An infant reciprocal walking orthosis: Engineering development

Abstract

The growing trend of prescription of reciprocal walking orthoses for children under the age of 5 years has created a requirement for a new design of orthosis in this category. In response to this new demand, a prototype orthosis for infants, incorporating a specially developed hip joint and manufactured as a rehabilitation engineering device within the provisions of the EC Medical Devices Directive, has been produced and tested. A design feature that strongly influences the efficiency of walking is the rigidity of the body brace structure. Monitoring the specific structural performance of the body brace intended for infants showed that it would equal or improve the stiffness achieved in an orthosis for adults. Additionally its strength was comparable with the adult design, which has proven to be safe and reliable in many years of routine prescription. Incorporation of the infant body brace within a complete orthosis provided a structure of more acceptable physical dimensions for these more diminutive patients. The orthosis showed no incipient sign of failure after 100,000 cycles of representative service loading equivalent to that imposed by a 20 kg (5-year-old) patient. The results of structural assessment and cyclic load testing confirm that the design of the orthosis sufficiently satisfies the statutory requirements for devices that are safe and fit for purpose to permit field trials with patients.

Evaluation of safety and reliability in an infant reciprocal walking orthosis

“…These were formed and welded to 40mm x 15mm x 3.2mm Qi") stainless steel flanges that permit the structure to be assembled using M5 bolts. Testing confirmed that equivalence had been achieved (Stallard et al, 2001). The knee-ankle-foot orthosis sections incorporated 12.7mm (0.5") Masser knee joints and were cross-braced with a steel thigh-brand, steel calf-band and aluminium alloy shoeplate.…”

“…A prototype orthosis of a size suitable for an infant patient was produced for initial structural testing (Stallard et al, 2001). This exercise provided sufficient reassurance regarding structural performance to enable prescription to a limited number of patients.…”

“…Additionally, relative strength was comparable with the adult version, which has proven to be safe and reliable in many years of routine prescription. This, together with the limited cyclic testing of the complete orthosis (Stallard et al, 2001), gave confidence that it was safe to proceed with controlled field evaluation of the infant design when supplied as a rehabilitation engineering device within the provisions of an ISO9001 and EN46001 QA System.…”

“…Earlier structural assessment, and limited cyclic load testing of key elements of the orthosis (primarily the body brace), confirmed that a safe device for evaluation with patients could, theoretically, be produced. A provisional prototype was therefore designed and manufactured for initial structural testing of the complete infant orthosis (Stallard et al, 2001).Efficiency of walking is strongly influenced by the lateral rigidity of the orthosis. Monitoring the structural performance of the provisional infant design indicated it would equal or improve on the stiffness of that achieved in the adult specification.…”

“…Earlier structural assessment, and limited cyclic load testing of key elements of the orthosis (primarily the body brace), confirmed that a safe device for evaluation with patients could, theoretically, be produced. A provisional prototype was therefore designed and manufactured for initial structural testing of the complete infant orthosis (Stallard et al, 2001).…”