What is a Hinge Joint
A hinge joint is a type of synovial joint that permits movement primarily in one plane, allowing flexion and extension motions similar to the opening and closing of a door.
Anatomical Characteristics
The knee is classified as a modified hinge joint with one primary plane of movement, distinguishing it from ball-and-socket joints like the hip which allow multiple planes of motion 1
Hinge joints sacrifice stability for their specific range of motion, making them more constrained than multi-planar joints but still vulnerable to injury when forces are applied outside their primary movement plane 2
Biomechanical Function
The primary movements are flexion (bending) and extension (straightening), with the joint surfaces designed to guide motion along a single axis 1
In the knee specifically, the hinge mechanism allows for the screw-home mechanism involving tibial rotation during terminal extension, which optimizes joint tracking and stability 3
Clinical Relevance in Orthopedics
Orthotic devices for hinge joints utilize mechanical hinges that attempt to replicate the natural joint motion, with designs ranging from simple monocentric (single-axis) to polycentric (multiple-axis) configurations 1
Functional knee braces employ hinge-post-shell or hinge-post-strap designs to control joint motion while allowing flexion and extension, with proper hinge placement relative to the femoral condyles being critical for optimal performance 1, 4
The elbow is another example of a highly constrained synovial hinge joint that frequently becomes stiff after injury, requiring specialized treatment approaches 2
Common Pitfalls
Not all "hinge joints" are purely uniaxial - the knee, while classified as a modified hinge, actually permits some rotation and gliding motions in addition to flexion-extension 1
Mechanical hinges in braces cannot perfectly replicate biological hinge joint motion, with even polycentric designs showing misalignment of up to 23.9 mm compared to natural knee motion 5