Do not concentrate on single muscles

There are a lot of muscle impairments associated with arthritis, proper knowledge of these impairments should allow us to develop more appropriate rehabilitation and fitness programs for individuals with knee arthritis.

Strength of quadriceps muscles

In many works of literature, quadriceps strength impairment is well documented. The quadriceps strength deficits ranging from 11-56% when compared to healthy controls, mentioned in previously published a paper. There is a 76% deficit reported in research paper When assessing eccentric strength.

This especially loss of eccentric strength deficits has a great influence on functional deficits. Eg: standing from a chair, getting up off the ground, ascending and descending stairs 

Inhibition of quadriceps muscles 

Atrophy and muscle inhibition are the two main factor in knee arthritis  The quadriceps has been shown to exhibit a 12% reduction in cross sectional area, representing atrophy, in patients with knee arthritis.  This atrophy certainly contributes to loss of strength.

Additionally, the exact mechanism is still unknown but there are some potential reasons that there is an alteration in muscle contraction which may be due to alterations in the afferent discharge of knee receptors.  This could be altered due to degenerative changes in joint structures, effusion, pain, inflammation, and joint laxity.

From literature,lower Extremity Strength Deficits

There many research papers have been published regarding muscles impairment

• 4-38% reduction in hamstring strength
• 16% reduction in hip extension strength
• 26-40% reduction in hip flexion strength
• 27-40% reduction in external rotation strength
• 20-43% reduction in internal rotation strength
• 22-24% reduction in abduction strength
• 26% reduction in adduction strength

B/L deficits in muscles 

 The contralateral leg has also been shown to a 16-26% deficit in quadriceps strength compared to healthy controls. Both limb should examine carefully. 

The mystery of contralateral deficit is completely unknown, but it could again represent general weakness and deconditioning of the patient gradually.

Clinical Implications

• There is impaired quadriceps strength in subjects with knee arthritis
• Weakness is due to activation deficit and atrophy of muscle
• Hip muscles and hamstring muscle impairment 
• Bilateral strength and activation impairments but the involved side shows greater impairments
• Strength plays a major contributing factor for functional activities
• Strength deficit is predictive of the development of knee arthritis

Summary of the recommendations from Roddy et al which we summarize as:

• Patients with knee and hip osteoarthritis,strengthening and aerobic exercise can reduce pain and improve function.
• Improve strength and proprioception, it may reduce the progression of osteoarthritis, although adherence is the principal predictor of long-term outcome from exercise.

In addition to these recommendations, we would suggest that we also include the following principles for the development of rehabilitation and fitness programs for people with arthritis:

• We emphasis on strengthening exercise of the entire lower extremity, with emphasis on quadriceps strength because muscle imbalance is part of osteoarthritis condition.
• Improve the strength of hip muscles
• Emphasis should be focused on the area of greatest muscle impairment. Bilateral exercise should perform.
• Exercise should include strengthening, dynamic stabilization, and neuromuscular control 
• Enhance mobility 
• Proper exercise prescription implement which reduces specific muscle impairment, mobility concerns, and movement impairments

The muscle impairments, strength deficits, and muscle imbalances are associated with knee arthritis.  Keep these findings and recommendations in mind whenever you are working with someone with knee arthritis.

References:

1. Roddy E, Zhang W, Doherty M et al. Evidence-based recommendations for the role of exercise in the management of osteoarthritis of the hip or knee–the MOVE consensus. Rheumatology (Oxford). 2005 Jan;44(1):67-73. Epub 2004 Sep 7.
2. Ali H Alnahdi et al. Muscle Impairments in Patients With Knee Osteoarthritis American orthopedic society of sports medicine June 19 2012