As defined, strong means able to withstand great force. For a synovial to be strong, it should have a good supply of synovial fluid. A synovial fluid prevents injuries of the cartilage because it acts as a shock absorber and grease for smooth bone movement. Enough supply of synovial fluid will also help the cartilage not to stiffened and worn out that may progress to inflammation.
A symbiosis is an evolved interaction or close living relationship between organisms from different species, usually with benefits to one or both of the individuals involved.