The proximity of the vascular structures traversing the AH in the distal femur may increase the risk of iatrogenic popliteal vascular injury during cerclage wiring. In the current study, reference values for safe distances from injury and the closest location of popliteal vessels to the femur were established using MRI in adult knees. The closest locations of popliteal vessels were at posteromedial aspect of the femur. The d-H and d-V were 7.38 ± 3.22 mm, and 57.01 ± 11.14 mm, respectively. We also assessed the effect of anthropometric factors on these distances and found thigh circumference and femoral length to be the most important indicators for the d-H and d-V, respectively.
Distal femur fractures account for about 6% of all femoral fractures [11–13], and vascular injuries around 2% . Injury to the SFA, deep femoral artery (DFA), or PA have been described as a result of broken sharp fragments or iatrogenic injuries such as external fixation pins, plunging drill bits, medial plating, or cerclage wiring. These damages could give rise to immediate bleeding, late presented pseudoaneurysm, limb ischemia, or below knee amputation [1, 5, 15–17].
Apivatthakakul et al. evaluated computed tomography angiography (CTA) of 80 patients, which divided the whole femur into eight equal segments (7 levels) from the tip of the GT to the lateral tibiofemoral joint line in the coronal plane and eight equal directions from anterior to posterior of the medial femur in the axial plane. They found that when the SFA was at levels 6 and 7, it was located between sectors F and H (posteromedial and posterior to the femur) and at a distance of about 13.63 ± 3.59 mm and 10.08 ± 3.09 mm, respectively. Their result was similar to the current study, which revealed closest point of popliteal vessels to situate posteromedial and posterior to the femur. During cerclage wiring, either from anterolateral or posterolateral direction, surgeons should be cautious of posteromedial and posterior aspects of the femur. The present study demonstrated the precariousness of popliteal vessels and that any distance shorter than the closest one shown here between the vessels and femur cortex could prove more detrimental than previously thought; we would also strongly suggest subperiosteal over blunt dissection during wiring, where the wire passer tips are as close to the bony cortex as possible or at low-risk position from the popliteal vessels, to avoid vascular injury.
To our best knowledge, this was the first study of d-H in the literature, which demonstrated smaller d-H in small thigh circumference patients. The explanation for this association is still uncertain. While the influence of obesity on the anatomical relationship between the PA and tibial nerve in the popliteal fossa had been reported, no direct evidence between the popliteal vessels and the femur cortex were described . Even though we had hypothesised the d-H was relevant to the thickness of the fatty tissue around the popliteal fossa, no correlation between the measurement and body weight or BMI was noted. Therefore, body fat percentage and regional distribution should be included for evaluation in future studies.
There is a transition zone in the hiatal area, from the adductor canal to the popliteal fossa. In comparison with the more flexible fatty tissue of the popliteal fossa, the region of AH is more rigid and fixes the junction of SFA and PA close to the femur cortex. Kwon et al. reported the level of AH to be over 59.8 mm proximal to the superior border of the patella . Cadaveric studies with 24 and 28 thighs described the level of AH to be above 10 cm (range 8.0-13.5 cm) and 7.4 cm (range 5.6–9.2 cm) from the AT, respectively [21, 22]. Kanawati et al. assessed 41 limbs using CTA to describe the relationship between the SFA and the whole femoral shaft and warned of the “danger zone” from 239.6 mm to 172.5 mm proximal to the AT . In the current study, the d-V (57.01 ± 11.14 mm) was shorter than the distance between AT and AH described in the literature [21, 22]. This suggests that the closest level of vascular bundle occurs slightly distal to the AH, at the point where the PA crosses posteriorly to the distal femur.
Kanawati et al. proposed doubled width of the femoral condyles as an estimated safe distance proximal to the AT for intervention . They also mentioned the danger zone where SFA crossed inferiorly by halving the distance between GT and AT. Both predictors could be measured on a true anteroposterior (AP) radiograph preoperatively or intraoperatively. In the current study, surgeon could estimate d-H and d-V preoperatively based on the thigh circumference and the femoral length, respectively, without CTA or MRI. The thigh circumference could easily be computed directly below the gluteal fold . The femoral length could be calculated from length between GT and AT on the AP view of a whole femur radiograph. Although there is a little difference between bilateral thigh, the thigh circumference and the femoral length could be used clinically by measuring the normal contralateral instead of the fractured limb.
This study has several limitations. First, our distances were measured on MRIs and not intraoperatively. Given that the MRIs were taken with the patient in a supine position, while some distal femoral fracture surgeries were performed with the patient in a lateral decubitus position, certain anatomical relationships may differ. Second, the direction of the femoral artery in the current study was dependent on the neutral position of the intact femur. Although the position was similar to most of the clinical conditions that used lateral approach in the distal femur, there were several factors including medial approach, extremity location, traction, soft tissue retractor, and the displacement of bony fragment that could influence the distance between the popliteal vessels and the femoral cortex. Third, instead of measuring the distances on 2D MRI scans, it would be more reliable to make 3D reconstructions using software such as Mimics® (Materialise, Leuven, Belgium) of the soft tissue of interest, i.e. the vessels, and relate those distances to the 3D bony landmarks. Furthermore, given that all subjects presented here were of unrelated Han Chinese ethnicity, it would be interesting to conduct this work in other populations.
Several methods of evaluating the location of femur artery have been utilised including cadaveric dissection [7, 22, 23], ultrasonography, angiography [14, 24], CTA [6, 9, 10, 17, 18, 25], and MRI [26–28]. We believed MRI provided more valuable information about relationships between soft tissues, including neurovascular bundle, muscles, and fatty tissues. In addition, the innovation of non-contrast-enhanced MR technique improved the resolution of soft tissue anatomy without the risk of contrast-induced complication as seen in angiography or CTA [26, 29]. Moreover, the sample size in our study was larger and the analysed MRIs were used to assess structurally pathologic knees, which was reflective of the anatomical reality in patients who were actually undergoing surgery. All distances were independently measured by three physicians. Therefore, the results provided could be viewed as reliable reference data in future work.