Background/Purpose: The development and growth of osteophytes are considered a radiographic surrogate for osteoarthritis (OA) at the knee. Methods to determine osteophyte burden are largely semi-quantitative and subjective. Quantifying osteophyte volume could potentially provide an improved measure of change for OA trials and observational research. We have developed a software method for semi-automated osteophyte segmentation on MRI. Our objective was to validate the responsiveness of this method to osteophyte volume change over four years in subjects with established knee OA according to Kellgren and Lawrence (KL) grade. We assume that OA is a progressive process, thus osteophyte burden should increase over time.

Methods:  Ninety subjects (51 KL 2 and 39 KL 3) were selected from the Osteoarthritis Initiative (OAI) Progression Cohort. Double echo steady state 3D sagittal images were obtained on a 3T Siemens Trio MR system. Measurements were performed on coronal reformatted series. A reader used the software method to segment marginal osteophytes of the knee at baseline and 48-month follow up. Readings were performed paired but blinded to order of visit. The reader identified the first and last slice of the central weight bearing region and an edge detection algorithm demarcated the bone edges. The reader marked the expected normal bone contour at the base of the osteophytes (Figure 1a). The software calculated the area of the osteophyte (Figure 1b) on each slice and generated volume measurements.

The primary outcome was change in osteophyte volume (ΔV) from baseline to follow-up. Statistics used were the average change in osteophyte volume from baseline to 48 months (ΔV), the standard deviation (SD) of ΔV, the standardized response mean (SRM) ΔV/SD of ΔV, and the percentage of subjects with net increase in osteophyte burden.

Results: The average change in osteophyte volume (ΔV) was 1240 mm³, the SD = 1557 mm³, and the SRM was 0.80. A net increase in osteophyte volume from baseline to 48 months was observed for 83% (75/90, 40 KL 2 and 35 KL 3) of the subjects. The average reading time was approximately 10 minutes per knee.

Table 1 – Responsiveness to change over 48 months

Conclusion: The results confirm that quantitative measure of osteophyte volume can be performed efficiently and is responsive to change over time. This method has the potential be a powerful tool for monitoring longitudinal osteophyte change, and could assess a large study cohort rapidly while potentially reducing study costs and allow for evaluation of large scale trials such as the OAI.

Figure 1a and b

This study was funded by NIH/NIAMS R01AR056664