I have started developing some weird back pain and symptoms I don’t know what to make of. First, it’s all in the low back right above my bum. Next, it feels like my bones are sliding around in there when I shift from my right side to my left (in bed). There’s no numbness or shooting pain like sciatica (I’ve had that before). And the weirdest of all — the symptoms all get worse when the weather goes bad. What do you make of this?

You may be describing the classic signs and symptoms of a problem referred to as lumbar segmental instability (LSI). Lumbar refers to the low back region composed of five large vertebrae numbered one through five (e.g., L1, L2, L3, and so on).

Segmental means a specific one of those vertebrae is involved. And instability describes too much movement or translation of the bone. The shift of the bone can be seen on X-ray when the spine moves — especially at the end of the spinal movement (e.g., bending forward/flexion or bending backward/extension).

The patient suffering from back pain as a result of lumbar segmental instability experiences a “catching” sensation when standing up straight after being bent forward. Another sensation described is one of the spine “slipping out” during spinal motion.

The pain is usually worse in the morning. Pain and slippage are key features when the person tries to roll over (just as you described). And like a weather gauge, changes in the barometric pressure also increase painful symptoms.

What can cause lumbar segmental instability? Age-related disc degeneration, surgical spinal fusion, surgical removal of a disc, or a history of trauma affecting the spine. The condition is diagnosed based on the patient’s history, physical exam (clinical tests), and imaging studies. It may be best to make an appointment with an orthopedic surgeon to get an accurate diagnosis and get started on some treatment.