A Cadaveric Study on Perforator Anatomy of the Medial Sural Artery Perforator Flap

Abstract

Background The medial sural artery perforator (MSAP) flap was described by Cavadas et al in 2001. The aim of this study was to analyze the flap characteristics in the regional population and was planned as a cadaveric dissection study.

Methods Thirty-three legs of fresh cadavers were studied for perforator characteristics, length, and origin of pedicle and skin paddle thickness. Observations were documented and analyzed.

Results Seventeen right legs (51.5%) and sixteen left legs (48.5%) were studied. Twenty-five pedicles originated from popliteal artery (86.2%) and four (13.8%) from the common sural trunk. No perforators were seen in four legs. The mean number of perforators is 2 (0–6). The mean distance of perforator from midpoint of popliteal fossa was 10.7 cm (8–13 cm) and from posterior midline it was 3.2 cm. The mean size of the perforator was 1.1 ± 0.8 mm (0.8–1.5 mm). The mean pedicle length was 9.3 ± 1.3 cm. The mean flap thickness was 4.3 ± 0.7 mm (3.0–5.5 mm). There was no correlation for flap or perforator characteristics with side of leg.

Conclusion This study concludes that MSAP is a good flap in terms of perforator characteristics, pedicle length, and flap thickness, when a medium sized thin flap with long pedicle is needed. The location of perforator on calf varies in different population. Being a perforator flap, anatomical variability is common and should be thought of while choosing this flap.

Keywords

perforator anatomy - MSAP - musculocutaneous perforators - gastrocnemius

Introduction

Free flaps from calf region have been described as early as 1984.[1] But it took 16 more years for the medial sural artery perforator (MSAP) flap to be described by Cavadas et al as a perforator-based fasciocutaneous flap.[2] It is an ideal choice when a thin supple flap of small-to-medium size is needed, but with minimal donor site morbidities. The MSAP flap is a thin flap with a long pedicle like radial forearm free flap (RFFF).[3] It has tremendous possibilities for applications in a variety of soft-tissue defects, like reconstruction of soft tissue defects in (1) lower extremities—as a pedicled flap for defects around the knee and as a free flap to the distal defects[4] [5] (2) small-to-medium-sized intraoral defects where a thin pliable flap is needed, for example, after hemi glossectomy[6] [7] (3) hand defects[8] and (4) pharyngoesophageal defect.[9] In oral cavity reconstruction, MSAP flap is emerging as a reliable choice since its invention, replacing both anterolateral thigh flap due to its bulkiness and RFFF due to its undesirable donor site morbidity.

MSAP flap is designed over the medial head of gastrocnemius muscle and the blood supply, namely median sural artery, comes from either popliteal artery, or in 30% cases, from a common sural trunk. After the initial few centimeters, the vessel enters and runs through the medial belly of gastrocnemius muscle and the course of the artery largely remains longitudinal between the muscle fibers before its division into lateral and medial branches, which usually occurs in the substance of the muscle (85%).[2] Muscle devascularization is not a concern as there are other vascular supplies to the muscle apart from medial sural artery.[10] The overlying fascial plexus and skin are supplied by the musculocutaneous perforators from the branches.

Taylor and Daniel were the first to propose the posterior calf as an option for perforator-based free flap reconstruction.[11] Later, Montegut and Allen and then Hallock described the topographical anatomy of the posterior calf laying the foundation for Cavadas et al to perform the first clinical series of six MSAP flaps.[2] [12] It has also been recognized that the MSAPs are more dominant, while the lateral perforators are typically fewer and less reliable.[2] An anatomical study of MSAP in Asian population has pointed out difference in the topography of perforators due to the difference in proportion of gastrocnemius to leg length in Caucasian and Asian populations.[13] This study investigates the perforator topography, and flap characteristics of MSAP flap in a sample of the regional South Indian population and was conducted as a cadaveric dissection study.

Methodology

This study was conducted as a prospective observational study with the help of department of forensic medicine and toxicology. Cadavers that are less than 24 hours old, properly preserved in freezer, and without damage to the region concerned were studied. Those cadavers with signs of putrefaction even if less than 24 hours and those which have been embalmed are not used for this study. Medial sural artery flap dissection was performed and the perforators supplying the region—their number, size, and position—were recorded. Flap thickness was also measured.

Technique of flap dissection was as follows—Though the flap is dissected with limb kept in “frog leg” position in the actual clinical situation, this was not possible in the autopsy room due to post mortem rigidity. Hence, all cadavers were positioned prone for ease of dissection. The line joining midpoint of popliteal fossa and prominence of medial malleolus drawn and its proximal 15 cm was marked ([Fig. 1]). An exploratory incision was put 4 cm anterior to the above line from 5 to 15 cm from popliteal fossa and the skin flap was raised in subfascial plane posteriorly ([Fig. 2]). Thickness of the skin flap was measured using a caliper. The perforators emerging from medial gastrocnemius and piercing deep fascia were identified and their size and number were noted. Position of the perforator was noted in terms of vertical distance from popliteal fossa, and horizontal distance from posterior midline. The largest perforator(s) were identified and then traced back toward the popliteal artery by splitting the muscle ([Fig. 3]). Length and its dimensions were measured using a caliper and a measuring scale ([Figs. 4] and [5]). Photographic documentation of the vessel and its perforators was also done. The data was entered in excel sheet and analyzed with SPSS software.

Fig. 1 Marking of axis and proposed incision.

Fig. 2 Incision over skin and fascia exposing muscle.

Fig. 3 Identification and intramuscular dissection of perforator.

Fig. 4 Pedicle dissection completed up to source vessel.

Fig. 5 Pedicle length measured after division from popliteal artery.

Results

In this study, 33 legs of cadavers were dissected for MSAPs. Seventeen right legs (51.5%) and 16 left legs (48.5%) were studied for the various characteristics of the perforators. Majority subjects were males, that is, 81.8% and only 18.2% subjects were female.

In 25/33 legs, the pedicle originated from the popliteal artery (86.2%) and four of them (13.8%) originated from the common sural trunk. The mean number of perforators of MSAP flap in a leg according to this study was 2(0–6). However, in four cases no perforator was identified after exploration and dissection. The mean distance of MSAP perforator from midpoint of popliteal fossa was 10.7 ± 1.1 cm and the mean horizontal distance of perforator from posterior midline was 3.2 ± 0.6 cm. The mean size of the perforator was found to be 1.1 ± 0.8 mm (0.8–1.5 mm). The mean pedicle length observed was 9.3 ± 1.3 cm. The mean flap thickness observed was 4.3 ± 0.7 mm (3.0–5.5 cm). There was no significant side predilection for characteristics like flap thickness and number and distribution of perforators observed in this study. The commonest anatomy of the perforator is depicted diagrammatically ([Fig. 6]).

Fig. 6 Schematic diagram of vessel anatomy of medial sural artery (MSA) perforator flap.

Discussion

MSAP flap was described and developed in early 2000. It can be used as a free flap or a pedicled flap.[14] [15] [16] The flap has a long pedicle, and it also provides a thin pliable and relatively hairless skin paddle, with minimal donor site morbidity. Being a perforator flap, it has the advantage of not sacrificing a major limb vessel. The other obvious advantage of MSAP flap is the relative thinness of flap that makes it favorable for intraoral reconstruction, reconstruction of dorsum of hand, dorsum of foot, etc. The donor site in most cases can be primarily closed or skin grafted, and the site can be covered well with cloths. The major disadvantages of this flap are variable perforator anatomy and reduced vessel caliber. Another main technical disadvantage is long harvesting time due to tedious and meticulous intramuscular retrograde perforator dissection. Being a perforator flap, one may encounter situations where a suitable perforator may not be seen. Perforators from median sural artery, lateral sural artery or further distally, and a posterior tibial artery perforator may be used as the basis of a flap from the same region.[17]

In this study, the median sural artery pedicle could be dissected only in 29 cases as no perforator could be identified in 4 out of 33 legs. In 25 legs (86.2%), the median sural artery originated from the popliteal artery and in 4 of them (13.8%), it originated from a common sural trunk. These findings were in line with the observations made by Altaf in his study “The anatomical basis of medial sural perforator flap” where they noticed that the medial sural artery originated from the popliteal artery in 70% of the cases or from a common sural trunk in 30% of the cases.[18] The mean number of perforators of MSAP flap in a leg according to this study is two. Maximum number of perforators obtained was six and there were four cases where not even a single perforator was obtained. The absence of medial sural perforator has been reported in other studies too.[19] In this study conducted by Sarah Al-Himdani et al in 2020, it was observed that a mean of 2.1 ± 0.99 perforators arose from medial sural artery.[4] Also, Cavadas et al observed in 2001 that a mean of 2.2 perforators in the range of 1 to 4 arose from medial gastrocnemius muscle.[2]

The mean distance of MSAP from midpoint of popliteal fossa was 10.7 ± 1.1cm (8–13 cm) and the mean distance of MSAP from posterior midline was 3.2 ± 0.6 standard deviation. Al-Himdani et al observed that the MSAPs arose from medial sural artery at 11.9 ± 2.07cm below popliteal fossa and Cavadas notes that the perforators are concentrated between 9 and 18 cm from popliteal crease.[2] [4] Kao et al reported that none of the perforators were found outside 6 to 8 cm below the popliteal crease[20] Kim reported that the perforator can be identified within 2 cm radius, at 8cm from above, on a line connecting the mid popliteal fossa to the medial malleolus.[21] The various studies show that though the number and size of perforators remain more or less the same in various populations, the distance range from popliteal crease having the maximum perforator concentration varies according to the body habitus of the population studied.[13]

In this study, the mean size of the perforator is found to be 1.1 ± 0.8 mm (0.8–1.5mm). According to many studies, the average external diameter of the largest perforator was 0.9 to 1.5 mm.[2] [18] [22] The mean pedicle length of the MSAP in our study was found to be 9.3 ± 1.3 cm. In a clinical series by Cavadas, a pedicle length of 6 to 11 cm is noted.[2] However, according to Altaf the pedicle length was noted to be longer. They observed a length of 18 ± 0.03 cm (15–21 cm).[18] A comparison of flap parameters from various studies is shown in [Table 1].[23]

Table 1 Comparison of flap parameters in various studies

Study	This study	Cavadas et al2	Altaf18	Al-Himdani et al4	Chiu24	Kao et al20	Okamoto et al13	Ngo et al23
Maximum perforator concentration (distance from popliteal crease)	8–13cm	8.5–19cm	10.2–15.9cm	8–14cm	8–12 cm	6–18cm	5–17.5cm	5.1–18.63 cm
Number of perforators	0–6	1–4	1–5	1–4	2–4	1–5	1–5	1–5
Pedicle length	8–12cm	6–11cm	15–21cm		9–16cm
Origin—popliteal: common sural trunk	86:14		70:30	60:40

The mean flap thickness of MSAP flap was found to be similar to that observed in other anatomical studies. However, we feel that the paucity of female subjects in this study sample might have made the value skewed toward the thinner side. There was no side predilection for characteristics like flap thickness and distribution of perforators observed in this study.

MSAP flap is a relatively new flap, and it is gradually coming up as a good alternative to radial forearm flap due to the similarities in flap characteristics, at the same time avoiding some of its major disadvantages like sacrifice of a major vessel and donor site morbidity.[17] [20] However, being a perforator flap, intramuscular dissection of perforator and anatomical variability makes it a “not so easy” flap. This study analyses the perforator characteristics in a sample of South Indian population, and it shows subtle differences in the topography of perforators and pedicle length compared with other studies.[2] [13] [20] The smaller sample size and a predominance of male subjects are limitations of this study.

Conclusion

MSAP flap is a good flap with relatively constant flap characteristics like flap thickness, pedicle length and caliber, but the location of perforator on calf is variable in different populations based on the body habitus of the specific population. Being a perforator flap, one should expect anatomical surprises like an absent perforator and must be ready with a backup plan.

Conflict of Interest

None declared.

Note

This study was submitted as thesis for MCh Plastic Surgery to Kerala University of Health Science by the first author.

Authors' Contributions

All the authors participated in designing this study. H.M.T. and S.R.S. did the data collection and prepared the manuscript. H.M.T. compiled and analyzed the data. S.C.P. and L.M. supervised data collection and analysis, reviewed, and approved the manuscript.

IRB Approval

This study was approved by the Institutional Review Board of Government Medical College Kottayam (38/2021).

• References

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• 3 Nugent M, Endersby S, Kennedy M, Burns A. Early experience with the medial sural artery perforator flap as an alternative to the radial forearm flap for reconstruction in the head and neck. Br J Oral Maxillofac Surg 2015; 53 (05) 461-463
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Publication History

Article published online:
18 March 2024