Location of the Neurovascular Bundle of the Knee during Flexed and Extended Position: An MRI Study.

BACKGROUND

The popliteal vessels and nerve are the structures most at risk during surgery of the posterior knee compartment. Common procedures that could interfere with or otherwise affect these structures include synovectomy, meniscal repair, proximal tibial osteotomy, knee replacement and fixation around the knee joint. Magnetic resonance imaging (MRI) can be used to locate the neurovascular structures from the posterior bony landmark. MRI imaging is routinely studied in the extended knee, but surgery of the posterior knee compartment is most often performed with the knee in a flexed position.

OBJECTIVE

The aim of this study was to investigate the location of the posterior neurovascular bundle relative to the posterior aspect of the femur, tibia, and posterior cruciate ligament during fully extended knee position and 90-degree flexed knee position using MRI.

MATERIAL AND METHOD

MRI images of 26 knees were obtained from 25 patients. Ten left knees, 14 right knees, and 1 bilateral knees were obtained from 18 males and 7 females. Axial plane and sagittal plane studies were used to measure the shortest distance of the popliteal artery, popliteal vein, and tibial nerve to the posterior bony aspect of the knee and the posterior cruciate ligament using a digital ruler tool from the PACS X-ray system. Measurement was performed at joint line level, 1 cm above joint line level, and 1 cm below joint line level in the fully extended knee position and in the 90-degree flexed knee position. At the joint line level, the mediolateral distance of the popliteal artery, popliteal vein, and tibial nerve to the posterior cruciate ligament were also measured.

RESULTS

At 1 cm above joint line level, mean anteroposterior (AP) distance from the distal femoral condyle to the popliteal artery, popliteal vein, and tibial nerve was 1.83+3.35 mm, 6.44+4.55 mm and 10.29+4.41 mm for full knee extension, and 15.60+5.01 mm, 20.63+4.62 mm and 26.24+7.70 mm for 90-degree knee flexion, respectively (p<0.001). At joint line level, mean AP distance from the posterior tibial cortex to the popliteal artery, popliteal vein, and tibial nerve was 5.43+3.22 mm, 8.75+3.72 mm and 13.10+4.15 mm for full knee extension, and 11.64+5.48 mm, 17.59+6.53 mm and 21.52+10.67 mm for 90-degree knee flexion, respectively (p<0.001). At 1 cm below joint line level, mean AP distance from the posterior tibial cortex to the popliteal artery, popliteal vein, and tibial nerve was 1.98+1.95 mm, 4.26+2.74 mm and 8.66+3.85 mm for full knee extension, and 6.91+2.86 mm, 12.34+5.23 mm and 16.58+9.22 mm for 90-degree knee flexion, respectively (p<0.001). At joint line level, mean distance from the posterolateral border of the PCL to the popliteal artery, popliteal vein, and tibial nerve was 11.12+2.62 mm, 11.30+4.05 mm and 15.14+5.05 mm for full knee extension, and 19.89+5.67 mm, 23.87+6.96 mm and 29.41+10.72 mm for 90-degree knee flexion, respectively (p<0.001).

CONCLUSION

During 90-degree knee flexion, the neurovascular structures move posterolaterally, as compared to fully extended knee position at joint line level and 1 cm above and below joint line level. To prevent neurovascular injury during surgery, surgeons should avoid or be cautious during blind penetration of the midline joint capsule and 90 degree flexed knee position increases the distance of the neurovascular bundle away from the posterior bony aspect.