What Is FUE Transection? Causes of Follicular Injury and Prevention Principles

Scientific summary: Transection is cutting or fragmentation of a follicle during FUE harvesting. Partial and complete injuries are not equivalent. The exit angle at the skin surface does not always reflect the deeper follicular curve. Punch diameter, angle, depth, device motion and extraction force jointly affect injury risk. [1][2][3]

Why may a follicle not follow its visible surface direction?

The hair shaft emerges at a visible angle, but the follicle can curve beneath the skin and hairs within one unit can diverge (splaying). A deep incision based only on the visible shaft can therefore injure follicular structures. Anatomical variability can be greater in curly hair and scarred tissue. [1][2]

Types of transection

Partial transection: cutting injury involving part of a follicle. Complete transection: full cutting of the follicle being assessed. Records must specify whether a classification concerns a single follicle or the entire follicular unit. Traction fracture, outer root sheath injury, stripping of surrounding tissue and crushing during implantation are additional, distinct injuries. A graft that appears intact cannot be assumed to have fully functional cells throughout.

Which technical variables matter?

• Punch diameter: a very narrow diameter may increase cutting injury in some units; an excessively wide one can increase tissue loss.
• Entry angle: the surface hair direction may differ from the deeper follicular axis.
• Depth: inadequate dissection can increase traction trauma; excessive depth can injure follicles and surrounding vessels.
• Rotation and oscillation: device motions produce different tissue forces; no single speed or device is superior for every patient.
• Tethering: excessive traction can injure a graft when its attachments to surrounding tissue are strong.

How should transection rates be measured?

Microscopic graft assessment should record partial and complete transection separately. A figure such as “1% transection” cannot be compared without its denominator and counting method. Low transection is a goal, but it does not independently guarantee final hair growth. [3]

Are transection and graft survival the same?

No. An apparently intact harvested graft can subsequently be injured by drying, forceps compression, storage or implantation. Conversely, the effect of partial injury can depend on which structures remain preserved. Histological viability and hair growth at 12 months must be evaluated as separate outcomes. [3]

Quality control within the KSD framework

The KSD quality objective is to assess the donor area, inspect follicular morphology through test extractions, avoid unnecessary force, document graft integrity and manage harvesting speed alongside quality. It does not mean using one fixed device or punch diameter for every patient.

Frequently asked questions

Scientific references