What muscles insert onto the tips of the fingers?

Muscles That Insert onto the Tips of Fingers

The flexor digitorum profundus (FDP) is the primary muscle that inserts onto the tips of the fingers, specifically attaching to the base of the distal phalanx of each finger. This muscle is responsible for flexion of the distal interphalangeal joints of the fingers.

Anatomical Insertions

Flexor Digitorum Profundus (FDP)

• Originates from the anterior and medial surfaces of the ulna and interosseous membrane
• Divides into four tendons that pass through the carpal tunnel
• Each tendon passes through a split in the flexor digitorum superficialis tendon (Camper's chiasm)
• Inserts onto the base of the distal phalanx of each finger (index, middle, ring, and little fingers)
• The insertion has specific dimensions 1:
  • Average insertion length: 6.2 mm (range 5.1-7.0 mm)
  • Average insertion width: 7.9 mm (range 6.9-8.4 mm)
  • Average surface area: 20% of the distal phalanx (range 15-27%)
  • Average distance from joint surface: 1.2 mm (range 0.4-2.1 mm)
  • Centroid of insertion: approximately 3.6 mm from the distal interphalangeal joint

Extensor Mechanism

While not directly inserting on the fingertips, the extensor mechanism contributes to finger extension:

• The extensor digitorum communis divides into tendons that form the extensor expansion (hood)
• The central slip inserts onto the middle phalanx
• The terminal tendon inserts onto the base of the distal phalanx on the dorsal aspect

Clinical Significance

Injuries and Pathology

• FDP avulsion ("Jersey finger"): Occurs when the FDP tendon is torn from its insertion at the distal phalanx, typically during forced extension while the finger is actively flexed
• MRI is ideal for evaluating these tendon injuries and helping with surgical planning 2
• In Jersey finger cases, MRI can evaluate:
  • Level of tendon retraction
  • Quality of the tendon stump
  • Associated injuries including pulley injuries

Anatomical Variations

• Rare variations in FDP insertion have been documented:
  • Absence of the FDP for the little finger has been reported 3
  • Variations in the fourth lumbrical muscle insertion can affect finger mechanics 4

Diagnostic Imaging

• MRI is the preferred imaging modality for evaluating tendon injuries of the hand 2
• Ultrasound can be useful for evaluating flexor tendons and tendon sheaths, particularly in trigger finger 5

Functional Importance

The FDP is the only muscle that can flex the distal interphalangeal joint of the fingers. This function is critical for:

• Precision grip
• Power grip
• Fine motor activities requiring fingertip control

Understanding the precise insertion of the FDP is crucial for hand surgeons when repairing zone I injuries (distal to the superficialis insertion) to ensure proper tendon reattachment and restore function.