Topographic Analysis of the Glenoid and Proximal Medial Tibial Articular Surfaces

Abstract

Background: Current knowledge is lacking concerning the appropriate site of osteochondral allograft harvest to match glenoid shape for the purposes of glenoid resurfacing. This has led to difficulty with adequate restoration of the geometry of the glenoid with currently available techniques. Hypothesis: The medial tibial plateau will provide a suitable osteochondral harvest site because of its concavity and anatomic similarity to the glenoid. Study Design: Descriptive laboratory study. Methods: Computed tomography (CT) was performed on 4 cadaveric proximal tibias and 4 scapulae, allowing for 16 glenoid-tibial comparative combinations. Three-dimensional CT models were created and exported into point-cloud models. A local coordinate map of the glenoid and medial tibial plateau articular surfaces was created. Two zones of the medial tibial articular surface (anterior and posterior) were quantified. The glenoid articular surface was defined as a best-fit circle of the glenoid articular surface maintaining a 2-mm bony rim. This surface was virtually placed on a point on the tibial articular surface in 3D space. The tibial surface was segmented, and its 3D surface orientation was determined with respect to its surface. The 3D orientation of the glenoid surface was reoriented so that the direction of the glenoid surface matched that of the tibial surface. The least distances between the point-clouds on the glenoid and tibial surfaces were calculated. The glenoid surface was rotated 360° in 1° increments, and the mean least distance was determined at each rotating angle. Results: When the centroid of the glenoid surface was placed on the medial tibial articular surface, it covered approximately two-thirds of the anterior or posterior tibial surfaces. Overall, the mean least distance difference in articular congruity of all 16 glenoid–medial tibial surface combinations was 0.74 mm (standard deviation, ±0.13 mm). The mean least distance difference of the anterior and posterior two-thirds of the medial tibial articular surface was 0.72 mm (±0.13 mm) and 0.76 mm (±0.16 mm), respectively. There was no significant difference between the anterior and posterior two-thirds of the tibia with regard to topographic match of the glenoid ( P = .187). Conclusion: The findings suggest that the medial tibial articular surface provides an appropriate anatomic match to the glenoid articular surface. Both the anterior and posterior two-thirds of the medial tibial articular surface are potential sites for osteochondral graft harvest. Clinical Relevance: This method can be applied to future studies evaluating the ideal sites of graft harvest to treat zonal glenoid bone wear and/or loss.