CHICAGO — A speaker at the American Academy of Orthotists and Prosthetists Annual Meeting and Scientific Symposium presented case studies that demonstrated prosthetic solutions to improve the function of electric digits for partial hand amputees.
“It is difficult for partial hand amputees,” John Miguelez, CP, FAAOP, president and senior clinical director at Advanced Arm Dynamics said. “We created unique socket and frame designs, retained functional range of motion in the wrist and reduced compensatory movements. We also improved functional grasp, biomechanical opposition to the thumb and programming that meets the individual needs of each patient, which I think is important.”
The studies followed four patients fit with i-limb (Touch Bionics, Mansfield, Mass.) digits, and compared varying design and control strategies.
The first case was a 28-year-old male, injured by an industrial punch press in 2006. A right partial hand amputee, he had an unstable thumb joint and limited range of motion.
“When a person does not have range of motion in the wrist, their ability to pick up different sized objects becomes infinitely more challenging,” Miguelez said.
At Advanced Arm Dynamics, therapists collaborate with prosthetists to create fitting solutions, and this particular patient was fit with two prostheses: an i-limb four-digit system as his primary, and a secondary custom silicone passive prosthesis with ratcheting finger joints.
The i-limb four-digit device applies EMG control using the interosseous and hypothenar muscles, has an anatomically contoured socket and frame made from lightweight carbon fiber and a custom rolled silicone inner socket. The graphical user interface (GUI) is BioSim, which provides simplicity along with a range of control options.
The patient performed 27 hours of prosthetic therapy with the i-limb digits, and now wears the prosthesis up to four hours a day.
“He is satisfied with the function of the device, uses the pinch and tripod pinch for functional activities and his body mechanics are improving,” Miguelez said.
This case followed a 41-year-old male, also a right partial hand amputee, caused by trauma from a Naugahyde roller.
The patient had a thumb interphalangeal amputation, a fused MCP joint, limited carpometacarpal range of motion, impaired sensation in the hand and congenital absence of the hypothenar muscle.
He was fit with an i-limb three-digit system, a secondary custom silicone passive prosthesis and a mechanical ratcheting thumb.
The patient controlled digit flexion with a force sensor (FSR), using the remaining fifth digit. Digit extension was controlled by electromyogram (EMG), using the second dorsal interosseous muscle.
“The FSR allows excellent proportional control, and the ratcheting thumb allows for positioning of objects that are wider than 1 inch,” Miguelez said.
The patient performed 25 hours of prosthetic therapy, wears the prosthesis most days and uses his fifth digit to pick up various objects.
“When he is picking up something small, the thumb is all the way in, and if it is a larger item, he will reposition the thumb to do different activities,” Miguelez said. “He is satisfied with the high-tech look and function of the prosthesis, and likes the improved pinch.”
The third case was a 49-year-old female, right partial hand amputee, who sustained an industrial carbide cutter injury in 1996. She was previously fit with a prosthetic device, but still had no wrist range of motion, according to Miguelez.
“The prior fitting was a single-site transcarpal hand,” he said. “So this patient got really used to not being able to use the wrist to position things, and to the limitations you have with single-site control.”
The new prosthetic solution was an i-limb five-digit device, with an anatomically contoured partial hand socket, custom rolled silicone interface and lightweight carbon fiber frame. EMG and BioSim served as the GUI.
Having performed 25 hours of prosthetic therapy, the patient now wears the device up to 8 hours a day, as it offers dual-site proportional control and the ability to switch between grip modes.
“What has been nice about the electronic system is the different grip modes,” Miguelez said. “Unlike the transcarpal hand, there are no range of motion restrictions of the wrist.”
The final case was a 34-year-old male, left partial hand amputation, caused by an industrial punch press injury in 2001.
According to Miguelez, initial fitting of a prosthetic device was not possible or practical due to severity of the injury and unsuitable limb length.
“The first step was to work with a surgeon to revise the residual limb to allow for a more manageable fitting solution,” he said.
Following revision surgery to shorten phalanges, the patient was fit with an i-limb there-digit system, performed 15 hours of prosthetic therapy, wears the device daily and has since returned to everyday household activities.
“We try to get patients back to doing their activities of daily living (ADLs), and one of those is learning how to cook,” Miguelez said. “He is satisfied with the appearance, functional grasp patterns and improved body mechanics.”
Necessary improvements of the devices include consistency of operation, improved cosmesis and increases in speed, responsiveness, grip and pinch strength and sensory feedback, according to study results.
Miguelez said that electric digits have been a key technological development in O&P, however, they are not yet fast enough.
“If someone has to wait on the electric digits to move, they are going to use their sound side in a lot of situations,” he said. “So we have to speed them up.” — by Shawn M. Carter
Disclosure: Miguelez is president and senior clinical director at Advanced Arm Dynamics.