Anthropomorphic and perforator analysis of anterolateral thigh flap in Indian population.

BACKGROUND: Anterolateral thigh (ALT) flap is one of the most common flaps in the reconstruction armamentarium of plastic surgeons, but there is no published data about the flap characteristics in the Indian population. The aim of this study is to analyse the anthropomorphic characteristics of the ALT flap and the perforator details in Indian population.
MATERIALS AND METHODS: ALT flap details were studied in 65 patients of Indian origin comprising 45 males and 20 females. The study period is from August 2011 to July 2012. A prospective database of the Doppler findings, perforator and pedicle details and the flap morphology were maintained. The variables are analysed by using the SPSS, PASW statistics 18 software IBM(®).
RESULTS: In nearly 75% of cases, the perforator was found within 4 cm of the pre-operative Doppler markings. The percentage of musculocutaneous and septocutaneous perforators was 61.8% and 38.2% respectively. The pedicle variation was found in 6 cases (9.23%). The average thickness of the thigh skin in Indians is similar to the western people, but thicker than the other Asian people. Flap thinning was performed in nine patients without any major complications.
CONCLUSION: The perforator details and type in the Indian population are similar to the published reports from other parts of the world. We advise pre-operative Doppler examination in possible cases. The variation in pedicle anatomy should not be overlooked to avoid complications. The thickness of subcutaneous tissue of the flap is higher in Indians, but still can be safely thinned. The data of this study will serve as a guide for the ALT flap characteristics in Indian patients.

INTRODUCTION

Anterolateral thigh (ALT) flap has the advantages of large dimension, adequate size and sufficient length of pedicle, possibility of chimeric flap and division of flap based on perforators, which has made it an ideal soft-tissue flap at present. However the variability of perforators, the difficulty in pre-operative planning, more subcutaneous thickness has been described as the principal disadvantages for choosing an alternate donor site. Though there have been many studies from East Asia and the west addressing these features, there has been no published data from the Indian sub-continent. The aim of this study is to analyse the perforator characteristics, Doppler correlation, pedicle details and the tissue characteristics of the ALT flap in the Indian population.

MATERIALS AND METHODS

The study was performed between August 2011 and July 2012. The study included 65 patients comprising 45 males and 20 females. The minimum and maximum age of the patients was 6 and 84 respectively. We prefer to harvest the flap from the left thigh unless contraindicated. The number of ALT flap dissected was 65 in which 56 were used as free flaps, 6 as pedicled flaps and in the other three patients the flap was dissected but not harvested. Among patients in which the flap was not harvested, two patients had no perforator. In the 3rd patient, the excision plan was changed intraoperatively before ligation of the pedicle and the flap was returned.

The Doppler used is EMCO MINIDOP D500, 8 MHz probe, made in India. The pre-operative Doppler examination was not carried out in 15 out of 65 patients due to certain practical difficulties and logical issues. The perforators are marked just after induction of anaesthesia, using the hand held Doppler probe and marked on the skin with indelible ink. All perforators are marked in the ALT flap territory, along the line joining anterior superior iliac spine (ASIS) to the superolateral border of the patella. The acoustic Doppler signals from closely located perforators are identified by moving the probe to and away from the marked spot and hence the perforators are identified by the change in signal intensity. The perforator signal is differentiated from that the deeper vessel by doing the same manoeuvre as described above and also by the perforator compression test.[1] In this test, when we apply pressure over the perforator, the acoustic signal from the perforator will decrease whereas the signal from the deeper vessel will persist. All dissections are performed using a 4.5× operating loupes. Intraoperatively, both musculocutaneous (MC) and septocutaneous (SC) perforators entering the flap are marked. Those perforators with visible pulsation are considered reliable. The pedicle is identified and dissected from the origin until the first perforator intended to use to attain the maximum length.

A prospective database was maintained that included the thigh dimensions, pre-operative Doppler markings, intraoperative perforator findings, pedicle details and the flap characteristics. The perforators were marked as distance from the ASIS. The perforator distribution corresponding to the midpoint of thigh (Point B), 5 cm proximal to the midpoint (Point A) and 5 cm distal to the midpoint (Point C) are also marked. The thickness of the thigh skin was measured 10 cm above and below the midpoint.

Statistical analysis

The variables are analysed using SPSS, PASW statistics 18 software. By using invariant analysis, we calculated the average and standard deviation. The bivariate analysis is performed using Pearson correlation.

RESULTS

Among the 65 flaps dissected, only 62 flaps were actually used for the above mentioned reasons. There was one total flap loss (1.61%) for a lower limb defect, which was managed with split thickness skin grafting (STSG). Partial flap loss occurred in four patients (6.45%) among which three cases were managed conservatively and the other flap was salvaged with a regional flap.

Flap dimensions and defect details

The minimum and maximum size of the flap harvested was 72 and 432 respectively. The average size of the flap used was 183 cm2. Most of these flaps are harvested in an elliptical fashion to aid primary closure. The flap was dissected on the left side in 56 patients and on right side in nine patients. The flap was used as single paddle in 42 patients [Figure 1], for both lining and cover (bipaddled) in 19 patients [Figures 2a and b] and as a patch flap for pharynx reconstruction [Figures 3a and b] in one patient. Among the 19 flaps used for reconstruction of composite defects, 10 flaps were de-epithelized and the remaining 9 flaps were divided on perforators.

Figure 1

Single paddle

Figure 2a

Double paddle – de-epithelized

Figure 2b

Double paddle – divided on perforators

Figure 3a

Pharyngeal defect

Figure 3b

Anterolateral thigh flap inset

Doppler assessment of perforators and intraoperative correlation

In the 50 patients in whom the Doppler examination was performed, the total number of perforators identified intraoperatively was 121. The intraoperative location of the perforators and the relation to the pre-operative Doppler signal is mentioned in Table 1.

Table 1

Doppler identification of perforators

The Doppler examination is able to identify 48 (39.7%) perforators exactly corresponding to the pre-operative findings. In almost three-fourth of the cases, the perforator lies within 4 cm of the Doppler signal. The number of perforators marked by Doppler pre-operatively and the number of perforators identified during the surgery is shown in Table 2. The most common finding on Doppler examination was two perforators and the common intraoperative finding was three perforators [Figures 4a-d]. One patient had no Doppler signal on the left thigh, but had a fracture femur on the right thigh. Hence, we went ahead with the harvest from the left thigh and there were three perforators found during the flap dissection, which were used. On the other hand, the two patients with absent perforators, the pre-operative Doppler examination has picked up two signals in each of the case.

Table 2

Perforator details

Figure 4a

Single perforator (P)

Figure 4d

Four perforators (P1, P2, P3, P4)

Two perforators (P1, P2)

Three perforators (P1, P2, P3)

In the 65 patients, the total numbers of perforators identified were 157, out of which 97 (61.8%) were MC [Figure 5a] and 60 (38.2%) were SC [Figure 5b] and the overall utilisation rate of the perforators was 84.1% (132/157). The number of perforators in males and females are 107 and 50 respectively. There is no difference between the distribution and type of perforators with respect to the gender of the patient [Graph 1].

Figure 5a

P-Musculocutaneous perforator

Figure 5b

P1, P2 – Septocutaneous perforators

Graph 1

Perforator type versus gender

The distribution of perforators varies from 11 cm proximal to 15 cm distal to the mid-point. The majority of perforators in ALT are concentrated around the mid-point of the thigh. The number of perforators in the midpoint of thigh is 18 (11.46%) and the total number of perforators that are concentrated within 4 cm of the midpoint is 97 (61.78%) with a standard deviation of 4.94 [Graph 2]. The other common site for the perforators is point A and Point C, which is 5 cm proximal and distal to the midpoint respectively. The number of perforators in Point A and C is 26 and 34 respectively, which together accounts for 25.46%. The number of perforators used in each flap is mentioned in Table 3. More perforators are included when the flap is large, for composite defects and when the other perforators are small. In our study, two patients (3.07%) had absent perforators intraoperatively. One patient was salvaged with free radial artery forearm flap and the other with Anteromedial thigh flap. In one patient, there were no good perforators such that the flap can be solely based on it. Hence, we harvested the flap with significant muscle bulk and the flap settled without problems.

Graph 2

Distribution of perforators from mid-point

Table 3

Perforators used per case

Pedicle details

In the 65 cases analysed, there was one pedicle in 60 cases and two pedicles in five cases [Figures 6a and b]. In one patient, the pedicle had two arteries and two veins. All other pedicles had one artery and 2 veins of different/same size.

Figure 6a

Two pedicles (case 10)

Figure 6b

Two pedicles (case 2)

Hence, the overall pedicle variation accounts to 9.23% (6/65). The average length of the pedicle (from origin to the point of first usable perforator) was 10.06 cm with a range of 6 cm to 20 cm. The point of entry of the pedicle into the vastus lateralis muscle or disappeared intermuscularly between vastus lateralis and vastus intermedius was measured and the average distance was 13.93 cm (range 2-34 cm). In seven patients, the entire course of the descending branch was seen in the septum. The more proximally the pedicle enters the muscle and then naturally there are more MC perforators.

Flap thickness

The dermal thickness of the flap was same throughout the flap with an average of 2.28 mm (1-3.5 mm). The average thickness of the sub cutaneous fat in the proximal and distal part of the flap was 21.5 mm and 14.7 mm respectively [Figures 7a and b]. The females have a greater distribution of fat in the thigh [Table 4] and the average thickness of fat in females is 24% greater than the males.

Figure 7a

Flap thickness

Figure 7b

Flap thickness

Table 4

Skin thickness

There is a negative correlation between the average fat thickness and the Doppler signals, which are matching (Pearson correlation − 0.294). Hence, greater is the thickness of the fat thickness lesser is the reliability of the Doppler signal.

Flap thinning

Flap thinning was performed in nine (13.9%) patients. We remove the deep layer of fat leaving the superficial layer of fat with the skin. We do not thin the flap for a diameter of 2-3 cm around the perforator. Thinning was performed most commonly for buccal mucosa defects followed by defects in the foot. One patient of foot defect had marginal necrosis at the site of thinning and all other thinned flaps settled uneventfully. Flap thinning was performed in five female and four male patients. The average size and thickness of the flap in which thinning was performed is 197.89 cm2 and 22.8 mm respectively.

DISCUSSION

ALT flap was first described by Song et al.[2] in 1984. Though described as a SC perforator flap initially, the clinical usage and the anatomical studies revealed that MC perforators are more common. There has been a wide spread application of this flap both in trauma[34] and cancer reconstruction. Koshima et al.[56] were the first to describe the use of the ALT flap to reconstruct head and neck defects. Since then, others have reported their experience, establishing the ALT flap as one of the major workhorse flaps used for head and neck reconstruction.[78910] The yield of more soft-tissue, adequate pedicle length and size, possibility of skin paddle division based on perforators, decreased donor site morbidity have made it a versatile soft-tissue reconstructive too from head to foot.

The factors that make this flap to be used with caution are the distribution and type of perforators, the variations in pedicle anatomy and the thickness of the flap. The initial studies in the clinical application of the flap are predominantly from the Asians. Though from the same region, none of these studies had representation of the population from the Indian subcontinent.

Perforator details

The incidence of MC and SC perforators in different studies from the various region[8111213141516] of the world varies from 51-90% to 10-49% respectively [Table 5]. The MC and SC perforators in our study are 61.8% and 38.2%. Hence, the MC perforators are almost 1.5 times more common than the SC perforators in the Indian population. The perforators[101718] of the ALT flap are concentrated around the midpoint of thigh. In our study, the number of perforators that are within 4 cm of the midpoint is 62%. Another 25% of perforators lie within 1 cm diameter in Point A and Point C.

Table 5

Comparison of perforator types with other studies

The initial report by Koshima et al.[19] showed high figures of absent perforators as the flap was then considered to be supplied by the SC perforators. The increased application and the clinical studies have revealed that the absence of perforators occurs between 4.3%[17] and 5.4%.[9] The cadaveric and clinical study by Rozen et al.[20] shows a lack of appropriate perforators that can be used surgically in up to 16% of patients. Wei et al.[10] in their large series of 672 flaps, there was no perforator/fasciocutaneous vessel in only six cases (0.89%). The incidence of variation depends upon the study population also and in our clinical study of Indian patients, two (3.07%) patients had absent perforators intraoperatively and one (1.54%) patient had small perforators that a flap could not be exclusively based on it accounting to a total of 4.61%.

The knowledge about the variable presentation of these perforators makes the surgeon more confident when such a situations occur and also be prepared for the alternate plans. In the unfortunate event of absence/lack of good perforators, the salvage options are:

Anteromedial thigh flap[2122]

Tensor fascia lata flap[819]

Harvesting the flap with significant VL muscle

Converting the plan into vastus lateralis muscle flap ± STSG

Harvesting ALT flap from Contralateral side

Flaps from different donor site.

The alternate option is chosen based on the intraoperative findings, the nature of defect, requirement of post-operative RT and the skill of the surgeon. A detailed discussion on this point is beyond the scope of this article. When one thigh is unsuitable, then ALT flap can be harvested from the opposite thigh. However, there is a possibility that the findings in the other thigh could be symmetrical.[23] Hence in such cases, it would have been better if colour Doppler/computed tomography (CT) angiography had been carried out previously to assess the quality of the perforator. Otherwise, it is better to go for an alternate donor site.

Doppler assessment

The described modalities for pre-operative identification of the perforators are acoustic Doppler examination,[1824] colour Doppler[25] and CT angiography.[26] Hand held Doppler examination is the simple, easiest and readily available diagnostic tool for locating the cutaneous perforators. Pre-operative acoustic Doppler examination was able to identify the perforators exactly in nearly 40% of cases and in other 35%, the perforator lies within 4 cm of the Doppler signal. The number of perforators found intraoperatively is more than the pre-operative Doppler findings. This can be partly explained by the decreased curiosity from the surgeon to search for more after they have identified the initial few. Shaw et al.[23] were able to accurately locate the perforators using Doppler examination in two-third of cases. But the disadvantages are the poor reliability with increasing body mass index (BMI), inability to differentiate the type and source of perforators. In spite of these drawbacks, we still prefer to use this as the primary modality because of its simplicity and serves as a rough guide for locating the perforators. By experience, the surgeon may also be able to assess the quality of the perforator.

Colour Doppler examination provides more information than acoustic Doppler flowmetry because it offers better images of the branches of the main vascular pedicles and their perforators including the calibre, courses, origins and flow velocity. The limitation for its application is, they are not readily available, takes longer examination time and needs a radiologist experienced with this modality. 3-D CT angiography is the latest investigation modality that provides a roadmap of the pedicle and the perforators and both limbs can be studied simultaneously. However, it exposes the patient to radiation and also requires contrast injection. In a developing country like India, it is not available everywhere and also has financial implications. Hence, we prefer to use the acoustic Doppler examination as the primary modality of assessment in all cases and the other investigations are performed depending on the need.

Side of flap harvest

The side of the defect does not restrict the side of the flap harvest. Chen et al.[26] prefer to the harvest on the opposite side of neck defect for ease of harvest as two team approach. Being a soft-tissue flap, with a long pedicle it can be harvested from any side irrespective of the side of the defect. We prefer to harvest the flap on left side unless contraindicated. This makes the surgeon to have more familiar orientation, routine organisation of instrument trolley and thus saves the overall operating time.

Pedicle variation

Though there are many variations described the perforator variations, there are few articles about the anatomic variants of the pedicle itself. Kimata et al.[27] has described the 8 types regarding the origin of the ALT perforators. They can be from the descending or transverse branch of the lateral circumflex femoral artery (LCFA), profunda femoris or from the femoral artery. In our series, there was pedicle variation in 6 cases (9.23%). In 5 cases (7.69%), there were 2 pedicles and in one case (1.54%) the pedicle had 2 arteries and 2 veins. Among patients with double pedicle, the second pedicle was arising from the LCFA in three patients and in two patients the descending branch itself was dividing and to form 2 pedicles. Though they may appear similar to Kimata et al. type 4 and Type 1 classification of perforators, they are mentioned as pedicles because their size was equal or greater than the other descending branch and they themselves give either SC or MC perforators. When there are 2 pedicles, then the surgeon should choose one, depending upon the length of the pedicle and the perforators chosen. The practical difficulty occurs when we are not sure about the origin of the MC perforators. Dissect the perforator retrograde towards the pedicle to confirm its origin and harvest the flap accordingly. The flap with double pedicles can also be used as two separate free flaps if required. There is a single case report of the duplication of the major artery in the pedicle by Bhujel et al.[28] He has suggested the anastomosis of the larger vessel or to do anastomosis of both the arteries. However, in our case, the arteries were of the same size and hence we clamped the arteries individually with microclamp and assessed the perfusion in the flap. The artery with the better perfusion was anastomosed.

One of the main reasons for the ALT flap to be not popular in the western population as in the Asian population is the thickness of the flap and the complications associated with thinning of the flap.[29] The average fat thickness in males and females of different ethnicity is shown in Table 6. The fat thickness in Indians is higher compared with people from other continents as well as other Asian population. Hence, flap thinning will be required when so much bulk is not required. Kimura et al.[3031] has shown the successful transfer of thinned ALT flaps. However, Alkureishi et al.[32] has studied extensively the effect of thinning on the blood supply to skin and has recommended not doing one stage thinning of the ALT flap in the western population. Kimura et al. thinned the flap to 3-4 mm thickness leaving a 2 cm cuff of fascia around the perforator. The superficial layer of fat is supplied by the sub-dermal plexus and the oblique branches from the perforator. The obliquity of the vessel then depends on the thickness of the fat. Hence, in Indian with thick thigh skin, we leave a 3 cm cuff of fascia around the perforator. In our series of 9 thinned ALT flaps, only one patient had marginal necrosis, which settled on conservative treatment. But when the flap is small, then this cuff of fascia surrounding the perforator has to bear the weight of the flap and there is a chance of compression to the perforator. Hence thinning technique can be definitely done in large flaps and should be cautiously done in cases of small flaps. It is always better to thin the flap before the pedicle is ligated. This is for better visualisation of the perforator and also helps to assess the perfusion of the flap after thinning.

Table 6

Flap thickness in different population

Limitations of the study

We have not calculated the BMI of the study population and compared it with the flap thickness and Doppler sensitivity. The study population is less (n = 65) and all patients except one are cancer patients in a different stage of the disease. Hence, these anthropomorphic features should be confirmed in the general population by further studies. The Doppler examination and the intraoperative assessment were done by different surgeons and hence there are possibilities of subjective variations both in the pre-operative and intraoperative assessment.

CONCLUSION

The study includes Indian population from different states and has compared with published data from other parts of the world. Though many findings are similar to the previous studies on ALT flap, some findings are unique to the Indian population. The thickness of subcutaneous tissue in the ALT flap in Indians is more than the western population, but still can be successfully thinned and applied for head and neck reconstruction like the other Asian population. The pedicle and perforator variation though uncommon, the surgeon should be aware of such variations and manage it accordingly. Acoustic Doppler findings serve as a guide for locating the perforators and should be done whenever possible. ALT flap has become an ideal soft-tissue flap in the armamentarium of the reconstructive surgeon. However, there are no perforator and the morphological study of this flap in the Indian population. This data will definitely serve as a valuable guide for surgeons and benefit the patients.