Subjects
The inclusion criteria were healthy elderly individuals (age > 50 years) without obesity (body mass index [BMI] < 30] and varus knee OA. The exclusion criteria were as follows: no history of trauma, valgus knee OA, postoperative prosthetic or osteotomy knees, or other diseases that influence the CBT, such as osteometabolic diseases, except for primary osteoporosis.
For the healthy subjects, a total of 107 elderly Japanese volunteers who had no knee complaints or histories of joint disease or major injury in the lower extremity were publicly recruited. The volunteers did not have any competing interests and were not paid any fees. Physicians assessed their general and lower extremity conditions using physical tests and radiographs and excluded seven subjects with radiographic evidence of knee OA. Out of 100 healthy elderly patients (50 males and 50 females) with grades 0–1 according to the Kellgren-Lawrence (K-L) classification and the absence of radiographic knee OA, 53 elderly (aged > 50 years) Japanese volunteers (28 males and 25 females) were randomly selected for this study [Fig. 1]. Two orthopedic surgeons (graders), who were not provided with any clinical information on the patients, performed the K-L classification. When the same subject was assigned different grades, the graders discussed and determined a common K-L grade. The average age ± standard deviation (SD) (range) of the elderly males and females was 71 ± 6 years (61 to 83 years) and 68 ± 6 years (60 to 83 years), respectively. The average BMI ± SD (range) of the elderly males and females was 23.0 ± 2.1 kg/m2 (17.6 to 27.0 kg/m2) and 20.0 ± 1.6 kg/m2 (17.1 to 23.0 kg/m2), respectively (Table 1).
Table 1
| OA group | Healthy group | Male vs Female | OA vs Healthy group |
| Male (n = 22) | Female (n = 38) | Male (n = 28) | Female (n = 25) | OA group | Healthy group | Male group | Female group |
| Mean ± SD | Mean ± SD | Mean ± SD | Mean ± SD | p value | p value | p value | p value |
Age (yr) | 73.5 ± 7.6 | 73.6 ± 6.5 | 71.3 ± 6.1 | 67.7 ± 5.5 | n.s. | n.s. | n.s. | .003* |
Height (cm) | 162.8 ± 6.4 | 148.9 ± 5.5 | 166.2 ± 4.6 | 155.4 ± 5.3 | < .001* | < .001* | n.s. | < .001* |
Weight (kg) | 66.0 ± 8.6 | 59.0 ± 8.6 | 63.6 ± 7.3 | 48.3 ± 5.0 | .005* | < .001* | n.s. | < .001* |
BMI (kg/m2) | 24.9 ± 2.9 | 26.6 ± 3.7 | 23.0 ± 2.1 | 20.0 ± 1.6 | n.s. | .001* | n.s. | < .001* |
FTA(°) | 186.8 ± 2.7 | 189.3 ± 4.5 | 178.5 ± 2.5 | 175.4 ± 2.1 | .024* | .006* | < .001* | < .001* |
MCT(°) | 12.2 ± 4.1 | 12.3 ± 4.5 | 9.3 ± 2.7 | 6.9 ± 2.3 | n.s. | n.s. | .035* | < .001* |
OA = knee osteoarthritis; SD = standard deviation; BMI = body mass index; FTA = femorotibial angle; MCT = medial compartment of the proximal tibia; *= < 0.05; n.s. = > 0.05 |
Patients with varus knee OA (age > 50 years) were initially selected from medical operation records from 2009 to 2020, with 1120 surgical knee OA patients using CT data. Participants with diseases affecting the CBT, such as skeletal dysplasia, infections, bone metabolic diseases, and those without CT or BMI data were excluded. Finally, using the above exclusion criteria, the lower extremities of 60 patients with varus knee OA (22 males and 38 females), randomly selected from 1,120 knees aged 50 years or older, were included. The mean ± SD (range) age of males and females was 74 ± 8 (54 to 86) years and 74 ± 7 (61 to 87) years, respectively. The mean BMI ± SD (range) of males and females were 24.9 ± 2.9 kg/m2 (32.4 to 18.5 kg/m2) and 26.6 ± 3.7 kg/m2 (34.7 to 20.7 kg/m2) (Table 1).
CT scanning condition
CT scans with a 1-mm interval in the lower extremities from the femoral head to the ankle joint were performed at two institutions using the Somatom Sensation 16 (Siemens Inc., Munich, Germany) and Canon Aquilion 64 CT scanners (Canon Medical Systems, Tochigi, Japan). The scans were obtained at a tube voltage of 120 kVp and a current of 50–400 mA. The field-of-view, matrix, and pixel parameters were 350–400 mm, 512 × 512, and 0.68–0.78 mm/pixel, respectively. The voxel size ranged from 0.68 × 0.68 × 1.00 mm to 0.78 × 0.78 × 1.00 mm. For CT radiation, the mean dose length product was 896.7 ± 129.9 mGy × cm.
Calculation of cortical thickness
The CBT of the tibial diaphysis was automatically calculated in 3D space using the high-resolution measurements reported by Treece et al. [2, 3] [Fig. 2], which allowed for accurate estimates of the CBT based on an estimate of cortical density. The technique was implemented using Stradwin software (version 5.3; Medical Imaging Group, Machine Intelligence Laboratory, Cambridge Engineering Department, Cambridge, UK), which is available for free download and is a new tool with demonstrated sub-voxel accuracy in assessing cortical bone properties using routine low-resolution CT. The method uses a complex model-based fit approach with a mathematical model of the anatomy and imaging system, calculates from thousands of data points across the bone surface, and performs assessments using semi-automatic segmentation [2]. The creation of the surface and use of the surface normal to guide the thickness estimation were performed as follows [Fig. 2]: A surface was generated by thresholding the entire dataset and extracting the contours in each plane to subpixel resolution. The contours were then edited locally to correct erroneously excluded regions and remove adjoining structures. A surface was interpolated through these contours, and the surface vertices and normal were used to guide the in-plane thickness estimates using a mathematical equation. The number of measurement points per subject was 2,752–11,296, depending on the tibial length and bone mineral density. The CBT was calculated for each point. Given the prior segmentation of the tibia, the CT values (Hounsfield units) were examined along the short lines that straddled and were perpendicular to the cortex [Fig. 2]. Once the CBT was estimated at each vertex, it was mapped back onto the surface as a color, using a cortical bone-mapping technique [Fig. 3]. A high-resolution thickness map is filtered over the surface.
Regarding accuracy, Treece et al. [2] tested the validity of the constant-density assumption by measuring the true density of cadaveric femurs on high-resolution CT, which had approximately seven times the resolution of low-resolution scans. They reported that the CBT estimates were accurate by up to 0.3 mm. The technique was validated in vivo in the context of osteoporosis and hip fractures within the laminar structures [2, 14].
Anatomical tibial coordinate system
An anatomical coordinate system for the tibia was constructed using original software [4] [Fig. 3]. First, a three-dimensional CT tibial model was downloaded, and the temporal z-axis was defined as the axis connecting the two centers of the approximated circles in the tibial diaphysis in the two transverse planes. Then, the line connecting the attachment of the posterior cruciate ligament to the medial edge of the tibial tuberosity was defined as the y-axis (positive anteriorly). The cross product of the temporal z-axis and y-axis was defined as the tibial x-axis (positive right). Finally, the cross-product of the y-axis and x-axis was the true tibial z-axis (positively superior). The origin of the tibial coordinate system was defined as the cross-point between the distal tibial articular surface and the true z-axis.
Evaluation parameters
Twenty-four regions were created by combining six heights (most proximal, 63–70%; proximal, 57–63%; central proximal, 50–57%; central distal, 43–50%; distal, 37–43%; and most distal, 30–37%) and four areas of the axial plane (xy-plane) at 90° (medial, anterior, lateral, and posterior). Height was defined as follows: The tibial length was defined from the midpoint of the tibial eminences to the midpoint of the medial and lateral points on top of the talar dome, representing 100% of the tibial length. The tibial diaphysis was defined as 30–70%, divided into six heights, and categorized as 6–7% (most proximal, 63–70%; proximal, 57–63%; central proximal, 50–57%; central distal, 43–50%; distal, 37–43%; and most distal, 30–37%). Each of the 24 regions (six heights × four areas in the xy-plane) comprised cortical thickness data from 20 to 948 points. The assessment parameter was the average cortical thickness from 20 to 948 points in each region of the tibial diaphysis, divided by the height and area. The cortical thickness in each of the 24 regions was compared among the four groups categorized by sex and OA (OA males, OA females, healthy males, and healthy females). When the data were compared, standardized values rather than actual values were applied. Standardized values divided by tibial length (CBT/tibial length) were applied because the CBT is influenced by body constitution (body weight and height). To standardize the values, because the units of the values must be identical, the tibial length proportional to body height, not body weight, was selected.
Precision and reproducibility through all processes
To ensure the precision and test–retest reliability of the measurement of CBT in 3D space through all processes, two researchers performed two measurements as one set on 10 subjects randomly selected from each group. CT was performed once for each subject, so that the precision in this study excluded the CT scanning conditions. The precision and reproducibility of the CBT of the total diaphysis were calculated [4]. The mean differences and 95% confidence intervals (Cis) of the differences in the standardized CBT of the total diaphysis were calculated. The mean and maximum differences were 0.1 × 10− 3 and 0.3 × 10− 3 for researcher #1 and 0.01 × 10− 3 and 0.03 × 10− 3 for researcher #2, respectively. The 95% CI of the differences was 0.0 ×10− 3–0.1×10− 3 for researcher #1 and 0.0–0.02 × 10− 3 for researcher #2, respectively. In the test–retest reliability (SPSS version 21, SPSS Inc., Chicago, IL, USA), intraobserver reproducibility via the intraclass correlation coefficient of the two measurements was 0.925 (p < 0.001) for researcher #1 and 0.998 (p < 0.001) for researcher #2. Inter-observer reproducibility via the interclass correlation coefficient was 0.989 (p = 0.001).
Three-dimentional lower extremity alignment assessment system
A 3D lower-extremity alignment assessment system (Knee CAS, LEXI Inc., Tokyo, Japan) based on biplanar long-leg X-rays was developed to assess lower-extremity alignment and bone morphology. This system uses a 3D to 2D image registration technique [6, 7] and enables automatic, strict measurement of all parameters under weight-bearing conditions with high accuracy in 3D space [6] [Fig. 4]. A stereophotogrammetric X-ray apparatus consisting of a 0–60° turn stage was used. The 3D position of the femorotibial bones can be estimated by superimposing 3D skeletal models onto the bony outline of the lower extremities under weight-bearing conditions [6] [Fig. 4]. The femoral and tibial coordinate systems constructed in the 3D skeletal model were determined as previously described [4, 7] [Fig. 4]. The overlapping procedure used the 3D to 2D image registration technique, with a matching error within a range of 0.68 mm in rotation and 0.5 mm in translation [6].
In terms of the femorotibial angle (FTA), anatomical reference axes were determined in 3D space to evaluate the true 3D lower extremity alignment. A point-group centroid was automatically calculated for the ten respective cross-sectional planes, which divided the femoral diaphysis into 11 equal sections using the femoral coordinate system. The same calculation was performed for 12 cross-sectional planes that divided the tibial diaphysis into 13 equal sections in the tibial coordinate system. The anatomical axes were defined as regression lines obtained by approximating the distances from these ten centroids in the femur and 12 centroids in the tibia using the least-squares method. The FTA is defined as the angle between the femoral and tibial anatomical axes projected onto the coronal plane in the femoral coordinate system [Fig. 5]. A larger FTA indicated a larger varus alignment.
Approximation plane of the MCT
The best-fitting “approximation plane” in the MCT was determined by the least-squares method, using eight points digitized on the MCT [8] [Fig. 5]. The least-squares method is an established approach in regression analysis used to approximate solutions for overestimated systems. The digitization points did not include osteophytes or large deformities such as excessive concavity to obtain high precision and reproducibility. The approximation plane of the MCT and the normal vector were mathematically calculated. The angle between the normal vector and each axis was the minimum angle in 3D space between the x-axis of the tibial coordinate system and the crossing line consisting of the approximation plane of the MCT and the xz-plane of the tibial coordinate system, defined as the coronal angle of the MCT [Fig. 5]. These MCT angles were not projected on each plane in 2D space but were defined in 3D space. The MCT morphology is a clinical interpretation. Smaller angles for each parameter indicated a greater inclination toward each axis of the tibial coordinate system. The coronal angles of the MCT were used as assessment parameters. The mean and maimum differences were set as 1.1° for precision. The intra- and interobserver reproducibilities, expressed as intra- and interclass correlation coefficients, were 0.958 and 0.893, respectively [8].
This study was performed in accordance with a protocol approved by the Institutional Review Board of Niigata University (IRB number 2015–2351). All participants provided written or verbal informed consent for participation in the study and for the use of their data.
Statistical analyses
The actual and standardized values are listed in Tables 2 and 3, respectively. In Table 4, the standardized cortical thicknesses at each height (total, most proximal, proximal, central proximal, central distal, distal, and most distal diaphysis) of the four groups (OA male, OA female, healthy male, and healthy female) were compared among the four areas of the transverse plane (medial, anterior, lateral, and posterior areas) using repeated measures ANOVA with Tukey’s test or Friedman’s test as the counterpart of repeated measures ANOVA. In Table 5, the standardized cortical thickness in each of the 24 regions is compared among the four groups categorized by sex and age (OA male, OA female, healthy male, and healthy female) using one-way ANOVA with post-hoc or Kruskal-Wallis tests as the nonparametric equivalent of ANOVA. In Table 6, the medial/lateral (M/L) and anterior/posterior (A/P) ratios at each height (total, most proximal, proximal, central proximal, central distal, distal, and most distal diaphysis) of the four groups (OA male, OA female, healthy male, and healthy female) were compared using one-way ANOVA with a post-hoc test or Kruskal-Wallis test as the nonparametric equivalent of ANOVA. Pearson’s product moment correlation coefficient or Spearman’s rank correlation coefficient was applied, depending on the Shapiro–Wilk test (Tables 7 and 8). Correlations between FTA (Table 7), MCT (Table 8), and standardized thickness at each height (total, most proximal, proximal, central proximal, central distal, distal, and most distal diaphysis) in the four groups (OA male, OA female, healthy male, and healthy female) were compared.
Table 2
Cortical thickness in tibia diaphysis (actual values)
| OA group (n = 60) | Healthy group (n = 53) |
| Male (n = 22) | Female (n = 38) | Male (n = 28) | Female (n = 25) |
Actual values (mm) | mean | 95%CI | mean | 95%CI | mean | 95%CI | mean | 95%CI |
Total diaphysis |
Medial | 5.9 | 5.5–6.3 | 5.3 | 5.1–5.5 | 5.6 | 5.4–5.9 | 5.4 | 5.2–5.6 |
Lateral | 5.5 | 5.3–5.7 | 5.2 | 5.0-5.3 | 5.7 | 5.5–5.9 | 5.6 | 5.5–5.8 |
Anterior | 7.8 | 7.2–8.3 | 6.6 | 6.2-7.0 | 7.9 | 7.5–8.3 | 7.3 | 7.0-7.6 |
Posterior | 5.2 | 4.9–5.4 | 4.6 | 4.4—4.7 | 5.3 | 5.1–5.5 | 5.0 | 4.8–5.1 |
Most proximal diaphysis |
Medial | 5.7 | 5.4-6.0 | 5.4 | 5.1–5.6 | 5.5 | 5.2–5.8 | 5.3 | 5.1–5.6 |
Lateral | 4.9 | 4.7–5.1 | 4.8 | 4.7-5.0 | 5.5 | 5.3–5.7 | 5.5 | 5.3–5.7 |
Anterior | 6.8 | 6.3–7.3 | 6.3 | 5.8–6.7 | 7.5 | 7.0–8.0 | 7.3 | 7.0-7.7 |
Posterior | 4.8 | 4.7-5.0 | 4.7 | 4.5–4.9 | 5.1 | 5.0-5.3 | 5.2 | 4.9–5.4 |
Proximal diaphysis | | | | | | | | |
Medial | 5.6 | 5.2-6.0 | 5.4 | 5.2–5.7 | 5.6 | 5.4–5.9 | 5.2 | 4.9–5.5 |
Lateral | 5.3 | 5.0-5.6 | 5.0 | 4.8–5.2 | 5.7 | 5.4–5.9 | 5.6 | 5.4–5.9 |
Anterior | 7.1 | 6.5–7.7 | 6.1 | 5.7–6.4 | 7.2 | 6.9–7.5 | 6.9 | 6.5–7.2 |
Posterior | 5.1 | 4.9–5.3 | 4.7 | 4.5–4.9 | 5.4 | 5.2–5.6 | 5.0 | 4.8–5.2 |
Central proximal diaphysis |
Medial | 5.6 | 5.1-6.0 | 5.2 | 5.0-5.5 | 5.4 | 5.0-5.8 | 5.5 | 5.2–5.8 |
Lateral | 5.3 | 5.1–5.6 | 5.2 | 5.0-5.4 | 5.7 | 5.3–6.1 | 5.6 | 5.4–5.9 |
Anterior | 8.0 | 7.3–8.7 | 6.5 | 6.0–7.0 | 7.9 | 7.5–8.4 | 7.5 | 7.1–7.9 |
Posterior | 5.2 | 4.9–5.5 | 4.6 | 4.4–4.8 | 5.2 | 5.0-5.4 | 4.8 | 4.7-5.0 |
Central distal diaphysis | | | | | | | | |
Medial | 6.3 | 5.8–6.8 | 5.3 | 5.0-5.6 | 5.8 | 5.4–6.2 | 5.4 | 4.9–5.8 |
Lateral | 5.7 | 5.4–5.9 | 5.4 | 5.2–5.6 | 5.8 | 5.5-6.0 | 5.7 | 5.4-6.0 |
Anterior | 8.8 | 8.0-9.5 | 7.1 | 6.6–7.6 | 8.9 | 8.3–9.5 | 7.6 | 7.2-8.0 |
Posterior | 5.3 | 5.0-5.6 | 4.4 | 4.3–4.6 | 5.4 | 5.1–5.6 | 4.8 | 4.6-5.0 |
Distal diaphysis |
Medial | 6.6 | 6.0-7.3 | 5.4 | 5.1–5.7 | 6.0 | 5.6–6.4 | 5.3 | 4.9–5.7 |
Lateral | 6.1 | 5.7–6.4 | 5.3 | 5.0-5.6 | 5.9 | 5.7–6.1 | 5.8 | 5.6-6.0 |
Anterior | 8.8 | 8.1–9.5 | 7.3 | 6.8–7.8 | 9.1 | 8.4–9.7 | 7.7 | 7.2–8.2 |
Posterior | 5.5 | 5.2–5.8 | 4.4 | 4.3–4.6 | 5.5 | 5.2–5.8 | 4.8 | 4.7–4.9 |
Most distal diaphysis | | | | | | | | |
Medial | 6.4 | 5.6–7.2 | 5.2 | 4.9–5.5 | 5.8 | 5.4–6.2 | 5.8 | 5.4–6.3 |
Lateral | 6.4 | 5.9–6.9 | 5.3 | 5.0-5.6 | 6.2 | 5.8–6.7 | 5.9 | 5.6–6.1 |
Anterior | 8.3 | 7.6-9.0 | 6.9 | 6.5–7.2 | 8.7 | 8.0-9.3 | 7.6 | 7.1–8.1 |
Posterior | 5.3 | 5.0-5.6 | 4.4 | 4.2–4.6 | 5.6 | 5.3–5.9 | 4.8 | 4.6-5.0 |
OA = knee osteoarthritis; 95%CI = 95% confidence interval |
Table 3
Cortical thickness in tibia diaphysis (standardized values)
| OA group (n = 60) | Healthy group (n = 53) |
| Male (n = 22) | Female (n = 38) | Male (n = 28) | Female (n = 25) |
Standardized values ( ×10− 3) | mean | 95%CI | mean | 95%CI | mean | 95%CI | mean | 95%CI |
Total diaphysis |
Medial | 17.9 | 16.7–19.1 | 17.5 | 16.8–18.1 | 17.1 | 16.4–17.7 | 17.4 | 16.6–18.2 |
Lateral | 16.6 | 15.8–17.4 | 16.9 | 16.3–17.6 | 17.3 | 16.6–18.0 | 18.1 | 17.5–18.7 |
Anterior | 23.5 | 21.8–25.1 | 21.6 | 20.3–22.8 | 23.9 | 22.7–25.1 | 23.5 | 22.5–24.5 |
Posterior | 15.6 | 14.9–16.2 | 15.0 | 14.5–15.5 | 16.1 | 15.6–16.5 | 16.0 | 15.5–16.5 |
Most proximal diaphysis |
Medial | 17.3 | 16.3–18.2 | 17.6 | 16.9–18.3 | 16.8 | 15.8–17.7 | 17.1 | 16.3–17.9 |
Lateral | 14.9 | 14.2–15.6 | 15.9 | 15.3–16.6 | 16.8 | 16.1–17.5 | 17.6 | 16.9–18.4 |
Anterior | 20.4 | 18.9–21.9 | 20.6 | 19.1–22.0 | 22.7 | 21.2–24.3 | 23.5 | 22.4–24.6 |
Posterior | 14.6 | 14.1–15.1 | 15.5 | 14.8–16.2 | 15.6 | 15.1–16.1 | 16.7 | 15.7–17.6 |
Proximal diaphysis | | | | | | | | |
Medial | 16.8 | 15.6–18.0 | 17.8 | 16.9–18.6 | 17.1 | 16.3–18.0 | 16.8 | 15.6–17.9 |
Lateral | 16.0 | 15.0-16.9 | 16.4 | 15.7–17.0 | 17.1 | 16.3–18.0 | 18.2 | 17.3–19.1 |
Anterior | 21.5 | 19.7–23.2 | 19.9 | 18.8–21.1 | 21.9 | 20.9–22.9 | 22.2 | 21.0-23.4 |
Posterior | 15.3 | 14.7–16.0 | 15.4 | 14.7–16.0 | 16.3 | 15.6–16.9 | 16.1 | 15.4–16.9 |
Central proximal diaphysis |
Medial | 16.8 | 15.5–18.1 | 17.2 | 16.4–18.0 | 16.4 | 15.3–17.5 | 17.6 | 16.6–18.6 |
Lateral | 16.1 | 15.2–16.9 | 17.0 | 16.3–17.8 | 17.2 | 15.9–18.5 | 18.2 | 17.2–19.2 |
Anterior | 24.2 | 22.2–26.2 | 21.4 | 19.9–22.8 | 24.0 | 22.7–25.3 | 24.1 | 22.9–25.3 |
Posterior | 15.7 | 14.8–16.6 | 15.2 | 14.6–15.9 | 15.8 | 15.2–16.4 | 15.5 | 15.0–16.0 |
Central distal diaphysis | | | | | | | | |
Medial | 19.1 | 17.4–20.7 | 17.5 | 16.5–18.4 | 17.4 | 16.2–18.6 | 17.4 | 15.8–18.9 |
Lateral | 17.1 | 16.1–18.0 | 17.7 | 16.9–18.6 | 17.5 | 16.6–18.4 | 18.4 | 17.3–19.5 |
Anterior | 26.4 | 24.3–28.5 | 23.2 | 21.5–25.0 | 27.0 | 25.2–28.9 | 24.4 | 23.2–25.7 |
Posterior | 15.9 | 15.0-16.8 | 14.5 | 14.0–15.0 | 16.2 | 15.5–16.9 | 15.4 | 14.8–16.1 |
Distal diaphysis |
Medial | 20.1 | 18.1–22.1 | 17.7 | 16.7–18.6 | 18.1 | 16.9–19.3 | 17.2 | 15.8–18.7 |
Lateral | 18.3 | 17.1–19.5 | 17.6 | 16.5–18.6 | 18.0 | 17.2–18.7 | 18.7 | 18.0-19.4 |
Anterior | 26.6 | 24.5–28.8 | 23.9 | 22.3–25.5 | 27.5 | 25.6–29.4 | 24.6 | 23.1–26.1 |
Posterior | 16.7 | 15.8–17.5 | 14.5 | 14.0-15.1 | 16.6 | 15.9–17.3 | 15.5 | 15.0–16.0 |
Most Distal diaphysis | | | | | | | | |
Medial | 19.3 | 16.7–21.8 | 16.9 | 16.0-17.8 | 17.5 | 16.3–18.8 | 18.9 | 17.3–20.4 |
Lateral | 19.4 | 17.8–20.9 | 17.4 | 16.5–18.3 | 18.9 | 17.7–20.0 | 19.0 | 18.1–19.9 |
Anterior | 25.1 | 23.0-27.3 | 22.6 | 21.4–23.7 | 26.2 | 24.3–28.1 | 24.5 | 22.9–26.1 |
Posterior | 16.1 | 15.2–17.0 | 14.4 | 13.8–15.0 | 16.9 | 16.2–17.5 | 15.5 | 14.9–16.1 |
OA = knee osteoarthritis; 95%CI = 95% confidence interval; standardized values mean the actual values divided by the tibia length |
Table 4
Comparison between medial and lateral or between anterior and posterior standardized thickness
| OA male | OA female | Healthy male | Healthy female |
p value | Summary | p value | Summary | p value | Summary | p value | Summary |
Total diaphysis | M–L | .001* | M > L | n.s. | — | n.s. | — | n.s. | — |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Most proximal diaphysis | M–L | < .001* | M > L | < .001* | M > L | n.s. | – | n.s. | — |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Proximal diaphysis | M–L | n.s. | – | .001* | M > L | n.s. | – | .008* | M < L |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Central proximal diaphysis | M–L | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Central distal diaphysis | M–L | .008* | M > L | n.s. | – | n.s. | – | n.s. | – |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Distal diaphysis | M–L | .023* | M > L | n.s. | – | n.s. | – | .049* | M < L |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
Most distal diaphysis | M–L | n.s. | – | n.s. | – | .026* | M < L | n.s. | – |
A–P | < .001* | A > P | < .001* | A > P | < .001* | A > P | < .001* | A > P |
The standardized cortical thickness in each height (most proximal, proximal, central proximal, central distal, distal and most distal diaphysis) of the four groups (OA male, OA female, healthy male, and healthy female) was compared among the four areas of the axial plane (medial, anterior, lateral, and posterior areas), using repeated measures ANOVA with Tukey test or the Friedman's test as the counterpart of repeated measures ANOVA. OA = knee osteoarthritis; M–L = comparison between medial and lateral standardized thickness; A–P = comparison between anterior and posterior standardized thickness; M = medial standardized thickness; L = lateral standardized thickness; A = anterior standardized thickness; P = posterior standardized thickness; *= < 0.05; n.s. = > 0.05 |
Table 5
Sex– and OA– related differences
| Male (M) vs Female (F) | OA (O) vs Healthy group (H) |
OA group | Healthy group | Male group | Female group |
p value | Summary | p value | Summary | p value | Summary | p value | Summary |
Total diaphysis | M | n.s. | — | n.s. | – | n.s. | — | n.s. | — |
L | n.s. | — | n.s. | – | n.s. | — | .043* | OA < H |
A | n.s. | — | n.s. | – | n.s. | — | n.s. | – |
P | n.s. | — | n.s. | – | n.s. | — | .031* | OA < H |
Most proximal diaphysis | M | n.s. | - | n.s. | – | n.s. | — | n.s. | — |
L | n.s. | – | n.s. | — | .003* | OA < H | .008* | OA < H |
A | n.s. | — | n.s. | – | n.s. | — | .018* | OA < H |
P | n.s. | – | n.s. | — | .021* | OA < H | n.s. | - |
Proximal diaphysis | M | n.s. | - | n.s. | – | n.s. | — | n.s. | — |
L | n.s. | – | n.s. | — | n.s. | - | .006* | OA < H |
A | n.s. | — | n.s. | – | n.s. | — | .037* | OA < H |
P | n.s. | – | n.s. | — | n.s. | – | n.s. | - |
Central proximal diaphysis | M | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
L | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
A | n.s. | – | n.s. | — | n.s. | — | .037* | OA < H |
P | n.s. | – | n.s. | — | n.s. | – | n.s. | — |
Central distal diaphysis | M | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
L | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
A | n.s. | - | n.s. | — | n.s. | — | n.s. | — |
P | .013* | M > F | n.s. | — | n.s. | – | n.s. | — |
Distal diaphysis | M | .047* | M > F | n.s. | – | n.s. | — | n.s. | – |
L | n.s. | — | n.s. | – | n.s. | – | n.s. | – |
A | n.s. | - | n.s. | – | n.s. | — | n.s. | – |
P | < .001* | M > F | n.s. | - | n.s. | – | n.s. | – |
Most distal diaphysis | M | n.s. | — | n.s. | – | n.s. | — | n.s. | – |
L | n.s. | — | n.s. | – | n.s. | – | n.s. | – |
A | n.s. | – | n.s. | – | n.s. | — | n.s. | – |
P | .005* | M > F | .049* | M > F | n.s. | – | n.s. | – |
The standardized cortical thickness in each of the 24 regions was compared among the four groups categorized by sex and age (OA male, OA female, healthy male, and healthy female), using one-way ANOVA with post hoc or Kruskal-Wallis test as the nonparametric equivalent of ANOVA. OA = knee osteoarthritis; M = medial thickness; L = lateral thickness; A = anterior thickness; P = posterior thickness; *= < 0.05; n.s. = > 0.05 |
Table 6
Comparison of M/L ratio and A/P ratio between each group
| Male (M) vs Female (F) | OA (O) vs Healthy group (H) |
OA group | Healthy group | Male group | Female group |
p value | Summary | p value | Summary | p value | Summary | p value | Summary |
Total diaphysis | M/L | n.s. | — | n.s. | – | .015* | OA > H | .046* | OA > H |
A/P | n.s. | — | n.s. | – | n.s. | — | n.s. | – |
Most proximal diaphysis | M/L | n.s. | - | n.s. | – | .007* | OA > H | .002* | OA > H |
A/P | n.s. | — | n.s. | – | n.s. | — | n.s. | — |
Proximal diaphysis | M/L | n.s. | - | n.s. | – | n.s. | — | .001* | OA > H |
A/P | n.s. | — | n.s. | – | n.s. | — | n.s. | — |
Central proximal diaphysis | M/L | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
A/P | n.s. | – | n.s. | — | n.s. | — | .018* | OA < H |
Central distal diaphysis | M/L | n.s. | – | n.s. | – | n.s. | – | n.s. | – |
A/P | n.s. | - | n.s. | — | n.s. | — | n.s. | — |
Distal diaphysis | M/L | n.s. | - | n.s. | – | n.s. | — | n.s. | – |
A/P | n.s. | - | n.s. | – | n.s. | — | n.s. | – |
Most distal diaphysis | M/L | n.s. | — | n.s. | – | n.s. | — | n.s. | – |
A/P | n.s. | - | n.s. | – | n.s. | — | n.s. | – |
M/L = medial/lateral ratio; A/P = anterior/posterior ratio; OA = knee osteoarthritis; *= < 0.05; n.s. = > 0.05 |
Table 7
Correlations between FTA and standardized thickness
| OA male | OA female | Healthy male | Healthy female |
CC | p value | CC | p value | CC | p value | CC | p value |
Total diaphysis | M | 0.278 | — | 0.264 | – | 0.11 | — | 0.107 | — |
L | 0.134 | — | 0.235 | – | -0.075 | — | -0.02 | – |
A | 0.068 | — | -0.004 | – | -0.185 | — | -0.037 | – |
P | 0.097 | — | 0.191 | – | -0.054 | — | -0.139 | – |
Most proximal diaphysis | M | 0.213 | — | 0.365 | .026* | -0.112 | — | -0.131 | — |
L | 0.261 | – | 0.126 | — | 0.324 | – | -0.079 | – |
A | 0.17 | — | 0.124 | – | -0.244 | — | -0.026 | – |
P | 0.188 | – | 0.162 | — | -0.144 | – | -0.178 | – |
Proximal diaphysis | M | 0.294 | – | 0.369 | .023* | 0.371 | — | 0.015 | — |
L | 0.23 | – | 0.188 | — | 0.031 | – | -0.023 | – |
A | -0.034 | — | 0.111 | – | -0.191 | — | -0.06 | – |
P | 0.212 | – | 0.243 | — | -0.041 | – | -0.25 | – |
Central proximal diaphysis | M | 0.087 | – | 0.257 | – | 0.463 | .013* | 0.289 | – |
L | 0.132 | – | 0.052 | – | 0.103 | – | 0.051 | – |
A | -0.069 | – | -0.002 | — | -0.028 | — | -0.172 | – |
P | -0.009 | – | 0.021 | — | 0.14 | – | -0.195 | — |
Central distal diaphysis | M | 0.147 | – | 0.143 | - | -0.002 | – | 0.341 | – |
L | 0.042 | – | 0.337 | .038* | 0.198 | – | -0.089 | – |
A | 0.013 | – | -0.103 | — | -0.041 | — | 0.05 | — |
P | 0.039 | – | 0.255 | — | -0.179 | – | -0.051 | — |
Distal diaphysis | M | 0.273 | – | -0.084 | – | 0.011 | — | 0.228 | – |
L | -0.034 | — | 0.354 | .029* | 0.022 | – | 0.13 | – |
A | 0.142 | – | -0.172 | – | -0.108 | — | -0.09 | – |
P | -0.055 | – | 0.295 | – | 0.005 | – | 0.144 | – |
Most distal diaphysis | M | 0.283 | — | 0.185 | – | -0.193 | — | -0.421 | .036* |
L | -0.112 | — | -0.082 | – | -0.01 | – | 0.211 | – |
A | 0.238 | – | -0.146 | – | -0.197 | — | 0.156 | – |
P | 0.155 | – | -0.01 | – | 0.014 | – | 0.3 | – |
FTA = femorotibial angle; CC = correlation coefficient; OA = knee osteoarthritis; M = medial thickness; L = lateral thickness; A = anterior thickness; P = posterior thickness; *= < 0.05; n.s. = > 0.05 |
Table 8
Correlations between MCT and standardized thickness
| OA male | OA female | Healthy male | Healthy female |
CC | p value | CC | p value | CC | p value | CC | p value |
Total diaphysis | M | 0.358 | — | 0.409 | .011* | -0.049 | — | 0.032 | — |
L | 0.166 | — | 0.398 | .013* | -0.078 | — | 0.007 | – |
A | 0.125 | — | 0.13 | – | 0.063 | — | -0.013 | – |
P | 0.263 | — | 0.273 | – | 0.04 | — | -0.078 | – |
Most proximal diaphysis | M | 0.594 | .004* | 0.554 | < .001* | -0.211 | — | 0.164 | — |
L | 0.245 | – | 0.066 | — | -0.154 | – | 0.048 | – |
A | 0.503 | .017* | 0.271 | – | -0.043 | — | 0.039 | – |
P | 0.227 | – | 0.124 | — | 0.189 | – | -0.155 | – |
Proximal diaphysis | M | 0.61 | .003* | 0.368 | .023* | 0.094 | — | 0.293 | — |
L | 0.032 | – | 0.267 | — | -0.148 | – | 0.096 | – |
A | 0.204 | — | 0.204 | – | 0.038 | — | 0.024 | – |
P | 0.163 | – | 0.290 | — | -0.132 | – | 0.015 | – |
Central proximal diaphysis | M | 0.416 | – | 0.375 | .020* | 0.188 | – | 0.006 | – |
L | -0.045 | – | 0.198 | – | 0.06 | – | -0.057 | – |
A | 0.165 | – | 0.112 | — | 0.208 | — | -0.349 | – |
P | 0.273 | – | 0.271 | — | 0.084 | – | -0.121 | — |
Central distal diaphysis | M | 0.151 | – | 0.380 | .019* | 0.012 | – | 0.044 | – |
L | 0.03 | – | 0.408 | .011* | 0.182 | – | -0.052 | – |
A | -0.038 | – | 0.021 | — | 0.112 | — | -0.004 | — |
P | 0.279 | – | 0.391 | .015* | -0.01 | – | -0.369 | — |
Distal diaphysis | M | 0.052 | – | 0.175 | – | -0.111 | — | -0.145 | – |
L | 0.185 | — | 0.448 | .005* | -0.227 | – | -0.066 | – |
A | -0.126 | – | -0.078 | – | 0.034 | — | 0.102 | – |
P | 0.26 | – | 0.304 | – | 0.035 | – | 0.082 | – |
Most distal diaphysis | M | 0.123 | — | 0.232 | – | -0.051 | — | -0.299 | – |
L | 0.271 | — | 0.307 | – | -0.117 | – | 0.068 | – |
A | 0.184 | – | 0.029 | – | 0.027 | — | 0.21 | – |
P | 0.123 | – | 0.07 | – | -0.025 | – | 0.105 | – |
MCT = medial compartment of the proximal tibia; CC = correlation coefficient; OA = knee osteoarthritis; M = medial thickness; L = lateral thickness; A = anterior thickness; P = posterior thickness; *= < 0.05; n.s. = > 0.05 |
Statistical significance was set at a p-value < 0.05 (SPSS version 21, SPSS Inc., Chicago, IL, USA).
A sample size calculation was performed to determine the main outcome of the correlation between MCT inclination and CBT of the most proximal-medial region in OA males and OA females. The sample size calculation used the following conditions: α error: 0.05; 1-β error: 0.80; correlation coefficient: OA male, 0.594; OA female, 0.554. Nineteen tibias in OA males and 23 tibias in OA females were needed to analyze the main outcomes. This study had a sufficient sample size of OA males and females with significant differences (22 tibias in OA males and 38 tibias in OA females).