Follicular Unit Excision Donor Area Management and Considerations of the Scalp

Abstract

Over the last several years, follicular unit excision (FUE) donor harvesting has become the predominant donor harvest method, surpassing the traditional method of linear strip excision donor harvesting. While this may offer advantages in specific clinical settings, the reality of ongoing losses with the natural evolution of male patterned hair loss places a premium on obtaining as much lifetime donor hair as possible to address this clinical reality. This lifetime demand requirement must be weighed against the possibility of a detrimental cosmetic appearance of the donor area with serial donor harvests utilizing FUE. This chapter will examine the important technical and artistic considerations critical for hair restoration surgeons to appreciate in order to maintain cosmetically high-quality donor area outcomes in patients choosing to undergo FUE harvesting for hair transplantation surgery.

Keywords

follicular unit excision - donor area outcomes - overharvesting - linear strip excision - artistic considerations - diffuse unpatterned alopecia - donor cosmesis

The donor area reflects the residual hair that remains in a Norwood (NW) 7 patterned patient and for that reason, doctors and patients think of the hair in this area as lifetime (permanent) hair. For convenience, most hair transplant doctors estimate that the donor area reflects 25% of the hair-bearing scalp; however, the 25% estimate may actually overestimate the residual hair in a typical NW 7 patterned patient.[1] [2] The surgeon needs to create an overall master plan for each patient on initial evaluation by determining the value of the donor area hair as it relates to the patient's needs. Hair transplant doctors must be able to quantify the amount of hair in the donor area as well as the cosmetic value of that hair in order to conduct an appropriate harvest. In addition, as there are diseases of the scalp such as alopecia areata and scarring alopecia which may involve the donor area, it is critically important to make sure that the donor scalp is not impacted by any of these before going forward with a hair transplant. Although the donor area is described as permanent hair, this is not strictly the case, as it may in fact decrease in density as a person ages, and this is known as senile alopecia.[3] Reductions in hair thickness or follicular unit (FU) densities within the donor are found in a substantial subset of the male population, and what happens to the donor area will be a mirror to what will happen to FUs grafted to the recipient area as these changes occur.

The donor hair is analogous to the painter's paint and the implantation of hair grafts like the painter's brush. The hair transplant surgeon must be an artist who knows how much paint he needs, where to place it, and how it will be used as the surgeon projects what the patient will look like after the hair has grown in. Metaphorically, we must know the value of the paint we use as we implant grafts of various sizes into the recipient area. Likewise, as we remove paint from the donor area, we must be aware of the cumulative impact this will have on the appearance of the donor area. This chapter shall be focused on what we must know to be able to deliver the best value from the donor area. The following subjects will be discussed: (a) FU supply basics, (b) donor density, (c) hair thickness or caliber, (d) hair curl, (e) the contrast between the color of the hair when compared to the color of the patient's scalp, (f) the number of FUs in the donor area available for hair transplantation, and (g) the residual hair mass of the donor area after harvesting, each and every time we perform a hair transplant on the same patient. We will also look at appreciating diseases which may present in the donor as well as the clinical presentation of diffuse unpatterned alopecia (DUPA).

Follicular Unit Supply Basics

From the very first interaction with the patient, the doctor must look forward beyond the initial surgery, as hair loss is progressive in every balding male patient. The impact of what is harvested on the first surgery will have a substantial influence on the patient's surgical plan in the future as he continues along his balding path. There are no simple rules to follow, as all donor areas are not equal. For instance, donor considerations that apply to a person with coarse hair may not apply to a person with fine hair. The average human has 50,000 FUs on his/her head. This is relatively constant across all men and women and all races (although it depends on the head size). The number of hair found in each FU varies when comparing race as follows: Caucasians average 2.2 hair/FU, Asians average 1.9 hair/FU, and Africans average 1.7 hair/FU.[4] Let us use a Caucasian with an average size head who typically has 110,000 hair on the head as we move forward. The number of follicular units remain constant at 1 FU per mm² or 50,000 FUs for the average Caucasian male[5] with a hair-bearing area of 77 square inches. The 2.2 hair/FU statistic for a Caucasian male will take on a bell-shaped curve with regard to donor density distribution, with 2.2 being the median point on the curve. On the high end, Caucasian males can have hair counts of 200,000 or more, while some can have total hair counts as low as 70,000. Clearly, the higher the hair count the better the transplant results, and so, conversely, great care must be exercised when the donor supply is limited. Every surgeon must carefully evaluate the donor density on all of their patients for many of the reasons discussed below.

Setting up realistic expectations is the surgeon's responsibility. Success, even for the NW 7 patient with fine hair, is a matter of setting these expectations appropriately. There are rare examples of fine-haired NW 7 patients who have been successfully transplanted. Those patients need to understand, prior to any surgery, to expect and be satisfied with a thin, see-through head of hair, as the predicted cosmetic outcome is based upon the natural quality of their hair and the low FU supply.

Donor Area Density Calculations

Assuming that the donor area is healthy and does not have any diseases, the math for determining donor area density and hair mass is straightforward. It is recommended that the surgeon purchase a handheld camera (dermatoscope) so that they can obtain photos of the FU quality similar to those used here in the chapter ([Fig. 1]).

Fig. 1 Handheld dermoscopy devices come in several styles and are an essential and powerful diagnostic tool, both for examining the presence of scalp diseases and evaluating the quantity and quality of follicular units over the surface of the scalp.

The donor area has relatively predictable density patterns. The central areas between the occipital notches of the donor area usually show the highest density, and this density is generally uniform. As one moves laterally towards the ear and past the ear, the donor area density usually drops from what is found in the mid-occiput area.[1] As one FU generally occupies 1 mm², sampling two areas of the donor area with between 10 and 20 FUs each and counting the hair in each of the FUs can help estimate the donor density. Cutting the hair short (1–2 mm) will give a clear view for counting the hair. To obtain the average hair per FU, the total number of hair counted is divided by the number of FUs containing the counted hair. For example, assume that 80 FUs were counted containing a total of 162 hair. The hair density equals 162 hair/80 FUs = approximately 2 hair/FU. That is slightly under average for a Caucasian male (average is 2.2 hair/FU), but slightly higher than for a typical Asian (who averages 1.9 hair/FU).

In the microview of the donor area ([Fig. 2]), we count 14 FUs and 44 hair. One can easily argue that the FU in the left lower corner (arrow) has 5 hair, not 4, but that will eventually average out as more sampling is performed. The donor density in this example would be 44 hair/14 FUs = 3.1 hair/FU. When viewing another section of his donor area, one would confirm that this person has a high donor density. This calculates to 150,000 hair on their head at birth (3.1 hair per FU multiplied by 50,000 FUs on the head), which is well above the average donor density for a Caucasian male.

Fig. 2 Trichoscopic (50× power) view of scalp follicular units showing follicular unit variations can help familiarize patients with basics of scalp hair anatomy.

Hair Caliber

Fortunately, in most individuals, donor hair thickness (caliber) is generally uniform across the entire donor area as long as the donor area is healthy. Hair shaft thickness is also a simple concept. Although the hair shaft cross-section is technically more oval than round,[6] we will assume it to be round for our general purposes here. The formula for the area of a circle is A = πr ² where A is area, π is 3.14, and r is the radius.

Let us take some simple examples comparing the differences between fine, medium, and coarse hair ([Table 1]). The appearance of hair thickness is a product of the number of hair multiplied by the thickness of the hair shafts. A good metaphor to share with patients is as follows. Ask the patient to think about building a snow fence that blocks the snow from getting through the fence. They have only three sizes of wood to use: 1 × 1 inch, 2 × 2 inches, and 4 × 4 inches. The patient is limited to only using 1,000 pieces of wood (an FU supply metaphor). Ask the patient which wood will make for a better fence? Then tell them about their hair caliber as measured with a micrometer and approximate which size of wood their hair mass resembles in the snow fence metaphor. In other words, compare a 1 × 1-inch piece of wood to very fine hair and a 4 × 4-inch piece of wood to coarse hair. Most patients understand the analogy with this example. A fence made of 1,000 1 × 1-inch wood planks will let more snow through the fence. A fence made of 1,000 4 × 4-inch wood planks will block far more snow than the 1 × 1-inch wood planks.

Table 1 Calculations comparing hair caliber (thickness) and the relative increase in coverage value from very fine to very coarse hair

Hair type	Diameter (µm)	Area coverage value (πr 2)	Power compared to very fine hair
Very fine	25	491	0.0
Fine	30	707	0.7
Medium-fine	40	1,257	2.6
Medium	50	1,964	4.0
Medium-coarse	60	2,828	5.8
Coarse	70	3,849	7.8
Very coarse hair	80	5,027	10.2

When applied to hair, one can study the calculations as the hair shaft caliber becomes greater from very fine (25 µm) to thick hair (80 µm). Very coarse hair has 10.2 times the coverage value of very fine hair (see [Table 1]). A medium-weight (50 µm) hair has four times the coverage value of a very fine hair. Older patients can tend to have finer hair. This is called “age-related thinning” or senile alopecia and it reflects changes in the hair that become uniformly “fine” throughout the scalp as men and women get older, usually past 60 to 70 years. This condition can also be rarely found in young men in their twenties as they move out of adolescence into adulthood.

The calculations in [Table 1] demonstrate the exponential nature of the increasing coverage values based upon increases in hair shaft diameter. It is very important to also appreciate that there is a big difference between arithmetic density and cosmetic density, which is the subjective appearance of density. Cosmetic density increases (or decreases) exponentially with numerical density and is dependent upon the combined characteristics of color, caliber, and curl of the hair. Manny Marritt performed the most interesting study in the late-1980s. He recruited a volunteer with black hair on white skin (medium-weight hair) and uniformly removed half of the hair on one side of his head. In-person observers as well as photos failed to identify the hair-depleted side. This tells us a great deal when evaluating how many hairs we need to transplant to give a patient a full “appearing” head of hair, and how many hairs we must leave behind in the donor area to keep the donor area looking healthy.

Hair Curl

Another characteristic of hair which plays a critical role on the cosmetic impact of FUE donor harvest is the tertiary structure of the hair shaft: it is the curl. This can vary from an extreme curl in African American hair, often referred to as “kinky,” to the very straight characteristic of Asian hair shafts. The coverage value of a hair shaft which is curly is much higher than a straight hair shaft. A surgeon should appreciate this very simple concept in assessing the donor area for estimating lifetime donor supply. Patients with curly hair will tolerate more FU deficits from FUE donor harvesting than straight-haired individuals, all other factors being equal.

Contrast Between Hair and Skin Color

When a blonde loses hair, it may not be visually detectable until 75 to 80% has been lost. This means that when replacing a blonde balding man's hair, less hair has to be moved to achieve a cosmetically satisfactory result. Black hair on white skin is another story, as loss of FU density will become apparent at a much lower numerical hair loss value.

This hair-to-scalp color contrast issue requires that the surgeon have an artistic sensibility as he/she assesses the coverage needs of the patient and, hence, the number of grafts that need to be harvested. Men with salt and pepper hair, regardless of skin color, often require a lesser number of grafts to harvest due to the way that white hair in multicolored hair strands reflect light, helping camouflage the contrast between the hair and scalp. This same principle of low contrast applies to men with dark skin and dark hair. Again, it is the surgeon's artistic sense that dictates how many grafts will be harvested and where they will be placed. Ultimately, this requirement for hair in the recipient area will impact decisions made regarding FUE donor harvesting. By observing these contrast issues related to removal of FUs, the surgeon will be able to forecast the short- and long-term cosmetic impact of FUE donor harvesting on the appearance of the back of the patients head.

Number of Donor Follicular Units Available For Hair Transplantation

Earlier in this chapter, the donor area size as it reflects the NW 7 pattern of balding was defined; however, this residual hair area may reflect varying amounts of the total hair-bearing area ranging from 12 to 25% in the NW 7 patient. Most surgeons would like to believe that the donor area is a 3-inch-high area running posteriorly around the head, immediately above the occipital notch and above both ears. However, with experience as one observes many NW 7-patterned patients, one may notice that this “3-inch” reference is inaccurate, in actuality being much more variable. In the photo ([Fig. 3]), this young man clearly is developing an NW 7 balding pattern. One can easily see that the donor area above the ears is not as full as the donor area in the mid-posterior scalp. As this patient is 25 years old, if he decides to have a hair transplant, very careful planning is needed. The patient's total numerical donor supply estimate plus his hair thickness will allow the surgeon to forecast realistic expectations that he should clearly communicate as part of the patient's personalized master plan during the initial consultation.

Fig. 3 Donor area in patient with a Norwood 7 balding pattern shows decreased density in the lateral supra-auricular areas, and a minimized height of the donor area in the midline occiput area.

The size of the donor area can range from 12 to 25% of the total surface area of the hair- bearing scalp. If the spread between the arrows in [Fig. 3] measured 2 inches, his total supply of follicular units will be cut by a-third when compared to the “average” 3-inch-high donor area. Unfortunately, many hair transplant practitioners have come to blindly assume the “3-inch rule,” obtaining informed consent based upon that assumption, many times not bothering to verify or measure the presenting patient's donor area. In those patients with that potentially smaller donor area, demonstrating even less supply that a classic NW 7 pattern, some of the that “permanent” hair transplanted will not really be permanent at all. Therefore, it is critical that we must be realistic when setting expectations in going forward on any hair transplant, and this therefore requires individualized close inspection of the potential donor area limitations. The total hair-bearing scalp measures 77 square inches, so the transplantable hair, using the 3-inch rule, reflect 12,500 FUs. Using Dr. Marritt's study observations,[7] for a medium-haired individual, 50% of the donor area can be removed without detectable thinning. However, when looking at the donor hair in [Fig. 3], it should be obvious that medium-weight hair standards cannot be applied to the reality of a person with fine hair. For finer haired individuals, significantly less than 50% of the donor area grafts may be harvested in order to leave enough hair to avoid a “balding or thinning” appearance due to overharvesting in the donor area. If one is to harvest donor hair from an area of low density and fine hair, the surgeon should question if the patient is a reasonable candidate for a hair transplant at all, especially if the hair loss due to androgenetic alopecia is significant. Those patients with coarse hair can typically tolerate harvesting more than 50% of the 12,500 grafts in the 3-inch-high donor area.

Residual Donor Hair Mass after Each and Every Harvest

The key to successful donor area management is to have enough residual hair mass to provide hair to cover the scars created from either linear strip excision (LSE) or FUE donor harvesting. The scars from FUE and LSE each have a unique impact on the donor area. LSE produces linear scars of varying widths and lengths, but typically, in the hands of a skilled surgeon, the width should be within 1 to 3 mm ([Figs. 4] and [5]). The length of the scar reflects the graft supply required for the procedure. The remaining donor area above and below the incision will expand, or stretch back, to offset the skin that was removed, often restoring the original scalp laxity. Stretching is uniform and covers a very wide area. Even the NW 7 patients eventually restore the height of the donor area over time after a strip excision is performed. Restoring the original scalp laxity is more the rule than not the rule. Scalp stretching reduces donor area hair density and obviously, the supply for future grafting. One must then be aware of how this stretch back will affect the cosmetic appearance of the linear scar. FUE is a different story. Uniform scalp stretching does not occur with FUE. FUE produces a nonuniform distribution of round scars ([Fig. 6]). Gaps, where follicular units previously existed, are not offset by donor area stretching. These gaps are often hypopigmented. They must be covered by the residual hair mass left behind after the FUE session is complete. Excessive number of FUE excisions will produce expansive gaps between remaining follicular units, making it difficult for the patient to hide the FUE donor sites ([Figs. 7] [8] [9]). Moreover, when the patient attempts to grow the hair longer to cover the hair mass deficit, the cosmetic appearance may be just as unacceptable, as the hair in this longer fashion may appear sparse, “stringy,” and unnatural due to its low density. Clearly, such depletion is offset when hair and skin color more closely match, or when a coarser hair affords the patient enough hair mass to cover the deficit.

Fig. 4 Linear strip excision donor scar showing 1 to 2 mm wide result, following proper surgical management should be a typical outcome.

Fig. 5 Linear strip excision donor scar with surrounding hair follicles retaining their presurgery cosmetic appearance of density is one of the benefits of linear strip excision donor harvest.

Fig. 6 Follicular unit excision donor scars are seen as round and hypopigmented areas through the donor area.

Fig. 7 Follicular unit excision scarring in the donor area after one session harvesting 1,800 follicular units illustrates the concept of changing density in the donor area following follicular unit excision donor harvesting.

Fig. 8 Appearance of the donor area after two follicular unit excision donor harvests totaling 2,870 follicular units. Once the hair mass becomes too low, the patient may not be unable to style their hair short. This is one of the cited benefits of electing for follicular unit excision donor harvesting over the linear strip excision method.

Fig. 9 Another example of serial follicular unit excision donor harvesting affecting the cosmetic appearance of the donor area, showing a significant decrease in hair mass.

Donor area depletion (overharvesting) is a matter of insufficient residual (remaining) hair mass. Hair density and thickness compose hair mass, so the thicker haired patient can afford to have more grafts removed from the donor area. For coarse-haired Caucasians with a typical density of 2.2 hair per FU, and medium-weight hair (50 µm), typically 7,000 grafts are a rule-of-thumb amount of hair that can be safely removed in lifetime of that patient.[1] On the other extreme, illustrated by a fine-haired patient with low follicular unit density, possibly less than 1,000 to 1,500 grafts might be that patient's lifetime donor supply. In the face of progressive, ongoing losses in a typical male androgenetic alopecia patient, this latter example should lead the surgeon to discourage surgery in any individual he/she believes would progress past a NW 2 or 3 pattern of balding. This is due to the demand which could not be met (using an FUE donor harvesting) without negatively impacting the appearance of the donor area. A higher original density changes the equation in favor of more graft potential regarding the lifetime supply of hair, but not necessarily enough to offset a very fine-haired donor patient presentation. As can be seen, this supply/demand relationship is not a simple linear relationship, and the surgeon must have the skills to make the judgments needed to balance the patient's desire for hair against the limitations imposed by total donor hair mass as reflected in the follicular unit density, hair caliber, curl, and color characteristics of the scalp and hair.

Addressing the 3-Inch Rule To Maximize Donor Hair Supply

Dr. Robert True introduced the concept that the NW 7 pattern harvesting area may be extended beyond the permanent 3-inch hair zone in selected patients.[8] His arguments are (1) most men do not progress to an NW 6 or 7 pattern and these advanced patterns can often be detected when hair transplants are considered; (2) careful graft placement can selectively implant grafts from outside the NW 7 patterned area into “low-priority areas,” that is, frontotemporal angles and portions of crown area; (3) young men want to frame their face with a more robust hairline while they are young and do not want to be bald while they are defining their manhood. These men, when they get older, may tolerate more posterior hair loss or loss from the lateral (not central) aspects of a reconstructed hairline made from grafts taken outside of the NW 7 donor area. With proper informed consent, such an approach may be reasonable in carefully selected patients.

The Unhealthy Donor Area

There are many dermatologic diseases, scarring and nonscarring alopecia, that impact the donor area such as lichen planopilaris (LPP) and alopecia areata. In addition, DUPA is an important clinical presentation to appreciate at the time of initial consultation, as this is virtually always an absolute contraindication for hair transplantation surgery. Many of these diseases may not be active at the time that a hair transplant is performed. Dr. Christine Shaver (bernsteinmedical.com) has been performing biopsies on many patients in both the recipient area and the donor area (verbal communication), targeting those hair transplant candidates where she identified physical signs of perifollicular scaling and redness in the frontal area as shown in [Figs. 10] and [11], and not infrequently in the central part of the whirl in the crown. She has taken biopsies on many young men and reported the presence of LPP in the donor area as well as the recipient area, often with little clinical evidence of disease in the donor area. She warns hair transplant doctors about performing surgery on these patients, or, at the minimum, informing the patients that this problem has been suspected so that appropriate informed consent can be conducted in the appropriate clinical setting. Typically, this requires performing a scalp biopsy ([Fig. 12]) in targeted areas where suspicion is high, including the donor, to rule out any active or past disease process.

Fig. 10 Perifollicular scaling and erythema in the frontal hairline of a patient with active lichen planopilaris. Scalp tissue surrounding the affected follicular units shows a flat, smooth appearance, and an absence of follicular ostia, characteristic of a scarring alopecia (Photo Courtesy of Robin Unger, MD).

Fig. 11 Under trichoscopic view of lichen planopilaris, erythema, scaling, and degradation of follicular units are visualized (Photo Courtesy of Christine Shaver, MD, at bernsteinmedical.com, used with permission).

Fig. 12 Histopathology showing loss of sebaceous units, perifollicular scaling, and perifollicular fibrosis, in donor area that clinically appeared normal (Photo Courtesy of Christine Shaver, MD, at bernsteinmedical.com, used with permission).

Diffuse Unpatterned Alopecia

This clinical presentation is a contraindication for any hair transplant. In this presentation, greater than 20% miniaturization is present throughout the scalp, including the donor area[2] ([Figs. 13] [14] [15]).

Fig. 13 Left supra-auricular and lateral parietal area showing diffuse unpatterned alopecia in a young patient.

Fig. 14 Posterior occiput demonstrating diffuse unpatterned alopecia.

Fig. 15 Note the greater than 20% miniaturization which characterizes low-quality donor hair in diffuse unpatterned alopecia.

Many people with this condition seek help in the form of a hair transplant to increase the density throughout their scalp. Unfortunately, this condition is sometimes not recognized by the novice hair restoration physician and the diagnosis is missed. Many of these patients with DUPA go on to have a hair transplant. Virtually all these patients will suffer from poor growth and visible scarring in the donor area. The diagnosis is easily made by close examination of the donor area both grossly and under trichoscopic examination. [Figs. 16] [17] [18] illustrate three examples of the donor area in men with DUPA under magnification. None of the patients presenting with this clinical characterization of the donor area should undergo hair transplantation surgery. Their hair transplants will likely fail to grow and they may end up with visible scarring and worse see-through appearance in the donor area. Virtually all of these patients will be upset with the physician for missing the diagnosis.

Fig. 16 This photo shows classic diffuse unpatterned alopecia with more than 50% miniaturization in the donor area above the occipital notch.

Fig. 17 Arrows pointing to the only terminal hair that were identified in this microscopic view of the donor area, while the rest of the field show hair with varying degrees of miniaturization.

Fig. 18 This photo shows early miniaturization of many hair in the donor area, some thread-like, while others just show thinning and/or significant loss of pigment.

Conclusion

Donor area management in the setting of FUE harvesting presents a challenging conundrum for the surgeon when faced with the typical lifetime demand for follicular units in patients presenting with male patterned hair loss. An artistic sensibility for the appreciation of how, when and why a “critical mass” point has been reached in harvesting the donor, beyond which no more donor hair should be removed, should be as strong if not stronger than the artistic sense required to create long-lasting, natural hair transplantation result in the recipient area. In addition to appreciating the caliber, density, and color contrast characteristics of the donor hair, the appreciation of the average hair per follicular unit and follicular units per square centimeter are details which inform the surgeon as to the overall hair mass, and, more importantly, the optical appearance of hair mass in the donor area. As an artist, the process of “seeing” is an appreciation of a “gestalt” behind the numbers and calculations which go into creating absolute measurements. In this day and age of FUE harvesting as the currently preferred method of donor harvest,[9] it is of critical importance that the cumulative cosmetic effects of serial FUE harvesting be discussed openly under full disclosure in the setting of informed consent in the initial consultation. [Figs. 19] [20] [21] [22] show the cumulative arithmetic decrease in FUs as they are removed from a section of donor area. The photos show removal of 25, 50, 75, and 100% of the initial FU density, respectively. As the surgeon utilizes the patient's donor hair for transplantation, that removal of FUs decreases the appearance of density in the donor area. In addition, it is important to appreciate that the subjective appearance of density (or lack thereof) is an exponential curve, not a linear one. In other words, depending upon the color, caliber and curl of the hair, a 50% FU loss may appear less dense on some patients than on others. In addition, with each subsequent surgery, the nuances of aging and lifestyle changes may possibly impact the quality of the donor area in a manner unforeseen in the initial phases of planning. Therefore, the surgeon-as-artist's approach to these possibilities needs to be fluid as he/she appreciates how these changes may affect the “gestalt” or bigger cosmetic picture of both the donor and recipient areas. Nowhere in hair transplantation surgery is the appreciation of the patient's entire scalp appearance more critical than in FUE donor harvesting. The well-versed hair transplant surgeon should be trained in the skillful use of LSE surgery as a necessary tool to utilize when FUE is not the preferred initial or subsequent harvest method of choice following an adequate clinical evaluation of the presenting donor area.

Fig. 19 The donor area after 25% of the follicular units are removed.

Fig. 20 The donor area after 50% of the follicular units are removed.

Fig. 21 The donor area after 75% of the follicular units are removed.

Fig. 22 The donor area after 100% of the follicular units are removed.

Conflict of Interest

None declared.

• References

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Publication History

Article published online:
04 December 2023