Bone formation and resorption in patients after implantation of β‐tricalcium phosphate blocks with 60% and 75% porosity in opening‐wedge high tibial osteotomy

Abstract Most of the implanted porous β‐tricalcium phosphate (β‐TCP) can be resorbed. However, β‐TCP block with 75% porosity is inadequate for weight‐bearing sites until bone incorporation occurs. Thus, the authors have recently developed β‐TCP block with 60% porosity, which is approximately sevenfold greater in terms of compressive strength than that of β‐TCP with 75% porosity. The authors investigated bone formation and resorption of β‐TCP after implantation in patients of β‐TCP blocks with two different porosities. From May 2003 to November 2004, medial opening high tibial osteotomy was performed in 25 patients with a mean age of 66 years. The opened defect was fixed with a Puddu plate. Then 6–8 cm 3 of β‐TCP block with 75% porosity was used to fill the cancellous bone defect, except on the medial side where 2.83–3.18 cm 3 of wedge‐shaped β‐TCP block with 60% porosity was implanted. At least 2 years after surgery, the 25 patients had no correction loss, and bone formation was noted in all cases. Complete or nearly complete resorption of β‐TCP with 60 and 75% porosity was obtained within 3.5 years. Thirteen biopsy samples obtained from the 60% porosity implantation sites showed good lamellar bone formation, and the percentage of β‐TCP remaining relative to the newly formed bone plus β‐TCP ranged from 0.3 to 14.5%, with a mean of 6.7%. The authors suspect that mechanical stress loading to the medial side of the tibia facilitated bone formation and resorption of β‐TCP with 60% porosity. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008