Platelet-rich plasma (PRP) (also known as blood injection therapy) is a medical treatment being used for a wide range of musculoskeletal problems. Platelet-rich plasma refers to a sample of serum (blood) plasma that has as much as four times more than the normal amount of platelets and growth factors. This treatment enhances the body’s natural ability to heal itself and is used to improve healing and shorten recovery time from acute and chronic soft tissue injuries.
The use of PRP to aid spinal fusion is still under investigation using animal models. In this study, researchers from Italy report on the use of PRP in experimental spinal fusion. They used rabbits and performed the fusion using a posterolateral approach (injecting the PRP from the back and side of the spine).
The rabbits were divided into three groups. One group received just the PRP (on the right side of the vertebrae) while the second group were injected with PRP combined with uncultured bone marrow (on the left side). Group three (control group) had a sham operation on both sides to simulate the other two groups but without actually injecting anything into the area.
The goal was to create a bony bridge between the transverse processes of the vertebrae. Each vertebra also has two bony knobs that point out to the side, one on the left and one on the right. These bony projections are called transverse processes.
A facet joint is made of small, bony knobs that line up along the back of the spine. Where these knobs meet, they form a joint that connects the two vertebrae. The alignment of the facet joints of the lumbar spine allows freedom of movement as you bend forward and back.
Each step of the experiment is described in the article (e.g., materials and methods used, statistical analysis) as well as the platelet concentrations used, surgical procedure, X-ray analysis of the fusion site. The results were measured based on how much bone growth and blood supply were stimulated.
Although they did find some new bone growth, none of the rabbits had formed a complete bridge of bone across the transverse processes. Signs of inflammation and some blood vessel formation were observed but no significant changes were seen in either of the PRP groups. The control group had significantly fewer changes seen in terms of bone growth or new blood supply.
Previous studies have used stem cells, bone morphogenetic protein (BMP), and bone graft in rabbit models to stimulate bone bridging and fusion. This is one of the first attempts to use platelet activation and release of growth factors (via platelet-rich plasma injection) in the bone healing process. But none of the studies so far have shown complete bony bridging needed for spinal fusion (including this study).
The authors made some suggestions that might explain why PRP did not work in promoting bone growth or blood supply in their rabbits. For example, no one really knows the ideal amount of platelets (and therefore growth factors) to use.
Growth factors don’t last long before they become inactive. Injecting them into the area is one challenge but they must also be released and activated. It is still unknown just what is the best way to deliver and activate them. Should they be “preactivated” or will they start up on their own once they reach the intended destination? Is there a way to create a “time-release” effect? These are just some of the questions that remain to be answered before platelet-rich plasma can be used routinely to enhance spinal fusion.