# Measurement of knee joint space width with bi-planar radiography

## TL;DR

This study compares the reproducibility of knee joint space width measurements using bi-planar imaging and conventional radiography.

## Contribution

The study demonstrates that bi-planar radiography can produce reproducible knee joint space width measurements comparable to conventional radiography.

## Key findings

- Bi-planar radiography showed comparable precision to conventional radiography (RMSCV 6.46% vs 7.66%).
- Bi-planar imaging measured greater joint space width than conventional radiography, especially in specific knee compartments.
- Accurate bi-planar measurements are feasible if knee position and alignment are controlled.

## Abstract

The objective of this study was to identify whether the joint space width (JSW) of the knee, measured by bi-planar imaging, is reproducible compared to the clinical reference radiography. Our cross-sectional study design included a cohort of uninjured individuals (N = 30, 26.7 ± 5.1 yr) who underwent scanning to determine the short-term precision of the technique, involving repeat scans by bi-planar radiograph. Additionally, repeat conventional tunnel view knee radiographs were used as a comparator. The minimum apparent tibiofemoral JSW was collected for each leg side and compartment for both modalities. The root-mean-square coefficient of variation (RMSCV) and least significant change (LSC) for bi-planar scans (RMSCV = 6.46%, LSC = 1.07 mm) were comparable to conventional radiography (CR) (RMSCV = 7.66%, LSC = 1.15 mm). There was a bias for greater JSW by bi-planar radiography than CR (9.0%, p < .01), particularly for the forward unloaded left leg lateral (15.5%) and medial (17.6%) compartments. In conclusion, we found that JSW measurements from bi-planar scanners are reproducible and comparable to CR. While radiography remains accessible clinically, accurate and precise JSW by bi-planar scanners is feasible provided knee position and alignment are controlled.

Graphical Abstract