How is the retinaculum on the upper limb structured?
On the upper limb, the extensor retinaculum is a distal formation of the antebrachial fascia (fascia antebrachii). The antebrachial fascia is a dense "cuff" that gives off septa to the crests of the radius and ulna, as well as the interosseous membrane. Distally, it forms the extensor retinaculum on the dorsum.
Six osseo-fibrous compartments are distinguished beneath the extensor retinaculum on the dorsal wrist. The compartments are counted from the lateral edge to the medial edge, using Lister's tubercle on the radius as a landmark:
- Compartment I: tendons of the abductor pollicis longus muscle (m. abductor pollicis longus) and extensor pollicis brevis (m. extensor pollicis brevis).
- Compartment II: tendons of the extensor carpi radialis longus and brevis (mm. extensores carpi radiales longus et brevis).
- Compartment III: tendon of the extensor pollicis longus (m. extensor pollicis longus), which curves around Lister's tubercle.
- Compartment IV: tendons of the extensor digitorum communis (m. extensor digitorum communis) and extensor indicis (m. extensor indicis).
- Compartment V: tendon of the extensor digiti minimi (m. extensor digiti minimi).
- Compartment VI: tendon of the extensor carpi ulnaris (m. extensor carpi ulnaris).
The tendons of the extensor pollicis brevis and abductor pollicis longus bound the "anatomical snuffbox".
Dorsal fascial spaces are also located in the dorsal hand region, and intertendinous connections (connexus intertendinei) are present between the tendons of the common extensor.
Topography and adjacent structures of the dorsal hand
The following structures are described in the radial region of the hand near the extensor retinaculum: cephalic vein (v. cephalica), superficial branch of the radial nerve (ramus superficialis n. radialis), radial artery (a. radialis), and its dorsal carpal branch (ramus carpalis dorsalis a. radialis).
The arterial structures of the dorsal hand include the radial artery, the dorsal carpal branch of the radial artery, the dorsal metacarpal arteries, and the dorsal digital arteries.
The neural structures include the dorsal digital nerves (nn. digitales dorsales) supplying the digits. The dorsal branch of the ulnar nerve (ramus dorsalis manus n. ulnaris) innervates the medial part of the dorsal hand.
Structure of the retinacula on the lower limb
On the lower limb, the crural fascia (fascia cruris) distally forms tendon retinacula, including the superior and inferior extensor retinacula.
- Superior extensor retinaculum (retinaculum mm. extensorum superius) is located between the anterior border of the tibia (tibia) and the lateral malleolus. It is also described as a fascial thickening in the lower third of the leg.
- Inferior extensor retinaculum (retinaculum mm. extensorum inferius) has a Y-shape, is located at the level of the ankle joint, and extends from the calcaneus (calcaneus) to the medial malleolus and the fascia of the dorsal foot.
The inferior extensor retinaculum forms fibrous tunnels for the tendons of the tibialis anterior (m. tibialis anterior), extensor hallucis longus (m. extensor hallucis longus), extensor digitorum longus (m. extensor digitorum longus), and fibularis tertius (m. fibularis tertius) when present.
The tendon of the extensor hallucis longus occupies a middle position, while the tendon of the extensor digitorum longus is located laterally. Within the osseo-fibrous compartment of the extensor hallucis longus runs the neurovascular bundle: the dorsalis pedis artery (a. dorsalis pedis), accompanying veins, and the deep fibular nerve (n. fibularis profundus). The bundle is separated from the ankle joint capsule by a layer of adipose tissue.
Synovial sheaths and clinical significance
The compartments beneath the extensor retinaculum on the dorsal wrist are lined with synovial sheaths that reduce tendon friction.
In the hand, the synovial sheath for the tendons of the extensor digitorum and extensor indicis is triangular in shape, with the base of the triangle facing toward the digits. Proximally, it extends 10 mm proximal to the extensor retinaculum, and distally it ends blindly at the mid-metacarpal level.
On the foot, the synovial sheath of the extensor hallucis longus begins 2–3 cm proximal to the intermalleolar line and extends distally to the level of the first cuneometatarsal joint. The sheath of the extensor digitorum longus extends 1–2 cm further proximally than the sheath of the extensor hallucis longus, and expands distally along the divergence of the tendons toward the digits.
Clinical significance: inflammation of the synovial sheaths of the 1st compartment on the dorsal wrist leads to de Quervain tenosynovitis.
Class and exam questions
Which tendons pass through the first compartment of the dorsal wrist?
Compartment I contains the tendons of the abductor pollicis longus (m. abductor pollicis longus) and extensor pollicis brevis (m. extensor pollicis brevis).
Where does the neurovascular bundle run on the dorsum of the foot?
The dorsalis pedis artery, accompanying veins, and deep fibular nerve run within the osseo-fibrous compartment of the extensor hallucis longus.
Which tendon curves around Lister's tubercle?
Lister's tubercle on the radius is curved around by the tendon of the extensor pollicis longus (m. extensor pollicis longus), which passes through compartment III.
What else to study on this topic
- Antebrachial and crural fasciae
- Flexor retinaculum (retinaculum mm. flexorum)
- Anatomical snuffbox
- Synovial tendon sheaths
Study the complete topic in the Anatomy course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Extensor retinaculum" and 1,363 other pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 295 video lessons by subject
Other topics in the "Anatomical Structures" section
Free video lessons: AnatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.