Friday 12th August 2022

A novel follicular unit excision device | CCID

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Introduction

Follicular unit excision (FUE), previously called follicular unit extraction, is currently the most popular and only minimally invasive follicle-harvesting method in hair transplantation. The term “excision” was adopted to reflect the surgical nature of the procedure. FUE is a 2-step surgical process that involves making a full-thickness circumferential incision into the skin around a follicular unit, enabling removal of a full-thickness skin graft containing an intact follicular unit bundle. FUE has advantages over follicular unit strip surgery for hair transplantation because it avoids creating a linear scar, nerve dissection, and the misalignment of the natural flow of scalp hairs. Furthermore, FUE enables the expansion of the donor supply to beard and body hair.

All FUE methods involve using a punch to cut the tissue and a punch driver that drives the punch cutting tip. The driver could be manual, whereby the operator manually rotates a handheld punch in a skin biopsy-type maneuver, or mechanical, where the punch is mounted on an electromechanical drill device typically adopted from existing dental drill systems. Existing FUE devices have various limitations, and to date, no single device has been able to adequately address the range of patient donor variables. Such variables include hair curliness, racial differences in skin and hair, body and head hair locations, and the growing demand for non-shaven and long hair FUE. Most devices are ineffective in harvesting hair from people of African descent1–3 or extracting follicles from various body areas.4 Additionally, they do not adequately perform when faced with changing skin and hair characteristics between and within patients from one body/head area to another.5,6 Consequently, not everyone can benefit from the advantages of FUE over other hair transplant methods. Some devices perform excellently in one type of harvest but not in others.7,8 Therefore, practitioners often acquire various devices hoping that one of these might suit the variety of patients they encounter since no single device suits all situations.9 Other practitioners seek to develop specialized skills in using conventional FUE tools to address challenging FUE scenarios.10

To address these limitations, we report a versatile device to accommodate most FUE presentations, including head hair extraction (shaven or non-shaven) in all races, all beard and body hair extractions, and long-haired graft harvesting that does not require switching punches, the driver, or the development of specialized skill sets. We here describe the device’s features and use.

Patients and Methods

Ethical Statement

All patients who underwent FUE provided written informed consent, including consent for publication, and all procedures were conducted in accordance with the Declaration of Helsinki (revised in 2013). Institutional Review Board approval was not required or sought as this study was not a prospective or systematic investigation of FUE treatment but described general principles for routine FUE practice.

The device consists of an all-purpose FUE punch mounted on a skin-responsive driver optimized at several levels when working in tandem.

All-Purpose Punch

An all-purpose punch called the Intelligent Punch – Dr. U Punch i (Dr. U Devices Inc, Manhattan Beach, CA), was developed to serve all FUE scenarios (Figure 1). The punch design was optimized at multiple levels to incorporate solutions to several technical challenges known to contribute to FUE graft attrition (lost or non-viable grafts from transections, crush injuries, and complete de-sheathing), poor scarring profiles, and user experiences.

Figure 1 The all-purpose punch, showing the frustoconically shaped, textured cutting end and a flared cutting tip.

Punch Cutting Axis Optimization

As it advances into the depths of the skin, an FUE punch must cut the tissue that envelops and anchors the hair follicle to its lateral surroundings. The cylinder of scored follicle ascends into the lumen of the punch, with tissue distal to the punch tip constantly in the crosshairs of the punch cutting tip, increasing the risk of transecting and damaging the graft (Figure 2A‒C). Thus, the cutting end of the all-purpose punch was flared to point the edges of the tip away from the graft axis to minimize this risk (Figure 2D‒F).11–17

Figure 2 Patent application schematics demonstrating the advantage of a flared punch cutting tip. (A) Outer beveled punch tip shows cutting vectors directed towards the follicle; (B and C) the outer beveled punch transects the follicle before advancing to the follicle’s level (D) a flared punch with cutting vectors pointing away from the follicle (E and F) show minimal tendency to transect grafts while reaching deeper levels of the follicle, unlike the outer beveled punch.

Punch Diameter and Wound Healing Optimization

Generally, large punches register fewer graft transections.5 The flaring of the punch (Figure 1) mitigates transection rates compared with straight punches of the same diameter. However, the diameter of the funnel-shaped rim (responsible for the first skin cut and wound size) of an ordinarily flared punch increases the diameter of the punch to exceed the diameter of the long cylinder (Figure 3A). The punch design was further optimized to impart the benefits of flaring without increasing the tip diameter beyond the perimeter of the punch’s long cylinder (Figure 3B), thus avoiding an increase in wound size. This was achieved by coring out concavities from the thickness of the outer surface of the punch end 1‒2 mm (Figure 3A).11,17

Figure 3 The diameter of an ordinarily flared punch (A) is broader than that of the all-purpose punch forged from the same outer-diameter punch and flared by coring the concavity of the first 1–2 mm of the tip (B).

Flaring of the device tip confers a wound-healing advantage because of the skin entry vectors of the cutting edge and the shape of the first 1‒2 mm of the wound’s edge. This creates an epidermis-to-wound edge angle that is relatively smaller. The result is a wound that heals more by primary than by secondary intention. Opposing epidermal wound edges meet mostly by wound contraction rather than exposed dermal tissue that heals mostly by secondary intention, resulting in a more prominent scar (Figure 4).18 Moreover, in studies focusing on scalp FUE, stretching the dermis by normal saline tumescence was used to achieve a similar objective.19 The wound shape and healing advantage conferred by the flaring of the punch allows for a relatively larger punch to achieve lower transection rates while still incorporating the wound healing benefits of a smaller punch. This advantage allows the use of at least one needle-gauge-size larger on the all-purpose punch to achieve a wound finish equal to or better than that conferred by a non-flared punch that is a needle-gauge-size smaller.

Figure 4 The wound-healing advantage of the flared all-purpose punch. (A) A1–A2: outer beveled punch cutting axis, directed downwards and inwards, cuts a cylindrical wound column with a relatively everted papillary dermal edge; A3: most of the wound closes primarily due to wound contraction. The top papillary portion remains patent, relying more on second intention healing for wound closure and resulting in a larger scar; (B) B1–B2: The flared punch cutting axis, directed outwards to bite into the tissue lateral to the punch. The first cut into the papillary dermis cuts a wound path that is relatively inverted compared to that of non-flared punches, resulting in a cylindrical wound column with a relatively inverted papillary dermal edge; B3: most of the wound closes primarily due to wound contraction, including the majority of the wound’s top papillary portion, bringing the edges closer together, such that the entire top part either closes by primary intention or recruits a relatively smaller degree of second intention, healing with less scarring.

Punch Optimization for Torsion Injury Reduction

When a punch scores the graft and advances along the deeper portions of the graft, the proximal portion of the graft is pulled into the rotating punch’s lumen (Figure 5A). Any friction between the punch’s inner surface and the graft results in the punch and the intraluminal portion of the graft rotating in unison, causing the punch to be out of sync with the graft outside the punch, which is still anchored to the…

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