Targeted muscle reinnervation for managing limb amputation pain

A limb may need to be amputated for a variety of reasons, including peripheral vascular disease, infection, trauma and cancer. When the limb is amputated, nerves at the end of the residual limb are cut. This can cause 2 types of persisting limb pain: residual limb pain (often resulting from nerve endings forming painful neuromas) or phantom limb pain sensed in the removed part of the limb. Pain can persist for many years after the amputation. It can have a substantial effect on quality of life and its management can be challenging.

Medicines that may be used to help relieve persisting limb pain after amputation include:

• non-steroidal anti-inflammatory drugs such as ibuprofen

• antiepileptics such as pregabalin or gabapentin

• antidepressants that are used to treat nerve pain such as amitriptyline or nortriptyline

• opioids such as codeine or morphine

• corticosteroid or local anaesthetic injections.

Surgical options for treating a painful neuroma include:

• removal of the damaged nervous tissue (neurolysis)

• transposition of the neuroma away from the exposed painful region into a suitable tissue

• repair and reconstruction of the damaged nerve to make the nerve fibres regenerate into the distal nerve end with the possibility to regain function.

Chronic pain after amputation is common and can be difficult to manage. It can be debilitating, with a negative impact on quality of life and preventing mobilisation on prosthetic limbs. Conventional surgical treatments for painful neuromas include excising and burying the nerve endings in muscle, but the neuroma can reoccur.

Targeted muscle reinnervation (TMR) is a procedure that redirects nerves severed by amputation to new muscle targets. The aim is to reduce residual limb pain or phantom limb pain. 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 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.