| Abstract |
The restoration of the normal retroversion consists a part of the replacement procedure of the humeral head. However, it is known that there is a great variation in the retroversion of the humeral head. In fracture cases, the implantation of the humeral prosthesis in a standard retroversion between 20-40 degrees has been recommended. The aim of this study is to examine if the bicipital groove of the humerus can be used as a landmark for a proper, individualized orientation of a humeral prosthesis, especially in fracture cases. Forty-five dry cadaveric humeri without evidence of degenerative changes or previous fracture were used for this study. Each specimen was put on a flat horizontal surface with its tangent elbow axis parallel to the horozontal plane and, in this position 1.5mm CT-scan sections were obtained at the following sites: a) at a level just below the lower portion of the head of the humerus (a common site where the fractures requiring prosthetic replacement occur), b) at the middle of humeral head and c) 5 cm below the first section, at the metaphyseal cylinder area. All CT slices were further analyzed using Image Pro Plus version 4.0 software (Media Cybernetics, L.P., USA). The three images for each humerus were overlaid on a pixel-by-pixel basis in order to form a merged image superimposing these slices on each other. The distance between the perpendicular to the middle of the anatomical head line and the posterior edge of the bicipital groove at the level just below the lower portion of the head was measured. This distance corresponds to the site where the lateral fin of a humeral prosthesis fitting the humeral canal seats. Intra- and inter-observer variation was evaluated using data of three operators. All operators measured five times each variable using the complete data set of 5 srecimens, and measurements showed that our technique provided reproducible results. The duration of the whole procedure did not exceed 30 minutes in each specimen. According to our results, to reproduse the individual posterior version of the head, when we implant a humeral prosthesis for fracture, the lateral fin of the prosthesis should be sit at a mean distance 5.2±2.6mm (-1.5 to 10.7 mm) from the posterior edge of the bicipital groove. If the lateral fin of the humeral prosthesis seats just behind to the posterior edge of the bicipital groove a difference from the normal posterior version -6.3 to 41.7 degrees occurs. When we deal with a fracture, it is rather a simplification to say that we can orientate the prosthesis just by putting the lateral fin of the prosthesis at the estimated mean distance. However, it could be possible to measure the respective distance from the groove on the sound humerus in a similar way we calculated it, using the cadaveric bones. Despite the fact that some authors have reported differences in retroversion between the left and the right humeral heads, the proximity to normal is better using the above methodology than to put the prosthesis in a standard retroversion.
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Η σημασία της αύλακας του δικεφάλου βραχιονίου μυός στον προσανατολισμό της βραχιόνιας πρόθεσης στα κατάγματα του ώμου
