Points of Consensus: Orthoses Designed to Be Worn in the Upright Position

ORTHOSES DESIGNED TO BE WORN IN THE UPRIGHT POSITION

It is recognized that numerous orthotic designs exist to treat IS. Regardless of design, the key elements of an acceptable approach are to apply forces that return the spinal column to as close to a normal alignment as possible in all reference planes (coronal, sagittal, and transverse). However, these forces must be applied in a way that renders the orthosis as tolerable as possible, both in comfort and cosmesis. The forces should be applied in ways which, as much as possible, minimize side effects, thus ensuring the patient's overall physical well-being.

The importance of reducing the Cobb angle of the curve and its positive correlation with a successful outcome are recognized, but minimizing the amount of trunk shift and spinal decompensation must not be ignored in the process.

Three basic strategies should be employed:

Patient comfort (after becoming accustomed to the orthosis). An orthosis that is rendered intolerable will not be worn, and thus will not be effective.
Reduce the apical lateral shift of the curve and any concomitant decompensation.
Observe the resultant Cobb angle(s) on an in-orthosis film.

The orthotist needs to consider some fundamentals regarding the biomechanics of orthotic treatment of IS:

Some orthotic forces are clearly beneficial, and others have simultaneously positive and negative consequences on spine alignment in analysis of the full three-dimensional effect. Still other forces between orthosis and patient have no direct therapeutic benefit; rather, they are to stabilize orthosis alignment. For example, a trochanter extension of the pelvic section of an orthosis may help keep the orthosis from being laterally tilted on the patient as a reaction to the forces exerted on the scoliotic spine. In essence, an orthosis that laterally tilts on a patient may well be evidence of it "giving in" to a scoliotic curve, rather than exerting the necessary force to positively influence the curve to a more satisfactory alignment.
A patient with IS is an "active" system. Neurological feedback and muscle power are used by the patient with IS to actively respond to passive orthotic forces. Active alignment (compensation) reflexes vary from patient to patient and can be an important biomechanical and orthosis design consideration. For example, a patient with adolescent IS requires relatively small forces (alignment "reminders") at the cephalad margin of the orthosis. As a point of contrast, when a neuromuscular condition prevents normal active response, the cephalad margin forces must be larger because the patient will be less able to actively effect periodic relief.
Although the Cobb angle is a useful measure, we must recognize the limitations of its usefulness. Curve compensation is also widely recognized as being extremely important to a satisfactory outcome. Ironically, a change in upper spine alignment in the direction of the curve convexity (a decompensation) will reduce the Cobb angle measurement. For instance, a progressive leftward decompensation of a left thoracolumbar curve pattern will improve the Cobb angle numbers.

(These fundamentals and their relationship to design are discussed in detail in the articles dealing with biomechanics.)

The orthotist and prescribing orthopedist should reach an agreement regarding the goals for in-orthosis correction (Cobb angle and alignment) for each individual patient. Follow-up discussion is necessary when a favorable outcome is in question or when better orthotic correction seems possible.

APPLICATION OF FORCES

KEY CONSIDERATIONS FOR APPLYING FORCES TO TREAT A THORACIC CURVE

A thoracic curve is noted as such when the apical vertebra (ie, the most horizontal, rotated, and laterally deviated vertebra) is at or between the second (T2) and eleventh (T11) thoracic vertebral levels. A thoracic curve is reduced in-orthosis by the application of forces to the ribs, which transmit forces and moments to the spinal column. The force should be focused on the rib that articulates with the apex of the curve. Abdominal compression and lumbar lordosis reduction (posterior pelvic tilt) can have a powerful effect in reducing Cobb angles, but there are sagittal alignment effects (usually thoracic kyphosis reduction) and a potential for temporary internal organ function changes (pulmonary, renal, digestive) that can occur and should be considered.

"Corrective" forces against the ribs cause a combination of forces and moments to be transmitted to the spine. For instance, a right thoracic pad applying a corrective force to the ribs below a right thoracic curve apex will push the spine toward centerline (desirable), but it may also tend to accentuate rightward tilt of the portion of the curve spine inferior to vertebral apex. Although broadening this force may be helpful for patient comfort, care must be taken to not place a thoracic pad too low. This is especially important when treating the typical right thoracic-left lumbar combination because this force may inhibit a lumbar or thoracolumbar curve from being as centralized as possible.The more hypokyphotic the thoracic spine, the smaller the amount of anteriorly directed forces and the greater the amount of medially directed forces that should be applied. In general, forces should minimize the risk for accentuating further sagittal plane deformity in those with thoracic kyphosis of less than 20°, as measured by the Cobb angle in a standing lateral film.

KEY CONSIDERATIONS FOR APPLYING FORCES TO TREAT A THORACOLUMBAR CURVE

A thoracolumbar curve is noted as such when the apical vertebra is at or between the twelfth thoracic (T12) and the first lumbar (L1) vertebral levels. A force should be applied ranging from the inferior limit of the curve (left, for example) to the apical vertebra. To further correct left lateral vertebral shift, it may be helpful to apply a force at the lower ribs on the convex (left) side of the curve, even though these ribs articulate with vertebrae cephalad to the apex of the curve. The low left thoracic pad force will push the lower thoracic elements toward the centerline and simultaneously reduce the rightward tilt of those vertebrae.

KEY CONSIDERATIONS FOR APPLYING FORCES TO TREAT A LUMBAR CURVE

A lumbar curve is noted as such when the apical vertebra is at or between the second (L2) and the fourth lumbar (L4) vertebral levels. The corrective force for a lumbar curve should be applied to the convex aspect of the lumbar paraspinal area, with the primary force being focused at the level of the apical vertebrae. Because this force is transmitted to the spine through the paraspinal musculature, it should be directed both anteriorly and medially in an attempt to derotate and shift the spine to as normal alignment as possible. Care should be taken to avoid pressure on the iliac crest, sacrum, and ribs. There is a general corrective effect of abdominal compression and lumbar lordosis reduction in treating lumbar curves. However, this technique typically is used in the absence of a thoracic curve to prevent potential detrimental effects of the sagittal alignment of the spine (eg, thoracic hypokyphosis).

KEY CONSIDERATIONS FOR APPLYING FORCES TO TREAT MULTIPLE CURVES

When determining application of corrective forces while treating multiple curves, there needs to be recognition of structural versus compensatory components of each curve. "Overcorrecting" a compensatory curve should not be allowed at the expense of satisfactorily correcting the more structural curve, and by extension, the overall balance of the spine.

RESEARCH PRIORITIES

In conjunction with the application of force vectors in various reference planes (sagittal, coronal, and transverse), the technique of increasing the intra-abdominal pressure through circumferential orthotic design is poorly understood with respect to if/how it may be effectively applied independently of lordosis reduction. In addition, if a positive correlation exists between independently increasing intra-abdominal pressure and curve correction, there needs to be a greater understanding of optimizing this technique without potentially compromising the healthy function of internal organs in the developing child or adolescent.
The role of active versus passive correction in-orthosis needs to be better understood. That is, how does a patient actively respond to a corrective force applied within an orthosis, and what role does this have in maximizing the normalization of spinal alignment in-orthosis. This question is of particular interest in the orthotic treatment of lumbar and thoracolumbar curves because there are generally two orthotic designs used to reduce the cephalad portion of a scoliotic curve: 1) A more "open" design, in which no corrective force is applied superior to the apical vertebrae on the concave side, so a patient's ability to actively respond to the convex corrective force is required for optimal, in-orthosis spinal alignment; and 2) A more "closed" design, in which a force is applied to the superior, concave portion of the spine in an effort to passively straighten the curve as much as possible.
There needs to be a greater understanding of what may be considered the most strategic application of corrective forces on the convex side of a curve. For instance, the application of a force that terminates superiorly at the apex of a curve versus one that is applied on the entire length of the curve's convexity has been studied only through mathematical modeling, but not as applied, clinical research. In addition, there is a need to objectively measure the magnitude of corrective forces within an orthosis to identify a strategic balance between patient tolerance and the goal of normalizing spinal alignment.