Challenges with properly positioning children treated with a hip spica cast: Does the vehicle or cast type matter?

Children treated with a hip spica cast for developmental dysplasia of the hip (DDH) or femur fractures often experience difficulty fitting properly within conventional child safety seats (CSS), potentially compromising safety. While prior laboratory crash studies have evaluated the crash performance of casted pediatric surrogates, these investigations have typically used a standardized test bench that does not represent the spatial constraints and seating geometry of modern passenger vehicles. The objective of the current study was to evaluate the ability to properly restrain pediatric surrogates fitted with hip spica casts in a range of contemporary vehicles using commercially available child restraint systems.

Two anthropomorphic test devices representing a 1-year-old and a 3-year-old child were used as surrogates. Each surrogate was fitted with three hip spica cast configurations: a bilateral developmental dysplasia of the hip (DDH) cast, a bilateral femur fracture cast, and a 1½-leg femur fracture ("walking") cast. Two convertible CSS (Wallenberg and Radian R100) were evaluated for both surrogates in rear-facing and forward-facing configurations where appropriate. For the forward-facing 3-year-old surrogate, an additional restraint system (RideSafer Vest with or without a BubbleBum booster) was also evaluated. Casted surrogates were installed in four representative vehicle types: compact car, sport utility vehicle, minivan, and pickup truck. Installations were performed by a certified Child Passenger Safety Technician Instructor. Each scenario was scored as either a 'Pass' or 'Fail' based on criteria including harness fit, spinal alignment, head clearance, pulmonary space within the cast, and absence of vehicle interference.

The 3-year-old forward-facing surrogate was properly restrained in an average of 83.3% of installations across vehicles. Failures occurred when using the RideSafer Vest with or without the booster in three of the four vehicles, where the cast geometry led to forward slouching, spinal misalignment, and chest contact with the interior of the cast. In contrast, the rear-facing 1-year-old surrogate was properly restrained in only 45.8% of installations. Proper installations occurred more frequently with the Wallenberg seat (58%) than with the Radian seat (33%). Nearly all failures involved femur fracture casts, where fixed hip flexion in the cast geometry prevented appropriate positioning and harness fit.

Hip spica casts substantially affect the ability to properly restrain children in passenger vehicles. Older forward-facing children were considerably more likely to achieve a proper restraint condition than younger rear-facing children. Cast type, vehicle interior geometry, and CSS design all influenced successful installation. Vehicles with greater interior space, such as minivans, and CSS designs accommodating cast geometry were more likely to allow proper restraint.