Klippel-Feil Syndrome

Klippel-Feil syndrome (KFS) is congenital fusion of two or more cervical vertebrae, the result of a failure of normal segmentation of the cervical somites during the 3rd to 8th weeks of gestation. The block itself is immobile; the trouble arises at the segments left mobile beside it, and in what else was affected at the same time.

Who. Prevalence is estimated at 1 in 40,000 to 42,000 births, and is likely under-reported because asymptomatic cases exist. There is a slight female predominance (60%). Most cases are sporadic; autosomal dominant and autosomal recessive forms exist, with GDF6, GDF3 and MEOX1 mutations identified.

The classic triad. The textbook description has three parts:

1. Low posterior hairline
2. Short neck
3. Limited cervical range of motion

Fewer than 50% of patients have all three, so the absence of the triad excludes nothing. Limited cervical range of motion is the most consistent single sign.

Natural history. Many patients with limited fusion (Type I) are asymptomatic and live normal lives. Symptomatic patients present with neck pain, radiculopathy or myelopathy, usually in the 2nd or 3rd decade, as the overdriven segments adjacent to the block degenerate.

Associations. KFS overlaps the VACTERL spectrum of segmentation and formation defects, and the diagnosis obliges a deliberate search for what else is affected. Hensinger's series of 50 patients established the constellation, and because it was a referral series its frequencies are likely upper estimates. Scoliosis is the commonest association, ahead of renal anomalies.

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Embryology. The vertebral column forms from the sclerotomes, and dividing them into segments requires precise regulation through the Notch signalling pathway. KFS is a failure of segmentation, to be contrasted with the hemivertebra, which is a failure of formation.

Which levels. The patterns to know:

• C2-C3 - most common; often autosomal dominant
• C5-C6 - second most common; autosomal recessive association (MEOX1)
• Occipitocervical - rare but dangerous

Biomechanics of the block. The fused segment is immobile, so the level above or below must compensate to maintain head motion, and that level experiences increased stress and range of motion. This hypermobility can lead to ligamentous laxity and frank instability. On flexion-extension views the segment moves excessively compared with normal, the appearance called wash-boarding.

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Samartzis's classification is the one to use, because the pattern of fusion predicts who gets into trouble. Feil's 1919 scheme is historical and less useful for prognosis.

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The most dangerous fusion pattern in KFS sits at the top of the spine. Occipitalization (atlanto-occipital assimilation), congenital fusion of the atlas to the occiput, concentrates motion at C1-C2 and opens the door to two linked problems.

Atlantoaxial instability. With the occiput-C1 segment fused, the C1-C2 joint becomes the compensating mobile level and can become unstable, threatening the cord at the cervicomedullary junction.

Basilar invagination. Progressive superior migration of the odontoid through the foramen magnum can compress the brainstem and upper cord and produce myelopathy, sleep apnoea or sudden death. The risk rises with the number of fused segments: four or more fused levels confer roughly a sevenfold risk of significant superior odontoid migration (more than about 4.5 mm), and occipitalization is an independent predictor.

What to do about it. In a long or high fusion, deliberately assess the craniovertebral junction for instability and invagination, because it is the lesion most likely to be catastrophic. Flexion-extension views test reducibility and occult instability, and superior odontoid migration is measured rather than described qualitatively. CT defines the bony lesion behind an abnormal dynamic study; review the canal, the facets and the C1-C2 relationships in every plane before deciding whether decompression, reduction and fixation are required. MRI supplies the neural-axis answer that CT cannot, so image the entire craniovertebral junction and cord for Chiari malformation, compression, syringomyelia and myelomalacia before treating the visible block vertebra.

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History. Parents notice a short neck or asymmetry, or that the child turns the whole body rather than the head. Ask about neck pain, which is mechanical, and radicular symptoms from nerve compression, and about weakness or clumsiness, which are signs of myelopathy.

Inspection. Look for:

• A short neck, the head appearing to sit on the shoulders
• A low hairline
• A webbed neck (pterygium colli), to be differentiated from Turner syndrome
• Torticollis or facial asymmetry
• Sprengel's deformity, a high scapula

Range of motion. Rotation and lateral bending are usually restricted; flexion and extension may be preserved if segments are open.

Neurology. Test reflexes, strength and sensation. Hyperreflexia or a positive Hoffmann's sign indicates myelopathy. Mirror movements (synkinesis), involuntary movement of one hand when the other moves, indicate failure of decussation of the corticospinal tracts.

Screening. You must examine for the other anomalies: listen for a heart murmur and check for scoliosis.

Plain radiographs. Three static views and a dynamic pair:

• AP
• Lateral
• Open-mouth odontoid
• Flexion and extension laterals, which are critical

The flexion-extension views are read for instability, translation greater than 3.5 mm or angulation greater than 11 degrees, and for hypermobility at the adjacent segments. The static films show the wasp waist, a narrowing at the fused disc space, with loss of disc height and fusion of the posterior elements (facets and laminae).

CT is best for bony architecture. It defines the extent of fusion, anterior versus posterior, and is the planning study before surgery.

MRI of the whole spine is mandatory if there are neurological signs or before surgery. It assesses cord compression from stenosis at the adjacent levels and screens for Chiari malformation, syringomyelia and diastematomyelia.

Renal ultrasound screens for agenesis and the other renal anomalies.

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Sprengel's deformity, a congenitally high, hypoplastic, medially rotated scapula from failure of scapular descent, is often the visible clue to the diagnosis, and it deserves its own assessment and plan. The quoted frequency varies with how the cohort was assembled: Hensinger's referral series found it in 21 of 50 patients (42%), while figures nearer a quarter to a third are commonly cited from other series, so quote "roughly a third, higher in referred and syndromic cohorts" rather than a single number.

Grading. Cavendish grades clinical severity from Grade 1, very mild and invisible when dressed, to Grade 4, severe, with the superomedial scapular angle near the occiput and neck webbing.

The omovertebral bone. In a substantial minority a fibrous, cartilaginous or bony bar tethers the superomedial scapula to a lower cervical spinous process or lamina. It restricts abduction and must be excised when the scapula is released.

Surgery. Repositioning is for function and cosmesis and is usually done around age 3 to 8 years, when remodelling and functional gain are greatest. The Woodward procedure detaches the medial parascapular muscle origins and reinserts them more inferiorly; the Green procedure is an extraperiosteal muscle detachment with cable traction. Either is combined with excision of the omovertebral bone and resection of the prominent superomedial scapular angle.

The hazard. Bringing the scapula down risks brachial plexus traction injury. Many surgeons add a clavicular osteotomy (morcellation) before repositioning to reduce this risk during caudal translation, and excising the omovertebral bone and superomedial angle lets the scapula descend without over-stretching the plexus.

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A short, stiff neck or congenital cervical fusion has several mimics. The key is to distinguish a true segmentation failure from acquired fusion and from syndromic short-neck appearances.

Algorithm

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Non-operative care is the mainstay for most patients, Type I and stable Type III. Regular follow-up monitors for symptoms of degeneration. Physiotherapy maintains range of motion and strength but avoids aggressive manipulation, which risks injury, and NSAIDs treat mechanical neck pain. Always counsel on the importance of avoiding high-velocity trauma.

Sport. Collision sports are avoided, per the Torg guidelines, in any of:

• Multi-level fusion (Type II or III)
• C1-C2 involvement
• Stenosis
• Demonstrated instability

Swimming, cycling and non-contact sports are allowed.

Operative indications. Surgery is reserved for instability or neurological compression:

• Progressive myelopathy
• Intractable radiculopathy
• Demonstrated instability
• Significant deformity (rarely for cosmesis alone)

Procedures. Decompression and fusion treats instability or stenosis, and the segment fused is the hypermobile adjacent one. Posterior fusion is often preferred in children to avoid an effect on anterior growth. Deformity correction by osteotomy is high risk.

Before the incision. Anomalous vertebral arteries are common in KFS. The artery normally enters the transverse foramen at C6; in KFS it often enters higher, at C4 or C5, so pre-operative CTA or MRA is recommended to map both arteries, and they are always screened before any screw is placed. Limited neck extension means a difficult airway is anticipated; intubate with a fibreoptic scope.

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Prognosis follows the Samartzis type described in the classification section, and is further modified by the associated anomalies. Life expectancy is generally normal unless severe cardiac or renal anomalies are present.

Living with the block. Open segments bear increased stress and degenerate early, so accelerated adjacent segment disease is a long-term concern. Patients with stable spines who avoid contact sports generally have good function, and jobs involving heavy lifting or neck strain may need activity modification.

After surgery. Fusion rates for posterior cervical fusion are generally high, greater than 90%, with good pain relief and neurological improvement in appropriately selected patients. Adjacent segment disease can progress despite a successful fusion, and revision may be required for pseudarthrosis or adjacent-level pathology.

The team. Optimal management needs orthopaedics, paediatrics, cardiology, nephrology and genetics working together to address the full spectrum of associated anomalies.

Global epidemiology

• Estimated prevalence approximately 1 in 40,000-42,000 live births, with under-reporting because many single-level (Type I) blocks are asymptomatic and found incidentally.
• Slight female predominance reported across series. Most cases are sporadic; familial autosomal dominant (often C2-C3, GDF6) and autosomal recessive (often C5-C6, MEOX1) forms are described.
• KFS overlaps the VACTERL spectrum and syndromes such as fetal alcohol syndrome, Goldenhar (oculo-auriculo-vertebral) and Wildervanck syndrome.

Side-by-side guidance (no single-country frame)

Registry context

• There is no disease-specific KFS implant registry; KFS is rare and surgery is uncommon. Cervical instrumentation outcomes are extrapolated from national spine and arthroplasty registries and from paediatric deformity databases rather than KFS-specific data.

High- vs limited-resource practice variation

• Well-resourced settings: routine MRI of the whole neuraxis, CT angiography/MRA for vertebral artery mapping, intra-operative neuromonitoring, and panel genetic testing (GDF6, GDF3, MEOX1, RIPPLY2).
• Limited-resource settings: diagnosis often rests on plain radiographs and a careful clinical examination; renal ultrasound (cheap, high-yield) remains the single most valuable screening test; advanced imaging and genetics may be unavailable, raising the importance of clinical screening for cardiac murmurs, hearing loss and scoliosis.

Which fusion pattern is truly "most dangerous"? Classic teaching emphasises the Type II intercalated open segment as the biomechanical risk for instability. However, the Samartzis 2006 cohort found radiculopathy/myelopathy in both Type II and Type III, with Type III carrying the highest neurologic rate. The honest answer for examiners: neurologic risk lives in multi-level patterns (Type II and III), and a single radiograph cannot fully predict an individual's trajectory.

Sports clearance thresholds are consensus, not trial-based. The Torg framework is built from registry data and expert opinion; there is no randomised evidence defining a safe level of collision-sport exposure in KFS. Practice therefore errs toward caution, particularly for high (C1-C2) or long fusions.

Prophylactic stabilisation is not established. There is no high-level evidence supporting prophylactic fusion of an asymptomatic hypermobile adjacent segment. Surgery remains reserved for instability, progressive deformity, or neurologic compromise.

Genetic heterogeneity. GDF6, GDF3, MEOX1 and RIPPLY2 explain only a minority of cases; many patients have no identified mutation, and newer panels implicate additional candidate genes. Genotype-phenotype correlation remains weak, limiting prognostic use of genetics.

Optimal screening cadence is undefined. While renal ultrasound and echocardiography at diagnosis are widely accepted, the frequency and duration of subsequent cervical surveillance imaging are not standardised across societies.