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Measurement of knee joint space width with bi-planar radiography
Isabella D Vandergaag1, Richard E A Walker1,2, Steven K Boyd1,2
1McCaig Institute for Bone and Joint Health, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4Z6, Canada.
JBMR Plus
|January 21, 2026
Summary
Bi-planar knee imaging offers reproducible joint space width (JSW) measurements comparable to conventional radiography. This technique is feasible for accurate JSW assessment when knee position and alignment are controlled.
Area of Science:
- Orthopedics
- Radiology
- Medical Imaging
Background:
- Joint space width (JSW) is a key indicator of knee health.
- Conventional radiography is the standard for JSW measurement but has limitations.
- Bi-planar imaging presents a potential alternative for JSW assessment.
Purpose of the Study:
- To evaluate the reproducibility of knee JSW measurements using bi-planar imaging.
- To compare the precision of bi-planar imaging with conventional radiography (CR).
Main Methods:
- A cross-sectional study involving 30 uninjured adults.
- Repeat scans using bi-planar radiography and conventional tunnel view knee radiographs.
- Measurement of minimum apparent tibiofemoral JSW for each leg and compartment.
Main Results:
- Bi-planar imaging showed comparable short-term precision (RMSCV 6.46%, LSC 1.07 mm) to CR (RMSCV 7.66%, LSC 1.15 mm).
- A slight bias towards greater JSW was observed with bi-planar radiography (9.0%, p < .01).
- This bias was more pronounced in specific knee compartments under unloaded conditions.
Conclusions:
- JSW measurements from bi-planar scanners are reproducible and comparable to CR.
- Bi-planar scanners can provide accurate and precise JSW measurements.
- Controlled knee positioning and alignment are crucial for reliable bi-planar JSW assessment.
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