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The Congruency of Radius of Curvature in Type 1. and 2. Lunates in Cadaver specimens
Olukemi K. Fajolu, MD1; Lauren M. MacCormick, MD2; James T. Kim, MD3; Fabio J.R. Pencle, MB, BS1; Gregory P. Kolovich, MD4; Hisham M. Awan, MD5
1LESS Institute, Fort Lauderdale, FL; 2University of Minnesota, Minneapolis, MN; 3University of Washington, Seattle, WA; 4Massachusetts General Hospital, Boston, MA; 5Ohio State University, Columbus, OH

Introduction: Proximal row carpectomy (PRC) is a treatment option for various wrist arthritidies. It has been suggested that when the lunate is excised, there is a mismatch with respect to the radius of curvature between the capitate and the lunate fossa of the distal radius. This mismatch is proposed to lead to failure of a PRC with subsequent progressive disease. The purpose of this study is to compare the articular morphology (radius of curvature) of the capitate in cadaveric wrists with type 1 and type 2 lunates.
Methods: Twelve specimens were used for a total of twenty wrists. Two groups were created based on type of lunate, group 1 wrists had type 1 lunates, and group 2 wrists had type 2 lunates. A NextEngine 3D scanner was used to create three-dimensional images (Figure 1) of each lunate and corresponding capitate bone. The scanned images were analyzed using the Rapidform XOV program in order to calculate radius of curvature.
Results: The specimens were 70% male and the average age was 50 +/- 10 years. A priori power analysis was performed using an effect size determined from a prior study. This analysis showed that we needed 9 total wrists to achieve a minimum power of 0.80. There were no statistical differences in age, gender and BMI between the two groups, p=0.06, 0.107, and 0.16 respectively. When the mean radii of curvature of capitates to lunates was compared, using paired t-test, there was a statistically significant difference, p=0.015. Likewise, the mean ROC of lunates in group 1, 0.113+/-0.01 was statistically different from lunates in group 2 which was 0.088+/-0.01, p=0.024. In group 2 (type 2 lunates) the mean radius of curvature between capitates and lunates showed a statistical difference in size, p=0.021. The lunate: capitate ratio in group 1 compared to group 2 showed no significance, p=0.531.
Conclusion: This cadaveric anatomical study has shown that in wrists with a type 2 lunate, the mean ROC is statistically different between capitates and lunates. This implies that more translational force could be applied to capitates, due to smaller radii of curvature, compared to lunates. Based on the data proximal row carpectomy may prove to be a better treatment option for patients with type 1 lunates, as the articular surface in these wrists are more comparable between capitates and lunates.

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