Despite a variety of bone graft substitute options, an ideal solution eludes surgeons

Understanding available bone graft alternatives and properly selecting them yields optimal results.

When the acetabulum is at risk for instability or compromised bone growth related to revision arthroplasty, using a bone graft substitute may make good clinical sense, according to a surgeon at the Hospital for Special Surgery.

Using these alternatives may also reduce infection risk during these procedures, said Mathias P.G. Bostrom, MD. “Look at patient safety, biology of the host tissue, as well as the cost.”

Surgeons can choose from materials made of calcium sulfate, calcium phosphate and synthetic substances, as well as a few bone morphogenetic proteins (BMP) and cell-based options, all of which are being used increasingly in hip arthroplasty revision surgery.

However, they vary greatly in terms of their osteoinductivity and osteoconductivity, Bostrom said.

Ultimate substitute

During a presentation at the Current Concepts in Joint Replacement Spring Meeting, Bostrom discussed bone grafting substitute options.

“If we look at our experience at Hospital for Special Surgery over a 4-year period, about 10% of our cases are revisions and about 50% of those cases required some use of bone graft or bone graft alternative. The problem is we have way too many choices,” Bostrom said. “Unfortunately, we don’t have the ultimate bone graft substitute.”

Bostrom reviewed how matrices, cells and growth factors figure into the efficacy of bone graft substitutes and how they perform, saying, “You start with a lattice of normal bone and then you use some sort of construct that has a similar porous material,” to permit ingrowth of blood vessels and new bone.

Calcium-based graft substitutes are one option for porous materials, with hydroxyapatite and tricalcium phosphate in forms like pellets, granules and block, among calcium phosphate-based products. These are resorbed over time and new bone forms on top of them.

Plaster of Paris-like calcium sulfate products involve a different biologic process and get dissolved through a chemical process. “They have been used for a number of bone defects and can be used around the acetabulum, as well,” Bostrom noted.

He said two popular calcium sulfate materials available from Wright Medical Technology are Minimally-invasive Injectable Graft 115 (MIIG) and Osteoset. Surgeons have also reported success using bone-bank supplied demineralized bone matrix (DBM) in the acetabulum comparable to that of autograft.

Factoring in bone growth

Osteoinductive bone graft substitutes include recombinant human BMP-2 on a resorbable collagen sponge (Infuse, Medtronic Sofamor Danek) and BMP- 7 (Osteogenic Protein-1, Stryker Biotech). “These osteoinductive agents basically ask undifferentiated mesenchymal cells to form osteoprogenitor cells and eventually form new bone,” Bostrom said.

Though mainly indicated for spine and long bone fracture applications, using them in the acetabulum is usually limited to pelvic discontinuities, he said.

Platelet concentration systems that enhance tissue repair factors like fibroblast growth factor and platelet-derived growth fact by four or five times are also available.

“If you have small contained defects, calcium sulfates are fine,” however using calcium phosphate substitutes or DBM depends on the size of the defect and how accessible it is, Bostrom noted. He recommended injectable materials for hard-to-reach areas.

“I still use allograft bone in a non-structural manner, however some of the newer calcium phosphate materials perform as well mechanically and biologically without the risk of infection,” Bostrom said.

For more information:

• Mathias P.G. Bostrom, MD, can be reached at the Hospital for Special Surgery, 535 East 70th St., New York, NY 10021; 212-606-1000; e-mail: Bostromm@hss.edu. He has no direct financial interest in any product or company mentioned in the article.

Reference:

• Bostrom MPG. Allograft alternatives: Bone substitutes & beyond. #100. Presented at the 9th Annual Current Concepts in Joint Replacement Spring 2008 Meeting. May 18-21, 2008. Las Vegas.