I had the same thing almost exactly happened to me and turns out it was severely infected even though that was the only sign of it.
Hi,
How are you? It is difficult to say what it is without examination. But the most common causes of non healing of a wound could be infection, disruption of blood supply to that part of the body, diabetes, infection etc.
As you mentioned that pus oozes from that wound, I would suggest to get a culture done of the pus, which would help in using the appropriate antibiotic for that infection.
Consult your orthopaedician to rule out all the possible causes for this.
Best.