Anatomy and Location
The muscle lies in the deep layer of the forearm, positioned medially, while the m. flexor pollicis longus lies laterally.
- Origin (origo) — anterior and medial surfaces of the ulna and the membrana interossea.
- Insertion (insertio) — base of the distal phalanges of digits II–V.
At the level of the proximal phalanges, the tendons of the flexor digitorum profundus pass through the split tendons of the m. flexor digitorum superficialis (chiasma tendineum) before continuing onward to insert onto the distal phalanges.
Function
- Finger Flexion — flexes the distal interphalangeal joints of digits II–V.
- Wrist Flexion — assists in flexing the wrist.
- Lumbrical Origin — the mm. lumbricales I–IV originate from the radial sides of the flexor digitorum profundus tendons. They flex the metacarpophalangeal joints and extend the interphalangeal joints (the "lumbrical plus" or writing position).
Blood Supply and Innervation
The muscle receives dual innervation:
- Medial (ulnar) part — innervated by the n. ulnaris; flexes the distal phalanges of digits IV and V.
- Lateral (radial) part — innervated by the anterior interosseous nerve, a branch of the n. medianus; flexes the distal phalanges of digits II and III.
Blood supply is provided by two main arteries:
- A. ulnaris
- A. interossea anterior, which runs along the interosseous membrane deep to the flexor pollicis longus and flexor digitorum profundus, supplying branches to both.
Topography and Related Structures
Several structures of the forearm, wrist, and hand are closely associated with the flexor digitorum profundus:
- In the forearm — a. ulnaris, m. flexor digitorum superficialis, and the deep fascial space of Pirogov-Parona.
- At the wrist — tendines m. flexor digitorum profundus passing deep to the retinaculum mm. flexorum (carpal tunnel).
- In the hand and digits — vagina communis musculorum flexorum (ulnar bursa), vagina synovialis tendinis flexoris, and vagina fibrosa tendinis flexoris digital sheaths.