Jonti
what the dormouse said
^^^ This ^^^...
Why can't you lie down and meditate? Why can't you sit on an armchair with legs at right angles at the knees, arms lightly resting on the side bits, back straight against the back of the chair, and just looking forwards? Very comfortable, and no internal organs stretched or out of place.
...
Notice that the guy dressed in black nearest the camera is kneeling on his zafu (his meditation cushion), and not sitting cross-legged in a lotus.
It is true, as physical yoga shows, and many posters have asserted, that particular postures can be conducive to particular mental states. And yeah, the full lotus has a great reputation for inducing the mindfulness of "sitting quietly doing nothing". But other positions are also good, including the kneeling posture illustrated in the picture, and even flat on one's back.
It's really a matter of choosing what works for one. Not all physiologies can comfortably hold a lotus (I've never been able to do it, despite being a life-long floor sitter!). Knee injuries, or hip troubles can rule it out. But they most certainly do not mean one cannot practice mindful meditation.