6. Spine MCQs

Patients with ankylosing spondylitis are highly susceptible to highly unstable shear fractures of the cervical spine even after minor trauma. Because these fractures are easily missed on plain radiographs due to altered anatomy, a CT scan is mandatory for any AS patient presenting with neck pain after a fall.

DISCUSSIONThe findings on MR imaging reveal a right-sided L4-L5 disk extrusion with cephalad migration of the disk fragment. The axial image shows marked displacement of the traversing right L5 nerve root. The physical findings noted in Response 4 above are typical of a right L5 sensory and motor radiculopathy that would be associated with this level of disk extrusion. Although an extrusion at this level can affect the exiting L4 nerve root resulting in an L4 radiculopathy as described in Response 1, the findings described in this response are contralateral to the disk herniation and not likely to be present. The other responses describe findings associated with left and right S1 radiculopathy, which more typically are associated with an L5-S1 disk herniation/extrusionRECOMMENDED READINGSHoppenfeld S: Orthopaedic Neurology: A Diagnostic Guide to Neurologic Levels. Philadelphia, PA, JB Lippincott, 1977, pp 7-49.Haak MH. History and physical examination. In: Spivak JM, Connolly PJ, eds. Orthopaedic Knowledge Update: Spine 3. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2006:43-55.

During the transition from standing to sitting, a normal pelvis retroverts (tilts backward), which functionally increases the anteversion of the acetabulum, providing clearance for the femur and preventing anterior impingement/posterior dislocation. In a patient with a stiff lumbar spine (e.g., prior fusion or ankylosing spondylitis), this dynamic pelvic retroversion does not occur. As a result, the functional anteversion of the cup remains fixed, predisposing the anterior femoral neck to impinge on the anterior rim of the cup, levering the head out posteriorly. To compensate for this lack of dynamic pelvic mobility, the surgeon should intentionally increase the operative anteversion (and often inclination) of the acetabular component to prevent posterior dislocation in flexion.

Patients with a long lumbar fusion to the pelvis have a 'stiff spine' and lose normal spinopelvic mobility. Normally, when moving from standing to sitting, the lumbar spine flexes and the pelvis tilts posteriorly (retroverts), functionally increasing acetabular anteversion to accommodate hip flexion and prevent anterior impingement. In a stiff, fused spine, the pelvis fails to retrovert upon sitting. This lack of dynamic functional anteversion leads to anterior impingement of the femur on the acetabulum during sitting, which dramatically increases the risk of posterior dislocation. To compensate, the surgeon must place the acetabular component in higher combined anteversion and slightly higher inclination than standard targets.

The patient has a flexion-distraction injury of the thoracolumbar spine that is often associated with wearing a seat belt. The fracture has a high risk of associated intra-abdominal injury; therefore, the initial evaluation should include a CT of the abdomen. The most common visceral injury is to the bowel.

The patient is showing signs of vertebral artery stroke. The signs of Wallenberg syndrome include those listed above, as well as contralateral loss of pain and temperature sensation throughout the body, an ipsilateral Horner’s syndrome, dysphagia, and ataxia. Vertebral artery injuries are not unusual in significant cervical facet injuries. A lesion in the cervical spinal cord is not associated with these symptoms, and an intracranial hemorrhage from trauma is unlikely to present in this manner.

During the initial healing phases of a dural tear, pia and arachnoid from adjacent nerve roots migrate, fill the dural defect, and create a pia-arachnoid plug. It is this initial plugging of the defect that is believed to prevent further egress of cerebrospinal fluid through the defect. The plug has been shown to develop by the second postoperative day. Fibroblastic proliferation occurs within the dura itself and accounts for the bulbous ends of the dura seen in the photomicrograph. The appearance of the material within the dural edges is inconsistent with the appearance of neural elements, and scar tissue formation occurs later in the healing process.

Denis Zone III sacral fractures involve the central sacral canal. These injuries carry a high risk (up to 60%) of cauda equina syndrome, presenting as bowel, bladder, and sexual dysfunction.

Denis Zone III sacral fractures involve the central sacral canal and carry a very high risk (>50%) of cauda equina syndrome. Injury to the lower sacral nerve roots classically results in saddle anesthesia, as well as bowel, bladder, and sexual dysfunction.

The arrow is pointing to a structure of medium signal intensity that is equivalent to the nucleus pulposus on T2-weighted sequencing. This represents a foraminal disk herniation. A lumbar synovial cyst would display high-signal intensity on T2-weighted sequencing. Lumbar synovial cysts arise from the facet joints as a result of facet joint degeneration and may be a source of nerve root compression. The dorsal root ganglion is a collection of sensory nerve cell bodies and can be seen just dorsal and lateral to the disk herniation in Figure 32. The ligamentum flavum is located on the ventral surface of the laminae and attaches between the laminae of adjacent vertebrae.

A normal spine allows the pelvis to tilt posteriorly during sitting, dynamically increasing functional acetabular anteversion and preventing anterior impingement. A fused spine fails to tilt posteriorly. To compensate and prevent posterior dislocation while seated, the cup must be placed in a higher degree of anteversion than standard.

Postoperative peroneal nerve palsy after correction of a severe valgus deformity is often due to traction. Initial management involves relieving tension on the nerve by removing constrictive dressings and flexing the knee.

Patients with a fused flatback lack normal spinopelvic mobility and cannot increase pelvic tilt when sitting, leading to relative acetabular retroversion and a high risk of posterior dislocation. Compensating by placing the cup in higher anteversion and inclination helps accommodate sitting clearance.

Patients with a stiff spinopelvic junction lack the normal posterior pelvic tilt when transitioning from standing to sitting. This lack of tilt fails to functionally increase acetabular anteversion, leading to anterior impingement and posterior dislocation; thus, more anteversion is often required.

DISCUSSIONThe figures are characteristic of a child with Klippel-Feil syndrome (congenital cervical spine abnormalities) in association with congenital scoliosis in the upper thoracic spine and a right-sided Sprengel deformity (congenital elevation of the scapula). Sprengel deformity occurs in as many as 30% of children with Klippel-Feil syndrome. Other congenital conditions that are commonly associated with Klippel-Feil, and that should be screened for, include deafness in 30%, genitourinary abnormalities in 25% to 35%, and cardiovascular abnormalities in 4% to 29% of children with Klippel-Feil syndrome.In Sprengel deformity, there is usually a tether called the omovertebral connection between the abnormally elevated scapula and the spinous processes in the upper thoracic region. This tether is most commonly bony but also may be cartilaginous or fibrous. Although there also may be abnormalities in the ribs, clavicle, or humerus, they are morphologic abnormalities only, not tethers.Patients with Klippel-Feil syndrome should be discouraged from participating in contact or collision sports if they have a massive fusion of the cervical spine, any involvement of C2, or limited cervical motion. Fusions at 1 or 2 interspaces below C3 and normal cervical motion do not preclude participation in activities. A Sprengel deformity may limit abduction of the shoulder and normal racquet or throwing mechanics, but, in the absence of pain, is not a contraindication to attempted participation.Klippel-Feil syndrome affects a heterogenous cohort of patients and different inheritance patterns have been seen, including autosomal-dominant and autosomal-recessive types, with varying levels of penetrance. The first human Klippel-Feil syndrome locus was identified on chromosome 8 and is called SGM1. Other candidates for mutations in Klippel-Feil include PAX genes and Notch pathway genes. In general, the involved genes help regulate the formation and segmentation of the vertebrae.Between days 20 and 30 following conception, the paraxial mesoderm subdivides into segments called somites. As they mature, somites develop into 3 layers called the sclerotome, myotome, and dermatome. The sclerotome undergoes a process of resegmentation during which the caudal section from 1 somite joins with the rostral section of the immediately caudal somite to form the vertebral bodies. It is during the processes of segmentation and resegmentation that the abnormalities leading to Klippel-Feil syndrome occur. Gastrulation refers to the phase early in embryonic development when the single-layered blastula is reorganized into a trilaminar structure with 3 germ layers: the ectoderm, mesoderm, and endoderm. Neurulation refers to the process by which the notochord induces formation of the neural tube from the neural plate, forming the brain and spinal cord.

Symptoms of activity-related low back pain, physical findings of pain with extension, lateral bending, and resuming an upright position, and relative hamstring tightness are consistent with spondylolysis. While the initial diagnostic work-up should include plain radiographs of the lumbosacral spine, the findings may be negative because it can take weeks or months for the characteristic changes to become apparent. SPECT has been a useful adjunct in the diagnosis of spondylolysis when plain radiographs are negative.

Neural monitoring during scoliosis surgery was initially developed to avoid the devastating effects of spinal cord injury, particularly paraplegia. Somatosensory-evoked potentials in the lower extremities will detect many but not all neurologic difficulties with the spinal cord. Anterior spinal cord vascular disruption also can be detected by monitoring motor potentials. Electromyography following stimulation of lumbar pedicle screws can prevent nerve root injury that is the result of misplacement of the screws. This is best documented in the lumbar spine and has not been routinely used in the thoracic spine. The most common neural deficits following spinal surgery, however, are in the upper extremities because of the positioning of the patient in the prone position for long periods. In Schwartz and associates' series of 500 patients, impending upper extremity neural injury was detected by somatosensory-evoked potentials in 18 (3.6%) patients. In contrast, lower extremity deficits were detected by combined motor- and sensory-evoked potentials in only 2 (0.4%) out of 500 patients in Padberg and associates' series. Neural compression in the upper extremity can be easily detected by somatosensory-evoked potentials, and injury can be prevented by repositioning the patient.

The change noted is focal and confined to the cortex, sparing the opposite side, both lower extremities, and the subcortical waveforms, making all the choices unlikely with the exception of carotid compression with focal cortical ischemia. This may be associated with poor collateral flow from the opposite hemisphere due to an incomplete circle of Willis.

Cervical laminectomy is an accepted treatment for multilevel cervical spondylotic myelopathy. When the compression is posterior, laminectomy addresses it directly; when the compression is anterior, it is addressed indirectly (the spinal cord floats posteriorly away from the anterior compression). Preexisting kyphosis is a contraindication to laminectomy because the cord is unable to float posteriorly away from the anterior compression, and the risk for increasing kyphosis is significant. Kyphosis after laminectomy is more likely to develop in younger patients who have fewer degenerative changes to stabilize the spine.

Disruption of the posterior ligamentous complex is an important determinant of the stability of a burst fracture. This patient is neurologically intact and his MR images do not reveal posterior ligamentous complex (PLC) disruption. The standing radiograph confirms that overall alignment is acceptably and relatively preserved. Nonsurgical treatment with or without a brace is acceptable in this scenario.