Baastrup's sign, or kissing spine, is an orthopedic and radiographic disorder that often occurs in elderly humans. It is characterized by enlargement of the posterior spinous projections of the lumbar spine, with normal intervertebral disc height and neuroforamina. 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, for example when flat on their stomach. The condition has been seen in humans, canines, particularly with boxer breeds, and certain breeds of horses. This disorder is named after Christian Ingerslev Baastrup.