Factors, characteristics and influences of the changes of muscle activation patterns for patients with knee osteoarthritis: a review.

Background: Knee Osteoarthritis (KOA) is a prevalent condition worldwide, significantly diminishing quality of life and productivity. Except for the alignment change, muscle activation patterns (MAP) have garnered increasing attention as another crucial factor contributing to KOA.

Objective: This study explores the factors, characteristics, and effects of MAP changes caused by KOA, providing a neuromuscular-based causal analysis for the rehabilitation treatment of KOA.

Methods: Keywords including the association of MAP with KOA will be included. "Knee, Osteoarthritis, Electromyography(EMG), Muscle Activity patterns, activation amplitudes, activation time, Muscle Synergy, Co-contraction/activation" were used to search the databases of Science Direct, PubMed, Scopus, and Wiley. The criteria include studies from the past fifteen years that document changes in muscle contraction characteristics and causality analysis in patients with KOA. we compared MAP changes between individuals with and without KOA, such as the activation amplitudes, activation time, muscle synergy and co-contraction index(CCI). Additionally, we explored the potential relationship between muscle weakness, pain, and lower limb mechanical changes with the variations of MAP.

Results: A total of 832 articles were reviewed, and 44 articles that met the inclusion criteria were selected for analysis. The changes in biomechanical structure, pain, and muscle atrophy may contribute to the formation and progression of the changes in MAP in KOA patients. In moderate KOA patients, the vastus lateralis (VL) and biceps femoris (BF) exhibits larger activation amplitudes, with earlier and longer activation times. The vastus medialis (VM) shows a delayed activation time relative to VL. Gastrocnemius activation time is prolonged during mid-gait, while the soleus exhibits lower activation amplitudes during the late stance phase. There are fewer, merged synergies with prolonged activation coefficients, and a higher percentage of unclassifiable synergies. Additionally, the CCI is positively correlated with task difficulty and symptoms. It is higher in the medial and lateral than hamstrings and quadriceps, and CCI specifically respond to joint stabilisation and load.

Conclusion: In patients with moderate KOA, changes in MAP are mainly related to symptoms and the difficulty of tasks. MAP changes primarily result in variations in amplitude, contraction duration, muscle synergy, and CCI. The MAP changes can subsequently affect the intermuscular structure, pain, joint loading, and stiffness.

Clinical Implications: These contribute to the progression of KOA and create a vicious cycle that accelerates disease advancement. Clinical rehabilitation treatments can target the MAP changes to break the cycle and help mitigate disease progression.