Quadratus Plantae Muscle: Anatomy, Function, Imaging

Topic

Quadratus plantae muscle

The quadratus plantae (also called the flexor accessorius) is a small but important intrinsic muscle of the sole of the foot. It arises from the calcaneus and inserts into the tendon of the flexor digitorum longus (FDL). By correcting the oblique pull of the FDL, it assists in producing straight flexion of the lateral four toes.

It lies deep within the sole, beneath the flexor digitorum brevis and lumbricals, and has two distinct heads of origin. The muscle is clinically important in maintaining toe flexion mechanics and is sometimes involved in foot pain syndromes, entrapment neuropathies, or muscular atrophy in chronic neuropathic disease.

Synonyms

Flexor accessorius
Plantar quadratus

Origin, Course, and Insertion

Origin:
- Medial head: medial surface of the calcaneus and medial border of the long plantar ligament
- Lateral head: lateral surface of the calcaneus
Course: Fibers run forward and medially within the sole, deep to the flexor digitorum longus tendons.
Insertion: Lateral margin of the flexor digitorum longus tendon in the sole, before its division into slips for the lateral four toes.

Tendon Attachments

Inserts directly into the FDL tendon, modifying its line of pull.
Lacks its own independent tendon to the toes.

Relations

Superiorly: Flexor digitorum longus tendons
Inferiorly: Plantar aponeurosis and flexor digitorum brevis
Medially: Medial head of quadratus plantae near calcaneus
Laterally: Lateral head, separated by septum from abductor digiti minimi

Nerve Supply

Lateral plantar nerve (branch of tibial nerve), fibers from S1–S3

Arterial Supply

Branches of the medial and lateral plantar arteries (terminal branches of the posterior tibial artery)

Venous Drainage

Tributaries of the medial and lateral plantar veins, draining into the posterior tibial vein

Function

Toe flexion assistance: Corrects oblique pull of the flexor digitorum longus to produce straight toe flexion
Force modulation: Helps maintain even pressure across toes during stance and propulsion
Gait role: Provides stability to the longitudinal arch and aids push-off during walking and running

Clinical Significance

Muscle weakness/atrophy: Seen in tibial nerve or lateral plantar nerve lesions
Foot pain: Can contribute to plantar foot pain and imbalance of toe flexion
Entrapment neuropathy: Compression of the lateral plantar nerve affects quadratus plantae function
Surgical importance: Must be preserved during plantar surgical approaches to maintain proper toe mechanics

MRI Appearance

T1-weighted images:
- Normal quadratus plantae: intermediate signal intensity
- Fat planes between muscle bellies: bright
- Tears/atrophy: focal high-signal fat infiltration or volume loss
T2-weighted images:
- Normal: intermediate signal, darker than T1
- Pathology: edema or inflammation produces focal bright hyperintense areas
- Muscle tears: high-signal intensity defect with surrounding edema
STIR:
- Normal muscle: intermediate-to-dark
- Pathology: bright hyperintensity with edema, denervation, or inflammation
Proton Density Fat-Saturated (PD FS):
- Normal: intermediate-to-dark homogeneous signal
- Pathology: focal bright signal intensity in muscle belly or tendon insertion, showing tear, strain, or inflammation
T1 Fat-Sat Post-Contrast:
- Normal: minimal homogeneous enhancement
- Pathology: enhancement in inflammatory or infectious changes, postoperative scarring, or neoplasm

CT Appearance

Non-Contrast CT:

Muscle: soft-tissue density, not sharply delineated
Indirect signs of pathology: calcification, fatty infiltration, or asymmetry compared to contralateral side

Post-Contrast CT (standard):