Marc-Frederic Pastor

Repetitive recombinant human bone morphogenetic protein 2 injections improve the callus microarchitecture and mechanical stiffness in a sheep model of distraction osteogenesis

Evidence suggests that recombinant human bone morphogenetic protein 2 (rhBMP-2) increases the mechanical integrity of callus tissue during bone healing. This effect may be either explained by an increase of callus formation or a modification of the trabecular microarchitecture. Therefore the purpose of the study was to evaluate the potential benefit of rhBMP-2 on the trabecular microarchitecture and on multidirectional callus stiffness. Further we asked, whether microarchitecture changes correlate with optimized callus stiffness. In this study a tibial distraction osteogenesis (DO) model in 12 sheep was used to determine, whether percutaneous injection of rhBMP-2 into the distraction zone influences the microarchitecture of the bone regenerate. After a latency period of 4 days, the tibiae were distracted at a rate of 1.25 mm/day over a period of 20 days, resulting in total lengthening of 25 mm. The operated limbs were randomly assigned to one treatment groups and one control group: (A) triple injection of rhBMP-2 (4 mg rhBMP-2/injection) and (B) no injection. The tibiae were harvested after 74 days and scanned by µCT (90 µm/voxel). In addition, we conducted a multidirectional mechanical testing of the tibiae by using a material testing system to assess the multidirectional strength. The distraction zones were tested for torsional stiffness and bending stiffness antero-posterior (AP) and medio-lateral (ML) direction, compression strength and maximum axial torsion. Statistical analysis was performed using multivariate analysis of variance (ANOVA) followed by students t-test and Regression analysis using power functions with a significance level of P<0.05. Triple injections of rhBMP-2 induced significant changes in the trabecular architecture of the regenerate compared with the control: increased trabecular number (Tb.N.) (treatment group 1.73 mm/1 vs. control group 1.2 mm/1), increased cortical bone volume fraction (BV/TV) (treatment group 0.68 vs. control group 0.47), and decreased trabecular separation (Tb.Sp.) (treatment group 0.18 mm vs. control group 0.43 mm). The analyses of the mechanical strength of regenerated bone showed significant differences between treatment group (A) and the control group (B). The bending stiffness anterior-posterior (treatment group 17.48 Nm vs. control group 8.3 Nm), medial-lateral (treatment group 18,9 Nm vs. control group 7.92 Nm) and the torsional stiffness (treatment group 41.17N/° vs. control group 16.41N/°) are significantly higher in the treatment group than in the control group. The regression analyses revealed significant non-linear relationships between BV/TV, TB.N., Tb.Sp. and all mechanical properties. Maximal correlation coefficients were found for the Tb.Sp. vs. the bending stiffness AP and ML with R2=0.69 and R2=0.70 (P<0.0001). There was no significant relation between Connectivity and the compression strength and the maximum axial torque. This study suggests that rhBMP-2 optimizes the trabecular microarchitecture of the regenerate, which might explain the advanced mechanical integrity of newly formed bone under rhBMP-2 treatment.

Anterior stability of the reverse shoulder arthroplasty depending on implant configuration and rotator cuff condition

IntroductionThe aim of this study was to investigate the stabilizing influence of the rotator cuff as well as the importance of glenosphere and onlay configuration on the anterior stability of the reverse total shoulder replacement (RTSR).Materials and methodsA reverse total shoulder replacement was implanted into eight human cadaveric shoulders, and biomechanical testing was performed under three conditions: after implantation of the RTSR, after additional dissection of the subscapularis tendon, and after additional dissection of the infraspinatus and teres minor tendon. Testing was performed in 30° of abduction and three rotational positions: 30° internal rotation, neutral rotation, and 30° external rotation. Furthermore, the 38-mm and 42-mm glenospheres were tested in combination with a standard and a high-mobility humeral onlay. A gradually increased force was applied to the glenohumeral joint in anterior direction until the RTSR dislocated.ResultsThe 42-mm glenosphere showed superior stability compared with the 38-mm glenosphere. The standard humeral onlay required significantly higher anterior dislocation forces than the more shallow high-mobility onlay. External rotation was the most stable position. Furthermore, isolated detachment of the subscapularis and combined dissection of the infraspinatus, teres minor, and subscapularis tendon increased anterior instability.ConclusionsThis study showed superior stability with the 42-mm glenosphere and the more conforming standard onlay. External rotation was the most stable position. Detachment of the subscapularis as well as dissection of the complete rotator cuff decreased anterior stability.

Total Versus Hemiarthroplasty for Glenohumeral Arthritis According to Preoperative Glenoid Erosion.

Clinical studies on primary osteoarthritis have shown better results of total shoulder arthroplasty (TSA) compared to hemiarthroplasty (HA) regarding the function, revision rate and postoperative pain relief. However, a clear recommendation for implantation of TSA or HA, depending on the glenoid type of erosion, does not exist. The aim of the study was to compare the results of TSA and HA with respect to the preoperative glenoid type. In this study, 41 patients were examined retrospectively; among them, 25 patients were treated with stemmed anatomic TSA and 16 with stemmed anatomic HA. The degree of osteoarthritis was determined according to Samilson and the glenoid erosion was classified according to Walch. The clinical outcome of the patients was determined by using the Constant Score (CS) and the Simple Shoulder Test at final follow-up. Patients after TSA demonstrated a significantly improved internal rotation compared to HA patients. Patients with preoperative B1 glenoid showed better pain relief after TSA compared to HA. For patients with preoperative type A2 glenoid a significantly higher CS was found after TSA compared to HA. We were able to show good short-term results after TSA and HA. Our findings suggest a better internal rotation for TSA compared to HA, superior clinical outcome for patients with preoperative A2 glenoid and lower pain level for patients with a preoperative B1 glenoid. However, these results need to be confirmed by further studies.