hello it is possible that there is some pressure of cutaneous nerve supply ,as I studied,of plantar nerve medial branch as a result of cast pressure/or on initial injury in the foot and swelling in foot often temporarily puts pressure on plantar sole aspect of foot causig pressure o erves and blood vessels,. normally, the numbness should overcome by itself after few weeks of subsidence of swelling/removal of cast.Essential part is whether the great toe movement is hampered or not-if you can move it alright -then nothing to worry-sensations would return.Another chance may be some arterial pressure in blood supply to toe-if nail blanches on release of pressure then circulation may be intact. what to do? I would suggest elevation of foot if swelling is there after every walk hot water fomentation toe drill exercise wait and watch Your physical therapist may consider TENS (muscle-nerve stimulation) if agrees