Knee osteoarthritis (OA) is a common degenerative joint disease that affects millions of people worldwide. One of the key symptoms associated with knee OA is muscle weakness, particularly in the quadriceps muscles. The quadriceps are crucial for stabilizing and supporting the knee joint during movement.
If these symptoms reduce a person’s ability to stay mobile, they may also develop muscle weakness. When a person injures their quadriceps, they may have small tears in the tendon. In severe cases, a person may experience a complete tear of the tendon. The quadriceps tendon is above the knee cap and connects the quadriceps muscles to the top of the knee.
Research has shown that individuals with knee OA often experience a decline in quadriceps strength, which can exacerbate their symptoms and lead to further joint damage. Muscle weakness in knee OA is thought to occur due to a combination of factors, including pain inhibition, disuse atrophy, and altered biomechanics.
The Impact of Muscle Weakness
Muscle weakness in knee OA can have a significant impact on an individual’s ability to perform daily activities and maintain independence. Weak quadriceps can lead to difficulty walking, climbing stairs, and getting up from a seated position. This can result in decreased physical activity levels, further contributing to muscle weakness and functional limitations.
The location of pain and other symptoms can help differentiate possible causes, such as tendonitis, strains, or arthritis. Hagbarth and colleagues were the first to demonstrate that excitatory input from Ia afferents is necessary to achieve full muscle activation [28]. These authors showed that preferential anaesthetic block of γ-efferents reduced the firing rate of tibialis anterior motor units during subsequent maximum-effort voluntary contractions (MVCs). These changes could be partially reversed by experimentally enhancing spindle discharge from the affected muscle. Further investigations into the importance of the γ-loop have relied on prolonged vibration to experimentally attenuate the afferent portion of the γ-loop.
This change results from chemical changes in the proteins that make up the ligaments. Ligaments tend to tear more easily, and when they tear, they heal more slowly. Older people should have their exercise regimen reviewed by a trainer or doctor so that exercises likely to tear ligaments can be avoided.
Additionally, muscle weakness can also increase the risk of falls and injury, as the quadriceps play a vital role in maintaining balance and stability.
Treatment Strategies
All study procedures were approved by the Partners HealthCare Human Research Committee, and all participants provided written consent prior to participation. The data that support the findings of this study are available from the corresponding author upon reasonable request. If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways. In some cases, surgery may be required if all other treatment options have been tried. A walking stick may be beneficial, if using, ensure it’s used on the opposite side from your affected leg.
Functional limitation is manifest as reductions in both self-reported difficulty performing activities of daily living and in objectively quantified mobility [3,4,5]. The 2 main factors that determine the muscle’s force production capability are the muscle cross-sectional area and the ability of the nervous system to fully activate the muscle. In the same study, quadriceps cross-sectional area explained 27% of quadriceps isometric strength.
We assessed structural damage using Kellgren-Lawrence grade and the magnetic resonance imaging osteoarthritis knee score (MOAKS) for cartilage damage. We used the Knee Injury and Osteoarthritis Outcomes Score (KOOS) to evaluate pain, symptoms, and activities of daily living (ADL), and the Timed Up and Go (TUG) test to assess mobility. We assessed quadriceps and hamstrings strength using a hand-held dynamometer and classified each into quartiles (Q). The primary objectives of this study are to track the changes in peak torque and fatigue index (FI) of isokinetic muscle strength over a period of 6 months. In the current study, quadriceps strength was reduced by 32% in the OA group compared with an age-matched and gender-matched control group. This compares well with previous studies in the literature that have observed quadriceps strength deficits of 20 to 45% in people with knee joint OA [1–3].
Also, changes on the x-ray often do not closely correspond with a person’s symptoms. For example, an x-ray may show only a minor change in a person who has severe symptoms, or an x-ray may show numerous changes in a person who has very few if any symptoms. These muscle impairments affect physical function and should be targeted in therapy. Further research is needed to explore the relationship between quadriceps strength and knee OA initiation and progression and to determine the optimal exercise prescription that augments outcomes in this patient population. After an ACL injury, patients experience a decline in neuromuscular function, which lasts even after the operation [15]. Vitamin D has been shown to play a role in improving neuromuscular function.
Addressing muscle weakness in knee OA is an essential component of treatment and rehabilitation. Physical therapy programs focused on strengthening the quadriceps and other surrounding muscles can help improve joint stability and function. These programs may include exercises such as leg presses, squats, and lunges.
In addition to exercise, other treatment strategies for muscle weakness in knee OA may include weight management, pain management, and assistive devices such as braces or orthotics.
