Human anatomy program petrotympanic
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Flexion at the metacarpophalangeal joints may be possible (because the interosseous muscles, innervated by the ulnar nerve, are still in-tact), but the fingers can't be flexed at the interphalangeal joints, especially at the 2nd and 3rd digit (the digitorum profundus and digitorum superficialis are responsible for this). Compromising the flexor digitorum superficialis, two lateral tendons of flexor digitorum profundus and flexor pollucis longus (in addition to the thenar muscle atrophy) is what leads to the papal benediction sign. At this point we can recognize the limits of the parotid gland. When you have median nerve injury at the distal shaft of the humerus, however, these 3 muscles are compromised (along with a bunch of other hand/wrist flexors, but we're focusing on finger flexors). 4.2.1 Elevation of the cutaneous flap must extend superiorly beyond the caput mandibulae, after dissection of the external auditory canal and ascend anteriorly to the zygomatic arch (posterior portion). Remember- Adduction of thumb is still possible because adductor pollucis is innervated by ulnar nerve. However, the tiny thenar muscles downstream from the carpal tunnel are compromised (abductor pollucis brevis, flexor pollucis brevis, opponens pollucis) and the lateral lumbricals. Thus, flexion of 2nd and third digit, along with thumb, should be fine (e.g. When you have median nerve injury at the wrist (seen in carpal tunnel syndrome), these 3 muscles are fine because they've already been innervated. Since the tendons of these muscles go through the carpal tunnel, the muscles themselves have already been innervated by the median nerve prior to passing through the tunnel. The first two muscles flex the digits at the interphalangeal joints and the other one flexes the thumb.
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The carpal tunnel contains the median nerve and the tendons of 3 muscles: Flexor digitorum superficialis, flexor digitorum profundus and flexor pollucis longus.