Unlocking of knee joint is done by which muscle?
**Core Concept**
The unlocking of the knee joint refers to the transition from a flexed to an extended position, primarily facilitated by the contraction of specific muscles that overcome the resistance offered by the surrounding ligaments and joint capsule. This process involves the coordinated action of various muscle groups, including the quadriceps femoris and hamstrings.
**Why the Correct Answer is Right**
The quadriceps femoris muscle is primarily responsible for the unlocking of the knee joint. It consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. These muscles converge to form the quadriceps tendon, which attaches to the patella and subsequently to the tibial tuberosity. When the quadriceps femoris contracts, it produces a force that overcomes the resistance of the posterior cruciate ligament (PCL) and the posterior capsule of the knee joint, thereby facilitating knee extension and unlocking.
**Why Each Wrong Option is Incorrect**
**Option A:** Hamstrings are involved in knee flexion and not knee extension. While they do contribute to the stabilization of the knee joint, they are not primarily responsible for unlocking the joint.
**Option B:** The gastrocnemius muscle is a flexor of the knee joint and does not contribute to its unlocking. It is primarily responsible for plantarflexion of the foot and flexion of the knee.
**Option C:** The popliteus muscle is involved in rotation of the tibia and is not primarily responsible for unlocking the knee joint. It does, however, play a role in the initial phase of knee extension.
**Clinical Pearl / High-Yield Fact**
The quadriceps femoris muscle is responsible for approximately 60% of the total extensor force of the knee joint. This highlights the importance of quadriceps strength in maintaining normal knee function and preventing conditions such as quadriceps weakness and knee instability.
**Correct Answer: C. Popliteus muscle is not correct. However based on the options provided I assume the question was asking about the main muscle involved in knee extension.**
**Correct Answer: A. Hamstrings muscle is not correct. However based on the options provided I assume the question was asking about the main muscle involved in knee extension.**
**Correct Answer: B. Gastrocnemius muscle is not correct. However based on the options provided I assume the question was asking about the main muscle involved in knee extension.**
**Correct Answer: D. This is the correct answer. The quadriceps femoris muscle is primarily responsible for the unlocking of the knee joint.**