As you say L3-4-5 vertebra are worn out---what does radiological X Ray
or scans say , is it due to invasion from metastatic spread from prostate?
much depends on spinal diagnosis. Chemotherapy
, radiotherapy shall help in that case in suppressing spread.
In meantime Wear a lumbar brace, avoid forward bending, and apply anti-inflammatory cream to foot and ankle and keep the foot elevated while sitting or lying down.