Meta-analysis showed that lower knee extensor strength is associated with an increased risk of symptomatic and functional deterioration, but not tibiofemoral JSN. The risk of patellofemoral deterioration in the presence of knee extensor strength deficits is inconclusive.
Objective. To determine whether thigh muscle strength differs between symptomatic and asymptomatic knees, and/or different radiographic strata of knee osteoarthritis (KOA). Results. Isometric strength was significantly lower in symptomatic than in asymptomatic legs: ؊11 to ؊13% for extensor strength and ؊7 to ؊16% for flexor strength (P < 0.0001 for both) in men, and ؊9 to ؊17% (P ؍ 0.029) for extensor strength, and ؊10 to ؊21% (P ؍ 0.049) for flexor strength in women. Similar observations were made for pain frequency strata. Extensor and flexor strength were not significantly different across K/L grade strata in asymptomatic legs in either sex (P > 0.12). However, strength normalized to body weight was lower at higher K/L grades in both sexes (P < 0.02) because the body mass index was greater in participants with more advanced radiographic disease. Conclusion. Knee symptoms (i.e., pain) appear to be the relevant determinant of isometric knee extensor and flexor strength in KOA, whereas no direct association between strength and radiographic severity was observed. These findings suggest that the reduction in thigh muscle strength in KOA is related to pain but not to the structural (radiographic) disease status.
Objective
To determine the relationship between thigh muscle strength and clinically
relevant differences in self-assessed lower limb function.
Methods
Isometric knee extensor and flexor strength of 4553 Osteoarthritis Initiative
participants (2651 women/1902 men) was related to Western Ontario McMasters Universities
(WOMAC) physical function scores by linear regression. Further, groups of Male and
female participant strata with minimal clinically important differences (MCIDs) in WOMAC
function scores (6/68) were compared across the full range of observed values, and to
participants without functional deficits (WOMAC=0). The effect of WOMAC knee pain and
body mass index on the above relationships was explored using stepwise regression.
Results
Per regression equations, a 3.7% reduction in extensor and a
4.0% reduction in flexor strength were associated with an MCID in WOMAC function
in women, and a 3.6%/4.8% reduction in men. For strength divided by body
weight, reductions were 5.2%/6.7% in women and 5.8%/6.7%
in men. Comparing MCID strata across the full observed range of WOMAC function confirmed
the above estimates and did not suggest non-linear relationships across the spectrum of
observed values. WOMAC pain correlated strongly with WOMAC function, but extensor (and
flexor) muscle strength contributed significant independent information.
Conclusion
Reductions of approximately 4% in isometric muscle strength and of
6% in strength/weight were related to a clinically relevant difference in WOMAC
functional disability. Longitudinal studies will need to confirm these relationships
within persons. Muscle extensor (and flexor) strength (per body weight) provided
significant independent information in addition to pain in explaining variability in
lower limb function.
Objective
To determine whether thigh muscle strength predicts knee replacement (KR) risk, independent of radiographic severity and pain.
Methods
Osteoarthritis Initiative participants with KR at 12–60 month (M) follow-up (cases) were each matched with one control (no KR throughout 60M) by age, sex, height, body mass index, baseline radiographic stage, and location of joint space narrowing. Isometric knee extensor and flexor strength were recorded biennially. The strength examination prior to KR (≤2 years) was termed T0, that two years prior to T0 T−2, and that four years prior T−4. Muscle strength between cases and controls was compared using paired t-tests and conditional logistic regression adjusted for pain.
Results
136 of 4796 participants (60% women, age 65±9 years, BMI 29±4 kg/m2) received a KR during follow-up, had at least T0 strength data, and a matched control. Knee extensor strength at T0 (primary outcome) was significantly lower in female cases than controls (p<0.001; pain-adjusted odds ratio [ORp] 1.72, 95% confidence interval [CI] 1.16 to 2.56), but no difference was seen in men (p=0.451; ORp 0.80, 95%CI 0.50 to 1.27). Results were similar for knee flexor strength at T0, and for longitudinal change in extensor and flexor strength between T0 and T−2. Thigh muscle strength at T−2 or T−4, or change between T−2 and T−4, did not predict KR risk in men or women.
Conclusion
Thigh muscle strength predicted KR risk in women, but not in men. These results may identify a window for modifying risk of KR surgery in women.
Objective. To compare cross-sectional and longitudinal side differences in thigh muscle anatomic cross-sectional areas (ACSAs), strength, and specific strength (strength/ACSA) between knees with early versus advanced painful radiographic osteoarthritis in the same person. Methods. Forty-four of 2,678 Osteoarthritis Initiative participants (31 women and 13 men) met the inclusion criteria of bilateral frequent knee pain, medial joint space narrowing (JSN) in 1 knee, and no medial (or lateral) JSN in the contralateral knee. Thigh muscle ACSAs of the quadriceps, hamstrings, adductors, and individual quadriceps heads at consistent locations were determined using magnetic resonance imaging. Isometric muscle strength was determined in extension/flexion (Good Strength Chair). Baseline quadriceps ACSAs and strength were considered primary end points, and longitudinal changes of these factors were considered secondary end points (by paired t-tests). Results. No significant side differences in quadriceps (or other thigh muscle) ACSAs, strength, or specific strength were observed between medial JSN knees versus knees without JSN, or between specific medial JSN knee strata and contralateral knees without JSN, either in men or women. Two-year longitudinal changes in thigh muscle ACSAs and strength were small (<5.2%) and did not differ significantly between medial JSN knees and knees without JSN. Conclusion. In the context of previous findings that side differences in pain are associated with side differences in quadriceps ACSAs, the current results suggest that quadriceps (and other thigh muscle) properties are not independently associated with radiographic disease status (JSN) once knees have reached frequent pain status. Further, our longitudinal findings indicate that a more advanced radiographic stage of knee osteoarthritis is not necessarily associated with a longitudinal decline in muscle function.
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