The Effect of Concavity Restoration on Glenohumeral Stability in a Glenoid Bone Loss Model: Comparing the Distal Tibial Allograft Reconstruction and the Latarjet Procedure

Abstract

Objectives: Glenoid bone loss occurs in more than 80% of patients with recurrent glenohumeral instability. The Latarjet procedure has become the gold standard for restoration of bone loss despite a high (15-30%) complication rate.1–3 Distal tibial allograft (DTA) reconstruction has recently gained interest due to its ability to restore width and concavity to the glenoid while providing a cartilage surface.4 The purpose of this study is to evaluate the restoration of glenohumeral anterior stability and glenoid concavity after DTA reconstruction when compared to the Latarjet procedure in a glenoid bone loss model. Methods: Five human cadaveric specimens (mean age: 62.2, range 57-69; 80% male) underwent preoperative computed tomography (CT) scans to assess native glenoid concavity as determined by the glenoid depth and bony shoulder stability ratio (BSSR). Stability testing was performed using a cadaveric shoulder simulator that allows 6 DoF at the glenohumeral joint. The specimens were placed with the scapula at 30° upward rotation and humerus at 60° glenohumeral abduction with a constant compressive force created by loading the supraspinatus, infraspinatus, teres minor, and subscapularis muscles (2lbs, 3lbs, 1lb and 4lbs respectively). A Kuka robot applied a 40N anterior force through the pectoralis tendon with the humerus in neutral as well as 60 degrees of external rotation. A motion capture system recorded humeral head translations for each condition. To create the Latarjet and DTA conditions, the coracoid was first harvested and the thickness was measured. A distal tibial allograft was then contoured to an identical size. A glenoid defect was created to match the thickness of the graft since both Latarjet and DTA aimed for a 100% glenoid restoration.. The following conditions were tested: 1. intact, 2. Bankart lesion, 3. bone loss model with DTA reconstruction, 4. Latarjet procedure without the conjoint tendon loaded, and 5. Latarjet with conjoint tendon loading (‘sling effect’). All specimens underwent post-testing CT scan to measure the BSSR of the DTA and Latarjet reconstructions. A repeated measures ANOVA was performed to determine if there was a significant difference in maximum anterior translation or BSSR between the distal tibial allograft reconstruction and Latarjet procedure (with or without the sling effect). Results: The mean preoperative glenoid depth measured 2.61±1.03mm with a BSSR of 0.40±0.16. However, postoperative measurements showed that BSSR for the DTA was greater than the Latarjet (0.46±0.11 vs 0.35±0.5). The maximum anterior translation was significantly lower after the DTA reconstruction than the Latarjet procedure without the sling effect (5.5mm vs 9.6mm, p = 0.044). However, there was no difference in anterior translation between the DTA reconstruction and Latarjet procedure with the sling effect applied (5.5mm vs 4.7mm, p = 0.36). The DTA reconstructed the glenoid with a significantly greater concavity than the Latarjet procedure (BSSR: 0.46 vs 0.35, p = 0.036). Conclusions: When addressing bone loss in glenohumeral instability, additional factors besides the restoration of glenoid width contribute to stability. The concave reconstruction produced by the distal tibial allograft decreases anterior translation compared to the flat reconstruction produced by the Latarjet, but there is no difference in translation between the DTA and Latarjet procedure when the sling effect is applied. The DTA reconstruction provides an alternative to the Latarjet procedure with equivalent biomechanical properties and less morbidity or change to the native shoulder structure.