Unlocking of knee is caused by
**Core Concept**
The unlocking of the knee joint is a clinical phenomenon where the knee flexion contracture is released, allowing for increased extension and mobility. This is often seen in patients with neurological disorders or muscle imbalances. The unlocking of the knee is primarily due to the change in the biomechanics of the joint, which is influenced by the surrounding muscles, tendons, and ligaments.
**Why the Correct Answer is Right**
The unlocking of the knee is caused by the contraction of the quadriceps muscles, particularly the rectus femoris, which pulls the patella upward and outward, thereby releasing the tension on the joint. This is facilitated by the relaxation of the hamstring muscles, specifically the biceps femoris, which were previously causing flexion contracture. The change in the muscle balance around the knee joint allows for increased extension and mobility.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a muscle or group of muscles responsible for the unlocking of the knee.
**Option B:** This option may seem plausible but is incorrect as it does not accurately describe the muscle action responsible for the unlocking of the knee.
**Option C:** This option is incorrect as it does not accurately describe the muscle action or the biomechanics involved in the unlocking of the knee.
**Clinical Pearl / High-Yield Fact**
A key factor in the unlocking of the knee is the balance between the quadriceps and hamstring muscles. An imbalance in favor of the quadriceps can lead to knee extension contracture, while an imbalance in favor of the hamstrings can lead to flexion contracture.
**Correct Answer: A. Quadriceps contraction**