In vivo Histological Examination of the Graft Site 3 Years after Open-wedge High Tibial Osteotomy with Nanohydroxyapatite Augmentation

INTRODUCTION: The open-wedge high tibial osteotomy (OWHTO) is a common technique for the treatment of medial compartmental osteoarthritis of the knee. There are many options to fill the osteotomy site gap. The autologous graft donor site morbidity can be avoided using heterologous bone grafts which represent a valid alternative. CASE PRESENTATION: This case report is about a 52-year-old male with knee osteoarthritis and varus deformity. Due to stiffness, swelling, and painful limitation during daily life activities, the patient underwent OWHTO. The osteotomy gap was filled with an equine cancellous bone wedge and nanohydroxyapatite (NHA) bone paste augmentation. After 3 years, the OWTHO was converted to total knee arthroplasty and a bone biopsy of the previous graft site was performed. The histological examination presented non-viable bone areas surrounded by viable bone without inflammatory cells, suggesting the presence of residual non-viable bone from the bone substitute graft. CONCLUSION: The in vivo histology of the graft site after 3 years has shown that heterologous bone is a safe and valid choice as a scaffold for bone regeneration. Augmentation with NHA bone paste achieved good osteoinduction without an inflammatory reaction and good integration of the bone substitute insert.