Review Article DiagnosticTestingforDegenerative ?· Review Article DiagnosticTestingforDegenerativeDiscDisease…
Post on 14-Sep-2018
Embed Size (px)
Hindawi Publishing CorporationAdvances in OrthopedicsVolume 2012, Article ID 413913, 7 pagesdoi:10.1155/2012/413913
Diagnostic Testing for Degenerative Disc Disease
Michael W. Hasz
Virginia Spine Institute, 1831 Wiehle Avenue, 2d Floor, Reston, VA 20190, USA
Correspondence should be addressed to Michael W. Hasz, firstname.lastname@example.org
Received 9 March 2012; Accepted 20 March 2012
Academic Editor: Brian R. Subach
Copyright 2012 Michael W. Hasz. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The diagnostic of degenerative disc disease should be reached with the help of various diagnostic studies. This article briefly reviewthe information gained by the following tests: radiographs, computed tomography, magnetic resonance, and discography. Thearticle explains how each modality provides a piece of the diagnostic puzzle and how discography confirms the origin of thepatients pain.
In the diagnosis and treatment of a patient with ongoing pre-dominantly midline low-back pain (axial back pain), degen-erative disc disease must be kept high amongst the possiblediagnoses. In addition to the appropriate patient history,examination, and patient response to nonoperative conser-vative treatment, various diagnostic studies can aid in thediagnosis of degenerative disc disease and the exclusion ofother diagnoses.
Common studies used to aid in the diagnosis of patientswith axial back pain include lumbar radiographs, computedtomography (CT) scan, magnetic resonance imaging (MRI),and provocative discography. These studies should be usedin conjunction with the patient history and physical exami-nation. They are useful to aid in the diagnosis but are not inand of themselves definitive studies for the diagnosis of pain.However, using the studies in conjunction with the patientsclinical status and response to treatment is very useful for theoverall diagnosis of degenerative disc disease.
2. Lumbar Radiographs
Lumbar X-rays should include a full series with standingor weight-bearing views: standing anterior-posterior (AP)pelvis and lateral flexion-extension views. These weight-bearing and dynamic studies can help identify many diag-noses which may otherwise be overlooked by a pure supineor non-weight-bearing X-ray: instability, increased angular
motion on flexion-extension lateral views, anterolisthesis orretrolisthesis (each of which can be either subtle or directindications of local instability), or indirect findings of lumbardisc degeneration.
Radiographs are more often used to exclude otherdiagnoses rather than directly diagnose degenerative discdisease. Diagnoses that can be more directly excluded withappropriate X-rays include scoliosis, spondylolisthesis, frac-tures, and gross instability. The actual radiographic findingsof lumbar disc disease encompass a range of findings used toinfer disc disease (Figure 1).
The radiographs are primarily used for assessing bonyanatomy and alignment. They do not directly view the discsand soft tissues. In the early stages of lumbar disc disease, thedisc heights may be unchanged. There may be annular tearsidentified and painful discs, but radiographs may not giveany significant indication of disc injury, particularly in theacute setting of a disc injury. The flexion-extension lateralviews may hint to muscle spasm and decreased excursionof range of motion. Therefore, muscle spasm or restrictioncan be inferred but not directly attributed to disc disease(Figure 2).
Some patients may have instability related to insuffi-ciency of the lumbar disc. Some authors have defined 11 orgreater of angular change on flexion-extension views tosuggest the disc to be unstable . Additionally lumbarretrolisthesis identified on radiographs has also been used toinfer instability at lumbar levels  (Figure 3).
2 Advances in Orthopedics
Figure 1: A lumbar radiograph with narrowing of the L5S1 discspace. This narrowing is suggestive of disc degeneration.
The angular changes as well as retrolisthesis in thedegenerative model of disc disease should not be confusedor associated with the trauma model associated with Whiteand Panjabi studies . These studies were performed oncadavers where acute injury models and structural defectswere made in order to assess instability in a trauma model.Applying these criteria in the degenerative disc disease modelwould be inappropriate.
Further suggestion of degenerative disc disease along thedegenerative cascade would lead toward the formation ofosteophytes along the edges of the endplates, narrowing ofthe disc space height, increased sclerosis along the endplatesat the disc segment level, and possible osteophytes or sclerosisof the facet joints. In conjunction with the loss of disc spaceheight, the foramina can be observed to narrow on the lateraland oblique studies  Toward the end of the degenerativecascade, a vacuum disc element can frequently be observed (Figure 4).
Many of these degenerative changes in the lumbarspine may not be symptomatic and are only suggestive ofthe diagnosis of degenerative disc disease. In symptomaticpatients, these radiographic findings are definitely suggestiveof degenerative disc disease although further studies wouldbe indicated.
3. Computed Tomography Scan
Overall a CT scan by itself is of limited value in the correctdiagnosis of degenerative disc disease. Often a CT scan canbe normal in the face of this disease. A CT scan has littledirect value beyond the lumbar radiographs in the directassessment of degenerative disc disease.
A CT scan is used to help exclude other diagnoses,as previously mentioned on the section on plain radiographs.A CT scan is very useful to help assess a pars defect orspondylolisthesis for example. Additionally, a CT scan can
demonstrate findings that are also found on radiographs aswell. A CT scan may be able to better demonstrate osteo-phytes as well as endplate sclerosis and vacuum disc sign, allrelated to findings of degenerative disc disease .
A CT scan is performed in a non-weight-bearing positionand is of limited use to assess any dynamic instability in thelumbar spine. The CT scan can be used to assess the spinalcanal and vertebral bony anatomy, as well as the posteriorjoint complex. It can further assess potential foraminalstenosis, and, when used in conjunction with myelography,it can assess possible nerve compression and indirectly discprotrusions (Figure 5).
4. Magnetic Resonance Imaging
MRI scanning, like CT scanning, can be used to evaluate thespinal canal and space available for neural structures. It canevaluate the overall bony alignment and the lumbar facets,but it has the additional benefit of allowing the direct assess-ment of the neural structures as well as the disc structures.This direct evaluation of neural and disc structures is notpossible by CT scan .
An MRI is capable of evaluating the hydration withinthe discs based on increased signal on the T2-weightedimages. Increased disc signal on T2-weighted images isassociated with dehydration of the lumbar discs. Change inthe disc signal, or darkening of the signal, is associated withdehydration or loss of hydrogen ions within the disc. This isoften associated with lumbar disc degeneration. Decreasedhydration leads to a loss of signal intensity on the T2images which leads to darkening of the disc on the image(Figure 6). An area of increased signal may be identifiedwithin the disc or along the annulus of the disc. This areaof increased signal is called a high-intensity zone. This high-intensity zone is thought to be correlated with an area ofincreased inflammation, thought to be associated with a disctear or annular tear, and often is associated with axial backpain .
In addition to the changes within the disc, changes at theendplate adjacent to the disc have been described . Modicnoted reactive endplate changes at the endplates of the discsand graded them as Modic 1, Modic 2, and Modic 3 changes.
(i) Modic 1 reactive endplate changes demonstrate de-creased disc signal on T1 images and increased discsignal on T2 images. These changes are associatedwith disruption and fissuring of the endplate andvascular fibrous tissue adjacent to the endplate.Modic 1 reactive endplate changes are infrequentlyassociated with axial back pain (Figure 7).
(ii) Modic 2 reactive endplate changes are represented byincreased signal intensity on T1 images and neutralsignal on T2 images. These changes are associatedwith degenerative disc changes on plain radiographs.These changes represent yellow marrow replacementin the adjacent vertebral body at the endplates. Thisincreased lipid content has been suggested to be aninflammatory response associated with a painful disc.
Advances in Orthopedics 3
Figure 2: Lateral standing, flexion and extension X-rays are important to identify motion and/or instability in the spine. Some patients haveunremarkable lateral upright X-rays but demonstrate a mobile spondylolisthesis upon dynamic testing.
Figure 3: Lateral X-rays demonstrating a L4-L5 grade 1 spondylolisthesis. The standing lateral dynamic flexion and extension X-rays areused to determine motion at this segment.
(iii) Modic 3 reactive endplate changes demonstrate de-creased disc signal on both T1 and T2 images. Thisrepresents bony sclerosis at each endplate. Thereare sclerotic endplate changes representing near-end-stage disease at the endplates. These are also associ-ated with decreased blood supply at the endplates.
As mentioned earlier, the discs themselves have a range ofintensity from high signal on the sagittal T2 images