The third FDB slip inserts into the middle phalanx of the third toe, providing PIP joint flexion and MTP stability for the third ray. It is slightly smaller than the second slip and works with the third lumbrical and FDL to control third toe alignment during gait.
| Origin | Medial process of the calcaneal tuberosity and plantar fascia |
|---|---|
| Insertion | Middle phalanx of the third toe via two slips |
| Nerve Supply | Medial plantar nerve (S1, S2) |
| Blood Supply | Medial plantar artery |
| Actions | Flexes the PIP joint of the third toe; Assists MTP flexion of the third toe |
|---|
The FDB third slip is involved in third toe hammer toe deformity and in plantar metatarsalgia from third MTP joint instability. Third interspace Morton's neuroma affects the adjacent common digital nerve and may alter FDB third slip loading patterns. Physical therapy targeting intrinsic toe flexors includes FDB strengthening exercises for all lesser toes.
Palpated plantarly over the third proximal phalanx during resisted PIP flexion of the third toe.
Combined MTP hyperextension and PIP flexion from FDB third slip dysfunction and intrinsic muscle imbalance, requiring tendon transfer or arthrodesis for correction.
