Interventional procedure overview of targeted muscle reinnervation for managing limb amputation pain

What the procedure involves

Targeted muscle reinnervation (TMR) is a procedure that redirects nerves severed by amputation to new muscle targets. The aim is to reduce phantom limb pain or pain that is felt in the residual limb. It also aims to reduce chronic pain that has not responded to conventional treatments (intractable pain), without the risk of neuroma recurrence. The procedure can be done at the time of initial amputation to prevent pain developing or secondarily to treat pain that has developed after amputation.

The procedure is done under general anaesthetic. There are 3 main steps: preparation of the donor nerve, identification of a motor branch to the targeted muscle, and finally, nerve coaptation. The major mixed motor and sensory nerves proximal to the amputation site are identified. A nerve stimulator is used to show the motor and sensory nerve branches within, and these are traced distally towards the stump. Motor nerve branches to muscles that are not functional after the amputation are identified and divided, and the involved sensory nerves are then coapted to these motor branches using 8-0 or 9-0 nylon sutures under magnification. It has been hypothesised that the nerve endings stop causing pain once they have found an alternative muscle, because their physiology is restored.

Regenerative peripheral nerve interface (RPNI) is another technique that involves innervation of denervated muscle. The severed nerve is dissected longitudinally into its main fascicles, which are then implanted into free muscle grafts. It might be done instead of TMR if no suitable muscle target is available. It is sometimes done at the same time as TMR, if multiple nerves are involved.