In a similar way, my wife and I started riding a tandem in 1975. However in the last few years her knees have been bad. The other day, she thought she would like to go for a ride on it. Well, somehow the chain caught on a screw and our forward movement was immediately halted. I had my feet clipped in and couldn't get them out in time to maintain balance. so over we went. Donna did a faceplant into the lawn only inches away from the cement pavement ... and she broke a finger. We are thankful to God that the lawn was resilient. Her glasses were bent, but we straightened that. Although I repaired the problem, we hesitate a little going on the tandem. I got her on our tadpole recumbent trike (Catrike) today and she actually enjoyed it as it wasn't so stressful on her knees or in the stoker position on the tandem.