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Spinal Balance and In-Orthosis Correction

Smith, Keith M. CO

JPO Journal of Prosthetics and Orthotics: October 2003 - Volume 15 - Issue 4 - p S40-S48

In-orthosis correction is typically looked upon as how much correction to the Cobb angle is achieved, but the practitioner must also look at overall spinal balance in relation to the central sacral line to determine the direction and application of forces. For instance, a decreased Cobb angle with a marked asymmetrical balance in relation to trunk shift and decompensation is unacceptable. As evidenced in Figure 1, both spinal balance and Cobb angle have been greatly improved. If there was good Cobb angle correction but poor spinal balance in the coronal plane, then the correction would be unacceptable. It is important to also pay particular attention to the sagittal plane when decreasing Cobb angle in-orthosis to prevent increasing hypokyphosis. A marked decrease in sagittal kyphosis should not be sacrificed for in-orthosis Cobb measurements.

Figure 1

Figure 1

Research is limited on spinal balance and decompensation. In 1998, Raso et al. 1 reported that little research has been done on trunk distortion. They proposed that the best treatment would improve both spine alignment and body deformity, not simply relying on the single-plane measurements of the Cobb angle. Watts 2 also noted the small amount of research and uncertainty concerning the topic of spinal balance, while emphasizing the desired position of the well-compensated spine and reduction of trunk shift. Rudicel and Renshaw 3 studied decompensation because of the concern that spinal decompensation can lead to back pain in adult life. They defined decompensation as the horizontal distance between two vertical lines, one bisecting the sacrum and the other bisecting the highest vertebra seen on a standing anterior-posterior roentgenogram. Figure 2 shows this relationship radiographically. Among 22 female compliant patients treated with the cervicothoracic-lumbosacral orthosis in Rudicel and Renshaw’s study, 3 there was no predictable improvement in decompensation in thoracolumbar and lumbar curves. However, it should be noted that half of their patients showed some mild improvement in decompensation.

Figure 2

Figure 2

Mellencamp et al. 4 reported that improvement of scoliosis with compensation could be a response expected from cervicothoracic-lumbosacral orthosis treatment. Winter and Carlson 5 emphasized the importance of using the neck ring on the cervicothoracic-lumbosacral orthosis to align the patient’s head over the pelvis and recognized that some patients with the thoracolumbar spinal orthosis (TLSO) had sufficient righting reflexes to bring their upper spine into a compensated position, thereby negating the need for any counterforce above the curve.

Bassett and Bunnell 6 used a TLSO to show that lateral trunk shift could be reduced in 58 percent of patients treated for thoracic curves, 65 percent of those treated with thoracolumbar and lumbar curve patterns, and 88 percent of those with double curve patterns. It is important to distinguish at this point that a well-compensated spine with C7 over S1 can still have substantially undesirable trunk shift. It is this trunk shift that Bassett and Bunnell are referring to, and they measure this trunk shift using Floman’s description, in which a horizontal line is drawn halfway between the seventh cervical and the first sacral vertebrae. A perpendicular line is then drawn at the horizontal line’s midpoint. The distance between this perpendicular line and the center of the first sacral vertebra represents the lateral trunk shift.

The position of side bending and drastic in-orthosis decompensation of the original nocturnal orthosis also raises the question of long-term effects. Federico and Renshaw 7 studied the decompensation issue with the bending orthosis and found that 6 of 11 patients experienced no change, 2 had improvement, and only 3 experienced decompensation, and it was on average only 0.9 cm.

d’Amato et al. 8 reported on a new TLSO that works by pushing the curves toward the midline, as opposed to being bent away from it. As with the other TLSOs, the research on this topic is limited. A long-term study will determine the efficacy of the two night TLSOs in spinal balance.

Although the literature is limited, the research cited points out an important concept. The practitioner should accept in-orthosis Cobb correction when the head is over the pelvis in the coronal plane while maintaining good overall spinal balance. The Cobb angle has been for years the gold standard of spinal orthosis efficacy, so it warrants a literature review to determine how much correction should be sought.

Moe and Kettleson 9 published the first classic study on in-orthosis correction in 1970, showing median corrections, at the end of treatment, of 23 percent in thoracic curves, 18 percent in lumbar curves, and 10 percent in higher thoracic curves in their study of 169 patients. Best correction in-orthosis in Moe and Kettleson’s group was 38 percent in thoracic curves, 55 percent in lumbar curves, and 17 percent for high thoracic. In 1980, Carr et al. 10 reported that of the patients in this same group (133 patients with 192 separate curves), those who had at least 50 percent correction in their orthosis had the best chance for maintaining a reasonable amount of correction after the orthosis use was discontinued. Two other reports cited exactly 50 percent as a standard for in-orthosis correction for successful outcomes to be achieved. 11,12 Wiley et al. 13 showed, in a study of curve magnitudes between 35° and 45° treated with Boston TLSOs, that compliance was also related to in-orthosis correction. Patients who were noncompliant with orthosis use averaged 33 percent initial correction, whereas the part-time wear group had 45 percent initial correction, and the full-time wearers 49 percent initial correction with the TLSO. It could be concluded from this relationship that gaining more correction may lead directly to better compliance with patients. Or one may conclude that the least correctable curves give pain in-orthosis, resulting in noncompliance with orthosis use.

In 1977, Watts et al. 14 showed that an average of 50 percent to 60 percent initial correction could be achieved without the use of a superstructure in the 98 patients in their study. In 1980, Lindh 15 studied six patients fitted with the TLSO without the force pads added and found a mean correction in-orthosis of 40 percent in lumbar curves and 36 percent in midthoracic ones. This emphasized the importance of a posterior pelvic tilt or reduced lordosis in-orthosis for optimal curve correction. In the same year, Bunnell et al. 16 maintained 62 percent average correction in-orthosis. Uden et al. 17 reported similar results in Sweden, with a mean 41 percent in-orthosis correction for 91 patients. One year later, Uden and Willner 18 reported that the TLSO reduced the lordosis angle by an average of 16°, while giving a 50 percent correction in the primary curves and 64 percent in the secondary curves. Aaro and Berg 19 reported a mean in-orthosis correction of 45 percent. Kehl and Morrissy 20 emphasized at least 30 percent but preferably 50 percent initial correction should be sought. Jonasson-Rajala et al. 21 reported a 54 percent initial correction at apex T8 to T9 and 50 percent to 60 percent for all curves with apices between T8 and T11, whereas those with thoracolumbar and lumbar curves showed an initial correction of 40 percent to 50 percent. Howard et al., 22 in a study of 45 patients, found a mean initial correction of 40.1 percent with the TLSO. In 1977, Katz et al. 23 reported a mean initial in-orthosis curve correction of 41 percent for the primary and 24 percent for the secondary. The study specifies curve types and percent correction needed for an expected successful treatment of each. For single thoracolumbar, lumbar, and double major-primary thoracic curve patterns, at least 30 percent correction was determined; for single thoracic curves, it was reported 40 percent correction is needed for a successful outcome. However, in recent research with curves greater than 35°, Katz and Durrani 24 reported 25 percent in-orthosis correction of the primary curve to be prognostic for successful outcomes. Emans et al. 25 reported a mean correction in-orthosis for 20° to 29° was 56 percent; for 30° to 39°, 50 percent; 40° to 49°, 39 percent; and 50° to 59°, 24 percent. They also reported initial in-orthosis correction at each apical level (Table 1). In 1975, Hall et al. 26 studied initial curve correction with the TLSO and cervicothoracic-lumbosacral orthosis in relation to curve type (Table 2). Laurnen et al. 27 have the most comprehensive study, breaking down each apex to curve ranges and their respective mean initial curve corrections in the thoracic region (Table 3). Aaro et al. 28 found the mean primary correction to be 54 percent at T10 or below and 40 percent above T10 with the TLSO in 33 patients.

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Renshaw 29 emphasized the theory that most curves tend to show the best correction at the initial application of the orthosis or a few months thereafter, and correction tends to have a gradual loss of effect after this initial period. Carr et al. 10 also reported that the best in-orthosis correction was observed in the first year. Emans et al. 25 pointed out that in their study of 295 patients, the mean correction in-orthosis fell from 50 percent initially to 23 percent at the stage for weaning to begin and then to only 15 percent at time of cessation of the orthosis use. Lonstein and Winter 11 recognized a peaking of curve correction at 6 months of 50 percent and then a gradual lessening of the improvement. Chase et al. 30 used interface pressure measurements to show that after 6 months, the force values remained unchanged but the mean correction of the curves had dropped from 37 percent to only 14 percent. Bassett et al. 12 also recognized this gradual loss of correction. This loss of initial correction emphasizes the need to pay particular attention to the biomechanical effectiveness of the orthosis in relation to factors such as growth and elasticity of the specific components related to the orthosis. All too often fitting parameters are inspected at follow-up sessions without paying particular attention to the magnitude and direction of forces on the growing body of the patient. It is vital to check the pad/push placement at follow-up examinations to ensure an optimal in-orthosis correction. For instance, a patient may grow enough that a pad/push may be undercutting the curve, leading to a less-than-optimal curve correction. This example alone emphasizes the importance of follow-up and maintaining correction in-orthosis.

So far these studies have applied to adolescent idiopathic scoliosis. Winter and Moe 31 recognized that, for the small percentage of curves in the infant that are not self-resolving, the orthosis must be able to keep the spine corrected to below 50° in-orthosis. Mehta 32 emphasizes the importance of using the child’s growth to correct the deformities of scoliosis in infantile and juvenile scoliosis, rather than simply preventing its progression. The necessity for frequent changes in casts or orthoses to make the spine as straight as possible is emphasized. Blount 33 emphasized the goal of achieving less than 10° of juvenile scoliosis in-orthosis. James 34 reported on eight cases of infantile scoliosis ranging from 38° to 73° treated first with plaster casts and then in an orthosis. One patient’s curve was more in the orthosis than out, but of the remaining seven, there was a mean correction of 54 percent, with a range of 25 percent to 93 percent. The literature about the infantile population is limited, but the consensus seems to be to achieve as much correction as possible because of the flexible nature of infantile idiopathic scoliosis and to monitor growth in relation to the position of forces.

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Since 1989, the implementation of nocturnal orthoses has led to more studies concerning the amount of in-orthosis correction that should be achieved to expect successful outcomes. Keeping in mind that the radiographs for the nocturnal designs are taken supine, there will be an observed higher in-orthosis correction observed than the diurnal designs. In 1990, Price et al. 35 published the first research on this design in which a mean initial in-orthosis correction of 73 percent was found in the 139 patients studied. However, in that article, the authors specify as a recommendation that the orthosis must achieve at least 50 percent reduction in-orthosis to be acceptable. In a long-term follow-up 7 years later, Price et al. 36 reported average in-orthosis curve correction of 87 percent for major curves and 33 percent for compensatory curves. In the same year, Katz et al., 23 in a comparison of the diurnal and nocturnal TLSOs, found a mean initial correction of 83 percent for the primary curve and 31 percent for the secondary. Howard et al. 22 had a mean initial correction of 83.9 percent in 95 patients. In the latest research, Trivedi and Thompson 37 obtained an average of 104 percent in-orthosis correction, ranging from 71 percent to 180 percent in single lumbar curves.

In 2001, a nocturnal TLSO used with 102 patients produced a 96 percent in-orthosis correction for the major curves and 98 percent in the compensatory, curves with a breakdown of 94 percent for thoracic, 111 percent for thoracolumbar, 103 percent for lumbar, and 90 percent and 91percent, respectively, for double curves. 8 Curve correction in-orthosis is biomechanically more efficient because patients wear the nocturnal orthosis and are radiographed in a position in which gravity is eliminated, as opposed to the diurnal orthosis, in which gravity makes it more difficult to gain curve correction in-orthosis.

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Scheuermann’s kyphosis and postural roundback (without vertebral deformity) have parameters for success. Just as in scoliosis, in which initial in-orthosis correction of the coronal Cobb angle and maintenance thereafter are important, in Scheuermann’s disease, in-orthosis progressive sagittal plane correction to allow for healing of the bony anterior wedging is important. 2,31,38–44 Montgomery and Erwin 45 cite that sagittal correction and alignment are rapidly gained in-orthosis, but that the true correction sought is the healing of this vertebral wedging to 5° or better. Bradford et al. 46 reported in-orthosis average correction to 30°, from an average of 58.9°, or 50.9 percent correction, in 75 patients with an average 41.7 percent improvement to vertebral wedging, translating to an average decrease to 5°. Concerning sagittal correction, Renshaw 29 asserts that the rule of thumb is that a sagittal curve greater than 80° must show an improvement to less than 50° on a supine hyperextension roentgenogram for successful management. Sachs et al. 47 divided their patient group into subgroups based on Cobb angle and average in-orthosis correction (Table 4). By averaging these numbers, we see a 50 percent in-orthosis correction for the first two groups between 45° and 64°; 54 percent for the 65° to 74° group, and 47 percent for the >74° group. Uden and Willner 18 showed that a reduction of lordosis in the TLSO averaged a 13° reduction in thoracic kyphosis. Watts 2 stresses the importance of getting as much correction as the rigidity of the thoracic spine will allow, while attempting to achieve a 40° sagittal Cobb angle. Keeping in mind this progressive sagittal correction, it is important to remember the goal, which is permanent vertebral wedge healing. As is true for idiopathic scoliosis, follow-up is extremely essential to the success of treating Scheuermann’s kyphosis. Consistent follow-up examinations in the treatment of Scheuermann’s kyphosis allow for permanent progressive correction of the sagittal curve and underlying vertebral wedging.

Table 4

Table 4

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Troubleshooting scoliosis management can be difficult but is necessary in successful treatment programs. Green 48 found an overall 20 percent noncompliance with treatment at Vanderbilt, emphasizing the need for troubleshooting. In another study, DiRaimondo and Green 49 found that patients wore their orthoses 65 percent of the time prescribed, and only 15 percent of patients were highly compliant with their orthoses regimen.

Gunnoe 50 suggests that back pain in-orthosis represents a fitting problem or psychosocial issue. Ramirez et al. 51 used this as a premise to study in-orthosis pain. They cite only an 11 percent incidence of back pain during orthotic treatment, compared with 33 percent in the general pediatric population and 32 percent in an adolescent idiopathic scoliosis study group. Renshaw 29 recognizes skin intolerance, lateral femoral cutaneous nerve compression causing anterior thigh paresthesias or numbness, and esophageal reflux as potential problems. Watts 2 emphasizes that pressure on the ribs should not restrict respiration, patients should be made aware of the discoloration that may appear in high pressure areas such as the iliac crests, and attention should be paid to skin care, especially in warmer times and climates. Watts also says that padding can be appropriately placed in the anterior pelvic section to draw the pressure away from any compression found on the lateral femoral cutaneous nerve. He emphasizes the need to pay attention to bulging tissues inferior to the orthosis caused by tight fit of the pelvic sections. Too much pressure from the orthosis has been shown by Aaro and Berg 19 to increase urinary sodium excretion, and if the pressure persists, it can cause sodium retention. Therefore, any renal issues should be referred to the treating physician and pressure relieved. Korovessis et al. 52 show that lung function is not harmed by the current accepted orthoses, so respiratory issues related to tightness of the orthosis should be relieved, especially because the patient is growing. Winter 53 emphasizes the importance of not constricting the chest to the point of decreased pulmonary function. Kennedy et al. 54 show a mean reduction in total lung capacity of 16 percent, thereby stressing the importance of monitoring this tightness.

Skin intolerance ranges from blistering to contact dermatitis. Winter and Carlson 5 reported on lined and unlined TLSOs, concluding that the latter cause more pressure areas that need to be relieved. They suggested that a natural fiber stockinet or T-shirt should always be worn under the orthosis. They also suggested preventing any wrinkles in the undergarment in higher-pressure areas, such as the waistline. Keiser and Shufflebarger 55 found occasional pressure sores around the pelvic section in their study of 123 patients. Watts et al. 14 found that 22 percent of their patients had some hyperemia and 5 percent experienced blistering. Hall et al. 26 recognized the importance of relief areas into which the curve may shift for static and dynamic correction in-orthosis, and concluded that particular attention should be paid in these areas as the patient grows. They found that a range of 22 percent to 38 percent of their patients, depending on the curve type, had mild skin irritation or hyperemia without blistering and that only 4 percent had any blistering. The blistering was noticed only in double major and single thoracic curve patterns. Bunnell et al. 16 pointed out the need to pay attention to the patient’s inability to dissipate body heat because of the coverage by the TLSO and recommended the use of an undergarment under the TLSO.

Of particular interest was a study presented by Chase et al., 30 which used interface pressure measurements and found that the magnitude of pressures and forces was not reduced in the recumbent position. Keeping in mind that this is when gravity is removed, this relationship deserves mentioning when dealing with the troubleshooting of the TLSOs. Aubin et al. 56 found that there was a decrease in strap tension when the patient was lying down. Blount 33 also emphasized that strap tension loosens as one gets better in-orthosis correction. These findings emphasize the need for troubleshooting in the nocturnal orthoses as well. This loosening effect could be from material expansion and wear, a patient’s growth, or a combination of both. Strap tension could be a direct link to the loss of the initial in-orthosis correction cited earlier and thus should be monitored at follow-up examinations.

Lindeman and Behm 57 suggest that the more sleeping problems the patient experiences, the less likely the patient is to use nocturnal orthoses. Price et al. 35 reported that two minor complications may occur with the bending system: transient neuropathy from axillary pressure that can be relieved by trimming lower in this region and local skin erythema. There was no reported skin breakdown caused by extra padding in high-pressure areas. Ramirez et al. 51 reported a higher incidence of pain in nocturnal orthoses than diurnal ones. d’Amato et al. 8 reported bursa forming over the ribs of some patients, which were resolved with orthosis modification, and one patient experienced a rash caused by an antifungal powder used with the orthosis to treat redness.

It is important to remember that the patient must be comfortable enough to wear the spinal orthosis. As with any orthosis, it must be both functional and practical. An orthosis that is purely functional but practically impossible or difficult to wear will fail. When troubleshooting, the patient’s function should be considered, as well as any practical issues the patient may express.

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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:

  1. 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.
  2. 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.
  3. 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.

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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.

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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.

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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).

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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.

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  • 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.
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Nocturnal orthosis biomechanics allow the orthotist the ability to take advantage of the recumbent position for increased reduction of the Cobb angle. There is a perceived value of the resultant stretch of the connective tissue on the concave side of the curve in the process.

The corrective forces for all curve types being addressed within the orthosis are applied at the level that is geometrically perpendicular to the apex of the curve. This approach enables the orthotist to increase the distance between the corrective forces applied to the spine. It is also theorized that this separation of forces may decrease the amount of force necessary to achieve an acceptable in-orthosis correction. With the elimination of the need to position the patient in an upright position with the head over the pelvis, a nocturnal orthosis can create a fulcrum from one or more vectors around which the spine may be rotated. This rotation around a fulcrum occurs primarily in the coronal plane, but rotatory correction also may be applied in the transverse plane. The combined effect of three factors [1) gravity eliminated application of forces that are 2) separated from each other because of their being placed perpendicular to the spine, and 3) where a fulcrum for shifting or bending is created] enables the orthosis designed for recumbent wear to achieve improved in-orthosis correction of the Cobb angle for a scoliotic curve compared with to orthoses designed to be worn in an upright position.

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  • There is a need to better understand the relationship of wear schedule with treatment outcome.
  • In those requiring at least 16 hours/day orthosis wear, the possibility of improving outcomes by the combined use of a nocturnal orthosis and an orthosis designed for upright wear during the day needs to be investigated.
© 2003 American Academy of Orthotists & Prosthetists