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Flexor carpi radialis tendon

The flexor carpi radialis (FCR) tendon is the distal tendinous continuation of the flexor carpi radialis muscle, located in the anterior compartment of the forearm. It plays a key role in wrist flexion and radial deviation, contributing to grip and wrist stabilization during hand movements. The tendon is a useful surgical landmark in wrist procedures and often utilized in tendon grafts or reconstructions due to its length and accessibility.

The tendon passes through its own fibro-osseous tunnel within the flexor retinaculum, separate from the carpal tunnel, and inserts on the base of the second metacarpal, occasionally sending slips to the third metacarpal or trapezium.

Synonyms

  • FCR tendon

  • Tendon of flexor carpi radialis muscle

  • Radial wrist flexor tendon

Origin, Course, and Insertion

  • Origin (muscle): Common flexor tendon from the medial epicondyle of the humerus, with muscular fibers extending into the middle third of the forearm.

  • Course:

    • The tendon forms in the distal third of the forearm and runs along the radial side of the palmar wrist.

    • It passes through a fibro-osseous tunnel formed by a split in the flexor retinaculum (not within the true carpal tunnel).

    • Crosses the wrist joint anteriorly, superficial to the scaphoid and trapezium.

  • Insertion: Base of the second metacarpal bone, occasionally sending additional fibers to the base of the third metacarpal or trapezium.

Tendon Attachments

  • Surrounded by a synovial sheath as it passes beneath the flexor retinaculum.

  • Firmly attached at the base of the second metacarpal, providing stable anchorage for wrist flexion.

  • May have accessory tendinous slips to adjacent metacarpals or carpal bones, especially in athletic or manual labor individuals.

Relations

  • Superficial: Skin and fascia of the distal forearm and wrist.

  • Deep: Flexor pollicis longus tendon, trapezium, and scaphoid bones.

  • Medial: Palmaris longus tendon (if present) and median nerve.

  • Lateral: Radial artery (closely related, separated by a thin fascial layer).

  • Distal: Overlies the flexor retinaculum, inserting at the base of the second metacarpal.

Nerve Supply

  • Median nerve (C6–C7), via its muscular branch before the tendon formation.

Function

  • Flexion of wrist: Acts as a primary wrist flexor.

  • Radial deviation: Works synergistically with the extensor carpi radialis longus and brevis to abduct the wrist.

  • Dynamic stabilization: Maintains wrist alignment during gripping and precision movements.

  • Secondary functions: Assists with forearm pronation and tension balance between radial and ulnar flexors.

Clinical Significance

  • Tendinitis / Tenosynovitis: Common in repetitive wrist flexion or pronation; produces pain over the radial wrist.

  • Partial or complete tear: May occur with trauma or chronic degeneration; leads to weakness in wrist flexion.

  • FCR tunnel syndrome: Compression or inflammation within its fibro-osseous canal causes localized tenderness over the trapezium.

  • Surgical relevance: FCR tendon frequently used for ligament reconstruction, basal thumb arthroplasty, and tendon grafting procedures.

  • Imaging role: MRI and CT are crucial for evaluating tendinopathy, partial tears, entrapment, and post-surgical assessment.

MRI Appearance

  • T1-weighted images:

    • Tendon: Low signal (dark), sharply defined linear structure.

    • Surrounding fat: Bright, providing natural contrast.

    • Muscle belly: Intermediate signal intensity proximally.

    • Pathology: Tendinopathy may show intermediate signal thickening; tears show discontinuity or focal bright gaps.

  • T2-weighted images:

    • Normal tendon: Low signal (black) with smooth contours.

    • Pathology: Increased signal within tendon substance or sheath in tenosynovitis.

    • Partial tear: Focal bright hyperintense clefts, often at or near insertion.

    • Chronic degeneration: Mildly hyperintense thickened tendon with irregular margins.

  • STIR:

    • Normal tendon: Dark flow void appearance.

    • Pathology: Bright hyperintense peritendinous or intratendinous signal in acute inflammation or strain.

    • Surrounding soft-tissue edema easily detected.

  • Proton Density Fat-Saturated (PD FS):

    • Normal: Dark homogeneous tendon structure.

    • Pathologic: Bright signal within or around tendon indicating edema, inflammation, or tear.

    • Excellent for distinguishing partial tears from tendinopathy and for detecting sheath fluid.

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: Minimal or no enhancement.

    • Inflamed tendon sheath (tenosynovitis): Linear or circumferential enhancement.

    • Tear: Peripheral enhancement surrounding fluid-filled tendon gap.

    • Post-surgical or chronic changes: Fibrosis enhances heterogeneously with low central signal.

CT Appearance

Non-Contrast CT:

  • Tendon: Soft-tissue density linear band along radial wrist.

  • Bony insertion: Base of second metacarpal may show cortical irregularity in chronic traction or degeneration.

  • Calcific tendinitis: Seen as high-density foci within tendon near insertion.

  • Useful in: Detecting calcifications, bone erosion, or postoperative anchor placement.

Post-Contrast CT (standard):

  • Normal tendon: No direct enhancement, though surrounding soft tissues may enhance mildly.

  • Inflammation or scarring: Focal or diffuse enhancement along tendon sheath.

  • Chronic tendinopathy: Thickened tendon with adjacent soft-tissue enhancement.

  • Valuable for evaluating entrapment, chronic scarring, or mass effect from post-surgical changes.