A 72-year-old man from Mumbai with a 10-year history of chronic kidney disease stage 3b (eGFR 35 mL/min/1.73 m²) presents with progressive bone pain and muscle weakness. On examination, there is proximal muscle weakness (hip and shoulder girdles). Laboratory investigations show: serum calcium 7.8 mg/dL (normal 8.5–10.5), phosphate 4.8 mg/dL (normal 2.5–4.5), alkaline phosphatase 95 U/L (normal 30–120), intact PTH 385 pg/mL (normal 10–65), 25-OH vitamin D 22 ng/mL (normal >30). X-ray of the pelvis shows a 'rugger jersey' spine appearance on lateral view. What is the most likely underlying bone pathology?