trigger point code

I have a coding question about injections into the ligaments and tendons of the knee. The doctor states trigger point injections were done into the MCL, PCL, and suprapatellar tendons bilaterally. im confused on which code to use for this.. I know it would either be 20550 or 20551 but would I bill multiple units per knee since these codes are for a single tendon/ligament? thank you!

trigger point code