IMO, the VMO focused training/rehab for patellar tendonitis/anterior knee pain is misguided. Especially when people state the source of the tendinopathy is too much isolation movement with knee extension. For one, it is extremely difficult to completely isolate the VMO and by doing TKEs or other "VMO" exercises you are placing additional stress on the patellar tendon by activating a quad that is already presumably tight and restricted.
The reasoning for anterior knee pain/patellar tendonitis is usually due to poor gluteal activity, poor hip mobility, poor ankle mobility, and poor trunk stability along with soft tissue restrictions. Instead of focusing on VMO work, most would be better off working of soft tissue quality of the hips and legs, lengthening of the quads and hip flexors, mobility at the hips, tspine, and ankles, and rehab/exercises focused on gluteal activation and trunk/lumbar control/stability.