Not sure if this belongs here, but here goes.
65+, wife and I race a Rebel and are 2 years into ownership of Horizon 39, cutter rigged ketch, center cockpit, over the "horizon" in 3 years or so, sailing Lake Huron in the meantime.
Right knee is getting buggy. Doc says only realistic option is knee replacement. Concerns: range of motion; kneeling (on deck, down below, on the beach, etc.); agility; durability; discomfort; which model.