About Advanced Casting Technology™
Peterson Laboratories pioneered the concept of weight bearing impression casting techniques. Originally starting out in the ski industry, the company recognized that their impression method for creating custom footbeds for ski boots actually had great benefits for other orthotic applications.
Concept:
Inconsistencies of casting techniques provide the greatest challenge in any orthotic fabrication facility. Modifying the casts to estimate the arch height, arch length and width of the weight bearing foot is subjective at best. Extensive discussion and debate has been ongoing over the years with no ultimate solution on how to make foot casting consistent whether using a plaster slipper cast, wax or foam impression tray. Simply “loading” the lateral column during casting does not effectively create a functional or comfortable foot model. Foam impression boxes, while allowing a load to be placed manually on the mid-foot; do not overcome the problem of inconsistency due to practitioner techniques. Common complaints of foot orthotics being intolerable or ineffective due to improper “interpretation” of the plaster model are essentially eliminated by creating a weightbearing foot impression. Utilizing a The A.C.T.™ impression pillow provides an accurate, reproducible and consistent plantar foot topography regardless of technician technique.
Design Features:
The A.C.T.™ Casting Pillow is designed to create an accurate and reproducible model of the foot. The unique pillow shape and density allows the uncompensated foot to be suspended while maintaining neutral subtalar joint alignment as it bears load. This produces a foot model that requires little if any modification in the lab.
The pillow contours and slow-recovery foam allow the rear-foot and mid-foot to be suspended, effectively enveloping the foot without the potential for ground reactive forces to cause distortion. The memory foam material gently compresses the soft tissue at the heel and mid-foot while the forefoot is allowed to splay naturally, as it does under normal load. With the subtalar joint in neutral the thinner memory foam layer under the ball of the foot and toe area will capture the forefoot plane as neutral unless there is a rigid forefoot varus or valgus present.
The A.C.T™ pillows are designed as a single component slow-recovery foam with a smooth durable exterior surface. The pillow surface can be cleaned with soap and water, disinfectant spray or simply brushed. Plaster, STS® socks and thermal moldable mediums will not stick to the surface.
Physiology:
It is generally accepted that during the contact phase of the gait cycle, the subtalar joint passes through neutral alignment twice. It occurs first just after heel strike as the ball of the foot comes into contact with the ground and as the mid-tarsal joint begins to pronate in order to absorb shock. The second time the subtalar joint passes through neutral is just before toe off as the mid-tarsal joint everts and the foot becomes a rigid lever for propulsion.
In casting with the A.C.T.™ Casting Pillow, the plantar foot shape is captured in the latter subtalar neutral position. The ankle is dorsiflexed approximately 17 to 22 degrees while the subtalar joint is maintained in a neutral position and load is placed on the foot. Depending on client requirements, the foot can be in partial weight bearing while seated, or a full or semi-weight bearing position while standing.
Methodology:
- Full and semi-weight bearing casting methods are achieved by standing and bearing load on the foot to be cast. The most common technique is to stand on the A.C.T.™ Casting Pillow with even weight on both feet (considered semi-weight bearing) during the curing or cooling period. This is the most accurate and reproducible casting technique. Assuming there is consistency in the distribution of patient weight, subtalar alignment and pillow density, the resultant impressions will be the same regardless of casting medium (material). Impressions are taken one foot at a time so as to not fully load the foot during the curing/cooling process.
- The seated or partial weight bearing casting method is best used when a compromise of weight bearing and non-weight bearing impressions is desired. This will produce a slightly “higher” arch profile. This is sometimes indicated for cases when patient weight makes subtalar alignment difficult to maintain. This technique is also employed when working with those who are unsteady while standing.
A.C.T.™ Pillow Applications:
The A.C.T.™ Casting Pillows are designed to be used with a wide variety of casting materials and orthotic devices. A.C.T.™ pillows can be used to make impressions for functional foot orthotic fabrication, direct molded shoe inserts, full contact diabetic inlays, custom molded shoes, and AFO’s. Materials which can be used include plaster, thermal cork, STS® casting socks, and direct moldable thermoplastics.
For improved control, the A.C.T™ Impression Stand is designed to simplify the casting process and provide diagnostic information (see A.C.T™ Impression Stand description below).
A.C.T.™ Impression Stand
The A.C.T.™ Impression Stand is uniquely designed to simplify the molding process utilizing the A.C.T.™ pillows. Once the subtalar joint has been aligned, the knee cups hold the patient in position for hands free molding/casting. The plumb bobs identify the alignment of the knee over the metatarsals providing both a reference point and diagnostic tool.
Step 1: We have you step onto the pillows taking care to locate the feet in the appropriate position with the ball of the foot at the transition and the heel centered in the back.
Step 2: The molding technician will loosen the knobs on the sides of the cross bar and position the bar slightly below the plane of the knees.
Step 3: The knee cup knobs and center the cups are adjusted to the knees and retightened. You will bend your knees so they fit securely into the knee cups. The technician will grasp the subtalar joint with one hand and the knee cup knob with the other. We will loosen the knob and slide the knee cup medially and laterally while feeling for subtalar alignment. Once alignment is achieved the knee cup knob is tightened.
Step 4: The plumb bobs are suspended and you will be checked for alignment. The plumb bob should locate between the first and third toes, normally over the second. A lack of symmetry may suggest that subtalar alignment should be rechecked or that perhaps there is a leg length discrepancy or other anomaly that needs to be explored.
Step 5: The molding/casting medium under one foot at a time and allowed to cool/cure.
