Summary
Targeted muscle reinnervation offers a proven method for the treatment of amputation-related pain in lower limb amputees. It is recommended for any patient suffering from painful terminal neuromas and/or phantom limb pain and has also shown good effects in preventing these conditions, when performed during the amputation procedure. Targeted sensory reinnervation may provide a similar approach for purely sensory nerves with the additional benefit of improved sensory feedback at the stump.
21 Modern Concepts of Prosthetic Rehabilitation in Amputation of the Lower Extremity
21.1 Introduction to Targeted Muscle and Sensory Reinnervation
The majority of lower limb amputees suffer from some type of amputation-related pain. 1 , 2 Generally, these painful sensations may include neuroma and/or phantom limb pain, which are both related to loss of continuity of the affected extremity nerves. 3 After a peripheral nerve loses its physiological target through trauma or surgery, its axons regrow at the nerve stump. If they do not find a target to innervate, they sprout in an unguided manner, leading to the formation of a terminal neuroma. 1 , 4 When sensory fibers are included, these neuromas are generally painful upon external stimuli such as increased pressure. Located at an area of weight bearing, stump neuromas frequently inflict pain upon loading and thereby prevent the use of a prosthetic device. Phantom limb pain, in contrast, is not directly associated with mechanical stimuli at the stump. It affects up to 80% of amputees and entails painful sensation of the missing parts of the limb. It usually appears as intermittent background pain, with intervals that range from 1 day to several weeks and some additional short exacerbations. 5 The underlying pathomechanisms of phantom limb pain are not well understood. While there are different theories about its origin, there is an agreement that various peripheral and central factors along the neuraxis are at play. 6 Furthermore, external factors such as emotional stress or psychiatric disorders might also contribute to an increase in pain. 7 , 8 , 9
Both stump neuromas and phantom limb pain do not respond well to standard pain medication. While as first-line medication the use of paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDs) is recommended before other pharmacologic agents, there is still limited evidence on the effect of these. 10 , 11 Regarding stump neuromas, over 150 surgical treatment methods 4 have been described and traditionally the best, although still limited, results have been achieved by shortening of the nerve and transposition into muscle tissue. Phantom limb pain treatment has generally been conducted in a multimodal manner, including pharmacological interventions, behavioral approaches, physical and occupational therapy, surgical approaches such as sympathectomy, aimed at lesioning certain neural pathways, and neurostimulation. Several studies have shown that most of these treatments are ineffective, often not exceeding the placebo effect. 6 , 12 Other studies showing positive effects of treatment approaches lack the methodological rigor and robust reporting needed to confirm effectiveness. 13
Targeted muscle reinnervation (TMR) was first introduced in 2004 by Kuiken et al as a technique for improved prosthesis control in upper limb amputees. 14 The main concept is the transferal of blindly ending nerves onto the motor nerves of remaining muscles in the stump, thereby creating novel neuromuscular units. While the primary emphasis of this technique was to create an increased number of intuitive myosignals for upper limb amputees in order to facilitate improved prosthetic control, it has also shown to be effective in the treatment of amputation-related pain. It also prevents neuroma formation by offering the nerves new terminal receptors. While it may be argued that muscles only provide a target for motor fibers, experience has shown that sensory fibers also regrow into the skin overlying the reinnervated muscles after TMR. 15 This “reafferentiation” of a peripheral target to the central nervous system, that is, the recreation of a complete and functional neuraxis, is believed to be a driving factor behind the positive effects of TMR on phantom limb pain.
In the first randomized clinical trial on surgical treatment of amputation-related pain, TMR has shown better outcomes for phantom limb pain and neuroma-related residual limb pain compared with conventional neurectomy, that is, shortening of the nerve. 16 More recently, it has also been explored as a preventive treatment performed during amputation, showing similarly encouraging results. 17 , 18
Targeted sensory reinnervation (TSR) applies the same concept to the reinnervation of sensory nerves. While theoretically providing the same benefits as TMR with regard to pain management, it offers the additional benefit of creating specialized sensation at the stump of lower limb amputees. For example, after transfer of the sensory tibial nerve onto the sural/saphenous nerve, a transtibial amputee will feel their planta pedis at the stump. 19 This can be employed with the idea in mind to create more natural gait feedback for the amputee. 20 It is hypothesized that such an approach to create meaningful and intuitive feedback can help improve postural stability and embodiment of the device, while reducing falls. 19 However, not much work has been done on this topic and its feasibility is yet to be investigated.
21.1.1 Indications and Contraindications
TMR should be considered for any patient with lower extremity amputation, suffering from either phantom limb or neuroma pain. In light of recent research, it is recommended to perform TMR already during the amputation procedure, thereby effectively preventing neuroma formation and acting against phantom limb pain after successful muscle reinnervation. 17 , 18 There are no specific contraindications for this procedure. In the cases where there is no viable musculature left at the stump or soft-tissue coverage at the weight-bearing area is insufficient, which may happen in certain avulsion traumas, a free muscle transfer may be used as target for nerve transfers.
21.1.2 Preoperative Management
In the case of terminal neuromas at the stump, these can in most cases be located in clinical examination by elicitation of a Tinel–Hoffmann sign. In addition, high-resolution ultrasound can be helpful to determine the exact location and type of neuroma, and ultrasound-guided nerve block may be used to secure the diagnosis. Phantom limb pain, on the other hand, is a purely clinical diagnosis, associated with painful sensations at missing parts of the limb. The availability of sufficient stump muscles for TMR may be assessed clinically. In the cases where there is doubt about the condition of stump musculature, high-resolution ultrasound and MRI may prove helpful and surface or needle electromyogram (EMG) is recommended to test muscular activity. 21
21.1.3 Technique
The patient is placed in a prone or lateral position. In above-knee amputees, the main nerves of the thigh are exposed via a longitudinal dorsal incision. In below-knee amputees, the incision crosses the knee joint in a Z-fashion, continuing laterally along the course of the peroneal nerve.
As an example, we report the case of a 17-year-old adolescent boy who lost his lower limb at the below-knee level in a traumatic accident with a boats’ propeller. Prosthetic fitting was not successful, as the patient developed chronic ulcerations at the scarred distal stump end as well as painful neuromas. To save the below-knee level of amputation and improve the soft-tissue quality, a free musculocutaneous latissimus dorsi flap was performed. In this case, the deep peroneal nerve was coapted to the thoracodorsal nerve of the latissimus flap, and the distal tibial nerve was coapted to the nerve branches of the gastrocnemius heads. With this complex procedure, painless weight bearing at the distal stump end and therefore excellent prosthetic use could be achieved (Fig. 21‑1, Fig. 21‑2, Fig. 21‑3).
The nerve transfers used in the treatment of neuroma and phantom limb pain should be chosen based on clinical examination (location of neuromas) and available anatomy. The donor nerves have to be neurotomized at least to a level of palpable healthy fascicles. Nerve transfers can be performed under loupe magnification in an end-to-end fashion using 8–0 or 9–0 nylon sutures and fibrin glue.
21.1.4 Postoperative Management
Depending on the exact site of nerve coaptation, successful reinnervation of the target muscles may take 3 to 6 months. If there is neuropathic pain during this period, this can be managed with specific analgesics such as pregabalin. Neuropathic and phantom limb pain should subside once the nerves have reached the targets. After reinnervation, selective activation and training of the newly innervated stump muscles can be helpful if phantom limb pain persists. This is done with the aim to effectively strengthen the cortical representation of the lost limb and may be guided by surface EMG biofeedback or approaches for sensory training. 21 , 22
21.1.5 Conclusion
TMR offers a proven method for the treatment of amputation-related pain in lower limb amputees. It is recommended for any patient suffering from painful terminal neuromas and/or phantom limb pain and has also shown good effects in preventing these conditions, when performed during the amputation procedure.
TSR may provide a similar approach for purely sensory nerves with the additional benefit of improved sensory feedback at the stump.
21.2 Introduction to Osseointegration at Below- and Above-Knee Level of Amputation
The quality of the interface between the residual limb and the fabricated socket is of utmost importance for the success and functional outcome of any prosthesis, regardless of whether the amputation is below or above the knee. However, the residual limb is a dynamic organ with surrounding soft tissue resulting in relative movements and stump volume changes. Additionally, the tibial and femoral bones only have a limited trans-sectional surface and the overlying skin is not designed for full weight bearing. Therefore, the most commonly faced issues with conventional sockets reported are skin irritations, sweating within the socket, and pain during activity 23 with skin problems alone affecting 24 to 74% of lower-limb amputees. 24 , 25 These issues can result in a significantly reduced walking distance or even prosthetic abandonment. 26
These problems led to the development of osseointegration. Adapted from early concepts of dental implants, the first osseointegration with a titanium implant in a lower limb amputee was performed in the 1990s by Rickard Brånemark. 27 The concept of osseointegration allows a direct prosthetic bone anchorage without interfering with skin and soft tissue. Thus, it avoids the inherent problems with conventional socket suspension. Additionally, studies have shown that patients using osseointegrated limbs receive some sensory feedback through this new interface, a phenomenon that was termed osseoperception. 28 Still, as osseointegration necessitates a percutaneous interface of the metal implant, there is the risk of superficial and deep infections. 29
21.2.1 Indications and Contraindications
Osseointegration is indicated if patients report about problems with conventional socket prostheses, for example, discomfort, pain, poor suspension, or inability to use conventional socket prostheses at all. However, it is important to rule out that these issues are due to a poorly fitted socket or inadequate training. In order to assess these indications, it is recommended to see the patient in a multidisciplinary team including a surgeon, a physical or occupational therapist, and a prosthetist. If there is any doubt on the patient’s psychological state allowing to fully follow clinical instructions, the consultation of a psychologist/psychiatrist is necessary. Furthermore, patients should have reached full skeletal maturity, have normal skeletal anatomy, and agree to comply with a strict treatment and follow-up program. Contraindications are severe peripheral vascular disease, diabetes, smoking, limb exposure to radiation, osteoporosis or current chemotherapy, as well as corticosteroid use. 23
21.2.2 Preoperative Management
For preoperative planning, a CT scan of the stump is performed to evaluate bone quality and determine the size and length of the implant.
21.2.3 Technique
Depending on the implant used, the surgical procedure can be done in a single stage or in two stages. Most of the currently available implants use the press-fit technique. The percutaneous interface is of great importance in regard to the risk of infection. Therefore, the skin surrounding the implant is thinned to a minimum and subcutaneous tissue is removed in this area. This enables a stable interface with minimum soft-tissue movement around the implant, minimizing fluid secretion and risk of infection (Fig. 21‑4, Fig. 21‑5).
21.2.4 Postoperative Management
The postoperative phase is divided into a healing period and a loading period. Depending on the surgical technique, single- or two-staged approach, the amount of time in the healing phase varies. During load training process, the patient is fitted with a short training prosthesis to stand on a bathroom scale. Weight bearing usually begins with 10 kg on the prosthesis and is increased every week by additional 10 kg until full body weight can be loaded painlessly. This process normally takes 6 to 8 weeks and varies depending on the used system and bone healing. If the loading training is successful, gait training is initiated at about 12 weeks postoperatively. In the beginning, the patient is asked to use two crutches and limit prosthesis use to no more than 2 hours per day. The wearing time, prosthetic activity, and weight bearing are then gradually increased over the following weeks. After radiologic control and successful gait training, about 6 months postoperatively, the patient can stop using walking aids. During the entire loading process, pain is an important indicator for implant loosening or overloading.
21.2.5 Conclusion
Osseointegration in below- and above-knee amputation has become an established treatment option in patients not tolerating or not applicable for conventional socket fittings. It has been shown that osseointegration is able to improve patients’ quality of life, functional prosthetic outcome, body image, range of motion of the hip joint, comfort especially in the sitting position, as well as easing donning and doffing of the prosthetic device. Additionally, osseoperception provides sensory feedback that improves the ability to walking and secureness, especially on rough surfaces. Nonetheless, patients have to be aware of the potential risks and complications. Additionally, some restrictions in the use of the system apply as for most current systems running or cycling is not recommended.
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