Total shoulder arthroplasty: Some considerations related to glenoid surface contact

Abstract

The area of prosthetic surface contact is an important surgeon-controlled variable in total shoulder arthroplasty and is related to the geometry of the glenoid and humeral articular surfaces and their relative positions. This study explores some of the factors that affect joint surface contact area. We measured the humeral and the glenoid articular surface angles in the superior-inferior and anteroposterior planes for two prosthesis systems representative of those in common clinical use. On the basis of these data we determined the range of glenohumeral positions providing full glenoid surface contact, a condition in which all of the articular surface of the glenoid component is in contact with the articular surface of the humeral component. We found a wide variability in the range of glenohumeral positions providing full glenoid contact with different prosthetic combinations. Some combinations do not even offer full glenoid surface contact with the joint in the centered position, for example, when the center of the humeral head articular surface is opposed to the center of the glenoid articular surface. The maximal range of glenohumeral positions providing full glenoid surface contact was 117° for a combination with a small radius of head curvature and a large articular surface angle. The relative positions of the humeral and glenoid articular surfaces also have a major influence on the joint contact area. Some combinations offer full glenoid surface contact only in a position of humeral abduction with respect to the scapula. Loss of full glenoid surface contact between the glenoid and humerus may allow for unwanted translations of the humeral head on the glenoid in the direction where contact is lacking. Furthermore, in positions where full surface contact is lacking, humeral bone or soft tissue may make unwanted contact with the glenoid. These results suggest that the design of the humeral articular surface and the surgical procedure should maximize full glenoid surface contact in functionally important positions.