Invited Discussion

Ichikawa et al. present an interesting study using a rabbit microvascular model to evaluate the mechanical properties of a biodegradable vascular coupling device. Within plastic surgery, it has been the trend to utilize biodegradable material, where once permanent alloplastic material was commonplace. This trend is no more apparent than in craniofacial surgery, in which the use of biodegradable plating systems has all but replaced metallic systems in the pediatric population.[1] The methodology has clear advantages, including the removal of the risk of plate translocation across the calvarium, and the decreased risk of transcutaneous plate or screw palpation.

In fact, great efforts have been made to develop composite materials that will not only be resorbed, but will be replaced by the missing tissue required. This inductive approach to surgery is likely the future path in our field. Like laparoscopy, in general surgery, the full utility of these techniques and resorbable materials are, to date, unclear.[2] Adding to this growing area of plastic surgery, the authors present the idea of a sutureless and completely resorbable vascular anastomosing system. Although the idea of this approach is not new, there has been no significant laboratory experience, until the recent use of this type of device. The device described has a fully resorbable body, a copolymer of L-lactic acid and glycolic acid (70/30 percent), with non-resorbable stainless-steel pins anchoring the anastomoses. These pins remain around the anastomotic site after the coupler resorbs.

Since the beginning of their development, non-resorbable coupling devices have become relatively commonplace in institutions performing high-volume microsurgery. In our own institution, coupled anastomoses for free-tissue transfer are not only common, but are preferred in many circumstances. Although the primary use for the device is within venous anastomoses, there is an increasing use of the system for arterial anastomoses under favorable circumstances. Although the most common use of the device is for elective breast reconstruction, it is also used frequently in lower extremity, facial, and upper extremity free-tissue transfer.[3] [4] [5] [6] We have also used it for traumatic vascular injuries requiring repair mainly in the upper extremity and hand.

The clear benefits of such a system are operative speed, anastomotic reliability (among experienced surgeons), anastomotic stenting against external compression, limiting spasm at the anastomotic site and, most important, intima-to-intima anastomotic contact without intraluminal foreign body.[7] We are most enthusiastic about this device for the reasons mentioned above, and have clinically noted excellent long-term results using this anastomotic device for both venous and arterial anastomoses.

Experimentally, there are few long-term data on the stability of the couplers in vivo, other than reports of vessel-wall thinning at the anastomotic site.[8] [9] The mechanical significance of this thinning is unknown, and likely not crucial since, clinically, the vascular anastomoses and flaps based on these non-resorbable coupled anastomoses have shown good long-term survival in multiple studies. Most sites in which we perform coupled anastomoses are in inconspicuous locations, such as the axilla; however, a point is raised by the authors about the palpability of these coupled anastomoses in more conspicuous locations, such as the hand. Although a seemingly trivial point during the time of anastomosis, one can be faced with the need to address this when the patient complains, just as when a plate or screw becomes palpable and requires removal. Even though this situation is rare, Kind and colleagues[10] report on their experience with two such patients, who had unpleasant, palpable, foreign-body sensation in the hand, which was related to the device, that required subsequent removal.

There are some flaws in this study, the main one being the lack of a third group utilizing a non-resorbable coupling system. The real comparison for this resorbable device is not to hand-sewn anastomoses, but to the traditional, non-resorbable devices. It can be inferred from previous studies that the tensile strength and thrombus formation of the non-resorbable coupling system should be similar to the findings of this study, but a direct comparison using the same model would have been useful.[11] To us, the most interesting results are the scanning electron microscopic findings of anastomotic thrombus within the sutured arterial anastomoses, found up to 1 week postoperatively. This finding helps to reaffirm the important benefit that coupled anastomoses offer, which is stable intima-to-intima contact. It is also useful to see that the mechanical strength of both the venous and arterial anastomoses is at least similar to, if not better than, their hand-sewn counterparts. These findings, in the time period examined, are similar to studies using the non-resorbable coupling device.[11] Tensile strength evaluations would have been interesting at later time points, to see if the resorbable anastomotic breaking strength is similar to the hand-sewn anastomotic strength.

The authors evaluated the effects of early motion on the coupled and hand-sewn arterial anastomoses, using scanning electron microscopy to evaluate the percentage of thrombus formation. They report no thrombus formation in the coupled anastomoses at 1, 3, and 7 days, and variable levels of partial thrombus in the hand-sewn group. They did not study a similar group without early range of motion through this period, to see whether the thrombus formation is part of the natural history of sutured anastomoses, or whether it is related to the early motion variable. They also did not perform a long-term evaluation of these anastomoses, to determine if the thrombi are transient, permanent, or become hemodynamically significant. Both of these analyses would have been interesting, and would not only have given us further information about the resorbable anastomoses, but also would have added knowledge about the natural history of sutured anastomotic healing.

Since such studies would be needed to answer the question of motion on anastomoses, it is not clear from the current study whether these resorbable anastomoses are mechanically better suited to early motion than their sutured counterparts. It is also unclear whether thrombus formation in the sutured anastomosis was due to early motion. We believe that all microanastomoses should be performed in a tension-free fashion and placed in a position to avoid kinking on motion, which would ultimately allow early motion in either hand-sewn or coupled anastomoses.

We are enthusiastic about the development of a partially, or fully, resorbable coupling device. Ichikawa and colleagues have shown nicely some of the mechanical and thrombogenic properties of one such device in the early postoperative period, with comparison to a hand-sewn control group. Although there seem to be few compelling reasons to change the coupling technique to an absorbable device, several good points are raised. With an absorbable device, the indications for its use may broaden to areas, such as the hand, where a coupler may become palpable. Another point raised was the possibility of future vessel expansion or growth in the resorbable vs. the non-resorbable coupled anastomoses. Although there are few data on the growth potential of vascular anastomoses or flow-related changes of a growing vessel around a vascular anastomosis of any type, in general, a non-resorbable device would certainly not expand beyond its core diameter.[12] This would be an interesting, updated study-to evaluate the growth potential of all types of anastomoses and anastomotic techniques, including hand-sewn, coupled, end-to-end, end-to-side, running, interrupted, sleeve, and spatulated.

If future studies show that the mechanical properties of resorbable anastomoses are equal to or greater than their hand-sewn and non-resorbable counterparts, over the long-term, and that the inflammation associated with resorption of the coupler continues to show no thrombogenic increase with the materials utilized, there will be few reasons not to make such a device part of the microvascular armamentarium.

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