LONGITUDINAL ANALYSIS OF THE RELATIONSHIP BETWEEN SERUM INSULIN-LIKE GROWTH-FACTOR-I AND RADIOGRAPHIC KNEE OSTEOARTHRITIS

Objective: To examine the relation between serum insulin-like growth f actor I (IGF-I) levels and both incident and progressive radiographic knee osteoarthritis (OA) in the Framingham Osteoarthritis Study. Desig n: Subjects had bilateral weight-bearing, anterior-posterior knee radi ographs performed in 1983-1985 and again in 1992-1993. IGF-I levels we re measured from blood specimens obtained in 1988-1989 by a competitiv e binding radio-immunoassay (RIA) after separation with octadecasilyl- silica cartridges of serum IGF-I from binding proteins. Participants w ithout baseline radiographic OA [Kellgren and Lawrence grades (K&L)= 0 -1] were classified as having incident disease if they had K&L greater than or equal to 2 grades at follow-up. Progressive OA was defined as an increase in K&L score of greater than or equal to 1 in knees with baseline OA (K&L greater than or equal to 2). All analyses were knee-b ased and sex-specific. We examined IGF-I tertiles in relation to the r isk of incident and progressive radiographic OA separately, adjusting. for age, body mass index (BMI), and baseline K&L score, and used gene ralized estimating equations to adjust for the correlation between fel low knees. Results: Four hundred and forty-one participants had knee r adiographs and serum IGF-I levels measured. No associations were found for serum IGF-I levels and incident [women: OR = 0.9 (0.6-1.7), men O R = 1.2 (0.6-2.6)] or progressive [women OR = 0.9 (0.6-1.6) men OR = 0 .9 (0.3-3.0)] radiographic knee OA in either sex. Neither did we obser ve any association between IGF-I and worsening of individual radiograp hic features of OA (i.e., osteophyte growth and joint space loss). Con clusion: In summary, this longitudinal study did not demonstrate arty association of serum IGF-I and incident or progressive radiographic kn ee OA. Further studies are needed to clarify the role of IGF-I in OA.