Radius and ulna consist of styloid process, radius dorsal tubercle, radius distal articular surface and 8 small carpal bones. These carpal bones are;
If we order the proximal row from outside to inside》
- Scaphoid= It is the largest proximal bone. It articulates with the radius in the upper part. It is the most fractured of the wrist bones.
- Lunatum= Articulates with the radius in its upper part. It is the most protruding wrist bone.
- Triquetrum= Articulates indirectly with the ulna through the disc.
- Pisiform= It is the last wrist bone to develop. It does not articulate with the bones of the forearm.
If we order the distal row from outside to inside》
- Trapezia = articulates with the first metacarpal.
- Trapezoideum= articulates with the second metacarpal.
- Capitatum = articulates with the third metacarpal. It is the first developing and largest wrist bone.
- Hamatum = articulates with the 4th and 5th metacarpal (2 metacarpal articulates with the bone)
1) Distal Radioulnar Joint
- The concave surface is the ulnar notch in the distal radius; the convex surface is the caput ulna.
- In between, there is a triangular fibrocartilaginous discus articularis. Both surfaces of the disc are concave.
2) Radiocarpal Joint
- In the ellipsoid type joint, the concave part is the articular surface distal to the radius and the lower surface of the articular disc in the distal radioulnar joint.
- When the wrist is in extension and ulnar deviation, the contact area is at the widest level. Also, maximal grip strength is provided in this position.
3) Midcarpal Joint
- It is the joint between the proximal and distal carpal rows.
- In the plana type joint, they make a sliding movement with respect to the axis.
4) Intercarpal Joint
- It is not as mobile as other joints.
- It is important for the wrist to complete its full range of motion.
*Palmar and Dorsal
*Lunotriquetral (one of the most frequently injured intrinsic ligaments, associated with triangular fibrocartilage/TFCC)
*Scofulanate (one of the most frequently injured intrinsic ligaments)
*Palmar intercarpal 5
*Palmar radiocarpal [Radiolunate,radioscapholunate (one of the main extrinsic stabilizers of the palmar surface),radiocapitate]
*Ulnarcarpal Complex (articular disc, ulnar collateral, palmar ulnacarpal)
☆TRIANGULAR FIBROCARTILAGE COMPLEX/TFCC
¿ Cartilage disc,
¿ A meniscus homologue which may not always be present, which is a Embryological residue,
¿ Palmar and dorsal distal radioulnar ligaments,
¿ Ulnar collateral ligament,
¿ The base of the muscle sheath of the extensor carpi ulnaris,
¿ The ulnalunat is a connective tissue complex consisting of ulnotriquetral ligaments.
*By filling the ulnocarpal space, it allows pronation and supination without inserting the carpal bones distal to the ulna.
*Major stabilizer of the distal radioulnar joint.
*It is responsible for the absorption of the stress placed on the wrist and the limitation of lateral deviation.
*With slight extension of the wrist, finger flexor muscles gain maximum functional length to reach full flexion.
*Slight flexion of the wrist, on the other hand, provides automatic opening of the hand and full finger extension by applying tension on the finger extensors.
Metacarpals= 2 and 5 when looking at the palmar face, the thumb metacarp is turned medially at 90 degrees. In this way, the 1st metacarp can freely move the whole thumb towards the fingers along the palmar surface.
*Located between the distal carpal knee and the base of the five metacarpal bones.
*Metacarpal joints are supported by strong transverse ligaments.
*Volar and dorsal ligaments are weaker.
*Carpimetacarpal joints have a slight concavity towards the palmar face. This is important for grasping skill.
*They are biaxial joints of ellipsoid or spheroid type.
*They make the extension, flexion, opening and closing movements.
☆IMPORTANCE OF THE THUMB
*In a healthy hand, the thumb is involved in 40 percent of all hand functions.
*Carpometacarpal joint; the capsule surrounding the joint has a loose structure that allows wide range of motion. Its stabilization is provided by the ligaments and the muscles placed on it.
*The main function of the PULLEY SYSTEM, which is important in the thumb, is to allow the flexion movement of the fingers by covering the tendons.
*Pulleys are of two types as annular (A) and cross (cruciform, C).
*Annular pulleys are thicker, robust and wide fibrous structures. By preventing tendon expansion during finger flexion, it provides optimal joint function for adequate tendon gliding.
*Cross pulleys provide flexibility of the flexor sheath and make the flexion movement more comfortable.
*Thumb flexion is performed by flexor pollicis longus and flexor pollicis brevis. In flexion, the dorsal capsule is stretched.
*In digitals, its flexion is performed by the flexor digitorum profundus and flexor digitorum superficialis. It causes stretching of the dorsal capsule and radial collateral ligament of the interphalangeal joints during movement.
The proximal transverse arch is formed by the carpal bones. The distal transverse arch is formed by the metacarpal heads of the fingers.
It is formed by the bones of 5 digital pathways (each pathway includes the MCF, DIF and PIF joints of that finger). So there are 5 longitudinal arches.
It is the arc formed between the thumb and the other four fingers during gripping on the hand. The arc between the one and the second finger is important in fine grip, while the arc in the other fingers is important in coarse grip.
MUSCLES OF THE HAND
*The origins of the extrinsic muscles are in the forearm, while the intrinsic muscles start and end in the hand.
*Extrinsic muscles are divided into 2 groups as flexor and extensor. Extensor group muscles make the thumb, other fingers and wrist extend. Flexor group muscles make fingers and wrist flexion.
*Intrinsic muscles work together with extrinsic muscles to ensure normal function of the hand.
》Intrinsic hand muscles:
M.Abductor Pollicis Brevis
Starting from the scaphoideum and trapezium, it inserts into the base of the proximal phalanx of the thumb. It is innervated by the N. Medianus. Thumb CMC flexion and abduction additionally makes MCP flexion.
M. Flexor Pollicis Brevis
It has two heads, caput superficiale and caput profundum. It starts from the trapezium and capitatum and inserts into the base of the proximal phalanx of the thumb. It is innervated by N. Medianus. It makes the thumb CMC and MCP flexion.
M. Opponens Pollicis
Starting from the trapezium and retinaculum flexorum, it makes an instertio on the anterolateral surface of the first metacarp. It is innervated by the N. Medianus. The thumb makes the CMC opposition.
b) Hypothenar muscles
M.Flexor Digiti Minimi
It inserts into the base of the proximal phalanx of the little finger by making origo into the hamatum. It is innervated by N. Ulnaris. The 5th finger makes MCP flexion.
M. Opponens Digiti Minimi
It ends by insertion of the 5th metacarpal by making origo to the hamatum and retinaculum flexorum. It is innervated by N. Ulnaris. The 5th finger makes CMC opposition.
M.Abductor Digiti Minimi
It starts from the os pisiform and ends by inserting into the base of the proximal phalanx of the little finger. It is innervated by N. Ulnaris. The 5th finger performs MCP abduction.
c) Middle Compartment
M. Adductor Pollicis
It has two heads, caput obliquum and caput transversum. Os capitatum starts from the 2nd and 3rd metacarpals and inserts the thumb into the base of the proximal phalanx. It is innervated by N. Ulnaris. It adducts the thumb.
It starts from the lateral two tendons of the M.Flexor digitorum profundus and inserts it into the lateral side of the extensor expansion of the 2nd and 3rd fingers. It is innervated by the N.Medianus. While performing the MCP flexion, it performs the PIF and DIF extension.
It starts from the medial two tendons of the M.Flexor digitorum profundus and ends in the extensor expansion of the 4th and 5th fingers. It is innervated by N. Ulnaris. While MCP flexion, it makes PIF and DIF extension.
It starts from the 2, 4 and 5 metacarps and ends at the base of the proximal phalanx of the 2, 4 and 5 fingers. It is innervated by N. Ulnaris. They perform MCP adduction to the 2, 4 and 5 fingers.
Dorsal Interosseous Solar
It starts from the adjacent parts of the 2 metacarpals (1 2 3 4) and ends in the proximal phalanges of the 2nd, 3rd and 4th fingers. It is innervated by N. Ulnaris. The 2nd and 4th fingers make MCP abduction, and the 3rd finger ulnar and radial deviation.
》Extrinsic Region Muscles
M.Abductor Pollicis Longus
It starts from the posterior surface of the ulna and radius and from the interossea to the membrane and ends at the base of the 1st metacarpal. It is innervated by the N. Radialis. It makes radial deviation, that is adduction, of the hand while performing abduction and extension of the thumb.
M.Extensor Pollicis Brevis
Starting from the posterior surface of the radius and the interossea to the membrane, it ends in the proximal phalanx of the thumb. It is innervated by the N. Radialis. The first finger extends the CMC and MCP joints.
M.Extensor Carpi Radialis Longus and Brevis
Both muscles start from epicondylus lateralis in common. The longus 2nd brevis ends at the base of the 3rd metacarp. It is innervated by N. Radialis. It performs extension and abduction in the wrist.
M.Extensor Carpi Ulnaris
Epicondylus starts from the lateralis and ends at the base of the 5th metacarp. It is innervated by the N. Radialis. While extending the wrist, it also performs the adduction movement.
M.Extensor Pollicis Longus
It starts from the posterior surface of the ulna and the interossea to the membrane and ends in the distal phalanx of the thumb. It is innervated by the N. Radialis. It extends the 1st finger.
Starting from the epicondylus lateralis, the extensor expansions of the 2nd and 5th fingers insertion into the bases of the middle and distal phalanges. It is innervated by the N. Radialis. They make extensions in the wrist and fingers.
M.Extensor Digiti Minimi
Epicondylus lateralis makes origo insertion into the extensor expansion of the 5th finger. It is innervated by the N. Radialis. It extends the little finger.
Starting from the posterior surface of the ulna and the interossea to the membrane, it inserts into the extensor expansion of the 2nd finger. It is innervated by the N. Radialis. It extends the 2nd finger.