to the other.

5 Conclusion

Both braces are very comparable to each other, each having generally better success rates for lower Graf grades, pointing to the importance of bracing earlier to improve the treatment outcome. The Tubingen splint surpasses the Pavlik harness when it comes to AVN and Graf 2 through 3 hips. For Graf 4, both braces had poor outcomes. Both braces had similar durations and ages of initiation. The Tubingen splint, especially for lower Graf grades, could be the preferred option over the Pavlik for DDH in infants. High grades point to a potential recommendation for more surgical intervention compared to lower grades.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Financial support and suponsorship

None.

Ethical statement

We confirm that this manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. This manuscript has not been submitted elsewhere. We appreciate that this respected journal has an excellent process of review and decision. Thank you for your time and please feel free to contact me if there are any further questions.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Guardian-patient's consent

Not Applicable.

CRediT authorship contribution statement

Ajay Nair: Data curation, Software, Formal analysis, and interpretation, Writing – original draft, Writing – review & editing. David Yatsonsky: Visualization, Investigation, Software, Formal analysis, and interpretation, Writing – review & editing. Jiayong Liu: Conceptualization, Methodology, Software, Formal analysis, and interpretation, Writing – review & editing, Supervision.