Orthobiologic reduced nonunion rates when used in foot and ankle fusions

Sixty-patient open-label study shows promise for bone graft substitute.

DENVER — Using recombinant human platelet-derived growth factor in a tricalcium phosphate matrix may aid in the bone healing of patients undergoing foot or ankle fusion.

Alastair S. Younger, MD, FRCSC, and colleagues prospectively studied 60 patients who underwent a combined 180 foot or ankle fusions aided with recombinant human platelet-derived growth factor in a tricalcium phosphate matrix (Augment Bone Graft, formerly GEM OS1; BioMimetic) and were followed for a minimum of 9 months.

The investigators discovered that 90% of the patients achieved clinical fusion, which was determined by a clinician's assessment of radiographs and outcome measures for pain, swelling and motion. In addition, they found that 88% of the patients had radiographic union, as evidenced by bony ridging, and 95% of the joints fused clinically.

CT scans also showed that 75% of patients had evidence of fusion at 16 weeks.

The study revealed no serious adverse events related to using the orthobiologic. Of the 60 patients, 59 underwent both radiographic and clinical review, he said.

Similar revision rate

“In a meta-analysis of foot and ankle fusions, the revision rate is 9% for 1,262 fusions,” Younger said during his presentation at the American Orthopaedic Foot and Ankle Society 24th Annual Summer Meeting. “The revision rate in this study is 10% with GEM OS1.”

All six cases of nonunion occurred in shear-loaded joints, including the talonavicular, metatarsophalangeal, navicular cuneiform and tarsometatarsal joints.

“The joints loaded in shear were at risk for nonunion with screw fixation, and as a result, we recommend that GEM OS may prevent bony apposition of joint, particularly if a lot of GEM OS is put in the space,” Younger said. He also noted that none of the ankle or subtalar fusions had nonunion.

Multicenter investigation

The study included patients who had midfoot, hindfoot or ankle fusions performed at three centers by four surgeons. The group had an average age of 53 years and included 20 men. Eighteen patients had one risk factor for nonunion and 21 had two or more risk factors. The study excluded patients who were unable to comply with follow-up, required more than 90 cc of graft filler, or had an infection at the fusion site.

During the procedure, surgeons debrided all cartilage and penetrated the subchondral bone. They used rigid internal fixation with a maximum of four screws at each fusion site, and placed the orthobiologic in the fusion gap prior to fixation, Younger said.

The patients underwent clinical and radiographic follow-up at 2, 6, 9, 12, 16 and 36 weeks. They had CT scans performed at 6 and 12 weeks and also at 16 weeks if possible. A blinded, independent radiologist reviewed the radiographic outcomes.

For more information:
Alastair Younger, MD, FRCSC, can be reached at Providence Health Care, 401-1160 Burrard St., Vancouver, BC V6Z 2E8, Canada; +1-604-683-3585; e-mail: asyounger@shaw.ca. He receives research support from BioMimetic and Wyeth.

Reference:
Younger AS, Daniels TR, Wing K, et al. The use of RhPDGF to promote bone healing in foot and ankle fusions: A prospective study of 130 fusions in 60 patients. Presented at the American Orthopaedic Foot and Ankle Society 24th Annual Summer Meeting. June 26-28, 2008. Denver.