Sub-Millimeter Accuracy in Weight-Bearing Orthopedic Imaging

Orthopedic decision-making depends on accurate representation of anatomy—particularly when joint alignment and bone relationships change under load. Conventional supine imaging can obscure these functional differences, creating uncertainty in assessment and surgical planning.

A recent internal investigation evaluated whether weight-bearing cone beam CT (WB-CBCT) can deliver geometric accuracy comparable to multidetector CT (MDCT) while capturing anatomy in a physiologic, standing position.

Study Overview

The investigation assessed geometric accuracy using full lower-body cadaveric specimens scanned from pelvis to foot. Four specimens spanning a BMI range of 26–40 were included to reflect a range of patient anatomies commonly encountered in clinical practice.

Each specimen was scanned using:

1. MDCT with a standard musculoskeletal protocol
2. WB-CBCT using two radiation protocols:
   1. Standard dose
   2. High dose

MDCT imaging was performed on a Siemens SOMATOM Perspective system. WB-CBCT imaging was performed using the CurveBeam AI HiRise system.

Images were segmented using 3D Slicer, reconstructed into three-dimensional bone models, and superimposed to assess congruency between modalities. Mean surface distance differences were calculated relative to MDCT, with <1.0 mm predefined as clinically acceptable.

Accuracy Results

Across all specimens and protocols, WB-CBCT demonstrated mean surface distance differences well within the clinical acceptability threshold, with differences consistently measured in tenths of a millimeter.

Notably, the upgraded WB-CBCT system achieved sub-millimeter accuracy in every case, including higher-BMI specimens.

“The upgraded WB-CBCT delivered sub-millimeter accuracy in every case across a wide range of body mass indices.”

— Grayson Ewing, Software Development Engineer, CurveBeam AI

For the highest-BMI specimen, use of the higher-dose protocol resulted in slightly reduced variability, suggesting that selective protocol adjustments may provide added consistency when imaging larger or more complex anatomies.

Why Weight-Bearing Matters

Beyond numerical accuracy, WB-CBCT offers a key clinical advantage: the ability to image patients under physiological load.

By capturing anatomy in a natural standing position, WB-CBCT enables direct visualization of alignment, joint space, and bone relationships as they function in daily life. This may provide additional insight for alignment assessment and preoperative planning in orthopedic applications where load-dependent changes are clinically meaningful.

Clinical Takeaway

This validation data demonstrates that upgraded WB-CBCT technology can achieve MDCT-comparable accuracy while enabling functional, weight-bearing imaging.

With consistent sub-millimeter accuracy across a broad BMI range and adaptable imaging protocols, WB-CBCT continues to be evaluated as a clinically valuable tool for orthopedic assessment and surgical planning.

Download the full investigation summary here.