Does Coronoid Process Replacement With Individually Designed 3D Printed Prosthesis Provide Superior Stability Over Grafted Reconstruction And Screw Fixation? A Biomechanical Study

Objectives Coronoid fractures account for 2 to 15% of the cases with elbow dislocations and usually occur as part of complex injuries. Comminuted fractures and non-unions necessitate coronoid fixation, reconstruction or replacement. The aim of this biomechanical study was to compare the stability of coronoid replacement using an individualized 3D printed prosthesis with a curved cemented intramedullary stem to both radial head grafted reconstruction and coronoid fixation with 2 screws. It was hypothesized that the prosthetic replacement will provide superior stability over the grafted reconstruction and screw fixation.

Methods Following CT scanning, 18 human cadaveric proximal ulnas were osteotomized at 40% of the coronoid height and randomized to 3 groups (n = 6). The specimens in Group 1 were treated with a 3D printed stainless steel coronoid prosthesis with curved cemented intramedullary stem, individually designed based on the contralateral coronoid scan. The ulnas in Group 2 were reconstructed with an ipsilateral radial head autograft fixed with two anteroposterior screws, whereas the osteotomized coronoids in Group 3 were fixed in situ with two anteroposterior screws [Fig. 1].

Fig. 1. Specimens in the 3 study groups prepared for biomechanical testing by means of prosthetic treatment (Group 1, left), radial head autograft reconstruction (Group 2, middle), and coronoid screw fixation (Group 3, right).

All specimens were biomechanically tested under ramped quasi-static axial loading to failure at a rate of 10 mm/min. Construct stiffness and failure load were calculated. Statistical analysis was performed using One-Way ANOVA with Bonferroni Post Hoc tests at a level of significance 0.05.

Results and Conclusion Prosthetic treatment (Group 1) resulted in significantly higher stiffness (1166.8 ± 316.6 N/mm) and failure load (1044.2 ± 301.9 N) compared to radial head autograft reconstruction (Group 2: 440.8 ± 99.1 N/mm; 441.5 ± 125.6 N; p ≤ 0.002) and coronoid screw fixation (Group 3: 267.9 ± 147.9 N/mm; 304.4 ± 171.1 N; p <  0.001), respectively. Stiffness and failure load did not reveal any significant differences between Group 2 and Group 3 (p ≥ 0.846). In cases of coronoid deficiency, replacement of the coronoid process using a patient specific 3D printed prosthesis with a curved cemented intramedullary stem seems to be an effective method to restore the buttress function of the coronoid under axial loading, providing superior stability over both radial head graft reconstruction and coronoid screw fixation, while achieving anatomical articular congruity. The stability provided by this prosthesis type with curved cemented intramedullary stem could allow for early patient mobilization. The implant may prove to be beneficial for patients with irreparable comminuted coronoid fractures, radial angulation or non-unions.

Stichwörter Elbow, Coronoid Process, 3D Printed Individualized Prosthesis, Intramedullary Stem, Biomechanical Testing

Publication History

Article published online:
15 October 2020