Abstract
Purpose
The coronoid and collateral ligaments are key elbow stabilizers. When repair of comminuted coronoid fractures is not possible, prosthetic replacement may restore elbow stability. A coronoid prosthesis has been designed with an extended tip in an effort to augment elbow stability in the setting of residual collateral ligament insufficiency. The purpose of this biomechanical study, therefore, was to compare an anatomic coronoid replacement with an extended tip implant both with and without ligament insufficiency.
Method
Two coronoid prostheses were designed and developed based on CT-derived images adjusted for cartilage thickness: an anatomical implant and an extended-tip implant. Passive elbow extension was performed in 7 cadaveric arms in the varus and valgus positions. Varus-valgus laxity of the ulna relative to the humerus was quantified with a tracking system with an intact coronoid, a 40% coronoid deficiency, an anatomical prosthesis, and an extended prosthesis, with the collateral ligaments sectioned and repaired.
Results
Laxity increased following a 40% coronoid deficiency with both repaired (p<0.01) and sectioned collateral ligaments (p<0.01). With the ligaments repaired, there was no significant difference in laxity between the intact coronoid, the anatomic implant or the extended implant (p=0.88). Ligament sectioning with an intact coronoid produced severe joint instability, resulting in an average laxity (standard error) of 42.94.4 (p<0.01). With ligament sectioning, the anatomic prosthesis produced no change in laxity compared to the intact coronoid (p=0.72), whereas the extended implant reduced laxity by 20.56.3 (p=0.05).
Conclusion
A coronoid prosthesis with an extended coronoid tip improves elbow stability relative to an anatomic prosthesis in the setting of collateral ligament insufficiency. This may prove useful in patients with comminuted coronoid fractures with concomitant ligament injuries, allowing for maintenance of elbow stability during ligament healing or reconstruction. Clinical studies are needed to evaluate the feasibility of these designs and to determine patient outcomes.
