Hand and Wrist Anatomy
Mark K. Solarz
Robert C. Matthias Jr.
Comprehensive knowledge of upper extremity anatomy is the foundation for the diagnosis and treatment of hand and wrist pathology.
SURFACE ANATOMY (Figure 61.1)
Kaplan’s cardinal line (KCL)—originally described in 1953 as the line from the “apex of the interdigital fold between the thumb and index finger … parallel with the middle crease of the hand”
However, several differing lines have been described using the same name with no consensus among hand surgeons as to which is correct.1
Using the original description as a surgical landmark
The motor branch of the median nerve lies 15 mm ulnar and proximal to the intersection of KCL and a longitudinal line drawn from the 2nd webspace.1
The superficial palmar arch (SPA) lies 14 mm distal to the intersection between KCL and a longitudinal line drawn from the 3rd webspace.1
The SPA was no closer than 11 mm from any of the four lines considered as KCL in a cadaveric study by Vella et al.1
The distal extent of the transverse carpal ligament lies 5 mm proximal to the intersection of KCL and a longitudinal line drawn from the 3rd webspace.1
Distal and proximal palmar creases—palmar creases are used by some to estimate the level of the A1 pulley.
Ring and small at the crease2
Long between the distal and proximal creases
Index at the proximal crease
The distance from the proximal edge of the A1 pulley to the palmodigital crease can be estimated by the distance from the palmodigital crease to the proximal interphalangeal (PIP) crease.3
Pisiform—sesamoid bone within the flexor carpi ulnaris (FCU) tendon, forms the ulnar border of Guyon canal, serves as an attachment point for the transverse carpal ligament
FCU tendon—ulnar artery is palpable deep and radial to the tendon as the artery enters Guyon canal.
Hook of hamate—forms the radial border of Guyon canal and the ulnar border of the carpal tunnel, provides a fulcrum for small and ring finger flexors
Flexor carpi radialis (FCR)—runs through the groove of trapezium, which is palpable along with distal pole of scaphoid, radial artery located immediately radial to the tendon
Lister’s tubercle—Bony prominence on the dorsum of the distal radius, which serves as a fulcrum for the extensor pollicis longus (EPL) tendon, which is located on its ulnar side and curves radially as it passes distal to the tubercle
The scapholunate (SL) ligament is located about 1 cm distal to Lister’s tubercle.
Anatomic snuffbox—bordered by the EPL and extensor pollicis brevis (EPB), location of the scaphoid
BONES (Figure 61.2)
Distal Radius (Figure 61.3)
Average radiographic parameters4
Angle formed by the line between the tip of the radial styloid and the central reference point (CRP: midpoint between the volar ulnar corner and dorsal ulnar corner) and a line perpendicular to the radial shaft
Height: 11.6 mm
Axial length from the tip of the radial styloid and CRP
Volar tilt: 11°
Angle formed on the lateral view between the line connecting the volar and ulnar dorsal corners and the line perpendicular to the radial shaft
Ulnar variance: 0.6 mm
Axial length from the ulnar head and CRP
Teardrop angle: 70°
Angle formed from a line parallel to the subchondral bone of the volar rim of the lunate facet and the radial shaft
Lunate facet—radius of curvature5 10.9 mm
Sigmoid notch—articulates with ulnar head at distal radial ulnar joint (DRUJ), radius of curvature 50% to 100% larger than ulnar head
Articular contact provides about 20% DRUJ stability6
Ulnar styloid—base serves as the attachment point for the triangular fibrocartilage complex (TFCC)
Extensor carpi ulnaris (ECU) groove—located at the dorsal-ulnar aspect of the ulnar head
Average depth of 1.4 mm and width7 of 9.0 mm
Ulnocarpal ligament complex—composed of the ulnotriquetral, ulnocapitate, and ulnolunate ligaments
Originates adjacent to the ulnar styloid at the volar foveal region and the individual ligaments fan out to their respective insertions
Serves as crutch to stabilize the proximal and distal rows
Blood supply—dorsal carpal branch of the radial artery makes up the primary vascular supply
Retrograde pattern predisposes scaphoid to avacsular necrosis (AVN) particularly with proximal pole fractures
Superficial palmar branch of the radial artery supplies distal pole
SL angle—formed by the longitudinal axis of the scaphoid and the line intersecting the body of the lunate on a lateral radiograph
Normal—30° to 60°, DISI deformity: >60°, VISI deformity: <30°
Blood supply variants8: Y-pattern (59%), X-pattern (10%), I-pattern (31%)
Radius of curvature5 10.4 mm
Variable distal medial facet for hamate articulation (type 1: absent, type 2: present)
Articulates with pisiform on volar side
Saddle articulation with the thumb metacarpal allows for wide range of motion.
Groove on volar surface provides fulcrum for FCR as it passes underneath the trapezium to attach at the second metacarpal base.
Forms scaphotrapezotrapezoidal (STT) joint with scaphoid and trapezium
Articulates with index metacarpal at carpometacarpal joint
Blood supply—largely from retrograde flow, though 70% have a specific volar supply to the proximal pole9
Radius of curvature5 6.1 mm
Articulates with long metacarpal at carpometacarpal joint
Hook projects volarly—serves as attachment point for transverse carpal ligament, pisohamate ligament, hypothenar muscles
Articulates with type 2 lunates
Articulates with ring and small metacarpals at carpometacarpal joint
Medial and lateral sides are concave to serve as attachment points for adjacent interosseous muscles (four dorsal and three palmar).
Metacarpal bases serve as the site of attachment for the abductor pollicis longus (APL; thumb), extensor carpi radialis longus (ECRL; index), extensor carpi radialis brevis (ECRB; middle), extensor carpi ulnaris (small), flexor carpi radialis (index and middle), flexor carpi ulnaris (small).
Each digit has three phalanges (proximal, middle, and distal), other than thumb (proximal and distal).
Proximal phalanx serves as attachment site for interosseous muscles.
Middle phalanx serves as attachment site for flexor digitorum superficialis (FDS) and central slip.
Distal phalanx serves as attachment site for flexor digitorum profundus (FDP) and terminal tendon of the extensor mechanism.
Metacarpophalangeal (MCP) Joint of the Thumb
Ulnar collateral ligament
Stabilizes the thumb during pinch and grasp
Origin is 4.2 mm from the dorsal cortex and 5.3 mm from the articular surface on the thumb metacarpal head.
Insertion is 2.8 mm from the volar surface and 3.4 mm from the articular surface of the proximal phalanx.15
Proper collateral ligament is the main stabilizer in midflexion while the accessory collateral ligament and volar plate stabilize the joint in extension.
Radial collateral ligament
Origin is 3.5 mm from the dorsal cortex and 3.3 mm from the articular surface on the thumb metacarpal head.
Insertion is 2.8 mm from the volar cortex and 2.6 mm from the articular surface.
MCP Joints of the Fingers (Figure 61.4)
Proper collateral ligaments
Origin is dorsal to the axis of rotation on the metacarpal head.
Along with an increasing diameter of the metacarpal head in the sagittal plane from dorsal to volar, the resulting cam effect tightens the proper collateral ligament in 70° to 90° flexion.
Proper collateral ligament is lengthened by 15% when flexing10 from 0° to 90°.
Accessory collateral ligament
Inserts onto and suspends the volar plate
Along with the volar plate, provides stability in extension
Deep transverse metacarpal ligaments
Attach adjacent volar plates of the index through small MCP joints to prevent ray separation
Proper collateral ligaments
Crescent-shaped origin is dorsal and proximal within the concavity on the head of the proximal phalanx.
Insertion includes the majority of the base of the middle phalanx.
Dorsal fibers of the ligament extend parallel to the axis of the middle phalanx and the volar fibers run in an oblique manner, giving the ligament its fan shape.11
Proper collateral ligament is tensioned throughout the interphalangeal (IP) range of motion.
Accessory collateral ligament
Volar to the proper collateral ligament, inserts onto the volar plate
Tensioned with IP joint extension and relaxes in flexion
Results in contracture with prolonged immobilization in flexion
“Position of Safety”
MCP joints placed in 70° to 90° of flexion to tension proper collateral ligament, and IP joints placed in full extension to tension accessory collateral ligament and volar plate
Failure to maintain this position during prolonged splinting results in joint contracture and limitations in motion.