Doctors removed a 2.5-inch-long knife lodged in Saif Ali Khan's spine and repaired the leaking spinal fluid. Cerebrospinal fluid (CSF) or spinal fluid provides protective cushioning to brain and spinal cord. "CSF leak is dangerous because there's risk of infection spreading to spinal cord and brain, a condition known as meningitis, which can be life-threatening," neurosurgeon Jayesh Sardhara said.