Validation of Laboratory Test for Predicting Bone Tissue Regeneration

Pseudarthrosis (or 'nonunions') is defined as a bone movement which occurs after about 6 months from the traumatic event as consequence of the inadequate healing of a fracture. The use of regenerative medicine for treating recalcitrant pseudarthrosis is considered a promising strategy to promote bone consolidation. Among the various approaches used, the local cell therapy based on autologous mesenchymal stromal cells (MSC), combined with or without growth factors, has been extensively used. MSC reside within the stromal compartment of bone marrow which may be obtained from the iliac crest. Growth factors may be discharged from platelet gel (PG) which is obtained after activation of autologous platelet concentrates. Nevertheless, the results of recent clinical studies show that the above mentioned regenerative approach shows a failure rate of approximately 30% (Calori et al, 2008). The availability of a laboratory test which may predict the regenerative capacity of the PG may help the orthopaedic surgeon in addressing the decisions regarding the regenerative approach, e.g. to use or non use autologous platelet concentrates or to enhance the use of autologous derivatives with recombinant factors.The rationale for the use of platelet concentrates in pseudarthrosis is the significant reduction of osteoinductive growth factors observed at the lesion site (Gandhi et al., 2005). Platelet gel mimics what happens physiologically after any bone injury, when platelets are entrapped in a clot within a fibrin matrix. Platelet activation determines the release of various growth factors promoting bone healing. The optimal level and ratio of growth factors and their synergistic effects should be more efficient than single recombinant molecules, even though no data are available on the most relevant molecules and on their optimal amount. In this context, the in vitro mineralization assay could be a valid tool to assess the pro-osteogenic activity of platelet gel, thus obviating the measurement of the myriad of platelet-derived substances.

The aim of the study is to determine whether the evaluation of pro-osteogenic activity of autologous serum may predict the effectiveness of PG in the regeneration of bone tissue in patients with nonunions of long bones. The rationale is based on the following issues:

• in 30% of long bone nonunions treated with PG, bone consolidation is not obtained (Calori et al, 2008);
• the proportion of growth factors in serum is comparable to that observed in platelet gel after activation, even if the concentration is lower;
• the autologous serum is able to support the 'in vitro' osteogenic differentiation of MSCs and the formation of mineral nodules (mineralization assay) (Granchi et al, 2010);
• the correlation between 'in vitro' mineralization and regenerative capacity has been demonstrated in various experimental models (De Bari et al, 2008);
• preliminary data obtained in our lab showed that in patients affected by congenital pseudarthrosis of the tibia the presence of osteoinductive growth factors in serum is an essential requirement to warrant the effectiveness of the local cell therapy with MSC and PG (submitted paper).

In order to evaluate the ability of the autologous serum in inducing the mineralization in vitro the investigators will use a bioactivity test (mineralization assay). For this purpose serum samples of patients candidates to the treatment with MSC and PG will be collected the day before the surgery and used for cultivating normal MSC, whose ability to mineralize in vitro will be previously verified in standard culture conditions.

Further analysis will be conducted in order to determine whether the pro-osteogenic properties are maintained over time, and serum samples will be collected the 1 month before the surgery.

In order to determine whether the pro-osteogenic activity of the serum is able to predict and discriminate between individuals who achieve or not achieve bone consolidation, the laboratory results will be correlated with clinical and radiographic results at 12 months, when patients will be considered as healed or not healed.