anatomy and physiology mcqs

Question #110

Considering the interossei of the hand, which of the following statements is incorrect?

The palmar interossei arise from the anterior aspect of the metacarpal bones of the 2nd, 4th and 5th digits. They have only one head and insert into the base of the proximal phalanx and the extensor expansion of the digit from which they arise. They act to adduct the fingers – in the hand the middle finger is taken as the midline and so the middle finger cannot adduct towards itself! It therefore has no palmar interossei.

The number of palmar interossei still remains debated. Some textbooks will say there are only three while others will consider there to be a ‘pollical palmar interosseous muscle’. Some studies have found this muscle to be present in as many as 86% of cadavers.

The dorsal interossei are bipennate, they arise from the metacarpal from which they insert and the adjacent metacarpal. As the palmar interossei they insert into the base of the proximal phalanx and the extensor expansion, but they abduct the fingers. Since the middle finger is considered to be the midline this digit can be abducted either medially or laterally and so has two dorsal interossei. Neither the little finger nor thumb have a dorsal interossei muscle making a total of 4.

Both groups of interossei are innervated by the deep branch of the ulnar nerve and act with the lumbricals to flex the metacarpophalangeal joints and extend the interphalangeal joints.

Remember: PAD and DABI (Palmar ADduct, Dorsal ABduct and are BIpennate).

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