Background: Knowledge of the proximal edge of the germinal matrix is essential to avoid injuries in the germinal matrix. The previous index such as terminal tendon insertion is not visible from the body surface. The purpose of this study was to examine the relationship between the proximal edge of the germinal matrix and the body surface indexes by ultrasonographic measurements.
Methods: All participants underwent X-rays of the hand and were grouped based on the presence or absence of osteoarthritis in the distal interphalangeal (DIP) joint. The distance from the proximal edge of the germinal matrix to dorsal distal interphalangeal crease (parameter D1), and to ''DIP joint extension boundary line'' (parameter D2) were measured using ultrasonography.
Results: Thirty middle fingers of 24 patients were enrolled; 13 fingers were in control group and 17 fingers were in Heberden's node group. The average of parameter D1 was 6.17 mm (SD 1.12) in the control group (N = 13), and was 7.04 mm (SD 1.31) in Heberden's node group (N = 17) without significant difference. The DIP joint extension boundary line was not visible in 7 fingers with severe DIP joint osteoarthritis. The average of parameter D2 was 0.00 mm (SD 0.00) in the control group (N = 13), and was 0.04 mm (SD 0.13) in Heberden's node group (N = 10).
Conclusions: We suggest that DIP joint extension boundary line and dorsal distal interphalangeal crease are valuable indexes to predict the proximal edge of the germinal matrix from the body surface. Though the DIP joint extension boundary line was not visible in some cases, once it has been sighted, the line shows where the germinal matrix exactly is.
Keywords: Body surface index; Germinal matrix; Heberden's node; Ultrasonography.
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