I

Smaller thumb, all structures present

No intervention

II

Hypoplastic thenar muscles, There is also hypoplasia of thumb metacarpal, phalanges and radial carpal bones. There may be only one neurovascular bundle. Narrow first web space. Instability of MCP joint especially UCL

Increase the first web space, stabilize the MCP joint, improve opposition, and improve flexion and extension at the IP joint

III

Absent thenar muscles, very reduced first web space, ulnar collateral ligament instability of the MCP joint. Varying degrees of partial aplasia of the proximal thumb metacarpal, and thumb extrinsic muscles (EPL, APL, EPB, FPL)

IIIa

With a CMC joint, and hypoplastic extrinsic muscles

As type II

IIIb

Without a CMC joint, and thumb extrinsic extensors absent

Debatable: some argue for reconstruction, others for removal and pollicization

IV

Pouce flottant, (floating thumb or pendel daumen). No metacarpal or musculo-tendinous structures

Pollicization of the index finger

V

Absent thumb

Pollicization of the index finger