Bicipital groove orientation: considerations for the retroversion of a prosthesis in fractures of the proximal humerus.

The bicipital groove anatomy is well documented, and this groove is used as a landmark to guide retroversion during implantation of a shoulder prosthesis. Whereas the proximal part of the groove is used in osteoarthritis, the distal part is used in fractures. If used in 4-part fracture cases, we must assume that the bicipital groove orientation is constant from proximal to distal. We measured the groove orientation in 40 cadaveric humeri using 3 superimposed computed tomography sections. The reference axis was the transepicondylar axis at the elbow level. The measured angle of the bicipital groove was 55.8 degrees +/- 4.5 degrees at the anatomic neck and 65.1 degrees +/- 3.5 degrees at the surgical neck. This difference (mean of 9.3 degrees, with extremes of -3 degrees and 22.5 degrees) was statistically significant. We confirmed a wide range of variation from 22 degrees to 89 degrees in the orientation of the groove. Because the values listed in the literature for lateral fin placement of a prosthesis have not been measured at the surgical neck level and because of the great variation in groove orientation, we caution surgeons about the use of the bicipital groove as a reliable landmark in shoulder replacement for fractures. Considering the risk of over- or under-retroversion of the prosthesis, we recommend the use of a fracture jig with retroversion set to 20 degrees.