Hydroxyapatite in knee arthroplasty

Summary HA interface remains controversial in knee replacement especially as regards the tibial component. When speaking about non cemented knees the poor results afforded by the porous coatings especially microbeads or fibermesh made many surgeons fall in doubt about non using acrylic cement. HA coatings provide us with a very new biologic system and has to be considered as definitely different :1- Biological evidence of reliable implant bonding: Histological analysis performed by many authors including Thomas Bauer from Cleveland demonstrated that there is a very intimate contact between bony formations and metallic substract thanks to HA. This provides very good interlock and long lasting fixation. If the coating resorbs after several years, this resorbtion is a part of the regular bony turn over and HA is replaced by bone. This is finally the ultimate goal of replacement when reliable and sound fixation is achieved directly by the host bone.2- Hip HA experience is very successful at 10 year of FU: We started our hip experience 12 years ago in May '87. To date our personal experience with HA hips reaches 2 000 cases. Results were reported at the Barcelona '97 meeting held by the European Federation of National Associations of Orthopaedic and Traumatology (EFORT). This paper summed up the results of a non selected series. Then global survival rate was 0.985 at 10 year and these results look encouraging and at least as good as the best cemented series.3- HA total knee arthroplasty. A 9-year experience: Our personal experience in TKR using the Omnifit knee started 9 years ago in 1990. The first implant was the 3000 distal-coated Omnifit knee and we now currently use the 7000 fully coated knee. Based upon a series of 51 cases over 5 year of FU (5 to 7 year) of which 100% were reviewed for this study, the knee score according to the International Knee Society score was 96.2 out of 100 (ranging 77 up to 100). The mean function score was 93.2 (ranging from 85 up to 100). To date the failure rate is 0% and we had no clinical failure and no evidence of loosening. Finally the most important finding as regards the HA biological interface was demonstrated by the ability for bone to fill in previous lucent line due to fibrous tissue layer.Finally HA seems to be considered as a reliable third track as our 7 year experience is very encouraging. Radiological stability of patterns over 5 to 9 year, the seal afforded by HA preventing from migrating osteolysis, and mainly the ability for HA to fill in gaps over the years and transform fibrous tissue into bone may be considered as critical assets.