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Page 2 of 12 Costa et al. Plast Aesthet Res 2020;7:32 I http://dx.doi.org/10.20517/2347-9264.2020.43

Figure 1. Anterior interosseous nerve (AIN) for thumb opposition. The axons of AIN at the level of pronator quadratus are coapted to
the thenar branch of median nerve, through a nerve graft. Yellow: functional nerve; pink: nonfunctional nerves

MOTORY NERVE TRANSFERS
Median nerve
The median nerve provides a large part of sensitivity to the palmar side of the hand, which is critical for
fine manipulation. It innervates and enables forearm pronation, has the most important role in wrist and
finger flexion, especially the thumb and index fingers, and plays a significant part in thumb opposition.

[5-7]
Depending on the location and severity of nerve injury, different interventions are possible .
In the distal forearm and in the hand, thumb opposition and restoration of sensibility of the thumb and
index finger are the main objectives of reconstruction.

Motor nerve transfers in the distal forearm and hand
Median nerve injuries, at all levels, are associated with atrophy of the thenar eminence and loss of thumb
opposition. Infrequently, atypical innervation patterns from the ulnar nerve can preserve opposition, and
[6]
these have to be evaluated closely .

In lesions of the motor fascicles of the median nerve, direct repair or interposition of a graft remains the
treatment of choice.

When the anatomy is significantly altered however, direct repair can lead to suboptimal results as the
nerve at this level is mainly sensory and, proximally, the scheme of the motor neurons is undefined [8-10] . An
interpositional nerve graft could result in abnormal regeneration in which sensory fibers branch out into
the motor fibers, and consequently without thenar function.

To obtain opposition of the thumb, tendon transfers are very effective, but it should be emphasized that
these procedures require long periods of reeducation and lead to abnormal ergonomics.

If available, the anterior interosseous nerve (AIN) is dissected at the level of the branch to the pronator
quadratus and coapted [Figure 1] to the thenar branch of the median nerve (TBMN). The AIN, at this
[11]
level, is composed mainly of motor fibers with only sensory branches for proprioception of the wrist ,
with a congruous number of axons (distal AIN ~ 900; thenar motor branch ~1,050 [10,12] ). It should also be

mentioned that this technique requires the use of a nerve graft, which inevitably leads to a loss of the total
number of fibers.