What muscles, vessels, and tendons are seen in the context of a second metacarpal fracture?

Muscles, Vessels, and Tendons in Second Metacarpal Fractures

In the context of a second metacarpal fracture, the key anatomical structures visible include the extensor tendons dorsally, flexor tendons volarly, intrinsic hand muscles, and digital vessels. 1

Dorsal Structures

Tendons

• Extensor tendons:
  • Extensor digitorum communis tendon overlying the metacarpal head 1
  • Extensor indicis proprius (specific to the index finger)
  • These tendons are clearly visible on dorsal transverse and longitudinal scans 1

Muscles

• Dorsal interossei muscles:
  • First dorsal interosseous muscle (between thumb and index metacarpals)
  • Second dorsal interosseous muscle (between index and middle metacarpals)
  • These muscles are particularly vulnerable to dysfunction with metacarpal shortening 2

Volar Structures

Tendons

• Flexor tendons:
  • Flexor digitorum superficialis
  • Flexor digitorum profundus
  • These tendons are visible on palmar longitudinal and transverse scans 1

Muscles

• Intrinsic hand muscles:
  • Lumbrical muscles (originating from the flexor digitorum profundus tendons)
  • Palmar interossei muscles (adduct fingers toward the middle finger)

Neurovascular Structures

Vessels

• Digital arteries:
  • Proper digital arteries running along the sides of the finger
  • Common digital arteries in the palm branching from the superficial palmar arch

Nerves

• Digital nerves:
  • Branches of the median nerve (radial side)
  • Branches of the ulnar nerve (ulnar side)
  • Median nerve can be visualized on volar transverse scans at the carpal tunnel 1

Clinical Implications in Metacarpal Fractures

Functional Considerations

• Metacarpal shortening of just 2mm can result in approximately 8% loss of interosseous muscle power 2
• At 10mm shortening, interosseous muscles may only generate about 55% of optimal power 2
• Extensor tendon subluxation can occur with fractures that disrupt the sagittal bands 3

Imaging Considerations

• Ultrasound allows dynamic examination of tendon function and integrity 1
• MRI is ideal for evaluating associated tendon injuries and surgical planning 1
• Dorsal transverse scans at the metacarpal head can visualize the extensor tendons and metacarpal head 1
• Palmar longitudinal scans can visualize the joint cavity, articular cartilage, and flexor tendons 1

Potential Complications

• Extensor tendon subluxation, particularly ulnar subluxation of the extensor digitorum communis 3
• Interosseous muscle dysfunction with metacarpal shortening 2
• Tendon adhesions or tears requiring surgical repair 1
• Stiffness of the metacarpophalangeal joint if early mobilization is not implemented 4

Early mobilization is critical following metacarpal fracture treatment to prevent stiffness and restore function, particularly when open reduction and internal fixation is performed 4.