Indications (Soft, Accomodative Custom Orthotics)

Plaster Cast Technique

Four-inch-wide Johnson & Johnson Extra-Fast Setting casting splints can be used, usually two layers thick. The casting tape is wrapped around the foot to completely cover the heel, medial and lateral margins, plantar aspect, and toes (Fig. 195-3). The casting tape is then smoothed to ensure full contact with the foot, and the foot is immediately placed in the desired functional position. The procedure is repeated for the other foot. When the casting tape dries, the feet are easily released from these “slipper casts.”

Figure 195-3 Casting tape applied to foot.

(Courtesy of Benefoot/Langer Biomechanics, Inc., Deer Park, NY.)

ScanCast Technique

Using ScanCast (Benefoot/Langer), the foot is placed in the desired functional position in front of the ScanCast screen (Fig. 195-4). Foot position is confirmed and visualized. The scan function is activated. Scanning takes approximately 1 second and is then repeated for the other foot. A digital image of the plantar surface of each foot is recorded. Orthotics are developed from these scans. (A positive model of each foot is constructed and the orthotic is molded onto this model.)

Figure 195-4 Using the ScanCast 3D to scan the foot.

(Courtesy of Benefoot/Langer Biomechanics, Inc., Deer Park, NY.)

Biofoam Impression Technique

With one of the clinician’s hands, the patient’s ankle should be stabilized and held in a neutral position (preventing pronation) by supporting the talus. The patient’s foot is then placed lightly over the foam in the impression kit, and the patient is instructed to avoid applying pressure. For additional stability, the clinician can quickly shift the stabilizing hand to the lateral aspect of the foot. Using the other hand, the clinician applies downward pressure on the patient’s knee to make an impression of the foot in the foam. The foot should be pushed 1 to inches into the foam while simultaneous, stabilizing pressure is applied to the lateral aspect of the foot. Finish the impression by using both hands to press the toes into the foam. In this manner, weight-bearing flow is simulated, from heel to midfoot to toes. Alternatively, with a good grasp on the lateral aspect of the foot, one hand can be used to both stabilize and push the foot into the foam and make the impression (Fig. 195-5A). Inspect each impression for defects, unevenness of the weight-bearing surface, or abnormal plantar contour (Fig. 195-5B). Repeat the procedure with the patient’s other foot.

Figure 195-5 Taking foam impressions. A, Ankle should not be supinated or pronated. B, Inspect each impression for defects or unevenness of the weight-bearing surface, or abnormal plantar contour.

(Courtesy of Smithers Bio-Medical Systems, Kent, Ohio.)

Subtalar Neutral Position, Non-Weight Bearing

This technique is used most frequently and captures the “neutral” position of the foot. The patient may be sitting, supine, or prone with the feet hanging free over the end of the examination table. The ankle is kept at right angles to the leg. This technique can be used for the casting tape (see Fig. 195-3), ScanCast Optical Scanner (see Fig. 195-4), or Biofoam Impression (see Fig. 195-5). First, get a feel for what is the neutral position of the foot by inverting and everting, pronating and supinating it while palpating the medial and lateral aspects of the head of the talus with the thumb and index finger (at the talonavicular joint) of one hand. Next, stabilize the talonavicular joint in a neutral, congruous position, midway between inversion and eversion, pronation and supination. Then, with the other hand, grasp the foot on the dorsal and plantar aspects of the fifth metatarsal head (at the MTP joint) and maximally pronate the mid-tarsal joint (see Fig. 195-4). (One author [GLS] grasps the great toe and gently pulls down and lateral so that the foot is in approximately 15 degrees of external rotation.) The foot is held in this position until the casting tape dries (see Fig. 195-3) or the scanning is completed, or while a biofoam impression is made.

NOTE: Useful when maximum biomechanical control of forefoot and rearfoot deformities is required (e.g., flexible pes planus [flat foot] deformity, tibialis posterior dysfunction or medial tibialis stress syndrome, most pediatric deformities). Best for pes planus with greater than 10 degrees ankle dorsiflexion mobility. Most commonly used with sport orthotics.

Subtalar Neutral Position, Partial Weight Bearing

With this technique, the patient sits comfortably with the knee flexed at 90 degrees, the ankle at 90 degrees, and the center of the patella located directly over the second MTP joint. The foot is placed in the neutral position (Fig. 195-6), the position of function, and is then either wrapped in casting tape or placed over the Biofoam Impression Kit and carefully pressed into the foam (see Fig. 195-5). If casting tape is used, the patient is placed on a 2-inch-thick, plastic-wrapped foam pad until the casting tape dries. Care is taken to avoid inverting or everting the heel during the impression stage.

Figure 195-6 Partial weight-bearing, neutral functional position.

NOTE: This technique is indicated for most flexible foot deformities (e.g., pes cavus, pes planus, plantar fasciitis, heel spurs, bunions, painful corns, or calluses on the plantar aspect of the foot).

Rectus Position

This technique is similar to the non–weight-bearing neutral position, except that the forefoot is held parallel to the plantar aspect of the rearfoot during the time the plaster is drying or the foot is being scanned.

NOTE: This technique is indicated for childhood foot deformities (e.g., metatarsus adductus, pes cavus, pes planus, and calcaneal valgus).

Full Weight Bearing

The practitioner can choose plaster or a scanning system similar to the ScanCast Optical Scanner. The patient is instructed to stand in a normal angle and base-of-gait (with the foot held in the neutral position by the clinician while palpating the talonavicular joint; Fig. 195-7) while plaster is drying or the foot is being scanned.

Figure 195-7 Weight-bearing, neutral position, demonstrated by palpating the talonavicular junction.

NOTE: Full weight-bearing impressions are useful for rigid and arthritic foot deformities, where accommodative padding under pressure points will be beneficial.