Table 1. Summary of outcomes over 96 months of follow-up in the OAI^*.

Outcome	Level	Description of each level
Incident or progressive radiographic OA (rOA)	1	Baseline KLG = 0–1, no follow up data (n = 0)
	2	Baseline KLG = 0–1, no incident rOA (n = 3127)
	3	Baseline KLG = 0–1, developed incident rOA (n = 557)
	4	Baseline KLG = 2+, no follow up data (n = 0)
	5	Baseline KLG = 2+, no progressive rOA (n = 2191)
	6	Baseline KLG = 2+, developed progressive rOA (n = 583)
	7	Baseline TKA (n = 0)
	999	No baseline and no followup KLG (n = 3)
Provision of total knee arthroplasty (TKA)	0	No TKA (n = 6060)
	1	Received TKA (n = 401)
Progressive structural damage, as quantitative joint space width [qJSW] loss‡		% loss of qJSW‡, in medial and lateral aspects
Progressive WOMAC† pain	1	Accelerated decrease in WOMAC pain from baseline
	2	No change in WOMAC pain over time
	3	Gradual worsening in WOMAC pain over time
	4	Increase then decrease in WOMAC pain

*Available at: https://nda.nih.gov/oai/outcomes, Outcome99; KLG = Kellgren-Lawrence Grade;

^†WOMAC: Western Ontario and McMaster Universities OA Index; Groups 1–4 defined by Group-based Trajectory modeling;

^‡Loss of qJSW = difference in qJSW from baseline to current divided by baseline in mm, expressed as a percentage (continuous).