Hands

The palm is characterized by:

• flexion creases: generated by mouvements of the skin in relation to joints motility.
• dermatoglyphics: dermal ridges on fingers, on the palm, and on the planta.

Creases:

• fingers: 2 flexion creases for each finger (except the thumb: only 1 crease).
• finger-palm creases.
• palm : 3 normal creases:
  • longitudinal radial crease (LRC in the Figure).
  • proximal transverse crease (PTC).
  • distal transverse crease (DTC).

Fusion of (complete fusion or bridge between) the 2 transverse creases is called single transverse crease, transverse palmar crease, or simian crease.

Dermatoglyphics:

Triradius: point of convergence of ridges from 3 different directions. Normally, there is:

• 1 axial triradius: normally in t, close to the wrist.
• 4 subdigital triradii (a.b.c.d.).
• On the pad of the distal phalanx, sometimes on thenar or hypothenar eminences, are triradii, accompanied with the following patterns:
  • worl: 2 triradii.
  • loops and equivalents (ulnar or radial orientated): 1 triradius.
  • arches: 0 triradius.

From each palmar triradius a, b, c, d, and t, is drawn the 3 lines separating the ridges at this convergence point. The longest is the main line (-- A B C D & T), ending at a side of the palm numbered from 1 to 14 (see Figure).

• T normally ends in 13.
• transversality index = A+B+C+D = 27 on the Figure.

On the fingers may be counted the number of ridges from the center of the pattern to the triradius. (example here: n = 4); in case of an arch, n=0. For the 10 fingers, males have 140 - 145 ridges, and female have 120 - 130 ridges, according to the formula: n = 187 - (30 * no of X) - (12 * no of Y); this may be very useful in the Underground to determine the sex of the person next to you, and to pass the time.

Metacarpo-or metatarso-phalangeal anomalies

Numerical anomalies

• Polydactyly: existence of supernumerary fingers. example: palmar and/or plantar hexadactyly trisomy 13.
• Syndactyly: union of 2 or more fingers or toes (more or less complete, only involving the skin or with bone fusion).

Size anomalies

• Brachydactyly: short fingers. Various types according to which phalanx is involved (e.g. brachymesophalangy: short medial phalanx).
• Brachymetacarpy: short metacarp(s) (example: in Turner syndrome).

Shape anomalies

• Clinodactyly: bend of fingers (often the 5th, as in trisomy 21).
• Camptodactyly: irreductible flexion of the 2nd phalanx on the 1st (without bone involvment).
• Arachnodactyly: long and slender fingers.

As isolated signs, these anomalies are often transmitted as autosomal dominant traits.