Gemini, a laminectomy was probably required because of damage to the cartilage caused by the stress fractures. I've had two of them and they are not fun.
Tragic could probably explain better but when the cartilage gets damaged, it can press against the spinal cord and cause a fair amount of pain.
The fact that Lillee could recover from that and adjust his running and bowling is a testament both to him and the people who helped him get there.
Biomechanics input is icing on the cake. As Shane said, it's not the answer to everything. What it can do is correct actions that lead to stress type injuries. Player availability is one important component in a successful season