Alignment · Our Planning Philosophy
Standing Tall: The Science of Spinal Alignment
Your spine’s job is simple to state and hard to do: hold your head balanced over your pelvis, all day, for a lifetime. Sagittal alignment — how you stack up when seen from the side — is a central emphasis of how Dr. Gerlach evaluates patients and plans surgery.
Why it matters
Balance is cheap. Imbalance is exhausting.
When the spine is well aligned, standing takes almost no muscular effort — your skeleton does the work. Spine specialists call the small zone where this is true the “cone of balance.” When disease, wear, or a previous surgery pitches the trunk forward out of that cone, muscles have to fire constantly just to keep you upright. That shows up as deep fatigue, aching that builds through the day, and the feeling of “running out of standing.”
Research in adult spinal deformity has repeatedly shown that the further forward a person drifts, the worse their pain and function scores become. And it drives one of the most important lessons in modern spine surgery: an operation that fixes a pinched nerve but leaves the spine poorly balanced usually gives a bad result. That is why alignment is measured — not eyeballed — in every surgical plan.
Measured goals in alignment surgery
- SVA under 5 cm — head stacked over the pelvis
- Pelvic tilt under 25° — the body isn’t straining to compensate
- PI–LL within ~10° — your lumbar curve matches your pelvis’s blueprint
Parameters and ranges from adult spinal deformity teaching literature (AANS / Scoliosis Research Society).
Interactive · Feel the Physics
What your body does when alignment slips.
Drag the slider to tip the spine forward and watch the body’s hidden compensations kick in — the same sequence surgeons look for on a standing X-ray.
Educational illustration — not a diagnosis. Your actual numbers come from standing full-length X-rays reviewed with Dr. Gerlach.
Interactive · The Measurements
The numbers on your standing X-ray, explained.
Click each measurement to see it drawn on the spine — and what it means for you in plain language.
PI = PT + SS
Your pelvis’s fixed shape (PI) is always the sum of its posture parts (tilt + slope). When one goes up, the other must come down — which is how surgeons detect hidden compensation on an X-ray.
LL ≈ PI ± 10°
Everyone’s ideal lumbar curve is personal — set by the pelvis they were born with. Alignment planning is measured against your blueprint, not an average.
In practice
How this changes your surgical plan.
Deformity correction
Realignment surgery is planned against your personal targets — not a generic curve.
Deformity correction →Revision surgery
Many failed surgeries trace back to alignment that was never restored — measuring it is step one of every revision workup.
Revision surgery →Scoliosis & deformity
Curvature is only half the story — side-view balance often matters more to how you feel.
Scoliosis & deformity →Wondering about your own alignment?
Standing full-length X-rays and a careful exam answer it in one visit.