Micro-hardness distribution of proximal tibia in human skeleton

Objective To investigate the microhardness distribution of cancellous bone in the proximal tibia and its clinical significance. Methods Three fresh tibias were obtained and examined by X-ray and CT to exclude skeletal pathologies, such as osteoporosis, osteoarthritis. According to the Heim's square, the proximal tibias were cut off. Each of the proximal tibias was divided into three parts, the medial condyle, the intercondylar area and the lateral condyle. Each part was divided into three sections, proximal, middle and distal sections. Each of the proximal tibias was divided into 9 regions. Bone specimens with a thickness of 3 mm were taken from each region using a high precision low-speed saw and fixed on flat sheets. The microhardness of the bone tissue was measured using a Vickers microhardness tester after polish. Ten effective micro-indentation tests were conducted in each region. After measurement the diagonal length of the indentations, the microhardness values were calculated via software provided by the hardness tester. Analysis of variance and Tukey method were used to compare the microhardness values of different parts, sections and regions of cancellous bone. The microhardness distribution of the proximal tibia was analyzed. Results A total of 270 effective indentations were made in the specimens, and the microhardness values were obtained. The average microhardness of the three proximal tibias was 40.98±3.44, 34.92±4.64 and 39.49±3.86 HV, respectively. There was a significant difference among the groups (F=55.87, P=0.000). The microhardness distribution of bone tissue in the three proximal tibias was similar. In the comparison of different parts, the microhardness of medial condyle was greater than that of the lateral condyle, which was larger than that of the intercondylar area. The difference between the parts was statistically significant (F=18.42, 8.236, 10.877; P=0.000, 0.001, 0.000). In the comparison of different sections, the microhardness of the distal section was greater than that of the proximal section, which was larger than that of the middle section. The difference between the sections was statistically significant (F=8.720, 17.140, 6.142; P=0.000, 0.000, 0.003). The microhardness distribution was similar among different regions. The region with the highest microhardness is the medial condyle of the distal section with microhardness of 44.87±3.25 HV (range 39.2-49.7 HV). The lowest microhardness was in the intercondylar area of the middle section with hardness of 29.41±4.53 HV (range 24.8-36.2 HV). Conclusion The microhardness value of cancellous bone near the articular surface at the proximal tibia was smaller, which could disperse the load and protect the fragile of articular cartilage. Furthermore, the microhardness of the transition zone is larger. The microhardness value of the cancellous bone in medial tibia condyle is the greatest, which is related to load-bearing. Key words: Hardness tests; Tibia; Biomechanics