This 1982 theoretical paper by Kirkaldy-Willis and Farfan defines lumbar spinal instability as a clinical entity and places it within a three-stage degenerative cascade. It asks: what is instability, how does it arise pathologically, how do you diagnose it radiographically, and how should stage guide treatment?
Before this framework existed, the decision to fuse or decompress depended largely on surgeon preference rather than a mechanistic rationale. Kirkaldy-Willis gave us a staging system that converts that decision into a diagnostic question: which phase is this patient in?
When you see recurrent low back pain and sciatica that transiently responds to manipulation or rest but reliably recurs with trivial provocation, think Stage 2 instability. Stress films showing asymmetric L4-5 motion or CT in rotation showing posterior joint opening with lateral canal narrowing confirm the diagnosis. At that point, planning decompression without fusion risks the outcome seen in this paper: all four patients with unrecognized instability after lateral decompression failed until fusion was added.
In Stage 3, resist the urge to fuse. Marked disc height loss, vertebral body approximation, and anterior osteophytes signal that nature has already stabilized the segment. Decompression alone is the correct operation.
This 1982 theoretical paper by Kirkaldy-Willis and Farfan defines lumbar spinal instability as a clinical entity and places it within a three-stage degenerative cascade. It asks: what is instability, how does it arise pathologically, how do you diagnose it radiographically, and how should stage guide treatment?
Before this framework existed, the decision to fuse or decompress depended largely on surgeon preference rather than a mechanistic rationale. Kirkaldy-Willis gave us a staging system that converts that decision into a diagnostic question: which phase is this patient in?
When you see recurrent low back pain and sciatica that transiently responds to manipulation or rest but reliably recurs with trivial provocation, think Stage 2 instability. Stress films showing asymmetric L4-5 motion or CT in rotation showing posterior joint opening with lateral canal narrowing confirm the diagnosis. At that point, planning decompression without fusion risks the outcome seen in this paper: all four patients with unrecognized instability after lateral decompression failed until fusion was added.
In Stage 3, resist the urge to fuse. Marked disc height loss, vertebral body approximation, and anterior osteophytes signal that nature has already stabilized the segment. Decompression alone is the correct operation.