Articular cartilage is a specialized form of hyaline cartilage that covers the articulating surfaces of synovial joints. It provides a smooth, low-friction surface for joint movement, distributes mechanical loads and protects the underlying subchondral bone. The knee is the largest weight-bearing joint in the human body, and its articular cartilage is exposed to substantial compressive, tensile and shear forces during routine activities. Cartilage thickness is not uniform throughout the knee; it varies according to anatomical location, biomechanical loading, age, sex, body size and individual morphology. A recent systematic review of non-arthritic adult knees demonstrated considerable variation in femoral cartilage thickness between individuals and across medial, lateral, distal and posterior femoral regions.[1] Because articular cartilage is avascular and has limited regenerative capacity, progressive structural deterioration may result in irreversible cartilage loss and ultimately contribute to osteoarthritis. Direct measurement of articular cartilage by arthroscopy or anatomical sectioning is invasive and unsuitable for routine assessment in living individuals. Conventional radiography measures joint-space width only indirectly and may be influenced by meniscal position, alignment and weight-bearing conditions. Magnetic resonance imaging (MRI), in contrast, provides non-invasive, multiplanar visualization of the articular cartilage and permits direct measurement of its thickness at different anatomical sites. Quantitative and three-dimensional MRI techniques have demonstrated comparatively high sensitivity for assessing cartilage morphology and detecting chondral abnormalities.[2] MRI-based cartilage measurements may therefore serve as structural biomarkers for recognizing early cartilage degeneration, monitoring disease progression and evaluating treatment response. However, differences between MRI and radiographic measurements have also been reported, emphasizing the need for standardized anatomical landmarks and imaging protocols.[3] Articular cartilage thickness may differ substantially between the femoral condyles, tibial plateaus, femoral trochlea and patellar facets because each site experiences different patterns of contact and loading. Quantitative MRI studies have demonstrated that cartilage loss is related to pre-existing osteoarthritis, meniscal damage and meniscal extrusion.[4] Age- and sex-related differences must also be considered when interpreting cartilage measurements. Recent normative research has reported greater cartilage thickness among men at most measured knee sites and significant variations across adult age groups.[5] Establishing the normal distribution of cartilage thickness and its association with age and sex is therefore important for distinguishing physiological variation from pathological thinning. The present study was undertaken to measure articular cartilage thickness at selected femoral, tibial and patellar sites of the adult knee joint using MRI and to compare these measurements according to anatomical location, age and sex. AIM To assess articular cartilage thickness at different anatomical sites of the adult knee joint using magnetic resonance imaging. OBJECTIVES 1. To measure articular cartilage thickness at selected femoral, tibial and patellar sites using MRI. 2. To compare articular cartilage thickness among the different anatomical sites of the adult knee joint. 3. To determine the association of knee articular cartilage thickness with the age and sex of the participants.

Source of Data The study data were obtained from adult patients who attended the Department of Radio-diagnosis of the participating medical college and tertiary-care hospital for MRI examination of the knee after referral from the Orthopaedics outpatient or inpatient services. Patients whose MRI demonstrated normal articular cartilage and who fulfilled the eligibility criteria were considered for enrolment. Demographic information, relevant clinical history and MRI measurements were recorded using a predesigned case-record form. Study Design A hospital-based prospective cross-sectional observational study was conducted. Study Location The study was carried out jointly in the Departments of Anatomy, Radio-diagnosis and Orthopaedics of the participating medical college and tertiary-care teaching hospital. MRI examinations were performed in the Department of Radio-diagnosis. Study Duration The study was conducted over a period of 12 months, from January 2012 to January 2013. Sample Size A total of 52 eligible adult participants were included. As cartilage thickness was a continuous outcome, the sample size was calculated using the formula for estimating a population mean: n=(Z_(1-α/2)^2 σ^2)/d^2 where: n= required sample size Z_(1-α/2)= 1.96 at the 95% confidence level σ= anticipated standard deviation of cartilage thickness, taken as 1.35 mm from previous MRI observations d= desired absolute precision, taken as 0.37 mm Therefore: n=((1.96)^2 (1.35)^2)/(0.37)^2 =(3.8416×1.8225)/0.1369=51.13 The calculated sample size was rounded upward, and 52 participants were included in the study. Inclusion Criteria Adults aged 20 years or older of either sex were included. Participants who underwent MRI examination of the knee during the study period were considered. MRI images that adequately demonstrated the femoral, tibial and patellar articular cartilage were included. Participants whose MRI showed no focal defect, marked thinning or other evident abnormality of the articular cartilage were included. Participants who provided written informed consent were included. Exclusion Criteria Patients with a previous history of knee replacement or other major knee surgery were excluded. Patients with known osteoarthritis, rheumatoid arthritis, inflammatory arthritis or infective arthritis were excluded. Patients with a history of significant knee trauma, intra-articular fracture or documented cartilage injury were excluded. MRI examinations showing cartilage defects, advanced degenerative changes, tumours, infection or major structural abnormalities were excluded. Images affected by motion artefacts or inadequate visualization of the cartilage margins were excluded. Patients with contraindications to MRI, including non-compatible cardiac pacemakers, aneurysm clips, cochlear implants, metallic prostheses or other ferromagnetic implants, were excluded. Patients who were unable to remain still or complete the MRI examination were excluded. Procedure and Methodology The study protocol was approved by the Institutional Ethics Committee before commencement. Permission was obtained from the concerned departmental authorities. Eligible participants were informed about the purpose and procedures of the study, and written informed consent was obtained. Each participant underwent MRI examination using a Philips Achieva 1.5-T superconducting MRI scanner with a standard phased-array FLEX-M surface knee coil. The participant was positioned supine, with the knee placed centrally within the dedicated coil in a neutral or minimally flexed position. MRI images of the right knee were acquired in sagittal, axial and coronal planes. The principal scanning parameters were as follows: Sequence Repetition time Echo time Slice thickness Field of view Matrix Axial sequence 739 ms 14 ms 3 mm 150 mm 155 × 256 Sagittal sequence 6824 ms 100 ms 3 mm 150 mm 258 × 480 Coronal sequence 500 ms 17 ms 3 mm 150 mm 258 × 512 The MRI images were transferred to a workstation and evaluated using DICOM-compatible measurement software. Articular cartilage thickness was measured perpendicular to the articular surface, from the cartilage-synovial interface to the cartilage-subchondral bone interface. Measurements were recorded in millimetres. Cartilage thickness was assessed at the following sites: Central patellar cartilage on the sagittal image at the midpoint of the posterior patellar surface where the cartilage appeared thickest. Medial and lateral patellar facet cartilage on axial images at the midportion of the respective facets. Medial and lateral femoral condylar cartilage on sagittal images at the weight-bearing regions located above the posterior horns of the corresponding menisci. Femoral trochlear cartilage, or facies patellaris femoris cartilage, on the sagittal image at the point of maximum thickness. Medial and lateral tibial plateau cartilage on sagittal images at the regions corresponding to the posterior horns of the respective menisci. Three measurements were obtained from each site on two consecutive images wherever the anatomical site was adequately visualized. The mean of these readings was used as the final cartilage thickness. All measurements were reviewed and confirmed by an experienced radiologist. The average femoral cartilage thickness was calculated from the medial femoral, lateral femoral and trochlear cartilage measurements. The average patellar cartilage thickness was calculated from the central, medial-facet and lateral-facet measurements. The average tibial cartilage thickness was calculated from the medial and lateral tibial plateau measurements. Overall average knee cartilage thickness was calculated from the mean femoral, tibial and patellar cartilage measurements. For age-related comparisons, participants were classified into four groups: 20-34 years, 35-49 years, 50-64 years and 65-79 years. Sample Processing No biological specimen was collected or processed because the study was based on MRI images. Image processing consisted of retrieval of DICOM images, selection of appropriate axial and sagittal sections, identification of predefined anatomical landmarks and electronic measurement of cartilage thickness. Images were anonymized by assigning a unique study identification number before analysis. Inadequate or artefact-affected images were excluded. The average of repeated measurements was entered into the final database to reduce random measurement error. Data Collection Data were collected using a predesigned and pretested case-record form. The recorded variables included study identification number, age, sex, relevant clinical history, indication for MRI, side examined and cartilage thickness at each predefined femoral, tibial and patellar site. Average femoral, tibial, patellar and overall knee cartilage thicknesses were subsequently calculated. Completed forms were checked for completeness and consistency before data entry. Participant identity was kept confidential throughout the study. Statistical Methods Data were entered into Microsoft Excel and analysed using IBM SPSS Statistics version 20.0. Continuous variables were summarized as mean, standard deviation, median and range, as appropriate. Categorical variables were expressed as frequency and percentage. Mean cartilage thickness was reported with a 95% confidence interval. The normality of continuous variables was assessed using the Shapiro-Wilk test and graphical methods. Cartilage thickness at different sites within the same knee was compared using repeated-measures analysis of variance; the Friedman test was used when the normality assumption was not satisfied. Appropriate post-hoc pairwise comparisons were performed with adjustment for multiple comparisons. Mean cartilage thickness between male and female participants was compared using the independent-samples t-test; the Mann-Whitney U test was used for non-normally distributed measurements. Differences among the four age groups were assessed using one-way analysis of variance followed by Tukey’s post-hoc test. The Kruskal-Wallis test followed by adjusted pairwise comparisons was applied when parametric assumptions were not fulfilled. The relationship between age and cartilage thickness was examined using Pearson’s correlation coefficient or Spearman’s rank correlation coefficient, as appropriate. Multiple linear regression analysis could be used to assess the independent association of age and sex with cartilage thickness. All statistical tests were two-tailed, and a p value below 0.05 was considered statistically significant.

Table 1. Demographic profile and overall MRI assessment of adult knee articular cartilage (N=52) Study parameter n (%) or Mean (SD) 95% CI Test statistic p value Age, years 42.13 (16.36) 37.58-46.68 Age group χ²=13.38 0.004 20-34 years 24 (46.2) 32.2-60.5 35-49 years 12 (23.1) 12.5-36.8 50-64 years 9 (17.3) 8.2-30.3 65-79 years 7 (13.5) 5.6-25.8 Sex χ²=1.23 0.267 Male 30 (57.7) 43.2-71.3 Female 22 (42.3) 28.7-56.8 Average femoral cartilage thickness, mm 4.43 (1.32) 4.06-4.80 Average tibial cartilage thickness, mm 4.10 (0.96) 3.83-4.37 Average patellar cartilage thickness, mm 4.81 (1.11) 4.50-5.12 Overall average knee cartilage thickness, mm 4.45 (1.05) 4.16-4.74 F=18.74* <0.001 *Repeated-measures ANOVA comparing average cartilage thickness among the femoral, tibial and patellar regions. The chi-square tests for age group and sex were goodness-of-fit tests. Table 1 presents the demographic characteristics and overall MRI measurements of knee articular cartilage among 52 participants. The mean age was 42.13±16.36 years (95% CI: 37.58-46.68 years). The largest proportion belonged to the 20-34-year age group (46.2%), followed by 35-49 years (23.1%), 50-64 years (17.3%) and 65-79 years (13.5%). The age-group distribution differed significantly (χ²=13.38, p=0.004). Males constituted 57.7% of the participants, while females constituted 42.3%; however, the sex distribution was not significantly different (χ²=1.23, p=0.267). The mean femoral, tibial and patellar cartilage thicknesses were 4.43±1.32 mm, 4.10±0.96 mm and 4.81±1.11 mm, respectively. The overall average knee cartilage thickness was 4.45±1.05 mm (95% CI: 4.16-4.74 mm). Patellar cartilage had the greatest average thickness, whereas tibial cartilage had the lowest. Repeated-measures ANOVA demonstrated a statistically significant difference in mean cartilage thickness among the three anatomical regions (F=18.74, p<0.001). Table 2. Articular cartilage thickness at selected femoral, tibial and patellar sites on MRI (N=52) Anatomical region and measurement site Mean (SD), mm 95% CI, mm Test statistic p value Femoral cartilage F=54.82* <0.001 Medial femoral condyle 3.92 (1.40) 3.53-4.31 Lateral femoral condyle 3.98 (1.42) 3.58-4.38 Femoral trochlea/facies patellaris 5.39 (1.35) 5.01-5.77 Average femoral cartilage 4.43 (1.32) 4.06-4.80 Tibial cartilage t=3.17† 0.003 Medial tibial plateau 3.92 (0.98) 3.65-4.19 Lateral tibial plateau 4.29 (1.09) 3.99-4.59 Average tibial cartilage 4.10 (0.96) 3.83-4.37 Patellar cartilage F=62.36* <0.001 Central patellar cartilage 5.81 (1.48) 5.40-6.22 Medial patellar facet 4.03 (0.94) 3.77-4.29 Lateral patellar facet 4.59 (1.31) 4.23-4.95 Average patellar cartilage 4.81 (1.11) 4.50-5.12 Overall average knee cartilage 4.45 (1.05) 4.16-4.74 *Repeated-measures ANOVA comparing measurement sites within the corresponding anatomical region. †Paired t-test comparing the medial and lateral tibial cartilage thicknesses. Table 2 shows MRI-measured articular cartilage thickness at the selected femoral, tibial and patellar sites. Within the femoral region, the trochlear or facies patellaris cartilage demonstrated the greatest thickness at 5.39±1.35 mm (95% CI: 5.01-5.77 mm), compared with 3.92±1.40 mm at the medial femoral condyle and 3.98±1.42 mm at the lateral femoral condyle. The average femoral cartilage thickness was 4.43±1.32 mm. Differences among the femoral measurement sites were statistically significant (F=54.82, p<0.001). In the tibial region, lateral tibial cartilage was significantly thicker than medial tibial cartilage (4.29±1.09 mm versus 3.92±0.98 mm; t=3.17, p=0.003), while the average tibial cartilage thickness was 4.10±0.96 mm. Within the patellar region, central patellar cartilage had the greatest thickness at 5.81±1.48 mm (95% CI: 5.40-6.22 mm), followed by the lateral patellar facet at 4.59±1.31 mm and the medial patellar facet at 4.03±0.94 mm. The average patellar cartilage thickness was 4.81±1.11 mm, and the difference among the patellar sites was statistically significant (F=62.36, p<0.001). The overall average cartilage thickness of the knee was 4.45±1.05 mm. Table 3. Pairwise comparison of articular cartilage thickness among different anatomical sites of the adult knee joint (N=52) Comparison First site Mean (SD), mm Second site Mean (SD), mm Mean difference, mm 95% CI of difference Test statistic Adjusted p value Femoral trochlea vs medial femoral condyle 5.39 (1.35) 3.92 (1.40) 1.47 1.14-1.80 t=8.94 <0.001 Femoral trochlea vs lateral femoral condyle 5.39 (1.35) 3.98 (1.42) 1.41 1.08-1.74 t=8.55 <0.001 Lateral vs medial femoral condyle 3.98 (1.42) 3.92 (1.40) 0.06 −0.10-0.22 t=0.75 0.456 Lateral vs medial tibial plateau 4.29 (1.09) 3.92 (0.98) 0.37 0.14-0.60 t=3.17 0.009 Central vs medial patellar cartilage 5.81 (1.48) 4.03 (0.94) 1.78 1.45-2.11 t=10.74 <0.001 Central vs lateral patellar cartilage 5.81 (1.48) 4.59 (1.31) 1.22 0.91-1.53 t=7.90 <0.001 Lateral vs medial patellar facet 4.59 (1.31) 4.03 (0.94) 0.56 0.30-0.82 t=4.31 <0.001 Average patellar vs average tibial cartilage 4.81 (1.11) 4.10 (0.96) 0.71 0.47-0.95 t=5.92 <0.001 Average patellar vs average femoral cartilage 4.81 (1.11) 4.43 (1.32) 0.38 0.13-0.63 t=3.06 0.011 Average femoral vs average tibial cartilage 4.43 (1.32) 4.10 (0.96) 0.33 0.10-0.56 t=2.88 0.018 Overall regional comparison: repeated-measures ANOVA, F=18.74, p<0.001. Table 3 compares articular cartilage thickness between different anatomical sites of the knee. Femoral trochlear cartilage was significantly thicker than cartilage over both the medial femoral condyle (mean difference: 1.47 mm; 95% CI: 1.14-1.80; t=8.94, adjusted p<0.001) and lateral femoral condyle (mean difference: 1.41 mm; 95% CI: 1.08-1.74; t=8.55, adjusted p<0.001). No significant difference was observed between the lateral and medial femoral condyles (mean difference: 0.06 mm; 95% CI: −0.10 to 0.22; p=0.456). Lateral tibial cartilage was significantly thicker than medial tibial cartilage by 0.37 mm (95% CI: 0.14-0.60; t=3.17, adjusted p=0.009). Central patellar cartilage was significantly thicker than both medial patellar cartilage (mean difference: 1.78 mm; p<0.001) and lateral patellar cartilage (mean difference: 1.22 mm; p<0.001). The lateral patellar facet was also significantly thicker than the medial facet by 0.56 mm (95% CI: 0.30-0.82; p<0.001). At the regional level, average patellar cartilage was significantly thicker than tibial cartilage by 0.71 mm (p<0.001) and femoral cartilage by 0.38 mm (p=0.011). Average femoral cartilage was significantly thicker than tibial cartilage by 0.33 mm (p=0.018). The overall regional comparison was statistically significant (F=18.74, p<0.001), confirming that cartilage thickness varied according to anatomical location. Table 4. Association of average knee articular cartilage thickness with age and sex (N=52) Participant characteristic n Average knee cartilage thickness, Mean (SD), mm 95% CI, mm Test statistic p value Age group F=42.17 <0.001 20-34 years 24 5.23 (0.34) 5.09-5.37 35-49 years 12 4.52 (0.74) 4.05-4.99 50-64 years 9 3.46 (0.81) 2.84-4.08 65-79 years 7 2.89 (0.49) 2.46-3.32 Sex t=3.37 0.002 Male 30 4.84 (0.85) 4.53-5.15 Female 22 3.91 (1.07) 3.44-4.38 Multivariable linear regression analysis Predictor Regression coefficient (β), mm 95% CI Standardized β Test statistic p value Age, per one-year increase −0.058 −0.069 to −0.047 −0.73 t=−10.54 <0.001 Male sex 0.62 0.29-0.95 0.31 t=3.77 <0.001 Female sex Reference Model statistics: R^2=0.68, adjusted R^2=0.67, F=52.06, p<0.001. Table 4 demonstrates the association of average knee cartilage thickness with age and sex. Mean cartilage thickness progressively declined from 5.23±0.34 mm among participants aged 20-34 years to 4.52±0.74 mm among those aged 35-49 years, 3.46±0.81 mm among those aged 50-64 years and 2.89±0.49 mm among those aged 65-79 years. This decreasing trend across age groups was statistically significant (F=42.17, p<0.001). Male participants had significantly greater average knee cartilage thickness than female participants (4.84±0.85 mm versus 3.91±1.07 mm; t=3.37, p=0.002). In multivariable linear regression, every one-year increase in age was independently associated with a 0.058-mm reduction in average cartilage thickness (β=−0.058; 95% CI: −0.069 to −0.047; standardized β=−0.73; p<0.001). After adjustment for age, male sex was associated with cartilage that was, on average, 0.62 mm thicker than that in females (β=0.62; 95% CI: 0.29-0.95; standardized β=0.31; p<0.001). The regression model explained 68% of the variability in average knee cartilage thickness (R²=0.68; adjusted R²=0.67; F=52.06, p<0.001), indicating that age and sex were important independent determinants of knee articular cartilage thickness.

The present MRI-based study evaluated articular cartilage thickness at different sites of the adult knee joint among 52 participants. The mean age was 42.13±16.36 years, with participants covering a broad age range from 20 to 79 years. The overall average knee cartilage thickness was 4.45±1.05 mm. Significant regional variation was observed, with average thickness measuring 4.81±1.11 mm in the patella, 4.43±1.32 mm in the femur and 4.10±0.96 mm in the tibia (F=18.74, p<0.001). This regional heterogeneity supports the understanding that articular cartilage morphology is influenced by the local geometry, contact area and mechanical loading pattern of each articular surface. Eckstein et al. (2024)[1] emphasized that MRI-based cartilage morphometry has substantially improved the assessment of regional cartilage morphology and physiological adaptation. Similarly, Chen et al. (2024)[2], in a systematic review and meta-analysis, found that quantitative and three-dimensional MRI techniques were more sensitive for evaluating knee cartilage than conventional two-dimensional techniques. The mean thicknesses at the medial and lateral femoral condyles were 3.92±1.40 mm and 3.98±1.42 mm, respectively. No significant difference was observed between these sites (mean difference 0.06 mm, p=0.456). In contrast, femoral trochlear cartilage was considerably thicker at 5.39±1.35 mm and was significantly thicker than both medial and lateral femoral condylar cartilage (p<0.001). Sidharthan et al. (2021)[3] also demonstrated significant regional differences in cartilage thickness and found the femoral trochlea to be thicker than the medial and lateral femoral condyles. Although their investigation involved paediatric and adolescent knees, the anatomical distribution was comparable with the present adult findings. The thicker trochlear cartilage may represent an adaptive response to the substantial patellofemoral contact forces generated during knee flexion, stair climbing, squatting and rising from a seated position. Giurazza et al. (2025)[4] systematically reviewed MRI measurements from 8,170 non-arthritic adult knees and reported weighted mean femoral cartilage thicknesses of approximately 2.05 mm at the distal medial condyle, 1.95 mm at the distal lateral condyle, 2.44 mm at the posterior medial condyle and 2.27 mm at the posterior lateral condyle. These measurements were lower than those in the present study. This difference may be attributable to variations in anatomical landmarks, whether mean or maximum thickness was measured, cartilage segmentation methods, MRI field strength, sequence parameters, participant anthropometry and inclusion criteria. The present study measured cartilage at predefined points of maximum thickness, whereas several quantitative studies calculated mean thickness across an entire segmented cartilage plate. Therefore, direct numerical comparisons require caution. The medial and lateral tibial cartilage thicknesses were 3.92±0.98 mm and 4.29±1.09 mm, respectively. The lateral tibial cartilage was significantly thicker than the medial tibial cartilage by 0.37 mm (95% CI: 0.14-0.60; p=0.009). This regional difference could reflect the unequal distribution of load between the medial and lateral compartments and differences in the congruity and mobility of the menisci. Robbins et al. (2019)[5] showed that tibiofemoral cartilage thickness differed across compartments and that lower-limb alignment contributed to regional variations, particularly in knees with osteoarthritis. Guermazi et al. (2015)[6] also demonstrated that meniscal damage, meniscal extrusion and radiographic osteoarthritis were associated with subsequent compartment-specific cartilage loss. Although participants with evident cartilage pathology were excluded from the present study, unmeasured differences in alignment, body weight and loading may have contributed to the medial-lateral variation. Among the patellar sites, central patellar cartilage demonstrated the greatest thickness at 5.81±1.48 mm, followed by the lateral facet at 4.59±1.31 mm and the medial facet at 4.03±0.94 mm. Central cartilage was significantly thicker than medial cartilage by 1.78 mm and lateral cartilage by 1.22 mm, while the lateral facet was significantly thicker than the medial facet by 0.56 mm (all p<0.001). Sidharthan et al. (2021)[3] similarly found that patellar cartilage was the thickest cartilage in the knee, although differences between medial and lateral patellar facets were not significant in their younger population. The thick central patellar cartilage observed in the present study is biomechanically plausible because the central ridge and adjacent facets are exposed to high compressive forces during knee flexion. Culvenor et al. (2019)[7] further highlighted the mechanical vulnerability of the patellofemoral compartment by demonstrating measurable loss of patellar and trochlear cartilage thickness during five years of follow-up after anterior cruciate ligament injury. The average patellar cartilage was 0.71 mm thicker than tibial cartilage (p<0.001) and 0.38 mm thicker than femoral cartilage (p=0.011). Average femoral cartilage was also significantly thicker than tibial cartilage by 0.33 mm (p=0.018). These findings confirmed that a single overall knee cartilage measurement cannot adequately represent the anatomical variability of the joint. Measurements should be interpreted in relation to the exact anatomical compartment and imaging plane. Schmitz et al. (2017)[8] reported that cartilage thickness estimates could vary between imaging methods and anatomical regions when ultrasonography was compared with MRI. Kauppinen et al. (2021)[9] also found that ultrasonography and three-dimensional MRI provided related but not necessarily interchangeable measurements of normal femoral cartilage. Standardization of knee position, measurement orientation and anatomical landmarks is therefore essential. The overall average knee cartilage thickness decreased progressively across the age groups, from 5.23±0.34 mm among participants aged 20-34 years to 4.52±0.74 mm at 35-49 years, 3.46±0.81 mm at 50-64 years and 2.89±0.49 mm at 65-79 years (F=42.17, p<0.001). Multivariable analysis indicated that each one-year increase in age was associated with an average reduction of 0.058 mm in cartilage thickness (β=−0.058; 95% CI: −0.069 to −0.047; p<0.001). The large standardized coefficient for age (β=−0.73) suggested that age was the strongest determinant included in the model. This finding was consistent with the established biological effects of ageing, including reduced chondrocyte activity, diminished proteoglycan synthesis, alterations in collagen organization and impaired cartilage repair. Nevertheless, age-related cartilage changes may not be uniformly linear across all knee regions. Sidharthan et al. (2021)[3] reported an inverse association between age and femoral cartilage thickness but a weaker association at the patella in younger participants. Sekiya et al. (2025)[10], using automated three-dimensional MRI in knees without radiographic osteoarthritis, demonstrated that the influence of age and sex varied according to the cartilage region. These observations suggest that regional measurements and age-specific reference standards are preferable to a single universal cut-off value. MRI may also identify biochemical alterations before substantial morphological thinning becomes apparent. Luo et al. (2024)[11] described the usefulness of compositional MRI techniques, including T2, T2*, T1ρ and diffusion-based imaging, for detecting early changes in collagen organization, proteoglycan content and water distribution. Male participants had significantly thicker cartilage than female participants (4.84±0.85 mm versus 3.91±1.07 mm; p=0.002). After controlling for age, male sex remained independently associated with a 0.62-mm greater average cartilage thickness (95% CI: 0.29-0.95; p<0.001). Sekiya et al. (2025)[10] similarly found that women had thinner cartilage than men in the medial femoral, medial tibial, lateral femoral and trochlear regions after adjustment for height, although sex differences were not observed in the patellar and lateral tibial regions. The sex difference in the present study may be related to differences in body size, subchondral bone dimensions, hormonal influences, muscle strength and mechanical loading. Because height, weight and body mass index were not incorporated into the reported model, some of the observed effect of sex may have reflected differences in overall skeletal size. The use of MRI allowed direct, non-invasive assessment of cartilage rather than indirect estimation through radiographic joint-space width. Mortensen et al. (2021)[12] found that relationships between MRI cartilage measurements and specialized radiographic measurements differed between the medial and lateral compartments, indicating that the two approaches should not be treated as interchangeable. Bedewi et al. (2020)[13] demonstrated that high-resolution ultrasonography could provide reliable femoral cartilage measurements in healthy adults; however, ultrasonography is primarily limited to the accessible anterior femoral cartilage. MRI remains advantageous for simultaneously assessing femoral, tibial, patellar and trochlear cartilage and associated intra-articular structures.

Magnetic resonance imaging provided a useful, non-invasive method for measuring articular cartilage thickness at different anatomical sites of the adult knee joint. Cartilage thickness varied significantly across the femoral, tibial and patellar regions. The central patellar cartilage was the thickest individual site, followed by the femoral trochlear cartilage, while the medial femoral condyle and medial tibial plateau had comparatively lower thickness. Patellar cartilage was significantly thicker than femoral and tibial cartilage. Increasing age was independently associated with progressive reduction in cartilage thickness, whereas males had significantly thicker cartilage than females. These findings indicate that anatomical site, age and sex should be considered when interpreting MRI-based knee cartilage measurements. Site-specific reference values may assist in distinguishing normal anatomical variation from early cartilage degeneration. LIMITATIONS OF STUDY 1. The study was conducted at a single tertiary-care hospital; therefore, its findings may not be generalizable to the wider population. 2. The relatively small sample size of 52 participants, particularly the limited number of older individuals, reduced the precision of age-stratified estimates. 3. The cross-sectional design demonstrated associations but could not establish the longitudinal rate of age-related cartilage loss. 4. Participants were selected from patients referred for knee MRI and might not have represented completely healthy community-based adults. 5. Cartilage thickness was measured at selected anatomical points rather than through three-dimensional segmentation of the entire cartilage plate. 6. Measurements were obtained from two-dimensional MRI images using a 1.5-T scanner. Partial-volume effects and limited spatial resolution might have affected the accuracy of thin cartilage measurements. 7. Only the right knee was assessed; therefore, possible differences between the right and left knees were not evaluated. 8. Potential determinants such as height, weight, body mass index, physical activity, occupation, lower-limb alignment, hormonal status and menopausal status were not adequately controlled. 9. Interobserver and intraobserver reliability statistics were not reported, although measurements were reviewed by a radiologist. 10. MRI findings were not validated against arthroscopy, histopathology or another reference method.

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