Response to: “The aberrant anterior tibial artery should be respected and can be protected in high tibial osteotomy (HTO) surgery”

We are pleased to note the interest in our study, the letter to the editor, the case presented and the thoughts behind it [7, 10]. We absolutely agree that osteotomies are an indispensable part of reconstructive surgery, especially in combination with ligamentous reconstructions [2, 8]. However, we would like to clarify that the conclusion of our work was not that an anterior tibial artery (ATA) is an absolute contraindication for an osteotomy. But it can very well constitute a contraindication in the field of elective surgery where one must weigh up what individual benefits are achievable and what individual risks are to be taken [10]. In particular, the aim of our work was to raise awareness of this relevant anatomical variant among orthopedic surgeons. And the very fact that this discussion has arisen shows that this goal has actually been achieved. The supposedly ‘best’ complication is certainly the one that can be prevented. Therefore, we would also like to put our thoughts on the letter to the editor here up for discussion, and present two exemplary cases in order to expand on this. Case 1 is a complication case of a friend of the first author added as a co-author here (PM). He is also a sports-orthopedic specialist in a high volume surgical knee centre. The surgery was performed by himself, and is presented with permission. A standard medial open wedge high tibial osteotomy (HTO) was performed in a middle aged and otherwise healthy patient. Although meticulous preparation was performed and the retractor was placed correctly (Figure 1a), a strong arterial bleeding occurred while performing the osteotomy. In this case an aberrant tibial artery was present and was not seen preoperatively (Figure 1b,c). The osteotomy was finished and together with a vascular surgeon a direct posterior explorative approach was performed (Figure 1d). A destroyed aberrant tibial artery was found (accompanied by its destroyed vein) which was running in a kind of bony sulcus directly attached of the tibia, lying underneath or within the periosteum. It would not have been possible to avoid this damage because it was impossible to place the retractor between the bone and the artery. As the artery could not have been reconstructed and with the supposedly knowledge that the ATA is usually of minor relevance only a ligature was performed. Unfortunately, the patient developed exaggerating pain and increasing swelling postoperatively, ending up in a compartment syndrome on Day 3 postop (Figure 1d,e). The prevailing view is that a lesion of this vessel is usually without consequences. This is difficult to argue against the aforementioned case. Further, the fact that we found ATAs with a considerably larger lumen than the remaining popliteal artery after the ATA branching also seriously calls this into question [10]. Presumably, in the majority of cases it is actually a ‘benign’ vascular injury. But obviously not in all cases and we do not know this beforehand. It must be noted that with the high prevalence of 2% and with hundreds of thousands of osteotomies performed worldwide, there is certainly a very high number of unrecognised iatrogenic injuries to this vessel that remain without consequences. This is especially the case for surgeons who operate with tourniquets—as they usually do not even notice this. But perhaps some of the compartment syndromes described, which are repeatedly mentioned in studies (and for which there is certainly a number of unreported cases) could be due to unrecognised injuries to this vessel [4, 5]. But we do not know this either. There is certainly agreement that an injury should be avoided whenever possible. This leads to the question of whether an adapted surgical technique as advocated by the authors of the letter to the editor can actually really prevent such an injury? The authors of the letter to the editor are surely extremely experienced trauma and orthopedic surgeons with an extraordinary experience in osteotomies of the proximal tibia. Nevertheless, we believe it is important to warn against a false sense of security through oversimplified suggestions: it was recommended to use chisels instead of an oscillating saw, and that the necessary retractor should be placed correctly and with particular care. Of course, it is also possible to injure an artery with a chisel. The deflection of a saw blade in posterior direction can also be safely controlled well using modern sawing techniques: By first entering the bone without cutting the dorsal cortex, establishing the sawing plane with this cut, and then going back again and very carefully cutting the dorsal cortex step by step from medial to lateral always with the very last dorsal deflection and the last tooth of the saw blade. In the case presentation in the letter to the editor the chisel also protrudes beyond the dorsal cortex of the central tibia some millimetres (Figure 2c) [7]. This does not make a difference to a correct sawing technique. We agree completely with the need to place the retractor precisely and very carefully. However, in the presented case in the letter to the editor the position of the retractor as shown in Figure 2a might be discussed: [7]. This placement might be not sufficient, as it is not positioned far enough laterally. The ATA would probably run directly in the area of the tip of the retractor or even laterally of its tip. In this position, the retractor would very likely not protect the ATA. The retractor should always reach all the way over to the medial border of the fibula; which can be felt well intraoperatively during placement. The retractor in our case of the iatrogenic injury presented in our original paper was placed by an experienced osteotomy surgeon with utmost caution. It was positioned correctly ranging all the way to the fibula (figure 8a of [10]). Nevertheless, the ATA was injured during the saw cut as it was lying between the retractor and the tibia, maybe attached to bone. We are therefore convinced that vascular injury cannot be reliably prevented in every case even with absolutely careful dissection performed by experienced surgeons. Especially if the artery does not run freely with at least some distance to the tibia, but really adherent to the tibia, as in the case described above. Having observed the same and trying to avoid this, Klecker et al. described a subperiosteal approach already 15 years ago [6]. However, to our knowledge, no data is available on whether this is reproducibly possible. We have also discussed the idea of larger incision or visual inspection e.g. with an arthroscope as recommended. This might be an option, however, we consider this might be difficult in practical application for two reasons: first, there are certainly doubts as to whether it can be adequately assessed. Second, the question naturally arises how one would proceed if the artery could be seen but not be detached from the bone… Would one then abort the operation - or would one risk to damage the vessel, in a purely elective procedure? We compliment the authors on their result of the case in the ‘letter to the editor’ with necessary correction in sagittal and frontal plane. However, this case might have been approached in an alternative way: Orientation-wise, there is only a slight varus deformity of about 4°–5°, with an also slightly elevated lateral distal femoral angle (LDFA) (around 89°). There is a pronounced pathological tibial slope of maybe slightly above 20° (according to the proximal anatomical axis), which can be problematic to be addressed to the necessary extent by a medial open wedge HTO [11]. Alternatively, an anterior closed wedge osteotomy of the tibia could have been performed to correct the slope, and the frontal axis could have been additionally corrected with a laterally closing distal femoral osteotomy to an at least neutral axis [1, 9]. One would have to accept that the overcorrection of approx. 1°–2° valgus would not have been achieved, but this does not seem to be necessary in view of the overall situation from our perspective. In this approach a low but still physiologically normal LDFA of approx. 85° would have resulted from a borderline high LDFA. However, this approach would have two substantial advantages: First, there would be virtually no risk of vascular injury, as the dorsal cortex of the tibia is not cut in an anterior closed wedge osteotomy. Consequently, the artery is not in any particular danger, regardless of how it runs. Secondly, the tibial slope as the central problem in this case could have been addressed more sufficiently. The PTS is still at around 12°–13° which might be seen as still rather high [3, 9]. A very similar case which was solved in this different approach is shown in Figure 2. But there's more than one way to crack an egg… And surely, the presented approach is not possible in all potential problematic cases. We again thank the authors for their letter to the editor, their comments and this discussion. We look forward to further reports and solutions to this problem, which in our view continues to be unsolved. We hope that we have been able to further raise awareness of the aberrant tibial artery in the orthopaedic community, because: The eye sees only what the mind is prepared to comprehend. The authors report no funding for this study. The authors declare no conflicts of interest.