VASCULARITY OF THE ANKLE JOINT AFTER ARTHRODESIS: A CADAVERIC STUDY
March 8th, 1995
Guy P. Paremain, MD, and Mark S. Myerson, MD
We designed a cadaveric study to assess and compare the disruption of blood supply to the ankle after alternative methods of arthrodesis: that performed via open arthrotomy with malleolar ostectomy and that using enlarged arthroscopic portals to the ankle. The popliteal artery of five pairs of fresh cadaver legs were cannulated and infused with a radiopaque mixture. A tibiotalar arthrodesis was then performed on each leg, using an open technique for one leg of a pair and a miniarthrotomy technique for the contralateral leg. Pre- and postoperative fluoroscopically controlled radiographs were obtained for each leg and evaluated for arterial disruption. Two of the five ankles undergoing malleolar ostectomy evidenced damage to the peroneal artery. There was no damage to clinically relevant vessels in the five ankles managed with a miniarthrotomy approach. This study suggests that additional clinical studies are needed to determine why the rate and success of arthrodesis is significantly faster with minimally invasive techniques.
The literature describes at least 30 different procedures for achieving a sound ankle fusion.1 Despite many refinements since it was first reported in 1879,2 successful fusion is not always easily achieved. The reported rate of pseudarthrosis varies from 0 to 40%.3,4 Patients with posttraumatic degenerative arthritis, who have minimal deformity, achieve better results than those with septic arthritis, rheumatoid arthritis, or neuropathic conditions.3-5
Because reducing the amount of movement between the tibia and the talus has led to improved rates of fusion, modern surgical techniques incorporate tibiotalar compression by means of internal or external fixation.6,7 Several recent biomechanical studies have sought to identify the best way of producing an inherently stable construct, which might further improve the rate of fusion.4,8,9 However, despite progress in this area, the problem of nonunion still exists.
As reported in the literature, minimally invasive techniques for ankle arthrodesis, performed either arthroscopically or via arthrotomy using small incisions, are associated with high rates of fusion and appear to heal more rapidly than arthrodeses using standard, open techniques.7,10-12 To determine whether these improved results could be attributed to limited vascular disruption at the time of surgery, we designed a cadaveric study to assess and compare the disruption to the blood supply that occurs when tibiotalar arthrodesis is performed via an open technique (arthrotomy with malleolar ostectomy) and a minimally invasive method. The goal was to quantify, indirectly, the relative risk of producing avascular areas of bone using these two different techniques.
Materials and Methods
We acquired eight fresh cadavers (aged 58 to 86 years) with no visible signs of external sign of previous lower limb surgery. All amputations (above-the-knee) and invasive procedures were performed 3 to 6 days postmortem because the interval between death and attempted limb perfusion has been reported to be an important factor in allowing deterioration of the capillary bed and subsequent prevention of passage of material injected into an artery into the venous circulation.13
After amputation, the popliteal artery in each of the 16 legs was cannulated 10 cm proximal to the knee joint and the cannula was ligated in place. This method was selected because a previous study of the talar blood supply had confirmed that perfusion of all vessels around the foot and ankle does not require individual cannulation of the posterior tibial, anterior tibial, and common peroneal arteries.13
Initially, 50 ml of a lubricating solution, used by professional embalmers to lubricate the endothelium and disperse postmortem clot, was infused via the cannula to facilitate passage of subsequent infusions. Then a radiopaque mixture (0.5 liter of 50% barium sulfate and 7 g of gelatine) was infused from a 50-ml syringe using manual pressure; it was anticipated that this dense mixture would "set" inside the arteries so that it would not extravasate, obscuring other vessels, should an artery be transected during surgery. To ensure that the correct vessel had been cannulated and that the mixture was filling all the major vessels below the knee, each leg was placed on an x-ray table and screened during the infusion. The infusion was stopped when it became apparent that no additional vessels were being filled. Adequate visualization of all the major vessels required between 50 and 100 ml of the barium mixture. Preoperative anteroposterior and lateral x-rays, centered on the tibiotalar joint, were taken of each leg.
We defined an arteriogram as being adequate if it showed filling of all the clinically relevant vessels in the lower leg, i.e. the three major vascular structures (the anterior tibial, posterior tibial, and peroneal arteries) that should be preserved to maintain flow to the distal parts of the limb or whose anatomic position is crucial to the surgeon during the surgical approach.14 The angiograms of three of the eight pairs of legs displayed evidence of peripheral vascular disease and did not visualize all three major vessels around the ankle. Where there was obstruction to flow in any of these arteries, we explored the vessel below the knee and attempted cannulation distal to the stenosis. This technique proved to be unsuccessful. Therefore, we excluded these three sets of legs from the study, leaving five pairs whose angiograms showed complete filling of the arterial system to form our study group. After obtaining satisfactory arteriograms for these five pairs of legs and waiting 45 minutes to allow the perfusate to set, the same surgeon then performed a tibiotalar arthrodesis on each leg.
One leg of each pair was fused with open arthrotomies and malleolar ostectomy. This technique, fully described elsewhere,7 was performed with an 8-cm incision over both the medial and lateral malleoli, subperiosteal dissection of the malleoli, and removal of the malleoli and articulating surfaces of the tibia and talus with a sagittal saw. Finally, two 7.0-mm cannulated screws were used to achieve internal fixation with compression of the joint. The second leg of each pair underwent arthrodesis using enlarged anteromedial and anterolateral arthroscopic portals, each incision 1.5 cm long.11 Through these small incisions, a high-speed burr was used to shave all the articular surfaces. The malleoli were left otherwise intact. The debris from the debridement was left within the joint. Internal fixation was again achieved with two 7.0-mm cannulated screws.
After fluoroscopic screening on the imaging table to ensure a position identical to that in preoperative radiographs, postoperative anteroposterior and lateral radiographs were obtained for each of the 10 legs. Since review of the radiographs of the first pair of legs indicated that the screws used for internal fixation were obscuring some vessels, the screws were removed from the subsequent pairs before obtaining postoperative films. We then systematically evaluated the disruption to the vessels by placing the pre- and postoperative films for each leg side by side on a viewing box and comparing the images. We also found that superimposing a tracing of one radiograph onto the other sometimes made it easier to detect any difference between the two sets of films. Because of the subjective nature of this film evaluation, no statistical analysis of our results was performed.
Preoperative radiographs confirmed that there were no differences between the site and size of the major vessels within each pair of legs, although the branching patterns of the minor vessels did vary. Postoperative radiographs confirmed that the barium mixture had remained contained within the arteries during the course of surgery; therefore, there was no extravasated barium to hinder interpretation of the films.
Two factors affected the determination of differences between films and the objective assessment of the true disruption to the minor vessels. First, minor rotational differences between the pre- and postoperative radiographs tended to alter the appearance of the fine network of smaller vessels and, second, the shortening secondary to bone removal (in the ostectomy group) made it hard to judge whether the difference in the film was due to vessel disruption or to projectional artifact. With reference to the minor vessels, however, neither of the surgeons interpreting these radiographs could distinguish a difference between the number of minor vessels that had been divided by the two techniques, but it was interesting to note that in the ostectomy group the vessels overlying the medial and lateral malleoli appeared undisturbed by the subperiosteal excision of these bones. Because of these constraints, we can make accurate comments only on the appearance of the major vessels around the ankle.
Of the five ankles that underwent miniarthrotomy arthrodesis, none evidenced damage to clinically relevant vessels secondary to the surgical procedure. However, there was some inconsistent division of several minor vessels (<0.5 mm) in each leg. Of the five ankles undergoing malleolar ostectomy, two evidenced damage to the peroneal artery. In one of the two, it appeared that the vessel had been excised along with the distal fibula (Figs. 1 and 2). In the second case, the anterior perforating branch had been divided at the level of the distal tibiofibula syndesmosis. There was no evidence of other damage to clinically relevant vessels.
Despite recent advances in surgical technique, the problem of ankle nonunion and instability after fusion still exists. Because patients who smoke, have avascular necrosis of the talus, or take high doses of steroids have poor results in terms of arthrodesis1,15 and because minimally invasive operative procedures have higher rates of fusion and faster time to healing than standard open techniques, it has been conjectured that nonunion may be associated with interruption of the arterial blood supply, leading to necrotic bone. It therefore follows that the vascularity of the ankle is an important factor in determining the eventual outcome of an attempted ankle fusion.
Arthrodesis remains the treatment of choice for the relief of pain and instability in patients with tibiotalar arthritis refractory to other, conservative treatment modalities.1 Over the past decade, arthroscopic ankle fusion has provided successful arthrodesis in a selected group of patients, i.e. those with minimal deformity of the ankle. Fusion rates for the arthroscopic technique appear to be equivalent to, if not better than, those obtained by open methods. The miniarthrotomy approach used in the current study is another method of achieving an "in situ" arthrodesis, and reported results are comparable to those of the arthroscopic technique.11 These minimally invasive operations also significantly decrease the time to fusion.7,11,12 In a comparative study of an arthroscopic versus an open method of treatment, the time to arthrodesis was 8.7 and 14.5 weeks, respectively.7
It is important to elucidate the reasons why these recently introduced operations produce such good results. It has been previously stated that care should be taken not to strip the periosteum when performing an open arthrodesis,16 but to our knowledge there has been no previous attempt to define the vascular disruption that routinely occurs during these operations. It is possible that the rapid consolidation seen with the minimally invasive procedures is directly related to limited periosteal stripping, which produces less devascularization than does an open arthrotomy with malleolar ostectomy.
The blood supply of the distal tibia is derived from the transverse perimalleolar arterial circle, the medial and lateral malleolar rete, and the lateral malleolar sagittal arterial loop. This extensive arterial network is supplied by all three of the major vessels in the lower leg. From this network, branches drop vertically downward to end in the subchondral capillary bed.13 The complex blood supply to the talus, which has been studied in great detail, involves contributions from each of the three major arteries and extensive intraosseous anastomoses. In view of the existence of these anastomoses around and within the distal tibia and the talus, cutting any one of the contributors to the network would not be expected to render a segment of bone avascular. It is unlikely therefore that the damage to the peroneal artery seen in two of our cases would be responsible for significant avascular necrosis with subsequent nonunion. To confirm this hypothesis, however, an additional study would have to be undertaken to investigate functional anastomoses around the ankle. Sevitt and Thompson17 looked at the functional anastomoses around the femoral head in relation to avascular necrosis. They selectively divided of one or more arteries around the hip before performing arterial injection studies.17 A similar study, applied to the ankle, would be a useful way of defining the significance, if any, of damaging the peroneal artery during arthrodesis.
Although this study did not conclusively show that either of the chosen operative techniques adversely affected the overall blood supply of the ankle, reports in the orthopaedic literature do highlight the potential damage that any operative procedure can cause to the blood supply of bones. For example, Scuderi et al18 performed postoperative technetium bone scans on 36 patients after total knee arthroplasty. They found a significantly increased incidence of vascular compromise of the patella in those knees that had undergone a lateral release. Duncan and Lovell19 reported that they eliminated a 6.5% rate of avascular necrosis of the talus, associated with the Hoke triple arthrodesis, after changing to a surgical technique that carefully preserved the origin of the artery to the tarsal canal.
It is possible that our methodology was not sensitive enough to detect all of the damage to the blood supply of the ankle caused by the surgical approaches used in this study. For example, although the vessels overlying the medial and lateral malleoli had been preserved by the subperiosteal excision of these bones, it may be that important contributions to the distal tibia were lost.
If our results are accurate and there is only minimal disruption to the blood supply using either method, then other reasons for the rapid consolidation and high fusion rates associated with the minimally invasive technique need to be considered and investigated. Patient selection may be important; generally, the patients that are selected for open arthrotomy have many more complex problems than those selected for miniarthrotomy.7 There are also biomechanical factors that have not yet been studied, such as the fact that the minimally invasive technique preserves the overall contour of the joint mortise, which may provide a more intrinsically stable construct than that afforded by malleolar ostectomy. It has been reported that postoperative movement between bones can cause damage to the fine capillary networks that are an integral part of the healing process.20,21
In conclusion, although the current radiologic cadaveric study found no conclusive evidence that vascular compromise was associated more with open than with minimally invasive techniques of tibiotalar arthrodesis, it does suggest that additional clinical studies are needed to determine why healing times are significantly faster with the minimally invasive technique.
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Fig. 1. Preoperative (A) radiograph of leg 1 undergoing open arthrotomies and malleolar ostectomy. The arrows demonstrate the position of the branches of the peroneal artery. Postoperative radiograph (B) demonstrating the disruption of the peroneal artery and its branches. The arrows indicate the position at which the arteries were disrupted.
Fig. 2. Preoperative (A) and postoperative (B) radiographs of leg 4 undergoing arthrodesis by open arthrotomy and malleolar ostectomy. The arrows demonstrate the peroneal artery (A) and disruption (B) after surgery.