The outside measurement study of micro-hardness distribution of ulna / 中华骨科杂志

ABSTRACT

Objective To study the micro-hardness distribution of ulna and explore its correlation with surgical procedures of ulnar fractures,internal fixator,total elbow arthroplasty and the epidemiology of ulna fracture.Methods The ulna wasdivided into proximal metaphysis,diaphysis,and distal metaphysis.The proximal metaphysis was divided into the olecranon and the metaphysis olecranon of ulna.Thedistal epiphysis included the head of ulna.The shaft of the ulna was divided equally into nine segments.Each ulna was sawed by a band saw into twelve parts,which were prepared for the micro-indention testing.The micro-indention testing samples precision cuts were conductedwith a Buehler Isomet 11-1280-250 low speed diamond saw.Each micro-indention sample was cut 3mm thickness and fixed on glass sheet with epoxy resin.The samples surface was polished with progressive grades of sandpaper.Micro-indentation was pedormed on each bone sample sudace using a vicker micro-hardness tester,and the hardness value were measured as Hardness value (HV,HV=kgf/mm2).Twenty indentions were randomly selected on each sample,which were equally divided into four quadrants (anterior,medial,posterior and lateral).Hence,a total of 720 micro-indentations were pedormed on the three ulna.Before indention,each sample was controlled under the optical microscope where the bone surface was intact and not damaged.The micro-indentations were performed on each sample with a load of 50 g.The indentation time was set to 12 s.Hardness value (HV/0.05) was computed for each indentation.The lengths of the diagonals were measured under reflected light microscopy,and the Vickers hardness value was calculated.Indentations in which one diagonal was 10％ longer or more than the other were ignored.The indention was repeated.These preliminary data were used to determine the appropriate sample size of micro =indentation to be performed on each bone segment.SPSS 19.0 statistical software was used for statisticalanalysis.The one =way ANOVA analysis was used to compare the difference of bone micro-hardness values in different parts,and P ＜ 0.05 was statistically significant.Results The hardest part of the ulna is the lower ulnaand the value of micro-hardness was 47.77 HV.The least hard part was the head of ulna and the value of micro-hardness was 29.64 HV.The proximal metaphysis hardness value was 34.39 HV.The shaft hardness value was 43.47 HV.Thedistal metaphysis hardness value was 29.64 HV.The hardness was higher in diaphysis than metaphysis in the ulna with statistical significance.There was no statistically significant difference in the hardness of ulna anterior,medial,posterior and lateral quadrant.Conclusion It is demonstrated that the micro-hardnessof ulna shaft is significant higher than other two parts of ulna.The micro-hardness value difference was not significant among the anterior,medial,posterior and lateral quadrant.This study revealed the distribution rule of ulna micro-hardness and provided data support for the total elbow arthroplasty with human physiological characteristics through 3D printing.