A reciprocal walking orthosis hip joint for young paediatric patients with a variety of pathological conditions

Abstract

A growing trend in the use of reciprocal walking orthoses for infant paraplegic patients, and their application for control of the lower limbs in very young total body involved cerebral palsy patients, has created a need for smaller components. A prototype design of a hip joint has been produced which provides the following features: adjustable range of flexion/extension control; override on stops to permit sitting; high lateral rigidity; no lateral bearing play; very high rigidity in the sagittal plane; low friction bearings; high resistance to torque about the vertical axis. In addition a size envelope which is more in keeping with the dimensions of infant patients was an important objective. Comparisons were made of the computed structural properties of the prototype joint and existing routinely available standard orthotic hip joints. In each plane of loading the prototype joint had the highest identified structural property. The hinge-bearing material was tested in a representative joint with 200,000 cycles of typical loading. It was also field tested on adult orthoses over a minimum of a 12-month period with the most vigorous of walkers. In neither test did excessive play develop. The mechanical properties of the joint were established using tests advocated in the British Standard on testing lower limb orthosis knee joints. These showed the joint had structurally equivalent performance to a successful reciprocal walking orthosis hip joint, and that the mode of failure was essentially ductile in nature. Production development of the joint is now being undertaken.

Evaluation of safety and reliability in an infant reciprocal walking orthosis

“…Because of the established relationship between walking efficiency and lateral orthosis stiffness (Stallard and Major, 1995), a primary design objective was that the structural performance of the infant body orthosis should be at least comparable with that of the adult model Parawalker. The prototype hip joint (Woollam et al, 2001) was designed so that smaller diameter cross-bracing tubes could be employed. Upper and lower stainless steel tubes of 12.7mm (0.5") external diameter were estimated to provide appropriate structural performance.…”

“…The development of a new, smaller, orthotic hip joint which has all the requirements of reciprocal walking for paraplegic patients (Woollam et al, 2001) provided an opportunity to re-examine the design parameters of the Parawalker. A theoretical analysis of potential designs of the Parawalker for paediatric patients incorporating the new hip joint was therefore undertaken.…”

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In response to new demands for infant walking orthoses consideration was given to the development of a device for this category of patient. A specially developed hip joint with the required structural properties (Woollam et al, 2001) provided an opportunity for this development. 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.

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