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Spinal fusion (spondylodesis) is an established method for the treatment of diseases of the spine that employs intervertebral implants, including the Harms Cage. The implant is provided with osteoconductive and inductive properties through augmentation with autologous iliac crest spongiosa bone. Yet, studies have shown that such augmentation is not necessary for successful spondylodesis. In today’s spinal surgery, depending on the defect, a metallic implant is used with or without augmentation, primarily with tricalcium phosphate. For bisegmental or polysegmental spondylodesis, a ventral osteosynthesis plate provides additional stability.
In this study, spondylodesis of cervical vertebrae C3/C4 was performed on a sheep model. A comparison was undertaken between spondylodesis using an augmented Harms Cage and spondylodesis using augmented and coated Harms Cages. For this purpose, a discectomy was performed on 32 animals and an augmented Harms Cage (Group I, n = 8) implanted. Coating was achieved using autologous platelet concentrate (Group II, n = 8), rhBMP-2 (Group III, n = 8), and cyclic RGD-peptide (Group IV, n = 7). The animals were euthanized after 12 weeks and vertebral segment C3/C4 was prepared and biomechanically tested. Using the uniaxial materials testing machine (Zwick 1455, Zwick GmbH, Ulm, Germany) the degree of stiffness was tested in flexion, extension, rotation and inclination, and the angular mobility was calculated using specialized software. Statistical analysis was performed using the Mann-Whitney-Wilcoxon U-test.
In our study it was clear that the augmented Harm Cage was suitable for spondylodesis, with or without coating, and during the time period tested in the study, resulted in stabilization of the C3/C4 vertebral segment.
Comparing the treated groups with the controls, there were a number of significant improvements in stiffness noted. Group II (PRP) showed improvement of stiffness in left-sided rotation; Group III (rhBMP-2) in hyperextension, left-sided inclination and in some areas of right-sided inclination and rotation; Group IV (cRGD) in hyperextension and right-sided inclination in the elastic zone.
The group (Group II) with platelet concentrate coating achieved better stiffness values compared to the controls (I) but these differences did not reach significance. There was no significant improvement in the spondylodesis. In the context of this study, one must conclude that PRP had no demonstrable effect on spondylodesis.
The results of the biometric analysis in Group III (rhBMP-2) proved the beneficial effect of rhBMP-2 on increasing stiffness, new bone formation and acceleration of spondylodesis. However, the level of significance was too low and the improvements in stiffness were too inconsistent. Before clinical application, rhBMP-2 needs to be examined in greater detail in further studies.
The group (Group IV) with c-RGD peptide coating showed erratic improvement in stiffness. Based on the data, one needs to be cautious about predicting a positive effect of c-RGD on accelerated spondylodesis.