FEMORAL-NECK BONE-DENSITY - DIRECT MEASUREMENT AND HISTOMORPHOMETRIC VALIDATION

The purpose of this study was to develop a method for directly measuri ng bone density of femoral neck sections. Three types of density were measured. Real density equals wet weight divided by the actual volume of bone tissue (real volume). Apparent density equals wet weight divid ed by the total volume occupied by the bone plus the pore spaces (tota l sample volume). Ash density equals the ash weight divided by the rea l volume. Corticocancellous cross-sections of the femoral neck were an alyzed for density at two levels: level 1, proximal neck and level 3, distal neck. Density measurements were compared with histomorphometric measurements performed on cross-sections at the midportion of the fem oral neck (level 2) and with a clinical radiographic measure of bone d ensity (cortical index 3 cm below the lesser trochanter). No correlati on was found between apparent density and either real (r = .12, P = .6 2) or ash density (r = -.09, P = .72) within a given femoral neck sect ion. There was, however, a strong correlation between real and ash den sity (r = .93, P = .0001). This was expected because real and ash dens ities are both reflections of bone mineralization. Apparent density sh owed better correlation, when comparing level 1 with level 3 sections (r = .76, P = .0001), than did ash (r = .57, P = .01) or real density (r = .55, P = .01). There was no correlation between either real or as h density with any histomorphometric parameter. Apparent density was m oderately correlated with total bone area expressed as a percentage of cross-sectional area (r = .66, P = .008). This finding tends to valid ate the direct measurement of apparent density in that both apparent d ensity and total bone area are measurements of the concentration of bo ne in space. No significant correlation was found between any of the d ensity measurements and the cortical index at 3 cm. This underscores t he necessity for precisely qualifying any definition or discussion of bone quality. The success or failure of hip implants may be at least p artially determined by the ability of the bone to withstand the insult of implantation of the prosthesis and to adapt successfully to the ne w mechanical environment. This study represents an early phase of defi ning parameters that may have prognostic value in long-term implant fi xation.