Pre-Operative Bone Marrow-Derived Cell Mobilization by G-CSF Enhances Osseointegration of Bone Substitute In Patients Undergoing Surgery with High Tibial Valgus Osteotomy
Authors: Marmotti Antongiulio , Filippo Castoldi , Roberto Rossi , Tron Alessia , Giacalone Francesco , Marenco Stefano , Realmuto Cristina , Risso Alessandra , Ruella Marco , Borrè Alda , Rossi Paolo , Tarella Corrado 
Published: October 2019

Abstract
Abstract 4773

Introduction.
Bone substitutes are widely used to improve bone repair in orthopaedic surgical procedures. Osseointegration is a slow process that takes place both at bone-implant interface and inside the tridimensional structure. The process might benefit from the addition of bone marrow-derived cells (BMC). In order to exploit this possible effects, a study protocol has been designed including preoperative BMC mobilization induced by granulocyte-colony stimulating factor (G-CSF). Aim of the study was to verify feasibility, safety and efficacy of BMC-mobilization in patients undergoing high tibial valgus osteotomy (HTVO).

Patients and Methods.
Overall, 24 patients undergoing medial open wedge HTVO to treat genu varum were enrolled in a prospective phase II trial. The osteotomy gap was filled by hydroxyapatite and tricalciumphosphate bone graft substitute. Two consecutive cohorts of 12 patients were assigned to receive (GROUP A) or not receive (GROUP B) a daily dose of 10 μ g/kg of G-CSF for 3 consecutive days, with an additional dose 4 hours before surgery. BMC mobilization was monitored by White Blood Cell (WBC) count and flow cytometry analysis of circulating CD34+ cells. All patients underwent a clinical (Lysholm Score and SF-36) and X-ray evaluation preoperatively, and at 1, 3 and 6 months after surgery. Anteroposterior standard radiographs were analysed to compare bone structure of the osteotomy areas. The percentage of integration at the interface between host bone and bone substitute (“host bone-substitute interface”) was estimated by 2 blinded observers. A computed tomography (CT) evaluation of the host bone-substitute interface was performed at 2 months. The osseointegration at the host bone-substitute interface was estimated through a semiquantitative score by 2 blinded observers and through a measure of bone density.

Results.
Patients of Groups A and B were well balanced in terms of age and clinical presentation. All patients of both groups completed the study. The most common adverse events among patients assigned to G-CSF were mild to moderate bone pain and muscle discomfort, well controlled by oral analgesics. There were no severe adverse events in both Group A and B, all patients are presently alive and well. Mobilization of CD34+ve cells occurred in all patients receiving G-CSF: mean preoperative WBC and CD34+ values were 39,09 × 103/μ l (21,57-51,11) and 131,58/ƒnμ l (29.1 - 404) in Group A, and 6,77 (2,8-12-06) and 7,67/μ l (5,4-12) in Group B, respectively. At the post-surgery clinical evaluation, patients of Group A experienced pain and a slight impairment in overall performance at 1 month assessment, whereas they displayed a slight increase in overall performance at 3 and 6 months compared to Group B. Semi-quantitative radiographic evaluation revealed a higher rate of bone substitute osseointegration in Group A than in Group B at 1, 3 and 6 months post-surgery. Also semiquantitative CT evaluation at 2 months showed an overall improved osseointegration at the host bone-substitute interface in Group A patients. Bone density was measured at the host bone-substitute interface by the Hounsfield score: Group A patients scored lower values at the upper interface compared to Group B, accordingly with advanced stage bone remodelling. The differences between Group A and B on assessment of host bone-substitute interface reached a statistical significance (p< 0,05). Bone mineral density at the host bone-substitute interface as measured with DEXA (Dual-energy X-ray absorptiometry), was lower, although without statistical significance, in Group A than in Group B, again suggesting a more advanced stage of bone remodelling in the treated group compared to controls.

Conclusions.
G-CSF administration given to induce pre-operative mobilization of bone marrow-derived cells: i. is feasible and safe in patients undergoing orthopaedic surgery; ii. allows the peripheral blood circulation of high numbers of CD34+ve cells; iii. may hasten bone graft substitute integration as suggested by both clinical and radiographical and CT evaluations. The enhanced osseointegration might be the result of a direct activity of G-CSF or of a cellular effect mediated by either hematopoietic or endothelial progenitors mobilized by G-CSF or by the combination of all these factors.

Disclosures:
No relevant conflicts of interest to declare.