Roentgen Coach Rheumatology

Bony structures within articulations: normal conditions

Normal conditions of Bone in the Wrist

The bony structures about the wrist are the distal portions of the radius and ulna, the proximal and distal rows of carpal bones, and the metacarpals. 
The distal aspects of the radius and ulna articulate with the proximal row of carpal bones. On the lateral surface of the radius is the radial styloid process, which extends more distally than the remainder of the bone, and from which arises the radial collateral ligament of the wrist joint. The articular surface of the radius is divided into an ulnar and a radial portion by a faint central ridge of bone. The ulnar portion articulates with the lunate and the radial portion articulates with the scaphoid. The articular surface is continuous medially with that of the triangular fibrocartilage. The medial surface of the distal end of the radius contains the concave ulnar notch, which articulates with the distal end of the ulna. The posterior surface of the distal radius is convex and grooved or irregular in outline to allow passage of tendons and tendon sheaths. A prominent ridge in the middle of this surface is the dorsal tubercle of the radius. The anterior surface of the distal portion of the radius allows attachment of the palmar radiocarpal ligaments. 
The distal end of the ulna contains a small round head and a styloid process. The lateral aspect contains an articular surface for contact with the ulnar notch of the radius. The ulna also has a distal articular surface, which is intimate with the triangular fibrocartilage. The ulnar styloid process, which extends distally from the posteromedial aspect of the bone, gives rise to the ulnar collateral ligament. Between the styloid process and inferior articular surface, the ulna has an area for attachment of the triangular fibrocartilage and a dorsal groove for the extensor carpi ulnaris tendon and sheath. 
The proximal row of carpal bones consists of the scaphoid, lunate, and triquetrum, as well as the pisiform bone within the tendon of the flexor carpi ulnaris. The distal row of carpal bones contains the trapezium, trapezoid, capitate, and hamate bones. The dorsal surface of the carpus is convex from side to side, and the palmar surface presents a deep concavity, termed the carpal groove or canal. The medial border of this palmar carpal groove contains the pisiform and hook of the hamate. The lateral border of the carpal groove contains the tubercles of the scaphoid and the trapezium. A strong fibrous retinaculum attaches to the palmar surface of the carpus, converting the groove into a carpal tunnel, through which pass the median nerve and flexor tendons. Evaluation of this tunnel in cases of median nerve entrapment is best accomplished with CT and MR imaging. 
The distal row of carpal bones articulates with the bases of the metacarpals. The trapezium has a saddle-shaped articular surface for the first metacarpal. The trapezoid fits into a deep notch in the second metacarpal. The capitate articulates mainly with the third metacarpal, but also with the second and fourth metacarpals. The hamate articulates with the fourth and fifth metacarpals. The bases of the metacarpals articulate not only with the distal row of carpal bones but also with each other. 
The alignment of the bones of the wrist joints varies with wrist position. When the wrist is in neutral position without dorsal or palmar flexion, the distal end of the radius articulates with the scaphoid and approximately 50 per cent of the lunate. The degree of radial shift of the carpus at the radiocarpal joint is determined by comparing the distance between the central axis of the distal end of the radius and the distal aspect of the radial styloid process in the two wrists. Several methods exist for the measurement of ulnar translocation, or ulnarward displacement, of the carpus at the radiocarpal joint. The degree of radial deviation of the radiocarpal compartment can be measured on a posteroanterior radiograph with the wrist in this neutral attitude. A line is drawn through the longitudinal axis of the second metacarpal at its radial cortex. A second line is constructed from the ulnar limit of the distal end of the radius to the tip of the radial styloid process. The second line intersects the first, creating an obtuse angle, which normally averages 112 degrees (range, 92 to 127 degrees). In the neutral position, the spaces between carpal bones are approximately equal in the normal wrist. An abnormal widening of the scapholunate space is termed scapholunate dissociation. On a posteroanterior radiograph of a normal wrist, a line drawn tangentially from the distal tip of the radial styloid through the base of the ulnar styloid process intersects a second line drawn along the midshaft of the radius with an average angle of 83 degrees (72 to 95 degrees).
On a lateral radiograph of a normal wrist in neutral position without palmar flexion or dorsiflexion, a continuous line can be drawn through the longitudinal axes of the radius, lunate, capitate, and third metacarpal. 6 A second line through the longitudinal axis of the scaphoid intersects this first line, creating a scapholunate angle of 30 to 60 degrees. A scapholunate angle of less than 30 degrees or more than 60 degrees suggests carpal instability, which can be classified as (1) dorsiflexion instability, or dorsal intercalated segment instability, in which the lunate is dorsiflexed and displaced in a palmar direction and the scaphoid is displaced vertically, or (2) palmar flexion instability, or volar intercalated segment instability, in which the lunate is flexed in a palmar direction. On the lateral view, a line drawn tangentially along the distal articular surface of the radius intersects a second line through the midshaft of the radius with an average angle of 86 degrees (79 to 94 degrees).
Radial and ulnar deviation and flexion and extension of the wrist cause changes in the alignment of the carpal bones. In radial deviation, palmar flexion of the proximal carpal bones is noted as the distal end of the scaphoid rotates into the palm. In ulnar deviation, the scaphoid is seen in full profile, the lunate and triquetrum become more closely apposed, and the pisiform becomes intimate with the tip of the ulnar styloid. Dorsiflexion of the wrist is particularly prominent at the capitate-lunate space, and palmar flexion is pronounced at the lunate-radial space. During wrist flexion, the pisiform tilts on the triquetrum and moves in a volar direction for 2 to 3 mm. During wrist extension, the pisiform slides distally and undergoes some rotation. 
The complexity of wrist motion has led to differing concepts of functional osseous anatomy. Some regard the wrist as composed of carpal bones arranged in two rows (proximal and distal) with the scaphoid bridging the two. Others describe a vertical arrangement of the joint as consisting of three columns. A mobile lateral column contains the scaphoid, trapezium, and trapezoid, in which osteoarthritis is most frequent. The central column, containing the lunate and capitate, is concerned with flexion and extension and is primarily implicated in most varieties of carpal instability. The medial column is composed of the triquetrum and hamate, and, on the axis of this column, the rotation of the forearm is extended into the wrist. A third concept considers the wrist as a dynamic ring, with a fixed distal half and a mobile proximal half. Distortion or rupture of the mobile segment with respect to the rigid part explains both instability and dislocation.

Normal conditions of Bone in the MCP-joints

At the metacarpo-phalangeal joints, the metacarpal heads articulate with the proximal phalanges . The medial four metacarpal bones lie side by side; the first metacarpal lies in a more anterior plane and is rotated medially along its long axis through an angle of 90 degrees. In this fashion, the dorsal surface of the thumb is aligned in a radial direction, whereas its ulnar surface is oriented superiorly. This position allows the thumb to appose the other four metacarpals during flexion and rotation.
The metacarpal heads are smooth and round, extending farther on the palmar than on the dorsal aspect of the bone. On the palmar aspect, the articular surface of the metacarpal head is divided in such a fashion that it resembles condyles. The head of the first metacarpal is less convex than those of the other metacarpals and has two palmar articular eminences, which relate to sesamoid bones. Tubercles are found on the heads of all metacarpals; these tubercles occur at the sides of the metacarpal heads where the dorsal surface of the body of the bone extends onto the head. Collateral ligaments attach to the metacarpal tubercles. The bases of the phalanges contain concave oval surfaces that articulate with the metacarpal heads.

Normal conditions of Bone in the PIP- and DIP-joints

The interphalangeal joints of the hand consist of four distal interphalangeal joints, four proximal interphalangeal articulations, and an interphalangeal joint of the first digit. 
At the proximal interphalangeal joints, the head of the proximal phalanx articulates with the base of the adjacent middle phalanx. The articular surface of the phalangeal head is wide (from side to side), with a central groove and ridges on either side for attachment of the collateral ligaments. The base of the middle phalanx contains a ridge that fits into the groove on the head of the proximal phalanx. 
At the distal interphalangeal joints, the head of the middle phalanx articulates with the base of the distal phalanx. This phalangeal head, like that of the proximal phalanx, is pulley-like in configuration and conforms to the base of the adjacent phalanx. This latter structure is relatively large. 
The interphalangeal joint of the thumb separates the proximal and distal phalanges of that digit. These phalanges are similar in structure to those of the other digits but in general are shorter and broader.

Normal conditions of Bone in the tarso-metatarsal joints

Osseous and Soft Tissue Anatomy  
The metatarso-phalangeal joints, which are synovial articulations, exist where the rounded heads of the metatarsal bones approximate the cupped surfaces of the proximal phalanges. The articular portions of the metatarsal heads include the distal and plantar aspects of the bone but do not include the dorsal surface. The plantar aspect of the first metatarsal bone is unique, containing two longitudinal grooves separated by a ridge. Each groove may articulate with a sesamoid bone.