<iframe data-testid="embed-iframe" style="border-radius:12px" src="https://open.spotify.com/embed/episode/7t7gBGJh6PsI4g1uZWyXuB?utm_source=generator&t=0" width="100%" height="352" frameBorder="0" allowfullscreen="" allow="autoplay; clipboard-write; encrypted-media; fullscreen; picture-in-picture" loading="lazy"></iframe> # Targeted Muscle Reinnervation (TMR) — Comprehensive Outline ## 1. What is targeted muscle reinnervation (TMR) and what are its underlying principles, history, and relevant anatomy/levels? ### a) When and by whom was TMR developed and first reported clinically? - Originators: Todd A. Kuiken and Gregory A. Dumanian (Center for Bionic Medicine, Rehabilitation Institute of Chicago/Northwestern). - First clinical case: ~2002; published 2004 (bilateral shoulder disarticulation). - Foundational work: Kuiken hyper-reinnervation rat model (1995); finite element/signal modeling (2001). - Timeline: - 1995: animal model. - ~2002: procedural development. - 2004: first published human case. - 2008+: expanded series and refinements. - Evidence: Multiple series, systematic reviews, and an RCT (Dumanian et al. 2019) support benefit for prosthetic control and neuroma/phantom limb pain (PLP) reduction. - Pearl: Early animal studies showed transferred nerves histologically resembled normal nerve, supporting clinical translation. ### b) What principle explains how TMR prevents neuroma formation and restores function? - Central principle: **“Somewhere to go and something to do.”** Redirect regenerating axons into denervated muscle to avoid chaotic neuroma formation. - Mechanism: End-to-end (or end-to-side) coaptation at the motor point → axons grow into muscle fibers, forming functional units. - Supporting data: - Rabbit model: transferred nerves resembled uninjured nerves. - Clinical: near elimination of symptomatic neuromas when performed at index amputation; delayed TMR also effective. - Surgical pearls: coapt near motor point; fully denervate target; stabilize neurorrhaphy; avoid tension. - Pitfalls: poor candidates include brachial plexus avulsion, inadequate motor targets, poor soft tissue vascularity. ### c) How does TMR “bioamplify” signals for myoelectric prosthesis control? - Concept: Reinnervated muscles amplify tiny motor axon signals into recordable EMG signals. - Practical effect: each transferred nerve → discrete muscle segment → independent EMG channel. - Clinical outcomes: - Myers et al.: 80% doubled usable EMG signals; dexterity improved up to 271% in tasks. - More channels enable proportional, simultaneous multi-DOF prosthetic control. - Timeline: robust EMG at ~3–6 months (longer for distant targets). - Pearls: thin subcutaneous tissue improves EMG detection; ≥4–5 cm muscle segments recommended. ### d) Which upper-extremity nerves and levels are commonly involved? - Common levels: shoulder disarticulation, transhumeral, transradial. - Donor nerves: median, ulnar, radial, musculocutaneous; sensory nerves (medial/lateral antebrachial cutaneous). - Example mappings: - **Shoulder**: Median → sternal pectoralis; Musculocutaneous → clavicular pectoralis; Ulnar → pectoralis minor; Radial → thoracodorsal/long thoracic. - **Transhumeral**: Median → short head biceps; Ulnar → brachialis; Radial → lateral triceps branch. - **Transradial**: Median → FDS; Ulnar → FCU; Radial → FDP/AIN branches. - Note: size mismatch common (large donor vs small motor branch); standard epineurial sutures suffice. ### e) Which lower-extremity nerves and levels are commonly involved? - Levels: above-knee (AKA), below-knee (BKA). - **AKA**: Tibial division → biceps femoris/semimembranosus; Common peroneal → semitendinosus; Saphenous → gracilis. - **BKA**: Posterior tibial → gastrocnemius/soleus/tibialis posterior; Deep peroneal → tibialis anterior/peroneals; Superficial peroneal → peroneus longus/brevis. ### f) What is targeted sensory reinnervation (TSR) and how does it relate to TMR? - TSR: reroutes transected sensory nerves to cutaneous targets, enabling referred sensation and prosthetic feedback. Often performed alongside TMR. --- ## 2. For which patients is TMR indicated, what are contraindications, and what preoperative assessments are required? ### a) Primary vs secondary indications - **Primary (preemptive)**: At index amputation (or ≤14 days) to prevent neuroma/PLP and optimize future prosthetic control. - **Secondary (delayed)**: For symptomatic neuroma, refractory pain, or poor EMG/prosthetic signals. Effective even decades later. - Evidence: Primary reduces neuroma/PLP rates; delayed reliably reduces pain and restores prosthesis tolerance. ### b) Principal goals 1. Prevent/treat neuroma & reduce PLP/RLP. 2. Bioamplify signals for prosthetic control. 3. Preserve options for reconstruction/sensory feedback. - Timelines: wound healing ~6 weeks; usable EMG signals ~3–6 months (longer for distant targets). - Outcomes: improved pain, prosthesis wear, signal quality, and patient satisfaction. ### c) Contraindications - **Absolute**: preganglionic brachial plexus avulsion, active infection, critical limb ischemia. - **Relative**: uncontrolled systemic disease (diabetes, malnutrition, cardiopulmonary instability), demyelinating neuropathies, centralized pain syndromes. - **Practical**: lack of suitable motor targets or inadequate distal nerve length. ### d) Preoperative assessment - History/exam: pain mapping, prosthesis tolerance, Tinel sign. - Imaging/adjuncts: - High-resolution ultrasound (visualize neuroma). - Ultrasound-guided diagnostic block (predicts response). - MRI selectively (deep/multiple lesions). - Prosthetics: baseline surface EMG, prosthetist input. ### e) Verifying motor targets - Clinical: confirm voluntary contraction; mark motor points and Tinels. - Intraop: nerve stimulator to identify true motor branches. - Optimization: ≥4–5 cm muscle segments; adipofascial separation; soft-tissue thinning for EMG pickup. --- ## 3. How is TMR performed—technique, level-specific strategies, and perioperative care? ### a) Core technique 1. Mobilize amputated nerves proximally to healthy fascicles. 2. Identify motor points with stimulator; denervate selected segment. 3. End-to-end epineurial coaptation with fine monofilament; stabilize with epimysial tacking. 4. Thin/shape soft tissue to optimize EMG signals. ### b) Secondary TMR for neuroma - Indication: refractory neuroma pain. - Approach: excise to healthy fascicles (often 4–6 cm), mobilize, transfer to motor point. - Outcome: reduces pain and enables prosthetic use. ### c) Managing size mismatch - Large donor → small motor recipient. - Strategy: interrupted epineurial sutures; cinch donor epineurium to recipient; offload with epimysial tacking. - Avoid fascicular matching attempts. ### d) Shoulder/forequarter mappings - Median → sternal pectoralis - Musculocutaneous → clavicular pectoralis - Ulnar → pectoralis minor/lateral pectoral branch - Radial → thoracodorsal or long thoracic ### e) Transhumeral mappings - Median → medial biceps motor point - Ulnar → brachialis - Radial (distal) → lateral triceps branch - Preserve native innervation to one biceps/triceps head for elbow control. ### f) Distal UE and LE options - **Transradial**: Median → FDS; Ulnar → FCU; Radial → AIN/FDP branches. - **AKA**: tibial → hamstrings; peroneal → hamstrings; saphenous → gracilis. - **BKA**: posterior tibial → gastrocnemius/soleus/tibialis posterior; deep peroneal → tibialis anterior/peroneals; superficial peroneal → peroneus longus/brevis. ### g) Optimizing EMG intraoperatively - Thin subcutaneous tissue over electrode fields. - Use adipofascial flaps between segments. - Fully denervate target segment. - Coapt directly at motor entry point. ### h) Postoperative care - Standard wound care; drains/quilting for seroma prevention. - Resume prosthesis at ~6 weeks. - New EMG sites become usable ~3–6 months. - Close collaboration with prosthetist/rehab team essential. --- ## 4. Outcomes, evidence, and limitations ### a) Pain outcomes - **Immediate TMR**: significantly lower pain scores and near-zero neuroma rates. - **Delayed TMR**: consistently reduces chronic pain; restores prosthesis tolerance. - **RCT**: small trial shows benefit in pain scores at 1 year. ### b) Prosthetic outcomes - More usable EMG signals, greater DOF, improved dexterity and ADL scores. - High prosthesis wear and tolerance rates. ### c) Systematic review summary - 338 patients / 341 limbs. - Mean age ~47. - Indications: trauma, infection, tumor most common. - Mean 2.2 nerve transfers/limb. - Average follow-up ~22 months. ### d) Immediate vs delayed comparison - Immediate: best for **prevention** (neuroma, PLP/RLP). - Delayed: effective **therapy** for chronic pain and poor prosthesis tolerance. ### e) Complications - Seroma, rare infection, transient PLP flares. - Symptomatic neuroma at coaptation site: not reported in large series. ### f) Evidence limitations - Mostly retrospective/prospective cohorts; one small RCT. - Heterogeneous populations, variable techniques and outcomes. - Need for multicenter, standardized trials. ### g) Outcome measurement gaps - PROMIS/NRS inadequate for amputee-specific domains (prosthesis wear, usable EMG channels, DOF, sensory outcomes). - Need validated amputee-specific instruments. ### h) Adoption recommendations - Strong preference for TMR **at amputation** when feasible — many authors argue this should be standard of care. - Delayed TMR remains effective for salvage. - Multidisciplinary planning and standardized outcome collection essential for best practice.