The Dorsum of the Hand and Dorsal Tendinous Sheaths

The Dorsum of the Hand and Dorsal Tendinous Sheaths

The dorsum of the hand refers to the back of the hand, which contains several structures, including tendons, muscles, and bones. It plays an important role in the extension of the fingers and the wrist. The dorsal tendinous sheaths are specialized structures that protect and guide the tendons of the muscles responsible for extending the fingers and wrist. These sheaths are crucial for the proper movement and function of the hand.

Anatomy of the Dorsum of the Hand

The dorsum of the hand is characterized by several features that enable movement and provide support:

1. Skin and Subcutaneous Tissue

  • The skin on the dorsum of the hand is thinner than the skin on the palm and is covered with hair follicles.

  • Beneath the skin lies a layer of subcutaneous tissue that contains the extensor tendons, blood vessels, and nerves.

2. Bones of the Dorsum of the Hand

  • The dorsum is supported by the bones of the metacarpals (which form the back of the hand) and the phalanges of the fingers.

  • The carpals (wrist bones) articulate with the metacarpals to allow for wrist movement, while the metacarpals connect to the phalanges to allow finger movement.

3. Tendons of the Dorsum of the Hand

  • The tendons on the dorsum are primarily responsible for the extension of the fingers and wrist.

  • These tendons pass through dorsal tendinous sheaths to protect and facilitate their movement.

Dorsal Tendinous Sheaths

The dorsal tendinous sheaths are specialized synovial structures that enclose and protect the tendons of the extensor muscles of the hand. These sheaths help reduce friction and ensure smooth movement of the tendons as they pass over the bony structures of the wrist and fingers.

1. Extensor Tendons of the Dorsum of the Hand

  • The extensor tendons are responsible for the extension of the fingers and the wrist. These tendons are primarily derived from the extensor muscles in the forearm:

    • Extensor Digitorum (ED): Extends the MCP, PIP, and DIP joints of the fingers.

    • Extensor Pollicis Longus (EPL): Extends the thumb at the IP joint and assists in wrist extension.

    • Extensor Pollicis Brevis (EPB): Extends the thumb at the MCP joint.

    • Abductor Pollicis Longus (APL): Abducts and extends the thumb.

2. Synovial Sheaths for the Extensor Tendons

  • The dorsal tendinous sheaths are synovial sheaths that surround these extensor tendons to reduce friction and allow smooth movement.

  • There are several compartments in the extensor retinaculum, a fibrous structure on the dorsum of the wrist that holds the tendons in place. The retinaculum is composed of bands of connective tissue, and each tendon of the forearm’s extensor muscles passes through a separate compartment.

3. Compartments of the Extensor Retinaculum

The extensor retinaculum is divided into six compartments, each of which contains specific tendons:

  • Compartment 1: Contains the abductor pollicis longus (APL) and the extensor pollicis brevis (EPB) tendons.

  • Compartment 2: Contains the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB) tendons.

  • Compartment 3: Contains the extensor pollicis longus (EPL) tendon.

  • Compartment 4: Contains the extensor digitorum (ED) and extensor indicis (EI) tendons.

  • Compartment 5: Contains the extensor digiti minimi (EDM) tendon.

  • Compartment 6: Contains the extensor carpi ulnaris (ECU) tendon.

These compartments are lined with synovial sheaths that provide lubrication and reduce friction as the tendons move during wrist and finger extension.

Blood Supply to the Dorsum of the Hand

The blood supply to the dorsum of the hand is primarily derived from branches of the radial and ulnar arteries, which form a network that supplies both the extensor tendons and the skin of the dorsum.

1. Radial Artery

  • The radial artery supplies the dorsal side of the hand, including the thumb and index finger.

  • It gives rise to several branches, including the dorsal carpal branch, which contributes to the dorsal carpal arch, supplying the wrist and the dorsal aspects of the fingers.

2. Ulnar Artery

  • The ulnar artery primarily supplies the medial side of the hand.

  • It contributes to the dorsal carpal arch, which supplies the 4th and 5th fingers and the palm of the hand, as well as the medial part of the dorsum.

3. Anastomoses

  • The radial and ulnar arteries form anastomoses that ensure adequate blood flow even in the event of injury or blockage. These anastomoses help maintain perfusion to both the dorsum and the palm.

Innervation of the Dorsum of the Hand

The innervation of the dorsum of the hand is primarily provided by branches of the radial nerve, with some sensory input from the median nerve.

1. Radial Nerve

  • The radial nerve provides motor innervation to the extensor muscles of the forearm and the dorsum of the hand, allowing for the extension of the wrist and fingers.

  • The superficial branch of the radial nerve provides sensory innervation to the dorsal side of the hand, including the thumb, index, and middle fingers, and the back of the hand.

2. Median Nerve

  • The median nerve provides sensory innervation to the distal tips of the thumb, index, and middle fingers, as well as the lateral half of the ring finger on the dorsal surface.

3. Ulnar Nerve

  • The ulnar nerve provides sensory innervation to the little finger and the medial half of the ring finger, including their dorsal aspects.

Clinical Significance of the Dorsum of the Hand and Tendinous Sheaths

1. De Quervain’s Tenosynovitis

  • De Quervain’s tenosynovitis is an inflammatory condition affecting the tendons in the first dorsal compartment, particularly the abductor pollicis longus (APL) and extensor pollicis brevis (EPB). It causes pain and swelling on the lateral side of the wrist, especially with thumb movements like gripping or pinching.

2. Tendon Sheath Infections

  • Infections of the dorsal tendinous sheaths can occur, especially after lacerations, and may result in tendonitis or tenosynovitis, causing pain, swelling, and restricted movement of the fingers.

3. Trigger Finger

  • Trigger finger is caused by stenosing tenosynovitis, which affects the flexor tendons but can also impact the dorsal tendinous sheaths of the fingers, leading to difficulty in extending the affected finger, often resulting in a "clicking" sensation.

4. Wrist Drop

  • Wrist drop occurs when there is damage to the radial nerve, leading to weakness or paralysis of the extensor muscles of the forearm and hand. This results in an inability to extend the wrist and fingers properly.

Summary

The dorsum of the hand is a complex anatomical region that houses critical structures, including the extensor tendons, tendinous sheaths, and various nerves and blood vessels. The dorsal tendinous sheaths play a vital role in facilitating smooth, friction-free movement of the tendons responsible for extending the wrist and fingers. Understanding the anatomy, blood supply, and innervation of this region is crucial for diagnosing and managing various musculoskeletal and neurological conditions, including De Quervain’s tenosynovitis, wrist drop, and trigger finger. Proper function and protection of the tendons and their sheaths are essential for the normal movement and dexterity of the hand.