Explanation:
The correct option is a. The popliteal artery runs directly posterior to the knee joint capsule, tightly tethered by the fibrous arch of the soleus muscle just distal to the joint line. It sits shockingly close to the posterior cortex of the proximal tibia (often less than 5mm away, especially in a flexed or severely arthritic knee). The most dangerous maneuver in all of TKA is the horizontal proximal tibial cut. If the surgeon loses control of the oscillating saw blade and allows it to plunge through the posterior tibial cortex, it will immediately lacerate the popliteal artery, resulting in a limb-threatening emergency. Specialized retractors (like a Z-retractor or PCL retractor) must be placed precisely behind the tibia to protect this vessel. Reference: Smith PN et al. The anatomic relationship of the popliteal artery to the tibial plateau in total knee arthroplasty. J Arthroplasty.