Characteristics of lower limb muscle motor activation in patients with unilateral knee osteoarthritis

Abstract

BACKGROUND: There are mechanical changes in the lower limb muscles in patients with knee osteoarthritis. These changes can be objectively reflected through surface electromyography. Currently, there is limited research on abnormal electrophysiological signals of lower limb muscles, especially of calf muscles, during walking in patients with unilateral knee osteoarthritis. OBJECTIVE: To investigate the motor activation status and activation mode of the medial thigh muscle, lateral thigh muscle, tibialis anterior muscle, and gastrocnemius muscle during daily walking in patients with unilateral knee osteoarthritis using surface electromyography. METHODS: Fifty subjects with unilateral knee osteoarthritis who met the inclusion criteria underwent surface electromyography walking tests. The target muscles were the medial thigh muscle, lateral thigh muscle, anterior tibialis muscle, and gastrocnemius muscle. The walking time was 60 seconds. Surface electromyography signals were collected from both healthy and affected sides. The main observation indicators were root mean square value, integrated electromyography value, median frequency, and muscle contraction ratio. Whether there is an abnormal activation status and its characteristics of lower limb muscles in unilateral knee osteoarthritis patients were investigated by surface electromyography. The abnormal movement activation of lower limb muscles in unilateral knee osteoarthritis patients was explored from an electrophysiological perspective. RESULTS AND CONCLUSION: (1) The integrated electromyography value and root mean square value of the medial and lateral thigh muscles on the affected side were significantly lower than those on the healthy side (P < 0.001); the median frequency values of the medial and lateral thigh muscles on the affected side were significantly lower than those on the healthy side (P < 0.001), with a more significant shift to low frequency, indicating a higher fatigue risk. (2) The integrated electromyography value and root mean square value of the tibialis anterior muscle on the affected side were significantly higher than those on the healthy side (P < 0.001); the median frequency value of the tibialis anterior muscle on the affected side was significantly lower than that on the healthy side (P < 0.001), with a more significant shift to low frequency, indicating a significantly increased fatigue risk. (3) The integrated electromyography value and root mean square value of the gastrocnemius muscle on the affected side were significantly higher than those on the healthy side (P < 0.001); the median frequency value of the gastrocnemius muscle on the affected side did not show a significant excessive shift compared with the healthy side (P > 0.05), indicating similar fatigue levels. (4) The muscle activation ratio on the affected side was significantly lower than that on the healthy side (P < 0.001), and the activation of the medial and lateral thigh muscles on the affected side was significantly unbalanced compared with the healthy side. These results indicate that during daily walking, patients with unilateral knee osteoarthritis exhibit insufficient activation and reduced activation efficiency of the medial and lateral thigh muscles, with high fatigue levels and risk, and unbalanced activation of these muscles, which is detrimental to knee joint stability and balance. The tibialis anterior and gastrocnemius muscles on the affected side show compensatory activation and abnormal co-activation levels, which are important factors aggravating joint stiffness, with the most obvious compensation in the tibialis anterior muscle, and there is a risk of fatigue-induced muscle atrophy.

1. Introduction

Knee osteoarthritis is a chronic degenerative disease affecting the joint and its surrounding tissues. Structural changes such as cartilage degeneration, subchondral bone sclerosis, and osteophyte formation are important markers of knee degeneration [1-2]. These issues lead to joint space narrowing, increased wear, reduced cushioning, and consequently pain, swelling, stiffness, and limited mobility [3]. As the disease progresses, patients experience symptoms such as joint weakness, soreness, and thinning of the lower limbs, along with muscle weakness and atrophy [4]. Clinical imaging studies have shown that patients with knee osteoarthritis have significantly increased fat infiltration and fat content in the vastus medialis and vastus lateralis muscles, leading to quadriceps dysfunction and atrophy [5], resulting in lower muscle health quality compared to normal individuals [6], and significantly reduced muscle cross-sectional area [7]. Clinical observations reveal that muscle atrophy around the joint occurs earlier than symptoms such as pain [8], and there is a close relationship between cartilage degeneration and muscle atrophy [9]. The association between muscle atrophy and aging has also been confirmed in osteoarthritis patients [10]. These findings indicate that the occurrence of muscle atrophy around the knee joint not only increases the risk of developing knee osteoarthritis but also, with the progression of cartilage degeneration, further leads to joint-derived muscle atrophy, creating a superimposed state of muscle degeneration that directly affects knee stability and exacerbates cartilage degeneration [11]. Therefore, the development of knee osteoarthritis is closely interrelated with pathological changes in the surrounding muscles, especially the quadriceps, which is one of the factors in the vicious cycle of joint-muscle changes.

Surface electromyography (sEMG) is a technique that records weak voltage signals from the skin surface, reflecting the electrical activity of muscle motor units. It is effective in assessing muscle activity. Currently, sEMG is widely used in knee osteoarthritis patients to evaluate lower limb muscle activation order, activation and coordination patterns, and muscle fatigue [13]. This technique can identify specific muscle activation characteristics based on electrical signals, providing objective data for clinical assessment and rehabilitation.