Spondylolysis

Not to be confused with spondylosis, spondylitis, or spondylolisthesis.

Spondylolysis
Classification and external resources
ICD-10	M43.0
ICD-9	738.4
DiseasesDB	12322
eMedicine	radio/650
MeSH	D013169

Spondylolysis is a defect of a vertebra. More specifically it is defined as a defect in the pars interarticularis of the vertebral arch. The great majority of cases occur in the lowest of the lumbar vertebrae (L5), but spondylolysis may also occur in the other lumbar vertebrae, as well as in the thoracic vertebrae.

Spondylolysis occurs in three to six percent of the population.

Causes

It is typically caused by stress fracture of the bone, and is especially common in adolescents who overtrain in activities such as tennis, diving, martial arts and gymnastics. Linemen in American football are also at risk due to their bending over at the line. It has been proposed that the pars interarticularis is especially vulnerable when the spine is in an extended position, and a force suddenly presses the vertebrae together, such as when landing on one's feet after a hop. This pressure acts like a nut-cracker on the pars interarticularis and can fracture it in susceptible individuals.

Spondylolysis (spon-dee-low-lye-sis) also runs in families and is more prevalent in some populations, suggesting a hereditary component such as a tendency toward thin vertebral bone.

Spondylolysis is the most common cause of spondylolisthesis (spon-dee-low-lis-thee-sis) in pediatric patients with a classic presentation that of a female gymnast. In the older population, degenerative disc disease commonly leads to spondylolisthesis without spondylolysis; in these instances, the spinal canal narrows because the spino-laminar arch at one level slides forward on the lower level effectively flattening the canal. The hereditary factor mentioned above is quite notable, since the frequency of spondylolisthesis among the Inuit peoples is 30–50%; however, there is controversy about this, as can be seen on the wiki page for spondylolisthesis: "(This statistic is controversial, however, because further anthropological studies have shown that the occurrence of spondylolysis in Inuit people living in Western-style communities is within the normal variancy at 7%. These people are hereditarily linked to the study group showing ~40%. It is theorized that the nomadic Inuit have a higher incidence of spondylolysis due to trauma acquired as infants by being carried in an amauti. While in an amauti, the baby is put into compressive extension with each step taken by the mother. Also, all other studies have shown a normal variance of spondylolysis within cultures of 6-10%, further suggesting that spondylolysis is an environmental abnormality and that a hereditary tie is very unlikely)."

Diagnosis

The defect is seen in this oblique lumbar radiograph: Image of Pars Defect. An oblique x-ray of the lumbar spine shows what appears to be a "scotty dog" first described by Lachapelle:

Apparent part of dog	Part of vertebra
nose	costal/transverse process
ear	superior facet
neck	pars interarticularis
collar	pars defect (dark on x-ray)
eye	pedicle seen end on
body	lamina
hind foot	spinous process
tail, if pointing straight up	the opposite superior articular facet
tail, if pointing horizontally	the transverse process of the opposite side
forefoot	the inferior articular process

• Image with Pars Defect outlined and fracture marked with arrow
• Image of a spine with the Scotty defect and no fracture

External links

• Information from the American Academy of Orthopaedic Surgeons
• A Patient's Guide to Lumbar Spondylolysis
• http://www.orthoseek.com/articles/spondyl.html