Uniarticular

Uniarticular is an adjective used in anatomy and medicine to describe structures or conditions that involve or act upon a single joint. It is commonly contrasted with biarticular, meaning crossing two joints, and multiarticular, referring to structures that span three or more joints. The term helps clinicians and educators specify the functional scope of muscles, tendons, ligaments, or diseases.

In anatomy, uniarticular refers to components that cross only one joint. For muscles, this means the muscle originates and inserts across a single articulation. Examples often cited include many knee extensors in which the muscle acts primarily at the knee joint. By contrast, biarticular muscles cross two joints and can influence the movement at both joints they span.

In clinical contexts, uniarticular is used to describe patterns of disease or injury that affect only one joint. The more common term for this usage is monoarticular. Monoarticular arthritis or monoarticular infections occur in a single joint, whereas diseases described as polyarticular or systemic involve multiple joints. The distinction helps guide diagnosis and treatment, as monoarticular conditions can have different etiologies and management compared with joint-wide disorders.

Examples help illustrate the distinction: the quadriceps femoris has uniarticular components (the vastus muscles) that act primarily on the knee, while rectus femoris is biarticular, acting on both the hip and knee. The gastrocnemius is biarticular (knee and ankle), whereas the soleus acts mainly at the ankle and is often treated as uniarticular in function.