Block Vertebrae

► [Congenital synostosis between two or more adjacent vertebrae]

The term 'block' vertebrae is applied to congenital synostosis of vertebrae in which bony continuity results from failure of normal segmentation of the vertebral somites at the preosseous stage during embryonic development (3-8 weeks of gestation). 'Fusion' is also widely used for these segmentation errors, although semantically it refers to intervening union between previously well-developed vertebrae and is therefore more appropriate for the acquired forms.

Congenital block vertebrae can occur as an isolated malformation or in association with other conditions, and may involve two or more contiguous vertebrae (Fig. 3.29). The vertebral body, the posterior elements, or both structures may be affected (Fig. 3.30). The intervertebral disc may be completely absent or may appear as a rudimentary irregularly calcified structure (Fig. 3.31).

Congenital 'bar' is the term applied to describe the osseous fusion between contiguous laminae (laminar bars) or pedicles (pediculate bars) in the vertebral arch. These are usually unilateral and unbalanced abnormalities, so that they tend to produce severe changes in spinal alignment, with the bar in the concavity of the curve. These bars may be cartilaginous in young children, thus precluding direct radiographic visualization of the tethering effect on one side of the spine.

Block vertebrae can be seen at any level in the spine. In the cervical spine, C5-6 fusion is the most common site, followed by C2-3. Cervical fused vertebrae cause restriction of motion, short neck, torticollis, and neurological abnormalities of variable degree, depending on the extent of involvement and the type and number of the associated malformations. Abnormal degrees of motion at the unfused levels may be responsible for impingement on neural structures. In the thoracic and lumbar spine, vertebral fusion is often limited in ex-

Synostosis Spine Lumbar

Fig. 3.29. Congenital block vertebrae involving L-1 through L-3. Impaired growth of involved vertebrae has resulted in concavity of their anterior surface in the shape of an inverted 'C' ('wasp waist' appearance) and lumbar kyphosis. Note atrophic intervertebral discs, and degenerative changes at the adjacent disc levels

Acquired Vertebral Surgical Block

Fig. 3.31. Isolated block vertebrae at C3-4.Note that fusion involves the vertebral bodies and posterior elements. The disc space is absent posteriorly, and rudimentary anteriorly. The constriction at the level of the intervertebral disc produces a wasp waist appearance

Fig. 3.29. Congenital block vertebrae involving L-1 through L-3. Impaired growth of involved vertebrae has resulted in concavity of their anterior surface in the shape of an inverted 'C' ('wasp waist' appearance) and lumbar kyphosis. Note atrophic intervertebral discs, and degenerative changes at the adjacent disc levels

Fig. 3.30. Congenital block vertebrae. Observe ankylosis of the second and third cervical vertebrae, involving both the vertebral bodies and posterior elements. The intervertebral disc is atrophic and contains minimal calcification. Note also fusion of the atlas with the skull base

Fig. 3.31. Isolated block vertebrae at C3-4.Note that fusion involves the vertebral bodies and posterior elements. The disc space is absent posteriorly, and rudimentary anteriorly. The constriction at the level of the intervertebral disc produces a wasp waist appearance tent and asymptomatic. However, significant changes in the spinal alignment are sometimes encountered, as discussed in more detail later in this chapter.

Block vertebrae in the cervical spine are currently designated Klippel-Feil syndrome (OMIM 148900). Other vertebral anomalies may be part of this sequence, including hemivertebrae, atlanto-occipital fusion, and stenosis of the cervical spinal canal. Frequent clinical signs include webbed neck, torticollis, and facial asymmetry. Primary or secondary neurological deficits may also arise, and especially cranial nerve palsies, hemiplegia, and paraplegia. The following defects have been found nonrandomly associated with Klippel-Feil sequence: deafness, whether sensorineural, conductive, or mixed; congenital heart defects; mental retardation; cleft palate; rib defects; Sprengel anomaly (failure of descent and lateral migration of the scapula); scoliosis; and renal abnormalities (Jones 1997). The name 'Klippel-Feil' probably includes several disorders, most of which are sporadic while a few have autosomal dominant inheritance and variable expression. The first classification system was based on the extent of vertebral fusion and included three morphologic types of Klippel-Feil anomaly: type I, characterized by exten

Klippel Feil Type

Fig. 3.30. Congenital block vertebrae. Observe ankylosis of the second and third cervical vertebrae, involving both the vertebral bodies and posterior elements. The intervertebral disc is atrophic and contains minimal calcification. Note also fusion of the atlas with the skull base

Klippel Feil Syndrome Pictures
Fig. 3.32. Klippel Feil syndrome (KFS), class I. Malsegmentation of the cervical spine, with fusion involving the posterior elements caudal to C-1. There is a clear interspace at C4-5 and fusion of C-5 through C-7 in association with a very short neck. (From Clarke et al. 1998)

Fig. 3.33. KFS in a child in class II. Note block vertebrae at C2-3 and C4-5, involving the vertebral bodies and posterior elements. Also note degenerative changes at C3-4. (From Clarke et al. 1998)

sive fusion into bony blocks of cervical and upper thoracic vertebrae; type II, consisting of fusion of two or three vertebrae; and type III, characterized by fusion in the cervical, lower thoracic, and/or lumbar spine, together with rib fusions (Klippel and Feil 1912). A fourth type of cervical vertebral fusion has been suggested,in which cervical fusion is associated with sacral segmentation defects (Raas-Rothschild et al. 1988). Confusion arising from the wide variability of vertebral fusion within affected families has prompted researchers to develop other classification systems, based not only on the location of vertebral fusion but also on the etiology and genetic origin of the syndrome (Gunderson et al. 1967; Clarke et al. 1998). Three classes have been recognized, in which numbering denotes the position of the most rostral fusion in the class. Class I, recessive, fusion involves C-1 and other vertebrae to a variable extent; the neck is very short (Fig. 3.32). Class II, dominant, fusion involves C2-3 and other vertebrae below this level; craniofacial anomalies predominate (Fig. 3.33). Class III, recessive with reduced penetrance, isolated cervical fusion occurs at any level except C1-2; single C5-6 fusion is included (Lubs et al. 1963); craniofacial anomalies are variably associated (Fig. 3.34). Congenital defects of the spinal cord or brain may occur in association with Klippel-Feil syndrome, including cervical cord dysraphism or diastematomyelia and Chiari I malformation (Ulmer et al. 1993). Suggested gene locations of the Klippel-Feil gene are 5q11.2, 8q22.2, and 17q23. Wildervanck syndrome (cervico-oculo-acoustic syndrome, OMIM 314600) is a combination of Klippel-Feil sequence, congenital conductive deafness, and abducens palsy with retractio bulbi (Duane syndrome) (Wildervanck 1960). The disorder affects only females, probably as a result of sex-linked dominance with lethality in the hemi-zygous male. The deafness is due to a bony malformation of the inner ear. Multifactorial inheritance with limitation to females is likely (Wildervanck 1978).

Among the different forms of arthrogryposis multiplex congenita,the distal type II (OMIM 108130) implies congenital contractures predominantly involving the hands and feet and a combination of other defects, including fused cervical vertebrae, webbed neck, kyphoscoliosis, congenital hip dislocation, cleft lip and palate, micrognathia, ptosis, and short stature (Hall et al. 1982; Reiss and Sheffield 1986).

Multiple pterygium syndrome (Escobar syndrome, OMIM 265000) consists in pterygia of the neck, axillae, and popliteal fossae, sternal deformity, male hypogonadism, multiple joint contractures, and short stature. Skeletal anomalies include cervical vertebral

Surgical Block Vertebra

Fig. 3.33. KFS in a child in class II. Note block vertebrae at C2-3 and C4-5, involving the vertebral bodies and posterior elements. Also note degenerative changes at C3-4. (From Clarke et al. 1998)

Failure Segmentation And
Fig. 3.34. KFS, class III. Note congenital fusion at C5-6, involving the vertebral bodies and posterior elements. The intervertebral disc is atrophic, with minimal disc calcification. (From Clarke et al. 1998)

fusion, scoliosis, flexion contraction of fingers, and clubfoot with vertical talus (Chen et al. 1980). The possible occurrence of abdominal muscle defects, together with joint contractures, suggests some overlap with prune-belly syndrome (OMIM 100100), in which urinary tract anomalies are prominent (Welling et al. 1975). This pterygium syndrome also has some overlap with the autosomal dominant Noonan syndrome (OMIM 163950), in which pterygium colli, deformed sternum, cryptorchidism, and myocardiopathy (coarctation of the aorta, pulmonary stenosis, patent ductus arteriosus) are cardinal features (Noonan 1968). Nuchal skinfold redundancy and pterygium colli are related to prenatal posterior cervical hygroma and can therefore be diagnosed prenatally (Witt et al. 1987). Patients with Noonan syndrome may have some features of LEOPARD syndrome (OMIM 151100) (Mendez and Opitz 1985; Coppin and Temple 1997). This acronym is used to designate the association of multiple lentigines, electrocardiographic conduction abnormalities, ocular hypertelorism, pul-monic stenosis, abnormalities of genitalia, retardation of growth, and sensorineural deafness (Gorlin et al. 1969). Skeletal abnormalities in this syndrome include cervical spine fusion, fusion of the posterior arches,spina bifida occulta,bone age delay,kyphosco-liosis, pectus carinatum or excavatum, rib anomalies, hypermobile joints, cubitus valgus, and syndactyly.

LEOPARD syndrome also has similarities with Watson syndrome (OMIM 193520), an association of pulmonic stenosis, café-au-lait spots, dull intelligence, and short stature. Neurofibromas and Lisch nodules are possible associated features in this disorder, which is allelic to neurofibromatosis type 1 (OMIM 162200) (Upadhyaya et al. 1992).Vertebral fusions in the cervical spine are also found in the asymmetrical short stature syndrome (OMIM 108450), a disorder resembling both Silver-Russell syndrome (OMIM 180860) and Hallermann-Streiff syndrome (OMIM 234100), which consists in asymmetrical short stature, facial anomalies (small nose,mandibular hypoplasia, dental crowding, esotropia, hyperopia), and skeletal defects (scoliosis,limb-length asymmetry, abnormal shape of the vertebral bodies, carpal bones, and ribs) (Jung and Smith 1980). While it is known that cervical fusion occurs more frequently in patients with Crouzon syndrome (craniofacial dysostosis, OMIM 123500) and Apertsyndrome (OMIM 101200),it is only recently that evidence has been provided showing that fusion is also very common in patients with Pfeiffer syndrome (acrocephalosyndactyly, OMIM 101600) (Anderson et al. 1996).

Goldenhar syndrome (oculo-auriculo-vertebral complex, OMIM 164210) consists in a nonrandom association of defects among which vertebral anomalies, including blocked vertebrae, hemivertebrae, supernumerary vertebrae, and hypoplastic vertebrae, are prominent features. A spectrum of anomalies closely resembling the Goldenhar complex, including the vertebral and craniofacial malformations, has also been reported in infants born to diabetic mothers (Ewart-Toland et al. 2000).

Acquired causes of vertebral fusion include inflammatory articular diseases, infectious processes, trauma and surgical procedures (implanted bone graft). Radiographic abnormalities in juvenile chronic arthritis are most prominent in the cervical spine, and consist in atlanto-axial subluxation, odontoid erosion, and apophyseal joint space narrowing and ankylosis. Apophyseal joint fusion is often predominant in the upper cervical spine and eventually progresses caudally to involve several, or even all, cervical vertebrae (Fig. 3.35). The vertebral bodies and disc spaces are hypoplastic, owing to growth disturbances possibly related to the early onset of the disease. The spinous processes are usually spared. In ankylosing spondylitis, spinal abnormalities initially appear in the thoracolumbar and lumbosacral junctions and may subsequently extend to the remainder of the spine. Classic radiographic abnormalities include thin, vertically oriented syndesmophytes

Vertebral Bodies Arthritis
Fig. 3.35. Juvenile chronic arthritis. Note extensive bony ankylosis of the apophyseal joint, associated with relative hypoplasia of the vertebral bodies and disc spaces

across adjacent vertebrae; ligamentous ossification; sclerosis and erosions of the anterior corners of the vertebral bodies; apophyseal joint fusion and capsule ossification; discovertebral erosions and sclerosis; and odontoid erosion with atlanto-axial subluxation. In the cervical spine, apophyseal joint fusion may extend to several levels, simulating juvenile chronic arthritis. In the latter condition, the presence of vertebral and disc space hypoplasia is distinctive (Resnick and Niwayama 1995).

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  • Ren Mauer
    What is a blocked vertebra at c56?
    7 years ago
  • mikaela uppa
    When would block veterbrae occur?
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  • Tristan
    When does block vertebrae occur?
    3 years ago
  • marigold
    What is blocked veetebrae?
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