Normal glenoid vault anatomy and validation of a novel glenoid implant shape

Current glenoid implants are designed to be secured to the articular surface. When the articular surface is compromised, a glenoid component could be implanted if it obtained fixation from the endosteal surface of the glenoid vault. The first step for designing such a glenoid implant is to define the normal three-dimensional anatomy of the glenoid vault. The purpose of this study was to define the variations in glenoid vault shape in a large group of cadaver scapula. Computed tomographic (CT) scans of 61 normal scapulae (mean, 25-34 years) from the Haman-Todd Osteological Collection, with a wide range of sizes, were examined to define the normal glenoid vault anatomy. A custom software program was used to manipulate and measure the scans to determine the morphologic variations among the different glenoid vaults. From these data, we defined a unique glenoid vault shape and empirically developed 5 sizes to represent the study population of the 61 scapulae. A second group of 11 cadaver scapulae were used to validate the shape defined using the other 61. Prototype implants were placed into the real 11 scapulae using standard surgical techniques and then CT-scanned to analyze the shape of the glenoid vault. In the 61 scapulae, 85% of the points defining the endosteal surfaces vary among scapulae by less than 2 mm. For each of the 11 cadaver scapulae, the implant size used in the virtual computer implantation was the same size used for the plastic components placed into the cadaver scapulae. Fifty percent of the measured distances between the outer dimensions of the plastic models was within 2.4 mm of the glenoid endosteal surface. Eighty percent of the surface area of the plastic models was within 3.1 mm of the glenoid endosteal surface. Five percent of the dimensions were less than 1 mm and were considered to be areas of point contact. Before designing implants that can be used in pathologic glenoids, the shape of the normal glenoid vault must first be defined. This study defined a normal glenoid vault shape that can accommodate different sized scapula with 5 sizes. This glenoid shape may be used as a template to design a glenoid implant that obtains fixation within the glenoid vault.