Brace technology: derotation brace

Authors: Theodoros B Grivas, Achilles Bountis, Irene Vrasami1 and Nikolaos V Bardakos
  1. Department of Trauma and Orthopaedics, "Tzanio" General Hospital - NHS, Tzani & Afendouli str, 18536, Piraeus, Greece
  2. Scoliosis & Spine Unit of "KAT" Orthopaedic Hospital, Athens, Greece
  3. The South West London Elective Orthopaedic Centre, Denbies Wing, Epsom General Hospital, Dorking Road, Epsom, KT18 7EG, United Kingdom

The dynamic derotation brace (DDB) was designed in Greece in 1982, as a modification of the Boston brace. It is a custom-made, underarm spinal orthosis featuring aluminium blades set to produce derotating and anti-rotating effects on the thorax and trunk of patients with scoliosis. It is indicated for the non-operative correction of most curves, barring the very high thoracic ones, (when the apex vertebra is T5 or above). The purpose of this article is to familiarize physicians with the DDB, analyze the rationale behind its design, and present the published results of its application.

Description & Principles
The key feature of the DDB is the addition of the aluminium-made derotating blades posteriorly. These function as a force couple, which is added to the side forces exerted by the brace itself. Corrective forces are also directed through pads. One or more of previously proposed pathomechanical models of scoliosis may underline the corrective function of the DDB: it may act directly on the apical intervertebral disc, effecting correction through the Heuter-Volkman principle; the blades may produce an anti-rotatory element against the deforming "spiral composite muscle trunk rotator"; or it may alter the neuro-motor response by constantly providing new somatosensory input to the patient.

Based on measurements of the Cobb and Perdriolle angles, up to 82% of patients remained stable or improved with the use of the DDB. Results have varied, though, depending on the type/location of the deformity. The overall results showed that 35% of the curves improved, 46% remained stable and 18% became worse, as assessed by measuring the Cobb angle. The DDB has also been shown to improve cosmesis (except for right thoracic curves) and leave several aspects of patient quality of life unaffected during use.

Conservative treatment of idiopathic scoliosis using the DDB has shown favorable results. Thoracic curves appear more resistant to both angular and rotatory correction. The published outcome data on the DDB support our belief that the incorporation of aluminium blades to other orthoses would likely improve their efficacy.

Scoliosis Background
Viewed in three dimensions, scoliosis is characterized by a constellation of deformities. Ideally, conservative management of scoliosis should aim at correcting simultaneously the lateral deviation of the spine in the frontal plane, the rotational and the rib cage deformity in the transverse plane and restore the sagittal plane.

Brace treatment should be instituted by means of appropriately manufactured orthoses, capable of achieving a satisfactory initial correction. In addition, the corrective forces must be sustained throughout the entire treatment period.

Dynamic Derotation Braces (DDBs) are custom-made, underarm spinal orthoses equipped with specially designed derotating blades that are set to produce a derotating or an anti-rotating effect on the thorax and the trunk of scoliotic patients. Derotation is defined as the correction of the rotational deformity (e.g. reduction of Perdriolle angle value). Anti-rotation is defined as the prevention of rotational deformity progression. When there is anti-rotation in a progressive curve, the Perdriolle angle remains unchanged during treatment. In other words, progression of vertebral rotation or rib cage rotational deformity in the transverse plane is prevented.

The purpose of this report is to present an overview of the DDB, including the historical background, the biomechanical principles of its function, technical aspects pertinent to its prescription, construction, and the so far published results on its use. The general theoretical principles of conservative treatment with braces will also be presented.

Scoliosis History
The DDB was designed and used by surgeons of the Scoliosis & Spine Unit of "KAT" Orthopaedic Hospital in Athens and the Certified Orthotist and Prosthetist (CPO), Mr. Nikolaos Vastatzidis of Athens. Based on their extensive experience with different types of braces, this group designed a modification of the classic modular Boston Brace, in order to address the rotational element of scoliosis. The first type of brace they developed was called Boston LP (Limited Pressure). Following its short-lived use, this was replaced by the Dynamic Derotation Brace. The new design, introduced in 1982, was based again on the basic BOSTON BRACE, with the addition of a system of light and slightly flexible blades made of aluminium. The construction of the new brace was based on the traditional plaster mould of the trunk of the patient, onto which the heat-treated PVC sheet was applied. The blades were added last and were placed at the highest point of the hump.

Initial results were very encouraging and, with increasing experience of its application, the brace became more elaborate. Radiological and clinical results showed the new brace to be an effective solution to the conservative treatment of scoliosis and provided evidence of true deformity correction, as opposed to mere curve maintenance. Although the use of this particular type of modification of the Boston Brace started to spread because of its encouraging results, formal presentations on its efficacy were delayed.

For historical and ethical purposes, the then "KAT" Hospital team consisted of Dr. P. Smyrnis (former Head of the Unit), Dr. D. Antoniou (Head of the Unit), Dr. J. Valavanis and Dr. C. Zachariou (both spine surgeons and members of staff).

The first official announcement on the use of the Dynamic Derotating Brace (DDB) was made in 1986. This brace is now considered the gold standard for the conservative management of idiopathic scoliosis in Greece. The DDB modules - principles of construction used by CPOs.

The DDB module is a type of Thoracic Lumbar Sacral Orthosis (TLSO). Its main characteristic is that it is supplied with metallic blade/s on its posterior surface which act as de-rotation or anti-rotatory device/s, as defined above.

Today, production of the DDB is based on a traditional cast mould, or on a pre-trimmed positive plastic trunk template produced after laser scanning of the patient, (CAD/CAM technology). A blueprint is thus designed, which is a systematic way of analyzing the curve and applying the appropriate force vectors.

the DDB production can be based on a cast mould.

the DDB production today is based on a pre-trimmed positive plastic template produced after laser scanning of the patient, or raster stereography (CAD-CAM technology).

The DDB is a custom-made, underarm hard orthosis, extending from underneath the axilla to the pelvis figures 3a, 3b. The core of the module is made of one 3 mm-thick piece of polyvinylchloride (PVC), which may have an inside lining of plastazote. It opens at the back and is fastened with three or, more commonly, four straps. The design is tailored to the body habitus of the patient. The waist section should be designed to provide maximal patient comfort.

The DDB extends from underneath the axillae to the pelvis, b: lateral view of a DDB.

The axillary extension lies just below the shoulder. It should be applied to the lateral surface of the upper part of the sides of the thorax, so as to maintain a direct inward force on this. In essence, it acts by shifting the upper part of the thoracic curve. It comprises the highest lateral component of the DDB module.

The abdominal apron is the front part of the module and extends in a way that includes the abdominal area and covers the edges of the sides and the xyphoid process, taking particular care not to impact on the sides. This part is flat on its front surface, allowing rectification of the body in the module.

Several parts of the brace are reinforced with pre-contoured, aluminium metallic bars (of approximately 1.6 cm in breadth and 0.35 cm in thickness) or bars of similar dimensions made of plastic similar to the plastic sheet of the brace proper. For a brace for a right thoracic curve, the right subaxillary metallic bar ascends up to the lateral third right subclavicular region, while the central metallic bar starts from the xiphoid process anteriorly and is turned laterally to the left, merging with the left subaxillary metallic bar placed opposite to the hump.

The two rear side halves ascend towards the upper border of the scapula, and are spaced approximately 5 cm apart when the brace is on. Both of these posterior halves are reinforced with posterior metallic bars (approximately 3 cm in breadth and 2.2 mm thick) along their free edges, starting from the scapula down to the pelvis, figure 3a. The pads inside the brace are also lined with plastazote.

The fundamental characteristic of this brace are the metallic derotating blades, figure 3a. These are rectangular, 2.0 - 2.5 mm thick blades, made of aluminium, (semi-rigid aluminium alloy). One side of the blade is fixed along the posterior metallic bar, while the free end is pre-curved to an obtuse angle, opening outside the structure. The amount of this opening is directly proportional to the magnitude of hump. Upon application, the free end of the blade is inserted under the opposite posterior half of the brace. The position of the blades is determined by the level of the hump: they are attached to the rear side of the brace, at the area corresponding to the most prominent area of the thorax or trunk of the patient (thoracic or loin hump; that is, the blade is positioned by the orthotist on the apex of the hump as it is detected clinically).

The blade covers most of the hump prominence. In longer curves, more than one blade may be required. The usual width of a blade is 8-10 cm and their length depends on the patient's somatotype. Hitherto there is no study to document the angle of the blade in relation to the scoliometer measurement. However, the angulation of the blade is done empirically by the very experienced CPOs.

The application of the brace is completed with fastening of four posterior straps.

Once the brace is finally fitted on the patient, the positioning of the blades can be checked on standing radiographs, especially in relation to their correspondence with the apex of the curve. If necessary, the blades can be easily repositioned.

The derotating function of the blades is accomplished through the continuous application of corrective forces at the pressure areas. At the same time, the two posterior halves of the brace move in opposite directions. The force couple thus created is added to the side forces exerted by the brace itself. The direction of action of the blades may be modified, if needed, by altering the (open outside) obtuse angle of the blades.

The trimline is usually at the level of the clavicle superiorly. It must cover the anterior superior iliac spine inferiorly, to maximize the lever arm controlling correction in the sagittal plane.

The trochanteric extension, for lumbar modules in particular, is designed so as to extend over the greater trochanter on the side of the convexity of the curve. This increases leverage and facilitates overall balance of the trunk, restoring the alignment of the patient back to neutral.

The thoracic extension is designed so as to exert an upward and medially directed force at the apex and below; its superior edge should be in line with the contour of the apical rib. Its height is determined by the individual patient's characteristics.

The antero-lateral thoracic window is meant to relieve the patient's torso. It is located directly opposite to the thoracic hump, extending well above the crest roll, which is placed inferiorly.

The pads are used to direct corrective forces within the DDB system. Their main role is to exert high forces on scoliotic curves. Opposite each force lies an area of relief. They are placed onto the inner surface of the module and apply high pressures at their points of contact with the body.

Curve classification used for prescription purposes

DDB designs are based on the commonly used classification, which distinguishes scoliotic curves into thoracic, thoracolumbar, lumbar, and double major.

Read more on the ScoliosisJournal website or download the PDF

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