Intra-and-Inter Observer Reproducibility Of Linear Measurements with Axial Images of L3 and L5 Vertebras

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1 ISSN X Kręgosłup i klatka piersiowa Intra-and-Inter Observer Reproducibility Of Linear Measurements with Axial Images of L3 and L5 Vertebras Powtarzalność i odtwarzalność metody pomiarów liniowych kręgów L3 i L5 w projekcji osiowej Juan A. Sanchez-Martinez 1, Jo-Yang Tan 1, Sarina Promthong 1, Mikołaj Dąbrowski 2, Andrzej Nowakowski 2, Łukasz Kubaszewski 2 1 Poznan University of Medical Sciences 2 Department of Spondyloorthopedics and Biomechanics of the Spine, Wiktor Dega University Hospital, Poznan University of Medical Sciences Abstract The primary cause of the loss of the lumbar lordosis is attributed as a sequel of disk height reduction. Secondary hypertrophy of the posterior column of the spine is observed in course of degenerative spine disease which may be due to the posterior column lengthening. There are no studies to prove or reject the hypothesis of the posterior column lengthening as a possible reason for the loss of the lordotic configuration in the lumbar spine. Purpose: The purpose of this study was to evaluate the intra-and-inter-observer reproducibility of measurements method of elements within the posterior column in the lumbar spine. Materials and methods: Linear measurements were performed by three medical students to assess the parameters of the posterior column structures in L3 and L5 vertebrae according to the methodology proposed by Kubaszewski et al. after initial training of the method utilizing RadiAnt DICOM. The analyzed group consisted of 15 patients (7 male patients and 8 female patients between the ages of 46 to 71 years of age). Measurements were made over the course of three months. The statistical analysis was performed with SPSS The data normality was confirmed using the Shapiro-Wilk test. To verify intra-and- -inter-rater reliability, the Intra-Class Coefficient (ICC) was calculated and classified according to literature as weak (ICC<0.40), moderate (ICC between 0.40 and 0.75), and excellent (ICC>0.75). The level of significance adopted for all tests was Results: Overall, the intra-and-inter observer reliability was excellent. The measurement tool accuracy is 0.1 mm which in our opinion, is sufficient. The statistical analysis showed high intra-and-inter-observer reliability for the measurements. The degree of disagreement may be due to a function of advancement of the degenerative process. Conclusions: The vertebrae as the irregular form bones are most difficult for analysis as for dimensions and internal distances. The CT reproduction grants the best possibility in both planar and volumetric analysis. The analyzed method yields in our opinion sufficient reproducibility to analyze the height of the elements in the posterior column of the lumbar spine in order to evaluate the role of posterior column in loss of the lordosis in course of degenerative changes. Key words: Interobserver, Intraobserver, Lordosis, Lumbar, Posterior column, Reproducibility, Spine, Variability Streszczenie Wstęp: Pierwotna przyczyna utraty lordozy lędźwiowej jest przypisywana jako zmniejszeniu wysokości krążka międzykręgowego. Wtórny przerost tylnej części kręgosłupa obserwuje się w przebiegu zmian zwyrodnieniowych co może być spowodowane wydłużeniem tylnej kolumny. Nie ma badań potwierdzających lub odrzucających hipotezę wydłużenia kolumny tylnej jako możliwej przyczyny utraty lordotycznej konfiguracji w części lędźwiowej kręgosłupa. Celem tego badania była ocena powtarzalności i odtwarzalności metody pomiaru elementów tylnej kolumny kręgosłupa lędźwiowego. Materiał i metody: Pomiary liniowe zostały przeprowadzone przez trzech studentów medycyny w celu oceny parametrów tylnych kolumny w kręgach L3 i L5 zgodnie z metodologią zaproponowaną przez Kubaszewskiego i in. wykorzystując oprogramowanie RadiAnt DICOM. Analizowana grupa składała się z 15 pacjentów (7 mężczyzn i 8 kobiet w wieku od 46 do 71 lat). Pomiary wykonano w ciągu trzech miesięcy. Analizę statystyczną przeprowadzono za pomocą SPSS Zgodność z rozkładem normalnym testowano za pomocą testu Shapiro-Wilka. oceny powtarzalności i odtwarzalności dokonano z użyciem współczynnika korelacji wewnątrzklasowej (ICC), sklasyfikowanego zgodnie z literaturą jako słaby (ICC <0,40), umiarkowany (ICC od 0,40 do 0,75) i dobry (ICC> 0,75). Wyniki: Powtarzalność i odtwarzalność pomiarów była doskonała. Analiza statystyczna wykazała wysoką wiarygodność między pomiarami i między obserwatorami. Niezgodność pomiarów może wynikać z zaawansowania procesu zwyrodnieniowego. Wnioski: Kręgi jako kości o nieregularnym kształcie są najtrudniejsze do analizy, jak wymiary i odległości wewnętrzne. Tomografia komputerowa daje najlepszą możliwość analizy płaszczyzny, jak i objętości. Analizowana metoda daje, naszym zdaniem, wystarczającą powtarzalność i odtwarzalność pomiarów elementów w tylnej kolumnie kręgosłupa lędźwiowego w celu oceny roli tylnej kolumny w utracie lordozy w przebiegu zmian zwyrodnieniowych. Słowa kluczowe: powtarzalność, odtwarzalność, lordoza lędźwiowa, tylna kolumna, kręgosłup, zmienność Author s address: Juan A. Sanchez-Martinez, Poznan University of Medical Sciences, jasmmd@gmail.com, tel.: Received: Accepted: Published:

2 Introduction Spinal degeneration is primarily attributed to the pathology of intervertebral disc tissue. The breakdown of extracellular matrix in the nucleus pulposus leads to the deterioration of the tissue s capacity for water absorption. The consequences are observed as signal loss in T2-weighted magnetic resonance images. The observed changes are summarized in the Pfirrmann grading system commonly used in clinical practice. The initial nucleus signal changes are accompanied by intervertebral disk height diminution. Further observation of lumbar spine degeneration through the use of CT scans and MRI exceeds beyond the intervertebral disc. Spondylosis, which involves the entire segment, results in bony spur formation, observed predominantly at the vertebral bodies and as hypertrophy of the facet joints. Further advancement of degenerative changes of the lumbar spine leads to significant loss of lordosis angle or advanced distortions in the sagittal, frontal or transverse plane described as degenerative scoliosis. The primary cause of the loss of the lumbar lordosis is attributed as a sequel of disk height reduction. Though as stated above secondary hypertrophy of the posterior column of the spine is observed in course of degenerative spine disease may be an additional cause of posterior column lengthening. There are no studies to prove or reject the hypothesis of the posterior column lengthening as a possible reason for the loss of the lordotic configuration in the lumbar spine. Such hypothesis along with the posterior column measurement method has been proposed by Kubaszewski et al (Kubaszewski Ł, Dąbrowski M, Bartoszcze B, Nowakowski A, Kaczmarczyk J 2016). In the method, the height of facet joint both superior and inferior as well as spinal processes are measured from the midplane constructed similarly to the Frobin et al.concept (Frobin et al. 1997) being in equal distance from the vertebral front and rear corners (Fig. 1). The final values are plotted as the relative values in relation to measured value that stays, least changed throughout the age i.e. pedicle height. The aim of this study was to evaluate intra-and-inter-observer agreement in the measurement of posterior column of the spine elements according to the method proposed by Kubaszewski et al. Materials and method Linear measurements were performed to assess the parameters of the posterior column structures in L3 and L5 vertebrae according to the methodology proposed by Kubaszewski and al. (Kubaszewski Ł, Dąbrowski M, Bartoszcze B, Nowakowski A, Kaczmarczyk J 2016). The measurements were performed on DICOM CT scans of 15 patients diagnosed for the back pain due to degenerative disc disease. The analyzed group consisted of 7 male patients (youngest being 46 years of age and the oldest being 71 years of age) and 8 female patients (youngest being 46 years of age and oldest being 70 years of age). The measured parameters were: pedicle height, superior facet height, inferior facet height, spinal process height and spinal process length. Measurements were performed by three medical university students after initial training of the method using Radi- Ant DICOM Viewer shareware version, Medixant, Poznan, Poland. To assess the intra-observer variability measurements were performed by three medical students after initial training of the methods of measurement. Measurements were made over the course of three months. Each student made measurements on weekends at the privacy of his/her residence. The statistical analysis was performed with SPSS Initially, a data descriptive analysis was carried out using descriptive statistics. The data normality was confirmed using the Shapiro-Wilk test. To verify intra-and-inter-rater reliability, the Intra-Class Coefficient (ICC) was calculated. ICC was based on a 2-way (random effects) repeated-measures analysis of variance model with an absolute agreement. The values found in the ICC were classified according to literature as weak (ICC<0.40), moderate (ICC between 0.40 and 0.75), and excellent (ICC>0.75). The level of significance adopted for all tests was Results Pedicle height In the analyzed group pedicle height measured with the method ranged from cm, a mean value of cm for observer no 1. For observer no.2, pedicle height ranged from cm, a mean value of cm. Pedicle height ranged from cm, a mean value of cm for observer no. 3. The interobserver ICC for pedicle height measurement was and for L3 and L5 vertebrae respectively. The intraobserver ICC value for L3 vertebrae analysis was: 0.92, and for observer no 1, 2 and 3 respectively. Intraobserver ICC value in measurement performed at L5 vertebrae was for observer no 1, 2 and 3 respectively: 0.904, and Superior facet height Superior facet height measured with the method ranged from cm, a mean value of cm for observer no. 1. For observer no. 2, superior facet height ranged from cm, a mean value of cm. Superior facet height 217

3 Fig. 1. In the first step, the corners of the projected vertebra are defined X and X at the frontal part and Y and Y in the dorsal part. Fig. 4. The method for measurement of disc height, vertebral height, and sagittal plane. The posterior column length (PCL) is between point Ym and the vertical straight tangent to the tip of the spinal process. Fig. 2. The method for measurement of disc height, vertebral height, and sagittal plane. Abbreviation: Xm and Ym - points defined by the middle of each section. Fig. 5. The superior facet height (sfh) is straight from midplane to the tangent of the tip of the superior facet; The inferior facet height (ifh) is the distance from midplane to the tangent of the tip of the inferior facet. Fig. 3. The method for measurement of disc height, vertebral height, and sagittal plane. Abbreviation: s1, s2 - straights parallel to midplane are produced as borders the pedicle cranially (s1) and caudally (s2); pedicle height (ph) is the distance between the straights s1 and s2. Fig. 6. The spinal processes height (sph) is measured from the midplane to the tangent of the inferior tip of the spinal processes. ranged from cm, a mean value of cm for observer no. 3. The interobserver ICC for superior facet height measurement was 0.77 and for L3 and L5 vertebrae respectively. The intraobserver ICC value for L3 vertebra analysis were 0.741, and for observer no. 1, 2 and 3 respectively. Intraobserver ICC value in measurement performed at L5 vertebrae were for observer no. 1, 2 and 3 respectively: 0.678, and Inferior facet height Inferior facet height measured with the method ranged from cm, a mean value of cm for observer n. 1. For observer no. 2, inferior facet height ranged from cm, a mean value of 3.06 cm. Inferior facet height ranged from cm, a mean value of cm for observer no. 3. The interobserver ICC for inferior facet height measurement was and for L3 and L5 vertebra, respectively. The intraobserver ICC value for L3 vertebrae analysis were 0.953, and for observer no. 1, 2 and 3 respectively. 218

4 Intraobserver ICC value in measurement performed at L5 vertebrae were for observer no. 1, 2 and 3 respectively: 0.871, and Spinal process length Spinal process length measured with the method ranged from cm, a mean value of cm for observer no. 1. For observer no. 2, spinal process length ranged from cm, a mean value of 5.22 cm, respectively. Spinal process length ranged from cm, a mean value of cm for observer no. 3. The interobserver ICC for spinal process length measurement was and for L3 and L5 vertebrae respectively. The intraobserver ICC value for L3 vertebrae analysis was: 0.988, and for observer no. 1, 2 and 3, respectively. Intraobserver ICC value in measurement performed at L5 vertebrae were for observer no. 1, 2 and 3 respectively: 0.973, 0.98 and Spinal process height Spinal process height measured with the method ranged from cm, a mean value of cm for observer no. 1. For observer no. 2, spinal process height ranged from cm, a mean value of cm. Spinal process height ranged from cm, a mean value of cm for observer no. 3. The interobserver ICC for spinal process height measurement was and for L3 and L5 vertebrae, respectively. The intraobserver ICC value for L3 vertebrae analysis was: 0.972, and for observer no. 1, 2 and 3 respectively. Intraobserver ICC value in measurement performed at L5 vertebrae was for observer 1, 2 and 3 respectively: 0.991, and Discussion Interobserver analysis Interobserver agreement was found as moderate in 6 cases and excellent in 4 cases. The worst interobserver agreement was found in measuring the spinal process height for L5 vertebrae (ICC 0.412). For the L3 vertebrae agreement was higher but still to be accounted as moderate (0.639). Pedicle height measurements agreement was higher for L5 vertebrae (0.811) while for L3 vertebrae it reached only (0.686). Facet height measurements agreement was excellent, bot superior and inferior, in L3 vertebrae (0.77 and respectively) while in L5 vertebrae it reached only ICC values and respectively. Spinal process length reached moderate reproducibility for L3 vertebrae (0.603) but was excellent in L5 vertebrae (0.757). Intraobserver analysis The intraobserver agreement reached a range of excellence for all three observers in pedicle height, inferior facet height, spinous processes height and spinous processes length measurements for both L3 and L5 vertebrae. For superior facet height measurement in L3 vertebrae, only one observer reached excellent reproducibility while other ICC values were and 0.713, which is upper bound for moderate reproducibility. In case of superior facet height measurement performed in L5 vertebra, no one achieved an excellent range of reproducibility, and ICC values for observers 1 through 3 were: 0.678, 0.554, respectively. The evaluated method consists of several steps to reach the final linear value. The first step seems to be most observer dependent for its demands to point four points at the corners of the vertebral silhouette in the sagittal plane. Subsequent steps, midplane construction and actual distance from the midplane measurements, are less observer dependent and variability is more related to measurements tool. The measurements in this study were performed with original digital Dicom images. The measurement tool accuracy is 0,1 mm which is in our opinion, sufficient. In the original Frobin method (Frobin et al. 1997) fourpoint for vertebral corners setting was intended to minimise distortion of the vertebral body picture characteristical for x-ray imaging. The distortion increments with the distance from central beam. In CT scans such distortion is not observed as the picture reflects the actual and 3-dimensional representation of the structure. Another issue is that Forbin s method encompassed for the analysis the image of the whole vertebral body using the outermost margin. In Kubaszewski et al. method the largest plane of the vertebral body section is sought which is the image of the body sectioned in the midline. Therefore observed distortion in this type of measurement is of other ground. It is due to rotational displacement of the vertebrae in frontal plane which is characteristic to asymmetrical subsidence of intervertebral space especially pronounced in degenerative scoliosis. The typical vertebral body remodeling in degenerative process i.e. bony spur formation may also influence the midline silhouette of the vertebral body because those are observed in the anterior and lateral aspects of the vertebral bodies (Benjamin et al. 2006). Those are observed 219

5 in mild stages of the degenerative process (Benneker et al. 2005). Aforementioned factors are of our opinion are key issues influencing lower than excellent interobserver agreement. The degree of disagreement may be a function of advancement of the degenerative process which needs to be confirmed in further studies. Conclusion The vertebrae as the irregular form bones are most difficult for analysis as for dimensions and internal distances. The CT reproduction grants the best possibility in both planar and volumetric analysis. The analyzed method yields in our opinion sufficient reproducibility to analyze the height of the elements in the posterior column of the lumbar spine in order to evaluate the role of posterior column in loss of the lordosis in course of degenerative changes. References [1] Benjamin, M. et al.: Where tendons and ligaments meet bone: attachment sites ( entheses ) in relation to exercise and/or mechanical load. Journal of anatomy, 2006; 208(4): [2] Benneker, L.M. et al.: Correlation of radiographic and MRI parameters to morphological and biochemical assessment of intervertebral disc degeneration. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society, 2005; 14(1): [3] Frobin, W. et al.: Precision measurement of disc height, vertebral height and sagittal plane displacement from lateral radiographic views of the lumbar spine. Clinical biomechanics, 1997; 12 Suppl 1: S1 S63. [4] Kubaszewski Ł., Dąbrowski M., Bartoszcze B., Nowakowski A., Kaczmarczyk J., Method for measurement of posterior column parameters in sagittal computer tomography reconstruction of the lumbar spine. Chir. Narz. Ruchu (d. Pol. Orthop. Traumatol.), 2016; 81(5):