Comparison of Glenohumeral Contact Pressures and Contact Areas After Posterior Glenoid Reconstruction With Iliac Crest or Distal Tibia Osteochondral Allograft

OBJECTIVES: Posterior glenoid bone deficiency in the setting of posterior glenohumeral instability is typically addressed with bone block augmentation with iliac crest bone graft (ICBG). While this technique aims at decreasing posterior shoulder instability, the concern for the development of early, symptomatic, glenohumeral arthritis remains. Reconstruction with distal tibia allograft (DTA) is an alternative option, with the theoretical advantages of restoring the glenoid articular surface and improving joint congruity. The purpose of this study was to evaluate glenohumeral contact areas, contact pressures, and peak forces in (1) the intact glenoid and after (2) 20% posterior glenoid surface area defect from 6 o’clock to 10 o’clock (right shoulder), (3) 20% glenoid defect with flush posterior bone block graft with ICBG; and (4) 20% glenoid defect with DTA. The hypothesis was that reconstruction with DTA would more effectively restore normal glenoid contact pressures (CP), contact areas (CA), and peak forces (PF) when compared to the deficient glenoid. METHODS: Eight fresh-frozen human cadaveric shoulders were randomly tested in four conditions as follows: (1) intact glenoid, (2) 20% posterior-inferior glenoid surface area defect, (3) 20% defect reconstructed with flush ICBG; and (4) 20% defect reconstructed with fresh DTA. For each condition, a 0.1mm-thick dynamic pressure-sensitive pad (sensor model 5051, Tekscan, Boston, MA) was pre-calibrated and placed between the humerus and glenoid. Each specimen was mounted onto a MTS testing machine (Insight 5, MTS systems, Eden Prairie, MN), which was used to apply a compressive load of 440-N for each condition in the following clinically relevant arm positions: (1) 30 degrees humeral abduction, (2) 60 degrees humeral abduction, and (3) 30 degrees humeral abduction-90 degrees flexion-45 degrees internal rotation (FIR). Glenohumeral CP (kg/cm2), CA (cm2), and joint PF (N) were recorded (Figure 1). All data was analyzed with a repeated measures one-way analysis of variance (ANOVA) with Tukey’s post- hoc test, when indicated. RESULTS: Glenoid reconstruction with DTA resulted in significantly higher CA compared to the 20% defect model at 60 degrees (P<0.01) and at FIR (P<0.01). The intact state exhibited significantly higher CA than the defect in all positions (P<0.01), and significantly higher CA than ICBG at 60 degrees (P<0.05) and at FIR (P<0.05) (Table 1). Reconstruction with DTA resulted in lower PF and higher CA compared to ICBG in all positions, however these results were not statistically significant (P>0.05). CONCLUSION: Reconstruction of posterior glenoid bone defects with DTA demonstrated at least equivalent biomechanical properties compared to reconstruction with ICBG. Given the concern over the association of the extra-articular, non-anatomic ICBG reconstruction technique with the development of early, symptomatic, glenohumeral arthritis, this study suggests that posterior glenoid reconstruction with DTA is a viable alternative solution, with the potential advantage of improving joint congruity via an anatomic reconstruction resulting in a cartilaginous, congruent articulation with the humeral head. While these mechanical properties may translate into clinical differences, further studies are needed to understand their effects over time.