Dear editor,

We read with interest the study of osteochondral transplantation for the treatment of osteochondral defects at the talus [1] and wish to congratulate the authors on work which adds to our knowledge and understanding of the difficult clinical problem of osteochondral defects. However, we have some concerns regarding the paper and wish to share them.

In the procedure of osteochondral transplantation at the talus, the author said that “The donor cylinders were pressed manually into the recipient talar site to fill the defect”. Then the author said “The patients were mobilized with partial weight-bearing for 6 weeks and with early physiotherapy to both the ankle and the knee. Unprotected weight-bearing was allowed after a radiological control. CPM for the ankle was used for the first 6 weeks” in rehabilitation protocol. However, it is so difficult to understand the rehabilitation protocol, which was not clearly expressed. In our experience, the ankle is fixed with a plaster 3 weeks postoperatively, which can not do any exercise to protect the just transplanted cartilage. But in this article the patients were mobilized earlier as above mentioned with partial weight-bearing for 6 weeks and so on as above mentioned, what the exactly meaning of partial weight-bearing? Do they have any influence for the transplanted cartilage?

The next question is that the author used biodegradable β-tricalcium phosphate ceramic to fill the donor defect in the posterior femoral condyles. Although β-tricalcium phosphate is one of the most mature orthopedic biomaterials used for promoting osteogenesis, there are still controversies on its degradation [2]. At least it can not be completely degraded to the current view [2, 3]. So the partially degraded β-tricalcium phosphate is likely to fall off into the knee joint cavity, become the joint foreign body in the future long-term follow-up. The mean time of follow-up was only 17 months, which was not long enough to observe these complications. However, there have been reports about adverse reactions of artificial bone graft substitutes, lessons learned from using tricalcium phosphate [3].