CT-Based 3D Printing of the Glenoid Prior to Shoulder Arthroplasty: Bony Morphology and Model Evaluation

Abstract

To demonstrate the 3D printed appearance of glenoid morphologies relevant to shoulder replacement surgery and to evaluate the benefits of printed models of the glenoid with regard to surgical planning. A retrospective review of patients referred for shoulder CT was performed, leading to a cohort of nine patients without arthroplasty hardware and exhibiting glenoid changes relevant to shoulder arthroplasty planning. Thin slice CT images were used to create both humerus-subtracted volume renderings of the glenoid, as well as 3D surface models of the glenoid, and 11 printed models were created. Volume renderings, surface models, and printed models were reviewed by a musculoskeletal radiologist for accuracy. Four fellowship-trained orthopaedic surgeons specializing in shoulder surgery reviewed each case individually as follows: First, the source CT images were reviewed, and a score for the clarity of the bony morphologies relevant to shoulder arthroplasty surgery was given. The volume rendering was reviewed, and the clarity was again scored. Finally, the printed model was reviewed, and the clarity again scored. Each printed model was also scored for morphologic complexity, expected usefulness of the printed model, and physical properties of the model. Mann-Whitney-Wilcoxon signed rank tests of the clarity scores were calculated, and the Spearman's ρ correlation coefficient between complexity and usefulness scores was computed. Printed models demonstrated a range of glenoid bony changes including osteophytes, glenoid bone loss, retroversion, and biconcavity. Surgeons rated the glenoid morphology as more clear after review of humerus-subtracted volume rendering, compared with review of the source CT images (p = 0.00903). Clarity was also better with 3D printed models compared to CT (p = 0.00903) and better with 3D printed models compared to humerus-subtracted volume rendering (p = 0. 00879). The expected usefulness of printed models demonstrated a positive correlation with morphologic complexity, with Spearman's ρ 0.73 (p = 0.0108). 3D printing of the glenoid based on pre-operative CT provides a physical representation of patient anatomy. Printed models enabled shoulder surgeons to appreciate glenoid bony morphology more clearly compared to review of CT images or humerus-subtracted volume renderings. These models were more useful as glenoid complexity increased.

Keywords: 3D printing; Computed tomography; Glenoid morphology; Shoulder arthroplasty; Surgical planning.

Fig. 1

Anteroposterior radiograph demonstrating the normal post-operative appearance of total shoulder arthroplasty. This device uses an all-polyethylene glenoid component, except for a small metallic marker in the central peg (arrow)

Fig. 2

Axial CT after shoulder hemiarthroplasty (SHA). In SHA, the humeral head is replaced without a glenoid component. While this avoids the problems of early glenoid component failure, humeral head replacement by itself does not address the morphologic derangements of the glenoid which often accompany the need for joint replacement. Here, the native glenoid continues to exhibit biconcavity (dotted line; see text and also Fig. 6) after SHA, interfering with the restoration of normal biomechanics

Fig. 3

Anteroposterior radiograph showing reverse shoulder arthroplasty. In this case, the presence of scapular notching (arrow) indicates impingement of the humeral component on the scapula

Fig. 4

Anteroposterior radiograph demonstrating reverse shoulder arthroplasty with glenoid component failure and inferior displacement

Fig. 5

Axial CT images in two different patients illustrating glenohumeral osteoarthritis with posterior bony thinning of the glenoid and concomitant glenoid retroversion. a Due to disproportionate load-bearing at the posterior aspect of the glenoid, the bone in this area may become markedly thinned (arrows). b Glenoid version is measured with respect to the axis of the scapular body (double line). The normal articular surface is approximately perpendicular to this axis (solid single line). With posterior bony thinning, the articular surface (dotted line) may become markedly retroverted (angle indicated by asterisk). At arthroplasty surgery, bony thinning and retroversion may require adjunctive surgical techniques such as bone grafting and glenoid reaming

Fig. 6

Axial CT image in a patient with glenoid biconcavity. In addition to bony thinning and retroversion (see Fig. 5), disproportionate load-bearing at the posterior glenoid also leads to biconcavity of the glenoid articular surface. Whereas the normal glenoid consists of a single shallow concavity, the biconcave glenoid exhibits two depressions (solid line and dotted line, respectively). This interferes with normal biomechanics and may require surgical correction

Fig. 7

Volume rendering of humerus-subtracted CT. By removing the humerus with image masking tools, the articular surface of the glenoid may be demonstrated with volume rendering techniques. This approach allows three-dimensional visualization of glenoid morphology

Fig. 8

Image-based surface modeling and model verification. Surface models of the glenoid were reconstructed from CT images using commercial image segmentation tools (a). The accuracy of final surface models was then verified by a musculoskeletal radiologist by review of model contours (yellow) superimposed on the source CT images (b)

Fig. 9

The model of one patient (patient 1, model A in Table 1), printed using selective laser sintering technology. a View from lateral demonstrates a large anteroinferior glenoid osteophyte (arrow). b View from inferior shows glenoid retroversion and posterior bony thinning (arrows)

Fig. 10

The model of another patient (patient 3, model D in Table 1), printed using a stereolithography printer. View from inferolateral demonstrates glenoid biconcavity with a ridge between the two depressions in the glenoid surface (dotted line)

Fig. 11

The model of a third patient (patient 8, model J in Table 1) printed in a translucent material using a stereolithography printer. View from lateral permits the observer to see through the model to the deep cortical surface and the margins of the glenoid neck (dotted lines), from the operative perspective

Fig. 12

The model of another patient (patient 9, model K in Table 1) printed using a binder jetting printer. a View from lateral demonstrates post-surgical changes of Bristow procedure (a variant of the more common Latarjet procedure), as demonstrated by the truncated coracoid (C) and the bony augmentation at the anteroinferior glenoid (arrow). b View from inferior demonstrates glenoid retroversion