• Age 45 years and older.

• Patients receiving long-segment posterior TL instrumented fusion using either supplementary rod constructs or dual-rod constructs (the index surgery).

‣ Long-segment is defined as the UIV at a thoracic level and the LIV at the sacrum/ilium.

⁃ Supplementary rod constructs are defined as: in addition to the traditional two primary rods, at least one supplementary rod (eg, accessory rods or satellite rods) is used, and at least one supplementary rod and one primary rod (ie, at least two rods) together must span multiple (≥ 2) vertebral levels. The supplementary rod constructs do not include rods connected end-to-end or side-to-side that do not bridge multiple vertebral levels.

⁃ The index surgery can be a primary surgery or a revision surgery.

⁃ The index surgery, staged or non-staged, must use posterior spinal fusion but can be in combination with other approaches such as an anterior procedure.

• If the index surgery is a revision surgery, the primary rods must be replaced in the revision surgery, with the exception of Harrington or Luque rods which can remain in place.

• o If the Harrington or Luque rods remain in situ, they must already have the UIV at the thoracic level and the LIV at the sacrum/ilium, or an extension of the existing Harrington or Luque is performed such that the UIV is at the thoracic level and the LIV at the sacrum/ilium.

• The index surgery was performed between January 1, 2014, and December 31, 2020, inclusive.

• Minimum 3 months of FU after the index surgery.

• Ability to provide informed consent according to the IRB/EC defined and approved procedures if applicable for retrospective data analysis.