The window of the knee
On a small set of three poses I learned from a knee specialist — and why doing them most evenings has saved a knee I thought I was going to lose.

Three years ago I started having a small persistent ache behind my right knee that I assumed would go away. It did not. After six months I went to a specialist who took an MRI, told me there was mild patellofemoral degeneration but nothing surgical, and suggested I try a small stretching protocol before considering any further interventions. He printed out a sheet with three poses and told me to do them every evening.
I did them. The knee, over the following six months, slowly got better. After a year the ache was gone. After two years the knee, used carefully but not babied, has been quietly working. I still do the three poses most evenings. They take about eight minutes.

The first pose: a long supported quad stretch
Standing, holding a wall for balance, knee bent and the foot held behind the body. Held for two minutes. The point is not depth. The point is duration. A short quad stretch will not reach the lower portion of the muscle where the connection to the patellar tendon lives. A long one will. Two minutes is the threshold.
The second pose: a deep low lunge with the back knee down
On a folded blanket or a thin mat, with the back knee resting and the front foot well forward. The hands rest on the front thigh. The hips press gently forward. Held for two minutes each side. This stretches the hip flexor, which when tight pulls the knee out of its proper tracking. The knee, with the hip flexor released, sits better in its joint.
The third pose: a long lying figure-four
On the back, with one ankle crossed over the opposite knee, hands holding the underside of the back thigh, pulling the legs gently toward the chest. Held for two minutes each side. This stretches the deep glute and the small external rotators, which when tight also affect knee tracking.
Eight minutes total. Done most evenings before bed. The specialist's hypothesis was that the knee pain was, mostly, a tracking issue caused by tightness in the surrounding muscles, and that adequate stretching would restore the tracking without surgical or pharmaceutical intervention. He was right. I have, in the last two years, been able to do everything I used to do — long walks, occasional easy runs, sitting on the floor — without the knee complaining.
If the knee is sore and the imaging is clean, this protocol is, in my own n-of-one experience, worth eight minutes a day for six months. It saved me a knee. Or rather it taught me how to use the knee I have without hurting it further. The eight minutes has earned a permanent place in my evening.