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Inferior peroneal retinaculum

The inferior peroneal (fibular) retinaculum is a fibrous band located on the lateral aspect of the ankle, forming part of the fibular retinacular complex that stabilizes the peroneal tendons as they course behind the lateral malleolus and onto the lateral calcaneus. It is the lower of the two peroneal retinacula, the superior one being located above it.

The inferior retinaculum anchors the peroneus longus and peroneus brevis tendons in their grooves on the lateral calcaneus, preventing subluxation or dislocation during ankle motion. It contributes significantly to ankle stability, particularly during eversion and plantarflexion movements.

Synonyms

  • Inferior fibular retinaculum

  • Inferior peroneal ligament

  • Lower peroneal retinacular band

Origin, Course, and Insertion

  • Origin: Lateral surface of the calcaneus, just anterior and inferior to the peroneal trochlea

  • Course: Passes obliquely upwards and posteriorly over the peroneal tendons

  • Insertion: Blends superiorly with the inferior extensor retinaculum and with fibers of the calcaneal periosteum posteriorly

  • Configuration: Forms a Y-shaped or fan-like structure, which divides into bands surrounding the peroneal tendon sheath

Tendon Attachments

  • Encloses the peroneus longus and peroneus brevis tendons in a common synovial sheath

  • Secures tendons in the retromalleolar groove and along the lateral wall of the calcaneus

  • Acts as a strong retentive band to prevent peroneal tendon dislocation during foot eversion

Relations

  • Superiorly: Continuous with the inferior extensor retinaculum

  • Inferiorly: Blends with the lateral calcaneal fascia and the abductor digiti minimi fascia

  • Anteriorly: Related to the lateral surface of the calcaneus and peroneal trochlea

  • Posteriorly: Covers the peroneal tendons and their common sheath

  • Deep: Closely associated with the peroneus brevis tendon and lateral calcaneal wall

  • Superficial: Covered by subcutaneous tissue and skin of the lateral ankle

Function

  • Tendon stabilization: Secures the peroneus longus and brevis tendons within their grooves during movement

  • Prevents dislocation: Stops peroneal tendons from snapping or subluxing over the lateral malleolus during eversion

  • Reinforcement: Strengthens the lateral ankle wall and peroneal sheath

  • Kinematic support: Assists coordinated ankle eversion and plantarflexion

  • Protective role: Reduces friction and stabilizes the tendon sheath during dynamic ankle movements

Clinical Significance

  • Tear or rupture: May cause peroneal tendon subluxation, often associated with ankle sprains or chronic instability

  • Thickening or scarring: Can lead to tendinopathy or frictional irritation of the peroneal tendons

  • Avulsion: Rarely, calcaneal avulsion can occur at the retinacular attachment after high-energy trauma

  • Surgical relevance: Frequently examined or repaired during lateral ankle stabilization procedures

  • Imaging relevance: MRI and CT help evaluate retinacular integrity and tendon dislocation

MRI Appearance

  • T1-weighted images:

    • Retinaculum appears as a thin, low-signal (dark) linear band overlying the peroneal tendons

    • The peroneal tendons show intermediate signal

    • Discontinuity or thickening of the retinaculum indicates partial or complete tear

    • Fat around the tendons appears bright, helping outline the structure

  • T2-weighted images:

    • Normal retinaculum remains low signal (dark)

    • Pathology such as tear or inflammation shows hyperintense signal within or around the retinaculum

    • Peroneal tendon subluxation may show abnormal tendon displacement relative to the fibula or calcaneus

    • Peritendinous fluid appears bright, highlighting inflammation or sheath distension

  • STIR:

    • Normal retinaculum: dark linear band

    • Pathologic conditions (edema, tear, inflammation): bright hyperintense signal around peroneal tendons and retinaculum

  • Proton Density Fat-Saturated (PD FS):

    • Normal: low-signal fibrous band superficial to peroneal tendons

    • Partial tears: focal bright signal with thickening

    • Complete rupture: discontinuity with peroneal tendon displacement

    • Excellent for visualizing subtle inflammatory changes and tenosynovitis

  • T1 Fat-Sat Post-Contrast:

    • Normal retinaculum: minimal enhancement

    • Inflamed or repaired retinaculum: linear or patchy enhancement

    • Adjacent peroneal tendon sheath may enhance with synovial inflammation or granulation tissue

CT Appearance

Non-Contrast CT:

  • Retinaculum itself not distinctly visualized, but soft-tissue thickening or calcaneal avulsion may be seen

  • Peroneal tendons appear as linear soft-tissue densities in the retromalleolar groove

  • Useful for identifying bony avulsions or calcaneal irregularities at the retinacular attachment

Post-Contrast CT (standard):

  • Enhances surrounding soft-tissue inflammation or scarring

  • Retinacular defects or thickened bands may appear as irregular soft-tissue structures along the lateral calcaneus

  • Assists in identifying chronic scarring or postsurgical changes

MRI image

Inferior peroneal (fibular) retinaculum axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Inferior peroneal (fibular) retinaculum axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Inferior peroneal (fibular) retinaculum coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

CT image

Inferior Peroneal (Fibular) Retinaculum ct axial