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Alterations in cartilage thickness (CTh) are a hallmark of knee osteoarthritis, which remain difficult to characterize at high resolution, even with modern magnetic resonance imaging (MRI), due to a paucity of standardization tools. This study aimed to assess a computational anatomy method producing standardized two-dimensional femorotibial CTh maps. The method was assessed with twenty knees, processed following three common experimental scenarios. Cartilage thickness maps were obtained for the femorotibial cartilages by reconstructing bone and cartilage mesh models in tree-dimension, calculating three-dimensional CTh maps, and anatomically standardizing the maps. The intra-operator accuracy (median (interquartile range, IQR) of &minus, 0.006 (0.045) mm), precision (0.152 (0.070) mm), entropy (7.02 (0.71) and agreement (0.975 (0.020))) results suggested that the method is adequate to capture the spatial variations in CTh and compare knees at varying osteoarthritis stages. The lower inter-operator precision (0.496 (0.132) mm) and agreement (0.808 (0.108)) indicate a possible loss of sensitivity to detect differences in a setting with multiple operators. The results confirmed the promising potential of anatomically standardized maps, with the lower inter-operator reproducibility stressing the need to coordinate operators. This study also provided essential reference data and indications for future research using CTh maps.

Summary Objective To test if sagittal plane gait mechanics parameters and serum inflammation levels differ between healthy asymptomatic subjects and asymptomatic subjects with magnetic resonance imaging (MRI) evidence of cartilage loss. Design Gait mechanics and resting serum tumor necrosis factor-α (TNFα) concentrations were measured for two groups of asymptomatic subjects recruited for a previous study: Pre-Osteoarthritis (OA) subjects had MRI evidence of partial- or full-thickness knee cartilage loss in at least one compartment ( n = 52 (30 female), 1.7 ± 0.1 m, 85.3 ± 18.9 kg, 44 ± 11 years); Control subjects had no MRI features of cartilage loss, osteophytes, bone marrow lesions, nor meniscal pathology in either knee ( n = 26 (13 female), 1.7 ± 0.1 m, 74.6 ± 14.9 kg, 34 ± 10 years). Discrete measures of sagittal plane gait kinematics and kinetics were compared between subject groups and adjusted for age and body mass index (BMI) using analysis of covariance (ANCOVA). Serum TNFα concentrations were compared between groups using bootstrap t -test. Results The Pre-OA group had less extended knees ( P = 0.021) and decreased maximum external knee extension moment ( P = 0.0062) in terminal stance during gait, as well as increased resting serum TNFα concentration ( P = 0.040) as compared to Control subjects. There were no group differences in heel strike flexion angle ( P = 0.14), in maximum knee flexion moment ( P = 0.91), nor in first peak knee adduction moment (KAM) (post-hoc analysis, P = 0.39). Conclusions The finding that asymptomatic subjects with cartilage loss had gait and inflammatory characteristics similar to those previously reported in symptomatic OA patients supports the idea that there are specific mechanical and biological factors that precede the onset of knee pain in the pathogenesis of OA.

While cartilage thickness alterations are a central element of knee osteoarthritis (OA), differences among disease stages are still incompletely understood. This study aimed to quantify the spatial-variations in cartilage thickness using anatomically standardized thickness maps and test if there are characteristic patterns in patients with different stages of medial compartment knee OA. Magnetic resonance images were acquired for 75 non-OA and 100 OA knees of varying severities (Kellgren and Lawrence (KL) scores 1-4). Three-dimensional cartilage models were reconstructed and a shape matching technique was applied to convert the models into two-dimensional anatomically standardized thickness maps. Difference thickness maps and statistical parametric mapping were used to compare the four OA and the non-OA subgroups. This analysis showed distinct thickness patterns for each clinical stage that formed a coherent succession from the non-OA to the KL 4 subgroups. Interestingly, the only significant difference for early stage (KL 1) was thicker femoral cartilage. With increase in disease severity, typical patterns developed, including thinner cartilage in the anterior area of the medial condyle (significant for KL 3 and 4) and thicker cartilage in the posterior area of the medial and lateral condyles (significant for all OA subgroups). The tibial patterns mainly consisted of thinner cartilage for both medial and lateral compartments (significant for KL 2-4). Comparing anatomically standardized maps allowed identifying patterns of thickening and thinning over the entire cartilage surface, consequently improving the characterization of thickness differences associated with OA. The results also highlighted the value of anatomically standardized maps to analyze spatial variations in cartilage thickness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2442-2451, 2017.

Articular cartilage is sensitive to mechanical loading, so increased risk of osteoarthritis in older or obese individuals may be linked to changes in the relationship between cartilage properties and extrinsic joint loads. A positive relationship has been reported between ambulatory loads and cartilage thickness in young individuals, but whether this relationship exists in individuals who are older or obese is unknown. This study examined the relationship between femoral cartilage thickness and load, measured by weight × height and the peak adduction moment, in young normal-weight (28 subjects, age: 28.0 ± 3.8 years, BMI: 21.9 ± 1.9 kg/m2), middle-aged normal-weight (27 subjects, 47.0 ± 6.5 years, 22.7 ± 1.7 kg/m2), young overweight/obese (27 subjects, 28.4 ± 3.6 years, 33.3 ± 4.6 kg/m2), and middle-aged overweight/obese (27 subjects, 45.8 ± 7.2 years, 31.9 ± 4.4 kg/m2) individuals. On the lateral condyle, cartilage thickness was positively correlated with weight × height for all groups (R2 = 0.26–0.20) except the middle-aged overweight/obese. On the medial condyle, weight × height was significantly correlated only in young normal-weight subjects (R2 = 0.19), as was the case for the correlation between adduction moment and medial–lateral thickness ratio (R2 = 0.20). These results suggest that aging and obesity are both associated with a loss of the positive relationship between cartilage thickness and ambulatory loads, and that the relationship is dependent on the compartment and whether the load is generated by body size or subject-specific gait mechanics. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:394–402, 2014.

There is a need to understand how obesity and aging interact to cause an increased risk of medial knee osteoarthritis (OA). This study tested whether the knee adduction and flexion moments increase with age in healthy normal-weight and obese adults, as well as the mechanism of this increase. We analyzed whether ground reaction force magnitude, knee alignment, step width, toe-out angle, body volume distribution, and limb position (knee position relative to the pelvis center) are associated with the adduction moment and whether these variables also change with age. Ninety-six healthy volunteers (60 normal-weight and 36 obese) were tested using marker-based gait analysis; knee alignment was based on marker positions during quiet standing. Adduction moment increased with age in obese (R(2) = 0.19), but not in normal-weight individuals (R(2) = 0.01); knee flexion moment did not change with age in either group. In the obese, only knee alignment and limb position were related to the adduction moment (R(2) = 0.19 and 0.51), but only limb position changed with age (R(2) = 0.26). The resulting increase in adduction moment suggests greater medial compartment loads, which may combine with elevated levels of inflammation to contribute to the increased risk of medial OA in this population.

Measures of mean cartilage thickness over predefined regions in the femoral plate using magnetic resonance imaging have provided important insights into the characteristics of knee osteoarthritis (OA), however, this quantification method suffers from the limited ability to detect OA-related differences between knees and loses potentially important information regarding spatial variations in cartilage thickness. The objectives of this study were to develop a new method for analyzing patterns of femoral cartilage thickness and to test the following hypotheses: (1) asymptomatic knees have similar thickness patterns, (2) thickness patterns differ with knee OA, and (3) thickness patterns are more sensitive than mean thicknesses to differences between OA conditions. Bi-orthogonal thickness patterns were extracted from thickness maps of segmented magnetic resonance images in the medial, lateral, and trochlea compartments. Fifty asymptomatic knees were used to develop the method and establish reference asymptomatic patterns. Another subgroup of 20 asymptomatic knees and three subgroups of 20 OA knees each with a Kellgren/Lawrence grade (KLG) of 1, 2, and 3, respectively, were selected for hypotheses testing. The thickness patterns were similar between asymptomatic knees (coefficient of multiple determination between 0.8 and 0.9). The thickness pattern alterations, i.e., the differences between the thickness patterns of an individual knee and reference asymptomatic thickness patterns, increased with increasing OA severity (Kendall correlation between 0.23 and 0.47) and KLG 2 and 3 knees had significantly larger thickness pattern alterations than asymptomatic knees in the three compartments. On average, the number of significant differences detected between the four subgroups was 4.5 times greater with thickness pattern alterations than mean thicknesses. The increase was particularly marked in the medial compartment, where the number of significant differences between subgroups was 10 times greater with thickness pattern alterations than mean thickness measurements. Asymptomatic knees had characteristic regional thickness patterns and these patterns were different in medial OA knees. Assessing the thickness patterns, which account for the spatial variations in cartilage thickness and capture both cartilage thinning and swelling, could enhance the capacity to detect OA-related differences between knees.

Articular cartilage is sensitive to mechanical loading, so increased risk of osteoarthritis in older or obese individuals may be linked to changes in the relationship between cartilage properties and extrinsic joint loads. A positive relationship has been reported between ambulatory loads and cartilage thickness in young individuals, but whether this relationship exists in individuals who are older or obese is unknown. This study examined the relationship between femoral cartilage thickness and load, measured by weight × height and the peak adduction moment, in young normal-weight (28 subjects, age: 28.0 ± 3.8 years, BMI: 21.9 ± 1.9 kg/m(2)), middle-aged normal-weight (27 subjects, 47.0 ± 6.5 years, 22.7 ± 1.7 kg/m(2)), young overweight/obese (27 subjects, 28.4 ± 3.6 years, 33.3 ± 4.6 kg/m(2)), and middle-aged overweight/obese (27 subjects, 45.8 ± 7.2 years, 31.9 ± 4.4 kg/m(2)) individuals. On the lateral condyle, cartilage thickness was positively correlated with weight × height for all groups (R(2) = 0.26-0.20) except the middle-aged overweight/obese. On the medial condyle, weight × height was significantly correlated only in young normal-weight subjects (R(2) = 0.19), as was the case for the correlation between adduction moment and medial-lateral thickness ratio (R(2) = 0.20). These results suggest that aging and obesity are both associated with a loss of the positive relationship between cartilage thickness and ambulatory loads, and that the relationship is dependent on the compartment and whether the load is generated by body size or subject-specific gait mechanics.

Obesity is a strong risk factor for knee osteoarthritis (OA) [1], but the mechanism of OA initiation associated with obesity is not clear. Increases in ambulatory knee joint load due to obesity have been implicated as a cause of increased OA incidence, since an increased adduction moment has been associated with the severity and progression of medial compartment OA [2]. However, previous work has not consistently shown increases or decreases in the adduction moment in the obese. Step width and toe-out reduce the adduction moment [3] and are increased in the obese [4], suggesting that the adduction moment could also be reduced in the obese. Furthermore, obesity may be associated with knee malalignment, which may also alter the adduction moment. However, the cumulative effect of these gait alterations on the adduction moment is unclear, given the increased risk of medial knee OA in the obese. Understanding this interaction is important in understanding the link between obesity and knee OA.Copyright © 2012 by ASME

In longitudinal studies, obesity has been shown to be a major risk factor for knee osteoarthritis (OA) (Felson, 1988), but the cause of this increased prevalence is not yet clear. A common hypothesis is that obesity increases joint loads due to increased body mass, causing the articular cartilage to experience higher load and degenerate more quickly (Griffin, 2005). However, it has been shown that in healthy, normal-weight subjects, knee cartilage thickness increases in proportion to the loads applied during ambulation (Andriacchi, 2004). It is not known whether this same relationship also holds true for obese people who do not have OA. Because it is difficult to measure joint loads directly in vivo, the external adduction moment can be used as a surrogate measure of the relative load distribution between the medial and lateral compartments of the knee (Andriacchi 2004). If cartilage responds positively to load, a higher adduction moment will be correlated with thicker cartilage on the medial side and thinner cartilage in the lateral compartment. Similarly, average cartilage thickness should be proportional to body mass index. Therefore the purpose of this study was to examine the following hypotheses in a group of healthy-weight, overweight, and obese individuals: 1. Average cartilage thickness in both compartments is proportional to body mass index (BMI). 2. Average cartilage thickness in the lateral compartment is inversely proportional to the knee adduction moment. 3. Average cartilage thickness in the medial compartment is proportional to the knee adduction moment. 4. The ratio of medial to lateral cartilage thickness is proportional to the adduction moment.Copyright © 2010 by ASME