ADI greater than 5mm | Down Syndrome Association | Transverse Ligament Key | Fusion if Symptomatic
- ADI greater than 5mm in children indicates transverse ligament incompetence
- SAC less than 14mm indicates cord compression risk
- Down syndrome: no routine radiographic clearance when asymptomatic; use clinical surveillance and neutral-position procedural precautions
- Neurological symptoms mandate surgical stabilization
- C1-C2 posterior fusion is gold standard treatment
- “Transverse ligament is PRIMARY restraint to anterior translation of C1
- “Alar and apical ligaments are SECONDARY restraints
- “Down syndrome has ligamentous laxity + os odontoideum association
- “Neurological deterioration can be sudden and catastrophic
Atlantodental interval (ADI) measured from anterior arch of C1 to front of dens. Normal is less than 3mm adult, less than 5mm child. Greater than 5mm indicates transverse ligament failure and instability.
SAC (posterior ADI) is distance from posterior dens to anterior C1 posterior arch. SAC less than 14mm indicates cord at risk. Steel's rule of thirds: 1/3 dens, 1/3 cord, 1/3 space.
Radiographic AAI is common in Down syndrome, but symptomatic disease is rare. AAP guidance does not recommend routine radiographs in asymptomatic children, including solely before anaesthesia or sport; use focused clinical surveillance, neutral-position precautions during procedures, and targeted imaging for symptoms or known pathology.
Absolute indications: Neurological symptoms (myelopathy, weakness). Relative: ADI greater than 10mm, SAC less than 14mm, progressive instability. C1-C2 posterior fusion is standard treatment.
- Neurological Status
- Asymptomatic
- Management
- Clinical surveillance; no routine serial screening films
- Neurological Status
- Asymptomatic
- Management
- Specialist review; assess PADI, progression and planned activities
- Neurological Status
- Asymptomatic
- Management
- Individualised MRI and stabilization discussion; no single ADI mandates fusion
- Neurological Status
- Any symptoms
- Management
- Urgent MRI, surgical stabilization
- Neurological Status
- Myelopathy/weakness
- Management
- Emergency C1-C2 posterior fusion
DOWNSDOWNS - Risk Factors
Hook:In Down syndrome, screen clinically for cervical myelopathy and image selectively
145-14-3 Rule
Hook:These numbers define when atlantoaxial instability becomes clinically significant
STEELSTEEL's Rule of Thirds
Hook:This explains why some subluxation is tolerated before cord compression
Overview and Epidemiology
Atlantoaxial instability (AAI) refers to excessive movement at the C1-C2 articulation, most commonly anterior subluxation of C1 on C2. This can lead to spinal cord compression and potentially catastrophic neurological injury.
Epidemiology:
- Down syndrome: radiographic AAI in roughly 6.8-27% (varies with age); fewer than 1-2% become symptomatic [FSEM 2020; Pueschel & Scola 1987]
- Rheumatoid arthritis: a leading adult cause; atlantoaxial subluxation prevalence relates to disease activity, and modern disease-modifying therapy has reduced its incidence [Veldman 2022]
- Os odontoideum: frequently associated with atlantoaxial instability
- Trauma: transverse ligament rupture, often with Jefferson (C1 burst) fractures
- Other conditions: Morquio syndrome, Grisel syndrome, Klippel-Feil
Causes by age group:
- Common Causes
- Down syndrome, os odontoideum, Morquio syndrome
- Common Causes
- Rheumatoid arthritis, trauma, ankylosing spondylitis
- Common Causes
- Infection (Grisel syndrome), tumor, congenital anomalies
Guidance differs. The AAP and recent systematic-review evidence do not support routine cervical radiographs in asymptomatic children with Down syndrome; they favour clinical surveillance and neutral-position procedural precautions. A 2025 WFNS spine consensus recommends controlled flexion-extension screening in syndromic populations. For examination answers, name the guideline being applied rather than presenting either approach as universal.
Rheumatoid arthritis is a leading adult cause of atlantoaxial instability, and its cervical disease is a high-yield set. RA produces three instability patterns, usually in this order of frequency:
- Atlantoaxial subluxation (commonest) - pannus and ligament erosion increase the anterior ADI.
- Cranial settling (vertical / basilar migration) - lateral-mass erosion lets the dens migrate upward; the most dangerous pattern.
- Subaxial subluxation - multilevel "staircase" subluxation below C2.
The PADI prognostic rule: in the rheumatoid neck the anterior ADI correlates poorly with neurology because pannus and settling distort it. The posterior atlanto-dental interval (PADI - the space available for the cord, equivalent to the SAC) is the better predictor. Boden showed a PADI less than 14 mm predicts paralysis and poor recovery, whereas a PADI of 14 mm or more predicts good recovery potential after surgery. This is why, in RA, you weight the PADI/SAC over the anterior ADI, and why MRI (pannus, cord signal, cervicomedullary angle) guides the timing of fusion before irreversible myelopathy develops.
Anatomy and Pathophysiology
C1-C2 articulation: The atlantoaxial complex is unique in the cervical spine - it has:
- No intervertebral disc between C1 and C2
- Specialized ligamentous stability rather than bony congruence
- Allows 50% of cervical rotation (approximately 45 degrees each side)
Key stabilizing ligaments:
- Function
- PRIMARY restraint to C1 anterior translation
- Clinical Significance
- ADI greater than 5mm = failure
- Function
- Limit rotation and lateral bending
- Clinical Significance
- Secondary restraint
- Function
- Connects dens tip to foramen magnum
- Clinical Significance
- Secondary restraint
- Function
- Continuation of PLL
- Clinical Significance
- Provides additional stability
- Function
- Transverse + vertical bands
- Clinical Significance
- Holds dens against C1
The transverse ligament is the PRIMARY restraint to anterior translation of C1 on C2. Rupture or laxity of this ligament (from trauma, RA, or congenital conditions) is the main cause of atlantoaxial instability and increases ADI.
Biomechanics of instability:
In flexion:
- Normal: Transverse ligament prevents anterior C1 translation
- AAI: C1 slides forward on C2, narrowing SAC
- Severe: Cord compression between posterior C1 arch and dens
In extension:
- May allow some reduction of subluxation
- Less dangerous position for cord
Steel's Rule of Thirds:
- Anterior 1/3: Odontoid process
- Middle 1/3: Spinal cord
- Posterior 1/3: Safety space (allows some subluxation before cord compression)
Sudden neurological deterioration can occur with AAI during intubation, trauma, or sports. This includes quadriplegia or sudden death. All patients with known AAI require careful cervical spine precautions during any procedure requiring neck manipulation.
AAIAAI - Anatomy at Risk
Hook:AAI reminds you of the key structures - the transverse ligament is the most important
Classification Systems
Fielding-Hawkins Classification - Rotatory Atlantoaxial Subluxation
- Description
- Rotatory fixation, no anterior displacement
- ADI
- Normal
- Treatment
- Collar, reduction
- Description
- Rotatory fixation with anterior displacement 3-5mm
- ADI
- 3-5mm
- Treatment
- Halter traction, surgery if fails
- Description
- Rotatory fixation with anterior displacement greater than 5mm
- ADI
- Greater than 5mm
- Treatment
- Traction, likely fusion
- Description
- Rotatory fixation with posterior displacement
- ADI
- Variable
- Treatment
- Rare, usually traumatic
Types II and III indicate transverse ligament incompetence. Type I may be treated conservatively with collar, but types II-IV often require surgical fusion if reduction cannot be maintained.
Clinical Presentation and Assessment
History:
- Neck pain (may be occipital headache)
- Torticollis (especially rotatory subluxation)
- Weakness, clumsiness, gait disturbance
- Bowel/bladder dysfunction (late sign)
- History of Down syndrome, RA, or other predisposing condition
- Precipitating trauma or infection
Physical examination:
- Significance
- Rotatory subluxation
- Next Step
- CT to confirm, attempt reduction
- Significance
- Myelopathy
- Next Step
- Urgent MRI, surgical consultation
- Significance
- Cord compression
- Next Step
- Emergency stabilization
- Significance
- Possible AAI
- Next Step
- Flexion-extension X-rays
- Significance
- Myelopathy
- Next Step
- MRI, consider surgery
- Significance
- Asymptomatic AAI
- Next Step
- Activity modification, monitor
Red flags requiring urgent workup:
- Progressive weakness or numbness
- Gait deterioration
- Bowel or bladder dysfunction
- Respiratory compromise (high cord compression)
- Worsening headache with neck movement
Look for myelopathy signs: hyperreflexia, clonus, positive Babinski, Hoffmann sign, gait disturbance, hand clumsiness. These indicate cord compression and mandate urgent imaging and surgical consideration.
Investigations
- Lateral flexion-extension views - KEY for assessing instability
- Measure ADI in flexion (should be less than 3mm adult, less than 5mm child). Those are plain-film numbers. On multidetector CT 95% of uninjured adults measure under 2mm, so a CT atlantodental interval of 2 to 3mm passes the radiographic rule while lying outside the normal range (PMID 17893223; 200 consecutive adult CT studies, level 4) - the error runs towards calling an abnormal interval normal.
- Measure SAC (should be greater than 14mm)
- Open-mouth (odontoid) view - assess dens, lateral masses
- Standard AP and lateral views
- Best for bony anatomy
- Identifies os odontoideum, fractures, bony anomalies
- CT with 3D reconstruction for surgical planning
- Dynamic CT (flexion-extension) in select cases
- Essential if neurological symptoms
- Shows cord compression, signal change (myelomalacia)
- Identifies transverse ligament integrity
- Shows pannus (in RA)
- Rule out other cord pathology
- Normal
- Less than 3mm adult, less than 5mm child - but under 2mm on CT
- Abnormal
- Greater than 3mm adult, greater than 5mm child; on CT, above 2mm is already outside normal
- Normal
- Greater than 14mm
- Abnormal
- Less than 14mm (cord at risk)
- Normal
- Less than 1.0
- Abnormal
- Greater than 1.0 suggests anterior subluxation
- Normal
- Normal
- Abnormal
- T2 hyperintensity = myelomalacia
Management
Non-operative management:
Indicated for:
- Asymptomatic radiographic AAI with ADI less than 10mm
- SAC greater than 14mm
- No neurological symptoms
- Stable on dynamic imaging
- Activity modification (avoid contact sports, high-risk activities)
- Cervical collar for acute symptoms (soft or rigid)
- Regular clinical and radiographic surveillance (annual flexion-extension X-rays)
- Patient and family education about warning signs
- No contact sports (football, rugby, wrestling)
- No diving
- No activities with high cervical hyperflexion risk
- Trampolines contraindicated
Conservative management requires regular follow-up. Instruct patients and families about neurological warning signs. Any new symptoms mandate immediate evaluation and imaging.
Surgical Technique
The operation itself — graft choice, the anterior and transoral alternatives, and the rehabilitation that follows — is set out in atlantoaxial (C1-C2) fusion. What an instability viva turns on is narrower: the anatomy that constrains each construct, and which patient it rules out.
- Prone on Jackson table or Mayfield
- Head secured in Mayfield pins (or halo if preoperative traction)
- Neck in slight flexion for access, neutral for fusion
- Neuromonitoring: SSEPs and MEPs
- Midline incision from occiput to C3
- Subperiosteal dissection exposing C1 posterior arch and C2 lamina/spinous process
- Identify C1 lateral masses (limit lateral dissection to avoid vertebral artery)
- Identify C2 pars interarticularis and pedicles
- Expose surfaces for fusion (C1-C2 facet joints)
The vertebral artery runs in the foramen transversarium and is at risk during lateral C1 exposure. Stay within 15mm lateral to midline at C1. Use fluoroscopy to confirm screw trajectories.
Complications
- Incidence
- 3.1% (95% CI 2.3-4.3) with transarticular screws in pooled series; lower with modern segmental constructs and planning
- Prevention/Management
- Careful screw trajectory, preoperative CT angiography if anomaly suspected
- Incidence
- Under 5% with segmental screw constructs; 15-30% with wiring alone
- Prevention/Management
- Adequate decortication, bone graft, rigid fixation, postoperative immobilization
- Incidence
- 2-5%
- Prevention/Management
- Prophylactic antibiotics, meticulous sterile technique
- Incidence
- Variable
- Prevention/Management
- Intraoperative imaging, navigation if available
- Incidence
- Rare if done properly
- Prevention/Management
- Careful reduction, neuromonitoring, avoid overdistraction
- Incidence
- 1-3%
- Prevention/Management
- Adequate screw purchase, proper rod contouring
- Incidence
- Long-term
- Prevention/Management
- May accelerate adjacent segment degeneration - rare issue in children
- Incidence
- 5-10%
- Prevention/Management
- Avoid C2 nerve root injury, consider nerve sectioning if severe
- Most serious complication
- Can cause stroke, death
- Prevention: Preoperative CT/CTA if anatomy abnormal, careful screw placement
- Management: Control bleeding (bone wax, hemostatic agents), consider endovascular if ongoing
- More common with wire techniques than screw fixation
- Check with CT at 3-6 months
- May require revision with more rigid fixation
The C2 nerve root exits beneath C1-C2 facet. It may be sacrificed for better visualization or screw placement. This causes occipital numbness (greater occipital nerve) which is usually well tolerated.
Postoperative Care and Rehabilitation
Immediate postoperative:
- ICU or close monitoring initially
- Wound check, drain management
- Neurological checks hourly then 4-hourly
- Hard collar or halo (depending on fixation stability)
- DVT prophylaxis
- Remove drain (typically day 1-2)
- Upright X-rays in collar
- Begin mobilization
- Soft diet initially (pharyngeal swelling possible)
- Discharge planning
- Wear collar full-time (rigid collar)
- Wound review at 2 weeks
- No lifting, bending, or neck rotation
- Light activities of daily living
- School/work return (sedentary) at 4-6 weeks
- Flexion-extension X-rays at 6-8 weeks
- CT for fusion assessment at 3 months
- Begin weaning collar if fusion progressing
- Gradual activity increase
- CT confirmation of solid fusion
- Discontinue collar when fused
- Return to most activities
- Contact sports typically not recommended long-term
- Rigid collar (Miami J or Philadelphia) for 6-12 weeks
- Halo vest if very unstable or poor bone quality
- Soft collar for comfort transition
- No contact sports permanently (fused motion segment)
- No high-risk activities for 6-12 months
- Full activities (non-contact) when fusion confirmed
Understanding these activity limitations is important for patient counseling.
Outcomes and Prognosis
- Screw-rod constructs (Harms/Goel): 97-98% in pooled series; Magerl transarticular about 95%
- Wire techniques alone (Gallie, Brooks): 70-85%, with halo dependence
- Patients with myelopathy: 60-80% improve, 10-20% stable, 5-10% deteriorate
- Prophylactic surgery in asymptomatic: Prevents deterioration in vast majority
- Established myelomalacia on MRI: Less likely to fully recover
- Expected Outcome
- Excellent, maintain function
- Expected Outcome
- Good, most improve
- Expected Outcome
- Fair to good, majority improve
- Expected Outcome
- Guarded, stabilize but limited recovery
Loss of motion:
- C1-C2 provides 50% of cervical rotation
- Fusion results in 50% rotation loss
- Well compensated in most patients
- May cause some adjacent segment stress long-term
Earlier surgery = better neurological outcomes. Patients with mild myelopathy have high likelihood of improvement. Severe, established cord damage (myelomalacia on MRI) has limited recovery potential - emphasizes need for timely intervention.
Guidelines, Registries & Global Practice
OrthoVellum is a worldwide resource. The principles below are framed for any board worldwide, with regional guidance cited as evidence rather than as the frame.
Global epidemiology:
- Burden of AAI
- Radiographic AAI ~6.8-27% (age-dependent); symptomatic in under 1-2%
- Source
- FSEM 2020; Pueschel & Scola 1987
- Burden of AAI
- Atlantoaxial subluxation prevalence tracks disease activity; falling with modern DMARD/biologic therapy
- Source
- Veldman 2022
- Burden of AAI
- Commonly associated with instability; may be congenital or post-traumatic
- Source
- Grob 1992 (biomechanics of fixation)
- Burden of AAI
- Pooled 137 operated patients across 51 studies
- Source
- Hofler 2019
Major guidance, side by side:
- Recommendation
- No routine asymptomatic radiographic screening in Down syndrome; use symptom-based myelopathy surveillance, neutral-position procedural precautions, and targeted imaging for clinical concern
- Evidence level
- Practice guideline (Level V)
- Recommendation
- Individualised clinical assessment for sport rather than blanket radiographic exclusion; catastrophic sports injury extremely rare
- Evidence level
- Position statement (Level V)
- Recommendation
- Rigid screw-rod (Goel-Harms) or transarticular (Magerl) fixation preferred over wiring for unstable C1-C2
- Evidence level
- Level III-IV technique evidence
- Recommendation
- Operate for myelopathy, progressive instability, ADI greater than 10mm or SAC less than 14mm with concern; reduce before fusing
- Evidence level
- Level III-IV
No dedicated joint registry exists for upper-cervical fusion (unlike hip/knee arthroplasty), so the best comparative evidence is pooled observational data. The Hofler 2019 meta-analysis [PMID 30790735] shows screw-rod constructs outperform wiring for union and complications in Down syndrome, and Badhiwala 2017 [PMID 28098742] reports 96.7-100% fusion with C1-C2 screw constructs.
- High-resource settings: navigation/robotics, CT angiography for vertebral artery mapping, and intra-operative neuromonitoring (SSEP/MEP) are routine for screw-rod constructs.
- Limited-resource settings: wiring techniques (Gallie/Brooks) supplemented by halo or prolonged rigid immobilisation remain in use where image guidance and polyaxial implants are unavailable, accepting higher non-union rates.
- Paediatric pathways: managed in tertiary paediatric spine units with transition to adult services at skeletal maturity and lifelong post-fusion activity counselling, regardless of health system.
MCQ Practice Points
High-yield MCQ facts:
-
Normal ADI: Less than 3mm adults, less than 5mm children
-
SAC less than 14mm indicates cord at risk - surgical consideration
-
Transverse ligament is the PRIMARY restraint to anterior C1 translation
-
Down syndrome has radiographic AAI in roughly 6.8-27% (age-dependent; FSEM 2020) but only 1-2% symptomatic
-
Steel's Rule of Thirds: 1/3 dens, 1/3 cord, 1/3 safety space
-
Harms technique (C1 lateral mass + C2 pedicle screws) is current gold standard for C1-C2 fusion
-
Os odontoideum - 60% have associated AAI, treat if unstable
-
Myelomalacia on MRI (T2 hyperintensity) indicates established cord injury - limited recovery potential
-
Vertebral artery at risk during C1 lateral mass screw placement - stay within 15mm of midline
-
Fusion rate: 97-98% with screw-rod constructs (about 95% for transarticular screws) vs 70-85% with wiring alone
Q: What is the normal ADI in children? A: Less than 5mm (vs less than 3mm in adults). The difference is due to greater ligamentous laxity in children.
Q: What SAC measurement indicates cord at risk? A: SAC less than 14mm indicates the spinal cord is at risk of compression. SAC less than 10mm is critical.
Q: What percentage of Down syndrome patients have symptomatic AAI? A: Only about 1-2% become symptomatic (1.5% needed surgery in Pueschel's 404), despite radiographic instability in roughly 6.8-27% depending on age. This is why routine screening is no longer recommended.
Q: What is the primary ligamentous restraint to anterior C1 translation? A: The transverse ligament is the PRIMARY restraint. The alar and apical ligaments are secondary restraints.
Q: What percentage of cervical rotation is lost after C1-C2 fusion? A: Approximately 50% of cervical rotation occurs at C1-C2. This loss is generally well tolerated functionally.
Q: Is routine screening X-ray recommended in Down syndrome? A: NO. The AAP 2022 guidelines no longer recommend routine screening X-rays - it is now symptom-based. However, many institutions still require pre-surgical screening. Know both guidelines and common practice.
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 6-year-old boy with Down syndrome requires general anaesthesia for dental extractions. The anaesthetist requests cervical spine clearance. How would you assess this patient?”
“A 12-year-old with Down syndrome presents with progressive gait deterioration and hyperreflexia. X-rays show ADI of 12mm and SAC of 10mm. MRI shows cord compression with T2 hyperintensity. How would you manage this patient?”
“A 14-year-old presents with neck pain after a minor fall. CT shows an os odontoideum with ADI of 7mm in flexion. She is neurologically intact. What is your management plan?”
Key Numbers
- ADI greater than 3mm adult, greater than 5mm child = abnormal
- SAC less than 14mm = cord at risk, less than 10mm = critical
- Down syndrome: radiographic AAI roughly 6.8-27% (age-dependent), 1-2% symptomatic
- C1-C2 provides 50% cervical rotation
- Fusion 97-98% with screw-rod constructs vs 70-85% with wiring alone
- Vertebral artery safety zone: within 15mm of midline
Critical Anatomy
- Transverse ligament = PRIMARY restraint to anterior C1 translation
- Alar and apical ligaments = secondary restraints
- Steel's Rule of Thirds: 1/3 dens, 1/3 cord, 1/3 safety space
- Vertebral artery - stay within 15mm of midline at C1
- C2 pedicle trajectory: medial 20-25 degrees, cephalad 20 degrees
Surgical Indications
- Neurological symptoms (myelopathy)
- ADI greater than 10mm (even if asymptomatic)
- SAC less than 14mm with concern
- Os odontoideum with instability
- Progressive instability on serial imaging
Surgical Technique
- Harms technique = gold standard (C1 lateral mass + C2 pedicle screws)
- Achieve reduction BEFORE fusion
- Neuromonitoring essential (SSEPs, MEPs)
- Autograft bone for pediatric patients
Complications
- Vertebral artery injury (3.1%, CI 2.3-4.3 with transarticular screws; lower with segmental constructs) - most serious, CT angiography for planning
- Nonunion (under 5% with segmental screw constructs; 15-30% with wiring alone)
- C2 nerve root sacrifice - causes occipital numbness, usually tolerable
- Hardware failure - more common with poor bone quality
- Adjacent segment degeneration - long-term consideration
Viva Essentials
- Down syndrome screening: now symptom-based (AAP 2022)
- MRI mandatory before surgery and if symptoms present
- Early surgery = better neurological outcomes in symptomatic patients
- T2 hyperintensity = established myelomalacia = guarded prognosis
- Os odontoideum: 60% have AAI, treat if unstable (ADI greater than 5mm)
- Preoperative halo traction for significant subluxation
Evidence Base
Harms and Melcher - Posterior C1-C2 Fusion with Polyaxial Screw and Rod Fixation
- Described individual polyaxial screw fixation of the C1 lateral mass and C2 pedicle connected by rods in 37 patients. The construct permits fluoroscopically controlled reduction after screw insertion and avoids the fixed-alignment and structural-graft requirements of transarticular screws. Solid fusion was reported in all patients with no neural or vascular injury.
Pueschel and Scola - Atlantoaxial Instability in Individuals with Down Syndrome
- Examined 404 individuals with Down syndrome. Atlantoaxial instability was present in 59 (14.6%): 53 (13.1%) asymptomatic and 6 (1.5%) symptomatic requiring surgery. Atlanto-dens interval measurements were significantly greater in flexion than in neutral or extension, confirming the need for dynamic views.
Grob, Crisco, Panjabi et al - Biomechanical Evaluation of Four Posterior Atlantoaxial Fixation Techniques
- In ten cadaveric specimens with sectioned alar, transverse and capsular ligaments, transarticular (Magerl) screw fixation, Brooks and Halifax constructs all controlled motion significantly better than the Gallie wire construct in flexion-extension, axial rotation and lateral bending. The Magerl transarticular screw tended to allow the least rotation.
Hofler, Pecoraro, Jones - Surgical Correction of AAI in Down Syndrome (Systematic Review and Meta-analysis)
- Pooled 137 Down syndrome patients across 51 studies. Screw-and-rod constructs achieved significantly greater bony union and lower rates of revision, loss of reduction or pseudarthrosis, halo use and early neurological decline than wiring alone (all p less than 0.05). Wire-and-rod constructs also fused better than wiring alone.
Badhiwala et al - C2 Nerve Root Transection during C1 Lateral Mass Screw Placement (Systematic Review and Meta-analysis)
- Across 8 studies (393 patients), bony fusion after C1-C2 screw fixation ranged 96.7-100%. Sacrificing the C2 nerve root reduced blood loss (mean -195 mL) and operative time (mean -57 min) and increased occipital numbness, but did not change the rate of occipital neuralgia.
Bull, Trotter, Santoro et al - Health Supervision for Children and Adolescents With Down Syndrome
- The AAP does not recommend routine cervical-spine radiographs in asymptomatic children with Down syndrome because films do not reliably predict later cervical disease. Symptomatic children should receive neutral radiography first and prompt specialist assessment; flexion-extension views may be considered with the specialist when the neutral film is not significantly abnormal.
Tomlinson et al / FSEM (UK) - Sport Preparticipation Screening for Asymptomatic AAI in Down Syndrome
- The UK Faculty of Sport and Exercise Medicine position statement reports AAI in 6.8-27% of the Down syndrome population (varying with age), with less than 1-2% later developing symptomatic AAI. It notes catastrophic sports-related cord injury is extremely rare and promotes safe physical activity rather than blanket exclusion.