A common complaint from amputees is phantom limb or residual limb pain (PLP) at the site of amputation. This occurs because the nerve endings that have been cut form "terminal neuromas", which are axons that get covered in scar tissue (Dumanian et al.). There are several types of treatment for PLP, including excising the neuroma and moving the remaining tissue to a better anatomical environment (bone, fat, vein, etc.), injecting neurotoxins, and nerve ablation. Despite the extensive amount of treatments that have been used to attempt to alleviate PLP, there has yet to be one that is consistently effective (Dumanian et al.). Because of this, new methods of treating PLP are being tested, including Targeted Muscle Reinnervation (TMR), performed for the first time in 2002 by Dr. Gregory A. Dumanian. TMR is a procedure focusing on the terminal neuroma, where it is removed and then the now fresh axon is attached to a nearby motor neuron. The benefit of this process is that the neuron can reinnervate denervated muscle without forming a neuroma, which tends to be a significant source of PLP.
The application of TMR is shown in Dumanian's research paper, "Targeted Muscle Reinnervation Treats Neuroma and Phantom Pain in Major Limb Amputees: A Randomized Clinical Trial" where Dumanian et al. explore the efficacy of TMR in treating PLP. In this study, 28 major limb amputees with chronic phantom limb pain (PLP) were selected and randomly assigned to be treated with either TMR or standard treatment. The data collected was based on the patient's report of pain level from a scale of 0-10 and a series of forms designed to assess pain. Patients also were scanned via MRI both preoperatively and one year postoperatively, radiologists who did not know which treatment the patient had received were asked to identify neuromas on the MRI. The resulting reduction in PLP, as per the patient reports using the Numerical Rating Scale (NRS), was not significantly different between the control and experimental group after statistical analysis. However, when measured by the Patient-Reported Outcomes Measurement Information System (PROMIS) scale, the difference is statistically significant. The researchers posited that the lack of statistical significance when using the NRS data could have been due to the presence of other, untreated neuromas and other painful conditions that result from major limb amputation.
In another, newer article on TMS titled, "Targeted Muscle Reinnervation Technique in Below-Knee Amputation" by Bowen et al., the researchers focused specifically on using TMR to treat PLP in below-knee amputations. In this study, 22 below-knee amputees were treated with TMR and then their pain, functionality, and overall satisfaction was monitored over the course of a year (Bowen et al.). Immediately after surgery, all participants noted that they did not have any neuroma pain. However, after one month, 72% of the subjects reported PLP. The more significant and fascinating result came at the 3 month mark, where the reports of PLP decreased to 19% of patients, and then again to 16% at the 6 month mark (Bowen et. al). The article also mentions the application of this treatment in limb prostheses. This particular article is important because while Dumanian's research primarily focuses on prostheses of upper-limb amputations, Bowen's research, being the first to explore TMR in below-knee amputees, allows TMR to reach a wider demographic, now including those with below-knee amputation. This field of research is important because not only can TMR help relieve PLP, it can also open the door to more sophisticated prosthetics for amputees.
References
Bowen, J. Byers M.D., M.S.; Ruter, Daniel B.S.; Wee, Corinne M.D.; West, Julie M.S., P.A.-C.; Valerio, Ian L. M.D., M.S., M.B.A. Targeted Muscle Reinnervation Technique in Below-Knee Amputation Plastic and Reconstructive Surgery: January 2019 - Volume 143 - Issue 1 - p 309-312
Dumanian GA, Potter BK, Mioton LM, Ko JH, Cheesborough JE, Souza JM, Ertl WJ, Tintle SM, Nanos GP, Valerio IL, Kuiken TA, Apkarian AV, Porter K, Jordan SW. Targeted Muscle Reinnervation Treats Neuroma and Phantom Pain in Major Limb Amputees: A Randomized Clinical Trial. Ann Surg. 2019 Aug;270(2):238-246. doi: 10.1097/SLA.0000000000003088. PMID: 30371518.
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