 Nail matrix

The nail matrix is the proliferative growth region near the nail root that produces material incorporated into the nail plate. Cells divide and become keratinized as the resulting plate advances towards the fingertip. It is distinct from the supporting nail bed and from the free edge already exposed beyond the fingertip.^[ref]

An original steady-volume model links production to motion. Let $J$ be net plate-material volume supplied per day, $w$ the plate width, $h$ its thickness and $v$ its advance speed. If material is approximately incompressible, the cross-section is uniform and losses before the free edge are negligible,For stipulated $J=0.30\mathrm{m}{\mathrm{m}}^3/day$, $w=10$ mm and $h=0.30$ mm, the advance is 0.10 mm/day. Doubling width at the same production and thickness halves that modeled advance. These are geometric consequences of a chosen model, not universal differences between individuals.

Matrix growth and plate-advection balance also shows why a measured advance speed does not alone determine a cell-division rate. Cell size, keratinization, plate geometry and the spatial distribution of production enter the conversion from proliferation to material flow. A marker on the plate measures movement of produced material.

A primary study measured nail advance using marks in 22 healthy young adults; the reported mean fingernail rate was 3.47 mm/month and mean toenail rate 1.62 mm/month.^[ref] Those measurements establish cohort growth observations, not direct counts of mitoses in the matrix.

A proposed comparison combines marked-plate displacement with measurements of plate width and thickness, keeping the observation interval and reference fold fixed. Interpreting changes in the inferred production rate requires checking the steady-geometry assumptions. The central anatomical distinction remains: the matrix supplies new material, while the mature plate records the movement and subsequent history of that material.