Dear user, Lower back pain history of spinal surgeries, fusion of L3-L5 weakness and numbness in right leg all suggest the possibility of nerve compression which may be responsible for your symptoms.Arachnoiditis
is a very tricky problem. It may be infectious in origin hence treatable or non-infectious such as due to trauma or even surgery. This condition is very difficult to treat. Treatment is usually symptomatic and supportive. Paradoxically surgical treatment
may worsen the condition so consult a good neurologist
and neurosurgeon and discuss about the outcome of various treatment options.
Do not hesitate to take second opinion
Thanks with regards