| "Like replaces like" is the basic principle in reconstructive microsurgery. Therefore, toe-to-hand transfer has been widely used for thumb and finger reconstruction with excellent results. However, the procedures are challenging mainly due to the great anatomical variations of the first dorsal metatarsal artery (FDMA). There are several classification systems of FDMA, with Gilbert’s classification is the most widely used one in clinical application. Fifty feet were injected with color latex and dissected in Gilbert’s original study in1976. Based on the anatomy of the first web space, FDMA was classified into three types depending on the relationship to the first dorsal interosseus muscle (FDIM). In most specimens in their study, FDMA was found to be superficial or lies in the FDIM. FDMA laid deep under FDIM in22%of their specimens. It also mentioned that FDMA were very slender in10%of the specimens. In1983, Leung classified FDMA into seven types based on their anatomical study of the first web space and the metatarsal area. The absence of the first plantar metatarsal artery (FPMA) and dorsalis pedis artery (DPA) were also included in their classification system. May and Lee reported different classification systems based on the sagittal course of FDMA. Lee (1997) classified FDMA into2groups based on both the origin of FDMA and the communication between FDMA and FPMA in the first metatarsal space. May concluded that the terminal branches of FDMA had three types of communication with FPMA, which included:(1) The terminal branch of FDMA joined the bifurcation of FPMA,(2) The terminal branch of FDMA joined the first plantar digital artery,(3) The terminal branch of FDMA joined the second plantar digital artery.From December,1998to December,2010, we performed more than600cases of toe-to-hand transfer for thumb and finger reconstruction and did48fresh cadaver dissections. The anatomy of FDMA was found to be different to that described in previous studies in the literature. We summarized our findings here and proposed a new classification system to help a surgeon to better understand the anatomy of FDMA and harvest FDMA based tissue transfer.MATERIALS AND METHODS:24fresh human cadavers were obtained from the Willed Body Program at Southern Medical University, Guangdong, China. Anatomical studies were done on the48foot specimens from these cadavers. The foot specimens were amputated at the ankle level, and the anterior or posterior tibial artery was cannulated and perfused with warmed saline until the venous return was clear. The specimens were then perfused with25ml red latex through anterior or posterior tibial artery and stored at-30℃until dissection. During the dissection, an incision was made on the dorsal aspect of foot from the ankle to the toes web space. Different parameters of FDMA were recorded, including its origin and diameter, relationship between FDMA and FDIM; diameter of its communicating branch with FPMA. The diameters of arteries were measured with a vernier caliper. The diameter of the FDMA’s communicating branch with FPMA was considered clinically significant if its diameter was0.5mm or larger.A total of30cast specimens were studied in our research.20ml of ethyl acetate was injected through the anterior or posterior tibial artery into each foot specimen to expand small blood vessels, and cast specimens were made by injecting a mixture of denture material and a perchloroethylene into the artery. Lixivium was used to corrode soft tissues while keeping bone intact in5of the cast specimens, whereas bones were removed in other cast specimens. The origin of FDMA and its communicating branch with FPMA were carefully examined.A total of148clinical cases were studied (116male,32female; aged5～58yrs, average33.5yrs). All patients had surgeries for free tissue transfer pedicled with FDMA, e.g.2nd toe transfer, and big toe wrap-around flap transfer, etc. Dissecting out FDMA (the pedicle) was the critical part of these procedures. The origin (arises), branches, and running course of FDMA were closely examined and recorded.CT angiography and three-dimensional reconstruction were done in5healthy adult volunteers. Informed consents were obtained from all5volunteers on CTA study. After the contrast media iohexol was injected into the cephalic veins, the feet were scanned with a multidetector CT (GE Discovery CT750HD). The data were processed by Volume rendering (VR), multiple planar reformation (MPR), curved planar reformation (CPR) and pseudo-color post-processing in a working-station (GE-ADW4.4).FDMA and DPA were examined by Ultrasound Color Doppler Imaging (CDI, GE Vivid7, M12L) in340feet of170healthy adult volunteers (98male,72female; aged15～60yrs, average37.5yrs). The origin and diameter of FDMA, and its relationship to the FDIM were recorded.ResultIn majority of our cases, FDMA originated from DPA, and ran toward the first web space. The average diameter of FDMA at the origin was (1.48±0.20)mm. Proximally, it passed under a muscular arch formed by the tibial head of FDIM. Distally, it proceeded superficially over the deep transverse metatarsal ligament. At the distal part of the1st web space, FDMA gave off two dorsal digital arteries, for blood supply of the great toe and the2nd toe. FDMA had many anatomic variations, including:its origin, running course in the first intermetatarsal space, anastomosis with FPMA, and diameters of FDMA and its branches.Anatomy of FDIMFDIM has two heads, the fibular head attached to the2nd metatarsal and the tibial head attached to the1st metatarsal. The muscle bellies from the two heads are fused together distally. It then passes dorsally over the deep transverse metatarsal ligament and inserts at the base of the proximal phalanx and dorsal digital aponeurosis of the2nd toe. The length of the attachment of the tibial head on the metatarsal is only about 1/5of that of the fibular head. Therefore, it is easy to cut the tibial head off the1st metatarsal instead of the fibular head.Anatomical relationship between FDMA and FDIMTwo different kinds of anatomical relationships between FDMA and FDIM in the first intermetatarsal space were observed in this study.1. FDMA runs superficial to FDIM. In this type, FDMA may branch directly from DPA or from the deep plantar branch of DPA when it perforates between the two head of FDIM. FDMA then courses distally towards the1st web space, lying superficial to FDIM. Around metatarsophalangeal joint level, FDMA sends out two dorsal digital arteries to supply the blood for the dorsal skin of the great and2nd toes. FDMA then proceeds over the deep transverse metatarsal ligament at the distal part of the first web space, and usually anastomoses with FPMA.2. FDMA runs in the space between FDIM and the first metatarsal. In84.29%of the specimens from our study, FDMA arose from DPA, coursed plantarly, and then passed under the muscular arch formed by the tibial head of FDIM. It ran closely to the first metatarsal. It coursed dorsally at the distal1/3of the space and superficially to the interosseus muscle. However, it always passed under the deep transverse metatarsal ligament. It gave off small muscular branches to FDIM.The anatomical patterns of FDMA can be easily observed in our cast specimens. The anatomical patterns of FDMA can be easily observed in our cast specimens. In86.67%of our cast specimens, FDMA arose from DPA (16.67%arose from DPA directly and70.00%from the deep plantar artery). In6.67%of the cast specimens, FDMA arose from the deep plantar arch directly or had a common trunk with FPMA that arose from the deep plantar arch. In83.33%of all the cast specimens, FDMA anastomosed with FPMA, and then gave off the fibular side plantar digital artery to the big toe and the tibial side plantar digital artery to the2nd toe. In13.33%of the cast specimens, FDMA and FPMA did not anastomose, or the diameter of the communicating branch between these two arteries was less than0.5mm. FDMA and FPMA individually sent out one main branch to supply one side of the first web space: fibular side of the great toe or tibial side of the2nd toe. This pattern was also found in the fresh cadaver dissections and clinical cases. In1case of all the cast specimens, FDMA did not anastomose with FPMA. FDMA gave off two branches of dorsal metatarsal arteries, while FPMA gave off two branches of plantar metatarsal arteries. There was no communication among these branches.CDI can quantitatively measure the real-time intravascular blood flow in the extremities noninvasively. In our study, CDI was used to monitor the blood flow to FDMA and DPA continuously. In84.12%of our340cases, FDMA lay in the space between FDIM and the first metatarsal. In11.76%of the cases, FDMA lay superficial to FDIM. We also recorded the origins of FDMA. FDMA arose from DPA in85.00%of the cases, and from the deep plantar arch along with FPMA about10.88%of the cases. FDMA was absent, or the diameter of FDMA was less than0.5mm in4.12%of our cases.It is convenient and accurate to illustrate the blood supply to the1st and2nd toes by using multidetector CT angiography. The continuous transformation images on the coronal plane show the positional relationship of the muscle and the artery. The artery and muscle were also located with the curved planar reformation technique, and3D reconstruction. In most of the cases in our study, FDMA coursed in the spaces between the first metatarsal and the FDIM. FDMA lies on the surface of the FDIM in a small percentage of our cases.In8.16%(16/196) of our fresh cadaver dissections and clinical cases, there was collateral FDMA. It arose from DPA along with FDMA, and runs superficial to FDIM. It usually anastomosed with the distal part of FDMA or FPMA and provided partial blood supply for the1st and2nd toes. The collateral FDMA had a small diameter (average0.5mm) in most cases. However, it had comparable diameter to FDMA in2cases in our study.In some cases, we could not find FDMA either in cadaver dissections or during surgeries. This could be due to the small caliber, or even absence of FDMA. This type is similar to Gilbert’s type III, and accounts for4.25%of all the cases. Intramuscular type of FDMA was described in the other classification systems in the literature, which refers to that FDMA went inside or through the FDIM. However, we didn’t find the intramuscular type of FDMA in all the surgical cases and anatomical specimens in this study, which contradict the previous classification systems.ABC classification method of FDMAWhen harvesting a FDMA based tissue for transfer, it is critical to know the origin, course and the main branches of the pedicle. Therefore, we proposed here a new clinical classification system to better describe the anatomy of FDMA based on these3key aspects of the artery:the origin of FDMA (Arise), the branches of FDMA in the first web space (Branch), and the course (Course) of FDMA in the first intermetatarsal space. We named this the "ABC" classification system of FDMA. First, the origin (Arise) of FDMA can be divided into3types:(1) the dorsal type (86.16%):FDMA originates from the DPA, as a direct continuation branch or derived from deep plantar artery, was denoted as A1;(2) the plantar type (9.46%):FDMA arises from the deep plantar arch or arising from the same branch of the deep plantar arch together with FPMA. It was denoted as A2;(3) slender type (4.38%):diameter of FDMA was smaller than0.5mm,or it was too slender to be found in operations and in perfused specimens. It was denoted as A3.Second, the main terminal branches (Branch) of FDMA in the first web space can be divided into3types:(1) B1, communication type (84.96%):FDMA and FPMA anastomoses with each other, and the diameter of the communicating branches larger than0.5mm.This type is safe for tissue transfer pedicled with FDMA.(2) B2, independent type (9.73%):FDMA and FPMA don’t anastomoses with each other, or the diameter of the communicating branch between these two arteries is less than0.5mm. FDMA and FPMA independently send out one main branch to supply one side of the first web space, fibular side of the great toe and tibial side of the2nd toe. Therefore, only one side of tissue, either great toe or the2nd toe, can be harvested based on FDMA.(3) B3, the slender type (5.31%):the diameter of the terminal branch of FDMA is smaller than0.5mm, or there is no significant anastomosis with FPMA. The great and2nd toes were mainly supplied by FPMA. Therefore, free tissue transfer can’t be harvested based on FDMA.Third, the course (Course) of FDMA in the first intermetatarsal space can be divided into3types according to the spatial relationship between FDMA and FDIM.(1)C1, interspace type (84.29%):FDMA goes under the tibial head of FDIM and courses into the interspace formed by FDIM and the first metatarsal. It stays closer to the first metatarsal at the distal part of the interspace and courses superficially towards the dorsum of the foot and passes over the deep transverse metatarsal ligament.(2) C2, superficial type (11.46%):FDMA runs superficial to FDIM during the whole course.(3)C3, slender type (4.25%):The diameter of FDMA is less than0.5mm and it is difficult to be found and dissected out. It is not suitable to do FDMA based free tissue transfer.Our ABC classification system is based on the three fundamental characteristics of FDMA:origin (arising), branches and its course. FDMA can be classified by combining these three basic characteristics, e.g. Type:A1B1C1and A2B1C1etc.DiscussionFDMA based free tissue transfer has been widely used in reconstructive microsurgery. Familiar with the anatomy of FDMA is the key to ensure the sufficient blood perfusion for the transferred tissue. The ABC classification system that we described here gives a more accurate and clear description of the anatomy of FDMA for surgery purpose.FDMA originates from DPA or one of its branches. However, the origin of the DPA also has many variations. DPA can be as a direct continuation of the anterior tibial artery, which is the most common type. It can also be a direct continuation of the peroneal artery, or from the communicating branch of the anterior tibial artery and peroneal artery. Regardless of its different origins, DPA is defined by its location on the dorsum of the foot and supply blood to tissues around the first web space. FDMA originating from DPA or the deep plantar artery is classified as type Ajin this study.Retrograde dissection of the pedicle was suggested in the toe-to-hand transfer surgery.The origin of the type A1of FDMA is superficial and the dissection of the pedicle is easy. If the origin of FDMA is type A2, the tibial head of the first interosseus should be divided and retracted to fibular side in order to dissect out the pedicle.Many detailed anatomical studies have been done to investigate the different anastomosing types between FDMA and FPMA. This is the basis for the type B (branches) in our classification system, which is also one of the critical parts in harvesting FDMA based tissue transfer. In type B1of FDMA, the anastomosing branch is big enough (the diameter>0.5mm) for the blood from FDMA to flow through to the plantar digital artery. Therefore, it is safe to harvest FDMA based2nd toe and/or great toe tissue transfer. There are2patterns of type B2for the anatomy of FDMA:it is either running towards the fibular side of the great toe or the tibial side of the2nd toe. Therefore, only one side of the tissue, either the great toe or the2nd toe, can be harvested for tissue transfer pedicled with FDMA. If the wrong side of tissue is harvested, the surgery will fail. In type B3, the anastomosing branch of FDMA to the plantar digital arteries will be too slender for harvesting any FDMA pedicled great toe or2nd toe tissue transfer.The intramuscular type described by Gilbert that FDMA coursed inside the interosseus muscle was not found in any cases of our study. The most common type was type C1of FDMA. Many literatures described that FDMA coursed inside or under FDIM and lots of surgeons have the misconception that this is the most common anatomy type of FDMA. Therefore, they may cut open FDIM and try to dissect out to FDMA. This will cause many pitfalls of the surgery:damaging FDIM, jeopardizing the blood supply to the skin, and making the procedure more complicated and prolonging the surgical time etc. According to our study, FDMA does not course inside FDIM. In type C1of FDMA, the tibial head is easy to be divided and retracted to the fibular side. FDMA can then be easily dissected out in the space between FDIM and the first metatarsal.The tibial head of the muscle can be sutured back as much as possible after the pedicle has been dissected out.CDI is noninvasive, convenient, safe and cheap. The results of CDI are consistent with intraoperative findings. It can be used preoperatively to quantitatively measure the intravascular blood flow and classify FDMA. Therefore, a surgeon can know the anatomical variations of FDMA before a surgery by using CDI study.We described detailed anatomical variations of FDMA in this study, especially the findings that were critical for harvesting a FDMA base vascularized free tissue transfer. We also propose an "ABC" classification system based on this study. It can give a surgeon a clear picture of different anatomical variations of FDMA and help him/her to easily and successfully harvest a vascularized tissue transfer based on FDMA. |
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