Posterior Tibial Artery Abnormality and the Role of CT-angiography in Planning Free Flap Transfer for Management of Chronic Osteomyelitis of Tibia: Case Report

INTRODUCTION

Post-trauma osteomyelitis may be a serious complication of the treatment of tibial fractures. One of the possible treatments is a radical debridement of soft tissues and the skeleton with sufficient exposure of the bone cavity and subsequent coverage of the resulting defect by a microvascular free flap transfer (10, 12). This method is used to replace poor quality scary soft tissues, to cover the affected skeleton and improve its perfusion (1, 9). Thus it addresses all aspects of a successful management of an infectious complication (2, 3). Within preoperative planning it is important to determine which vessels will be suitable as recipients for the microvascular free flap. Such information may be obtained by means of angiography. However, opinions on its indication vary, ranging between recommendation of angiography as the method of choice and its rejection due to its invasiveness and risks (2, 4, 8, 10, 11). The aim of this study is to report on an intraoperative atypical finding on the posterior tibial artery complicating a free flap transfer that would be revealed by CT-angiography performed prior to the surgery.

A Case Report

A 43-year-old patient was treated for a fistula at the site of the healed fracture (Fig. 1) 14 months after the motorcycle accident (spiral wedge fracture of the left tibia 42.B1 AO/ASIF classification, primary reduction and stabilisation with a hybrid fixator, subsequent conversion to predrilled locking screw). Bacteriological examination revealed the presence of Staphylococcus aureus and Staphylococcus epidermidis sensitive to common antibiotics. Radiography proved a radiolucent zone around the distal part of the nail. Therefore a radical interdisciplinary treatment was employed. The nail was removed, a 6x1 cm hole was made in the tibia at the site of the healed fracture and the tibial cavity was prereamed by flexible 15-mm reamers (Fig. 2). Antibiotics (oxacillin, gentamicin) were administered intravenously during operation and in the postoperative period.

Based on repeated negative cultures of samples taken from the defect surface, microvascular free muscle transfer was planned. Pulsation of posterior tibial artery behind the medial malleolus was slightly palpable and fully detectable by the Doppler ultrasonography. Therefore, we selected as the recipient artery the posterior tibial artery bundle close to the defect. With regard to the size of the defect and expected location of the recipient vessels we indicated the gracilis free flap transfer (Fig. 3). Excision of poor quality scary soft tissues and exposure of the cavity of the tibia produced a 6 x 10 cm defect located on the anteromedial aspect of the distal third of the tibia (Fig. 4). The posterior tibial artery bundle was found posterior and proximal to the defect. To our surprise, the posterior tibial artery was in this segment unfilled, without pulsation, stenosed, with blood only slowly flowing out. As a result, in this region it could not be used as the recipient artery (Fig. 5). By dissection more distally we verified that the palpable pulsation behind the malleolus was real and was caused by blood backflow. Although after partial arteriotomy the blood was flowing out pulsating, the outflow was not sufficient for the use as the recipient artery. This unusual finding had complicated the course of the surgery. We supposed that the stenosed part of the posterior tibial artery resulted from the trauma and that we would find an intact artery proximal to the fracture. Therefore we extended the incision proximally and continued dissecting the stenosed posterior tibial artery as far as the nearest functional muscle perforator. Approximately 10 cm proximal to the defect we found the posterior tibial artery bundle (the artery and both comitant veins) acceptable as the recipient vessels. The distance between the recipient vessels and the planned flap placement was almost on the border of the limits of the gracilis flap use. Yet another problem arose due to a significant discrepancy between the diameters of the recipient artery and the pedicle artery. This situation was addressed by an oblique narrowing of the posterior tibial artery stump and its end-to-end anastomosis with the flap pedicle artery (Fig. 6c), while venous drainage of the flap was ensured by end-to-end anastomosis of the flap pedicle vein and one of the comitant veins of the posterior tibial artery.

The excision of the scary skin coverage of the tibia was enlarged to meet the flap size and the peripheral end of the flap filled the cavity in the tibia (Fig. 7). As the pedicle was too short we moved the sufficiently long gracilis into the incision left after the exposure of the recipient vessels (Fig. 8).

After the surgery, the flap was well vascularized (Fig. 9) and after three days we covered it by an autologous splitness skin graft. Bacteriological findings of the removed drains were negative.

The patient was allowed full weight bearing of the treated extremity two months after the surgery, i.e. after healing and integration of soft tissues. At the latest follow-up, two years after coverage of the defect, the patient was without pain, without any inflammatory signs in the region of the flap and the extremity was fully functional (Fig. 10).

DISCUSSION

The first serious problem that we encountered during the surgery was finding of a stenosed posterior tibial artery at the site of the planned anastomosis. Verification of the condition of the recipient vessels for a free microvascular muscle transfer is one of the key criteria for this operation (3, 6, 9, 12). Such evaluation may be obtained clinically, by the Doppler ultrasonography or CT-angiography. Some authors prefer angiography and recommend it as the method of choice while others use it only in case of abnormalities or doubts about recipient vessels (1–4, 6, 8–10, 12). For instance, Lutz et al. published a report on a group of 48 patients with free flap transfers without preoperative angiography (4). We are aware that CT-angiography would reveal the stenosed part of the posterior tibial artery at the site planned for anastomosis. However, it would have little or no impact on the selection of the recipient vessels as the tibial posterior artery bundle is better accessible than the anterior tibial vessels and that is why we prefer to use the former one. In other words, CT-angiography would only prepare us for the fact that a suitable site for anastomosis will be more proximal to the defect. CT-angiography could probably influence selection of another muscle flap. For an end-to-end anastomosis we would consider the use of the latissimus dorsi flap or the rectus abdominis flap. However, for coverage of minor defects we prefer the free gracilis flap transfer as it offers a number of benefits. It allows to place the patient in the supine position, provides sufficient soft tissue to cover minor defects and is associated with a minimum donor site morbidity. These benefits sufficiently compensate for certain disadvantages of this choice, such as the short vascular pedicle of the flap (6 cm) and the gracile lumen of vessels (approximately 2 mm) (8, 11). Therefore we conclude that indication of CT-angiography prior to the surgery has its specified limits.

We indicate angiography in the following cases when:

1. None of the arteries on the periphery is palpable.
2. The recipient artery on the periphery is provable only by the Doppler ultrasound examination – according to our experience, from the viewpoint of the blood flow quality, this vessel cannot be always used as the recipient artery.
3. Swelling on the periphery hinders a sufficiently palpable pulsation.
4. The patient underwent a vessel reconstruction.
5. It is necessary to check the system of blood supply of the lower extremity to find out if the planned recipient artery is not the only one that ensures its vascularization.

We do not indicate angiography in the following cases when:

1. Both arteries on the periphery are palpable.
2. The artery planned as the recipient one is well palpable.

Another factor complicating the operation was the difference in the diameter between the ultimately chosen recipient artery and the pedicle artery. In such situations we have three options (Fig. 6):

• a – Blinding of the posterior tibial artery and an end-to-side anastomosis of the pedicle to the tibial posterior artery,
• b – Rectangular narrowing of the posterior tibial artery end, leaving an adequate lumen for the flap pedicle artery and an end-to-end anastomosis,
• c – Oblique narrowing of the posterior tibial artery end, leaving an adequate lumen for the flap pedicle artery and an end-to-end anastomosis. In our case we chose the third option.

The two above mentioned problems that occurred during operation could be naturally solved by means of the use of another free muscle flap with a longer pedicle and a larger lumen of the pedicle vessels allowing additional lengthening of the flap pedicle by venous grafts (5). However, the team of surgeons thanks to their experience and good knowledge of the topographic anatomy evaluated correctly the situation and performed the initially planned transfer of the gracilis muscle flap which was in the given case the most efficient and patient-friendly procedure.

Finally, the question arises whether a markedly limited functionality of the posterior tibial artery at the fracture site could be one of the causes of protracted and complicated healing of the fracture, which implies that a well and autonomously vascularized tissue of the transferred muscle flap significantly contributed to an early healing after an aggressive interdisciplinary treatment of soft tissues and the skeleton of the affected region.

We consider the described posterior tibial artery abnormality, most probably trauma-related, in combination with a normal clinical preoperative finding to be exceptional. In our view, in the treatment of chronic osteomyelitis of the tibia we should continue to follow our established criteria of indication of CT-angiography performed prior to the planned microvascular free tissue transfer.

The study was supported by a grant of Internal Grant Agency of Ministry of Health, Czech Republic (NR 85 34-4/2005 “Comprehensive treatment of infectious complications of devastating injuries of the tibia”).

Address for correspondence:

A. Nejedlý, M.D., Assoc. Prof.

Department of Plastic Surgery

Third Faculty of Medicine, Charles University

and University Hospital Královské Vinohrady,

Šrobárova 50

100 34 Prague 10

Czech Republic

E-mail: nejedly@volny.cz