Hi, thanks for writing to HCM.
Generally, Surgery is not indicated for a depressed lateral tibial condyle fracture
measuring only 3mm. But as you are already of 55 years age and degenerative arthritis
might have set in your knees. This 3mm depression
may lead to speeding up of the degeneration in the joint further.
As long as you don't bear weight on the leg, crutches are sufficient. Premature weight bearing on the leg may lead to displacement of the fracture, in which case surgical fixation is the only option.
So, I suggest you to be on non-weight bearing for atleast 6-8 weeks and check the progression of fracture union by serial xrays. Afterwards you may start bearing weight subject to your pain tolerance
Hope this information is helpful. Good day