The fourth FDB slip is smaller than the second and third slips, reflecting the reduced load-bearing role of the fourth ray. It inserts into the fourth middle phalanx after splitting for FDL passage. Its loss contributes to fourth toe claw deformity in intrinsic minus foot.
| Origin | Medial process of the calcaneal tuberosity and plantar fascia |
|---|---|
| Insertion | Middle phalanx of the fourth toe via two slips |
| Nerve Supply | Medial plantar nerve (S1, S2) |
| Blood Supply | Lateral plantar artery (distal branches) |
| Actions | Flexes the PIP joint of the fourth toe; Assists MTP flexion of the fourth toe |
|---|
The FDB fourth slip is atrophied in peripheral neuropathy affecting the medial plantar nerve. Fourth toe deformities are less common than second and third toe problems. The FDB fourth slip may be absent in individuals with congenital absence of the fourth toe middle phalanx (brachymetatarsia). Evaluation of fourth toe intrinsic strength requires specific testing with the foot in neutral.
Palpated plantarly over the fourth proximal phalanx during resisted PIP flexion of the fourth toe.
Loss of FDB fourth slip function in neuropathy or fibrosis producing fourth toe MTP instability and crossover tendency managed with orthotic support and toe-stabilising exercises.
