1. Field of the Invention
The invention relates generally to a method for computer aided design. More specifically, the invention relates to automated design for orthotic and prosthetic devices.
2. Background Art
The design and manufacture of prosthetic and orthotic devices requires custom fitting for a proper and comfortable fit for a patient. FIG. 1 shows a prior art example of an attached prosthetic limb 10. A patient's limb 12 is first fitted with a liner 14. The limb 12 and liner 14 then fit into the socket 16 of the prosthetic limb 18. FIG. 1b shows the patient's limb 12 with the liner 14 before the limb is inserted in the socket. FIG. 1c shows a liner 14 with an optional distal attachment mechanism 20. The mechanism 20 is used to physically attach the liner to the interior of the socket.
The liner is typically made of a malleable gel material, such as urethane or silicone that is sometimes covered on the exterior with a cloth layer called a “wick”. The purpose of the liner is to provide cushioning and comfort to the patient. The liner provides a pseudo-hydraulic action that absorbs the energy exerted by gravity and the weight of the patient. The vast majority of the mass of a typical liner is gel while the wick only serves as an exterior cover. A liner is usually tapered in shape with the thickest portion being the distal end. It typically has a decreasing thickness towards the proximal end. The thickness of the liner usually ranges from 2–16 mm. The proximal end thickness typically varies from 2–6 mm, while the distal end thickness varies from 5–16 mm. However, the thickness may vary outside these ranges based on the needs of the individual patient.
FIGS. 2a and 2b show a prior art example of a custom molded orthosis 22. The patient's limb fits into a frame 26 that is customized for the individual patient. The limb is held in place by multiple straps 28. The limb may also be covered with a liner or similar device to ensure a comfortable fit and provide protection for the limb. An orthosis of the type shown is typically used to support and stabilize the compromised limb.
Prior art methods of customizing prosthetic and orthotic devices for individual patients involved taking an anatomical impression of the patient's limb. The impression is made by taking a casting of the patients' limb by wrapping the limb with plaster wrappings. After drying, the casting is removed from the limb and a model of the limb is made by using the casting as a mold. The model of the limb is the used to fashion a customized prosthetic or orthotic device for the patient.
Even with a skilled practitioner, the casting of the limb is messy, time-consuming, and it is prone to errors. Typically, the casting practitioner must manipulate the limb's soft tissue and bony prominences to achieve a proper anatomical alignment. This technique often requires multiple re-castings due to inconsistencies in the alignment.