'Baastrup's sign', or ''kissing spine'', is an orthopedic and radiology disorder, notably in elderly humans. It is characterized by enlargement of the Posterior (anatomy) spinous projections of the lumbar Vertebral column, with normal intervertebral disc height and Vertebral column. The reason it is referred to as ''kissing spine'' is because the posterior spinous processes 'kiss' and touch one another as the individual goes into lumbar Extension (kinesiology), for example when flat on their stomach. This disorder is named after Christian Ingerslev Baastrup.