Articular cartilage is a specialized specialized0 specialized form of hyaline cartilage that covers the articulating surfaces of synovial joints. It provides a smooth, low-friction surface, distributes mechanical loads and protects the underlying subchondral bone. The thickness of articular cartilage is not uniform throughout the knee joint because the patellar, femoral and tibial surfaces are exposed to different contact pressures and loading patterns. Magnetic resonance imaging (MRI) enables direct, non-invasive and multiplanar assessment of articular cartilage and is widely used for quantitative evaluation of cartilage morphology. Advances in MRI-based cartilage morphometry have improved the understanding of normal cartilage anatomy, physiological adaptation and osteoarthritisthritis-related cartilage loss.[1] Quantitative and three5 three-dimensional MRI techniques also demonstrate better sensitivity for detecting chondral abnormalities than conventional two-dimensional techniques.[2] Sex may be an important determinant of knee cartilage morphology. Men generally have larger joint surface areas, greater skeletal dimensions and higher cartilage volumes than women. However, the extent to which these differences represent actual variation in cartilage thickness rather than differences in bone size remains uncertain. Sex-related differences may also be influenced by height, body weight, lower-limb alignment, muscle strength, physical activity and hormonal factors. Sek In an MRI-based study of normal knees, Sekiya et al. reported that females had significantly thinner cartilage in several femoral and tibial regions even after adjustment for height, although the magnitude of the difference varied according to anatomical region.[3] Cartilage thickness should be evaluated separately at different knee sites because the influence of sex may not be uniform. The patella and femoral trochlea are generally covered by thicker cartilage because they sustain substantial patellofemoral contact forces, particularly during knee flexion. In contrast, the femoral condyles and tibial plateaus experience compartment-specific weight-bearing forces. A systematic review of non-arthritic adult knees demonstrated considerable interindividual and regional variation in femoral cartilage thickness, indicating that a single fixed value cannot adequately represent normal cartilage morphology.[4] Regional differences may also have clinical importance because cartilage loss, lower-limb alignment and meniscal abnormalities demonstrate compartment-specific relationships.[5] AIM To compare patellar, femoral and tibial articular cartilage thickness between adult males and females using magnetic resonance imaging. OBJECTIVES 1. To measure articular cartilage thickness at selected patellar, femoral and tibial sites among adult males and females using MRI. 2. To compare site-specific and region-specific knee cartilage thickness between male and female participants. 3. To determine whether sex remained independently associated with average knee cartilage thickness after adjustment for age

Source of Data The study data were obtained from adults referred by the Department of Orthopaedics to the Department of Radio-diagnosis of the participating medical college and tertiary-care teaching hospital for MRI examination of the knee. Patients whose MRI images adequately demonstrated normal articular cartilage and who satisfied the eligibility criteria were included. Demographic details, clinical history and cartilage measurements were recorded using a predesigned case-record form. Study Design A hospital-based prospective comparative 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 hospital. MRI examinations and image retrieval were performed in the Department of Radio-diagnosis. Study Duration The study was conducted over 12 months, from January 2012 to January 2013. Sample Size The sample size was calculated for comparing mean cartilage thickness between two independent groups adult males and females using the following formula: n=(2σ^2 (Z_(1-α/2)+Z_(1-β) )^2)/Δ^2 where: nrepresented the required sample size in each group; Z_(1-α/2)=1.96at a 95% confidence level; Z_(1-β)=0.84at 80% statistical power; σ=1.05mm was the anticipated pooled standard deviation of average knee cartilage thickness; and Δ=0.82mm was the minimum expected difference between males and females. Therefore: n=(2(1.05)^2 (1.96+0.84)^2)/(0.82)^2 n=2(1.1025)(7.84)/0.6724=25.70 The required sample size was approximately 26 participants per group, giving a total sample size of 52 participants. Consecutive eligible adults were enrolled until the total sample size was achieved. The final study included 30 males and 22 females because enrolment reflected the sex distribution of eligible participants attending during the study period. Inclusion Criteria Adults aged 20 years or older were included. Participants of either sex who underwent MRI examination of the knee during the study period were eligible. Participants whose MRI images adequately demonstrated the patellar, femoral and tibial articular cartilage were included. MRI examinations showing no focal cartilage defect or evident cartilage pathology were included. Participants who provided written informed consent were included. Exclusion Criteria Patients with a previous knee replacement or other major knee surgery were excluded. Patients with a history of osteoarthritis, rheumatoid arthritis, inflammatory arthritis or infective arthritis were excluded. Patients with a history of significant knee trauma, intra-articular fracture or known articular cartilage injury were excluded. MRI examinations showing focal cartilage defects, advanced degeneration, tumours, infection or other major structural abnormalities were excluded. Images with motion artefacts, inadequate sequences or poorly defined cartilage margins were excluded. Patients with MRI-incompatible 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 submitted to and approved by the Institutional Ethics Committee. Permission was obtained from the concerned departmental authorities. Eligible participants received detailed information about the study, and written informed consent was obtained before enrolment. Age, sex and relevant clinical history were recorded. MRI of the right knee was performed using a Philips Achieva 1.5-T superconducting MRI scanner and a standard phased-array FLEX-M surface knee coil. Participants were positioned supine, and the right knee was placed centrally within the coil in a neutral or minimally flexed position. Images were acquired in axial, sagittal and coronal planes using standardized sequences. The principal scanning parameters included a slice thickness of 3 mm and a field of view of 150 mm. The axial sequence was obtained with a repetition time of 739 ms, echo time of 14 ms and matrix of 155×256. The sagittal sequence was obtained with a repetition time of 6824 ms, echo time of 100 ms and matrix of 258×480. The coronal sequence was acquired with a repetition time of 500 ms, echo time of 17 ms and matrix of 258×512. The acquired images were transferred to a workstation and evaluated using DICOM-compatible measurement software. Cartilage thickness was measured perpendicular to the articular surface from the cartilage-synovial interface to the cartilage-subchondral bone interface. All measurements were expressed in millimetres. Patellar cartilage measurements Central patellar cartilage thickness was measured on the sagittal image at the midportion of the posterior patellar surface where the cartilage was maximally visualized. Medial patellar cartilage thickness was measured on the axial image at the midportion of the medial patellar facet. Lateral patellar cartilage thickness was measured on the axial image at the midportion of the lateral patellar facet. The mean of the central, medial and lateral patellar measurements was calculated as the average patellar cartilage thickness. Femoral cartilage measurements Medial femoral cartilage thickness was measured on the sagittal image over the medial femoral condyle at the weight-bearing region corresponding to the posterior horn of the medial meniscus. Lateral femoral cartilage thickness was measured at the corresponding weight-bearing region of the lateral femoral condyle. Femoral trochlear or facies patellaris femoris cartilage thickness was measured on the sagittal image at the point of maximum trochlear cartilage thickness. The mean of these three measurements was calculated as the average femoral cartilage thickness. Tibial cartilage measurements Medial tibial cartilage thickness was measured on the sagittal image over the medial tibial plateau at the region corresponding to the posterior horn of the medial meniscus. Lateral tibial cartilage thickness was measured at the corresponding site of the lateral tibial plateau. The mean of the medial and lateral measurements was calculated as the average tibial cartilage thickness. The overall average knee cartilage thickness was calculated from the average patellar, femoral and tibial cartilage measurements. Three readings were taken at each measurement site on two consecutive images whenever adequately visualized. Their mean was used as the final measurement to reduce random error. The measurements were reviewed and confirmed by an experienced radiologist. Participants were subsequently classified as male or female for comparative analysis. Sample Processing No biological specimen was collected or processed. Image processing involved retrieval of MRI data in DICOM format, anonymization of the images, selection of appropriate axial and sagittal sections, identification of predefined anatomical landmarks and electronic measurement of cartilage thickness. Each participant was assigned a unique study identification number. Images were screened for adequate quality before measurement. Artefact-affected images and those showing articular cartilage pathology were excluded. Repeated measurements were averaged and entered into the final database. The same anatomical definitions and measurement procedure were applied to males and females. Data Collection Information was collected using a predesigned and pretested case-record form. The recorded variables included study identification number, age, sex, relevant clinical history, indication for MRI and cartilage thickness at each selected site. The following outcome variables were documented: Medial and lateral femoral condylar cartilage thickness; Femoral trochlear cartilage thickness; Medial and lateral tibial plateau cartilage thickness; Central, medial and lateral patellar cartilage thickness; Average femoral cartilage thickness; Average tibial cartilage thickness; Average patellar cartilage thickness; and Overall average knee cartilage thickness. Completed forms were examined for completeness and internal consistency before data entry. Participant identifiers were removed from the analytical database, and confidentiality was maintained. Statistical Methods Data were entered into Microsoft Excel and analysed using IBM SPSS Statistics version 20.0. Continuous variables were summarized using mean, standard deviation, median and range, as appropriate. Categorical variables were reported as frequencies and percentages. Mean cartilage thickness was presented with a 95% confidence interval. The normality of continuous variables was assessed using the Shapiro-Wilk test and graphical methods. Age and site-specific cartilage thickness were compared between males and females using the independent-samples t-test when data were normally distributed. The Mann-Whitney U test was used when parametric assumptions were not satisfied. Mean differences between sexes were presented with their 95% confidence intervals. Within each sex, cartilage thickness at different anatomical sites was compared using repeated-measures analysis of variance. The Friedman test was applied when the assumptions for repeated-measures analysis were not fulfilled. Post-hoc pairwise comparisons were conducted with Bonferroni adjustment. The association between age and cartilage thickness was examined using Pearson’s or Spearman’s correlation coefficient, as appropriate. Multiple linear regression analysis was performed to determine the independent association between sex and average knee cartilage thickness after adjustment for age. Regression coefficients, standardized coefficients, 95% confidence intervals and p values were reported. All tests were two-tailed, and p<0.05 was considered statistically significant.

Table 1. Demographic profile and comparison of regional articular cartilage thickness between adult males and females using MRI (N=52) Study parameter Male (n=30), n (%) or Mean (SD) 95% CI Female (n=22), n (%) or Mean (SD) 95% CI Test statistic p value Number of participants 30 (57.7) 43.2-71.3 22 (42.3) 28.7-56.8 χ²=1.23 0.267 Age, years 40.17 (17.12) 33.78-46.56 44.82 (15.24) 38.06-51.58 t=-1.03 0.309 Average patellar cartilage thickness, mm 5.12 (1.00) 4.75-5.49 4.39 (1.14) 3.88-4.90 t=2.40 0.021 Average femoral cartilage thickness, mm 4.88 (1.25) 4.41-5.35 3.81 (1.17) 3.29-4.33 t=3.16 0.003 Average tibial cartilage thickness, mm 4.52 (0.56) 4.31-4.73 3.52 (1.11) 3.03-4.01 t=3.88 <0.001 Overall average knee cartilage thickness, mm 4.84 (0.85) 4.52-5.16 3.91 (1.07) 3.44-4.38 t=3.37 0.002 Table 1 presents the demographic profile and regional cartilage thickness measurements of 52 participants, comprising 30 (57.7%) males and 22 (42.3%) females. The sex distribution was not statistically significant (χ²=1.23, p=0.267). The mean age was 40.17±17.12 years among males and 44.82±15.24 years among females, with no significant difference between the groups (t=-1.03, p=0.309), indicating age comparability. Males had significantly greater average cartilage thickness than females in the patellar region (5.12±1.00 versus 4.39±1.14 mm; t=2.40, p=0.021), femoral region (4.88±1.25 versus 3.81±1.17 mm; t=3.16, p=0.003) and tibial region (4.52±0.56 versus 3.52±1.11 mm; t=3.88, p<0.001). The overall average knee cartilage thickness was also significantly greater in males than females (4.84±0.85 versus 3.91±1.07 mm; t=3.37, p=0.002). Table 2. MRI measurements of articular cartilage thickness at selected patellar, femoral and tibial sites among adult males and females (N=52) Anatomical region and measurement site Male (n=30), Mean (SD), mm 95% CI Female (n=22), Mean (SD), mm 95% CI Test statistic p value Patellar cartilage Central patellar cartilage 6.23 (1.36) 5.72-6.74 5.23 (1.47) 4.58-5.88 t=2.50 0.016 Medial patellar facet 4.06 (0.81) 3.76-4.36 3.99 (1.12) 3.49-4.49 t=0.25 0.804 Lateral patellar facet 5.06 (1.35) 4.56-5.56 3.95 (0.95) 3.53-4.37 t=3.48 0.001 Average patellar cartilage 5.12 (1.00) 4.75-5.49 4.39 (1.14) 3.88-4.90 t=2.40 0.021 Femoral cartilage Medial femoral condyle 4.40 (1.34) 3.90-4.90 3.27 (1.22) 2.73-3.81 t=3.16 0.003 Lateral femoral condyle 4.44 (1.38) 3.92-4.96 3.35 (1.24) 2.80-3.90 t=2.98 0.005 Femoral trochlea/facies patellaris 5.81 (1.36) 5.30-6.32 4.82 (1.12) 4.32-5.32 t=2.87 0.006 Average femoral cartilage 4.88 (1.25) 4.41-5.35 3.81 (1.17) 3.29-4.33 t=3.16 0.003 Tibial cartilage Medial tibial plateau 4.32 (0.51) 4.13-4.51 3.36 (1.18) 2.84-3.88 t=3.58 0.001 Lateral tibial plateau 4.72 (0.83) 4.41-5.03 3.69 (1.13) 3.19-4.19 t=3.62 0.001 Average tibial cartilage 4.52 (0.56) 4.31-4.73 3.52 (1.11) 3.03-4.01 t=3.88 <0.001 Overall average knee cartilage 4.84 (0.85) 4.52-5.16 3.91 (1.07) 3.44-4.38 t=3.37 0.002 Table 2 shows site-specific MRI measurements of knee articular cartilage in males and females. In the patellar region, males had significantly greater central patellar cartilage thickness than females (6.23±1.36 versus 5.23±1.47 mm; t=2.50, p=0.016). Lateral patellar cartilage was also significantly thicker in males (5.06±1.35 versus 3.95±0.95 mm; t=3.48, p=0.001). However, no significant sex difference was observed at the medial patellar facet (4.06±0.81 versus 3.99±1.12 mm; t=0.25, p=0.804). Consequently, average patellar cartilage thickness remained significantly greater in males (p=0.021). All femoral measurements were significantly higher among males, including the medial femoral condyle (4.40±1.34 versus 3.27±1.22 mm; p=0.003), lateral femoral condyle (4.44±1.38 versus 3.35±1.24 mm; p=0.005) and femoral trochlea (5.81±1.36 versus 4.82±1.12 mm; p=0.006). Similarly, males had significantly thicker medial tibial (4.32±0.51 versus 3.36±1.18 mm; p=0.001) and lateral tibial cartilage (4.72±0.83 versus 3.69±1.13 mm; p=0.001). Table 3. Site-specific and region-specific differences in knee cartilage thickness between male and female participants (N=52) Measurement site or region Male-female mean difference, mm 95% CI of difference Test statistic p value Site-specific differences Central patellar cartilage 1.00 0.20-1.80 t=2.50 0.016 Medial patellar facet 0.07 -0.49-0.63 t=0.25 0.804 Lateral patellar facet 1.11 0.47-1.75 t=3.48 0.001 Medial femoral condyle 1.13 0.41-1.85 t=3.16 0.003 Lateral femoral condyle 1.09 0.36-1.82 t=2.98 0.005 Femoral trochlea/facies patellaris 0.99 0.30-1.68 t=2.87 0.006 Medial tibial plateau 0.96 0.41-1.51 t=3.58 0.001 Lateral tibial plateau 1.03 0.46-1.60 t=3.62 0.001 Region-specific differences Average patellar cartilage 0.73 0.12-1.34 t=2.40 0.021 Average femoral cartilage 1.07 0.39-1.75 t=3.16 0.003 Average tibial cartilage 1.00 0.47-1.53 t=3.88 <0.001 Overall average knee cartilage 0.93 0.38-1.48 t=3.37 0.002 Table 3 quantifies the site-specific and region-specific differences in cartilage thickness between males and females. The largest site-specific difference was observed at the medial femoral condyle, where male cartilage was 1.13 mm thicker than female cartilage (95% CI: 0.41-1.85; t=3.16, p=0.003). This was followed by the lateral patellar facet, with a difference of 1.11 mm (95% CI: 0.47-1.75; p=0.001), and the lateral femoral condyle, with a difference of 1.09 mm (95% CI: 0.36-1.82; p=0.005). Significant male-female differences were also observed at the lateral tibial plateau (1.03 mm), central patella (1.00 mm), femoral trochlea (0.99 mm) and medial tibial plateau (0.96 mm). The medial patellar facet demonstrated the smallest difference at 0.07 mm, and its confidence interval included zero (95% CI: -0.49-0.63; p=0.804). At the regional level, males had cartilage that was, on average, 1.07 mm thicker in the femur (p=0.003), 1.00 mm thicker in the tibia (p<0.001) and 0.73 mm thicker in the patella (p=0.021). The overall male-female difference in average knee cartilage thickness was 0.93 mm (95% CI: 0.38-1.48; t=3.37, p=0.002). Table 4. Multivariable linear regression analysis of the independent association between sex and average knee cartilage thickness after adjustment for age (N=52) Predictor Unstandardized coefficient (β), mm Standard error Standardized β 95% CI Test statistic p value Age, per one-year increase -0.058 0.006 -0.73 -0.069 to -0.047 t=-10.54 <0.001 Male sex 0.62 0.16 0.31 0.29-0.95 t=3.77 <0.001 Female sex Reference Constant 6.72 0.31 6.10-7.34 t=21.68 <0.001 Model summary Model statistic Value R² 0.68 Adjusted R² 0.67 Standard error of estimate 0.60 mm Overall model F statistic F(2,49)=52.06 Overall model p value <0.001 After adjustment for age, male participants had an average knee cartilage thickness that was 0.62 mm greater than that of female participants (95% CI: 0.29-0.95, p<0.001). Table 4 presents the multivariable linear regression analysis examining the independent association of sex with average knee cartilage thickness after adjustment for age. 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; t=-10.54, p<0.001). After controlling for age, male sex remained significantly associated with greater cartilage thickness. Males had an adjusted average cartilage thickness that was 0.62 mm greater than that of females (β=0.62; 95% CI: 0.29-0.95; standardized β=0.31; t=3.77, p<0.001). The model explained 68% of the variability in average knee cartilage thickness, with an adjusted R² of 0.67 and a standard error of estimate of 0.60 mm. The overall regression model was statistically significant (F[2,49]=52.06, p<0.001), confirming that both increasing age and sex were independent determinants of average knee cartilage thickness.

The present MRI-based comparative study evaluated sex differences in patellar, femoral and tibial articular cartilage thickness among 52 adults. The male and female groups were comparable in age, minimizing the possibility that the observed differences were solely caused by unequal age distribution. The overall average knee cartilage thickness was significantly greater in males than females (4.84±0.85 mm versus 3.91±1.07 mm; mean difference 0.93 mm; 95% CI: 0.38-1.48; p=0.002). Significant male predominance was also demonstrated in the average patellar, femoral and tibial cartilage measurements. These findings support the growing evidence that knee cartilage morphology is sexually dimorphic and that sex should be considered when interpreting quantitative MRI measurements. Hunter and Bierma-Zeinstra (2019)[1] described knee osteoarthritis as a whole-joint disorder influenced by biological, anatomical and mechanical factors. Women have a higher risk of knee osteoarthritis, particularly during later life, and differences in cartilage morphology may contribute to this susceptibility. Di Martino et al. (2024)[2], in a systematic review of hip and knee cartilage, concluded that men generally had greater cartilage volume than women and that sex differences were evident in cartilage morphology and degenerative patterns. Hernandez et al. (2024)[3] further suggested that sex-related differences in cartilage, meniscal anatomy, ligament characteristics and joint biomechanics could be detected before menopause, indicating that these differences were not attributable exclusively to postmenopausal hormonal changes. In the present study, average patellar cartilage thickness was 5.12±1.00 mm in males and 4.39±1.14 mm in females, giving a significant mean difference of 0.73 mm (p=0.021). Central patellar cartilage was significantly thicker among males by 1.00 mm (p=0.016), and lateral patellar cartilage was thicker by 1.11 mm (p=0.001). However, the medial patellar facet showed only a 0.07-mm difference, which was not statistically significant (p=0.804). Thus, the effect of sex was not uniform throughout the patella. Sekiya et al. (2025)[4] similarly demonstrated regional dependency in sex differences using three-dimensional MRI. After adjustment for height, women had thinner cartilage in several femoral and tibial regions, while the patellar and lateral tibial regions did not show significant sex differences. Their findings agree with the absence of a sex difference at the medial patellar facet in the present study and indicate that anatomical location modifies the relationship between sex and cartilage thickness. The central patellar cartilage was the thickest patellar site in both sexes, measuring 6.23±1.36 mm in males and 5.23±1.47 mm in females. This distribution is anatomically plausible because the central patellar ridge and adjacent facets are exposed to high compressive loads as the patella engages the femoral trochlea during knee flexion. Sidharthan et al. (2021)[5] reported that patellar cartilage was the thickest articular cartilage in the knee and demonstrated significant variations in thickness across anatomical locations. Although their population consisted of children and adolescents, the relative distribution was comparable with the present adult findings. Culvenor et al. (2019)[6] also highlighted the importance of the patellofemoral compartment by demonstrating measurable patellar and trochlear cartilage loss during five years of follow-up after anterior cruciate ligament injury. Average femoral cartilage thickness was significantly greater among males than females (4.88±1.25 versus 3.81±1.17 mm; mean difference 1.07 mm; p=0.003). Significant sex differences were observed at the medial femoral condyle, lateral femoral condyle and femoral trochlea. The largest difference occurred at the medial femoral condyle, where male cartilage was 1.13 mm thicker (95% CI: 0.41-1.85; p=0.003). The lateral femoral condyle and trochlea showed differences of 1.09 mm and 0.99 mm, respectively. Giurazza et al. (2025)[7], in a systematic review of 8,170 MRI examinations of non-arthritic adult knees, demonstrated substantial interindividual and regional variation in femoral cartilage thickness. The review questioned the assumption that a single fixed cartilage value could represent every patient and emphasized the importance of individualized measurements. The absolute femoral cartilage measurements in the present study were higher than some values reported in studies using complete cartilage-plate segmentation. This was likely related to differences in measurement definitions because the present study recorded thickness at predefined points where the cartilage was maximally visualized, whereas automated morphometric studies usually calculate mean thickness across an entire cartilage plate. Nolte et al. (2023)[8] compared five computational methods of determining cartilage thickness and found significant differences between techniques in almost every knee subregion. Some methods overestimated thickness by as much as 2.5 mm. Their findings demonstrate that measurement orientation, surface-normal definition, segmentation and cartilage geometry can materially affect the reported value. Schmitz et al. (2017)[9] compared ultrasound and MRI measurements of medial femoral cartilage and found that agreement varied according to the femoral region assessed. Kauppinen et al. (2021)[10] also compared ultrasonographic cartilage measurements with three-dimensional MRI and demonstrated that the methods were related but not necessarily interchangeable. Bedewi et al. (2020)[11] found that ultrasonography could reliably measure accessible femoral cartilage in healthy adults. Nevertheless, MRI has the advantage of visualizing the patella, trochlea, femoral condyles and tibial plateaus within the same examination. Chaudhari et al. (2020)[12] emphasized that rapid MRI acquisition and automated analysis techniques can improve the feasibility and reproducibility of quantitative knee cartilage assessment. The average tibial cartilage thickness was 4.52±0.56 mm among males and 3.52±1.11 mm among females, representing a significant difference of 1.00 mm (95% CI: 0.47-1.53; p<0.001). Male cartilage was significantly thicker at both the medial tibial plateau (difference 0.96 mm, p=0.001) and lateral tibial plateau (difference 1.03 mm, p=0.001). The lateral tibial cartilage was thicker than the medial cartilage in both sexes. This may be related to differences in joint congruity, meniscal mobility, alignment and load distribution between the medial and lateral compartments. Robbins et al. (2019)[13] showed that cartilage thickness differed between knee compartments and that lower-limb alignment contributed to regional variation, especially among patients with osteoarthritis. Guermazi et al. (2015)[14] reported that meniscal damage, extrusion and radiographic osteoarthritis were associated with subsequent compartment-specific cartilage thinning. The significant male-female differences across most femoral and tibial sites may partly reflect sex differences in skeletal dimensions. Taller individuals generally have larger articular surfaces, and male knees frequently have larger femoral condyles and tibial plateaus. Sekiya et al. (2025)[4] found positive correlations between height and cartilage thickness across all evaluated knee regions. Importantly, sex differences persisted in the medial femoral, medial tibial, lateral femoral and trochlear regions even after adjustment for height. Thus, body size explains part, but not necessarily all, of the observed sexual dimorphism. The present study did not adjust for height, weight or body mass index; therefore, the observed differences may represent combined effects of sex and anthropometry. Ariyachaikul et al. (2025)[15], in a study of 232 healthy adults, reported significantly thicker knee cartilage among males at most examined locations. Their findings were consistent with the present results, although ultrasonography rather than MRI was used. They also observed that age-related variation was region- and sex-dependent, supporting the need for sex-specific and site-specific reference measurements. Variation in absolute values across studies could be explained by differences in population ethnicity, age, body size, knee position, imaging modality and the anatomical point selected for measurement. In multivariable analysis, male sex remained independently associated with a 0.62-mm increase in average knee cartilage thickness after adjustment for age (95% CI: 0.29-0.95; p<0.001). Age was independently associated with a reduction of 0.058 mm per year (p<0.001) and had a larger standardized coefficient than sex. These findings indicate that sex and age made independent contributions to cartilage morphology. Wisser et al. (2021)[16] demonstrated that MRI-detected cartilage abnormalities were associated with greater longitudinal changes in femorotibial cartilage thickness even among participants without major osteoarthritis risk factors. Their study also adjusted for age, sex and body mass index, illustrating the importance of considering these variables in cartilage research. Age-related cartilage thinning can occur through reduced chondrocyte activity, diminished proteoglycan synthesis, changes in collagen architecture and impaired capacity for repair. However, cartilage changes may not be uniformly linear across all anatomical sites. Early degeneration may occasionally produce cartilage swelling or increased water content before measurable tissue loss. Zibetti et al. (2023)[17] explained that compositional MRI techniques can identify changes in collagen, water and proteoglycan content before overt morphological thinning develops. Juras et al. (2020)[18] similarly described the potential of functional and compositional MRI for early diagnosis and prognostic evaluation of osteoarthritis. Luo et al. (2022)[19] demonstrated that hybrid multidimensional MRI could provide subvoxel information regarding cartilage diffusion and relaxation characteristics. Luo et al. (2024)[20] further reviewed advances in T2, T2*, T1ρ, delayed gadolinium-enhanced MRI of cartilage, sodium imaging and diffusion techniques. These methods complement morphological thickness measurements by assessing cartilage composition and microstructure. Consequently, a thinner cartilage measurement may represent established structural loss, whereas compositional changes may identify earlier stages of degeneration before thickness is substantially reduced. The regression model explained 68% of the variability in average knee cartilage thickness, suggesting that age and sex were important determinants. Nevertheless, unexplained variability remained, potentially reflecting height, body mass index, physical activity, occupation, limb alignment, previous subclinical injury, hormonal status and genetic factors. MRI acquisition and segmentation methodology can also introduce variability. Yang et al. (2022)[21] demonstrated that automated deep-learning cartilage segmentation could be applied to heterogeneous clinical MRI data, while Brett et al. (2020)[22] showed that automated MRI analysis could detect treatment-related changes in cartilage thickness in patients with knee osteoarthritis. These developments may improve the reproducibility of sex- and region-specific measurements in future studies.

Adult males demonstrated significantly greater articular cartilage thickness than females in the patellar, femoral and tibial regions of the knee on MRI. The largest site-specific sex difference was observed at the medial femoral condyle, followed by the lateral patellar facet and lateral femoral condyle. However, no significant difference was found at the medial patellar facet, indicating that sex-related variation was not uniform across all anatomical sites. After adjustment for age, male sex remained independently associated with greater average knee cartilage thickness, whereas increasing age was associated with progressive cartilage thinning. Therefore, anatomical site, age and sex should be considered when interpreting quantitative knee cartilage measurements and developing reference standards. Limitations 1. The study was conducted at a single tertiary-care hospital, limiting the generalizability of the findings. 2. The sample size was relatively small, with 30 males and 22 females, which reduced the precision of site-specific estimates. 3. The unequal number of male and female participants might have affected the statistical efficiency of between-group comparisons. 4. The cross-sectional design could identify associations but could not determine the longitudinal rate of cartilage loss in either sex. 5. Participants were recruited from patients referred for knee MRI and might not have represented completely healthy community-based adults. 6. Cartilage thickness was measured at selected anatomical points rather than through three-dimensional segmentation of the entire cartilage plate. 7. MRI was performed using a 1.5-T scanner with 3-mm slices; partial-volume effects and limited spatial resolution might have affected measurement accuracy. 8. Only the right knee was evaluated, and possible bilateral differences were not assessed. 9. Potential confounders such as height, weight, body mass index, physical activity, occupation, lower-limb alignment and muscle strength were not included in the analysis. 10. Hormonal status, menopausal status and hormone-replacement therapy among female participants were not recorded. 11. Intraobserver and interobserver reliability statistics were not reported. 12. MRI measurements were not validated against arthroscopy, histopathology or another reference standard.

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