Function and Structure of Spine

1.0 Introduction

The spine is central support structure of the body which functions to keep us upright by connecting the different parts of our skeleton together. These parts include the skull, ribcage, pelvic girdle, shoulder girdle, long bones of the upper limbs and lower limbs. It is made up of bones, intervertebral discs and elastic ligaments which make it flexible. It has an average length of 71cm and 61 cm in men and women respectively. It allows the movement of the body while at the same time bearing the weight of the skull, long bones of the upper limbs and torso. The human spine is naturally slightly curved and is divided into four parts. These are the cervical area found in the neck region, the lumbar region which covers the lower region of the back and these have an inward curvature. The cervical spine which is found in the neck area is the most flexible part of the spine. The outer curvature consists of sacral and thoracic curvature. The inner part of the spine is the spinal cord which is protected by vertebrae which cover it. An injury to the spinal cord refers to an insult or trauma which results in either temporary or permanent change in the motor-sensory or autonomic functions of the central nervous system. This causes permanent and devastating deficits in the patient’s neurological system and as a result can cause extensive disability (Joseph et al, 2017). The American Spinal Injury Association (ASIA) defines the extent of injury using an impairment scale where category A represents complete injury with a complete loss of sensory and motor function in the sacred segments. B represents the loss of only sensory function while the motor function is preserved below neurological level (. The prevalence of SCI in the US is about 250000 and 500,000 people and about 40,000 people in the UK. In the UK there are 2500 new injuries per year. In the US SCI is mainly caused by violence. In the UK SCI is mainly caused by falls and road traffic accidents. Other causes of SCI are stiff falls and injuries sustained in sporting activities. All the causes of SCI can be prevented. In its severe form, SCI affects systems in the body that regulate breathing, blood pressure, control of bladder and heart rates. Most cases of SCI greatly reduces a person’s quality and leads to increased mortality to about two to five times like those who have not suffered such an injury. SCI increases the risks of developing secondary conditions such as deep vein thrombosis, infections of the urinary tract, chronic pain, osteoporosis, muscle spasms and complications of respiration. These conditions add to the burden of care for persons suffering from SCI. SCI may completely incapacitate a person so as to make them completely dependent on caregivers and may require assistive technology to enable them to communicate, for mobility and for daily living (Qin, Bauman and Cardozo, 2011). SCI is expensive to manage and because of these secondary conditions.

Inadequate medical care and rehabilitation services can exacerbate patient outcomes in some countries. Barriers in the physical, policy and social environment further escalate the consequences of SCI. A careful investigation of the level and extent of the injury and the development of secondary conditions associated with injury is necessary to plan for acute and long-term care and rehabilitation of persons suffering from SCI. Various musculoskeletal tissue changes occur after an injury to the spinal cord. These changes occur also as a result of miscommunication involving the brain and body parts below the location of the injury and involve a reduction in size and composition of the musculoskeletal system. These changes include muscle atrophy, contractures, osteopenia, fractures, heterotrophic ossification overuse syndrome and changes in posture.

1.1 Aim of the study

i. To analyze the musculoskeletal changes following spinal cord injury

ii. To analyze literature on imaging techniques used in imaging SCI

iii. To evaluate the use of CT for imaging of SCI

Literature review

2.1 Musculoskeletal changes following spinal cord injury

2.1.1Fractures

Fractures are a common secondary complication which results from spinal cord injury. The incidence of fractures is 2.2% on average and its first occurrence after spinal cord trauma is about eight years (Eser et al. 2010). Fractures predominantly affect the lower extremities and mainly occur in the diaphyseal or distal femur and also the proximal lower leg (Kralj et al. 2015). The typical fracture type in persons suffering from SCI is low energy fractures which are normally referred to as fragility fractures. The risk of fractures’ in chronic SCI is increased by the extensive bone mass loss which occurs in the paralysed extremities. There is a 50% decrease in bone density of the lower extremities following spinal injury (Cirningliaro et al. 2017). This reduction in bone density is associated with an increase in the prevalence of fractures to about two fold that of able bodied individuals (Gutie’rrez, Soto and Rada, 2017). Women with spinal cord injuries show a greater risk of suffering from fractures of the long bones as compared to their male counterparts and thus women are more risks of fractures. Patients with lesions are more prone to fractures especially those with lumbar lesions as compared with cervical lesions (Frotzler et.al 2015). Several complications in chronic SCI patients result from the presence of fractures. These include non-union, decubitus ulcers, venous thromboembolic events, mal-alignment, mal-union and venous thromboembolic events (Bethel et al. 2015).

2.1.2 Muscle atrophy

Muscle atrophy is the adaptation of the skeletal system following spinal injury. The skeletal muscle has been shown to experience a reduction in size to about 45% that of persons not suffering from spinal injury (Power et al. 2016). The cause of muscle atrophy has been stipulated to be the result of a loss in central activation followed by unloading. It causes glucose intolerance and insulin resistance and may result into the development of type II diabetes (Li et al.2017). It has also been shown that there is a relationship between muscle atrophy and intramuscular fat accumulation especially in patients suffering from stroke and elderly patients with complete chronic SCI (Gorgey and Dudley, 2007). There are two types of atrophy that is muscle atrophy and disuse atrophy. Denervation atrophy results following the loss of communication between the muscles while disuse atrophy is the failure of the muscles to undergo voluntary contraction. In disuse atrophy the brain still has communication with the muscle but a lack of physical activity and disuse leads to muscle atrophy (Thomas et al. 2016).

2.1.3 Contractures

Contractures are a common complication resulting from SCI and are characterized by a loss in passive range of motion of the joints (Hardwick et al. 2018). Identification of contractures is important for the identification of appropriate treatments (Moriyama et al. 2019). Quantitative measurements can be done using goniometer. It is however recommended that visual and physical assessments be used to diagnose a loss the range of motion of the joints unless the loss in range of motion of the joints can be felt or seen (Watanabe et al. 2015). If the loss in joint range of motion is subtle it should only be classified as contracture if it has marked implications on the function, hygiene, quality of life and skin management (Schubert, Dietz, 2018). When there is loss of movement at the joints muscles tendons and ligaments shorten causing contraction. This loss of movement can substantially reduce a person's functional morbidity (Ragnarsson, 2015).

2.1.4 Osteopenia

Osteopenia results when there is more bone breaks down as compared to bone creation leading to decreased bone density and is a secondary complication following chronic SCI. The injury is immediately followed by a rapid and linear decline in both the mass and the density of the sublesional bone. The bones which are specially affected are the ones found in the metaphyseal and epiphyseal areas of the distal femora and proximal tibiae. The bone lost is so much than it is many folds time that which happens during prolonged bed rest, microgravity or even early menopause. The mineral content of the bone is also substantially reduced (Lan et.al. 2013). There is also an increase in the levels of type I collagen C-telopeptide and N-telopeptide in the urine a marker of increase in the bone resorption as early as two weeks following injury and a continual increase in these markers peaking between the second and fourth month after injury while the markers for bone formation are either found to be either normal or increased (Jiang, Dai, Jiang, 2006). This further suggests that during the acute phase of chronic SCI bone resorption might be responsible for the loss in bone mass (Zamarioli et al. 2013). As the chronic SCI becomes chronic the loss in bone mass continues and may result into the person suffering from fractures following even minor traumas such as transfer from a bed, bending, motion exercises or minor falls (Biering‐Sørensen et al. 2009). Persons who have suffered from SCI suffer from osteopenia because they lack the ability to bear weight. Osteopenia leads to risks of breaking of bones otherwise referred to as bone fractures (Battaglino et al. 2012). Persons suffering from SCI experience abnormal stress in their backs, long bones of the upper limbs and neck and this is a potential source of fractures, following spinal cord injuries one may experience heterotrophic ossification which is the formation of bones in places which are abnormal for instance in the soft tissues leading to stiffening of the muscles on joints and as results causing pain and reduced or lack of motion (Qin, Bauman and Cardozo, 2011). The sublesional fractures resulting from bone mass loss are associated with a delay in union and nonunion making them very difficult to treat (Lin et al. 2013).

Unlike other forms of osteoporosis, osteoporosis following chronic SCI is not characterized by demineralization in supralesional areas. The bone mass loss in chronic SCI is also subject to factors such as age and sex of the individual, the degree to which they are injured, muscle spasticity and the duration after injury. The long bones of the sublesion area show more demineralization than their counterparts in the lumbar spine. It takes about 2 years after chronic SCI to reestablish a balance between bone formation and resorption (Jiang, Dai, Jiang, 2006)

2.1. 5Heterotrophic ossification

Heterotrophic ossification is the abnormal bone formation occurring in soft tissues mostly around joints such as the, knees, hips, shoulder girdle and elbows. Its first indicators are normally swelling of these joints and inflammation and limited range of movement of the joints. The presence of hyperemia and pain are also symptoms of Heterotrophic ossification. Heterotrophic ossification is connected to elevation in the levels of alkaline phosphate in the serum. The presence of heterotrophic ossification can be confirmed using CT and X-rays where the formation of a calcified bone or triple phase bone preceding calcification can be detected. A further confirmation can be done using MRI and ultrasound. This adaptation of the musculoskeletal system following chronic SCI occurs within the first 2-3 weeks following injury and has a variable occurrence ranging from 10-53% in SCI patients.

2. 1.6 Overuse syndrome

Spinal cord injuries put much pressure on the long bones of the upper limbsas much as motion is now carried out by the arms. This overuse places much danger of breakage of the long bones of the upper limbs and more especially at the shoulder girdle, proper body mechanics are necessary to prevent this form of harm after SCI (D’Souza et al. 2017). Overuse mainly occurs at the musculotendinous junction and can also occur in the cartilage, bursa and bone. It causes pain and discomfort to individuals suffering from spinal cord injuries. Overuse experience depends on the severeness of SCI, the age of the individual, the duration one has been injured, the use of a wheelchair, sitting posture, the stability of the shoulder joint and the body mass index of the individual. Overuse syndrome is thus more common in elderly people as compared to young people and in women as compared to men. Overuse is especially experienced by persons who use wheelchairs and may limit their ability to perform some activities such as reaching for something overhead. The most prevalent overuse syndrome is shoulder girdle pain which mostly occurs in people who use crutches, canes and manual wheelchairs. Overuse injuries in the elbows cause the straining of tendons and muscles and entrapment of nerves. Overuse syndromes of the wrist result into carpal tunnel syndrome. The management and diagnosis of SCI requires the use of imaging technology as an integral part. These techniques can be used to evaluate both chronic and acute injuries of the spinal cord. They are useful for confirming the exact location of injury, for assessing the stability of the spine and to determine the compromise occurring to the neurons following spinal trauma. Imaging can be used to surgical interventions of spinal injury. The most commonly used imaging techniques are radiology, computerized tomography and magnetic resonance imaging. Together with these there are new imaging techniques that have been adopted or are being currently tested these include diffusion tensor imaging (DTI), MR spectroscopy (MRS), positron emission tomography (PET), single photon emission computed tomography (SPECT), and functional MRI (fMRI. MRI has been used in conjunction with clinical features to help provide a clear picture of the morphological sequence of spinal cord lesion. After about 3 weeks from the time of the injury, the MR signal has been able to indicate edema and hemorrhage. It has also pointed to the formation of a well-demarcated cyst at about six months.

2.2 IMAGING TECHNIQUES USED FOR SPINAL CORD INJURY

2.2.1 Magnetic resonance imaging (MRI)

The MRI trauma protocol consists of images which are sagittal T1-Weighted, T2-weighted, short tau inversion recovery (STIR) and T2 or T2* weighted axial sequences. Sagittal T1-weighted images provide an excellent description of the anatomy of the spine. STIR or T2-weighted images with fat saturation lead to an increase in the visibility of edema occurring in the bones and ligaments and the abnormalities of the discs, spinal cord and epidural space. When fat suppressed the T2-weighed images became very sensitive and specific in the evaluation of complex injuries in the posterior ligament. Ligamentous injuries could also be evaluated using proton density-weighted images. The appearance of MRI images is dependent on the oxidative state of the hemorrhage. Ligaments can be optimally assessed by MRI as they appear in all MRI sequences as hyperintense structures. This is because when ligaments are stretched or raptured abnormally they show intrasubstance T2 hyperintensity or STIR discontinuity. In the acute stages of spinal trauma, the epidural collection is both isointense to spinal cord and cerebrospinal fluid on TI-weighted images and T2-weighted images respectively. MRI techniques are used in the acute stage of spinal injury for the identification of hemorrhagic lesion this is enabled by the use of microscopic magnet perturbations from products of iron following the trauma of the spine. MRI can also be used to assess the changes in the cross-sectional area of the spinal cord. The challenges that are encounter here is the small size of the spinal cord on the fact that the anatomy of the spinal cord is heterogeneous and therefore different when it comes to sensitivity to the magnetic field of the MRI. There is also a significant drop out of MRI signal as a result of the interaction of between orthopedic fixation screws and bolts which are normally used for the stabilization of Vertebrata which are fractured and the magnetic field of the MRI. This, however, can be overcome by assessing the change induced by the trauma on the spinal cord above the site of the trauma. Longitudinal MRI studies have also shown great potential especially in improving the resolution of the anatomical structures of the spinal cord (Frend et al, 2012).

MRI techniques are best suited for use in evaluating injuries of the soft tissues and the spinal cord computed tomography is best suited for evaluation of spinal fractures, for vascular injuries either CT or MRI angiography can be used. MRI enables a non-invasive visualization of the spinal cord in a way that was never thought possible before (Biering et al. 2009). The MRI technique is based on the principle that the powerful static magnetic field of the body causing changes in the spins of hydrogen atoms thus producing an image of the spinal cord. The scanning sequence parameters of an MRI machine can be altered to generate either T I weighted or T 2 weighted images (Martin et al. 2017). The T1 weighted images enhance signals of the proteinases fluids fact sub-acute hemorrhage and intravascular contrast agents. T2 weighted images are of bulk phase and edema fluid (Goldenberg, Kershaly, 2009). When conducting MRI care has to be taken to ensure there are no metallic objects on the body of the patient. Such are jewelry or pacemaker ear implants as these are unsafe as they can cause potential death of the patient. MRI provides a detailed appearance of the spinal cord following injury, (Goldenberg, Kershaly, 2009). Hemorrhagic lesions are identified using MRI because the iron products produced after trauma to the spine are sensitive to microscopic magnetic perturbations. Pre-contrast T1-weighted images may also show blood products as hyper intensity due to shortened relaxation rates of tissues caused by iron products. Dynamic contrast enhanced (DCE) and Arterial spin labeling are MRI techniques which are customized to perform specific imaging tasks in the imaging of spinal cord injuries. Arterial spin labeling has been successfully used to quantify blood flow in the spinal cord of a mouse. It has magnetization tagged blood water in an artery for this purpose. DCE is used to measure the volume of blood and the permeability of the vascular system (Biering et al. 2009). It uses a pharmacokinetic model for extravasation of the contrast agent from the vascular to the extravascular space. This has only been done on animal models and has shown a decrease in the volume and flow of blood following chronic SCI. Interestingly DCE has been applied to CT and has shown feasibility in human models (Shah, Ross, 2016).

MRI can provide explicit information regarding injuries which relate to extrinsic compression resulting from disc extrusions fractures and epidural hematomas and those that cause trauma on the parenchyma of the cord and can be successfully used to differentiate compressive abnormalities based on the criteria of signal and the morphological characteristics. The high sensitivity of MRI to detecting injury of the ligaments is in itself a disadvantage. This is because not all injuries of the ligaments are in themselves able to cause instability (Goldenberg, Kershaly, 2009). MRI also shows different levels of sensitivity to the different parts of the spine. It is very sensitive to injuries of the discs, interspinous soft tissues and posterior longitudinal ligament. Studies have also found that MRI may overestimate the extent to which the ligamentous function has been inhibited since surgical results reveal a different story (Biering et al. 2009). This may result into serious clinical consequences. A further challenge of the use of MRI is the difficulty encountered in the identification of complete ligaments in many subjects who are healthy (Shah, Ross, 2016). Recent developments in MRI systems have provided an option of shimming the magnetic field of the MRI machine thus creating a more uniform magnetic field. MRI images are obtained transverse to the spinal cord are therefore better than coronial slices since there is less field variation across slice thickness. The effects of inhomogeneity on MRI imaging can be reduced by choosing a suitable pulse sequence on gradient echo (Udina et al. 2011). The spinal echo has a refocusing pulse which is able to reverse the effect of inhomogeneity caused by the static field for a small instant of time. It is, however, noteworthy that when the faster acquisition of data is necessary gradient-echo acquisitions is used despite its limitations. The spinal cord moves within the spinal canal as the cerebrospinal fluid flows and the entire spine can also be subject to small motions during respiration. These present a major challenge in MRI.

2.2.2 Computerized Tomography (CT)

CT is useful in identifying acute hemorrhage following SCI. The hemorrhages seen under CT are seen in the central grey matter which is adjacent to the central canal. It is also seen to spread from the central canal radially into the white matter which neighbors it and the anterior horns. The CT clearly shows the hyperdense regions in areas of blood products. Xenon-enhanced CT can be used to image the flow of blood. CT is useful in the detection of the changes in the radiographic attenuation of tissues just like plain radiography. CT is useful when planning for operations and gives a precise description of the bony details (Ellingson, Salamon, Holly, 2014). CT angiography has been indicated to give a an effective demonstration of the injuries of the carotid and the vertebra as compared to other imaging techniques and is thus a standard imaging technique following a documentation of cervical vertebra fracture by noncontrast CT. CT scans use X-rays and produce multiple cross-sectional images of the internal body it can display the image of vertebrae and intervertebral discs accurately (Bialosky et al. 2009). ` During a CT of the spine it is important to consider radiation doses as this methord is associated with high doses of radiation which may be detrimental to the health and wellbeing of the individual undergoing the CT scan (Tins, 2010). During a CT scan the patient is made to lie on their back. This is done to ensure that the patient is comfortable and the process is less disrupted with respiratory movements. In some cases though rare a different positioning of the patient is required and in these cases care is taken to ensure the CT table does not move and the patient does not fall from the table. During CT scanning of patients who are sedated care is taken to ensure that the airways are not obstructed. The scanner operates with its z-axis aligned with the spine. The best quality CT images are usually obtained with the following parameters high kV and mAs settings, thin collimation and low pitch. The limitation of these parameters is the high radiation dose with results from their use (Tins, 2010). The processing of data from a CT scanner starts with a reconstruction. This is where the images are calculated from the raw data. It is first performed on thick slices and if no problem is identified the patient is released from the scanner and other reconstructions done later. An appropriate window setting for each algorithm is important for the best quality images while viewing the images (Tiens, 2010).

CT is best suited to answer specific questions involving focal areas of the spine. These questions are spondylolysis, abnormalities in the development of bony spine, characterization of lesions of soft tissue and areas of showing abnormal bones on MRI. CT angiography is also more suitable for evaluating vertebral arteries as compared to MR angiography with the only limitation being suboptimal timing of the contrast bolus and the overlapping of the bony structure. These challenges are however overcome by technical expertise and advances in the post processing of images. Abnormalities which can be detected using CT angiography are dissection, vascular occlusion, formation of pseudoaneurysm, and free-contrast extravasation from an uncontained rupture (Goldberge and Kershah, 2010) Multidetector CT is the primary imaging technique used for patients who have a blunt injury In the cervical spine. A CT is able to detect 97% to 100% of fractures occurring after spine trauma. It is possible to produce even 3-dimensional images of the spine on a screen using CT. It takes about 15-30 minutes to scan a section of the spinal cord. The CT procedure does not require a rest or a recovery period and does not hurt the patient. While CT scans provide valuable information about bones they do not provide precise information about ligaments. A radiologist is required to interpret the results of CT scans. (Kalichman, Carmeli and Been, 2017). CT provides a highly detailed contrast between bone structures and soft tissues of the spinal cord. A CT scan is advantageous in that it not only shows the image of the spine but also shows images of the adjacent tissues and organs. Although the use of CT in the imaging of spine is limited to the spinal cord it has several advantages. It is the most available imaging technique, is fast, it is capable of producing three dimensional multiplannar images, shows improved contrast resolution when compared to radiography and has limited operator independence For anomalities of the osseous it shows the greatest the greatest sensitivity and specificity in comparison with other imaging techniques. It also provides information that may be useful in determining whether there is need to do additional imaging of the spine. CT is also useful in cases where MRI cannot be done for instance in children and can be used to identify and characterize calcifications, mass lesions and hemorrhage. The most important limitation of CT is that it is unable to provide i to provide ligamentous and SCI screening even if this is needful and is difficult to provide an interpretation of CT especially in patients who are suffering from neurodegenerative diseases and osteopenia. It strongly advised that expectant women should not undergo CT scans (Tins, 2010). A CT scan occurs in a closed and confined environment greatly limiting patient size and in also not appropriate for patients who have extreme fears of confined places. CT scans can only provide valuable information about the bone but not ligaments and intervertebral discs.

2.2.3 Single-photon emission computerized tomography (SPECT)

This is a technique of nuclear medicine which has been used to produce scans of the spine and bones especially diagnosis of in bone cancer. A radioactive tracer, technetium is injected into the body and gamma cameras used to produce pictures of the distribution of the radioactive tracer in the tissues. The internal images of the body produced using this technique are precise and can enable a precise determination of the lesion (Kalichman, Carmeli and Been, 2017). SPECT can either be performed by a nurse and a technologist together where the nurse can inject the radioactive tracer while the technician operates the gamma camera. During the procedure the patient is required to remain still or follow the directions of the technician in their movement. Although the procedure in itself does not cause any discomfort to the patient, the requirement to remain still does. When the SPECT detectors are placed in positions parallel to the anatomical plane, a clear view of the anatomical structures is obtained. This happens when the detectors are arranged in an oblique orientation (Filling, Schwab, 2015). Due to tracer intensity SPECT is useful in distinguishing between old and new injuries of the spine. The radioactive tracer used in SPECT may cause dizziness and vomiting in patients and is also responsible for the radiation exposure in SPECT. The radiation exposure is so high that it is equivalent to the amount of exposure from x-rays of the chest. SPECT is generally avoided for expectant women even though it has not been confirmed to have any deleterious effect on them. In SPECT the radioactive tracer is usually injected directly into the vain and this makes it less invasive. In Positron-emission tomography (PET) different tracers can be injected to provide unique information regarding the injured spinal cord. It enables the assessment of metabolic activity in the tissues of the spinal cord which remain after injury and also allows the monitoring of the extent of axonal connectivity. The tracer F-Labeled fluorodeoxygluycose has been used in both clinical and preclinical studies to evaluate the function of the nervous systems. A major setback to PET is spatial resolution it can achieve a spatial resolution which is way less than that achieved in MRI (Filling, Schwab, 2015).

The new development in the use of this imaging technique in the imaging of the spinal cord is its use together with CT in a fused manner. There are a range of SPECT/CT scanners, starting from a low radiation dose four slice CT scanner being added on to a SPECT machine to a setup consisting of fully integrated SPECT and multidetector CT system (Ritt et al. 2011). The patient is in this case subjected to external radiation depending on the CT component and a consistent internal radiation. One test is essentially performed directly after the other and the resulting images are overlaid. This hardware fusion of SPECT and CT has resulted into more accuracy in diagnostics and an improvement in the localization and definition of specific lesions (Vitor et al. 2019).

2.2.4 DIFFUSION MRI

Diffusion MRI is used to measure water molecules displacement occurring in tissues. During diffusion MRI scanning the water molecules which are displaced produces an attenuated signal. The diffusion of water is promoted by the axonal architecture of the white matter of the central nervous system. The diffusion of water occurs in a parallel direction rather than a perpendicular one, the perpendicular motion being limited by the cell membrane (Vedantam et al. 2013).

2.2.5 Diffusion tensor imaging (DTI)

Diffusion tensor imaging is a magnetic resonance technique which is useful for measuring the direction and magnitude of diffusion of molecules of water in various tissues (Vedantam et al. 2013). DTI was developed from diffusion weighted imaging, which tests the depletion of MR signals due to diffusion, and was initially used for imaging of the brain (Nouri et al. 2016). DTI uses anisotropy to indicate the orientation of axonal fibers and to show the boundaries of different anatomical structures (Vedantam et al. 2013). This technique has been subsequently improved and developed into a tool for delineating white matter tracts found in the brain (Labelle et al. 2011). The small area of the spinal cord substantially limited the use of DTI in imaging spinal injuries. Susceptibility, cardiac and respiratory motion artefacts are some of the issues that limited the use of DTI. This technique is specifically useful for detecting damages in the spinal cord which otherwise appear as normal in the T2-weighted MRI images. The use of DTI faces a challenge of difficulty in spatial resolution and difficulty in visualizing the individual funicular. It also uses a tensor framework to show movement of molecules in a three dimensional space in multiple directions (Nouri et al. 2016). DTI indices are then calculated using three principal axes. The indices calculated for spinal cord DTI are transverse apparent diffusion co-efficient (tADC), fractional anisotropy (FA), and apparent diffusion co-efficient (ADC) and longitudinal apparent diffusion co-efficient (lADC). There is always a decrease in anisotropy in an injured spinal cord caused by the disruption of axons which are longitudinally aligned. This exhibited in DTI by a decrease in Fractional anisotropy (Vedantam et al. 2013). Any abnormalities which can be seen in a CT scan always need to be re-evaluated by a scan which is more detailed. Other novel imaging techniques have been developed which mainly focus on the biochemical function or the microstructural function of the spinal cord. These are diffusion tensor imaging (DTI), MR spectroscopy (MRS), single-photon emission computed tomography and functional MRI abbreviated as (f MRI). (Dakes et al. 2017)

The acute stage of SCI is characterized by mechanical injury as well as other effects such as ischemia, immediate death of the cells occur in the area of insult causing a disruption of neural tissues. MR spectroscopy is a useful technique in this stage of SCI as it demonstrates a clear decrease in the levels of N-acetyl aspartate (NAA) which is a neuronal marker. Diffusion MRI has shown that early axonal death and cell membrane disruptions result in an elevation of the apparent diffusion coefficient. This is possible since MRI is sensitive to the magnitude of self-diffusion of water. CT is used to identify hemorrhage following SCI and indicates this by the presence of hyperdense regions in areas of blood products. (Nouri et al. 2016) DTI is used to measure ADC in the transverse plane. This is enabled by an increase in extracellular volume fraction. DTI imaging can also indicate a reduction in the levels of ADC parallel to the spinal cord which results in the decrease in fractional anisotropy or diffusional anisotropy (Parizel et al. 2010).

3.0 Methodology

We used the following search terms spinal cord injury, musculoskeletal changes in spinal cord injury, imaging techniques in spinal cord injury, the use of CT in imaging of the spine, the use of MRI to observe musculoskeletal changes following spinal cord injury to search journal articles from Medline, PubMed, NCBI, Google scholar and Embase. The search was carried out in English. The study included journals documenting SCI in all age groups. Three of these journal articles were then analyzed to take note of the musculoskeletal change they measured and their findings as provided in the results section.

4.0 Results and discussion

4.1 Case study 1

A study done by (Frotzler et.al 2015) documented the characteristics of 156 fractures of the long bones in a study population consisting of 206 persons suffering from spinal injuries. Most of the long bone fractures were found to be occurring in the distal femur and another majority also in the proximal lower leg. 75% of the fractures studied were either found to be simple fractures or extra acticular. The study found no fractures in the upper limbs. About 13.5% of the test population was found to suffer from complications which resulted from the fractures. The study found out that most of the fractures were treated through operation and this sometimes resulted into complications. The severity of the fracture remained the same for all the types with spinal injury be it lumbar, thoracic or cervical SCI.

4.2 Case study 2

(Gorgey and Dudley, 2007) measured Skeletal muscle atrophy and increased intramuscular fat after incomplete SCI. Their study aimed to measure skeletal muscle CSA of patients with incomplete chronic SCI after a few weeks after correcting for IMF and to determine the changes occurring in the skeletal muscle CSA and content of IMF in incomplete chronic SCI individuals after three months elapse from three initial measurement. The study hypothesized that the skeletal muscle CSA affected by incomplete chronic SCI would be smaller while the IMF content would be larger in chronic SCI individuals as compared with the controls. Another hypothesis was that that during the re measurement of IMF content and skeletal muscle CSA after three months, the skeletal muscle CSA continues to decrease while the IMF content will be increase. The study used six subjects who suffered from incomplete chronic SCI who were recruited from Shepherd Center found in Atlanta, GA, USA and six controls from university of Georgia and Shepherd Center (Atlanta, GA, USA. Proton weighted MRI was used in the study to determine skeletal muscle CSA. A 1.5 tesla magnet was used to produce MR images of both thighs of the patients and a coil of the whole body. The region between the hip and the knee joint was imaged using T1-weighted MRI. Since a repeat scan of the same region was required after three months, a mark was places 6 inches proximal to the patella. X-Vessel software was used to analyze the MR images. The images of the thigh were segmented into three regions as follows; into fat (high intensity), skeletal muscle (mid intensity) and background/bone (low intensity). The findings were as follows there was no statistically significant difference in the skeletal muscle cross-sectional area in chronic SCI patients who were involved and those who were not involved in both assessments. The thigh skeletal muscle was found to be smaller than that of the AB control group by 33%. This measurement was done after correction for IMF. An underestimation of 6% was the result of not correcting for IMF before measuring skeletal muscle atrophy. The change in skeletal muscle CSA of the thigh after three months was found not to be statistically significant. In the chronic SCI group an increase of 126% was recorded after the first six weeks of injury in comparison with the AB control.

The IMF CSA unlike the skeletal muscle CSA continued to change in the three months with an increase of 26% recorded in chronic SCI individuals. The study further found that the Relative IMF was three-times higher in the chronic SCI group as compared to the AB group at 6 weeks and continued to increase in the next three months. The study argued that the increase in IMF CSA could be attributed to failure of the skeletal muscle to make use of glucose following paralysis. This leads to reduced oxidation of fat thus leading to fat accumulation. This accumulation of fat is responsible for 70% of intolerance to glucose experienced by patients in suffering from chronic SCI. IMF has been indicated to cause insulin resistance. This happens through the release of intermediates of intracellular fatty acids such as diacylglycerol, long-chain acyl-CoA and ceramide which impair insulin signaling. In this study, MRI was used to separate between muscle and fat pixels based on their signal intensities. The choice was because MRI had been used to quantify the response of skeletal muscles to unloading. It was chosen over X-ray absorptiometery (DEXA) and CT because DEXA overrates the muscle proportion in fat free mass following spinal cord injuries and provides an inaccurate reflection of the degree of muscle atrophy in comparison with MRI. In CT only a single slice is used while MRI promotes the acquisition of multiple slices. The multiple slices are better equipped to represent the correct changes in the size of the muscle unlike just one slice. MRI is a non-ionizing radiation while CT is an ionizing radiation.

4.3 Case study 3

Lin et al. 2015 measured long term skeletal changes following an injury of the spinal cord. The specific skeletal change measured was osteoporosis. In their study they used adult Fischer 344 male rats. They fast gave the rats the anaesthetic isoflurane and then incised their skin at the back along the midline. The spinal cord of the rats was then subjected to a modest injury. After sixteen weeks the Sublesional bones and supralesional bones obtained from the rats. The study showed that there was a significant effect of chronic SCI on the lengths of the long bones of both sublesional and supralesional bones. These results were interpreted to mean that chronic SCI impairs the longitudinal growth of bones. The most severe loss of bones in chronic SCI patients was found to be at the knee joint with distal femur and proximal tibia being the most affected. Within the knee joint there are three trabecular bones formed by endochondral ossification. These are subchondral trabecular bone which is found in the epiphyseal area formed inside the secondary ossification center and the primary and secondary spongiosa which are found in the metaphyseal area and inside the primary ossification center. The knee joint of the rats was subjected to μCT scanning after the 16 week period to establish the effect of chronic SCI on the bones found at the knee joint. The secondary spongiosa showed the most drastic loss in bone mass followed by the primary spongiosa while the subchondral region only showed modest bone loss. This led to the conclusion that even within the same bone the bone loss as result of chronic SCI is site specific. The study also showed that chronic SCI alters the structure of the cortical bone and also reduces the strength of the cortical bone especially the femur. This conclusion was arrived at after finding out that the bones in the test population were slimmer as compared to those of the control population leading to a reduction of the ability of the bones in the cortical region to bend as a result of a drastic decrease in pMOI. This study also studied the impact of chronic SCI on the ones above the region of injury such as in the upper extremities like the forelimbs. This was achieved by scanning and analyzing supralesional proximal humeri using μCT.

There were no changes observed in the primary spongiosa and the subchondral site while the changes in the secondary spongiosa were statistically insignificant. A reduction in bending strength of these bones was however noted thus it was concluded that chronic SCI has a detrimental effect on the immobilized forelimbs even though this effect is less than that on the sites below the site of injury. The study proposes the use of anabolic treatments which have the potential to stimulate the formation of new bones by promoting the number and activity of osteoblast for chronic SCI patients in the chronic stage of injury. This acts to restore the masses of the bones, repairing the small damages to the bone architecture and reduces the risk of suffering from fractures. The FDA has approved the teriparatide (recombinant human PTH1-34), as the only treatment for severe osteoporosis occurring after menopause and monoclonal antibody against Sclerostin (Scl-Ab) which has shown good results in clinical trials and is now in phase two of clinical trial. Studies have found out that immediately after chronic SCI if one is injected with ScI-Ab for three weeks the result is a complete restoration of the structure of the trabecular bone and the strength of the cortical bone. In general the study illustrated that SCI has harmful effects on the entire human skeleton. It causes a more severe loss in bone mass and deterioration in structures in the lower extremities as compared to the upper extremities. Since chronic SCI is characterized by elevated bone resorption and reduced bone formation anabolic treatments is one of the most effective treatments for patients suffering from chronic SCI.

5.0 Conclusion

In conclusion musculoskeletal changes occurring after spinal injury occur as a result of the skeletal and the muscular system trying to adjust itself following injury. These changes mainly occur to the areas of the spine which are below the site of injury. Spinal cord injuries affect ligaments and nerves and also the bony structures. Imaging techniques are used for the diagnosis of musculoskeletal changes and to inform the treatment of these changes. Among the imaging techniques currently in use are computerized tomography and magnetic resonance imaging. Magnetic resonance imaging techniques are best suited for use in evaluating injuries of the soft tissues and the spinal cord while computed tomography is best suited for evaluation of spinal fractures and bone changes.

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