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The Orthotic Management of Infants With Plagiocephaly: Modification Procedures of the Positive Model

Ammanath Peethambaran, MS, CO


Changing the shape of the head need not be painful. The skull is a solid case with uniform walls, and the capacity remains the same regardless of the shape molded during infancy.

For infants diagnosed with deformational plagiocephaly, determination of head shape is an important part of orthotic management. It is also particularly important for assessment and positive cast modifications. The need for proper documentation with reliable, measurable, and related functional data is essential for insurance payments in this changing world of managed health care. Researchers have identified various methods of measuring deformational head shapes, 1 including computed tomography scans, radiographs, and photographs. The use of a measuring tool for orthotic practitioners must be practical, reliable, and easy to use.

This article presents a positive cast modification technique for a cranial molding orthosis using a cranial mapping instrument developed at the University of Michigan Orthotics and Prosthetics Center.

MATERIALS AND METHODS

A simple craniometry mapping instrument, adapted from a Bremer pediatric halo crown (DePuy Spine, Inc., Raynham, MA), was developed to measure deformational head shapes. The instrument measures the position and amount of depression or flatness, the amount of displacement, and the orientation of head shape within the instrument. It also allows the orthotist to create a blueprint and establish the predicted shape of the skull after orthotic treatment.

CREATING THE BLUEPRINT

After a plaster impression of the infant's head is made, it is essential to critique the positive model for quality and biomechanical accuracy. The model must be assessed to ensure that it represents the exact model of the cranium and to ensure that all anatomic positions and marks are captured. The anthropometric data collected during the evaluation must be compared with the cast.

PROCEDURE

Clean and remove excess plaster from the model. Remove all ridges and unnatural bumps using smooth finishing. The positive model must be free of plaster irregularities. The indelible pencil marks are transferred and reinforced on the mold ( Figure 1 ). Mark the following bony prominences and landmarks:

  1. Glabella (the center at which the eyebrows meet);

  2. Tuberosity of the frontal bone (left and right);

  3. Frontozygomatic bone (at the level of the tragus);

  4. Pinna beginning from the anterior inferior lobule to the posterior inferior lobule (called auricle or trumpet);

  5. External occipital protuberance;

  6. The inferior edge of occipital bone; and

  7. Sagittal and coronal lines dividing the mold into quadrants.

ESTABLISH THE TRIMLINES


Anterior Trimline
Mark the glabella and make a horizontal line around the cast at the level of the supra orbital margin (eyebrow) extending to the superior edge of the pinna. This serves as a primary reference line for anterior trim lines ( Figure 2 ).

Lateral Trimline for Temporal Extension
In the sagittal plane, draw a vertical line 1 cm lateral to the supraorbital margin and another 1 cm distal to the frontozygomatic bone. These lines connect to create the anterior trim line. The width of the temporal extension is maintained with 0.5-cm clearance anterior to tragus. A width approximately 3 to 3.5 cm seems to be appropriate to distribute any pressure exerted at the temporal area. Draw another line starting from the frontozygomatic line following the mark of pinna to the posterior inferior lobule. The line terminates 12 mm distal to the inferior border of occipital bone ( Figure 3 ).

Posterior Trimline
The posterior trimline is established by joining two points drawn with the anatomic curvature to facilitate neck extension without impingement ( Figure 4 ).

Length and Width Dimensions
Once the trimlines are established, measure the length and width dimensions of the cast. Compare these measurements with the anatomic measurements recorded in the craniometry form.

ESTABLISHING SYMMETRY

Symmetry is an attribute of a shape, an exact correspondence of form on opposite sides of a dividing line or plane. The mapping instrument measures the position and amount of flatness, the amount of displacement, and the orientation of the head within the instrument. The crown houses eight measuring pins that measure the distance from the crown to the skull. The lateral pins also serve to measure the displacement of ears from predetermined centers.

Mild asymmetry is usually found in human craniofacial bones and is present in both affected and unaffected groups. 2 The left and right side differences occur in variable degrees and could affect appearance. Absolute symmetry could be considered when each half of the skull is exactly the same, like in a mirror image.

ESTABLISHING PROPORTION (DISPLACEMENT AND ORIENTATION)

Proportion is the relationship of various parts of the skull to the overall whole.

Maintaining proportion of the skull is an essential element of cranial molding therapy. Many beginners could have trouble establishing proportion during the positive cast preparation. Without some sense of proportion, a mold easily becomes visually different. Although the basic concept of proportion is easy to understand, it is difficult to implement. Here is an easy way to develop a sense of proportion by using a simple cranial mapping instrument ( Figure 5 ).

This step dictates the positioning and orienting of the positive model. Start with positioning the mapping instrument at the equator of the skull model. Divide the instrument into quadrants, sagittal and coronal. Remember to think of this as a three-dimensional sphere because your model is three-dimensional. Once the model has been evenly divided, the cross-section dictates and determines the shape, orientation of the mold, displacement, and proportions of the positive mold. The cross-section determines the anatomic center and divides the plane in half with a centerline. These divisions also help determine where the ears are positioned (Figure 5).

CRANIAL MAPPING INSTRUMENT

Use the cranial mapping instrument and orient the positive model as shown in Figure 5 . The anterior and posterior center pins are placed at marks of glabella and occipital protuberance, respectively. Join these two points with a straight line. Similarly, the lateral lines are joined at the midline from the center of the superior border of the left pinna to the superior border of the right pinna (ie, ear to ear). The geometric center of the instrument is marked by length and width lines. Quadrant II is displaced laterally compared with the geometric center (Figure 5). The ear displacement is measured from the centerline and documented (Figure 5).

CRANIOMETRY FORM

A craniometry form ( Figure 6 ) was developed to document the linear measurements of the cranium. The distance is measured from the inner border of the craniometry mapping instrument to the outer surface of the positive mold. This measurement determines the amount of asymmetry present in the mold. Repeat the measurements at the glabella, lateral one third of the eyebrow, ears, lateral one third of occipital bone, and occipital protuberance. Repeat measurements two or more times to ensure consistency. Make further notations regarding the skin condition, muscle tightness, range of motion, facial asymmetry, and any other relevant information.

FACTORS AFFECTING MODIFICATION SPECIFICATION

AGE OF THE INFANT

The skull expands as the brain grows so that normal head growth is a sign of healthy brain growth. The philosophy behind the cranial molding orthosis is that the brain and the skull grow very quickly during the first year of life. This growth curve is quite steep in the early months and then starts to level off after 6 months of age. The cranial molding orthosis is designed to take advantage of that rapid growth. Therefore, the sooner the treatment is initiated, the better the result.

DEGREE OF SEVERITY

Degree of severity affects potential outcomes and protocols of the orthotic treatment program. In general, moderate to severe deformities can be treated satisfactorily with a cranial molding orthosis. The positive asymmetric model should be modified to achieve the best symmetry for cranial orthosis fabrication. The model is made symmetric by building the areas of flatness at occipital and frontal parts of the skull. The preparation of the positive model is completed with the matching measurements of the craniometry form.

HEAD SHAPE

The cranial base forms the platform on which the rest of the skull grows and attaches, and it provides and protects the crucial foramina through which the brain connects to the face and the rest of the body. It is predicted that variations in the shape of the human neurocranium (those bones of the skull enclosing the brain, as distinguished from the bones of the face) are influenced by variations in the shape of the neurocranium growth and endocranial expansion driven by brain growth. During normal growth in humans, the upper half of the neurocranium enlarges and the cranial growth assumes that overall shape. This integrated growth occurs through many processes, the most important of which are sutural expansion, deposition, and drift. Length and width changes of the skull occur through coronally oriented and sagittally oriented sutures. 3

TREATMENT PROTOCOLS AND GOALS

Goals of the orthotic treatment program are to: 1) achieve maximum correction of the deformity, 2) establish symmetry and/or proportion of the skull, 3) provide stimulus to calvarial growth, and 4) encourage passive expansion of the calvarium.

CONCLUSION

The central purpose of the project is to develop protocols and analysis procedures in cast modifications for cranial remolding programs. A simple, reliable instrument has been developed for orthotists to establish a consistent approach for evaluation of head shape in infants diagnosed with deformational plagiocephaly.

Correspondence to: Ammanath Peethambaran, MS, CO, University of Michigan Orthotics and Prosthetics Center, Department of Physical Medicine and Rehabilitation, 2850 S. Industrial Hwy., #400, Ann Arbor, MI 48104; e-mail: peeth@umich.edu .


AMMANATH PEETHAMBARAN, MS, CO, is affiliated with the University of Michigan Orthotics and Prosthetics Center, Ann Arbor, MI.

References:

  1. Chang NC, Chang PY, Perng DB. Computer aided measurement and grading of cranial asymmetry in children with and without torticollis. Clin Orthodont Res 2001;4:200-205.
  2. Rossi M, Ribeiro E, Smith R. Craniofacial asymmetry in development: an anatomical study. Angle Orthodont 2003;73:381-385.
  3. Lieberman DE. Basicranial influence on overall cranial shape. J Hum Evol 2000;38:291-315.