ARRS 2022 Abstracts

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2069. Pilot Prospective Pre-Operative MR Neurography Evaluation of Upper Extremity Amputations Implanted with FAST-LIFE Electrode Interfaces
Authors * Denotes Presenting Author
  1. Bayan Mogharrabi *; University of Texas at Southwestern Medical Center
  2. Raghu Ratakonda; University of Texas at Southwestern Medical Center
  3. Edward Keefer; Nerves Incorporated
  4. Jonathan Cheng; University of Texas at Southwestern Medical Center
  5. Avneesh Chhabra; University of Texas at Southwestern Medical Center
Objective:
Fascicular targeting of longitudinal intrafascicular electrode (FAST-LIFE) interfaces enables hand dexterity using a platform with microstimulation for sensory restoration and deep learning-based artificial intelligence to decode the intricate motor control signals of peripheral nerves. This prospective case series illustrates pre-operative 3-T MR neurography (MRN) features of upper extremity nerves of amputees with clinical and electrophysiology findings.

Materials and Methods:
After obtaining consent, all patients with upper extremity amputations underwent pre-operative 3-T MRN, x-rays, and electrophysiology. MRN findings of neuromuscular tissues correlated with electrophysiology reports. Descriptive statistics were performed.

Results:
Patient ages ranged from 21-59 years (2/5 left and 3/5 right) and 2/5 patients had digital amputations, 1/5 had mid-hand amputation, and 2/5 had transradial amputations on X-rays. The median and ulnar nerve end-bub neuromas measured 10.1 +/- 3.04mm (range: 5.5-14mm, median:10.5mm) and 10.9 +/-7.64mm (2-22mm, 9.75mm) respectively and the distance from cutaneous stump margin were 45.75+/-39.2mm (19-113mm, 25.5mm) and 21.75 +/- 14.6mm (5-40mm, 21mm) respectively with the maximum nerve dimensions were 6.38+/-1.86mm (4-9mm, 5.9mm) and 4.26+/-1.71mm (3-7.3mm, 3mm) respectively . 1/5 did not show a neuromas. The ADC of median and ulnar nerves were 1.64+/-0.1 x 10-3 mm2/s (range:1.5-1.8, median:1.64 x 10^-3 mm^2/s) and 1.70+/-0.18 x 10^-3 mm^2/s (1.49-1.98 x 10^-3 mm^2/s, 1.65 x 10^-3 mm^2/s) respectively, which are higher than normal nerves (1.1-1.3x10-3mm2/s) Other identified neuromas were superficial branch of the radial nerve neuroma (1/5), anterior interosseous nerve neuromas (2.5), and medial cutaneous nerve of the forearm neuroma (1.5). On electrophysiology, 2/5 were unremarkable, 2/5 showed mixed motor-sensory neuropathies of median and ulnar nerve along with radial sensory neuropathy, and 1/5 showed sensory neuropathy in lateral cutaneous nerve of forearm. Patchy edema was seen in multiple muscles at the amputation site with fatty infiltration. 2/5 showed proximal denervation in forearm. MRN directed anatomy allowed successful placement of electrodes in all patients - both the median and ulnar nerves (1 right and 1 left) in 2/5 patients and 3/5 in the ulnar nerves (2 right and 1 left).

Conclusion:
3-T MRN allows excellent demonstration of forearm and hand nerves and their neuromas, which allowed successful technical placement of FAST-LIFE interfaces. Peripheral nerve distance from stump margin varies significantly, and pre-operative MRN allows demonstration of presence or absence of neuroma, and their distance from the stump margin, despite unremarkable electrophysiology.