Measurements of metacarpal length and cortical thickness: a longitudinal assessment of hand radiographs from the osteoarthritis initiative

Abstract

Purpose: Metacarpal cortical thickness (TC) – a surrogate for bone density – is associated with rheumatoid arthritis and possibly hand osteoarthritis. However, few investigators have studied adults to assess changes in metacarpal TC, which can be measured using a custom-image-analysis software applied to digital hand radiographs. The goal of our study is to perform a high powered validation study of a new software method to quantify TC and metacarpal length (LM) using baseline and longitudinal hand radiographs from the Osteoarthritis Initiative (OAI). Based on the literature, we hypothesize that females will have less metacarpal TC and a greater decline in metacarpal TC than males. Furthermore, LM will be shorter among females. Methods: We assessed the baseline and 48 mo visit hand radiographs of 3225 (1,879 female) subjects enrolled in the OAI. We selected participants from the ,614 OAI subjects who had undergone hand radiography at both time points, and where our method could assess all four metacarpals for digits 2–5. A reader manually marked 4 points on cropped images of the metacarpals (Figure 1). Points A and B, were on either end of the metacarpal and Points C and D were placed on the on the radial and ulnar margins of the bone. The software then automatically determined the inner and outer margins of the projected cortices. TC was calculated in a central region of the metacarpal (shaded region between the horizontal lines). LM was defined as the distance between Points A and B. We measured the average TC and ML at the baseline visit as well as the change in TC from baseline to 48 mo. For TC change we report the average and standard deviation of the change, as well as the standardized response means (SRMs). All results are stratified by gender and digit number. We also investigated TC change for Digit 2 as a function of age by separating the data into seven 5-year age groups from 45 to 80 years. Results: Table 1 gives the baseline TC and ML results showing a pattern of reduced values for higher digit number (e.g., 5th digit < 2nd digit) and female gender. Table 2 shows the average TC change in mm and SRM values stratified by digit number and gender. A similar reduction is observed as a function of digit number but with increased thinning for women. Figure 2, a graph of SRM as a function of baseline age, demonstrates distinct patterns for each gender. Conclusions: The pattern of less metacarpal TC and ML (Table 1) for increased digit number and female gender is expected and offers evidence that the method is robust and accurate. Table 2 shows increased cortical thickness change for women versus men and for the larger digits, which is consistent with patterns of increased bone loss for women observed with conventional bone density methods. Finally, we observed distinct pattern of cortical thinning as a function of age for each gender, which supports prior evidence that females experience considerable bone loss after menopause. In summary, we have performed a high-powered evaluation of a software method to measure metacarpal length and cortical thickness that offers evidence for patterns of cortical thinning associated with gender, age, and digit type.Tabled 1Tc (All participants N = 3,225)Ml (All participants N = 3,225)Tc (Female participants N = 1,879)Ml (Female participants N = 1,879)Tc (Male participants N = 1,346)Ml (Male participants N = 1,346)Digit 21.8067.91.6665.61.9871.2Digit 31.6665.81.5263.51.8669.0Digit 41.3058.61.1956.41.4461.8Digit 51.2453.91.1451.81.3956.9Average Tc and Ml in mm for the baseline visit stratified by gender and digit number. Open table in a new tab Table 2Baseline to 48mo average change in Tc, the standard deviation (SD) of the change, and SRM values. Average change and SD are in mmAverage (All N = 3,225)SD (All N = 3,225)SRM (All N = 3,225)Average (Female N = 1,897)SD (Female N = 1,897)SRM (Female N = 1,897)Average (Male N = 1,346)SD (Male N = 1,346)SRM (Male N = 1,346)Digit 2−0.200.14−1.39−0.220.14−1.55−0.160.13−1.24Digit 3−0.200.14−1.39−0.220.15−1.48−0.170.13−1.32Digit 4−0.140.11−1.26−0.150.12−1.31−0.130.11−1.22Digit 5−0.140.12−1.20−0.140.12−1.22−0.140.12−1.18 Open table in a new tab View Large Image Figure ViewerDownload Hi-res image Download (PPT) Average Tc and Ml in mm for the baseline visit stratified by gender and digit number.