Lumbar spine trauma and cauda equina

An organ system that includes bone and cartilage, muscles, tendons, ligaments and joints is known as musculoskeletal system. Low back spine injuries can be fractures which affect the bone, herniation which affect the disk, sprain which affects ligaments or muscles, (Truumees, 2007). Common injuries of the spine are associated with falls from a height and motor vehicle accidents. When a force is exerted to the lumbar spine and exceeds the stability and strength of the spinal column it results in a fracture, (Nadalo, 2007). In trauma this can result in impingement of the nerves and can cause cauda equina syndrome. Cauda equina syndrome involves weakness in the legs, bladder paralysis and bowel, (Larson & Maiman, 1999).

Truumees (2007) suggests that there is a range of fractures that are linked with the spine. These range from compression fractures, where the bone collapses to when pieces of bone explode into the tissue known as burst fractures. Fracture dislocations are the worst as the bones break and slide away from each other; ligaments are torn in the process. Normally these situations require surgery. This essay focuses on lumbar spine trauma and cauda equina.

Primary imaging protocol for investigating spinal pathology comprises conventional (CR) radiography, computed tomography (CT), and magnetic resonance imaging (MRI), (Kim, 2009). Nuclear medicine can also be used post-surgery. MRI is the modality of choice for cauda equina.

The spinal cord extends from the foramen magnum to L1-L2 disc space. It is continuous with the medulla oblongata and terminates in the conus medullaris. Below this level the nerve roots running inferiorly are collectively called the cauda equina. The cauda equina runs within the spinal canal, which is bordered anteriorly by the vertebral bodies and posterior by the dorsal bony arch, (Vaccaro, 2003).

The membranous layers covering the spinal cord are referred to as the meninges. The meninges consist of three layers; the Dura, arachnoid and pia mater. The Dura is attached anteriorly to the posterior longitudinal ligament. The pia mater is composed of a superficial layer epi-pia and a deep layer pia-glia, (Clark & Letts, 2001).

The first changes evident in spinal cord anatomy following traumatic injury are punctate haemorrhages in the gray and white matter. The movement of the lumbar spine is largely confined to flexion and extension with a minor degree of rotation. The region between the superior articular process and the lamina is the pars interaticularis, (Nadalo, 2007).

As indicated above the fractures of the lumbar spine occur any time the combined forces of compression, distraction, and rotation exceed the strength of the spinal column. The predominant force determines the nature of the fracture dislocation. It is common that axial rotation occurs in the upper lumbar region. With great rotational forces, subluxation and a combined fracture occur, and this results with the injury to the conus medullaris. Compression of the conus medullaris and nerve roots results in weakness and pain, (Clark & Letts, 2001).

Any injury that involves the spinal cord is serious. If the conus medullaris is injured patients will have problems with the bowel, bladder and sexual function. A group of individual nerves called cauda equina are found below the conus medullaris. Pressure on these nerves can cause long term leg weakness, bowel and bladder problems therefore is treated as an emergency, (Truumees, 2007).

Cauda equina can be diagnosed by clinical examination and evaluating history. The symptoms associated with the compression of the lumbar or sacral nerve roots include; weakness of muscles below the knees, impairment of skin sensation in the saddle area, difficult micturition, and radiating symptoms which can be pain, tingling or numbness. Constipation representing change in bowel habits can also be a symptom. It is known to have poor prognosis but the only way of improving it is early diagnosis and operative treatment, (Shephard, 1959).

Spinal intervertebral disc distribute the forces that travel through the whole spine. They lie between two adjacent vertebral bodies and act as shock absorbers. Disc herniation occurs when the inner nucleus pulposus ruptures through the weakened annulus (outer layers) of the disc. Disc herniation in the lower back can be due to trauma. Symptoms include lower back pain, leg pain, numbness or weakening and tingling of one or both legs. In serious cases nerves to the bowel and bladder can be compressed leading to incontinence, (Knaub, 2007).

Compression from large central lumbar disc herniation at L4/5 and L5/S1 level is a common cause of cauda equina. Thickening of the ligamentum flavum and degenerative changes as a result of spinal stenosis is another cause of cauda equina. Spinal injury with fractures or subluxation is another less common cause. Compression can also be caused by spinal neoplasm of metastatic lesions, (Lavy, James, Wilson-MacDonald & Fairbank, 2009).

The symptoms are less predictive although they are associated with the impairment of the bladder, bowel and sexual function and to some extend perianal (saddle numbness). Cauda equina results from dysfunction of many sacral and lumbar nerve roots. It is also believed to be caused by interverbral disc herniation. Loss of perianal sensory and sphincter disturbance and this could be with or without urinary retention. Complete cauda equina has established urinary retention and incomplete cauda equina there is reduced urinary sensation, (Lavy, James, Wilson-MacDonald & Fairbank, 2009).

With disc herniation, if the degenerative process progresses, small circumferential fissures develop in the fibrosus, which later coalesce to form radial, tear. Distinction between focal extrusion of disc material and a circumferential enlargement is important, as the former is typically treated surgically, whereas the later can be treated conservatively. Disc herniation refers to a focal, incomplete extension of the contents of the nucleus pulposus through an incomplete tear of the annulus fibrosus, (Lee, 2006).

Imaging of the spine can be performed by conventional radiography (CR), ultrasound (US), computerised tomography (CT), digital subtraction angiography (DSA) or magnetic resonance imaging (MRI). With conventional radiography, anteroposterior (AP), lateral and oblique projections of the vertebral column should be obtained. CR provide valuable information regarding bony structures of the spinal column, facet joints, disc spaces, and foramina while limited information regarding the paraspinal soft tissues can be obtained. The spinal cord is well seen with US in the first few months of life, (Browner, 2003).

Multislice CT demonstrates the vertebral column, vascular structures and disc very well together with better visualisation of the spinal cord and paraspinal soft tissues while conventional CT demonstrates the vertebral body and posterior elements very well with only limited visualisation of the soft tissue and spinal cord. DSA is used for imaging and interventional procedures of spinal vascular structures. DSA is time consuming, invasive technique that has the disadvantages of high levels of radiation. MRI imaging has become the modality of choice for imaging of the spinal cord, thecal sac, nerve roots, epidural space, vascular structures, neural foramina, vertebral body, intervertebral discs, facet joints, spinal ligaments and paraspinal soft tissue, (Goethem, Hauwe & Parizel, 2007).

Trauma patients with pain in the lumbar sacral region require lateral and AP radiologic views. If these studies are negative but clinical symptoms are suggestive, further imaging by CT is indicated. CT is helpful in characterising complex injuries such as fracture dislocations and in distinguishing burst fractures from anterior compression fractures. Acute onset of radicular symptoms after acute trauma may warrant CTM or MRI to exclude acute intervertebral disc herniation, (Browner, 2003).

Radiographic evaluation starts with the AP (supine) and lateral radiographs. When clinically inappropriate a horizontal beam with the patient recumbent is taken instead of the lateral position. Initial evaluation of the overall alignment of the thoracolumbar junction and lumbar spine is clearly assessed with a lateral radiography taken in the supine position. Many fractures demonstrate not only a comminution of the vertebral body but also a local area of kyphosis. Oblique projections should be obtained only when the AP and lateral radiographs are inconsistent with the clinical evaluation. The patient's condition must also allow the rotation into the oblique position. The oblique projections provide excellent visualisation of the pars interaticularis and the facet joints, (Browner, 2003).

When viewed in an oblique projection, the outline of the facets and the pars interaticularis appear like the neck of a Scottie dog, (Nadalo, 2007). Soft tissue swelling may indicate a fracture even if the fracture is not directly visualized. Structures that are best seen on the oblique views include the transverse process, pedicle and the pars interaticularis.

Plain X ray is advantageous as it is readily available and inexpensive. It also provide a rapid assessment of a specific spinal region and depending on the patient ability, weight bearing and dynamic views maybe obtained. Conventional radiography is useful in confirming normal osseous structures, vertebral alignment and structural integrity of the spine, (Devlin, 2003).

On the contrary plain x ray has low sensitivity and specificity in identifying symptomatic spinal pathology. It cannot visualise neural structures and other soft tissue lesions (disc herniation). It is limited in the diagnosis of early stage tumour or infection because significant bone destruction must occur before a radiographic abnormality is detectable, (Devlin, 2003).

CT allows images to be obtained in any plane to demonstrate the pathology in question. Multi-planar computed tomography is CT with routinely obtained sagittal and coronal reformatted images. Multi-planar CT including three dimensional CT is currently the imaging technique of choice for spinal injury. The value of CT is in the axial image, which demonstrates the neural canal and the relationship of the fracture fragments to the canal. Axial data obtained in the supine patient are converted electronically into images displayed in the sagittal and coronal planes, without requiring movement of the patient. (Browner, 2003)

Thin-section axial CT scanning with a bone algorithm is the single most sensitive means by which to diagnose fractures of the lumbar spine. Routine helical CT scans of the lumbar spine are valuable because multi-section CT scanners can generate high-resolution spinal images, even during a primary multi-systemic evaluation for trauma. Good-quality CT images can be used to identify more lumbar spine injuries than conventional radiographic studies, (Oskouian, & Johnson, 2002).

The improvements in CT technology, introduced with spiral CT and the newer multi-detector array systems create the potential for CT to provide screening of the thoracic and lumbar spine as part of a routine thoracic cavity and abdominal-pelvic CT study in a multiple trauma patient. Single-slice or spiral CT used in conjunction with scout AP and lateral radiographs may ultimately provide more accurate identification of lumbosacral injuries than is achieved with conventional radiography, (Browner, 2003).

CT is known to be the best for bone anatomy assessment and the use of multiple cross sectional images which can be reconstructed to provide images in orthogonal planes is an added advantage. It is the main substitute when MRI is contraindicated, (Devlin, 2003). CT scans are quick and have the ability to image several body regions without moving the patient. Computed tomography has an advantage over MRI for the evaluation of post-operative stenosis due to arthrosis, (Stoller, 1997).

The disadvantages of CT follow the exposure to ionizing radiation. It provides poor delineation of neural elements and adjacent structures. Ligaments, disc, dural sac, and nerve roots appear as different shades of gray. Significant pathology can be missed. Sagittal images are not routinely reconstructed at many institutions, (Devlin, 2003). CT does not distinguish between post-surgical fibrosis (scarring) and a recurrent disc lesion even with the use of contrast agents of which MRI can, (Stoller, 1997).

MRI is unique in its ability to detect acute injury to the spinal cord. Fat appears bright on T1 images and less bright on T2 images. T1 images are good for evaluating structures that contain fat, haemorrhage or proteinaceous fluid as they demonstrate high signal. T2 images are weighted towards water. Water appears bright on T2 images and dark on T1 images. T2 images are most useful in contrasting normal and abnormal anatomy, (Devlin, 2003).

Atlas (2008) suggest that cord odema appears isointense in relation to the normal spinal cord on T1-weighted spin echo images but becomes brighter than normal spinal cord on T2-weighted image sequences. MRI signals have the ability to identify the histopathology of acute spinal cord injury. MRI depicts normal ligaments as regions of low signal intensity because of lack of mobile hydrogen. Disruption of the ligament is seen on MRI scans as an abrupt interruption of the low signal, ligament attenuation or stretching of ligament, association of a torn ligament with an attached avulsed bone fragment, (Browner, 2003).

The focus is usually on spinal structures when interpreting spine MRI examinations and only the routine sagittal and axial images are used. Coronal scout images are acquired for localisation purpose before each routine lumbar spine MRI examination. This routine usually includes the hip joints and proximal femurs, (Lavelle & Bell, 2007).

Acute intervertebral disc herniation may accompany fractures or dislocations or may occur as an isolated lesion. If the disc impinges on the spinal cord or roots, a neurologic injury may result. MRI demonstration of a single-level acute intervertebral disc herniation is crucial in surgical management in spinal trauma to optimise neurologic recovery, (Browner, 2003).

Lumbar spine MRI can demonstrate many vertebral fractures and most abnormalities of alignment. MRI is superior to CT in the identification of indirect signs of a fracture such as pre-cervical edema or haemorrhage, epidural bleeding, and sprains of the paraspinal and intra-spinal ligaments. Associated injuries to intracranial structures are evaluated better by using MRI than by using CT images, (Jarvik, Bowen & Ross, 2001).

MRI avoids ionizing radiation and provides imaging in orthogonal planes which makes it advantageous over other modalities. It can be used to visualise an entire spinal region and avoids missed pathology at transition zones between adjacent spinal regions. It also provides exquisite soft tissue contrast resolution and excellent visualisation of intrathecal neural elements. MRI is sensitive to marrow abnormalities, (Atlas, 2008).

Implanted devices are contraindications to MRI and claustrophobic patients may have difficulty because of the small diameter of the imaging machine, (Devlin, 2003). According to Brant & Helms, (2007) MRI is limited in its ability to demonstrate dense bone detail or calcifications. It involves long imaging times for many pulse sequences and possess limited spatial resolution compared to CT. MRI has limited availability in some geographical areas, and is expensive.

The principal treatment for unstable lumbar spine fractures is surgical fixation with spinal canal decompression as needed. A posterior approach involves pedicular fixation in which 2 segments are fused. The procedure results in both fracture reduction and fixation. The injured vertebra is grafted through the pedicle. Clearance of bone fragments from within the spinal canal is an important goal for most surgical approaches to lumbar spine fractures. Patients with complete paraplegia can be expected to remain unchanged, (Holmes, Miller & Panacek, 2001).

As for cauda equina syndrome surgical decompression is recommended after confirmation by MRI imaging of reversible cause of pressure, (Lavy, James, Wilson-MacDonald & Fairbank, 2009).

New MR imaging techniques such as diffusion (DWI), perfusion (PWI), functional imaging (FMRI) and magnetic resonance spectroscopy (MRS) provide more specific, detailed and physiological information about the spine and spinal cord and also enable quantitative evaluation. Contrast enhanced (high dose) spinal MRA is a very promising technique, particularly for screening examinations of the spinal veins and arteries, (Goethem, Hauwe & Parizel, 2007). Work and research is being carried out to improve the speed of MRI scanning and maintenance of image quality.

The development of the multi-slice CT technology with 0.5 second gantry rotation allows up to eight axial images to be acquired per second is expected to expand to more images per second in the near future. Addition of more detector arrays is anticipated to lead to further increases in the speed of image acquisition and improvements in image quality, (Browner, 2003). According to Armstrong, Wastie and Rockall (2004) the recent multi-detector CT can acquire up to sixteen slices during one rotation of the x-ray tube. The examination can be performed much faster allowing many more thinner slices which in turn allows high quality multi-planar and three dimensional reconstructions as well as CT angiography.

According to Brant & Helms (2007) multi-detector helical CT (MDCT) is the latest technical advancement in CT imaging. It uses the principle of the helical scanner but incorporates multiple rows of detector rings. This optimises acquisition of multiple slices per tube rotation. It increases the area of the patient that can be covered in a given time by the x ray beam.

Brant & Helms (2007) also states that "available systems have moved from two slices to 64 slices, which covers 40mm of the patient length for each 1-second or less rotation of the tube." Photo-type 256-detector scanners are being developed. The advantage of MDCT is speed. This allows image reconstruction in any anatomical plane without loss of resolution. The downfall of MDCT is radiation dose. As the diagnostic capability of CT expands, so does its utilisation. The advancement in technology is carrying with it an increase in radiation exposure to each patient imaged.

The use of paraspinal ultrasound is limited to the localization of pleural effusions, which is usually associated with upper lumbar spine and chest wall injury. Paraspinal abscess may be localized prior to aspiration in selected patients. Because of the proximity of the kidneys and urethras to the lumbar spine, the findings may indicate perinephric haemorrhage or urinary obstruction. The primary findings of soft tissue swelling and possible haemorrhage are not specific to lumbar trauma, (Nadalo, 2007).

Nuclear medicine studies have a limited role in the acute phase of lumbar spine injury. Nuclear medicine studies can be used for patients with congenital abnormalities. RNI can differentiate an acute fracture from a failure of an epiphysis endplate to fuse, (Nadalo, 2007).

A bone scan cab be obtained after a day and will demonstrate an increased uptake in the area of a fracture. A longer delay may be necessary to identify some fractures. Back pain caused by a non displaced facet injury or pedicle fracture, is associated with an area of increased uptake. RNI bone imaging is fairly sensitive. It is not specific for trauma. Single-photon emission computed tomography (SPECT) imaging should be used in all patients with suspected spinal trauma if bone scan is required. SPECT imaging improves accuracy and specificity, (Devlin, 2003).Bone scan using RNI and additional tests will include Bone densitometry. Dual energy x-ray absorptiometry (DEXA) is used to assess bone mass.

Contrast media add a great value to CT and magnetic contrast provides useful diagnostic information with MRI. The common agents used in MRI are gadolinium compounds. Contrast enhanced MRI in magnetic resonance angiography and CT angiography are gradually replacing conventional angiography, (Armstrong, Wastie and Rockall, 2004).

In osteoporotic fractures of the lumbar spine, chronic pain is relieved with the use of injections of radiopaque bone cement. Usually this is performed using fluoroscopic or CT guidance. The semi-solid cement is injected using imaging control to avoid spilling the cement into the epidural spaces. The resulting cast supports the vertebral endplate relieving pain in patients, (Ryu, Park, Kim, & Kang, 2002).

Surgical repair of anterior decompression, posterior fusion with decompression, and the use of multi-segmental hook system, adds spinal canal diameter and multiple points of distraction on the same spinal rod. If the cause of compression is removed, patients usually do not lose further code or cauda equina function after anterior decompression. Patients with conus medullaris injury have neurogenic bowel and bladder recovery, (Guiot & Fessler, 2002).


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