Consider the architectural need in seeking bone graft substitutes for the distal radius

Surgeon cautions that the industry is market-driven and there are few comparative studies on products.

At a recent meeting, Amy L. Ladd, MD, chief of the Robert A. Chase Hand and Upper Limb Center at Stanford University Medical School, discussed her 19-year experience using bone graft substitutes to treat distal radius fractures. The discussion focused on her experience with synthetic, calcium phosphate-based mineral substitutes, which are osteoconductive in nature.

“You want to match the substitute with the architectural need,” she said during her presentation at the American Academy of Orthopaedic Surgeons annual meeting. “The porous substitutes are typically those for defects with intact cortices or have been reconstituted with hardware and can be either used for metaphyseal or diaphyseal defects because the structure is shared with the cortical reconstitution. [They are] a useful tool for enchondromas. Cement, however, is for metaphyseal defects only. Cortical reconstitution need be addressed with something else.”

Cement can be useful for cases of extra-articular and intra-articular fractures, and can be used in more simple procedures, such as those requiring pinning, to more involved osteotomy cases.

Porous substitutes, Cement

Ladd, who is a member of the Orthopedics Today Editorial Board, uses autograft, such as iliac crest bone, olecranon, or vascularized radius to treat scaphoid fractures.

“For defects such as enchondroma, whether it is in the radius or more commonly in the hand, I will tend to use ß-tricalcium phosphate now with venous blood more so than bone marrow aspirate, as it was originally thought to be indicated,” she said. “I have not used autograft in about 8 years.”

“The caveat – if you wish to do it with pins, make sure that you can either fill it ahead of time or that your pins are sufficiently stable.” — Amy L. Ladd, MD

There are special considerations when using calcium phosphate cement. Unlike polymethylmethacrylate (PMMA), calcium phosphate cement is not an epoxy.

“This is a cement that is excellent for load bearing and compression, but resists shear and torsion poorly,” Ladd said. “That is why you need to reconstitute cortices as well if you are using it in large metaphyseal defects.”

Since Ladd often uses the cement for larger defects, she tends to use the putty-type formulations more than the injectable varieties.

“Mixing is a critical step because there is a liquid and a solid phase that you bring together and you need a uniform mix,” she said. Therefore, the mixing is typically done by the surgeon or an experienced staff member.

Hardware

Cement can be used for simple intra-articular fractures or more comminuted cases in conjunction with pins.

“The caveat — if you wish to do it with pins, make sure that you can either fill it ahead of time or that your pins are sufficiently stable,” she said.

Most of her cement usage currently involves opening wedge osteotomy cases with hardware.

“You can use cement in children, although osteotomies are uncommon in this age group” Ladd told Orthopedics Today. “Obviously, you have got to avoid the growth plate.”

The future

When dealing with bone graft substitutes, surgeons should be aware that resorption can mean different things. For example, Ladd noted that calcium sulfate resorbs by dissolution.

“In the future, there will be many promising substitutes out there,” Ladd said. “[Some] of these mineral substitutes will likely be carriers for organic compounds and cell markers, as well as antibiotics and other pharmaceuticals. Eventually we may get a true composite of osteoconductive, osteoinductive and, the ultimate, osteogenic material.”

She added: “Remember this is a market-driven industry. There are minimal studies comparing apples to apples.”

For more information:

• Amy L. Ladd, MD, can be reached at Robert A. Chase Hand & Upper Limb Center, 900 Welch Road, Suite 15, Palo Alto, CA 94304; 650-723-6796; e-mail: alad@stanford.edu. She is a consultant for AcuMed and a shareholder of Biomineral Holdings LLC.

Reference:

• Ladd AL. Bone graft substitutes. Symposium L: Distal radius fractures: New concepts in treatment. Presented at the American Academy of Orthopaedic Surgeons 76th Annual Meeting. Feb. 25-28, 2009. Las Vegas.