All right, so as a background, the incidence of long head of the biceps tendon procedures has been increasing, however there really is a lack of long-term outcome studies looking at how these procedures do, particularly greater than five years and specifically with radiographic outcomes. Now the role of the biceps tendon in glenohumeral kinematics is not fully understood and there have been prior biomechanical studies looking at its effect on humeral head translation, however these were all performed in the scapular plane and activities in daily living frequently occur in forward flexion which can stress the posterior aspect of the unconstrained glenohumeral joint due to the posterior line of pull of the deltoid. And so determining the mechanisms of the shoulder-maintained stability through functional ranges of motion may help us understand the potential consequences of sacrificing the long head of the biceps tendon, such as whether this predisposes to further posterior labral injuries or could eventually lead to the posterior glenoid wear we see in patients with glenohumeral osteoarthritis. So the purpose of our study was to assess the role of the biceps tendon on translation of the humeral head during forward flexion and our hypothesis was that loading the long head of the biceps tendon would resist posterior translation of the humeral head by tensioning the posterior capsule ligamentus complex. This is a cadaveric study, we used 10 fresh frozen specimens, dissected them free of soft tissue preserving the deltoid, rotator cuff, capsule and biceps tendon. We then placed motion markers on the humerus and the scapula, obtained a CT to register the motion markers and ensure that there was no underlying glenoid dysmorphism or osteoarthritis and the specimen was then secured to a shoulder stimulator that the humerus allowed to move through varying degrees of forward flexion and rotation. So this is what our shoulder stimulator looks like and here is what our specimen looked like when it was loaded onto the shoulder stimulator, so you can see that as we increase the forward flexion we see a more posterior line of pull from the deltoid. So the loads that we applied to the muscle tendon system was derived from a previously published three-dimensional shoulder model, so we used 100 newtons across the deltoid and 22 newtons each in the infraspinatus and the subscapularis and then our testing state was comparing the humeral head position with the long head of the biceps tendon loaded with 45 newtons or unloaded, so no tension at all. We tested at 30 and 60 degrees of glenohumeral forward elevation and at each of those positions we did maximum internal rotation, neutral rotation and external rotation. Each trial was repeated three times and the accuracy of our motion markers was 0.2 millimeters. So this is a demonstration of our overall results, so the light blue represents the position of the humeral head in the loaded state of the biceps tendon and the royal blue or sorry the navy blue represents the unloaded state, so you can see when the biceps tendon is unloaded the humeral head shifts posteriorly as well as slightly superiorly. And then looking at our specific position, so at 30 degrees of forward flexion the y-axis on the right here demonstrates the three positions we tested, again with the light blue representing the loaded state and the navy blue representing the unloaded state and you can see that the as the biceps tendon is unloaded you see posterior translation of the humeral head at external where it was most prevalent and then neutral and internal and all of these were statistically significant. Then looking at 60 degrees we see that the change in posterior translation was greater at all positions here and again all were statistically significant, so the biceps tendon played more of a role in posterior translation as we get to higher degrees of forward flexion. We also examined the role of the biceps loading on superior translation and we can see on the graphs here that it also resisted superior translation of the humeral head although the change the millimeter difference was less in the superior direction than in the posterior direction and this was at 30 as well as 60 degrees of forward flexion. So the limitations of this study is that while the loads applied across the deltoid and rotator cuff were determined from this previously established model, the 45 newton load to the biceps tendon may not be physiological during forward flexion. Also this is a cadaveric study that focused on the mechanics of the capsule but doesn't simulate how soft tissues may adapt over time whereas stiffer shoulders may be less dependent on the biceps where in the more ligamentously lax patients they may be more dependent on the biceps tendon resisting this posterior translation and we also did not report on changes in contact pressure rather just humeral head translation. So to conclude, long head of the biceps tendon loading resists posterior translation of the humeral head during forward flexion. This data supports the role of the biceps tendon as a posterior stabilizer in the shoulder particularly when people are carrying objects in front of them in that forward flexion state and unloading the biceps tendon as is done with a tenonomy or tenodesis where you're removing it from any impact it could potentially have on the glenoid may contribute to micro instability of the glenohumeral joint and shift the contact point posteriorly and further work is needed to determine the clinical relevance of this and whether the biceps tenonomy or tenodesis may eventually contribute to posterior glenoid wear or posterior labral pathology down the road. I want to thank the RAF for funding this project. Thank you.

cadaveric study

long head of the biceps tendon

shoulder joint stability

forward flexion

posterior glenoid wear