Overview:
The focus of this module is on the functionality of prosthetic and orthotic devices, especially in the context of how the devices are used during relevant life tasks; the biomechanical principles of the human technology interface and physical interfaces in prosthetics and orthotics was addressed in Module 3.
Infrastructure
Prosthetics
Overall Aims
- Depend in part on functional of level of amputation
- Depend on relative importance of aesthetics versus function
- Lifestyle needs and task analysis
Upper Extremity Prosthetics (with historical perspective)
- Body powered (by early 1950s, post-WWII, core technology was pretty mature)
- Harness and residual limb interface (see Module 3)
- Key points:
harness can be for stable suspension and/or control; also non-harness systems; concepts of "relief" and "buildup" (biomechanics)
- Bowden cables (to transmit control and power to 1-DOF terminal device)
- Terminal device (0- or 1-DOF hook or hand)
- Options of Voluntary Closing (VC) and Voluntary Opening (VO)
- Function of user abilities and preferences (VC more natural but often more sustained effort)
- Either way, spring-loaded return (e.g., elastic band, mechanical spring, pneumatic spring)
- Externally-powered (1960 to present)
- Electric power (typically DC motors)
- Challenges include housing the motor, gearing and battery
- Pneumatic power (e.g., Simpson group, McKibbon muscles)
- Advantage is that the mechanical stiffness range is more similar to actual muscles
- We have used various braided pneumatic actuators (also called McKibbon muscles, artificial muscles, air muscles) laying around, as do other groups.
- They are easy to make - we had a "make your own" booth at a rehab robotics conference in 1995 (Delaware) that turned on some other groups, and past students have documented their properties. We used them for various projects ranging from anthorobots with large numbers of muscles (late 1980s, early 1990s) to variable stiffness airsprings for large joysticks (here at Marquette). Here's a recent senior design project on YouTube (not sure of university) that used them.
- During mostly 1980s, some to present:
- Diversity of Terminal Devices for Body-Powered
- Novel Electrically-Powered
- Overview of some basic performance capabilities of natural vs artificial elbows and hands
- Based in large part on article by Heckathorne in Winters 2008 issue of Capabilities magazine
- Typical capability in elbow torque (for slow lifts):
- Natural: ~60-70 Nm typical young adult male, ~50 Nm typical female
- Otto Bock Dynamic Arm; 18 Nm, Liberating Technologies Boston Digital Arm: 14.2 Nm; Motion Control Utah Arm 3: 4.3 Nm
- Typical capability for peak elbow speed, for goal-directed point-to-point movement:
- Natural: ~3 deg/sec for every 1 deg of movement magnitude
- Prosthetic elbows listed above: can maintain this for up to about 40 deg movements, after which it reaches its peak, such that for large movements its about 1/4 to 1/5 of the natural limb value.
- Typical capability for finger speed:
- Natural: over 2000 deg/sec maximum, but for functional "pick-and-grip" tasks, about 170 deg/sec.
- Prosthetic hands/hooks: cannot attain speeds anywhere near peak finger speeds, but all can get into the "pick-and-grip" range of 170 deg/sec, so are competitive in this regard.
- Typical capability for grip force (palmer prehension)
- Both natural and all of the high-end prosthetic hands/hooks (from Otto Bock, Motion Control, Hosmer) are all on the order of about 100 N (or 22 Ibs).
- Sample of Continuing Research
- CyberHand - work by Dario biorobotics group (mostly in Italy), with focus on the hand
- DARPA Prosthetics Program - Work on Neurally-Controlled Prosthetics
- Dean Kamen's team (DEKA) and Biorobotic "Luke" arm
- Alternatives to prosthesis suspension
- Osseointegration - direct skeletal attachment of the prosthesis to the transected bone
- Subfascial Implant Supported Attachment (SISA) - T-shaped distal end on humerus to assist with mechanical coupling (similar to strategy of what is called the Marquadt angulation osteotomy)
- Body-powered research challenges (RERC P&O team):
- Extending to multi-axis shoulder (including humeral axial) and wrist control
- Hybrid systems with both body- and externally-powered components
Lower Extremity Prosthetics (with historical perspective)
Orthotics
Overall Functional Aims
- To Serve as Functional Splint Across Joint(s)
- Often at a desired angle for the joint(s), e.g., neutral (note that this can be used to set a posture)
- Assumes that splint functions as a very stiff spring
- To Limit Joint Range of Motion (ROM)
- Low stiffness over a specified ROM, then very stiff splint-like stops
- Many have a variable lock mechanism
- To Serve as Functional Spring and/or Dashpot
(passive device)
Across Joint(s)
- Springs: provide stiffness, resulting in a length-dependent force and stored potential energy
- Often designed with a spring functioning in one (weaker) direction
- Design parameters include stiffness (sometimes variable as function of length), offset
- Spring materials include conventional springs, bands made of rubber or plastics, pneumatic airsprings, plastic shells
- Dashpot: provide a viscous-like damping (e.g., to smooth tremors during movements)
- To Serve as Functional Actuators
- Many research efforts (since 1950s), but few devices on the market
- Electric motors (e.g., DC), pneumatic actuator-springs (e.g., braided pneumatic artificial muscles)
Spinal/Cervical Orthotics
- General list of products
- Many are 3- and 4-point force systems (e.g. limiting torso flexion)
- Others are general soft splints (e.g., cervical collars, generally with limited biomechanical effectiveness)
- Some try to provide a degree of traction for a region of spine (e.g., lumbar)
- Classic Braces for Scoliosis
- Halos - External Fixation for Unstable Cervical Spine
- Components: Halo ring, skull pins (mostly typically 4), bars (crossing cervical spine), torso vest
- A "Godsend" (for high neck, e.g. C1/C2/C3/C4 injuries)
- Challenges include shifting of vest (over time; during certain arm use), loosening of skull pins
- Medical perspective (e.g., indications, technique)
- Skill in setting position of head relative to torso (e.g., amount of traction; anterior-posterior shift)
- Short You Tube view of Halo being worn
Upper Extremity Devices Available for Purchase
Lower Extremity Devices
- Most via classic orthotics fabrication approach (e.g., for AFOs, KAFOs) covered Module 3
- General list of products, and key companies listed on oandp (some of these are high-tech sports devices)
- Notice that while there are AFO products, most commonly these are fabricated by the orthotist rather than purchases off-the-shelf - most items are components
- Notice that there are many products for the knee (with different strategies for different torn ligaments, cartilage)
- Notice that are are also a good number of fracture braces (e.g., tibial)
- Notice that some are specific to support of gait or standing tasks
- Example: Gait-specific Reciprocating Gait Orthosis (RGO) that helps the legs rotate 180 deg out of phase
- Example: Knee Braces used by Athletes
(see summary, example product list, another product list)
- Functional knee braces: designed to substitute for damaged ligaments, cartilage
- Prophylactic knee braces - design to protect the knee, i.e. minimize risk of knee injury
- Rehabilitative - limits excessive or harmful knee movements, post event (e.g., injury, surgery)
- NWU PRL/RERC lower extremity orthotics research (mostly on biomechanical analysis)
|
|
