# Prediction of screw loosening by measuring the insertion torque in non-osteoporotic patients: an in vitro study

## TL;DR

This study investigates whether insertion torque can predict pedicle screw loosening in non-osteoporotic patients using an in vitro model.

## Contribution

The study introduces a potential intra-operative method using insertion torque to predict screw stability in non-osteoporotic patients.

## Key findings

- Insertion torque showed the highest influence on screw loosening stability.
- Bone mineral density had no effect on screw loosening in non-osteoporotic patients.
- Screw size and vertebral level also significantly influenced loosening stability.

## Abstract

Pedicle screws are commonly used in spinal surgeries, but screw loosening remains a major concern, even in non-osteoporotic patients. Predicting pedicle screw stability via the insertion torque is a controversial topic, mainly studied on osteoporotic cadavers. Whether the insertion torque is suitable for patients with healthy bone mineral density (BMD) remains unknown. The aim was to investigate the influencing factors, namely insertion torque, BMD, screw diameter, length, surface area, volume, screw-in rotations, vertebral level, on the screw loosening stability during distractions and to understand if intra-operative predictions are possible.

Non-osteoporotic thoraco-lumbar vertebrae (n = 50) were used to implant five different pedicle screws (n = 100) while measuring the insertion torque. After embedding the endplates, the force needed to distract the screw head by 1 mm was tested.

The insertion toque (2.3 ± 0.9 Nm) showed the highest influence on the distraction force (324.8 ± 84.4 N) followed by the screw size and vertebral level. BMD did not show any effects.

The linear correlation of insertion torque and the bending force suggests an alternative prediction metric for screw loosening which could improve the outcome of surgeries and patients’ safety. This is potentially a simple, intra-operative method, which can be used in future.

The online version contains supplementary material available at 10.1186/s12891-025-08654-4.