Anatomically there is no popliteal nerve. The sciatic nerve separates just above the popliteal fossa into the common peroneal nerve and the tibial nerve. You need to verify with the physician which specific nerve was injected.
The saphenous nerve, as indicated in another post, is a distal branch of the femoral nerve. The saphenous nerve can be injected at the patient's ankle which would be quite different from a femoral nerve injection in the groin.
Codes are based on the physician work, risk and practice expense associated with performing the service. Injecting the main nerve is much different in terms of physician work and malpractice risk than injecting a distal branch. For example, injecting the medial cutaneous nerve of the leg, a branch of the saphenous nerve which is a branch of the femoral nerve takes less physician work / expertise and carries much less risk than inserting a needle into the patient's groin area which has large arteries, veins and other nerves in close proximity.
With this in mind, the physician should be injecting the specific nerve, i.e. sciatic or femoral and not a distal branch in order to code the injection for that specific nerve. If the distal branch does not have a specific injection code and it is likewise a somatic nerve, then it would be appropriate to code the distal nerve injection with 64450.