A patient-specific model of the biomechanics of hip reduction for neonatal Developmental Dysplasia of the Hip: Investigation of strategies for low to severe grades of Developmental Dysplasia of the Hip

Abstract

A physics-based computational model of neonatal Developmental Dysplasia of the Hip (DDH) following treatment with the Pavlik Harness (PV) was developed to obtain muscle force contribution in order to elucidate biomechanical factors influencing the reduction of dislocated hips. Clinical observation suggests that reduction occurs in deep sleep involving passive muscle action. Consequently, a set of five (5) adductor muscles were identified as mediators of reduction using the PV. A Fung/Hill-type model was used to characterize muscle response. Four grades (1-4) of dislocation were considered, with one (1) being a low subluxation and four (4) a severe dislocation. A three-dimensional model of the pelvis-femur lower limb of a representative 10 week-old female was generated based on CT-scans with the aid of anthropomorphic scaling of anatomical landmarks. The model was calibrated to achieve equilibrium at 90° flexion and 80° abduction. The hip was computationally dislocated according to the grade under investigation, the femur was restrained to move in an envelope consistent with PV restraints, and the dynamic response under passive muscle action and the effect of gravity was resolved. Model results with an anteversion angle of 50° show successful reduction Grades 1-3, while Grade 4 failed to reduce with the PV. These results are consistent with a previous study based on a simplified anatomically-consistent synthetic model and clinical reports of very low success of the PV for Grade 4. However our model indicated that it is possible to achieve reduction of Grade 4 dislocation by hyperflexion and the resultant external rotation.

Developmental dysplasia of the hip: A computational biomechanical model of the path of least energy for closed reduction

“…This supports the previously reported finding that the Pectineus muscle resists reduction in addition to resistance by the adductor muscles for Grade IV hip dislocations 14. The findings of this study suggest that release of the Pectineus muscle during medial open reduction may also be considered to facilitate hip reduction in Grade IV dislocations.…”

“…The adductor muscles are frequently released prior to closed reduction, while the Pectineus remains intact. However, tension in the Pectineus during abduction also exacerbates entrapment of the femoral head posterior to the acetabulum 13, 14. In order to further study the role of the Pectineus the least energy path was determined with the effect of the Pectineus “switched off.” Moreover, the indirect path of the Hoffman–Daimler method was studied with and without the effect of the Pectineus by prescribing the beginning point of a Grade IV dislocated hip, an intermediate point on the ischium near the acetabular notch, and an ending point at the center of the acetabulum.…”

“…In‐house codes are written in MATLAB. Details of the computation model are in previous publications 13, 14, 15, 16, 17. A collision detection algorithm was used to determine the location of the femoral head center coordinates while the femoral head is in contact with the pelvic surface as it travels from an original start point (computational dislocation) towards the center of the acetabulum.…”

“…Figure 3 shows the active, passive, and total muscle tension with L o . Details of the muscle model and calibration can be found in Huayamave et al14 It should be noted that the calibrated muscle model exhibits an exponential behavior that becomes very pronounced after a stretch value of about 1.35 accounting for the iliofemoral, pubofemoral and ischiofemoral hip joint ligaments that prevent any further abduction of the legs past an angle of 80° and help to stabilize the hip joint. Stress is computed as σ  =  F/ PCSA and strain is ϵ = λ‐1 .…”

“…However, tension in the Pectineus muscle during abduction also exacerbates entrapment of the femoral head posterior to the acetabulum. 13 A second biomechanical study suggested that hyper-flexion and external rotation may overcome the entrapment and allow the femoral head to enter the acetabulum by following the path proposed by Papadimitriou et al 14 Calculation of the energy required for reduction along the two proposed pathways with and without the effect of the Pectineus muscle may also provide clinically relevant information.…”