# Association Between Lower Instrumented Vertebra Selection and Mechanical Complications After Surgical Correction for Kyphotic Deformity Following Osteoporotic Vertebral Fracture

## TL;DR

This study finds that the choice of lower instrumented vertebra in surgery for kyphotic deformity after osteoporotic fractures affects the risk of mechanical complications.

## Contribution

The study identifies specific patient factors associated with distal junctional failure in short-fixation surgeries for kyphotic deformity.

## Key findings

- Short fixation reduced proximal junctional failure compared to long fixation.
- Distal junctional failure occurred only in the short-fixation group and was linked to preoperative malalignment and muscle degeneration.
- Short fixation preserved better postoperative lumbar function.

## Abstract

Background: Kyphotic deformity following osteoporotic vertebral fracture (KDOVF) often requires corrective surgery to restore sagittal alignment; however, mechanical complications, such as proximal junctional failure (PJF) and distal junctional failure (DJF), remain major concerns. Selection of the lower instrumented vertebra (LIV) plays a critical role in balancing mechanical stability and functional preservation; however, the optimal criteria for LIV selection have not been fully established. Methods: This multicenter retrospective cohort study included 52 patients who underwent corrective surgery for KDOVF, with a minimum 1-year follow-up. The patients were classified into a long-fixation group with pelvic fixation (n = 27) and a short-fixation group with lumbar LIV fixation (n = 25). Mechanical complications, radiographic parameters, patient-reported outcomes, and paraspinal muscle fatty degeneration were compared between groups. Subgroup analysis was performed within the short-fixation group to identify the factors associated with DJF. Results: The incidence of PJF was significantly higher in the long-fixation group than in the short-fixation group (37% vs. 8%, p < 0.01), whereas DJF was observed only in the short-fixation group (24%). Within the short-fixation group, patients who developed DJF demonstrated significantly greater preoperative sagittal malalignment, a lower rate of cement-augmented pedicle screw, and more advanced fatty degeneration of the paraspinal muscles. The short-fixation group also showed better postoperative lumbar function. Conclusions: LIV selection in KDOVF surgery is associated with distinct patterns of junctional mechanical complications. Short fixation may be feasible in carefully selected patients who demonstrate preserved compensatory capacity.