After 20 years, researchers are still trying to find surgical cement that can be easily injected into the spine to fuse it. The cement must be able to fuse the bones together, keep the spine aligned properly, and hold up against twisting and shearing forces.
Currently, spine fusion is done with pieces of bone or bone dust called a bone graft. There are many problems with bone grafts, especially when the bone is grafted from the patient’s own body (an autograft). Scientists are looking for cement that will substitute for bone to avoid these problems.
In Germany, an injectable calcium phosphate cement (CPC) was used in sheep models. The size and shape of sheep and human spines are similar, making comparisons possible. The fusion was done using a method called transpedicular lumbar interbody fusion (TLIF).
TLIF requires making a hole through the pedicle bone. The pedicle is part of the bony ring that circles the spinal cord. The disc is removed from between the vertebral bones. Then, the cement is injected into the disc (interbody) space through the hole in the pedicle. The cement sets up between the two vertebral bones, allowing them to grow, or fuse, together.
Two groups of sheep were studied. One group received a bone graft or bone chips to fuse the spine. CPC was used with the second group. In almost all cases, the cement cracked and broke into pieces. The cement and nearby bone was absorbed, and inflammation occurred in that area. The spine was unable to withstand the force of movements such as twisting or bending.
No problems occurred in the bone graft group and fusion took place. The authors of this study conclude that no cement exists yet that will fuse the spine using the TLIF method and hold up against shear forces. Fusion with bone graft is still the preferred method. More research is needed in animal models before clinical trials for humans can be done.