The Latin technical term for the tendon sheath is “vagina tendinis”. A tendon sheath is a tubular structure that surrounds a tendon like a guide channel, for example to guide it around a bony prominence. A tendon sheath thus protects the tendon from mechanical injuries.
Structure
A tendon sheath consists of two layers. The outer layer is called stratum fibrosum, the inner stratum synoviale. The stratum fibrosum consists of strong collagen-containing connective tissue and is firmly attached to the surrounding structures.
These adhesions attach the tendon sheath and the tendon within it to bones and ligaments. The stratum synoviale is formed by an outer leaf belonging to the wall and an inner, visceral leaf. The outer leaf also consists of connective tissue and is located between the stratum fibrosum and the inner leaf, which is directly connected to the tendon.
Between the stratum fibrosum and the stratum synoviale there is a lubricating fluid, also called synovial fluid or synovial fluid. The stratum fibrosum and the stratum synoviale are connected via the so-called mesotendinous, a strand of connective tissue. This mesotendineum contains blood vessels and nerves that supply the tendon and tendon sheath.
Occurrence
Tendon sheaths always occur when tendons run near joints or have to be guided around bony projections and retaining ligaments, which occurs exclusively on the long tendons of the muscles of the arms, hands, legs and feet.
Tendon sheaths of the hand
The hand can perform many different movements and has a high degree of fine motor skills. This wide range of movement is made possible by many different muscles and joints. The tendon sheaths of the palm are covered by the carpal ligament (Ligamentum carpi transversum).
The superficial and deep finger flexors (Musculus flexor digitorum superficialis or profundus) have a common tendon sheath that runs under this ligament. This tendon sheath only partially envelops the tendons of these two muscles for the 2nd, 3rd and 4th finger and does not enter the finger itself, but the tendon for the little finger is completely enveloped by this tendon sheath and ends only at the terminal phalanx of the 5th finger. The 2nd, 3rd and 4th fingers have a new tendon sheath to protect the tendon in the finger joint area.
The long thumb flexor muscle (M. flexor pollicis longus) possesses its own tendon sheath, which likewise runs under the carpal ligament and ends only at the thumb end phalanx. The flexor carpi radialis muscle, which causes flexion in the wrist, also has its own tendon sheath under this ligament. The tendon sheaths of the second to fifth fingers are attached to the knuckles of the fingers by ring-shaped ligaments.
In addition, the ligamentous apparatus is stabilized by cross-shaped ligaments at the joints. In 70% of cases, the anatomical position of the tendon sheaths described here is found on the palm of the hand with a long tendon sheath for the thumb and little finger and interrupted tendon sheaths for the three remaining fingers. Anatomical variations therefore occur in 30% of the population and have no disease value.
On the back of the hand, the tendons of the finger extensors and the surrounding tendon sheaths run in so-called tendon compartments, which are located under a holding band called the retinaculum musculorum extensorum. The first tendon compartment contains the long thumb spreader (abductor pollicis longus) and the short thumb extensor (extensor pollicis brevis). The first tendon compartment is subdivided again in many people.
The second tendon compartment contains the long and short radial hand extensors (extensor carpi radialis longus and brevis). The third tendon compartment accommodates the long thumb extensor (M. extensor pollicis longus) and the fourth tendon compartment contains the common extensor muscle of the 2nd -5th finger and an additional extensor muscle for the index finger (M. extensor digitorum or indicis). The little finger also has an additional extensor muscle (extensor digiti minimi muscle), the tendon of which runs through the fifth tendon compartment.
The tendon of the ulnar hand extensor (M. extensor carpi ulnaris) runs through the sixth tendon compartment. There are no longer any tendon sheaths in the finger area on the extensor side, because the tendons of the muscles on the back of the hand merge into a connective tissue plate, the dorsal aponeurosis. This dorsal aponeurosis begins in the area of the metacarpophalangeal joints of the fingers and ends at the distal phalanx of the respective finger.
