Layer-by-layer structure and innervation of the dorsum of the hand
On the dorsum of the hand, all metacarpal bones are easily palpable through the skin, and upon maximal extension, the taut extensor tendons are clearly visualized. The skin here is significantly thinner than on the palm, and the subcutaneous tissue is poorly developed and has a loose structure. Hair of varying degrees of density is present on the dorsal surface of the proximal phalanges.
Sensory innervation of the skin of the dorsal hand is strictly divided between two nerves:
- Ulnar side: innervated by the dorsal branch of the ulnar nerve (r. dorsalis n. ulnaris). It originates at the apex of the ulnar styloid process and divides into five dorsal digital nerves (nn. digitales dorsales). They provide sensation to the skin of the 5th, 4th digits, and the ulnar side of the 3rd digit.
- Radial side: innervated by the superficial branch of the radial nerve (r. superficialis n. radialis). It originates at the apex of the radial styloid process, also gives off five branches, and innervates the 1st, 2nd digits, and the radial side of the 3rd digit.
Fascia, muscles, and fascial spaces
The superficial fascia (fascia dorsalis manus) is well-defined on the dorsum of the hand. Its most important topographical feature is firm fixation to the bones: on the radial side, it fuses with the 2nd metacarpal bone, and on the ulnar side, with the 5th metacarpal bone. Deeper lies the deep fascia, which covers the second, third, and fourth dorsal interosseous muscles. Notably, absolutely all interosseous muscles of the hand (both dorsal and palmar) receive motor innervation from the deep branch of the ulnar nerve.
Between the superficial and deep fascia lies the subaponeurotic space of the dorsum of the hand, bounded laterally by the sites of fascial attachment to the 2nd and 5th metacarpal bones. The main contents of this space are the extensor tendons of the digits.
The topography of the first intermetacarpal space is distinguished separately. It is occupied by the well-developed first dorsal interosseous muscle. Its anterior (palmar) surface adheres to the adductor pollicis muscle (m. adductor pollicis), which belongs to the thenar compartment. These two muscles are reliably separated by a dense fascial plate.
Topography of tendons and synovial sheaths of the digits
On the palmar surface of the digits, the flexor tendons have a complex interrelationship. The most proximal annular ligament is located at the level of the metacarpophalangeal joint. At the level of the head of the proximal (base) phalanx, the tendon of the superficial flexor splits into two slips that attach to the lateral surfaces of the middle phalanx. The tendon of the deep flexor passes through the resulting cleft to attach to the base of the distal phalanx.
The synovial sheaths of the 2nd, 3rd, and 4th digits are isolated. The synovial sheath (vagina synovialis) consists of two layers:
- Parietal layer — adheres to the inner surface of the fibrous sheath.
- Visceral layer (epitenon) — directly covers the tendon itself.
At the transition point from one layer to the other, the mesotendineum (mesotendineum) is formed. It contains blood vessels and nerves running from the phalanx periosteum to nourish the tendon. The mesotendineum is absent in the region of the interphalangeal joints. Surgical or traumatic damage to the mesotendineum leads to inevitable necrosis of the corresponding part of the tendon.
Extensor apparatus and movement features
In the subaponeurotic space at the level of the metacarpal heads between the extensor tendons lie intertendinous connections (connexi intertendinei). Their functional significance is immense: because of them, full extension of the 3rd and 4th digits is possible only together. The index (2nd) digit and little finger (5th) have independent extensor muscles, thus fully retaining independent movement.
On the dorsum of the digit itself, the extensor tendon divides: its middle part attaches to the base of the middle phalanx, and the two lateral parts continue and attach to the base of the distal phalanx. An aponeurotic expansion is formed over the proximal phalanx. The tendons of the lumbrical and interosseous muscles attach to it. This biomechanics allows these muscles to perform a combined function: flexing the proximal phalanges while simultaneously extending the middle and distal ones.
Briefly: answers to topical questions
What are the contents of the subaponeurotic space of the dorsum of the hand?
The contents of the subaponeurotic space of the dorsum of the hand include the extensor tendons of the digits. At the level of the metacarpal heads between the tendons lie intertendinous connections (connexi intertendinei). Due to these structures, extension of the 3rd and 4th digits is possible only together. Meanwhile, the index finger and little finger retain full independence of movement due to the presence of independent extensor muscles.
Which hand muscles are innervated by the deep branch of the ulnar nerve?
The deep branch of the ulnar nerve innervates:
- hypothenar muscles: the abductor digiti minimi (m. abductor digiti minimi), opponens digiti minimi (m. opponens digiti minimi), and flexor digiti minimi brevis (m. flexor digiti minimi brevis);
- 3rd and 4th lumbrical muscles (mm. lumbricales);
- all palmar and dorsal interosseous muscles (mm. interossei palmares et dorsales);
- adductor pollicis muscle (m. adductor pollicis);
- deep head of the flexor pollicis brevis (m. flexor pollicis brevis).
The "2.5 to 2.5" rule of dorsal hand innervation: the radial nerve from the thumb side innervates exactly two and a half digits (1st, 2nd, and the radial half of the 3rd), while the ulnar nerve from the little finger side innervates the remaining two and a half (5th, 4th, and the ulnar half of the 3rd).
Class and exam questions
Why cannot the 3rd and 4th digits be fully extended independently?
At the level of the metacarpal heads between their tendons lie dense intertendinous connections (connexi intertendinei). Because of this, extension of these digits is possible only together. Exceptions are the 2nd and 5th digits, which have independent extensors.
What is the danger of damage to the mesotendineum?
The mesotendineum (mesotendineum) carries nourishing blood vessels and nerves from the periosteum to the tendon. Damage to it, including during careless surgery, inevitably leads to necrosis of the corresponding tendon segment.
Where does infection spread from the dorsum of the hand?
The subcutaneous tissue of the dorsal subaponeurotic space communicates proximally with the carpal canals. Through them, a purulent process can unhinderedly spread into the posterior fascial compartment of the forearm.
Where do the neurovascular bundles run on the fingers?
Dorsal digital arteries, veins, and nerves run in the weak, loose subcutaneous tissue on the lateral surfaces of the digits, located closer to the dorsal side.
What else to study on this topic
- Anatomy of the fibrous sheaths of the fingers and annular ligaments
- Cross-section of a finger at the level of the middle phalanx: syntopy of structures
- Pathways of purulent process spread through the carpal canals
- Topography of the thenar compartment and adductor pollicis muscle
Master the complete topic in the "Topographic Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Dorsum of the hand and fingers" and 2,777 more pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 91 video lessons on the subject
Other topics in the "Upper Extremity" section
Free video lessons: topographic anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.