Quadriceps Strength Benefits Those with Knee Osteoarthritis

Newswise — A stronger quadricep, the muscle responsible for straightening the leg at the knee joint, does not lead to damage in the knee and helps prevent the deterioration of cartilage behind the knee cap among those with knee osteoarthritis, according to research presented this week at the American College of Rheumatology Annual Scientific Meeting in Washington, DC.

Strengthening exercises for the quadriceps muscle of the leg generally have been viewed as beneficial to the knee joint in those with knee osteoarthritis. However, there has been some concern that greater quadriceps strength may actually be harmful to the tibiofemoral joint, the main joint in the knee, especially if the knee is malaligned because altered biomechanics may put more stress on the joint. Also, little information has been available on how quadriceps strength may affect the patellofemoral joint of the knee (the smaller joint between the knee cap and femur), which is a frequent site of osteoarthritis at the knee.

To examine this further, researchers followed 265 men and women, average age 67, with symptomatic knee osteoarthritis for 30 months. Each participant's quadriceps strength was measured at the outset of the study, and MRIs of the knee were taken at the beginning of the study as well as at 15 and 30 months of follow-up. Cartilage loss based on knee MRIs at both the tibiofemoral and patellofemoral joints was then determined during follow-up.

Study results indicated that, in fact, greater quadriceps strength leads to no worsening of cartilage loss at the tibiofemoral joint even in those with malaligned knees. Further, this increased strength, which tends to better maintain knee cap (patella) stability towards the inner side of the knee, does protect against cartilage loss at the outer (lateral) part of the patellofemoral joint.

"Those with better quadriceps strength were less likely to lose cartilage behind the knee cap," explains Shreyasee Amin, MD, Assistant Professor of Medicine, Mayo Clinic, Rochester, Minnesota, and principal investigator of the study. "This makes sense as a stronger quadriceps would be better able to keep the knee cap from moving laterally and tracking abnormally with joint movement. This study should encourage patients with knee osteoarthritis to speak with their doctors about how best to improve quadriceps strength."

The American College of Rheumatology is the professional organization for rheumatologists and health professionals who share a dedication to healing, preventing disability and curing arthritis and related rheumatic and musculoskeletal diseases. For more information on the ACR's annual meeting, see http://www.rheumatology.org/annual.

Presentation Number: 2092

Quadriceps Strength and its Relation to Cartilage Loss in Knee Osteoarthritis

S. Amin1, K. Baker2, J. Niu2, M. Clancy2, J. Goggins2, A. Guermazi3, M. Grigoryan3, D. J. Hunter2, D. T. Felson2. 1Mayo Clinic, Rochester, MN; 2Boston University, Boston, MA; 3UCSF, San Francisco, CA

Among those with established knee osteoarthritis (OA), greater quadriceps (quad) strength has either had no effect or, paradoxically, increased radiographic joint space progression in the tibiofemoral (TF) joint, especially in malaligned knees. High quad strength pulls the patella away from the lateral compartment, the site of most patellofemoral (PF) OA. The effect of quad strength on cartilage loss in TF and PF joints has not been evaluated.

We studied men and women with ACR criteria for symptomatic knee OA who had baseline, 15- and 30-month follow-up knee MRI. Cartilage was scored at the TF (central and posterior femur, anterior, central and posterior tibia), and PF (patella and anterior femur) joints, medial and lateral compartments separately, using WORMS.

We used a 0-4 scale in analyses (0=normal; 1=partial thickness defects; 2=diffuse (>75%) partial thickness defects; 3=full and partial thickness defects; 4= diffuse full thickness defects). Cartilage loss was defined as an increase in score (range 0-4) in any 5 regions for the TF or either region for the PF joint. Quad strength was measured at baseline isokinetically during concentric knee extension (60°/sec; maximal strength of 3 repetitions). Knee alignment was measured on long-limb x-rays at the first follow-up visit. We performed an ordinal logistic regression analysis to examine the relation between quad strength (using gender-specific tertiles) and cartilage loss at the TF and PF joints (medial or lateral), adjusted for age, body mass index (BMI), gender and baseline cartilage scores, using GEE to account for correlations within subjects. We then examined the effect of strength on medial TF cartilage loss adjusting for quartiles of alignment and if there was ≥5° varus malalignment. There were too few knees with valgus malalignment for evaluation.

There were 265 participants (mean age and BMI (± SD): 67 ± 9 years; 31.5 ± 5.8 kg/m2; 111 women) who had quad strength measured and follow-up MRI. There was no association between quad strength and cartilage loss at the TF joint (see table). However, greater quad strength was protective for cartilage loss at the lateral compartment of the PF joint.

Quadriceps Strength(Gender-Specific Tertiles) Adjusted* Odds Ratio (95% CI) for Cartilage Loss Tibiofemoral Joint Patellofemoral Joint Medial Lateral Medial LateralLow (referent) 1.0 1.0 1.0 1.0Middle 0.8 (0.5, 1.4) 1.3 (0.6, 2.7) 1.5 (0.8, 3.0) 0.8 (0.4, 1.6)High 0.9 (0.5, 1.6) 1.1 (0.5, 2.4) 0.8 (0.4, 1.8) 0.4 (0.2, 0.8)* adjusted for age, BMI, gender and baseline cartilage scores

Results were similar after adjusting or stratifying for alignment. Even in those with ≥5° varus, there was no increased risk for medial TF cartilage loss (OR: 0.8 (95%CI: 0.3, 1.7) for the highest tertile of strength).

In summary, greater quad strength had no effect on cartilage loss at the TF joint, even in malaligned knees. Greater quad strength, which prevents lateral offset and tilt of the patella, did protect against cartilage loss at the lateral PF compartment, a frequent site of OA.

Disclosure Block: S. Amin, None