The Spine Journal 5 (2005) 615–622
Congenital lumbar spinal stenosis: a prospective, control-matched, cohort radiographic analysis Kern Singh, MDa, Dino Samartzis, Dip EBHCb,c,d, Alexander R. Vaccaro, MDe, Ahmad Nassr, MDa, Gunnar B. Andersson, MD, PhDa, S. Tim Yoon, MDf, Frank M. Phillips, MDa, Edward J. Goldberg, MDa, Howard S. An, MDa,* a
Department of Orthopedic Surgery, Rush University Medical Center, 1725 West Harrison Street, Chicago, IL, USA 60612 b Division of Health Sciences, University of Oxford, Kellogg College, 1 Wellington Square, Oxford OX1 2JA, England c Graduate Division, Harvard University, 51 Brattle Street, Cambridge, MA 02138-3722, USA d London School of Economics and Political Science, University of London, Senate House, Malet Street, London WC1E 7HU, England e Thomas Jefferson University and the Rothman Institute, 925 Chestnut St., Philadelphia, PA 19102, USA f Department of Orthopedic Surgery, Emory University, 59 Executive Park, Atlanta, GA 30329, USA Received 11 January 2005; accepted 10 May 2005
Abstract
BACKGROUND CONTEXT: Degenerative lumbar spinal stenosis manifests primarily after the sixth decade of life as a result of facet hypertrophy and degenerative disc disease. Congenital stenosis, on the other hand, presents earlier in age with similar clinical findings but with multilevel involvement and fewer degenerative changes. These patients may have subtle anatomic variations of the lumbar spine that may increase the likelihood of thecal sac compression. However, to the authors’ knowledge, no quantitative studies have addressed various radiographic parameters of symptomatic, congenitally stenotic individuals to normal subjects. PURPOSE: To radiographically quantify and compare the anatomy of the lumbar spine in symptomatic, congenitally stenotic individuals to age- and sex-matched, asymptomatic, nonstenotic controlled individuals. STUDY DESIGN/SETTING: A prospective, control-matched, cohort radiographic analysis. PATIENT SAMPLE: Axial and sagittal magnetic resonance imaging (MRI) and lateral, lumbar, plain radiographs of 20 surgically treated patients who were given a clinical diagnosis of congenital lumbar stenosis by the senior author were randomized with images of 20, asymptomatic age- and sex-matched subjects. OUTCOME MEASURES: MRIs and lateral, lumbar, plain radiographs were independently quantitatively assessed by two individuals. Measurements obtained from the axial MRIs included: midline anterior-posterior (AP) vertebral body diameter, vertebral body width, midline AP canal diameter, canal width, spinal canal cross-sectional area, pedicle length, and pedicle width. From the sagittal MRIs, the following measurements were calculated: AP vertebral body diameter, vertebral body height, and AP canal diameter at the mid-vertebral level. On the lateral, lumbar, plain radiograph (L3 level), the AP diameters of the vertebral body spinal canal were measured. METHODS: The images of these 40 individuals were then randomized and distributed in a blinded fashion to five separate spine surgeons who graded the presence and severity of congenital stenosis utilizing a five-tier scale. Images consisting of 15 symptomatic individuals, graded definitely congenitally stenotic (mean age, 51.7 years; range, 43–65 years), and 15 asymptomatic individuals, graded definitely not stenotic (mean age, 50.7 years; range, 41–55 years), were age- and sexmatched and included for further review. From these 30 patients, a lateral, lumbar, plain radiograph and axial and sagittal MRIs (T1/T2 weighted) from L2-L5 were quantitatively analyzed. Rater reliability was assessed by Kappa coefficient testing.
FDA device/drug status: not applicable. Nothing of value received from a commercial entity related to this manuscript. 1529-9430/05/$ – see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2005.05.385
* Corresponding author. Department of Orthopaedic Surgery, RushPresbyterian-St. Luke’s Medical Center, 1725 West Harrison Street, POB 1063, Chicago, IL 60612. Tel: (312) 243-4244; fax: (312) 942-1516. E-mail address:
[email protected] (H.S. An)
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RESULTS: The cross-sectional area of the canal was significantly smaller in the congenitally stenotic patients at all lumbar levels measured (L2: 176 mm2 vs. 259 mm2, L3: 177 mm2 vs. 275 mm2, L4: 183 mm2 vs. 283 mm2, L5: 213 mm2 vs. 323 mm2, p!.05). Pedicle length was markedly shorter in the stenosis group at each lumbar level (L2: 5.9 mm vs. 8.9 mm, L3: 6.0 mm vs. 8.8 mm, L4: 6.5 mm vs. 9.2 mm, L5: 5.8 mm vs. 9.1 mm, p!.05). Furthermore, midline, axial AP canal diameter, vertebral body width, and sagittal AP canal diameter were all significantly smaller than the control patients (p!.05). A ratio of the AP diameter of the pedicle length to the vertebral body was also noted to be statistically significant on both the lateral plain radiographs (L3: 0.426 vs. 0.704) and sagittal MRI (L2: 0.343 vs. 0.461, L3: 0.361 vs. 0.461, L4: 0.362 vs. 0.481, L5: 0.354 vs. 0.452, p!.05). No difference was noted comparing the AP diameter of the vertebral body (axial and sagittal images), vertebral body height, canal width, and pedicle width. Kappa testing coefficient indicated a strong rater reliability (k50.81, 95% confidence interval: 0.62–0.94). CONCLUSIONS: Congenital lumbar stenosis has not been clearly defined radiographically. Clinically, congenitally stenotic patients present at a younger age with fewer degenerative changes and multiple levels of involvement. Radiographically, these patients have a shorter pedicular length and as a result a smaller cross-sectional spinal canal area (mean critical values of 6.5 mm and 213 mm2 were observed, respectively). The mean critical ratios were 0.43 (2:1 AP vertebral body: pedicle length) on the lateral lumbar radiograph and 0.36 on the sagittal MRI. The altered canal anatomy resulting from a decreased pedicle length may anatomically predispose these patients to earlier complaints of symptomatic neurogenic claudication. Identification of the presence of congenital stenosis should increase the treating surgeon’s awareness of the potential need for multilevel treatment. Ó 2005 Elsevier Inc. All rights reserved. Keywords:
Congenital; Developmental; Idiopathic; Stenosis; Lumbar; Spine; Pedicle; Canal; MRI; X-ray; Quantitative
Introduction In the early 1950s, Verbiest published a series of papers that initially described lumbar spinal stenosis and its successful operative management, which included the decompression of the neural elements [1–3]. Since Verbiest’s original treatise, the clinical presentation of lumbar spinal stenosis has been well described [4–23]. One of the first definitions of spinal stenosis was by Arnoldi et al. who classically defined the pathology as ‘‘any type of narrowing of the spinal canal, nerve root canals or intervertebral foramina’’ [4]. Others, such as Kirkaldy-Willis, were also instrumental in further delineating the pathology and pathogenesis of lumbar spinal stenosis [24–27]. The sequelae of neuroanatomical stenosis in the lumbar spine have been investigated in several studies. Delamarter et al. found that the effect of graded stenosis in the lumbar spine of a canine animal model adversely affected cortical evoked potentials long before any clinical signs occurred [28]. Furthermore, venous congestion and arterial constriction was noted around the neural elements and it was found that motor and sensory deficits may develop with a 50% or greater constriction of the cross-sectional area of the spinal canal [28]. Cadaveric studies have demonstrated an increase in pressure among the nerve roots when the dural sac is constricted to a cross-sectional area less than 77613 mm2 at the level of L3 [29–31]. Several studies have noted the importance of intraneuronal congestion, capillary restriction, and neuronal conductance dysfunction in cauda equina syndrome [32–36]. However, the clinical hallmark finding of lumbar stenosis
is neurogenic claudication, which presents as intermittent pain or paresthesia in the legs brought on by walking and standing, and classically relieved with flexion. Amundsen et al. reported that the most common symptoms in patients with lumbar spinal stenosis were back pain (prevalence of 95%), claudication (91%), leg pain (71%), weakness (33%), and voiding disturbances (12%) [37,38]. Even in the presence of symptoms, there may be few associated physical findings. Historically, confirmation of the diagnosis was obtained with myelography [3]. However, recently, magnetic resonance imaging (MRI) has become the imaging standard of choice because of its less invasive nature and excellent visualization of the thecal sac and neural elements in the neuroforamina. Several authors have since attempted to quantitatively measure the radiographic dimensions of patients with degenerative lumbar stenosis [5–8,14,16,17, 37,39–44]. Varying studies have reported that the anteriorposterior (AP) and transverse diameters of the spinal canal and its shape are reliable indicators of spinal stenosis [7,8]. According to Verbiest, two subgroups can be identified and include the following: absolute stenosis (AP diameter on myelography #10 mm) and relative stenosis (AP diameter between 10–12 mm) [20,21]. Sortland et al. described improved myelographic techniques with flexion-extension views and determined that 10.5 mm in extension was the lower value of normal [15]. The majority of patients evaluated in the aforementioned radiographic studies were patients in their 60s. Radiographic evidence of extensive degenerative changes was often apparent and included hypertrophy of the apophyseal
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joints, ligamentum flavum, and degenerative spondylolisthesis [45–48]. However, a small subset of patients, also primarily males, present at an earlier age with clinical symptoms of lumbar spinal stenosis. These patients are typically in their late 40s and early 50 years of age. Radiographic studies, namely plain X-ray and MRI, often show fewer degenerative changes with a markedly narrowed spinal canal involving multiple levels of stenosis [7,17,23,37,41,49]. Arnoldi et al. classified these patients as possessing congenital stenosis [4]. However, the authors never commented on the distinct anatomic characteristics of congenitally stenotic spinal canals. Congenital stenosis has been largely attributed to an abnormal anatomic development of the spinal canal [20,50]. A ‘‘normal’’ spinal canaldfor some unidentifiable reasond does not fully develop, predisposing these patients to spinal stenosis with fewer degenerative changes at an earlier stage in life. To the authors’ knowledge, no reliable or validated quantitative radiographic assessment of symptomatic congenital lumbar spinal stenosis exists. The importance of defining this subgroup of stenotic patients is clear. Congenitally stenotic patients classically present at an earlier age with multiple level involvement as opposed to their degenerative counterparts [21]. As such, operative planning must consider the need for multilevel intervention (ie, the presence of more global pathology). The following study attempted to quantitatively evaluate specific radiographic parameters based on axial and sagittal MRI (modality of choice for the evaluation of thecal sac compression) and lateral plain radiographic comparison (excellent, cost-effective screening study) of symptomatic, congenitally stenotic
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individuals to nonsymptomatic, nonstenotic individuals in a prospective, age- and sex-matched cohort design. Methods Axial and sagittal MRIs and lateral lumbar plain radiographs of 20 consecutive symptomatic patients who were given a clinical diagnosis of congenital lumbar stenosis by the senior author and who underwent surgical intervention were randomized with images of 20 consecutive asymptomatic age- and sex-matched controls (Fig. 1). Indications for surgical decompression included intractable back pain and the presence of neurogenic claudication exacerbated by activity. In addition, patients had to demonstrate rest relief of symptoms. The control group consisted of asymptomatic individuals who were nonlaborers with no prior history of smoking, heavy labor, back problems, or surgery. All patients were evaluated after informed consent was obtained following institutional review board approval. An individual blinded to the patient’s condition then randomized the MRIs and plain radiographic images of these 40 patients via a computerized randomization coded technique. The images were then distributed in a blinded fashion to five separate spine surgeons who graded the presence and severity of stenosis by a five-tier scale (Table 1). This evaluation and grading of the presence or absence of stenosis was performed on three separate occasions by each spine surgeon, with continuous blinding and randomization of the images. Only those patients who were deemed to be definitely congenitally stenotic (Type I) or definitely not congenitally stenotic (Type V) were chosen for further radiographic
Fig. 1. Schematic detailing the radiographic measurements calculated on the (A) axial, (B) lateral, and (C) close-up axial images.
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Table 1 Tier-structured classification of congenital stenosis Type Type Type Type Type
I II III IV V
Definitely congenital stenosis Probably congenital stenosis Indeterminate Probably not congenital stenosis Definitely not congenital stenosis
evaluation. From these stringent selection criteria, images from 30 patients representing 15 congenitally stenotic (mean age, 51.7; range, 43–65) and 15 nonstenotic (mean age, 50.7; range, 41–55) were obtained. In the definitely congenitally stenotic group, 13 males and 2 females were identified. In the definitely not congenitally stenotic group, 14 males and 1 female were selected. All 30 patients had lateral plain radiographs of the lumbar spine in the neutral position. Only the L3 level was measured on the lumbar plain radiographs because of variability of positioning with the radiographic technique. Furthermore, Pavlov’s ratio (canal diameter/vertebral body diameter) was measured on the lateral plain film, thereby controlling for radiographic magnification between patients [51]. In addition, each patient also had axial and sagittal MRIs (T1/T2 weighted) from L2-L5. Using a DICOM software analyzer (Osiris, Version 4.0.7, University Hospitals of Geneva), the magnetic resonance (MR) images were analyzed quantitatively by two individuals who were blinded by classification type. Measurements obtained from the axial MRIs included (Fig. 2A,B): (a) midline AP vertebral body diameter, (b) vertebral body width, (c) midline AP canal diameter, (d) canal width, (e) cross-sectional canal area, (f) pedicle length, and (g) pedicle width. From the sagittal MRIs, the following measurements were calculated (Fig. 2B): (h) AP vertebral body diameter, (i) vertebral body height, and (j) AP canal diameter at the mid-vertebral level. On the lateral plain lumbar radiograph (L3 level), the AP (k) vertebral body and (l) canal diameters were measured (Fig. 3). Descriptive and frequency statistics were analyzed. Tests for parametricity were conducted to determine appropriate statistical analyses. Log transformations were considered for data sets that exhibited absence of normal distribution. In the event that log transformations failed to establish normal distribution, nonparametric tests were considered. Various nonpaired and regression analysis tests were conducted to evaluate all parameters of interest. The threshold for statistical significance was established at p!.05. In addition, rater agreement reliability regarding quantitative image analyses was assessed using the Kappa coefficient test. A statistician performed the statistical analysis in a blinded fashion.
Results Axial MRI radiographic measurements, highlighted in Table 2, were obtained for every patient included in the
study. Evaluation of the cross-sectional area of the canal (e) was significantly smaller in the congenital stenosis patients at all lumbar levels measured (p!.05). Pedicle length (f) was markedly significantly smaller in the stenotic group at each lumbar level (p!.05). Midline, axial AP canal diameter (c) was also noted to be significantly smaller at each lumbar level for the congenital stenosis group (p!.05). Vertebral body width (b) was also found to be significantly smaller at each lumbar level for the congenital stenotic group (p!.05). The congenital stenosis patients were found to have statistically smaller AP canal diameters (j) on sagittal MRI in comparison to the control group (Table 3) (p!.05). In addition, a comparison of the ratio of pedicle length to AP vertebral body diameter (Table 4) was also noted to be statistically significant on both the lateral plain radiographs (L3: 0.43 vs. 0.70) and sagittal MRI (p!.05). No statistically significant difference was noted among axial MRI radiographs (Table 2) regarding vertebral body AP diameter (a), spinal canal width (d), and pedicle width or diameter (g) (pO.05). With regard to sagittal MR images (Table 3), nonsignificance was noted in vertebral body AP diameter (h) and in vertebral body height (i) (pO.05). In addition, testing for the Kappa coefficient yielded a strong rater reliability (k50.81, 95% confidence interval: 0.62–0.94).
Discussion Anatomically, lumbar stenosis is caused by a reduction in the space available for the neural elements as a result of osseous or soft-tissue hypertrophy [7,10,28,39,52–56]. Degenerative lumbar stenosis begins with a loss of disc height, resulting in bulging of the annulus fibrosus and ligamentum flavum into the spinal canal. These changes alter the loading of the facet joints leading to facet arthrosis and osteophytic overgrowth [38]. The AP diameter of the canal is concordantly reduced by the bulging annulus anteriorly and the hypertrophic facets posteriorly. Debate continues over which morphologic measurement is most accurate in diagnosing spinal stenosis since the concept was introduced by Verbiest in the early 1950s [1–3]. Several authors have measured dried vertebrae in an attempt to establish normal and abnormal canal sizes [6–8,38,57–59]. The degree of constriction of the spinal canal necessary to elicit symptoms is not clear and various critical values have been proposed, including an absolute stenosis value of #10 mm in the AP canal diameter or a cross-sectional area less than 77613 mm2 of the thecal sac [5,7,8,13,14,21,28, 40,43,57,58]. Typically, in degenerative lumbar spinal stenosis, the area of maximal constriction is often limited to a single level, particularly L4-L5 [45,47,59]. However, in congenital stenosis, the spinal canal is narrowed much more uniformly. Unquestionably, and as noted in the present study, one sign of developmental stenosis is a uniform narrowing of the
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Fig. 3. Lateral plain radiograph of a congenitally stenotic patient with the pedicle length to vertebral body ratio demarcated at the L3 level.
Fig. 2. Magnetic resonance imaging (T2-weighted) of a patient determined to be congenitally stenotic. Radiographic measurements have been drawn on the (A) axial and (B) sagittal images at the L3 level. Note the decreased pedicular length and the compressed (anterior-posterior) appearance of the spinal canal.
spinal canal throughout the lumbar spine. Another interesting finding commonly observed with congenital stenosis is that clinical presentation, as in this study, classically occurs earlier in life (fourth to sixth decade) with few degenerative changes (ie, bulging annulus fibrosus, facet hypertrophy). Our study confirmed what is commonly assumed, that congenitally stenotic patients all exhibit significantly smaller bony canal areas than their ‘‘normal’’ counterparts at all
lumbar levels measured (L2-L5). In fact, all the stenotic patients exhibited less than 200 mm2 canal area at all levels except L5, whose mean value in this study was 213 mm2. This is in distinct contrast to the control group where canal areas all measured above 250 mm2. To explain the difference in cross-sectional area between congenitally stenotic patients and the control group, certain other radiographic findings were analyzed. The most striking difference between the two groups was the pedicle length. Congenitally stenotic patients exhibited pedicle lengths approximating 6 mm with an apparent critical cutoff of 6.5 mm, whereas the control subjects had measurable pedicle lengths closer to 9 mm. This decrease in pedicle length directly affects the AP diameter of the canal as measured on both the axial and sagittal MR images. Approximately a 2–3 mm difference was noted in the congenitally stenotic patients in the AP dimensions of the canal in both the axial and sagittal views. An interesting finding was that no appreciable difference was identified when measuring the transverse diameter of the spinal canal, suggesting that the decrease in cross-sectional area was due primarily to a decreased AP diameter of the canal. Though vertebral body width was noted to be smaller in the congenitally stenotic patients, this did not result in a decrease in the canal width. Interestingly, when asked to subjectively comment on the most striking feature of the MR images of the stenotic
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Table 2 Axial MRI radiographic measurements (statistically significant values have been italicized) Congenital stenosis SD Vertebral body AP diameter (mm) (a) L2 38.5 L3 38.2 L4 40.2 L5 41.1 Vertebral body width (mm) (b) L2 45.2 L3 44.5 L4 45.7 L5 49.5 Spinal canal AP diameter (mm) (c) L2 13.9 L3 14.2 L4 14.4 L5 14.7 Spinal canal width (mm) (d) L2 21.1 L3 21.0 L4 21.3 L5 23.1 Cross-sectional canal (mm2) (e) L2 175.6 L3 176.9 L4 182.5 L5 212.6 Pedicle length (mm) (f) L2 5.9 L3 6.0 L4 6.5 L5 5.8 Pedicle width (mm) (g) L2 10.8 L3 11.6 L4 12.2 L5 13.7
Control SD
Table 3 Sagittal magnetic resonance imaging radiographic measurements (statistically significant values have been italicized) p Value
5.3 4.9 5.6 5.9
38.1 38.5 39.0 38.5
2.8 3.2 3.8 4.6
0.68 0.93 0.38 0.18
4.1 4.6 6.7 7.0
51.3 53.2 51.6 53.9
3.4 3.7 4.0 4.3
!0.05 !0.05 !0.05 !0.05
3.7 3.2 3.0 2.1
16.3 17.5 18.0 18.8
2.1 1.7 2.7 3.6
!0.05 !0.05 !0.05 !0.05
2.5 3.8 4.5 3.4
21.9 24.3 23.7 26.0
1.4 2.8 2.4 4.2
0.92 0.08 0.31 0.13
32.4 30.8 25.3 41.6
258.8 275.3 282.7 323.0
36.3 24.4 32.9 68.5
!0.05 !0.05 !0.05 !0.05
0.8 1.1 1.0 1.1
8.9 8.8 9.2 9.1
0.8 0.9 1.3 0.8
!0.05 !0.05 !0.05 !0.05
1.9 2.0 2.1 2.2
9.9 10.8 11.5 12.3
2.2 2.4 2.2 2.9
0.29 0.25 0.26 0.26
AP5anterior-posterior; MRI5magnetic resonance imaging; SD5standard deviation.
patients, a uniform agreement among the five spine surgeons was made that pedicle length was markedly diminished. All reviewers noted a ‘‘compressed’’ appearance of the spinal canal as compared with the more round/ovoid canal of the ‘‘normal’’ patients. Additionally, minimal canal encroachment from facet hypertrophy was identified in the congenitally stenotic group. Furthermore, no difference was observed in the measurements obtained for vertebral height, as well as the AP vertebral body diameter and pedicle width. These anatomic similarities suggest that congenitally stenotic patients cannot be assumed to have overall smaller vertebrae. Rather, the anatomic measurements are very much similar in control and congenitally stenotic patients except for pedicle length and the dependent AP diameter of the canal. Radiographic ratios of pedicle length to vertebral body also revealed statistically significant findings on both the lateral lumbar radiographs and sagittal MR images. A mean
Congenital stenosis
SD
Vertebral body AP diameter (mm) (h) L2 35.3 3.5 L3 36.0 3.4 L4 36.2 3.9 L5 37.0 3.9 Vertebral body height (mm) (i) L2 27.2 3.6 L3 27.5 3.3 L4 26.9 4.8 L5 28.0 5.9 Spinal canal AP diameter (mm) (j) L2 12.1 1.6 L3 13.0 1.6 L4 13.1 2.1 L5 13.1 2.9
Control
SD
p Value
34.1 35.0 35.2 36.8
2.9 3.1 2.6 3.5
0.28 0.24 0.25 1.0
26.3 26.6 26.6 27.8
1.9 1.3 1.4 2.5
0.26 0.11 0.47 0.54
15.7 16.1 16.9 16.6
1.7 2.0 1.4 2.6
!0.05 !0.05 !0.05 !0.05
AP5anterior-posterior; SD5standard deviation.
critical value of 0.43 was noted for the pedicle length:AP vertebral body diameter ratio on the lateral L3 radiograph. This finding was confirmed on the sagittal MRIs where a mean critical value of 0.36 was noted as being the cutoff between normal and congenitally stenotic patients. That is, the vertebral body AP diameter to pedicle length ratio was approximately greater than 2:1 in normal patients and less than 2:1 in congenitally stenotic patients on the lateral radiograph. Several radiographic studies regarding degenerative lumbar stenosis have evaluated critical vertebral body and canal dimensions. Epstein et al. found that approximately 15 mm was the lower limit of normal for the sagittal canal diameter [9]. Eisenstein measured 2,166 vertebrae from 433 adult, dried skeletons and found that any lumbar vertebrae having a mid-sagittal diameter of less than 13 mm was considered stenotic [6–8,57]. These values correlate extremely well with the AP canal dimensions obtained on our MR images (L2: 13.9, L3:14.2, L4:14.4, L5:14.7). Schonstrom et al. identified a mean AP canal diameter of 14.1 mm in computed tomographic scans of the lumbar spine in 24 patients who underwent lumbar decompression [44]. Furthermore, the authors also noted a mean cross-sectional area of approximately 225 mm2 that also correlated with our findings in
Table 4 Calculated pedicle length:vertebral body ratio for the lateral lumbar plain radiograph (L3) and the sagittal magnetic resonance images (L2-L5) (statistically significant values have been italicized) Congenital Level stenosis SD Plain X-ray L3 Magnetic resonance L2 imaging L3 L4 L5
0.43 0.34 0.36 0.36 0.35
0.03 0.05 0.03 0.05 0.07
Normal SD
p Value
0.70 0.46 0.46 0.48 0.45
!0.05 !0.05 !0.05 !0.05 !0.05
0.06 0.07 0.04 0.05 0.06
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congenitally stenotic patients (L2: 176 mm , L3: 177 mm , L4: 183 mm2, L5: 213 mm2). It appears that symptomology from spinal stenosis, as observed by a review of the literature, correlates with certain critical canal measurements (cross-sectional area, AP canal diameter) regardless of the etiology (degenerative vs. congenital). However, it appears that congenitally stenotic patients exhibit certain unique features that differentiate the spinal canal anatomy from degenerative stenosis. In congenitally stenotic patients, the spinal canal is not as profoundly narrowed by osteophytic (facet) or soft-tissue overgrowth as observed in degenerative lumbar stenosis. Rather, the canal narrowing is primarily a result of the decreased pedicle length (critical value of |6.5 mm). The decrease in pedicle length thereby proportionally decreases the AP canal diameter, spinal canal area, as well as the pedicle length:vertebral body diameter ratio. Undeniably, short pedicles also give the canal an overall flattened ovoid appearance. In addition, by visual appearance, as the lateral recess decreases the central canal proportionally appeared to decrease. It is well known that congenital stenosis represents a spectrum of disease reflecting various anatomic differences. However, certain limitations of this study exist. One clear shortcoming of this study was that all congenitally stenotic patients evaluated were treated surgically; however, the preoperative MRI and plain radiographs of all congenitally stenotic patients included in this study were implemented for evaluation. Nonetheless, these patients represent severe or clinically symptomatic individuals at the extreme end of the spectrum. In reality, congenital stenosis represents a gradation of changes and not an absolute cutoff. Evaluation of symptomatic congenitally stenotic patients, managed by conservative measures, may aid in our understanding of the anatomic subtleties that predispose these patients to presenting with clinical complaints. In conclusion, though the clinical presentation of congenital lumbar stenosis may be similar in nature to degenerative lumbar stenosis, the underlying pathology is a developmental narrowing of the spinal canal. Congenitally stenotic patients present at an earlier age (40–50s) with less radiographic evidence of spondylosis. Screening lateral plain radiographs may identify a decreased pedicle length to vertebral body ratio (0.43) at the L3 vertebral level. Furthermore, axial MR images may reveal significantly decreased pedicular length (#6.5 mm) with a ‘‘compressed’’/‘‘flattened’’ appearing canal and a decreased cross-sectional canal area (#213 mm2). Careful attention must be paid to identify the subtle anatomic differences in congenital stenosis in order to render the most appropriate surgical treatment.
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