No abstract

Surgical nerve transfers are used to efficiently treat peripheral nerve injuries, neuromas, phantom limb pain or improve bionic prosthetic control. Commonly, one donor nerve is transferred to one target muscle. However, the transfer of multiple nerves onto a single target muscle may increase the number of muscle signals for myoelectric prosthetic control and facilitate the treatment of multiple neuromas. Currently, no experimental models are available for multiple nerve transfers to a common target muscle in the upper extremity. This study describes a novel experimental model to investigate the neurophysiological effects of peripheral double nerve transfers. For this purpose, we developed a forelimb model to enable tension-free transfer of one or two donor nerves in the upper extremity. Anatomic dissections were performed to design the double nerve transfer model (n=8). In 62 male Sprague-Dawley rats the ulnar nerve of the antebrachium alone (n=30) or together with the anterior interosseus nerve (n=32) was transferred to reinnervate the long head of the biceps brachii. Before neurotization, the motor branch to the biceps’ long head was transected at the motor entry point and resected up to its original branch to prevent auto-reinnervation. In all animals, coaptation of both nerves to the motor entry point could be performed tension-free. Mean duration of the procedure was 49 ± 13 min for the single nerve transfer and 78 ± 20 min for the double nerve transfer. Twelve weeks after surgery, muscle response to neurotomy, behavioral testing, retrograde labeling and structural analyses were performed to assess reinnervation. These analyses indicated that all nerves successfully reinnervated the target muscle. No aberrant reinnervation was observed by the originally innervating nerve. Our observations suggest a minimal burden for the animal with no signs of functional deficit in daily activities or auto-mutilation in both procedures. Furthermore, standard neurophysiological analyses for nerve and muscle regeneration were applicable. This newly developed nerve transfer model allows for the reliable and standardized investigation of neural and functional changes following the transfer of multiple donor nerves to one target muscle.

The facial dermato-muscular system consists of highly specialized muscles tightly adhering to the overlaying skin and thus form a complex morphological conglomerate. This is the anatomical and functional basis for versatile facial expressions, which are essential for human social interaction. The neural innervation of the facial skin and muscles occurs via branches of the trigeminal and facial nerves. These are also the most commonly pathologically affected cranial nerves, often requiring surgical treatment. Hence, experimental models for researching these nerves and their pathologies are highly relevant to study pathophysiology and nerve regeneration. Experimental models for the distinctive investigation of the complex afferent and efferent interplay within facial structures are scarce. In this study, we established a robust surgical model for distinctive exploration of facial structures after complete elimination of afferent or efferent innervation in the rat. Animals were allocated into two groups according to the surgical procedure. In the first group, the facial nerve and in the second all distal cutaneous branches of the trigeminal nerve were transected unilaterally. All animals survived and no higher burden was caused by the procedures. Whisker pad movements were documented with video recordings 4 weeks after surgery and showed successful denervation. Whole-mount immunofluorescent staining of facial muscles was performed to visualize the innervation pattern of the neuromuscular junctions. Comprehensive quantitative analysis revealed large differences in afferent axon counts in the cutaneous branches of the trigeminal nerve. Axon number was the highest in the infraorbital nerve (28,625 ± 2,519), followed by the supraorbital nerve (2,131 ± 413), the mental nerve (3,062 ± 341), and the cutaneous branch of the mylohyoid nerve (343 ± 78). Overall, this surgical model is robust and reliable for distinctive surgical deafferentation or deefferentation of the face. It may be used for investigating cortical plasticity, the neurobiological mechanisms behind various clinically relevant conditions like facial paralysis or trigeminal neuralgia as well as local anesthesia in the face and oral cavity.

OBJECTIVE Intrinsic function is indispensable for dexterous hand movements. Distal ulnar nerve defects can result in intrinsic muscle dysfunction and sensory deficits. Although the ulnar nerve’s fascicular anatomy has been extensively studied, quantitative and topographic data on motor axons traveling within this nerve remain elusive. METHODS The ulnar nerves of 14 heart-beating organ donors were evaluated. The motor branches to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) muscles and the dorsal branch (DoBUN) as well as 3 segments of the ulnar nerve were harvested in 2-cm increments. Samples were subjected to double immunofluorescence staining using antibodies against choline acetyltransferase and neurofilament. RESULTS Samples revealed more than 25,000 axons in the ulnar nerve at the forearm level, with a motor axon proportion of only 5%. The superficial and DoBUN showed high axon numbers of more than 21,000 and 9300, respectively. The axonal mapping of more than 1300 motor axons revealed an increasing motor/sensory ratio from the proximal ulnar nerve (1:20) to the deep branch of the ulnar nerve (1:7). The motor branches (FDP and FCU) showed that sensory axons outnumber motor axons by a ratio of 10:1. CONCLUSIONS Knowledge of the detailed axonal architecture of the motor and sensory components of the human ulnar nerve is of the utmost importance for surgeons considering fascicular grafting or nerve transfer surgery. The low number of efferent axons in motor branches of the ulnar nerve and their distinct topographical distribution along the distal course of the nerve is indispensable information for modern nerve surgery.

<b><i>Background:</i></b> Radical excision of debilitating hidradenitis suppurativa lesions is the only curative approach in the advanced stages of the disease. Different concepts for axillary reconstruction do exist, but data on their clinical outcome are scarce. <b><i>Methods:</i></b> This is a retrospective cohort study of two reconstructive methods (posterior arm flap vs. vacuum-assisted closure [VAC] + split-thickness skin graft [STSG]) for axillary defects in patients with severe axillary hidradenitis suppurativa treated at the University Hospital Zurich between 2005 and 2020. <b><i>Results:</i></b> A total of 35 patients (mean age 36 ± 10 years, mean BMI 29 ± 5 kg/m², Hurley stage II–III) with 67 operated axillae were stratified according to their type of reconstruction. Median operation time in the flap group was 144 min (IQR 114–207) (cumulative 181 min [IQR 124–300]) and 50 min (IQR 40–81) in the VAC + STSG group (cumulative 151 min [IQR 94–194], <i>p</i> &#x3c; 0.01; <i>p</i> = 0.20 [cumulative time]). The cumulative length of stay was 6 ± 3 days in the flap group and 14 ± 7 days in the VAC + STSG group (<i>p</i> &#x3c; 0.01). Time to complete wound healing was 27 days (IQR 20–49) in the flap group and 62 days (IQR 41–75) in the VAC + STSG group (<i>p</i> &#x3c; 0.01). Vancouver Scar Scale score was 6 (IQR 4–9) in the flap group and 11 (IQR 9–12) in the VAC + STSG group (<i>p</i> &#x3c; 0.01). Protective sensory recovery was most satisfactory in the flap group (<i>p</i> &#x3c; 0.01). Forty-four percent of patients of the VAC + STSG group demonstrated functional impairment of arm abduction. Time to return to work was less in group A with 42 days (IQR 27–57) needed as compared to group B with 48 days (IQR 34–55) needed (<i>p</i> = 0.32). The average cost saving was 25% higher for the flap group than for the VAC + STSG group. <b><i>Conclusion:</i></b> Despite an increased operation time, axillary reconstruction by the posterior arm flap yields a reduced length of stay, less time to complete wound healing along with restoration of a protective sensibility, and less axillary scarring avoiding functional deficits – eventually allowing earlier return to work.