Spondylolysis / Pars Interarticularis Stress Fracture

The classic story is an adolescent or young adult athlete with insidious-onset, activity-related low back pain reproduced or worsened by lumbar extension and twisting. Pain is typically unilateral or central in the lower lumbar region, often with referred buttock or proximal posterior thigh pain. Pain at rest is uncommon early on - a constant ache or pain at night should raise concern for an alternative diagnosis.

Examination: pain reproduced by single-leg hyperextension (the stork test) - the patient stands on the ipsilateral leg and extends, loading the same-side pars. The test supports the diagnosis but is neither sensitive nor specific enough alone. Range of movement is typically full but extension is painful. Look for hamstring tightness and a hyperlordotic posture. Neurological examination is usually normal in isolated spondylolysis; new neurological features suggest associated spondylolisthesis or alternative pathology and warrant urgent imaging.

For patients aged 16 and over, apply NICE NG59 red flag screening: night or rest pain, systemic features (fever, weight loss), neurological deficit, saddle anaesthesia, bladder or bowel disturbance, deformity, significant trauma. In younger adolescents, paediatric principles apply with a lower threshold for specialist referral.

Consider axial spondyloarthritis in older adolescents and young adults when inflammatory features dominate (more than three months of morning stiffness improving with exercise, alternating buttock pain, family history, psoriasis, uveitis, IBD) and refer per NICE NG65.

MRI is favoured in UK SEM and paediatric spinal practice as the first advanced imaging test for suspected active pars stress injury in adolescent athletes. It detects early marrow oedema (the earliest sign), shows established fractures, screens for disc and neural pathology, and avoids ionising radiation.

Plain AP and lateral radiographs assess alignment, established spondylolisthesis, deformity, trauma, tumour, or infection. Routine oblique views are increasingly avoided because of limited sensitivity (around 30-50% for active spondylolysis) and additional gonadal radiation, although the classic Scotty dog with a collar sign on oblique remains a high-yield exam image - a broken collar at L5 indicates a pars defect.

The Hollenberg MRI staging classifies pars stress injury:

• •Grade 0: normal
• •Grade 1: marrow oedema only
• •Grade 2: incomplete fracture
• •Grade 3: acute complete fracture
• •Grade 4: chronic non-healing defect

CT characterises cortical fracture morphology, chronicity, and healing and is useful for surgical planning. Reserve for cases where MRI is equivocal or fracture characterisation will change management - not preferred as a screening test in adolescents because of radiation. SPECT-CT is reserved for specialist cases where MRI is contraindicated or equivocal. Image-guided diagnostic local anaesthetic pars injections are occasionally used by specialists in atypical or multi-level cases.

Bone-health screening in any adolescent with a bone stress injury: vitamin D, calcium, focused RED-S assessment including menstrual history in female athletes.

The pillars are activity restriction, structured rehabilitation, and time.

Initial conservative management:

• •Cease provocative sport-specific loading (extension and rotation) for an initial 6-12 weeks (commonly around three months)
• •Continue non-provocative cardiovascular fitness (cycling, swimming, elliptical) where tolerated
• •Simple analgesia per NICE CKS for adults (paracetamol, short-course ibuprofen); follow paediatric prescribing in younger adolescents

Healing potential depends on stage, chronicity, and laterality:

• •Early stress reactions and acute incomplete fractures (Hollenberg 1-2) heal well
• •Acute complete fractures (Hollenberg 3) have moderate bony union rates
• •Chronic non-healing defects (Hollenberg 4) often progress to a fibrous union which can still be clinically asymptomatic
• •Unilateral acute defects heal more reliably than bilateral

The clinical goal is a pain-free patient with safe return to sport, not necessarily a radiographically healed pars.

Rigid bracing is not routinely required. Most adolescents do well with activity restriction and rehab alone. Reserve bracing for selected cases (pain control, difficulty avoiding extension loading, or specialist-directed healing protocols).

Address modifiable bone-health drivers: vitamin D replacement if deficient, RED-S management, training load review, recovery optimisation.

Surgical referral indications:

• •Failure to respond to six months or more of optimised conservative care
• •Neurological deficit
• •Progressive spondylolisthesis (Meyerding grade III or higher, or progression on serial imaging)
• •High-grade dysplastic anatomy

Direct pars repair (Buck screw, Scott wiring, modified techniques) is considered for symptomatic non-healing defects with preserved disc health and no or low-grade slip, typically in younger patients. Posterolateral fusion is reserved for high-grade slips, significant disc degeneration, instability, neurological compromise, multilevel pathology, or failed motion-preserving options.

Rehabilitation runs in parallel with activity restriction and is the active ingredient.

Phase 1 (weeks 0-6): pain control, removal of provocative loading, gentle pain-free mobility.

Phase 2 (weeks 6-12): deep core control (transversus abdominis, multifidus), pelvic stability, hip mobility (especially extension and internal rotation), hamstring flexibility.

Phase 3 (3-6 months): graded reintroduction of sport-specific loading. Technical correction of the underlying mechanical driver (mixed bowling action, dismount technique, throwing kinematics) is as important as the rehab itself.

Progression and return to sport are criteria-based, not time-based:

• •Pain-free daily activity
• •Pain-free lumbar extension and rotation control under load
• •Restored hip and lumbopelvic strength and mobility
• •Tolerance of graded sport-specific tasks
• •Correction of training load and technique factors

Recurrence risk is real if the underlying technique or training load is not addressed, so coach engagement is essential.

• •Hollenberg MRI staging (2002): standard adolescent staging system (Grade 0 normal through Grade 4 chronic non-healing) guiding healing prognosis and rehab pacing.
• •Meyerding classification (1932): grades any associated vertebral body slip - Grade I (under 25%), II (25-50%), III (50-75%), IV (75-100%), V (spondyloptosis). Drives surgical referral threshold when spondylolysis progresses.
• •NICE NG59 (2016, updated 2020): UK red flag and management framework for back pain in over-16s.
• •NICE NG65: Spondyloarthritis in over-16s - inflammatory back pain referral pathway when axial SpA is suspected in this age group.
• •Standaert and Herring (Clin J Sport Med 2007): early conservative care with activity restriction yields high rates of return to sport in symptomatic spondylolysis in young athletes.
• •British Association of Spine Surgeons (BASS) standards: UK framework for spinal-surgery referral including direct pars repair and lumbar fusion outcomes.

• •Classic vignette: adolescent athlete in an extension-and-rotation sport (cricket fast bowler with mixed action, gymnast, diver, dancer) with extension-loaded back pain. L5 accounts for 85-95% of cases.
• •MRI is first-line advanced imaging - picks up early marrow oedema and avoids radiation. CT is reserved for fracture characterisation and surgical planning.
• •Plain oblique radiographs show the Scotty dog (with collar sign for a pars defect) but are insensitive (around 30-50%) and no longer routine.
• •Hollenberg staging is for the pars injury itself; Meyerding grades any associated slip (spondylolisthesis). Do not confuse the two.
• •Unilateral acute defects heal more reliably than bilateral. Rigid bracing is not routinely required - activity restriction and rehab are the cornerstone.
• •Surgical referral for failed 6 months of optimised conservative care, neurological deficit, progressive Meyerding III or higher slip, or high-grade dysplastic anatomy.