Targeted Muscle Reinnervation: Prosthetic Fitting - Rehabilitation Institute of Chicago

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Targeted Muscle Reinnervation: A Neural Interface for Artificial Limbs

Targeted Muscle Reinnervation: A Neural Interface for Artificial Limbs (CRC Press, 2013) can be purchased at the CRC Press website or on Amazon.

RIC Center for Bionic Medicine

TMR research was pioneered at the Center for Bionic Medicine (CBM). The CBM combines science, engineering, and clinical skill to improve function and life quality for persons with limb loss.

Development of this website was supported by the National Library of Medicine of the National Institutes of Health, Award Number G13LM011221. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Prosthetic Fitting before and after Targeted Muscle Reinnervation

Prosthetic Fitting

Principles of Prosthetic Fitting

TMR surgery creates at least two additional control sites in transhumeral patients and up to four sites for shoulder disarticulation patients, depending on the number of nerve transfers. Proper prosthetic fitting –including component selection and socket design – is necessary so that users can experience the full benefits of TMR.

Although many standard prosthetic fitting techniques apply to those who undergo TMR, the prosthetic fitting of TMR patients poses some unique challenges. These include:

  • Identifying optimal locations for additional control sites.
  • Placing additional electrodes into well-fitting sockets.
  • Accommodating increased soft tissue movement.
  • Allowing additional time for strengthening contraction and isolation of signals from reinnervated muscles.

Successful fitting requires collaboration between an experienced prosthetist with a comprehensive understanding of myoelectric fittings, a physiatrist, an occupational therapist, and the surgical team.

Importantly, in addition to careful fitting of the prosthesis before and after TMR surgery, the device must be adapted to accommodate control changes during the lengthy reinnervation process.

Prior to TMR

The prosthetist and physician should evaluate a person’s residual limb length, nerve and muscle health, past experience using a myoelectric prosthesis, willingness and aptitude to learn new control techniques, and emotional health, among other factors.

For recent amputees, fitting with a traditional myoelectric or body-powered prosthesis prior to TMR surgery may help them adjust to the weight and function of a prosthesis. After TMR surgery, these patients can then focus solely on the new control techniques.

Pre-surgical fitting for patients who undergo TMR long after their initial amputation depends on their previous experience with a prosthetic device.

Interim Reinnervation Period

After surgery, as the limb is stabilizing, a prosthetist should begin discussing and considering with the patient:

  • RIC Prosthetic FittingA two-site myotester can be used to evaluate the
    additional EMG sites after TMR. (Click image to enlarge)

    Prosthetic Fitting Considerations
  • Control Strategies/Mode Selection (transhumeral vs. shoulder disarticulation)
  • Socket Fitting (tolerance to force distribution, active/passive use, suspension)
  • Post-surgical education and training

During this interim period, it may also be necessary to:

(1) Alter electrode locations to accommodate any muscle body shifts that occurred during surgery.

(2) Increase electrode gains to accommodate the decrease in active muscle mass following surgery as a result of the denervation of some muscle segments.

After Reinnervation

Control site selection should be delayed until reinnervation begins to stabilize around 6 months after surgery.

During this time, an occupational therapist may provide training to help the person increase their muscle endurance to strengthen EMG signals.

Once reinnervation has stabilized, myotesting, prosthetic fitting, component selection, and training can begin. Ideally, before myotesting begins, the prosthetist and surgeon should examine the patient to review the nerve transfers performed.

Table 1: Available control sites in transhumeral patients after TMR
Muscle Nerve Innervation Control signal
Biceps, long head Musculocutaneous Native Elbow flexion
Triceps, long head Proximal radial Native Elbow flexion
Biceps, short head Median Reinnervated Hand-close
Triceps, lateral head Distal radial Reinnervated Hand-open
Brachialis* Ulnar Reinnervated Hand-control

*If available, in longer residual limbs.

Table 2: Candidate target muscles for nerve transfer after shoulder disarticulation amputation
Control Signal Nerve Candidate muscles
Elbow flexion Musculocutaneous Clavicular head of pectoralis major
Elbow extension

Radial

Proximal radial*

Lower sternal head of pectoralis major

Residual lateral triceps

Hand close Median/Ulnar Upper sternal head of pectoralis major
Hand open

Median

Distal Radial

Upper sternal head of pectoralis major

Latissimus (via thoracodorsal nerve)

Serratus anterior (via long thoracic nerve)

Pectoralis minor

*Native innervation, left intact if possible/present

Authors

Laura A. Miller, PhD, CP

Laura A. Miller, PhD, CP, received a BS in biomedical engineering from Tulane University, New Orleans, LA and MS and PhD degrees in biomedical engineering from Northwestern University, where she also obtained certification in prosthetics. She works as a Research Prosthetist for the Center for Bionic Medicine at the Rehabilitation Institute of Chicago, and is an Associate Professor in Physical Medicine and Rehabilitation at Northwestern University. Her research interests include fitting and evaluation of new advanced prosthetic devices. Dr. Miller is a member of the International Society of Prosthetics and Orthotics and the American Academy of Orthotists and Prosthetists.

Robert D. Lipschutz, BS, CPRobert D. Lipschutz, CP, received a BS in mechanical engineering from Drexel University, and earned a certificate in prosthetics and orthotics from the Post Graduate Medical School, New York University. He completed his prosthetics training at the Shriner’s Hospital for Crippled Children in Springfield, MA and continued his clinical work at Newington Children’s Hospital in Newington, CT. He worked as a Research Prosthetist for the Center for Bionic Medicine, and is currently Director of Prosthetics and Orthotics Education for the Prosthetics and Orthotics Clinical Center at the Rehabilitation Institute of Chicago, and is an assistant professor in the Department of Physical Medicine and Rehabilitation at Northwestern University. His research interests include fitting and evaluation of new advanced prosthetic devices.