The forearm in densitometry Nomenclature

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The nomenclature used to describe the various sites in the forearm that are assessed with densitometry is confusing. Commonly measured sites are the 33% or 1/3rd site3, the 50%, and 10% sites, the 5-mm and 8-mm sites, and the ultradistal site. The sites designated by a percentage are named based on the location of the site in relation to the overall length of the ulna. This is true for the site regardless of whether the site is on the ulna or the radius. In other words, the 50% site on the radius is located at a site on the radius that is directly across from the site on the ulna that marks 50% of the overall ulnar length, not 50% of the overall radial length. The 5-mm and 8-mm sites are located on either bone at the point where the separation distance between the radius and ulna is 5- or 8-mm,

3 Although a mathematical conversion of 1/3 to a percentage would result in a value of 33.3%, the site when named as a percentage is called the 33% site and is located on the radius or forearm at a location that represents 33%, not 33.3%, of the length of the ulna.

Fig. 2-26. The forearm. The scale at the bottom of the figure indicates ulnar length. The numbers reflect the percentage of ulnar length at which commonly measured sites are centered on either bone. The arrow between the two bones indicates the 8-mm separation point. R identifies the radius. U identifies the ulna. (Adapted from McMinn RMH, Hutchings RT, Pegington J, and Abrahams PH. [1993] Colour Atlas of Human Anatomy, 3rd edition, p. 110. By permission of the publisher Mosby.)

Fig. 2-26. The forearm. The scale at the bottom of the figure indicates ulnar length. The numbers reflect the percentage of ulnar length at which commonly measured sites are centered on either bone. The arrow between the two bones indicates the 8-mm separation point. R identifies the radius. U identifies the ulna. (Adapted from McMinn RMH, Hutchings RT, Pegington J, and Abrahams PH. [1993] Colour Atlas of Human Anatomy, 3rd edition, p. 110. By permission of the publisher Mosby.)

Fig. 2-27. A DXA study of the forearm acquired on the Norland pDEXA. Note the location of the regions of interest called the distal (dist.) and proximal (prox.) regions of interest. BMD values are given for the radius and ulna combined at both regions and for the radius alone at the proximal region of interest.

Fig. 2-27. A DXA study of the forearm acquired on the Norland pDEXA. Note the location of the regions of interest called the distal (dist.) and proximal (prox.) regions of interest. BMD values are given for the radius and ulna combined at both regions and for the radius alone at the proximal region of interest.

respectively. In Fig. 2-26, the approximate location of these sites is indicated. The 33% and 50% sites are both characterized as proximal sites, whereas the 10% site is considered a distal site. The ultradistal site is variously centered at a distance of either 4% or 5% of the ulnar length. There is nothing inherent in the definition of distal, ultradistal and proximal however, that specifies the exact location of sites bearing these names. In Figs. 2-27, 2-28, 2-29, and 2-30, the location of variously named regions of interest from several different DXA forearm devices can be compared.

» Demographics *

fige : 55 years

Sex : Female

" BoneNass Results « radius ulna N-DIS N-uROI BMC : 1.514 0.716 2.230 0.600 grams Area: 1.14 3.09 ?.52 0,00 cm2 BHD : 0.311 0.232 0.Z96 0.0(30 g/cmz

* Measurement * File :0000lcOÖ.ODA Study : Sep^23/00 Site : N-DIS Neas. : 1

Fig. 2-28. A DXA study of the forearm acquired on the Osteometer DexaCare DTX-200. The region of interest is called the distal (DIS) region and begins at the 8-mm separation point. Values are given for each bone and for both bones combined. This distal region of interest is not the same as the distal region of interest shown in Fig. 2-27.

» Demographics *

fige : 55 years

Sex : Female

" BoneNass Results « radius ulna N-DIS N-uROI BMC : 1.514 0.716 2.230 0.600 grams Area: 1.14 3.09 ?.52 0,00 cm2 BHD : 0.311 0.232 0.Z96 0.0(30 g/cmz

* Measurement * File :0000lcOÖ.ODA Study : Sep^23/00 Site : N-DIS Neas. : 1

Fig. 2-28. A DXA study of the forearm acquired on the Osteometer DexaCare DTX-200. The region of interest is called the distal (DIS) region and begins at the 8-mm separation point. Values are given for each bone and for both bones combined. This distal region of interest is not the same as the distal region of interest shown in Fig. 2-27.

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