Seasonal variation in adult hip disease secondary to osteoarthritis and developmental dysplasia of the hip

Figure 1 The cosinor fit for Indiana patients with hip osteoarthritis and month of birth. The best fit is represented by the equation: Number of OA births = 646.4 + 55.3 [cos(36t - 18)-324], where t = 1 is January, 2 is February, 3 is March, etc. This was statistically significant (r² = 0.56, P = 0.025). The peak is 1^st October (solid arrow). The data points are the black triangles and the best fit represented by the bold black line. OA: Osteoarthritis.