Good heavens! - I forgot to mention that the right knee has had 4 operations: a medial meniscectomy, followed by two manipulations under anesthesia to unfreeze the knee after poor post-op care (which I blame the chronic tendonitis on), and then a lateral release (which accomplished nothing).

Knotted, thanks for your responses. I'll get a PT to evaluate me before I plunge into getting clipless pedals.