providing a stable base against which the thumb pinches. It is a function largely of the first dorsal interosseous muscle.
Tendons most frequently used are extensor indices, EPB, palmaris longus, APL
Extensor Indices transfer – simply take the EI insertion off the ulnar aspect of the extensor hood, then transfer it radially to the insertion of the first dorsal interosseous.
Abductor Pollicis Longus transfer – identify a slip of APL (usually there are two) and route it via a free palmaris longus graft to the insertion of the first dorsal interosseous
Restoring Intrinsic Function
– low median and ulnar nerve lesions cause paralysis of the intrinsics, but spare the long extrinsics to act unopposed, resulting in a clawhand.
– without the intrinsics, grasp strength is diminished by 50% because of lack of flexion at the MCP joints; also, the dynamics of finger flexion are altered, so that the fingers ï¿½roll upï¿½ rather than flex properly – flexion begins distally at the DIP joints. This makes it difficult to grasp large objects.
– it should be noted that the long extensors ARE able to extend the fingers fully, but only when the MCP joints are stable and not hyperextended (when hyperextended, the long extensors exert and lose all their power at the level of the MCPs and cannot act at the PIP or DIP joints)
Techniques to restore intrinsics
One approach is to just stabilize the MCPs so that they donï¿½t fall into hyperextension (this allows the fingers to be flexed by the extrinsics and extended by the extrinsics.
Zancolli – volar capsulodesis
Riordan – tenodesis
The other approach is to perform tendon transfers that will extend the IP joints and flex the MCP. There are many procedures advocated – all are based on the principle of moving something volar to the deep transverse metacarpal ligament, then back up to the dorsal hood.
Bunnell – FDS transfer from volar to dorsal hood (often makes the strong PIP flexor into too strong of an extensor, creating an intrinsic plus deformity – can be avoided by only taking one of the two slips of FDs)
Fowler – split extensor communis tendon from index and little fingers to form four slips, which are then re-routed volar to the deep transverse metacarpal ligament and then back dorsally to the extensor hood of each finger.
Riordan – FCR transferred dorsally to a free plantaris graft divided into four slips, each then passed through the interossei to lie volar to the deep transverse metacarpal ligament. Good for when a wrist flexion contracture exists.