Using quantitative imaging methods to investigate the association between quadriceps stiffness and knee cartilage volumes

Abstract

Aims

Sex- and compartment-specific associations between quadriceps weakness and knee cartilage loss have been reported, and stiffer quadriceps has been related to clinical knee symptoms. Nevertheless, the relationship between quadriceps stiffness and knee cartilage health remains unclear. The primary aim of this study was to investigate the association between quadriceps stiffness and knee cartilage volumes.

Methods

This study included 82 older adults (46 females (56.1%); mean age 65.9 years (SD 3.9)). Passive stiffness of three superficial quadriceps muscle heads was evaluated by using shear-wave elastography ultrasound. Quadriceps strength was measured by a Cybex dynamometer. Cartilage volumes of the tibia, femur, and patella were quantitatively assessed using MRI. Linear regressions were used to examine relationships of quadriceps stiffness and strength with cartilage volumes across different knee compartments, while controlling for potential covariates. Benjamini–Hochberg false discovery rate (FDR) correction was applied to account for multiple tests. Sex-specific relationships were evaluated when significant sex and quadriceps interactions were detected.

Results

Negative associations were observed between quadriceps stiffness and cartilage volumes of tibia (estimate –33.7 mm³/kPa (95% CI –63.2 to –4.2), p = 0.026), femur (–72.4 mm³/kPa (95% CI –128.8 to –16.0), p = 0.013), and total knee (–92.0 mm³/kPa (95% CI –183.2 to –0.7), p = 0.048). However, those associations became statistically non-significant after FDR corrections (FDR-corrected p = 0.104 to 0.128). Quadriceps strength was not associated with cartilage volumes in the full cohort, while a significant sex and strength interaction was observed for patellar cartilage. Sex-stratified analyses showed a positive association between quadriceps strength and patellar cartilage in females (558.2 mm³/Nm*kg^–1 (95% CI 126.1 to 990.3), p = 0.013), but not males.

Conclusion

Lower quadriceps strength is associated with smaller patellar cartilage volumes in females. Although there is a trend showing negative associations between quadriceps stiffness and tibiofemoral cartilage, there is insufficient evidence in the current sample supporting an affirmative conclusion. Future research is needed to confirm these preliminary findings, and to clarify potential causal effects and clinical implications.

Cite this article: Bone Joint Res 2026;15(7):775–783.

Article focus

• This study investigated the associations of quadriceps stiffness and strength with cartilage volumes across different knee compartments, using shear-wave elastography ultrasound (SWEU) and quantitative MRI. Potential sex-specific quadriceps–cartilage relationships were also evaluated.

Key messages

• Negative associations were observed between quadriceps stiffness and knee cartilage volumes, particularly at the tibiofemoral compartments, while none of the stiffness–cartilage associations remained statistically significant after multiplicity corrections.

• Quadriceps strength was not significantly associated with knee cartilage compartment volumes across the full cohort; however, a significant sex and strength interaction was observed for patellar cartilage volume.

• In sex-stratified analyses, lower quadriceps strength was associated with smaller patellar cartilage volume in females but not in males, indicating a sex-specific moderation effect localized to the patella cartilage.

Strengths and limitations

• This study is the first to examine quadriceps stiffness in relation to cartilage volumes across individual knee compartments using SWEU and quantitative MRI.

• Compartment- and sex-specific patterns were observed for quadriceps–cartilage associations; however, the stiffness–cartilage findings did not survive false discovery rate correction and should be interpreted with caution.

• The modest sample size may limit statistical power for multiplicity corrections with confounder adjustments, and the cross-sectional design precludes causal inference. Future research is needed to confirm these preliminary findings, and to clarify potential causal and clinical effects.

Introduction

Knee osteoarthritis (OA) is a common long-term condition, affecting 37% of people aged 60 years and above.¹ Quadriceps weakness has been associated with the risk of symptomatic knee OA.^2-4 Compartment-specific^5,6 and sex-specific^7,8 associations between quadriceps weakness and knee cartilage loss have also been reported. More recent studies reported that greater quadriceps stiffness was associated with the risk of clinical knee symptoms.^4,9,10 However, the association between quadriceps stiffness and knee cartilage health remains unknown.

It has been reported that age-related changes in quadriceps muscles include increased stiffness with decreased strength.^11,12 Greater passive stiffness in skeletal muscles leads to a steeper length-tension relationship, reflecting reduced compliance during joint motion,¹³ and elevated stiffness in the quadriceps has been linked to a reduced capacity for force generation by the muscle.¹⁴ Softer and stronger quadriceps can be beneficial for attenuating impact knee loading, and quadriceps contraction produces internal forces to counterbalance external knee loads during weightbearing activities, thus protecting the knee cartilage from mechanical damage.^15,16 This theoretical framework is likely supported by a recent study, using mediation analysis, which demonstrated that increased quadriceps stiffness may cause limited knee flexion excursion during the mid-stance phase of gait, and thus may lead to excessive medial knee loading,¹⁷ contributing to knee cartilage loss.^18,19 Through this connection, increased passive stiffness of the quadriceps has been found to be related to a greater risk of developing knee symptoms in asymptomatic older adults.^4,9 However, the link between quadriceps stiffness and knee cartilage health remains unexplored.

The primary aim of this study was to examine the associations of quadriceps passive stiffness and strength with cartilage volumes across different knee compartments, using shear-wave elastography ultrasound (SWEU) and quantitative MRI. We hypothesized that higher quadriceps stiffness and lower quadriceps strength would be associated with smaller knee cartilage volumes. Potential sex-specific quadriceps–cartilage associations were also examined, given prior evidence of sex differences in age-related changes in quadriceps strength and stiffness,²⁰ as well as in knee cartilage volumes.²¹ We further sought to explore whether stiffness–cartilage relationships were muscle-head-specific, in light of the distinct effects of individual quadriceps muscle stiffness on knee biomechanics,¹⁷ and previously reported differential age-related increases in stiffness across quadriceps muscle heads.²⁰ In addition, because meniscal abnormalities²² and anterior cruciate ligament (ACL) injuries²³ may influence knee cartilage volumes, these factors were considered as potential confounders in the statistical analyses.

Methods

Study design and sample

This study employed a cross-sectional observational design. Participants were recruited through convenience sampling from local communities. People were included if they were aged between 60 and 80 years and able to walk 10 m without an assistive device. Individuals were excluded if they had self-reported knee pain or arthritis, knee or hip joint arthroplasty, knee injury or surgery within the past year, or neurological conditions (e.g. stroke or Parkinson’s disease).¹⁷ We also documented age, sex, body height, body mass, and BMI for each participant.

Quadriceps stiffness

The SWEU assesses the velocity of shear waves in skeletal muscles, offering a reliable and accurate technique for measuring muscle stiffness.²⁴ The overall quadriceps stiffness was quantified as the average muscle shear modulus, an indicator of muscle stiffness,²⁵ measured from the three superficial quadriceps muscle heads (rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM)), using a SWEU system paired with an Aixplorer ultrasound scanner (Aixplorer Version 4.2; Supersonic Imagine, France) and a linear ultrasound probe (4–15 MHz, Super Liner 15-4; Supersonic Imagine), using a previously developed protocol.²⁶

Participants lay in a supine position with their knees flexed at 60° and their hips in a neutral alignment. This posture was selected to ensure that the muscle fibres were positioned beyond the slack length.²⁷ The measurement sites were determined as follows: halfway between the anterior superior iliac spine (ASIS) and the superior border of the patella for the RF; one-third of the distance from the ASIS to the lateral border of the patella for the VL; and one-fifth of the distance from the ASIS to the medial border of the patella for the VM.²⁶

Ultrasound gel was applied to the skin, and minimal pressure was used with the ultrasound probe to avoid compressing the underlying muscle. An 11-second video was recorded at a rate of one sample per second, with a spatial resolution of 1 × 1 mm, while the muscle was at rest. The video was divided into 11 frames, and the middle five frames were averaged for analysis. The region of interest was defined based on the muscle thickness beneath the marked area (Figure 1). Shear modulus values (in kPa) for each muscle head were calculated using MATLAB (MathWorks, USA). Overall quadriceps stiffness was estimated as the sum of RF, VL, and VM shear modulus values.²⁶ All measurements were conducted by a single examiner (ZL). Intrarater reliability values were 0.94, 0.89, and 0.94 for the RF, VL, and VM, respectively, as reported in our recent publication.²⁰

Fig. 1.

Shear-wave elastography ultrasound images of the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles, with colourful boxes (regions of interest) representing the shear modulus maps used for muscle stiffness estimation.

Quadriceps strength

The isokinetic peak torque of the quadriceps was assessed with a Cybex isokinetic dynamometer (Cybex Co., USA) at a constant angular velocity of 60°/s, according to a previously established protocol.²⁶ Participants were seated and asked to perform concentric knee movements, moving from maximal flexion to maximal extension with maximal effort, completing the motion five times. The peak torque values from the middle three extension trials were averaged and normalized to body mass (Nm/kg).²⁶ The test-retest reliability was 0.90, as reported in our recent publication.²⁰

Knee cartilage volumes on MRI

Knee structures were imaged using a 3.0 T whole-body MRI scanner (Philips, Netherlands) with a commercial transmit-receive knee coil. The tested knee was randomly chosen. Participants were asked to stay fully relaxed, with their back and hips in a neutral alignment and their knee positioned on the coil during the scan.²⁶ Knee cartilage volumes were measured using the following imaging sequence and parameters: T2-weighted 3D water-selective excitation with fat saturation (field of view: 15 × 15 mm, flip angle: 35°, echo time: 4.38 ms, repetition time: 20 ms, slice thickness: 0.7 mm, pixel matrix: 560 × 560).²⁸ We extracted the volumes of individual cartilage plates (tibia, femur, and patella) from the total volume by manually delineating the cartilage boundaries with disarticulation contours on each section. Sagittal MRI scans were acquired with a slice thickness of 2.1 mm and an in-plane resolution of 0.268 × 0.268 cm. These images were then resampled to generate continuous sections for the final 3D reconstruction, which was performed using Mimics Research software (v.17; Materialise, Belgium). The cartilage volume of each specific knee compartment was calculated by summing all relevant voxels within the corresponding binary volume. Particular cartilage volume was then determined by summing all the pertinent voxels within the resulting binary volume (Figure 2).^21,29 The full cartilage segmentations were performed by a physiotherapist with eight years of post-qualification experience (JH), after completing training sessions that achieved excellent agreement with an experienced radiologist (AW, see Acknowledgements) on ten sample knee MRI scans (tibial cartilage: r = 0.92; femoral cartilage: r = 0.98; patellar cartilage: r = 0.94). Test–retest reliability for cartilage volume measurements of the tibia, femur, and patella was high, with intraclass correlation coefficients (ICCs) of 0.92, 0.93, and 0.91, respectively. In brief, cartilage volumes for the tibia, femur, and patella were segmented from MRI scans of ten individuals in two separate sessions. Test–retest reliability was then quantified by calculating the between-session ICC for each cartilage region. We added the cartilage volumes of the tibia, femur, and patella to represent the total knee cartilage volumes. Radiologists also evaluated the presence of meniscal abnormalities and ACL injuries, which were included as potential covariates in the analysis.

Fig. 2.

MRI showing the measurements of tibial, femoral, patellar, and total knee cartilage volumes.

Statistical analysis

In the primary analyses, linear regressions were used to examine the relationships of quadriceps properties (stiffness and strength) and knee cartilage volumes (tibia, femur, patella, and total knee). The stiffness-cartilage associations were adjusted for the potential covariates including age, sex, BMI, meniscal abnormalities, and ACL injuries. The strength-cartilage models were adjusted by age, sex, body height, meniscal abnormalities, and ACL injuries, as quadriceps strength had been normalized by body mass. For each regression model, we reported unstandardized β (for quadriceps variables) with its 95% CI and corresponding two-tailed p-value, as well as the adjusted model R². Assumptions of linear regression were assessed through visual inspection of scatter plots, Q–Q plots, and residuals versus fitted value plots. To address multiplicity across the 2 (quadriceps variables) × 4 (cartilage variables) primary tests, we applied Benjamini–Hochberg false discovery rate (FDR) correction across all eight primary associations being examined.³⁰ The statistical significance was preset as FDR-corrected p < 0.05. Exploratory analyses were performed to examine potential muscle head-specific associations of RF, VL, and VM stiffness with knee cartilage volumes, using linear regressions with the adjustment by the potential covariates as stated above.

To evaluate potential sex-specific association, an interaction term between sex and quadriceps variable was entered into each multivariable linear regression model (quadriceps variable + sex + sex and quadriceps variable + other potential covariates). When a significant interaction term was observed, sex-stratified linear regression analyses were conducted, adjusting for the remaining covariates (age, BMI or body height, meniscal abnormalities, and ACL injuries). The significance threshold was set at p < 0.025 to account for multiple tests in females and males.

This study was exploratory in nature, and no formal sample size calculation was performed. Participant enrolment was guided by the availability of eligible individuals during the recruitment period. Data analyses were performed using SPSS (v.23.0, IBM, USA).

Results

A total of 87 eligible participants were recruited with five participants declined to scan MRI. Therefore, 82 eligible participants (mean age 65.9 years (SD 3.9), 56.1% (n = 46) female) were included in the analysis. Their demographic and descriptive data are presented in Table I.

Table I.

Study sample characteristics.

Characteristic	Data (n = 82)
Demographics
Mean age, yrs (SD)	65.9 (3.9)
Female sex, n (%)	46 (56.1)
Mean BMI, kg/m2 (SD)	23.4 (3.6)
Presence of meniscus pathology, n (%)	46 (56.1)
Presence of ACL injury, n (%)	20 (24.4)
Quadriceps properties
Mean quadriceps shear modulus, kPa (SD)	23.9 (5.0)
Mean RF shear modulus, kPa (SD)	12.8 (3.6)
Mean VL shear modulus, kPa (SD)	6.0 (1.6)
Mean VM shear modulus, kPa (SD)	4.9 (1.1)
Mean quadriceps strength, Nm*kg–1 (SD)	1.14 (0.31)
Mean cartilage volume, mm 3 (SD)
Tibia	3,118.5 (877.8)
Femur	7,316.4 (1,649.8)
Patella	1,946.3 (625.0)
Total knee	12,381.2 (2,847.9)

ACL, anterior cruciate ligament; RF, rectus femoris; VL, vastus lateralis; VM, vastus medialis.

Quadriceps stiffness and knee cartilage volumes

Linear regression analyses indicated that the greater quadriceps stiffness was associated with smaller cartilage volumes of the tibia (β: –33.7 mm³/kPa (95% CI –63.2 to –4.2), p = 0.026; Figure 3a) and femur (β: –72.4 mm³/kPa (95% CI –128.8 to –16.0), p = 0.013; Figure 3b), and the total knee (β: –92.0 mm³/kPa (95% CI –183.2 to –0.7), p = 0.048; Figure 3d), adjusted by age, sex, BMI, meniscus pathology, and ACL injury. However, none of those associations remained statistically significant after FDR corrections (FDR-corrected p = 0.104 to 0.128).

Fig. 3.

Associations of quadriceps stiffness with the a) tibial, b) femoral, c) patellar, and d) total knee cartilage volumes. Associations were adjusted by age, sex, BMI, meniscus abnormalities, and anterior cruciate ligament injury. FDR-corrected P: Benjamini–Hochberg false discovery rate corrected p-value.

No significant association was observed between the passive stiffness of individual quadriceps muscle heads and cartilage volumes of any knee compartment. We did not observe any significant sex and stiffness interaction on cartilage for any knee compartment (Table II).

Table II.

Associations of quadriceps stiffness and strength with knee cartilage volumes.

Quadriceps variables	Tibia	Femur	Patella	Total
Primary analysis
Quadriceps stiffness	β = –33.7 mm3/kPa 95% CI -63.2 to -4.2 p = 0.026 FDR-corrected p = 0.104 Adjusted R2 = 0.497 Interaction term (with sex) p = 0.904	β = –72.4 mm3/kPa 95% CI -128.8 to -16.0 p = 0.013 FDR-corrected p = 0.104 Adjusted R2 = 0.479 Interaction term (with sex) p = 0.348	β = 14.1 mm3/kPa 95% CI -10.1 to 38.3 p = 0.250 FDR-corrected p = 0.400 Adjusted R2 = 0.333 Interaction term (with sex) p = 0.706	β = –92.0 mm3/kPa 95% CI -183.2 to -0.7 p = 0.048 FDR-corrected p = 0.128 Adjusted R2 = 0.543 Interaction term (with sex) p = 0.605
Quadriceps strength	β = 243.4 mm3/Nm*kg-1 95% CI -208.1 to 694.9 p = 0.286 FDR-corrected p = 0.381 Adjusted R2 = 0.620 Interaction term (with sex) p = 0.518	β = 124.5 mm3/Nm*kg-1 95% CI -784.0 to 1033.0 p = 0.786 FDR-corrected p = 0.786 Adjusted R2 = 0.565 Interaction term (with sex) p = 0.695	β = 368.2 mm3/Nm*kg-1 95% CI -36.6 to 773.0 p = 0.074 FDR-corrected p = 0.148 Adjusted R2 = 0.398 Interaction term (with sex) p = 0.049	β = 736.1 mm3/Nm*kg-1 95% CI -629.0 to 2101.2 p = 0.286 FDR-corrected p = 0.327 Adjusted R2 = 0.670 Interaction term (with sex) p = 0.642
Exploratory analysis
RF stiffness	β = -20.4 mm3/kPa 95% CI -62.7 to 22.0 p = 0.341 Adjusted R2 = 0.469 Interaction term (with sex) p = 0.494	β = -55.0 mm3/kPa 95% CI -136.2 to 26.2 p = 0.181 Adjusted R2 = 0.447 Interaction term (with sex) p = 0.756	β = 28.2 mm3/kPa 95% CI -5.3 to 61.6 p = 0.098 Adjusted R2 = 0.345 Interaction term (with sex) p = 0.170	β = -47.2 mm3/kPa 95% CI -177.6 to 83.2 p = 0.473 Adjusted R2 = 0.521 Interaction term (with sex) p = 0.705
VL stiffness	β = -70.0 mm3/kPa 95% CI -167.1 to 27.1 p = 0.155 Adjusted R2 = 0.477 Interaction term (with sex) p = 0.267	β = -130.0 mm3/kPa 95% CI -317.5 to 57.4 p = 0.171 Adjusted R2 = 0.448 Interaction term (with sex) p = 0.073	β = -9.3 mm3/kPa 95% CI -88.0 to 69.4 p = 0.815 Adjusted R2 = 0.321 Interaction term (with sex) p = 0.480	β = -209.4 mm3/kPa 95% CI -507.9 to 89.1 p = 0.166 Adjusted R2 = 0.530 Interaction term (with sex) p = 0.094
VM stiffness	β = -69.4 mm3/kPa 95% CI -211.3 to 72.6 p = 0.333 Adjusted R2 = 0.469 Interaction term (with sex) p = 0.490	β = -218.1 mm3/kPa 95% CI -489.0 to 52.9 p = 0.113 Adjusted R2 = 0.453 Interaction term (with sex) p = 0.920	β = 66.0 mm3/kPa 95% CI -47.3 to 179.3 p = 0.249 Adjusted R2 = 0.333 Interaction term (with sex) p = 0.357	β = -221.4 mm3/kPa 95% CI -657.3 to 214.5 p = 0.315 Adjusted R2 = 0.525 Interaction term (with sex) p = 0.599

Each model was adjusted by age, sex, BMI (body height for strength), meniscus injury, and anterior cruciate ligament injury. β, unstandardized coefficient of the variable of interest; 95% CI and P: 95% CI of β and its corresponding p-value. FDR-corrected P: Benjamini–Hochberg false discovery rate corrected p-value across 8 primary tests (2 quadriceps variable * 4 knee cartilage variables).

RF, rectus femoris; VL, vastus lateralis; VM, vastus medialis.

Quadriceps strength and knee cartilage volumes

With the adjustment by age, sex, body height, meniscus pathology, and ACL injury, only a non-significant trend indicated a positive association between quadriceps strength and patellar cartilage volume (β: 368.2 mm³/Nm*kg^-1 (95% CI –36.6 to 773.0); p = 0.074; FDR-corrected p = 0.148; Figure 4c) (Table II). A significant sex and strength interaction was observed for patellar cartilage volume (interaction p = 0.049). Results from sex-stratified analyses indicated that the significant positive association only existed in females (β: 558.2 mm³/Nm*kg^-1 (95% CI 126.1 to 990.3), p = 0.013), but not in males (β: 105.9 mm³/Nm*kg^-1 (95% CI –714.4 to 926.2), p = 0.794) (Figure 5).

Fig. 4.

Associations of quadriceps strength with the a) tibial, b) femoral, c) patellar, and d) total knee cartilage volumes. Associations were adjusted by age, sex, body height, meniscus abnormalities, and anterior cruciate ligament injury. FDR-corrected P: Benjamini–Hochberg false discovery rate corrected p-value.

Fig. 5.

Sex-stratified relationships between quadriceps strength and patellar cartilage volumes. Associations were adjusted by age, body height, meniscus abnormalities, and anterior cruciate ligament injury. FDR-corrected P: Benjamini–Hochberg false discovery rate corrected p-value.

Discussion

This study examined the associations of quadriceps stiffness and strength with cartilage volumes across different knee compartments. Negative associations were observed between quadriceps stiffness and knee cartilage volumes, particularly at the tibiofemoral compartments, although none of the stiffness–cartilage associations remained statistically significant after multiplicity corrections. The greater quadriceps strength was associated with larger patellar cartilage volume in females but not in males, suggesting a compartment- and sex-specific pattern.

To the best of our knowledge, this was the first study to investigate the association between quadriceps stiffness and knee cartilage health. Consistent with our priori hypothesis, greater quadriceps stiffness showed nominal negative associations with knee cartilage volumes, particularly at the tibiofemoral compartments. Specifically, a one‐unit (kPa) increase in quadriceps stiffness was associated with average decreases of 33.7 mm³ (95% CI −63.2 to–4.2) in tibial cartilage volume, 72.4 mm³ (95% CI −128.8 to –16.0) in femoral cartilage volume, and 92.0 mm³ (95% CI −183.2 to –0.7) in total knee cartilage volume, after adjustment for age, sex, BMI, meniscal abnormalities, and ACL injuries. However, none of the stiffness–cartilage associations across knee compartments remained statistically significant following FDR correction, indicating insufficient evidence to support a robust independent association in the current sample. The attenuation of statistical significance after multiplicity correction with confounder adjustments likely reflects limited statistical power. Accordingly, these findings should be interpreted as preliminary, and confirmation in larger, well-powered cohorts is warranted. Nevertheless, the direction of the observed associations is consistent with previous studies reporting that increased quadriceps stiffness is associated with a greater risk of developing knee symptoms in asymptomatic older adults,^4,9 and with the severity of knee pain in patients with clinical knee OA.¹⁰ Collectively, these preliminary findings suggest that, beyond its established relationship with knee pain and symptoms, quadriceps stiffness may also be related to tibiofemoral cartilage health. However, given the cross-sectional design and the attenuation of associations after multiplicity correction, these observations should be interpreted cautiously and require confirmation in larger, prospectively designed studies.

Several biomechanical mechanisms may plausibly link increased quadriceps stiffness to tibiofemoral cartilage degeneration. Greater quadriceps stiffness has been associated with reduced sagittal-plane knee motion and altered frontal-plane load sharing during the loading phase of gait,^17,31 both of which are biomechanical features linked to radiological tibiofemoral OA.^18,19 In addition, age-related increases in quadriceps stiffness have been reported.¹¹ Research suggests that age-related declines in muscle mass and integrity may accelerate bone breakdown,³² whereas excessive degradation of the extracellular matrix is thought to play a central role in OA onset and progression.³³ Given these findings, further investigation is needed to determine whether age-related increases in skeletal muscle stiffness influence OA development, possibly through shared mechanisms of ageing and muscle-bone crosstalk.^34-36 Such studies could underscore the need to mitigate elevated passive stiffness in the quadriceps of older adults as a strategy to preserve knee cartilage health with advancing age.

After adjustment for pre-specified covariates, including age, sex, body height, meniscal abnormalities, and ACL injuries, only a non-significant positive trend was observed between quadriceps strength and patellar cartilage volume. The association of greater quadriceps strength with larger patellar cartilage volume is consistent with a 2009 study which suggested a protective role of quadriceps strength for patellofemoral cartilage, but not for tibiofemoral cartilage degeneration.⁵ We found that the positive relationship between quadriceps strength and patellar cartilage volume is only evident in females, an observation which is also consistent with previous reports that quadriceps weakness is more likely related to knee OA^37,38 and cartilage loss^7,8 for women than men. Potential explanations include sex-related differences in neuromuscular capacity,²⁰ hormonal influences on musculoskeletal tissues,³⁹ and differences in joint loading patterns.⁴⁰ Future clinical trials could investigate whether strengthening quadriceps may be beneficial specifically for patellofemoral cartilage health, especially in females.

The significance of this study lies in the use of SWEU and quantitative MRI, and its preliminary data on the potential link between greater quadriceps stiffness and tibiofemoral cartilage degeneration in older adults. Such observations could inform future prospective cohort studies to investigate the predicted effect of quadriceps stiffness on tibiofemoral cartilage loss. Although quadriceps strengthening has been a cornerstone of rehabilitation for knee OA, the influence of quadriceps stiffness remains largely overlooked. Clinical investigations may also examine whether interventions designed to reduce quadriceps stiffness, such as soft-tissue release, stretching, foam rolling, and exercises, can optimize knee joint loading and mitigate mechanical knee cartilage degradation.^41,42 Elucidating these relationships would provide a foundational evidence base for developing more effective, mechanism-driven prevention strategies for knee OA in ageing populations.

This study has potential limitations. We evaluated the stiffness of the three superficial quadriceps heads but did not assess the vastus intermedius, as it is located deep beneath the superficial muscles and cannot be reliably measured using SWEU.⁴³ This exploratory study included a modest sample size. To control the risk of Type I error and the potential confounding factors, multiplicity correction was applied and pre-selected covariates were considered in the analyses, after which none of the stiffness–cartilage associations remained statistically significant. Accordingly, the observed negative associations should be interpreted as preliminary and require confirmation in larger, well-powered cohorts. Another potential limitation is that because of the cross-sectional design, causal relationships cannot be established. Future prospective cohort studies could validate whether greater quadriceps stiffness would predict knee cartilage loss, while clinical trials could evaluate the effectiveness of interventions aimed at reducing quadriceps stiffness to prevent tibiofemoral cartilage degeneration in ageing populations.

In conclusion, lower quadriceps strength is associated with smaller patellar cartilage in females. Although there is a trend showing negative associations between quadriceps stiffness and tibiofemoral cartilage, there is insufficient evidence in the current sample to support an affirmative conclusion. Future research is needed to confirm these preliminary findings, and to clarify potential causal effects and clinical implications.

Data Availability

The datasets generated and analyzed in the current study are not publicly available due to data protection regulations. Access to data is limited to the researchers who have obtained permission for data processing. Further inquiries can be made to the corresponding author.