Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA
There are seven interosseous muscles of the hand- four dorsal interosseous muscles and 3 palmar interosseous muscles. The muscles arise from the shaft of metacarpal bones and inserted to the base of proximal phalanges. The dorsal interosseous muscles also insert to the extentsor expansion of the corresponding extensor digitorum tendon. There is no insertion of dorsal interosseous into the thumb and little finger and palmar interosseous into the middle finger.
Function of dorsal interossei muscles is to abduct the finger where as the palmar interossei muscles adduct the finger and also assist the lumbricals in flexing the MCP joint and extending the PIP joints through lateral bands and the central slip of extensor digitorum communis which helps in the writing movement of hand.
Nerve supply of all interosseous muscles is by deep branch of ulnar nerve. In case of low ulnar nerve palsy there will be clawing of 4th and 5th fingers. This is due to hyperextension of MCP joint (due to the unopposed pull of long extensors) and flexion of PIP joint (due to the unopposed action of long flexors). The intrinsic muscles are week and cannot extend the PIP joints. The ulnar nerve compression can be assessed by two tests –
Test
Abduction of index finger against resistance : it tests the function of 1st dorsal interosseous muscle. Here the patient is asked to abduct the index finger against resistance the inability to do so indicates severe atrophy of 1st dorsal interosseous muscle which could be due to severe ulnar nerve compression and is a bad prognosis for recovery of this nerve. This can result in claw hand deformity.
Test
Adduction of index finger against resistance- the function of palmar interossei is adduction and the patient is asked to adduct the index finger against resistance. Inability to do so indicates palmar interosseous muscle atrophy.
This helped confirm my findings on an initial exam of a patient who came to her first appointment with the MD’s dx of CTS. However she presented with “stiff hand.” I checked for intrinsic vs extrinsic interossei tightness. She has intrinsic tightness fingers 1-3 the most (thumb and small finger no involved). I love this surgeon’s videos. They are perfect for clinicians of all levels. Thank you! OT Hand Therapist.