Orthotic Pelvis Control in Spina Bifida
H.R. Lehneis, Ph.D., C.P.O.
Control of the pelvis has been typically problematic in high level spina bifida patients due to the imbalance of motor power around the hip joint. This can be readily appreciated when one considers the differential innervation particularly of the hip flexors versus the hip extensors (Table 1). Note that the hip flexors are at least partially innervated at the L2 and L3 level, whereas the hip extensors are innervated below the L3 level. Such imbalance at the L2 and L3 level of involvement is the cause of lordosis so often seen in these patients, which is often aggravated by hip flexion contractures. Control of the pelvis and thus lordosis has been difficult with conventional designs.
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Table 1. Innervation of the Lower Limb
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In analyzing the force system required to prevent hip flexion and thus lordosis, it becomes clear that the rigid portion of the pelvic band needs to be reversed from the conventional location (Fig. 1). It should be noted that this consists of a plastic molded Subortholen panel which extends superiorly to the level of the xyphoid process. The uprights of the hip joints are attached to this panel. An anteriorly directed force is provided by a leather hammock covering the buttocks (Fig. 2). Straps attached on each of the four corners of the hammock run through D rings, attached equi-distant above and below the orthotic hip joint center. This system has worked quite effectively in controlling lordosis since first initiated approximately five years ago.
In cases where the patient presents a relatively severe hip flexion contracture, the hip joint uprights are attached to the panel by means of a single pivot placed approximately 5 cm. below the lateral trim line of the panel. By gradually tightening the straps of the buttock pad, some correction can often be achieved. The pivot allows the anterior panel to adapt to the changing angulation as correction is attempted.
It should also be noted that in our practice, patients up to the age of approximately six years old are provided with solid ankles and knees since their legs are still short enough to sit through hip flexion without obstructing much of the space in front of the chair. The purpose of this is to provide the patient with maximum stability and lightweight orthoses. As the patient gains upper limb strength and mobility, knee joints with drop locks are added, usually of the lateral single bar type. Double bars are only used when the patient is relatively heavy and when there is a torsional problem in the orthosis. The ankle-foot portion of the orthosis remains of the solid ankle type to provide the largest possible base of support over which the patient's center of gravity can be maintained with a greater degree of latitude than is possible if orthotic ankle joints were to be used.
Acknowledgment
The assistance of Barry Gosthnian, CPO in developing the system described is gratefully acknowledged.
