Background: Quadriceps weakness is a known risk factor for the onset of knee osteoarthritis (OA). In addition to muscle weakness, increased passive stiffness of the quadriceps may affect knee biomechanics and hence contribute to the pathogenesis of knee OA. However, the association between quadriceps stiffness and the risk of knee OA development has not been prospectively investigated.

Aim: The aim of this study was to investigate how baseline quadriceps passive stiffness predicts the incidence of clinical knee OA at the 12-month follow-up.

Design: Prospective cohort study.

Setting: University laboratory.

Population: Community-dwelling adults aged 60-80 years were recruited. We excluded participants with: 1) knee pain or known arthritis; 2) knee injury; 3) knee or hip joint replacement, 4) cognitive impairment; or 5) neurological conditions.

Methods: At baseline, passive stiffness of the three superficial quadriceps muscle heads (rectus femoris [RF], vastus lateralis [VL], and vastus medialis oblique [VMO]) was evaluated using shear-wave ultrasound elastography. Knee muscle (quadriceps and hamstrings) strength was tested using a Cybex dynamometer. Knee OA was defined based on clinical criteria 12 months after baseline measurements. Generalized estimating equations were used to examine the associations of quadriceps stiffness and knee muscle strength with the risk of knee OA, controlling for age, sex, Body Mass Index, comorbidities, and activity level.

Results: The analyses included 158 knees (58.2% females, age: 65.6±4.1 years). Twenty-eight knees (17.7%) were classified as having clinical OA at 12 months. Compared with the lowest stiffness tertiles, the highest stiffness tertiles of the RF (relative risk =5.31, 95% CI: 1.34-21.0), VMO (4.15, 1.04-16.6), and total superficial quadriceps (6.35, 1.48-27.3) at baseline were significantly associated with a higher risk of knee OA at the follow-up. The highest strength tertile of quadriceps has a trend of association with a lower risk of knee OA than the lowest tertile (0.18, 0.03-1.25, P=0.083).

Conclusions: Greater passive stiffness of the quadriceps at baseline was associated with a higher risk of clinical knee OA incidence at the 12-month follow-up.

Clinical rehabilitation impact: Interventions for reducing the passive stiffness of the quadriceps should be included in preventative training programs for older adults.