Evaluation of the fibular cutaneous flap for monitoring the microanastomosis in microsurgical fibula transferences

Abstracts

O enxerto ósseo vascularizado tem sido utilizado com mais frequência nas últimas duas décadas, principalmente no tratamento de perdas ósseas extensas difíceis de serem tratadas com métodos convencionais. A viabilidade e a consequente hipertrofia do enxerto ósseo vascularizado depende da presença de microanastomoses pérvias. A monitoração das microanastomoses é extremamente importante no período pós-operatório para se identificar eventuais tromboses e dessa forma poder planejar a exploração cirúrgica precoce. Dentre os métodos disponíveis para esta avaliação a cintilografia óssea, a angiografia e a ultrassonografia convencional com aparelho tipo Doppler apresentam limitações pois fazem controles pontuais. A monitoração contínua , por outro lado, pode ser realizada com instrumentos através da medida do fluxo arterial com implantação de eletrodos acoplados ao ultrassom tipo Doppler , com eletrodos que medem temperatura e pela geração eletroquímica de hidrogênio local ou ainda clinicamente com o retalho cutâneo baseado em perfurantes da artéria fibular. Apesar de estarmos usando o retalho fibular como monitor das microanastomoses desde a sua descrição por Yoshimura, em 1983, existem controvérsias a respeito de sua eficácia. Por essa razão, desenvolvemos o presente trabalho com o objetivo de analisar a sensibilidade e a especificidade desse método para monitoração das microanastomoses em transplantes vascularizados da fíbula.

Fíbula vascularizada; Retalho cutâneo fibular; Microanastomoses

ORIGINAL ARTICLE

Evaluation of the fibular cutaneous flap for monitoring the microanastomosis in microsurgical fibula transferences

Arnaldo V. Zumiotti^I; Edgard N. França Bisneto^II; Yussef A. Abdouni^II; João C. Nakamoto^III; Teng.H. Wei^IV

^IAssociate Professor and Head of the Traumatology Discipline at the Orthopedics Department of FMUSP

^IITrainee doctor at the Hand and Microsurgery Group of the FMUSP's DOT

^IIIResident doctor of the FMUSP's DOT

^IVAssistant Doctor of the Hand and Microsurgery Group of the FMUSP's DOT

^{Correspondence}

SUMMARY

The use of free vascularized fibular graft (FVFG) is nowadays a common procedure for severe segmental bone loss. Thrombosis of the microanastomosis leads to a lack of bone incorporation of the FVFG unless a successful early exploration would have been performed. Due to this fact, the continuous monitoring of the FVFG viability in the immediate postoperative period needs to be executed. The use of a variety of methods has been proposed to asses the viability on an intermittent basis. These include selective angiography, monitoring of healing and hypertrophy with serial radiographs, bone scan and Doppler ultrasound scanning. Intermittent monitoring methods, however, will not detect acute thrombosis. Continuous monitoring is possible with instrumental methods such as the laser Doppler implants, the thermocouple probes, and the measurement of electrochemically or clinically produced hydrogen or using the fibular cutaneous flap that works as a buoy. Since the last method was proposed in 1993, we started to use it in our unit, but many controversies arised regarding its efficacy. For this reason we decided on the current study, to analyze the sensibility and the specificity of the fibular flap as a monitor of the microanastomosis in the FVFG.

Key words: Fibular flap; Free bone transfer; Microsurgery

INTRODUCTION

The vascularized bone graft of the fibula has been used frequently in the treatment of segmental bone losses resulting from post-traumatic, tumorous, and infectious causes, and also still in the congenital pseudoarthrosis of the shinbone and of the bones of the forearm. That technique is based on the retreat of a bone segment of the diaphysis of the fibula, together with the fibular vessels that will be responsible for its irrigation. The microvascular anastomosis of the fibular vessels into the receiving vessels is carried out after the osteosynthesis. The success of the surgery depends on the viability of the transferred fibula that, on its turn, needs the presence of pervious microanastomosis. The continuous monitoring of microanastomosis in the first week of the postoperative period is essential for the early identification of the occurrence of arterial or veined thrombosis and to correct this as soon as possible. The postoperative control of the microvascular anastomosis can be made using bone scintigraphy, arteriography and Doppler ultra-sound. However those methods make punctual controls and are not useful to diagnose acute thromboses during the first two weeks of the postoperative period⁽¹⁷⁾. The methods that make the continuous monitoring need the implantation of special electrodes for measuring arterial flow through a Doppler ultrasound^(7,9,10) or for measuring the temperature⁽⁵⁾, or still for the electrochemical production of hydrogen⁽⁸⁾. Those methods, although effective, need special apparels and are not available in our area. On the other hand, the monitoring with the cutaneous flap based on perforators of the fibular artery is a simple method, without costs and that just depend on the systematic clinical exam of the flap. In spite of those advantages, there are controversies as to its effectiveness particularly in the cases in that the flap presents alterations of the blood perfusion. For that reason, in the present study we analyzed the sensibility and the specificity of the fibular cutaneous flap for monitoring the microanastomosis in the microsurgical transfers of the fibula.

CASUISTRY AND METHODS

During the period from 1985 to 2000, a prospective study of the microsurgical transfers of the fibula was performed at the Institute of Orthopedics and Traumatology of the Hospital das Clinicas of the School of Medicine of the University of Sao Paulo and in the Lebanese Syrian Hospital (SP), with the objective of analyzing the effectiveness of the fibular cutaneous flap for the monitoring of the microanastomosis. The following inclusion criteria were considered for the patients' selection:

1 - presence of bone infections ineligible for the conventional orthopedic treatment, such as: congenital pseudoarthrosis of the shinbone or of the bones of the forearm and extensive segmental bone losses in sequels resulting from traumas, infection or tumors;

2 - the use of vascularized grafts of the fibula associated to the cutaneous flap used as a monitor of microvascular anastomosis;

3 - the control of the viability of the fibula with bone scintigraphy until the second week of the postoperative period;

4 - the postoperative radiographic documentation for studying the fibula hypertrophy. The exclusion criteria contemplated all microsurgical transfers of the fibula that didn't present the fibular cutaneous flap and, in the cases with absence of bone scintigraphy up to the end of the second week of the postoperative period, or without enough radiological studies to document the fibula hypertrophy.

From the 41 patients selected in that study, 27 were males and, 14 females. The minimum follow-up period was of 3 years. Age varied from 2 to 38 years of age, with an average of 13 years. The affections and the respective numbers of patients in whom the vascularized graft was implanted are listed below.

Tibial congenital pseudoarthrosis - 20

Congenital pseudoarthrosis of the forearm bone — 2

Tibial post-traumatic pseudoarthrosis — 6

Post-traumatic pseudoarthrosis of the radio or the ulna — 5

Pseudoarthrosis per acute hematogenic tibial osteomyelitis — 2

Post-traumatic pseudoarthrosis of the humerus - 2

Pseudoarthrosis after tumoral resection of the tibial- 2

Pseudoarthrosis after tumoral resection of the humerus — 1

Post-traumatic pseudoarthrosis of the femur- 1

The patients were operated with general anesthesia with two surgical teams acting simultaneously. While one prepared the receiving area, the other proceeded with the dissection of the vascularized graft of the fibula. The fibula was exposed by means of an incision executed in the projection of the space between the soleus and the long fibular muscles^(1,14). After the proximal osteotomy of the fibula, the fibular vases were dissected and connected close to the tibial-fibular trunk. Soon afterwards, the distal osteotomy of the fibula was executed, as well as the distal bondage of the fibular vases. In the dissection of the fibular cutaneous flap one or two perforates, previously identified with a Doppler ultrasound, were included. In 35 cases the cutaneous flap was maintained connected to the fibula by the posterior crural septum (Figure 1), and in 6 cases the perforators were skeletized in their entire itinerary. (Figure 2). The donor area was closed by direct suture in 30 cases, and complemented with a skin graft in 11 cases.

A debridement was executed at the receiving area, with the resection of the bone tissue and of the bad quality soft parts, and with the dissection of the receiving vases. The vascular sutures were made with microsurgical technique with monofilament nylon 9 or 10 zeros. The fibular artery of the vascular pedicle was rebuilt with the utilization of two end-terminal anastomosis, one proximal and other distal, in patients with Congenital pseudoarthrosis of the Shinbone and of the bones of the forearm. In the pseudoarthrosis of the humerus and of the femur, the arterial anastomosis was end-lateral, respectively, in the humeral artery and in the superficial femoral artery. In the fibular veins the anastomosis was, in all the cases, of the end-terminal type with the receiving veins.

The control of the microanastomosis was executed clinically by the observation of the coloration of the fibular cutaneous flap and of its perfusion, using capillary refill test. The suspicion of arterial thrombosis was observed when the flap presented paleness instead of its rosy characteristic coloration, and there was also absence of arterial perfusion during capillary refill test. In the veined thrombosis the cutaneous flap showed edematization and cyanotic, and with a negative capillary refill test. In those cases the exploration of the microanastomosis was executed and, if at the end of the procedure the flap had normal perfusion again it was maintained, otherwise it was removed. The evaluation of the viability of the transplanted fibula was performed by bone scintigraphy with methyldiphosphate marked with the technetium-99 metastable isotope (^{99 m} Tc-MDP). In all of the patients the exam was made until the end of the second week of the postoperative period, taking care not to inform the radiology doctor of the clinical result of the cutaneous flap of the fibula (Figure 3 a and 3 b).

The presence or absence of fibula hypertrophy documented with serial x-rays was used as a late parameter of the viability of the vascularized graft of the fibula.

RESULTS

In 35 patients the cutaneous flap of the fibula presented normal coloration and perfusion (Figure 4)(Table1). Alterations of the coloration and perfusion were detected in 6 cases, confirming by surgical inspection the arterial thrombosis in 2 cases and the veined thrombosis in 4 patients (Figure 5)(Table 2). From those 6 patients operated again, in only 3 the reperfusion was accomplished for the cutaneous flap at the end of the surgical exploration (Table 3). On the remaining cases the flap was removed, because at the end of the exploration of the microanastomosis the perfusion was not accomplished. In the 38 cases that the flap survived, the scintigraphy taken until the second week of the postoperative period demonstrated the presence of an uptake in the transplanted fibula (an arterial thrombosis and two veined were reverted after the microsurgical exploration)(Table 4). In 2 cases of veined thrombosis and in 1 of arterial thrombosis, in spite of the surgical exploration the proven revascularization of the fibula was not achieved due to the non-reperfusion of the cutaneous flap, due to the uptake absence in the bone scintigraphy, and due to the absence of hypertrophy during the late postoperative period (Table 5).

DISCUSSION

The postoperative continuous monitoring of the microsurgical transplants of the fibula is very important in order to construct the diagnosis of an eventual obstruction of the microanastomosis and, thus, to plan the precocious surgical exploration^(1,13,14). The methods that make that evaluation in a punctual way are not appropriate because they are insufficient to surprise the acute thrombosis of the microanastomosis⁽¹⁾. The periodic clinical examination for the evaluation of the viability of the cutaneous microsurgical and musculocutaneous flaps has been enough for monitoring the microanastomosis^(2,4,5). The strategy for that control is based on a window opened on the bandage to allow the exam of the flap and, in that way, to observe its coloration and to perform the capillary refill test for the control of blood perfusion. When the arterial thrombosis of the microanastomosis occurs, the flap presents a pale aspect, unlike its characteristic rosy coloration, in addition to evident ischemia signs demonstrated by the capillary refill test. The bleeding test should be performed in the case any doubts persist, manipulating the edges of the flap, or perforating the flap with a needle. In the veined thrombosis the flap presents is cyanotic and the speed of capillary refill becomes very fast. Those measurements are perfectly enough to monitor the flap continually in the postoperative period, except when there are concomitant clinical alterations, such as, hypotension, hipovolemy or intense anemia. If those alterations are detected their correction is mandatory to avoid unnecessary surgical explorations. This forces us to perform an untransferable task, which is the task of making the exam of the flap, at least, every 6 hours or at every 4 hours, in the cases of a reserved prognostic.

Some continuous monitoring methods were developed to detect alterations to the blood flow for the veined or arterial thrombosis of the microanastomosis, and they are based on transcutaneous measurements of the capillary oxygenation, or of the temperature⁽⁴⁾. Doppler ultrasound apparatus that receive information captured by electrodes implanted near the microanastomosis were also developed^(6,8,9). In our environment we have not been using these resources for the control of the microsurgical flaps, because they are methods that use imported apparels, which involve high costs, in addition to their need for frequent maintenance. Another disadvantage is the possibility of false positive false resulting in the unnecessary surgical exploration^(6,8,9). The difficulty in the monitoring of the microsurgical transfers of the fibula lasted until the publication by Yoshimura et al., in 1983, of the fibular cutaneous flap⁽¹²⁾. For being nurtured by direct branches of the fibular artery that flap reflects the alterations of the blood flow occurred due to arterial or veined thrombosis. In that work the authors report only 1 case of necrosis of the skin monitor in 17 operated patients and that, in spite of the surgical exploration, there was no reversion of the vascular occlusion. The controversies about the effectiveness of the fibular flap as a monitor of the microanastomosis arise particularly in the cases of color alteration and of perfusion and could characterize - in the opinion of the method's critics - false positive results. The unfeasibility of the cutaneous flap could mean, therefore, a technical flaw during its removal, or that it is badly positioned or there is a compression to its vascular pedicle. It is evident that those hypotheses find some theoretical support. However they have little practical meaning if we consider that the rigidity in the application of the surgical technique includes all of the operative times, such the dissection of the osteocutaneous flap of the fibula, the skeletal stabilization, the appropriate positioning of the cutaneous flap and the microanastomosis. As such, the fibular cutaneous flap can be considered a trustworthy monitor of the blood flow of the vascularized graft of the fibula⁽¹⁴⁾.

The perforator arteries in the third proximal of the leg make an itinerary through the long fibular muscle, while those in the medium and distal thirds and are truly septiocutaneous⁽³⁾. In order to avoid any difficulties in the medical examination of the flap, it is advisable that its dimensions should have, at least, 2 cm of length and 1 cm of width (Figure 6). Those dimensions allow the closing of the primary donor area. Sometimes due to the bad quality of the cutaneous covering of the receiving area, we opted for the removal of a larger flap, for the simultaneous repairing of the bone loss and of the cutaneous covering⁽¹³⁾ (Figure 7). Under these circumstances the donor area should be repaired with a skin graft. The maintenance of the posterior crural septum in the osteocutaneous flap of the fibula is not obligatory, and one or more perforators could be mapped with a Doppler ultra-sound and included in the flap. The presence of the posterior crural septum creates a larger protection for the flap, preventing the sprain of the perforator arteries. However it reduces the rotation arch hindering its positioning during the deepest reconstructions, such as the one of the femur and of the humerus. Another option to avoid the use of the posterior crural septum is include the perforators of the proximal or medial third of the leg that present a greater length and, therefore, a larger rotation arch.

The bone scintigraphy and the serial x-rays were used, respectively, as methods for the precocious and late evaluation of the viability of the vascularized fibula⁽¹⁾. Used with this purpose, the bone scintigraphy should be made until the end of the second week of the postoperative period, to avoid the effects of the revascularization of the bone graft generated by the creeping substitution. In that period the reception of the radiopharmaceuticals by the osteocytes demonstrates that the viability of the bone graft is dependent exclusively on the presence of blood flow due to pervious microanastomosis. The bone hypertrophy observed in the serial x-rays occur according to the principles of the law of Wolf, and it is only noticed when the fibula is viable (Figures 8, 9 and 10). The bone hypertrophy is less evident in the reconstruction of the bones of the forearm, unlike the observed in the femur, in the shinbone and in the humerus, where the serial x-rays clearly demonstrate that phenomenon. The bone consolidation was not used as a method for evaluation the viability of the fibula because it could occur even in the cases of microanastomosis obstruction. The analysis of the results showed a perfect correlation between the clinical outcome of the fibular cutaneous flap and the intra-operative findings. The bone scintigraphy and the serial x-rays were useful to corroborate those findings. The statistical study revealed that the sensibility and the specificity of the fibular cutaneous flap in the present study were, respectively, 98,6% and 91,7% for a level of significance of 5% (Table 6). Those data prove that the fibular cutaneous flap presents elevated sensibility and specificity to detect alterations to the blood flow resulting from the obstruction of the microanastomosis. In spite of that, we didn't have a high success index in this study after the exploration of the microanastomosis, unlike the other authors' experience^(2,5,6), due to the prolonged time between the detection of the obstruction and the new surgery. In addition to its effectiveness, we should emphasize the great cost-benefit relationship, because it is a simple method that involves precision and creativity in the study of the surgical technique, rigidity in the postoperative surveillance, sparingly usage of imported sophisticated apparatus.

REFERÊNCIAS BIBLIOGRÁFICAS

Trabalho recebido em 22/12/2003.

Aprovado em .26/03/2004

Work performed at the Orthopedics and Traumatology Department of the University of Sao Paulo School of Medicine.

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Correspondence

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Publication Dates

• Publication in this collection
  16 Nov 2004
• Date of issue
  Sept 2004

History

• Accepted
  26 Mar 2004
• Received
  22 Dec 2003