Which joint lacks a joint capsule and synovial fluid?

Which joint lacks a joint capsule and synovial fluid?

• A. Glenohumeral Joint
• B. Acromioclavicular Joint
• C. Scapulothoracic Joint
• D. Sternoclavicular Joint

Answer: (C)

The key idea here is that some joints aren’t true synovial joints with their own capsule and synovial fluid. The scapulothoracic articulation isn’t a true joint at all; it’s a functional interface where the scapula slides over the thoracic wall, separated from the ribs by muscle and connective tissue (and supporting bursae). Because it lacks a joint capsule and synovial cavity, it doesn’t have synovial fluid. In contrast, the other joints listed are genuine synovial joints with their own capsules and synovial fluid: the glenohumeral joint is a ball-and-socket joint with a fibrous capsule enclosing a synovial cavity; the acromioclavicular joint is a plane-type synovial joint with its own capsule (often with an articular disc); and the sternoclavicular joint is a synovial saddle joint that also has a capsule and synovial fluid.

The key idea here is that some joints aren’t true synovial joints with their own capsule and synovial fluid. The scapulothoracic articulation isn’t a true joint at all; it’s a functional interface where the scapula slides over the thoracic wall, separated from the ribs by muscle and connective tissue (and supporting bursae). Because it lacks a joint capsule and synovial cavity, it doesn’t have synovial fluid.

In contrast, the other joints listed are genuine synovial joints with their own capsules and synovial fluid: the glenohumeral joint is a ball-and-socket joint with a fibrous capsule enclosing a synovial cavity; the acromioclavicular joint is a plane-type synovial joint with its own capsule (often with an articular disc); and the sternoclavicular joint is a synovial saddle joint that also has a capsule and synovial fluid.