New bone formation around porous hydroxyapatite wedge implanted in opening wedge high tibial osteotomy in patients with osteoarthritis.

A porous hydroxyapatite (highly purified synthetic Ca10(PO4)6(OH)2) wedge was inserted into the tibia in 10 knees of 7 patients with osteoarthritis of the knee who underwent high tibial osteotomy. The interface of this HA wedge with bone was histologically examined in undecalcified specimens obtained at the time of hardware removal in all 10 knees, and total incorporation of the HA into bone was observed, with no inflammatory reaction. The proportion of pores that were filled with regenerated bone within 300 microm from the interface was 71.8 +/- 10.1% (mean +/- S.D.), and it was positively correlated with the time from implantation to biopsy. Radiodensity of the HA wedge was measured during the follow-up period, and it did not change significantly within 36 months after osteotomy. Our study concluded that bone ingrowth into the HA block slowly progressed and was correlated with the passage of time.