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S E C T I O N I I : O R T H O S I S B I O M E C H A N I C S

Clinical Biomechanics of Orthotic Treatment of ThoracicHyperkyphosisJ. Martin Carlson, CPO

NORMAL SPINE MECHANICS ANDGEOMETRY IN THE SAGITTAL PLANE

Sagittal curvature of the lumbar spine is discussed interms of how it relates or responds to the thoracicspine. Unless otherwise specified, geometric and me-

chanical analyses refer to upright stance posture in the sag-ittal plane.

To analyze the abnormal, we must first be familiar withwhat is normal. In the normal spine, there exists a long-termequilibrium between the bending moments imposed by bodyweight and the spine’s ability (together with its attachedmusculature) to resist those loads. The spine maintains itsconfiguration within the limits of normal sagittal curvatures.

Gravitation forces acting upon the head, arms, shoulders,and thorax result in a flexion moment on the thoracic spinalcolumn for virtually all common standing and sitting pos-tures. The spine extensors act in tension, pulling the poste-rior elements of the neighboring vertebrae toward one an-other, generating a thoracic extension moment to maintainequilibrium (Figure 1). The intervertebral disks act as com-pression elements, maintaining space between neighboringendplates. The disks and endplates are loaded quite evenlyunder normal conditions of adequate bone and muscle. Thatis because of the partially hydraulic nature of the nucleuspulposus component of the disk.

Spine geometry in the sagittal plane can be described as acombination of four elements:

1) Sacral anterior tilt2) Lumbar lordosis3) Thoracic kyphosis4) Cervical lordosisThe author is not aware of any accepted criteria for normal

but estimates a normal posture to consist of a sacral anteriortilt of about 40°, lumbar lordosis of 40° to 60°, and thoracickyphosis of 20° to 45°.

Because the patient tends to stand in a balanced, comfort-able posture, these four postural elements are not indepen-dent. They are strongly interrelated.

ABNORMAL SPINE MECHANICS ANDGEOMETRY IN THE SAGITTAL PLANEExcessive thoracic kyphosis results from a failure of thethoracic spine complex to respond effectively to the flexionmoments imposed by body weight (Figure 2). Flexion mo-ments related to body work may be a part-time factor. The-oretically, failure may be in the anterior compression ele-ments (ie, the anterior vertebral bodies or disks), in theposterior tension elements (ie, spine extensor muscles), orboth.

Of the two types of thoracic hyperkyphosis presenting in theadolescent, posterior roundback is less severe. The lateral x-raydoes not show pathological changes in the vertebral bodies. Thekyphotic curve is long and smooth, and the patient usually canactively extend her/his spine to bring the kyphosis to withinnormal limits.

However, Scheuermann’s disease is characterized on thelateral x-ray by wedging and other pathological changes, suchas Schmorl’s nodes, to the vertebral bodies (Figure 3). Thesechanges are localized in two to four neighboring vertebrae.Vertebrae above and below the affected zone appear normal.This creates a localized, sharply angulated hyperkyphosis,that is very noticeable on forward bending (Figure 4). Thepatient is unable to actively correct this condition to withinnormal limits.

The human spinal support system, because of its verticalorientation, is in a sense an unstable system. As a deformitydevelops, the mechanical advantage of the original deformingforce grows larger.

To come up with some numbers to illustrate how thisworks, the author has calculated the approximate spine for-ward-bending moments caused by gravity forces on segmentsof the upper body. Those approximate calculations indicatethat an increase in thoracic kyphosis from a value of 40° to avalue of 65° will increase the deforming bending moment byabout 50 percent at the T10 level. In other words, a spinalsupport system inadequate to prevent the initiation of ahyperkyphosis becomes less and less adequate as the defor-mity grows. Intervention must force a strengthening of theextensors, passively improve alignment, or both.

As the vertebrae angle forward on one another, therange of motion of the disk is exhausted, the nucleus pulpo-sus can no longer equalize pressure, and compression loadingis more and more shifted toward the anterior edge (Figure 2).The excessive/unrelenting compression slows (Hueter-Volk-mann variation of Wolf’s law) growth in the anterior portionof the ring apophysis. Gradual wedging occurs (Figure 3). Thespine system is naturally most unstable during the growth

J. MARTIN CARLSON, CPO, is affiliated with Tamarack HabilitationTechnologies, Inc., Blaine, Minnesota.

Copyright © 2003 American Academy of Orthotists and Prosthetists.

Correspondence to: J. Martin Carlson, CPO, Tamarack HabilitationTechnologies, Inc., 1670 94th Lane NE, Blaine, MN 55449-4323;e-mail: martycarl@qwest.net.

S31Volume 15 • Number 4 • Supplement • 2003

years and the geriatric years when bone is most likely torespond unfavorably to this excessive loading.

As mentioned, thoracic kyphosis is only one member of aninterrelated family of curves that together comprise spinalposture. Deformity in one area of the upright spine requirescompensation in one or more other areas of the spine. If

Figure 1. Active extensors adequately balancing gravitational bend-ing moments.

Figure 2. The consequence of inadequate extensor activity/strength.

Figure 3. Lateral radiograph showing wedging and Schmorl’s nodestypical of Scheuermann’s disease.

Figure 4. Typical lateral, forward-bending profile of a youngster withScheuermann’s disease.

Figure 5. A: Sagittal spine posture if thoracic hyperkyphosis devel-oped without compensation. B: This diagram illustrates how a levelgaze and sagittally balanced alignment are maintained when com-pensating lumbar lordosis develops close behind thoracic hyperky-phosis.

Carlson JPO Journal of Prosthetics and Orthotics

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thoracic hyperkyphosis developed as an isolated entity with-out compensation somewhere else in the body, it would causethe head and shoulders to be brought forward and downwardto an awkward, poorly balanced position (Figure 5A). Toprevent this, the body usually compensates by developingincreased cervical and lumbar lordosis to bring the upperthorax and head back into balanced alignment (Figure 5B).

An additional compensating mechanism used to move theupper thorax back into balance is increased extension at thehip joint (this reduces the amount of anterior sacral tilt).

HYPERKYPHOSIS CORRECTIONThe most effective treatment of thoracic hyperkyphosis con-sists of creating a situation whereby the thoracic spine ex-tensors are forced to work and thereby strengthen. They arethus (re)habilitated to a condition of adequacy, able to main-tain active thoracic extension moments equal to the gravita-tional bending moments.

The interrelationship of thoracic kyphosis and lumbarlordosis can be used to advantage in accomplishing this goal.Passive reversal of the lumbar lordosis compensatory mech-anism obviously tends to pitch the patient’s head and shoul-ders forward and downward. The patient who is neurologi-cally normal will be induced to actively extend his thoracicspine to bring his head and shoulders up and back to a morebalanced, more normal position (Figure 6).

This may be all that is necessary orthotically to correct,over time, a flexible, postural roundback type of hyperkypho-sis. Remember that this correction mechanism is not oper-ating when the patient is recumbent, nor is it operating inmany sitting postures. Figure 7 shows a patient with round-back wearing a thoracolumbosacral orthosis that simply re-duces her lumbar lordosis. An induced strengthening of herthoracic extensors corrected her thoracic hyperkyphosis.

Figure 6. The active reversal of thoracic kyphotic collapse whenlumbar spine compensation is passively prevented.

Figure 7. This thoracolumbosacral orthosis corrected the patient’spostural roundback. There is no anterior orthosis element above thexiphoid process.

Figure 8. This photograph perfectly illustrates proper anterior cer-vical stimulus and adequate posterior superior space needed foractive hyperkyphosis correction.

Clinical Biomechanics of Orthotic Treatment of Kyphosis/LordosisJPO Journal of Prosthetics and Orthotics

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Scheuermann’s disease is a more difficult problem be-cause of its severity and rigidity. As noted, in Scheuermann’sdisease the vertebral bodies have become wedged. Correctioninvolves reducing the compression stress on the anteriorportion of the growth plate of the vertebral bodies so thatcorrective growth will occur. The patient has a much moredifficult task in extending the thorax. However, by strongpassive reduction of lumbar lordosis and by using an anteriorcervical or sternal component as a positive, ever-presentstimulus, the thoracic extensors can be forced to exercise anddramatically strengthen. In a relatively short time, thoraxextension range of motion increases, and the hyperkyphoticdeformity lessens. To give the corrective growth processenough time, the preferred alignment must be maintainedwhen the patient is recumbent and sitting, as well as whenshe/he is standing. The orthosis must provide space in theposterior neck and shoulder area so the patient can pull upand away from the anterior neck aspect of the orthosis(Figure 8). This is an example of a proper fit. When theorthosis is properly configured and fit, remarkable results areachieved (Figures 9 and 10).

Occasionally, the kyphosis is aggravated (or perhaps eveninitiated) by tight pectoral muscles. When this is the case,physical therapy exercises and/or some type of shoulder pador harness are indicated to stretch the pectorals. One optionis to use a shoulder sling-type accessory. This consists of aplastic cap molded to the anterior deltoid surface. The capextends inferiorly and then posteriorly through the axilla. Itis shaped to bridge over the pectoralis major tendon withminimum pressure. Dacron straps extend posteriorly fromthe top and bottom to the deltoid cap to separate outriggersattached to the posterior upright (Figure 11).

Figure 9. A: T.M. presented with a thoracic kyphosis measuring 85°(Scheuermann’s disease). B: T.M.’s lateral photo and radiograph atthe end of orthotic treatment (Milwaukee orthosis fitted as in Figure8) 18 months later.

Figure 10. Left: S.R. presented with a 93° Scheuermann’s. Center: Three months later in his orthosis (67°). Right: His in-orthosis correctionlater during treatment.

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Again, the thing to remember about postural roundbackand Scheuermann’s disease is that correction is an activemechanism. We use passive pressure on the sternal and/orsubclavicular area to correct hyperkyphosis in paralytic casesonly. Such forces have little or no legitimate role in thetreatment of postural roundback or Scheuermann’s disease.Passive forces are much less efficient than the correctioneffected by the neurologically normal patient actively pullingup and back, away from uncomfortable contact with an an-terior cervical or sternal component. Such components mustbe made as forceful and comfortable as possible for thepatient with neuromuscular difficulties, but that is not nec-essary or appropriate for the patient with idiopathic hyperky-phosis.

ACKNOWLEDGMENTSVirtually all of the analysis, diagrams, biomechanic models, patientradiographs, and orthotic examples presented in this documentoriginated during the author’s tenure as Director of HabilitationTechnology at Gillette Children’s Hospital. Spinal orthotic serviceswere delivered under the orthopedic leadership of Dr. Robert B.Winter, Chief of Gillette’s spine service. Dr. John Lonstein alsoprovided direction and review to spinal orthotic progress at Gillette.

The importance of Drs. Winter and Lonstein to the author’s worknotwithstanding, the reader should not assume total endorsement ofthis article by either of those men.

The Gillette Medical Education and Research Fund underwrote amultitude of costs associated with photographic documentation andartwork. The author acknowledges the important contributions ofthe very capable spinal orthotists and technicians (Fred Sutterfield,Douglas Grimm, Frank Ransom, James Isenor, Charles Schemitsch,Paul Swanlund, Catherine Voss, and others) he had the privilege tosupervise. Finally and most importantly, the author acknowledgesand thanks the patients and parents who trusted us to do our bestand suffered the consequences of our ever-present limitations.

This document includes some excerpts, photos and drawingswhich were published in 1980 and 1981 by Gillette Children’sHospital within a set of booklets, A Thoraco-Lumbo-Sacral Orthosisfor Idiopathic Scoliosis, part I and part II, which were authored byJ. Martin Carlson. The biomechanical principles illustrated in thephotos and drawings are as accurate today as they were 20 years ago.The Gillete staff have continued to evolve and change material anddesign details to further improve cosmesis and orthotic options. Mr.Carlson and the JPO thank Gillette Children’s Specialty Health Carefor their permission to republish.

There are some excerpts, photos and drawings in this documentwhich were published in Orthopadie-Technik in articles authored byJ. Martin Carlson, October 1991. Mr. Carlson and JPO thank VerlagOrthopadie-Technik for their permission to republish.

Figure 11. When tight pectorals are a part of the hyperkyphosis presentation, it is important to somehow stretch them. Orthotic stretchingpresents a difficult design challenge.

Clinical Biomechanics of Orthotic Treatment of Kyphosis/LordosisJPO Journal of Prosthetics and Orthotics

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