Mr Muhammad Adeel Akhtar
BSc, MBBS, MRCSEd, Dip SEM (UK), PG Dip CAOS, MD (Res), MFCI, MFSEM, MFSTEd, FFSTEd, FEBOT, FRCSEd (Trauma & Orthopaedics)
Consultant Trauma and Orthopaedic Surgeon with Special interest in Lower Limb Arthroplasty, Arthroscopy, Trauma and Sports Injuries, NHS Fife.
Honorary Clinical Senior Lecturer, Deanery of Clinical Sciences, College of Medicine & Veterinary Medicine, University of Edinburgh.
Honorary Clinical Senior Lecturer, School of Medicine, University of St Andrews.
Ethan Gilmour
BSc,Medical Student, St Andrews University, Scotland.
Background
Prosthetic limbs offer a chance to improve quality of life and restore amputees to a higher level of function. The standard prosthetic limb uses a socket design which fits over the end of the residuum and is secured in place using a harness.
Prostheses can be active or passive.
Active prostheses include motors to assist with or carry out movements, whereas with passive prostheses all movements are performed completely by the patient.
Passive prostheses for the upper limb can be body-powered, meaning they are moved by actions of the remaining musculature. These movements are achieved by attaching a cable to the distal aspect of the prosthesis, such as a hand or grabber, that closes it when the arm is flexed. Passive prostheses tend to be cheaper, lighter, and more hard-wearing than active prostheses due to their relative simplicity and a lack of intricate components. They also allow for some sensation transfer via the harness.
Passive prostheses can be useful in less active patients or if the prosthesis is simply for aesthetic reasons, whereas active prostheses are more useful in patients with higher functional demands.
Myo-electric prostheses.
Myo-electric prostheses utilise electromyography (EMG) as a control method. Electromyography is the detection of electrical signals from muscles. The concept behind this technique is that muscle tissue acts to amplify motor signals allowing them to be detected with greater ease. The muscle groups selected for EMG are generally antagonistic to prevent concurrent contraction leading to confusing signals. Muscles with previous function related to the desired action are also ideal, because control is then intuitive (1). An example of this is the use of biceps and triceps to control flexion and extension of a prosthetic elbow joint (2). The electrical signals detected, and the amplitude of these signals are then processed via software in the prosthesis and are used to trigger movements. More advanced prostheses make use of pattern recognition systems to increase control.
Myo-electric prostheses can use socket or osseointegrated attachment systems and can use internal or surface electromyography, (sEMG). Internal electromyography uses implanted electrodes whereas surface electromyography uses electrodes placed on the skin or in the socket.
Surface electromyography is more susceptible to interference than internal electromyography since the electrical signals need to pass through a greater number of layers of tissue before they reach the electrodes. The patient’s sweat may also cause difficulties in obtaining reliable signals as it can interfere with the conductivity of the skin (1). A further issue is that due to the intermittent nature of prosthetic limb use, patients need to remove and replace electrodes when doffing and donning the prosthesis, respectively. Consequently, the positioning of the electrodes may vary between use affecting the accuracy of measurements (1).
Other methods have also been proposed such as sEMG combined with gaze control. The theory proposed behind this was that grasping movements can be anticipated by observing eye movements, as grasping is usually prefaced by looking at the target (3).
Movements at different joints that can be carried out by a myoelectric prosthesis are referred to as degrees of freedom. Initially myoelectric prosthesis only allowed for control of one degree of freedom at a time. To carry out different actions or a combination of actions, as is often required, patients had to switch between these degrees of freedom. This could be achieved by contracting multiple muscle groups simultaneously (2). Thanks to recent advances including targeted muscle reinnervation (TMR), for the creation of extra signals, myoelectric prostheses can offer multiple concurrently controlled degrees of freedom (2), with more intuitive control providing the patient with a greater level of function.
Literature Review.
Aman et al. (1) reported the case of a 53-year-old male patient with a transhumeral amputation caused by trauma. Neuroma and phantom limb pain were reported as moderate. The patient received both an osseointegrated myoelectric prosthesis and underwent TMR, to provide signals for EMG, as well as to restore his ability to perform activities of daily living, which he reported difficulties with beforehand. Follow up was reported at 2 and 5 months post-operatively. At two months weight bearing rehabilitation was in progress and 2 separate EMG signals were detectable. At 5 months full weight-bearing was possible and 4 EMG signals were available. No information was reported on changes in pain level or the presence or absence of adverse events, however it was reported that the patient is currently using their prosthesis which suggests that there were no serious adverse events which precluded continuation with the use of the implant or prosthesis. This omission of adverse events may be due to none occurring, lack of recording or may represent reporting bias.
This paper gives a promising early indication of the full potential of the aforementioned advances in amputee rehabilitation by combining them to maximise the level of function returned to the patient. This co-therapy represents an excellent target for further research and development and will likely be seen more in the future as the field progresses and respective costs decrease.
The ability to carry out the surgical operations together may be beneficial as it reduces demand on healthcare systems and makes the process easier and safer for the patient. As this paper only includes 1 patient with a limited amount of information reported on that patient, further research is required to investigate the combined use of these therapies and provide solid evidence for their further use. Comparison with mono therapy of each method may also be beneficial to quantify the magnitude of any benefits of co-therapy.
Ortiz-Catalan et al. (4) also reported on the combined use of osseointegration, TMR and myo-electric prostheses. 4 patients were included in this study, 3 of whom were available for follow up. The patients in this study had all previously been fitted with an osseointegrated implant of the OPRA design and had previously used a myoelectric prosthesis controlled via surface electromyography, however all reported problems with its use.
To detect signals for EMG, all 4 patients received surgically implanted electrodes, which were secured to the epimysium of the biceps and triceps, 3 patients underwent TMR prior to this procedure, in the fourth the biceps and triceps retained their native innervation. Patients were also fitted with spiral cuff electrodes, which were fitted to the median and ulnar nerves, though one patient did not receive a 2nd electrode on the median nerve. The purpose of these electrodes was to stimulate the nerve to provide sensory feedback. Three sensors were included in the thumb of the prosthesis to generate this feedback. The wires from these electrodes passed through the cortex of the bone, along the intramedullary space and exited via a custom designed screw system in the abutment which allowed passage to the prosthesis. The prosthetic limb was designed to be self-contained and require no external components for function.
Three patients were available for follow up (3-7 years) and only these patients had sensory feedback enabled, however all patients used the implanted electrodes to control their myoelectric prosthesis and used their prosthesis in their daily lives. Precision of control of the prosthesis was measure pre- and post-operatively with results showing an improvement in all patients post-operatively. The sensory feedback provided was likened to a “touch by the tip of a pen”, over time patients’ sensitivity to the level of stimulation increased. No complications were reported.
This study again demonstrates the co-therapy of osseointegration and TMR and shows significant effectiveness in maximising function and reducing difficulties and complications. Though the study size is small, the results are promising and indicate the progress that has been made and gives a glimpse into the future of amputee rehabilitation where co-therapy could become the new standard of treatment.
Conclusions:
There have been many advances in amputee rehabilitation over the last decade. We have summarized some of the key papers which highlight the progress made do far and have identified future directions of research into the role of both currently available implants/techniques and how they may be improved in future. Digital technology, artificial intelligence and the engineering of smart implants are all likely to play a part.
References:
1. Aman M, Festin C, Sporer ME, Gstoettner C, Prahm C, Bergmeister KD, et al. Bionic reconstruction : Restoration of extremity function with osseointegrated and mind-controlled prostheses. Wien Klin Wochenschr. 2019;131(23-24):599-607.
2. Pierrie SN, Gaston RG, Loeffler BJ. Current Concepts in Upper-Extremity Amputation. J Hand Surg [Am]. 2018;43(7):657-67.
3. Cognolato M, Gijsberts A, Gregori V, Saetta G, Giacomino K, Hager AM, et al. Gaze, visual, myoelectric, and inertial data of grasps for intelligent prosthetics. Sci Data. 2020;7(1):43.
4. Ortiz-Catalan M, Mastinu E, Sassu P, Aszmann O, Branemark R. Self-Contained Neuromusculoskeletal Arm Prostheses. N Engl J Med. 2020;382(18):1732-8.