The emergence of TMR in amputation claims

When dealing with amputation claims, it has become increasingly common for there to be at least some consideration given by the claimant’s treating and medico-legal team to Targeted Muscle Reinnervation or “TMR” as an option for treating phantom limb pain and/or neuroma. 

Phantom limb pain and pain associated with neuromas can limit an amputee’s use of their prosthetic limb and can require further surgical intervention, cause dependence on pain medication, lead to issues with depression and drastically impact on quality of life.

Mr Norbert Kang, Plastic Surgeon at The Royal Free Hospital and Co-Founder of Relimb,[1] is the leading Consultant in the UK for osseointegration and nerve surgery for amputees. He performed his first osseointegration procedure in 2005 and has been performing TMR surgery since 2013. Osseointegration is not a procedure which is available on the NHS, although this may change in the future. TMR on the other hand, is a procedure which is funded by the NHS. Mr Kang has become a familiar name in claims where osseointegration and/or TMR is being considered and there seems to have been an increase in uptake of both procedures in recent years. TMR can be performed at the same time as the initial amputation as a preventative measure in terms of pain, or it can be undertaken in isolation to address pain which is established post-amputation. It can also be undertaken at the same time as osseointegration surgery, although the two are not mutually exclusive. Some amputees, however, remain cautious when exploring TMR as an option, owing to the lack of data around what the outcomes are in the medium to long term.

What is TMR?

TMR is a surgical procedure involving the transfer of the large peripheral nerves in a patient’s amputation stump and connecting them to the motor nerves of carefully selected “target” muscles within or close to the residual limb, using microsurgical techniques. The target muscles are usually muscles in the residual limb which are functionally redundant due to the amputation. For example, muscles which were intended to move parts of the limb which no longer exist, such as the biceps after a transhumeral amputation. Until recently, TMR has mainly been used in relation to upper limb amputations to achieve a reduction in pain and also to improve an amputee’s ability to control myoelectrical prosthetic limbs.

The intention is that axons in the peripheral nerve stumps start to grow into the motor nerves of the target muscles, and reinnervation occurs. The newly reinnervated muscles will not start to work until approximately three months after the surgery. A period of intense therapy is required post-surgery without the prosthesis, and then a further period once the prosthesis is fitted. The process, to include the surgery itself and post-surgery rehabilitation, can take 12 to 18 months in total. Once the process is complete, the muscles will contract voluntarily, responding to signals coming from the previously transected peripheral nerves. For example, when the amputee imagines moving their thumb or wrist, the medial head of the biceps contracts and the muscle serves to amplify the electrical signals in the median nerve stump. That electrical activity, produced by contractions of the medial head of the biceps, can also be detected by electrodes on the skin surface and used to control a myoelectric prosthetic limb.

Mr Kang now considers that the same principle can be used in lower limb amputees in order to address phantom limb pain, as well as relieving neuroma pain by reducing the sensitivity of the peripheral nerves by providing feedback from the target muscle. The same feedback also then reduces phantom limb pain by providing feedback to the central nervous system that is normally absent when a limb has been amputated. It is very early days in terms of the use of TMR in lower limb amputees, however it is likely that we will see an increase in claimants wanting to explore TMR as an option to address phantom limb pain and neuroma, particularly as this procedure is available on the NHS as well as privately.

In a recent Keoghs case, an above knee amputee underwent TMR under the care of Mr Kang to relieve recurrent neuroma and phantom limb pain. The claimant had already undergone one excision and shortening of the residual limb in an attempt to remove a neuroma. Prior to the TMR procedure, the claimant, who was in his 30s with no other health issues, had a very poor rehabilitation outcome, despite having had significant therapeutic input. He was mobilising inconsistently at four years post-accident and was spending periods of time in a wheelchair.

Whilst it was in both parties’ interests in that case to maximise the claimant’s recovery, when TMR was initially proposed, there were concerns around the fact that there was no clinical body of evidence to support the use of TMR to address phantom pain or neuroma, and also due to the fact that there is no data on the medium to long term outcomes. In this case, the defendant’s amputation rehabilitation expert was reluctant to endorse it definitely as an approach, however notwithstanding that, the Court allowed the claimant’s application to set aside the Court timetable and vacate the trial which had been listed, to enable the claimant to undergo the TMR procedure. It is perhaps to be expected that the Court will have sympathy with a claimant who wants to explore this procedure as an option to improve their condition, even if at the expense of a trial date.

The claimant in the above mentioned case was told that he would have worse phantom limb pain for three to six months post-surgery, which would then quickly reduce over two to three weeks. The prosthesis can be worn thereafter, dependent on pain. The NHS waiting list for the TMR was 6-7 months and therefore the claimant opted to have it undertaken on a private basis, at a cost of £12,750. The claimant was noted in the records to have fully recovered from the surgery six months post-accident. There continued to be complaints of phantom limb pain until around seven months post-accident, but by that time, the claimant was described as having made significant progress with his prosthetic use, when compared with the pre-TMR position. The claimant made sufficient progress post-TMR to enable the parties to reach a settlement 12 months post-surgery and therefore he had a positive outcome.

The difficulty for defendant practitioners is that a number of medico-legal experts that are instructed in amputation cases, have little or no experience of the outcome of TMR treatment. They are not therefore in a position to comment with any authority on the likely success or otherwise of such treatment and/or timescales for recovery. However, encouraging outcomes have been reported and TMR is emerging as a leading surgical technique for pain prevention in patients undergoing major limb amputations and pain management in patients with pre-existing amputations[2].

[1] About us – Relimb – Relimb
[2] Targeted muscle reinnervation for the management of pain in the setting of major limb amputation - PMC (nih.gov)