A 78-year-old woman complains of lumbar pain. The pain increases during movements, decreases at rest, and does not irradiate to other areas. Her temperature is normal, the body weight remains unchanged. Her peripheral joints are normal, she has moderate obesity, the mobility of the lumbar spine is limited. A local tension is observed in the soft tissues over the L2 vertebra. In the blood: Hb – 147 g/L, leukocytes – 8.8 · 109/L, platelets – 222 · 109/L, ESR – 5 mm/hour, Na+ – 140 mmol/L, K+ – 4.2 mmol/L, Ca2+ – 2.35 mmol/L. Make the right diagnosis: