Lumbar stress reaction and spondylolysis (pars interarticularis stress fracture)

What it is

On the back of each vertebra there is a narrow strut of bone called the pars interarticularis, joining the joint above to the joint below. Repeated arching combined with rotation loads that strut in bending, which is the one thing it is poorly built for. First the bone gets irritated and swollen inside, which is a stress reaction and shows on MRI but not X-ray. If loading continues, a crack forms, which is spondylolysis. It is almost always at L5, usually on one side, and it is the single most common cause of persistent low back pain in an adolescent athlete.

How volleyball causes it

The cocking phase of the spike is extension plus rotation plus side-bend under speed, which is the exact loading pattern the pars fails under, and a hitter repeats it hundreds of times a session. Jump serving is worse per rep because the athlete chooses maximum arch with no defender forcing a compromise. The risk peaks between roughly 12 and 17, when the growth spurt leaves bone lagging behind the muscular force being applied to it, and a year-round schedule of club plus school plus beach plus open gym removes the offseason that would otherwise let the bone catch up. Setters who back-set heavily and blockers who land arched with the hips ahead of the shoulders add reps of the same shape.

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What it feels like

• Deep one-sided low back pain that you can point to with one finger, just off the midline near the belt line
• Standing on one leg and arching backwards reproduces it, and it is worse standing on the leg on the painful side
• Worse the day after a heavy jumping or serving day, and worse late in a session rather than at the start
• Unlike a muscle strain, it does not warm up and disappear after ten minutes
• Pain sitting up from lying, or arching to reach an overhead shelf
• Sometimes a vague ache into the buttock, but rarely true pain down the leg

Stop and get it seen if

• Pain, numbness, tingling or weakness travelling down a leg, or any change in bladder or bowel control, which suggests the injury is affecting nerves
• A sense of the back giving way or catching, or a step or shelf that you or someone else can feel along the line of the spine, which can mean the vertebra has slipped forward
• Back pain in a growing athlete that persists beyond two weeks despite reduced load, which should be imaged rather than managed as a muscle problem
• Night pain unrelated to position, fever, or unexplained weight loss
• Sudden severe pain after a fall or collision rather than a gradual build

What recovery usually looks like

Stages, not a schedule. Everyone moves through these at their own pace, and the ranges are wide because real recoveries are.

1. 1. Unload the bone

   6 to 12 weeks, sometimes longer for a frank crack

   Take away the loading that caused it so the bone can heal, which means stopping jumping, hitting and serving rather than reducing them.

   • Daily life, walking and school are pain free
   • Standing on one leg and arching no longer hurts on either side
   • Some players are put in a brace during this period, some are not, and both are normal practice
   • Repeat imaging or a clinical review, not a calendar date, is what ends this phase

2. 2. Rebuild control in neutral

   4 to 8 weeks, overlapping the first phase

   Build trunk, hip and glute strength in positions that do not push the spine into end-range extension.

   • Can hold front plank, side plank and bird dog positions with a neutral spine and no symptoms
   • Hip flexors and quads have regained length after weeks of reduced activity
   • Hip hinging and squatting are comfortable
   • Sustained standing and walking are completely unremarkable

Ready to play again when

• Single-leg standing arch (stork test) pain free on both sides
• Full approach, swing and landing at match speed with no pain the following morning
• Jump serving at full effort with no pain during or after
• A complete practice week, including consecutive high-jump days, without the pain returning
• Clearance from the clinician managing the case, based on symptoms and where relevant on repeat imaging

Keeping it from coming back

This is ordinary training, so unlike the rest of this page it does tell you what to do.

• Track total hard jumps, swings and jump serves per week across every team and gym the athlete plays in, and build load up gradually rather than doubling it the week club season starts. Volume, not technique, is the main driver.
• Dead bugs, front planks and Pallof presses to train the trunk to resist extension, so the arch does not run out of muscle and end up on bone.
• Half-kneeling hip flexor stretching and couch stretch, because a tight front of the hip forces extension to happen in the lumbar spine instead.
• Thoracic extension over a foam roller plus overhead reach drills, so the upper back contributes to the arch and L5 is not doing all of it.
• Romanian deadlifts and hip thrusts to build the posterior chain that finishes the jump and absorbs the landing.
• During growth spurt years, plan at least one genuine offseason block per year with no jumping or hitting, and avoid back-to-back maximum jump-serve days.