Biomechanical evaluation of different abduction splints for the treatment of congenital hip dysplasia

The effect of the design of the orthosis on the axial load transmission of two flexion abduction orthoses used in treating congenital hip dysplasia

Background

With an incidence of 2-4% in all newborns, developmental dysplasia of the hip, DDH, represents the most frequent congenital disorder of the skeletal system in Germany. The therapy options are deduced with the help of a sonography. The conservative therapy approach includes the application of flexion abduction orthoses, which lead to a development of the child's hip through abduction and flexion angle. The overall structure of the orthoses puts a strain on the axial skeleton of the children. The following work is intended to clarify what role the design of the orthoses plays in this respect.

Methods

Inclusion criterion for the study was fully developed newborns without an indication of skeletal malformations with Type I hip joints according to Graf verified by ultrasound. A total of 19 newborns were recruited and included in the period 3/2013-01/2015. Two types of orthoses used in treating developmental dysplasia of the hip (Tübinger splint, Otto Bock; hip flexion abduction orthosis (Superior orthosis) according to Mittelmeier-Graf, AIDAMED e.K (Kreuz et al., 2012; Mittelmeier et al., 1998; Schmitz et al., 1999), constructions differ, were used. Force was measured with the help of three force sensors, which were even able to be integrated into these without changing the design of the orthosis. In this closed system, force transmission was measured for the duration of a fixed period of two minutes.

Findings

The greatest axial force development (overall force) is in the Tübinger splint with an average force of 15.1 N (min. 0.59 N, max. 53.09 N, mean 15.1, SD 2.46). 4.09 N (min. 0.96 N, max. 20.99 N, mean 4.09, SD 0.65) resulted in the Superior orthosis. Significant correlations between body weight and resulting axial traction - on average during the entire measurement period and in movement - can be taken from the statistical analysis regarding the Tübinger splint. Such a correlation cannot be depicted for the Superior orthosis.

Interpretation

The analysis of the load transmission of the examined flexion and abduction orthoses reveals differences between the models. The construct of the orthoses in itself appears to play a significant role. Long-term effects of orthosis therapy on a child's axial skeleton have not been studied to date. Furthermore, it seems reasonable to expand the test series to orthoses, the design of which is configured in a similar matter compared to the examined aids.

Conclusion

This study proves that the orthotic design has an influence on the infant's axial load.

Principles of Bracing in the Early Management of Developmental Dysplasia of the Hip

Bracing is considered a gold standard in treating Developmental Dysplasia of the Hip (DDH) in infants under 6 months of age with reducible hips. A variety of braces are available that work on similar principles of limiting hip adduction and extension. This paper summarises the current evidence regarding bracing in DDH. Most of the literature pertains to the Pavlik harness (PH) and there are few studies for other brace types. Bracing eliminates dislocating forces from the hamstrings, the block to reduction of the psoas and improves the muscle line of pull to stabilise the hip joint. Recent studies have shown no benefit in bracing for stable dysplasia. The rates of PH treatment failure in Ortolani-positive hips have been reported to be high. Barlow positive hips have lower Graf grades and are more amenable to PH treatment. There is consensus that the earlier the diagnosis of DDH and initiation of PH treatment, the better the outcome. Failure rates due to unsuccessful reduction and AVN are higher with treatment initiated after age 4-6 months. Studies have shown no benefits of staged weaning of braces. While there is no maximum time in brace, current consensus suggests a minimum of 6 weeks. The key to successful bracing lies in education and communication with the family.

A Comparison of the Contact Force Distributions on the Acetabular Surface Due to Orthopedic Treatments for Developmental Hip Dysplasia

We used a three-dimensional rigid body spring model (RBSM) to compare the contact force distributions on the acetabular surface of the infant hip joint that are produced by three orthopedic treatments for developmental dysplasia of the hip (DDH). We analyzed treatments using a Pavlik harness, a generic rigid splint, and a spica cast. The joint geometry was modeled from tomography images of a 1-year-old female. The articular cartilage was modeled as linear springs connecting the surfaces of the acetabulum and the femoral head, whereas the femur and the hip bone were considered as rigid bodies. The hip muscles were modeled as tensile-only preloaded springs. The treatments with the Pavlik harness and the generic rigid splint were modeled for an infant in supine position with a hip flexion angle of 90 deg. Also, since rigid splints are often recommended when children are initiating their gait phase, we modeled the treatment with the infant in standing position. For the spica cast, we only considered the infant in standing position with a flexion angle of 0 deg, and the fixation bar at two heights: at the ankle and at the knee. In order to analyze the effect of the hip abduction angle over the contact force distribution, different abduction angles were used for all the treatments modeled. We have found that the treatments with the infant in supine position, with a flexion angle of 90 deg and abduction angles between 60 deg and 80 deg, produce a more homogenous contact force distribution compared to those obtained for the treatments with the infant in standing position.