Spondylolysis:
Low Back Pain in Young Athletes

What spondylolysis is

Each vertebra in the lower back has a narrow segment of bone at the back called the pars interarticularis ("the part between the joints"), which links the upper and lower facet joints. Spondylolysis is a defect or crack in this segment — in Japan it is commonly called yōtsui bunrishō (腰椎分離症). In young people it is generally understood as a stress fracture: repeated extension (backward bending) and twisting of the lower back concentrates load on the pars until the bone begins to fail, in much the same way a shin or foot bone can develop a stress fracture in a runner.

It most often affects the lowest lumbar vertebra, L5, and may occur on one side (unilateral) or both sides (bilateral). There also appears to be an inherited component: defects cluster in families and are more common in people with spina bifida occulta, a minor and usually harmless incomplete closure of the back of the spine.

Who gets it

Pars defects are surprisingly common in the general population, and most people who have one never know. In a classic American study that followed 500 schoolchildren from first grade, defects were present in 4.4% at age six, rising to about 6% by adulthood. A large Japanese study that reviewed abdominal and pelvic CT scans taken for unrelated reasons found a very similar figure.

In young athletes with back pain the picture is very different. Sports that involve repeated hyperextension and rotation — baseball (batting and pitching), football, volleyball, gymnastics, dance, tennis, cricket bowling, judo and weightlifting among them — place particular load on the pars during the growth years, when the bone is still maturing. A 2023 meta-analysis of nine studies (835 athletes) estimated that about 42% of athletes presenting with low back pain had spondylolysis, though the figure varied widely with age, sex and sport (Li et al., Medicine, 2023). That is why back pain in a sporty teenager is generally taken more seriously than the same complaint in an adult.

Symptoms

The typical story is low back pain in an active child or teenager that comes on gradually, worsens with sport — especially with arching backwards, twisting, or landing — and eases with rest. Pain is usually felt across the lower back or to one side, and is sometimes felt in the buttock. Leg pain, numbness or weakness is not typical of uncomplicated spondylolysis in young people, and these symptoms should prompt evaluation for other causes such as a disc problem or nerve compression.

Doctors often examine for pain on standing back-extension, sometimes on one leg. It is worth knowing, though, that a systematic review found that no single history question or physical test reliably confirms or excludes spondylolysis on its own (Grødahl et al., Manual Therapy, 2016). In practice, the combination of age, activity, persistent extension-related pain and imaging is what leads to the diagnosis.

How it's diagnosed — and why staging matters

Imaging serves two purposes: confirming that a pars defect is present, and working out how "fresh" it is — because a fresh fracture behaves very differently from an old, established one.

Test	What it shows	Limitations
X-ray	Established defects and any vertebral slip (spondylolisthesis); low cost and low radiation	Frequently misses early fractures
MRI	Bone-marrow oedema around the pars or pedicle — a sign of an active, early stress reaction; no radiation	Less precise than CT at showing the fracture line itself
CT	Detailed bony anatomy: a hairline crack (early), a widening gap (progressive), or a rounded, sclerotic defect (terminal)	Involves radiation, so its use in children is usually limited

Imaging recommendations vary between centres. A 2017 systematic review suggested plain X-rays as a reasonable first step, MRI for early diagnosis, and CT for persistent or unclear cases, while acknowledging that the underlying studies are not strong enough to dictate a single algorithm (Tofte et al., Spine, 2017). Japanese spine surgeons, in particular, have contributed much of the research showing how MRI and CT findings together predict healing.

The practical message for families is that timing matters. A teenager whose back pain is evaluated early, while the fracture is still at an early stage, has a realistic chance of the bone healing; a defect that has been present for a long time and has become a terminal "pseudarthrosis" generally won't unite with rest, although it may still become painless.

Treatment options

The great majority of young people with spondylolysis are treated without surgery. The aims are to relieve pain, give an early fracture the best chance to heal, and return safely to sport.

For athletes, the most common question is whether — and when — they will play again. The available data are reassuring, though they come mostly from observational studies rather than randomised trials.

Importantly, a defect that does not heal with bone is not necessarily a failure of treatment. Many people with a non-united pars defect become pain-free and live active lives — the population studies above show how many adults have one without symptoms.

Spondylolysis and spondylolisthesis

When the defect is on both sides, the vertebra can slip forward on the one below — a condition called isthmic spondylolisthesis. In most people this slip is small and does not progress much after adolescence. A remarkable 45-year follow-up of the original American schoolchildren cohort found that slip progression slowed with each decade, no one with a unilateral defect developed a slip, no subject reached a 40% slip, and back-pain-related quality of life was similar to that of the general population (Beutler et al., Spine, 2003). Larger slips, slips in younger children, and slips causing nerve symptoms are monitored more closely by spine specialists.

When to see a specialist

Back pain in a child or teenager that persists for more than a few weeks, that is clearly worse with arching backwards or with sport, or that keeps returning when training restarts is worth evaluating by a doctor rather than simply "playing through it." Seek prompt attention for night pain, fever, unexplained weight loss, leg weakness or numbness, or changes in bladder or bowel control, as these point to other causes that need urgent assessment. For a suspected pars stress fracture, a spine or sports orthopaedic specialist with access to MRI is the most appropriate first contact.