Saddle joints have concave and convex surfaces. Identify a saddle joint of the skeleton.

Choice A reason: Scoliosis is the correct answer. It is characterized by a lateral curvature of the spine, often diagnosed in adolescence. It can range from mild to severe and may require bracing or surgery depending on progression.

Choice B reason: Lordosis refers to an exaggerated inward curvature of the lumbar spine. It is a spinal deformity but not the most common.

Choice C reason: Kyphosis is an exaggerated outward curvature of the thoracic spine, leading to a hunched posture. It is less common than scoliosis.

Choice D reason: Osteosis is not a recognized spinal deformity. It may be a misused or fictional term.

Choice E reason: A slipped disc, or herniated disc, involves displacement of intervertebral disc material. It causes pain and nerve compression but is not classified as a spinal deformity.

Choice A reason: Synarthrotic joints are immovable, not slightly movable. Examples include sutures in the skull. They are designed for stability rather than movement.

Choice B reason: Synovial joints are the only type of joint that is always freely movable. They include hinge joints (e.g., elbow), ball-and-socket joints (e.g., shoulder), and others that allow a wide range of motion due to the presence of a synovial cavity and lubricating fluid.

Choice C reason: A gomphosis is a type of fibrous joint found between teeth and their sockets. It is immovable and not freely movable.

Choice D reason: Cartilaginous joints do not have a joint cavity. They are connected entirely by cartilage and allow limited movement, such as the intervertebral discs and the pubic symphysis.

Choice E reason: Immovable joints are called synarthroses, not amphiarthroses. Amphiarthroses are slightly movable joints, such as those between vertebrae.