Your spine is made up of 33 bones called vertebrae, 9 are usually fused together, the remaining 24 can be thought of as ‘floating’, all held in place by ligaments and muscles. The vertebrae hold onto each other through facet joints, which are hook like bones that grow off the back of your vertebrae. Intervertebral disks lie between them to cushion the bones from compressive forces. Each vertebra should sit comfortably on this disk and be balanced over the vertebrae bellow, unless you have a congenital (from birth) condition, wear and tear or suffered trauma to the back that caused misalignment of the spine. A vertebrae that has ‘slipped’ forward out of alignment could be caused by a condition called Spondylolisthesis (spon-dee-lo-lis-thee-sis). This will almost always follow a condition called Spondylolysis (spon-dee-lo-lye-sis) which is a condition where the facet or hook like bones on the back of the vertebrae are broken off from the main body of the bone. Which makes the vertebrae truly ‘floating’ as there is now very little keeping it in place. This branch of injuries is termed ‘Spondy’ for short. So whenever you hear someone talking about their ‘spondy’, you now know roughly what their on about.
Figure 1: Typical side view of the lumbar spine
Spondylolysis, is a fracture of the pars interarticularis, the part of the bone that joins the facet joint (the part that links the top and bottom vertebrae together) and the vertebral body (the part the nerve passes through). This commonly occurs in L5, the lowest of the ‘floating’ vertebrae as this is where most of the pressure is compared to the other floating vertebrae. There are numerous factors that can play a part in developing this condition, including anterior pelvic tilt, tight hip flexors and weak hamstrings, arguably these are tied in an infinite loop as they are all unavoidably linked. Over time, with this anterior tilt, additional compressive and sheer force is applied to a relatively smaller surface area as the spine has less range of movement. If we tilt the sacrum forwards, it increases the slope on which the lumbar vertebrae sits. This increases the sheer/sliding force between the facet joints leading in part to this fracture.
Figure 1: Side view of spine with fracture of pars interarticularis
The fracture heals over time, however, there is a duration where the vertebrae is for all intents and purposes free to move as it wills. More accurately, free to be pulled and pushed at the will of the muscles, ligaments and gravity that influence the bones. Looking at the diagrams above, it can only move forward, thanks to gravity. When the vertebrae moves forward it is called Spondylolisthesis. When this happens the vertebral foramen (the whole the nerve passes through in each vertebrae) no longer lines up with the ones from the vertebrae above and below. This can lead to a ‘trapped