Foot bent underneath

From UroWiki

Sometimes you will see an uromastyx at rest (or at least, temporarily paused) with one food bent backwards underneath it. This is commonly observed among uromastyx (and among bearded dragons), and although it looks like something may be wrong, it is in fact perfectly normal.

Possible indicators of injury

One should, however, be careful to observe the lizard during active times to ensure that it isn't limping, favouring that foot, or displaying any other abnormal behaviour which could indicate a leg injury. If the uromastyx is dragging that leg as it walks, this is a definite sign that something serious may be wrong.

If your animal presists in walking in this manor, go over your husbandary. Ensure the proper calcium supplement and UVB light are being provided. Along with other skeletal abnormalities, this is a common sign of MBD in other reptiles.