A patient, aged 40, ailing during approximately 8 years, complains of exertion pain in the lumbar part of the spine, in cervical and thoracal part (especially when coughing), pain in the hip and knee joints on the right. On examination: the body is fixed in the forward inclination with head down, gluteal muscles atrophy. Spine roentgenography: ribs osteoporosis, longitudinal ligament ossification. What is the most likely diagnosis?