I'm Evan O'Donnell, one of the sports medicine and shoulder guys at MGH. Special thanks to Matt Fiore, who put together the slide deck and this talk. So our paper was, How Does Anchor Position Affect Isometry of the Internal Brace Construct in UCL Repair? A 3D Computer Modeling Study. I have no relevant financial disclosures. So as many of you heard in our recent talks, UCL Repair is gaining in popularity. There's been excellent clinical outcomes and a shortened rehabilitation time when utilized for the correct athlete. This is in contrast to, you know, the gold standard UCL reconstruction. And there have been numerous studies identifying the optimal placement of your tunnel as well as the orientation to optimize ligament isometry in that surgery. However, to date there's been no studies looking at where to place our suture anchors for UCL Repair to optimize isometry. So the purpose of this study was twofold. We wanted to develop a patient-specific 3D elbow model to simulate normal motion. And the second part was to determine the effect of small changes in suture anchor position on the isometry of the UCL Repair. So what we did is we went to our clinical database. We looked for patients who were older than 18, had concurrent CTs and MRIs with no history of a UCL injury, elbow fracture, elbow surgery or arthritis. And then looked at these patients. They also had to have sufficient quality of the MRI such that we could see the footprint of the UCL and the UCL ligament itself. We then took the CT and mapped the MRI on top of it using a volumetric analytical tool. And what this developed was a static model where we could measure three-dimensional distances looking at the plane of the bone. We then applied this to three different models. The first was we made a geometric cloud map from the PD MRI. So we mapped what the UCL looked like on the MRI and then back mapped it onto the CT. We then went to our literature and in two anatomic studies, one by Camp et al and one by Frangimore et al, and used their quantitative anatomical mapping to define the centroid of the UCL attachment on the humerus and the ulna. These are these two studies. That was a static model and we dynamized it by the use of a gaming engine. So this is the Unreal Engine and we are able to range the shoulder, or sorry, range the elbow from 0 to 120 degrees at 10 degree increments. We then measured the distance between the humeral attachment and the ulnar attachment throughout this arc of motion. We measured two main things, the maximum excursion, which is max distance minus the minimum distance, and also the percent change of the length of the tendon, or the ligament rather. This is functionally what it looked like when we mapped the CT and the MRI and the centroids. So what you can see here is the red sphere is the actual centroid of the humeral attachment and the ulnar attachment, and then we put in a clock face to represent subtle deviations from this centroid, and the radius there is 1.75 millimeters, or about half of a typical anchor that you'd use to repair the UCL. The data that it spit out was essentially the distances from either the centroid to centroid or each point on the clock face to the centroid, and what we found was that our first model, the geometric cloud, so mapping the MRI to the CT, was actually quite poor. There was a large amount of excursion of the UCL throughout the arc of motion, which correlated about a 46% change. Interestingly, when we used or referenced the Camp et al. paper and Frangimore et al. paper, they had excellent ligament isometry, or much improved at 3.9% and 9.4%. We then looked at that clock face and looked at how changing the anchor position on the ulna affected the ligament length, and as you can see here, as you went around this clock face, the lengthening or shortening of the ligament was actually quite minimal. This is in stark contrast to the humerus, where as we went around that clock face, the UCL length was quite variable with increasing elbow flexion. So this was statistically significant. To kind of boil that down, because it's hard to interpret those two slides, we made a heat map where we mapped the UCL variance in length, and what you can see here on the ulna, these are all green dots. So as you move around the ulnar footprint, it really doesn't have a significant effect on the ligament isometry, and you contrast that to the humeral side, you can very easily have 10 to 20% or over 20% of excursion difference if you kind of vary from that centroid point. So in sum, in UCL repair, small deviations on the humeral anchor position may significantly influence ligament repair isometry. Using quantitative measurements by Camp et al. and Frangimore et al. that use anatomic landmarks can improve repair isometry, and when addressing injuries at the proximal footprint, be critical of the humeral anchor position to restore native anatomy and the optimal biomechanics. Thanks so much.

Evan O'Donnell

anchor position

Internal Brace Construct

UCL Repair

isometry