Multiple grafting options available for defects seen in acetabular revisions

Particulate allografts offer utility; bulk allografts should be reserved for salvage procedures.

Orthopedic surgeons have access to many bone graft substitutes, but particulate allograft may provide an excellent option for many acetabular revision cases.

Andrew A. Freiberg, MD, of Boston, discussed the applicability of different grafts for acetabular defects and the versatility of particulate allografts at the annual Insall Scott Kelly Institute sports medicine and total hip & knee symposium.

"There is a wide variety of bone grafts that can be used in revision surgery," Freiberg said. "I think, for the most part, particulate allografts are the most useful."

Bone substitutes are useful for contained defects and to augment larger grafts, he said. "We need to continue to work on metal substitutes and other biological solutions for very large defects."

Freiberg commonly uses particulate allografts, which can be used in ample amounts for large and contained defects. The graft can also be combined with bulk allografts to fill large, uncontained holes.

"With the trabecular metal implants, we get excellent initial fixation, I think that will augment our ability to do complex cases," Freiberg said.

During particulate grafting revision procedures, he removes the cemented cup, membrane and fibrous tissues.

After treating the osteolytic lesions, Freiberg reams the femoral head to obtain the correct fit. He fills the defect with the particulate graft and reverse reams the site.

"Actually while I reverse ream, I like to impact it a little bit," he said. "I find that it helps make the bone graft tight."

Other options for filling acetabular defects include demineralized bone, calcium sulfate, composite grafts and bulk allografts. While demineralized bone grafts provide a moldable option for surgeons, some products lack sufficient amounts of bone morphogenetic proteins (BMPs).

"The problem is that the actual amount of BMP is quite low because of the [sterilization] treatment, but these are useful in some situations," Freiberg said.

He uses calcium sulfate Orthoset beads (Wright Medical Technology Inc.) for cases with contained osteolytic lesions.

"When we're doing acetabular liner exchange, they can be placed in cementless shells through the holes or around the rim. I think they are useful to augment healing in contained osteolytic acetabular defects," Freiberg said.

He also fills defects with composite grafts, such as Collagraft (Zimmer). Freiberg noted that the product contains collagen types I and II with porous calcium phosphate.

"We use this through holes around the shells and sometimes even around the rim of the shell when we find an osteolytic rim defect [and] that we want to do some grafting for it," he said. "We often combine this with some particulate grafting as a graft expander."

Frieberg also places trumpets in acetabular components with holes to impact the graft in large defects. "These are commercially available and I think they are useful as an adjunct for allografting," he said.

While better metal implant designs have decreased the use of bulk allografts, Freiberg said that the grafts still play a significant role in salvage procedures. Yet, he noted that using bulk allograft has many shortcomings.

"Bulk allografts have the potential problem of immunogenicity, obviously possible disease transmission, there are very limited osteoinductive and conductive properties and, of course, there are problems of late resorption."

For more information:
Freiberg AA. Use of bone grafts in revision THA. Presented at the Ninth Annual Insall Scott Kelly Institute Sports Medicine and Total Knee & Hip Symposium. Sept. 15-17, 2006. New York.
Andrew A. Freiberg, MD, chief of arthroplasty service, Massachusetts General Hospital, 55 Fruit Street, Suite 3700, Boston, MA, 02114, 617-726-8575, afreiberg@partners.com. He indicated that laboratory research funding was received from Zimmer and Biomet.