| Severe, disabling spastic upper-limb deformities, which usually affect flexor muscles of the upper extremities, are common complications in patients with brain injury, cerebral palsy, and vascular hemiplegia. Although patients with spasticity generally gain the abilities required for daily living, these patients experience high levels of functional and cosmetic disability, particularly finger flexor spasticity, which may contribute to disability by restricting the amplitudes of wrist and finger movements.The forearm flexor muscles act on the wrist joint and fingers, and are classified as: superficial flexors, intermediate flexors, and deep flexors. The flexor digitorum superficialis (FDS) is a superficial flexor. The FDS is an important target muscle in the context of reducing finger flexor spasticity by neuromuscular blockade, not only because of the contribution it makes to forearm flexion, but also because of its superficial location and suitability for motor point and botulinum toxin injections.In clinical practice, phenol and alcohol are injected, as denervating agents, into motor entry points (MEPs) to alleviate the symptoms of severe spasticity despite their side effects. Botulinum toxin therapy, as used to treat spasticity, involves injection into the muscle belly of the FDS. The curative effect of the toxin is dose-dependent, and animal studies have demonstrated that muscle paralysis release is greatest when the toxin is injected as close as possible to the motor end plates (intramuscular endings), which are densely distributed between the proximal and distal limit points (PLPs and DLPs, respectively). Therefore, improvements in the accuracy of localizing PLPs and DLPs could reduce toxin costs, and more effectively and efficient injection into the FDS could enable additional muscles beyond the FDS to be treated within toxin safety limits, and thus, nearby non-injected muscles could also be freed from weakness.The precise localizations of MEPs and intramuscular nerve endings of the FDS are indispensable for the management of finger flexor spasticity. Our aims were to identify extramuscular branching patterns and precise distributions of MEPs as well as intramuscular nerve endings of the FDS, and to provide an accurate zone for botulinum toxin and other denervating agents for injections of the FDS.The following sites and regions (presented as one-tenth percentage distances using our coordinate system) were recommended to treat FDS spasticity:(1) For the proximal main branch from 2/10 to 3/10 on the x-axis, 58.7% of MEPs in the 2/10 portion and 41.3% of MEPs in the 3/10 portion.(2) For the proximal main branch from 1/10 to 3/10 on the y-axis, 58.7% of MEPs in the 2/10 portion and 40.2% of MEPs in the 3/10 portion.(3) For the distal main branch from 3/10 to 4/10 on the x-axis, 38.9% of MEPs in the 3/10 portion and 61.1% of MEPs in the 4/10 portion.(4) For the distal main branch from -1/10 to 2/10 on the y-axis, 68.5% of MEPs in the 1/10 portion and 22.2% of MEPs in the 2/10 portion.Based on the results of the present study and taking into account the ease of accessibility in clinical practice, we recommend that the following site as target region of botulinum toxin injections to the FDS:(1) For the proximal main branch in the 2/5 portion on x-axis (PLPs 16.4%, DLPs 37.7% and mean 27.1%).(2) For the distal main branch in the 3/4 portion on x-axis (PLPs 50.9%, DLPs 73.1% and mean 62.0%) with the needle directed to the medial side of midline to avoid injuring the median nerve.In our research, the incidence of the proximal main branches was 41.3% and the distal ones was 100%, therefore we recommend that the 3/4 portion on the x-axis should be injected first in clinical procedure, if the blocking efficiency was insufficiency, the 2/5 portion on the x-axis should be injected subsequently.The neural and vascular anatomy of the human forearm muscles, especially the flexor carpi ulnaris and flexor carpi radialis muscle, had been studied extensively. The flexor carpi ulnaris has been used clinically in functional local tendon transfers, in local resurfacing procedures, and in complex forearm reconstructions. In previous studies, the muscles were studied as a whole and was transferred intact, with or without the overlying skin .The aim was to demonstrate that there are two functioning compartments of the flexor carpi ulnaris and flexor carpi radialis.The fiber length and physiologic cross-sectional area of the flexor carpi ulnaris and flexor carpi radialis were measured in three fresh-frozen human cadaver upper limbs. The muscle was then split in two along the intramuscular tendon, and fiber length and physiologic cross-sectional area were again recorded for each neuromuscular compartments. Fresh human flexor carpi ulnaris and flexor carpi radialis muscles were stained using the modified Sihler's staining technique and Perfusion Studies. The Sihler's staining showed that the nerve branches to the flexor carpi radialis muscle arose from the median nerve as three primary branches and penetrated the muscle belly at its proximal end, and the nerve branches to the flexor carpi ulnaris muscle arose from the ulnar nerve as two primary branches and penetrated the muscle belly at its proximal end. The vascular pedicle entered the muscle at the junction of the proximal third and distal two-thirds of the belly. Soon after its entry, the vessel split and could be identified as two distinct branches running distally toward the musculotendinous junction. Several smaller branches were also given to the proximal third of the muscle belly by these two branches. The muscle and nerve architecture (fiber length and physiologic cross-sectional area, the fiber numbers of the branches innervating to flexor carpi ulnaris and flexor carpi radialis, the percentage of nerve fiber and connective tissue in the branches innervating to flexor carpi ulnaris and flexor carpi radialis) of the common muscles that need to be replaced in cases of radial nerve palsy and compares that with the architecture of the humeral and ulnar compartments of the flexor carpi ulnaris and flexor carpi radialis. The neuromuscular compartments of the flexor carpi ulnaris become more crucial in tendon transfers as forearm deficits become more complex, with deficiency of functioning muscle units.
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