The geometry of the humeral head and the design of prostheses

Abstract

The articular surface of the humeral head is usually described as facing posteromedially, making an angle of between 16 degrees and 35 degrees with the transepicondylar plane. At hemiarthroplasty the articular surface also appears to be offset posteriorly with respect to the humeral shaft. Coracoid impingement may occur if this offset is not accommodated. An analysis was made of 29 cadaveric humeri using an industrial co-ordinate measuring machine. The position of the centre of the head was defined with respect to the humeral shaft and transepicondylar plane. The humeral articular surface was found to be retroverted by 21.4 degrees and its centre offset posteriorly by 4.7 mm. Previous interpretation of retroversion did not take into account the posterior displacement, and this may be of importance in improving future prosthetic design.

Differences in reconstruction of the anatomy with modern adjustable compared to second-generation shoulder prosthesis

“…The anatomy of the proximal humerus can vary with respect to inclination, retrotorsion and the medial and dorsal offsets (the offset of the centre of rotation in relation to the humeral axis) [1,6,9,14,17,20,21]. Due to this, many groups call for this anatomy to be repaired as precisely as possible when implanting a humeral prosthesis in order to achieve optimal postoperative joint function [1,4,5,7,8,10,13,15,16,18,20,22,23].…”

Mathematical approximation of fibular malleolus curvature

“…A line perpendicular to the horizontal line was positioned through the lowest point of the bone. [8][9][10]12,[16][17][18] Then, a point on the vertical line and a point on the perpendicular line were marked, and their distances from the point of intersection between the two lines were measured. Such image was then loaded in Engauge Digitizer© v4.1 (Free Software Foundation, Inc., Boston, Massachusetts, USA).…”

“…This served to place every fibula in the same position within the Cartesian coordinate system (first quadrant) enabling the comparison between them. 16,19,20 Each fibula was digitized and its edge marked by 60 -70 points, each point defined by its position in the coordinate system, creating a couples of points representing the contour of the fibula (Figure 1). Digitized fibulas were then loaded into OriginPro© v7.5 (OriginLab Corporation, Northampton, Massachusetts, USA) in order to perform statistical analysis and their mutual relations could be established.…”

Variability of medial and posterior offset in patients with fourth-generation stemmed shoulder arthroplasty

“…This applies to inclination and retroversion of the articular surface and to displacement of the centre of rotation medially and dorsally [1,5,11,14,16,17]. When implanting a shoulder endoprosthesis, it is therefore difficult to restore the normal anatomy precisely, and the use of advanced technology may be required.…”

“…Studies on the variability of the proximal humerus anatomy cited most often were conducted on human corpses with no pathological conditions [1,5,10,11]. Other authors do not provide detailed information about their patient populations or sample materials [6,16,17].…”