Abstract: An interbody spinal cage when implanted can be manipulated non-invasively to change dimensions conforming to contours of adjacent vertebral bones. The interbody spinal cage includes a flexible shell that encases multiple variable-length rods. Each of the multiple variable-length rods includes telescoping tubes and an actuator for increasing and decreasing the length of the telescoping tubes. Each of the variable-length rods includes a retention member to limit movements of the telescoping tubes, wherein the retention member can be engaged and disengaged. Both the retention member and the actuator can be operated from outside the body in which the interbody spinal cage is implanted.