What does the Flexor Carpi Radialis (FCR) insert onto?

Insertion of the Flexor Carpi Radialis (FCR)

The flexor carpi radialis tendon primarily inserts onto the base of the second metacarpal bone, with secondary insertions onto the base of the third metacarpal and the trapezium.

Anatomical Insertions of the FCR

The FCR has a complex insertion pattern that includes:

1. Primary insertion (80%): Base of the second metacarpal bone 1
2. Secondary insertions:
   • Base of the third metacarpal (20%) 1
   • Small slip to the trapezial crest or tuberosity 1

Anatomical Course and Relationships

The FCR follows a specific path before reaching its insertion points:

• The musculotendinous portion begins approximately 15 cm proximal to the radiocarpal joint 1
• Muscular fibers end about 8 cm proximal to the wrist 1
• The tendon enters a fibro-osseous tunnel at the proximal border of the trapezium 1
• Within this tunnel, the tendon occupies 90% of the available space and directly contacts the trapezium 1
• The tendon passes in close proximity to:
  • Distal aspect of the radius
  • Scaphoid tubercle
  • Scaphoid-trapezium-trapezoid joint
  • Carpometacarpal joint of the thumb 1

Variations in FCR Insertion

Recent research has identified variations in the FCR insertion pattern:

• Six different types of insertions have been documented based on their positions on the carpal and metacarpal bones 2
• The insertion can sometimes include attachments to the scaphoid in addition to the standard insertions 2

Clinical Significance

Understanding the FCR insertion is important for:

1. Biomechanical function: The FCR uses the scaphoid tuberosity as a pulley to reach its distal insertion, which affects carpal mechanics 3

2. Wrist stability: When the FCR contracts, it causes the scaphoid to rotate into flexion and supination while the triquetrum rotates into flexion and pronation, affecting scapholunate joint dynamics 3

3. Surgical considerations: The deep palmar arch is located only 2-3 mm distal to the FCR insertion, making this an important anatomical landmark during surgical procedures 1

Anatomical Variations

Accessory muscular bundles of the FCR have been documented:

• Found in approximately 5.88% of cadavers 2
• Can be bilateral or unilateral 2
• Four types of variations with accessory muscular bundles have been classified based on their origin and relationships with surrounding structures 2

Additionally, a rare anomalous muscle called the flexor carpi radialis brevis (FCRB) can be present:

• Incidence varies between 2-8% 4
• Originates from the volar surface of the distal radius 4
• May cause clinical symptoms or be encountered during surgical procedures 4

Understanding these anatomical details is crucial for accurate diagnosis, effective surgical planning, and proper treatment of hand and wrist conditions.