Lower limb

Plantar interossei

Musculi interossei plantares

Origin

Medial side of the shaft of metatarsals 3, 4 and 5 (unipennate)

Insertion

Medial side of the base of the proximal phalanx and the extensor expansion of toes 3-5

Function

Adduction of toes 3-5 toward the second toe, flexion of the MTP joints and extension of the IP joints

Innervation

Lateral plantar nerve

Movement & chain

Work together with the dorsal interossei and the lumbricals in the 'intrinsic plus' movement (MTP flexion with IP extension), essential during foot rollover.

Palpation

Deep between metatarsal shafts on the plantar aspect; not individually palpable.

Clinical

Adduct digits 3–5 toward the second toe; intrinsic foot muscle imbalance leads to metatarsalgia and hammer toe deformities.

Segmental innervation

S1-S2 (lateral plantar nerve).

In clinical practice

Diabetic foot inspection and pressure ulcer prevention; monitor for friction points from footwear or bedding and ensure correct anti-embolism stocking fit.

Region in the model

Lower limb