Study on micro-hardness distribution characteristics of human metacarpal bones

Objective To report the micro-hardness of human metacarpal bones, compare and analyze the hardness values between different anatomical parts, and explore the distribution characteristics of micro-hardness of human metacarpal bones. Methods The metacarpal bones were collected from three fresh healthy frozen specimens. The soft tissue of the right metacarpal bone was dissected. These metacarpal bones were cut into 3 mm-thick slices perpendicular to the long axis with a low-speed saw in metacarpal base, shaft and head. The Vickers method was used to measure the hardness of different areas of the palmar, dorsal, medial and lateral site of bone slices, and the standard operation method with 50 g force loading for 50 s and maintenance for 12 s was used to determine the hardness. The hardness value was compared by one-way ANOVA, and P<0.05 was statistically significant. Results Totally, 45 specimens and 900 indentations at different bones and anatomic sites were involved. The overall hardness of metacarpal bone was (38.23±7.15) HV. The third metacarpal bone had the highest hardness (41.04±6.75) HV, followed by the second metacarpal bone (39.62±7.64) HV, the first metacarpal bone (37.83±6.52) HV, the fifth metacarpal bone (36.69±7.30) HV, and the fourth metacarpal bone (35.97±6.28) HV. The metacarpal shaft hardness (43.45±6.35) HV was higher than metacarpal basal (35.82±6.17) HV and metacarpal head (35.43±5.85) HV (F=16.415, P<0.01). There was no significant difference in palmar (37.58±7.35) HV, dorsal (38.93±7.08) HV, medial (38.26±7.00) HV and lateral site (38.15±7.14) HV in hardness (F=1.352, P=0.256). Conclusion The results of this study have deepened the understanding of metacarpal micro-biomechanical properties, and can guide the placement, direction and number of internal fixators in metacarpal fracture surgery, and provide data support for 3D printing of artificial metacarpophalangeal joint for the treatment of comminuted metacarpal fracture or defect. Key words: Metacarpal bones; Biomechanics; Vickers hardness; Micro-hardness