Pictorial review: The radiological investigation of lumbar spondylolysis

Clinical Radiology (1998) 53, 723-728

Pictorial Review: The Radiological Investigation of Lumbar Spondylolysis C. J. HARVEY, J. L. RICHENBERG, A. SAIFUDDIN and R. L. WOLMAN*

Departments of Radiology and *Rheumatology/Sports Medicine, The Royal National Orthopaedic Hospital Trust, Stanmore, Middlesex, UK

Lumbar spondylolysis represents a stress fracture of the pars interarticularis and occurs most commonly at the L5 level. Pars defects can be imaged with plain radiography, bone scintigraphy, computed tomography (CT) and magnetic resonance imaging (MRI). Plain radiographic projections of particular value include the coned lateral view of the lumbosacral junction, which displays the majority of defects, and the anteroposterior view with 30 ~ cranial angulation. The value of oblique radiography is unproven. Planar bone scintigraphy (PBS) is more sensitive than radiography and single photon emission computed tomography (SPECT) more sensitive and specific than PBS. Both these techniques, however, are less specific than radiography and CT. CT, when performed with a reverse gantry angle and thin sections, is the investigation of choice for identifying radiographically occult lyses. Conventional lumbar spine MRI techniques are valuable for demonstrating normality of the pars, but may be associated with a high false positive rate for the diagnosis of pars defects. Harvey, C. J., Richenberg, J. L., Saifuddin, A. & Wolman, R. L. (1998). Clinical Radiology 53, 723-728. The Radiological Investigation of Lumbar Spondylolysis

Accepted for Publication 6 May 1998 Spondylolysis is a defect in the pars interarticularis believed to be due to a stress fracture, secondary to chronic low grade trauma from repetitive spinal hyperextension and rotation [1,2]. The incidence in the general population is 4-8% but reaches 23-63% with certain sporting activities [3,4]. Ninety-five per cent of defects occur at the L5 level [5]. Spondylolysis is commonly asymptomatic or may be associated with low back pain from other causes. Therefore, in a symptomatic patient, the radiologist may be asked to determine if a lysis is present, and if so whether it is the cause of symptoms. The radiological diagnosis of lytic spondylolisthesis is straight forward, but in the absence of slip, the identification of a lysis can be difficult. The aim of this article is to review the radiological diagnosis of lumbar spondylolysis.

PLAIN RADIOGRAPHY Plain radiography of the pars is difficult since the pars lies oblique to all three orthogonal planes. Various angled projections demonstrate the pars and lamina in true anteroposterior (AP) and lateral view, including the 45 degree lateral oblique [6], the AP view with 30 degree cranial angulation [7], and the combination of lateral oblique with cranial angulation [8]. Libson et al. [6] stated that 20% of pars defects were seen only on oblique views, suggesting that oblique radiographs were essential in young adults with low back pain. However, they had no CT or surgical proof of the presence of lyses in these cases and the possibility of false positive diagnoses on oblique views was not considered. Amato et al. [9] detected only 87% of pars defects with Correspondence to: Dr A. Saifuddin, Consultant Radiologist, The Royal National Orthopaedic Hospital Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. 9 1998 The Royal College of Radiologists.

oblique views and proposed that the single best projection was the collimated lateral view of the lumbosacral junction (Fig. 1). Markwalder et al. [10] found that the 45 degree lateral oblique radiograph detected the defect in every case, but all their patients had established spondylolisthesis, so this is not surprising. Fractures are optimally demonstrated when the X-ray beam is tangential to the plane of the fracture (Fig. 2). Therefore, for the 45 degree oblique radiograph to be of real value for demonstrating pars defects, the majority of defects should lie perpendicular to the pars. However, a study of the orientation of defects on axial computed tomograpby (CT) indicates that the majority of lyses lie closer to the coronal plane than the 45 degree oblique plane [11], explaining why most defects are seen on the lateral view. Some defects also lay close to the sagittal plane and would therefore not be identified on any radiographic projection. Similarly, stress reactions that have not progressed to complete defects will be radiographically occult. The 45 degree lateral oblique radiograph should therefore not be relied upon for the detection or exclusion of pars defects. Libson and Bloom [7] advocated the 30 degree cranially angulated AP view to clearly image the pars interarticularis of L5 in the frontal plane. This significantly increases the detection of pars defects compared to the full length AP view, and also allows differentiation of unilateral from bilateral defects (Fig. 3). Additional signs of spondylolysis on the AP radiograph include lateral deviation of the spinous process [12] and sclerosis of the contralateral pedicle [13]. The former results from lengthening of one lamina due to recurrent fracture and healing of the pars interarticularis, causing the spinous process to rotate toward the shorter of the two laminae. The latter sign occurs due to reactive sclerosis of the contralateral pedicle and lamina from the increased stress

724

CLINICAL RADIOLOGY

(a)

Fig. 1 - Coned lateral radiograph of the lumbosacral junction in a patient with bilateral L5 spondylolyses (arrow). The defects are best demonstrated on this view.

passing through the contralateral neural arch in the presence of a unilateral lysis (Fig. 3).

RADIONUCLIDE IMAGING Initial studies using 99m-technetium methylene diphosphonate bone scintigraphy (PBS) [14,15] found discrepancies with radiography. It was suggested that lesions identified radiographically but showing no activity on PBS were chronic and healed (Fig. 4) whereas those with increased activity were early injuries that represented radiographically occult stress reactions (Fig. 5). Lowe et al. [16] demonstrated that patients with spondylolysis and symptoms related to recent trauma or strenuous activity showed increased activity on PBS, whereas those with a history of chronic low back pain had normal scans. Similar findings were reported by Elliott et al. [17]. These studies suggest that PBS is more sensitive than radiography in the detection of early stress reaction in the pars. However, in both these studies, the nature of the scintigraphic abnormality was not investigated further with CT. Collier et al. [18] compared PBS and single photon emission computed tomography (SPECT) in patients with radiographically evident spondylolysis/lytic spondylolisthesis and found SPECT to be more sensitive than PBS and better able to localize abnormalities (Fig. 6a). Asymptomatic lesions were associated with normal SPECT scans. Bellah et al. [19] suggested that a normal SPECT study virtually excluded spondylolysis as a cause of back pain while Read [20] considered SPECT to be an essential investigation in children with extension related low back pain. The increased sensitivity of SPECT in patients with chronic low back pain of various aetiologies was also reported by Ryan et al. [21] who further demonstrated that the majority of abnormalities identified by SPECT corresponded

(b) Fig. 2 - (a) Oblique radiographs of a patient with spondylolysis at both L3 and L4. The right oblique shows a lysis at the L3 level only (arrow). The fight L4 pars appears intact. The left oblique shows lyses at both the L3 and L4 levels (arrows). (b) CT at the L3 (above) and L4 (below) levels demonstrates bilateral lyses at both levels. The right L4 lysis was not identified on the oblique radiograph since it lies closer to the coronal plane than the oblique plane.

Fig. 3 - AP radiograph (left) and AP radiograph with 30 ~ cranial angulation (fight) in a patient with unilateral left L5 pars defect. The AP view shows sclerosis of the fight pedicle and lamina of L5 (black arrow) but the left pars cannot be assessed. However, the pars defect is clearly seen on the angled up view (white arrow). 9 1998 The Royal College of Radiologists, Clinical Radiology, 53, 723-728.

RADIOLOGICAL INVESTIGATIONOF LUMBAR SPONDYLOLYSIS

Fig. 4 - Posterior view PBS (left) and CT (right) in a patient with a left L5 pars defect (arrow). There is no uptake in the region of the left L5 pars on the bone scan.

725

to recognized lesions on CT [22]. This raises an important point with regards PBS and SPECT; although they are sensitive techniques, they are relatively non-specific in that increased activity in the region of the pars may be due to pathology other than spondylolysis. The current literature therefore suggests that SPECT can identify patients with painful spondylolyses by the demonstration of activity at the site of the pars. This is supported by the findings of Raby and Matthews [23] who correlated the outcome of spinal fusion for painful spondylolysis, with the results of pre-operative SPECT. Patients with successful surgical outcome had positive SPECT scans pre-operatively whereas those with persistent postoperative pain had normal scans, suggesting that their back pain was not due to spondylolysis. Fluoroscopically or CT-guided local anaesthetic block of the pars defect is also a good predictor of successful spinal fusion [24]. Van den Oever et al. [25] suggested that increased activity in the pars indicates a capacity for healing of the defect if the patient is rested and braced. However, it has recently been shown that CT can show chronic non-union in up to 45% of such cases [26] (Fig. 7). The main value of SPECT therefore is in the identification of an acute stress reaction of the pars before it manifests radiographically, so that steps may be taken to prevent progression to a complete fracture. However, SPECT cannot reliably distinguish between spondylolysis and facet arthritis, and if the abnormality is unilateral, infection and osteoid osteoma must be considered. If SPECT shows abnormality related to the pars in the presence of normal plain radiographs, CT should be performed to clarify the cause.

COMPUTED TOMOGRAPHY

(a)

CT is superior to plain radiography and PBS for consistent and accurate demonstration of spondylolysis [5,27,28]. Langston and Gavant [29] described the 'incomplete ring' sign on axial slices at the level of the pedicle/lamina, as a feature of a neural arch defect, either spondylolysis (Fig. 8) or spina bifida occulta, depending upon its position. CT also identifies accompanying features of spondylolysis [30], such as facet joint changes, spondylolisthesis, disc herniation and foraminal or lateral recess stenosis and also gives the best indication of the potential for a defect to heal, based on the demonstration of callus formation around the fracture. Conversely, a fracture with wide, well-corticated margins, indicating an established non-union (Figs 8 & 9) has no potential for healing with conservative management. The CT technique for demonstration of spondylolysis is important. With CT, a fracture is optimally demonstrated when the plane of the scan is perpendicular to the plane of the fracture. Pars defects at the L5 level lie in approximately the plane of the L5/S 1 disc. Therefore, if the CT gantry is angled to the plane of the L5/S 1 disc, the scan plane will be approximately parallel to the defect, which may consequently be missed [31]. If CT is performed specifically to demonstrate a pars defect, a reverse gantry angle technique should be employed such that the scan plane is perpendicular to the fracture (Fig. 9).

(b) Fig. 5 - (a) Posterior :r PBS in a professional football player showing increased uptake in the region of the right L5 pars (arrow). (b) CT showing a stress reaction in the right L5 pars (arrow). Plain radiographs were normal. 9 1998 The Royal Conege of Radiologists, Clinical Radiology, 53, 723-728.

M A G N E T I C RESONANCE I M A G I N G Grenier et al. [32] described the MRI features of pars defects. Established spondylolysis appeared as a discontinuity

726

CLINICAL RADIOLOGY ransa:xial

LT L

P

>i :;!i!84 p ~orona I

I ii~:

Planar

s

(a)

R

L

:~

(a)

(b) Fig. 7 - (a) PBS in a patient with bilateral L5 pars defects showing increased activity at the left pars. (b) CT at the L5 level. Both pars defects have sclerotic margins indicating established non-union,

(b)

of the cortex and marrow through the pars, best seen on T1weighted sequences (Fig. 10). However, Johnson et al. [33] found that similar MRI features could be produced by sclerosis of the neck of the pars, partial volume imaging of an osteophyte from the superior facet of S1, partial facetectomy and osteoblastic metastasis to the pars. Saifuddin and Burnett [34] assessed the ability of routine lumbar spine MRI to detect pars defects using plain radiographs as the gold standard. In 26.5% of cases the pars could not be visualized and no statement about the presence or absence of lyses could be made. A pars defect was thought to be

(c)

Fig. 6 - (a) Posterior view PBS (left) and axial SPECT (right) of a professional cricketer with back pain, PBS shows increased activity in the left side at the L3 level (arrow). The SPECT scan localizes the abnormality to the left side of the neural arch in the region of the facet joint or pars (arrow). (b) Sagittal T2-weighted MR image showing increased signal intensity in the left pedicle of L3 (arrow) indicating oedema. (c) Axial CT at the L3 level showing a stress reaction in the left L3 pars (arrows). (Courtesy of Dr S. J. D. Bumett) 9 1998 The Royal College of Radiologists, Clinical Radiology, 53, 723-728.

RADIOLOGICALINVESTIGATIONOF LUMBARSPONDYLOLYSIS

727

Fig. 8 - Six contiguous axial CT slices (a-f) from the LA/5 disc to the inferior end-plate of L5. Pars defects are identifiedat the junction of the pedicle and lamina (black arrow) as opposed to the facet joints which are best seen at the level of the disc/end-plates(white arrows). present in 14.5% of cases while plain radiographs demonstrated pars defects in only 5.5% of cases, suggesting that routine MRI had a high false-positive rate for the diagnosis of pars defects. The poor results of this study were related to the MRI technique employed (5 m m slice thickness with I m m interslice gap) and it was suggested that use of thinner slices or volume imaging with multiplanar reconstruction may increase diagnostic accuracy. The results also need to be considered in the light of the fact that plain radiographs were used as the gold standard. The limitations of plain radiography in the diagnosis of pars defects have been highlighted previously. Ulmer et al. [35] found that posterior subluxation of the neural arch on midline MR images was a sensitive indicator of bilateral spondylolysis, even in the absence of spondylolisthesis (Fig. 10). The same authors [36] described reactive marrow changes in the pedicles adjacent to pars defects, suggesting that identification of these may aid in their diagnosis. The signal changes are similar to those occurring adjacent to degenerate intervertebral discs [37] (corresponding to oedema or fatty replacement) and are related to patient age. It is possible that oedematous changes (Fig. 6b) correspond to painful pars defects, whereas fatty changes (Fig. 10) are associated with chronic defects. Unfortunately, this aspect was not investigated but deserves further attention. Yamane et al. [38] demonstrated reduced SI in the pars on coronal Tl-weighted MR sequences in young children with extension related back pain, prior to the development of spondylolysis as shown by radiography and CT. MRI therefore clearly has the potential for demonstrating stress reactions in the pars, similar to SPECT but without the associated ionizing radiation. MRI also demonstrates associated spondylolisthesis, nerve root entrapment, disc degeneration and herniation [39].

Fig. 9 - CT scanogram(left) showingthe scan plane for the reverse gantry angle techniquefor optimal demonstrationof pars defects. The resulting scan (right) shows bilateralL5 pars defects (arrows). 9 1998The RoyalCollegeof Radiologists,Clinical Radiology, 53, 723-728.

Fig. 10 - Midline sagittal (left) and parasagittal (right) Tl-weighted MR images in a patient with an L5 pars defect appearing as a discontinuityof the marrow through the region of the pars (white arrow). There is posterior subluxation of the L5 spinous process (black arrow) in the absence of spondylolisthesis.Note also the increasedsignalintensity(correspondingto fatty replacement) in the L5 pedicle (curved arrow).

CONCLUSIONS The radiologist asked to image a young patient with extension related low back pain is faced with two questions: (1) is there a spondylolysis? and (2) if so, is it the cause of the symptoms? The first question is usually answered by good quality radiography, of which the coned lateral of the lumbosacral junction and AP view with 30 degree cranial angulation are particularly important. If the radiographic series is nondiagnostic, limited thin section CT using the reverse gantry angle technique will demonstrate both stress reactions and established defects. The diagnosis of spondylolysis being the cause of pain is more difficult. Positive SPECT suggests that this is the case. The role of MRI in both diagnosis of pars defects and in assessment of their relationship to symptoms needs further research.

REFERENCES

1 Wiltse LL, Widell EH, Jackson DW. Fatigue fracture: the basic lesion in isthmic spondylolisthesis.Journal of Bone Joint Surgery (American) 1975;57A:17-22. 2 TroupJDG. Mechanicalfactors in spondylolisthesisand spondylolysis. Clinical Orthopaedics 1976;147:59-67. 3 Jackson DW, Wiltse LL, CirincioneRJ. Spondylolysisin the female gymnast. Clinical Orthopaedics 1976;117:68-73. 4 Rossi F. Spondylolysis,spondylolisthesisand sports. Journal of Sports Medicine and Physical Fimess 1988;18:317-340. 5 GroganJP, HemminghyttS, WilliamsAL, Carrera GF, HaughtonVM. Spondylolysis studied with computed tomography. Radiology 1982;145:737-742. 6 Libson E, Bloom RA, Dinari G, Robin GC. Oblique lumbar spine radiographs: Importancein youngpatients.Radiology 1984;151:89-90. 7 Libson E, Bloom RA. Anteroposteriorangulatedview: A new radiographic techniquefor the evaluationof spondylolysis.Radiology 1983; 149:315-316. 8 DubowitzB, FriedmanL, Papert B. The oblique cranial tilt view for spondylolysis.Journal of Bone and Joint Surgery (British) 1987;69-B: 421. 9 Amato M, Tony WG, Gilula LA. Spondylolysisof the lumbar spine: Demonstrationof defects and laminal fragmentation.Radiology 1984; 153:627-629. 10 Markwalder TM, Saager C, Reulen HJ. Isthmic spondylolisthesis-an

728

CLINICAL RADIOLOGY

analysis of the clinical and radiological presentation in relation to intraoperative findings and surgical results in 72 consecutive cases. Acta Neurochirugica 1991;110:154-159. 11 Saifuddin A, White J, Tucker S, Taylor BA. Orientation of lumbar pars defects; implications for radiographic demonstration and surgical management. Journal of Bone and Joint Surgery (British) 1998;80-B: 208-211. 12 Ravichandran G. A radiologic sign in spondylolisthesis. American Journal of Roentgenology 1980;134:113-117. 13 Araki T, Harata S, Nakano K, Satoh T. Reactive sclerosis of the pedicle associated with contralateral spondylolysis. Spine 1992; 17:1424-1426. 14 Gelfand MJ, Strife JL, Kerelakes JG. Radionuclide bone imaging in spondylolysis of the lumbar spine in children. Radiology 1981;140: 191-195. 15 Papanicolaou N, Wilkinson RH, Emans JB, Treves S, Micheli LJ. Bone scintigraphy and radiography in young athletes with low back pain. American Journal of Roentgenology 1985;145:1039-1044. 16 Lowe J, Schachner E, Hirchberg E, Shapiro Y, Libson E. Significance of bone scintigraphy in symptomatic spondylolysis. Spine 1984;9:653655. 17 Elliott S, Hutson MA, Wastie ML. Bone scintigraphy in the assessment of spondylolysis in patients attending a sports injury clinic. Clinical Radiology 1988;39:269-272. 18 Collier BD, Johnson RP, Carrera GF, Meyer GA, Schwab JP, Flatley TJ et al. Painful spondylolysis or spondylolisthesis studied by radiography and single photon emission computed tomography. Radiology 1985; 154:207-211. 19 Bellah RD, Summerville DA, Treves ST, Micheli LJ. Low back pain in adolescent athletes: detection of stress injury to the pars interarticularis with SPECT. Radiology 1991;180:509-512. 20 Read MT. Single photon emission computed tomography (SPECT) scanning for adolescent back pain. A sine qua non? British Journal of Sports Medicine 1994;28:56-57. 21 Ryan RJ, Gibson T, Fogleman I. The identification of spinal pathology in chronic low back pain using single photon computed tomography. Nuclear Medicine Communications 1992;13:497-502. 22 Ryan PJ, Evans PA, Gibson T, Fogelman I. Chronic low back pain: Comparison of bone SPECT with radiography and CT. Radiology 1992;182:849-854. 23 Raby N, Mathews S. Symptomatic spondylolysis: Correlation of CT and SPECT with clinical outcome. Clinical Radiology 1993;48: 97-99. 24 Suh PB, Esses SI, Kostuik JP. Repair of pars interarticularis defect. Prognostic value of pars infiltration. Spine 1991 ;16:$445 -$448. 25 van den Oever M, Merrick MV, Scott JHS. Bone scintigraphy in

symptomatic spondylolysis. Journal of Bone Joint Surgery (British) 1987;69:453-456. 26 Congeni J, McCulloch J, Swanson K. Lumbar spondylolysis. A study of natural progression in athletes. American Journal of Sports Medicine 1997;25:248-253. 27 Teplick JG, Laffey PA, Berman A, Haskin ME. Diagnosis and evaluation of spondylolisthesis and/or spondylolysis on axial CT. American Journal of Neuroradiology 1986;7:479-491. 28 Rothman SLG, Glenn WV. CT multiplanar reconstruction in 253 cases of lumbar spondylolysis. American Journal of Neuroradiology 1984; 5:81-90. 29 Langston JW, Gavant ML. 'Incomplete ring': A simple method for CT detection of spondylolysis. Journal of Computer Assisted Tomography 1985;9:728-729. 30 Elster AD, Jensen KM. Computed tomography of spondylolisthesis: patterns of associated pathology. Journal of Computer Assisted Tomography 1985;9:867-874. 31 Hession PR, Butt WP. Imaging of spondylolysis and spondylolisthesis. European Radiology 1996;6:284-290. 32 Grenier N, Kressel HY, Schiebler ML, Grossman RI. Isthmic spondylolysis of the lumbar spine: MR imaging at 1.5T. Radiology 1989;170: 489-493. 33 Johnson DW, Farnum GN, Latchaw RE, Erba SM. MR imaging of the pars interaticularis. American Journal of Roentgenology 1989;152: 327-332. 34 Saifuddin A, Burnett SJD. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clinical Radiology 1997; 52:666-671. 35 Ulmer JL, Matthews VP, Elster AD, King JC. Lumbar spondylolysis without spondylolisthesis: recognition of isolated posterior element subluxation on sagittal MR. American Journal of Neuroradiology 1995;16:1393-1398. 36 Ulmer JL, Elster AD, Matthews VP, Allen AM. Lumbar spondylolysis: reactive changes seen in adjacent pedicles on MR images. American Journal of Roentgenology 1995;164:429-433. 37 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology 1988; 166:193-199. 38 Yamane T, Yoshida T, Mimatsu K. Early Diagnosis of Lumbar Spondylolysis by MRI. Journal of Bone and Joint Surgery (British) 1993;75-B:764-768. 39 Jinkins JR, Matthes JC, Sener RN, Venkatappan S, Ranch R. Spondylolysis, spondylolisthesis and associated nerve root entrapment in the lumbosacral spine: MR evaluation. American Journal of Roentgenology 1992;159:799-803.

9 1998 The Royal Collegeof Radiologists,ClinicalRadiology, 53, 723-728.