Strange, fleeting but increasing uncomfortable leg sensations causing leg (s) to buckle. What might be causing this? History of disc fractures, sciatic pain, mostly on one side, born breach, wore braces for first 3 years of life, had a serious back injury

My . My biggest concern, especially considering your history of disc problems and sciatica as well as previous serious back injury would be that the buckling and strange painful leg sensations are due to ongoing and perhaps progressive nerve irritation/entrapment from your lower spine. While nonspecific, numbness or tingling may also be present with nerve damage. More serious signs of problems, necessitating immediate evaluation would include loss of bowel or bladder control. You really should be evaluated by at least your primary care physician if not an orthopedic specialist.