What is the origin of the flexor carpi ulnaris (FCU) and flexor carpi radialis (FCR) muscles?

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Anatomical Origin of Flexor Carpi Ulnaris and Flexor Carpi Radialis

The flexor carpi ulnaris originates from two heads: a humeral head from the medial epicondyle (as part of the common flexor tendon) and an ulnar head from the medial border of the olecranon and posterior border of the ulna, while the flexor carpi radialis originates from the medial epicondyle as part of the anterior common tendon. 1

Flexor Carpi Radialis Origin

The FCR converges with other superficial flexor muscles to form a common tendon at the medial epicondyle called the anterior common tendon (ACT). 1

  • The ACR includes the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis, all sharing this proximal attachment point. 1
  • This common tendon attaches to the medial epicondyle and joint capsule, positioned just anterior and parallel to the anterior bundle of the medial ulnar collateral ligament. 1
  • The histological structure of this common tendon is remarkably similar to ligamentous tissue, suggesting it contributes to dynamic elbow stabilization during valgus stress. 1

Flexor Carpi Ulnaris Origin

The FCU has a dual origin that distinguishes it from other flexor-pronator muscles:

Humeral Head

  • Arises from the medial epicondyle as part of the common flexor origin, though it is positioned more posteriorly than the FCR. 1

Ulnar Head

  • The ulnar head originates from the medial border of the olecranon and the posterior border of the proximal two-thirds of the ulna. 2, 3
  • This ulnar head was observed in 92.3% of specimens, positioned just behind the humeral head. 1
  • The upper portion of the ulnar head transitions directly into the thickened joint capsule anterior to the anterior bundle of the medial ulnar collateral ligament. 1
  • The proximal attachment extends from the tubercle (the most medial prominent part of the coronoid process) posteriorly to the olecranon. 3

Clinical Significance

The FCU consists of two distinct neuromuscular compartments (humeral and ulnar), which allows for potential surgical splitting of the muscle while preserving wrist function. 2

  • The ulnar nerve innervates the FCU through 2-4 motor branches, with the first branch typically arising approximately 1.4 cm distal to the medial epicondyle. 4
  • However, in approximately 13% of cases, the first FCU branch may arise at or proximal to the medial epicondyle (up to 2 cm above). 4
  • Despite common misconception, sparing of FCU in ulnar neuropathy at the elbow is not related to the level of origin of its innervating branch, but rather to internal neural topography and the severity and level of nerve compression. 5

References

2
Research

Case report: the split flexor carpi ulnaris as a local muscle flap.

Clinical orthopaedics and related research, 2007

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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