In meniscus injury, ‘Locking’-that is sudden inability to extend the knee fully is a feature of: March 2004, March 2003
**Core Concept**
Meniscus injuries in the knee joint can result in mechanical blockage of the joint, leading to locking or catching sensations. The menisci are two C-shaped cartilages that provide cushioning and support to the knee joint. Injuries to the meniscus can cause fragments to break off and get stuck in the joint, obstructing movement.
**Why the Correct Answer is Right**
The "locking" sensation in meniscus injuries is typically due to a meniscal tear that causes a fragment to become wedged in the intercondylar notch of the femur, preventing full extension of the knee. This is often associated with a bucket-handle tear, where a longitudinal tear in the meniscus causes a flap to break off and get stuck in the notch. The resulting mechanical blockage prevents the knee from fully extending, leading to the characteristic locking sensation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specifically relate to meniscus injuries. Other knee injuries, such as ligament sprains or osteochondral fractures, may cause locking sensations but are not directly related to meniscus tears.
**Option B:** This option is incorrect as it refers to a condition where the patella (kneecap) becomes displaced or trapped in the trochlear groove of the femur. While this can cause knee pain and stiffness, it is not typically associated with the locking sensation seen in meniscus injuries.
**Option C:** This option is incorrect as it refers to a condition where the quadriceps muscle is weakened or paralyzed, leading to knee weakness and instability. While this can affect knee function, it is not typically associated with the locking sensation seen in meniscus injuries.
**Clinical Pearl / High-Yield Fact**
To diagnose meniscus injuries, it's essential to perform a thorough physical examination, including a knee examination to assess range of motion, joint stability, and meniscal tenderness. A McMurray's test can be performed to detect meniscal tears, and an arthroscopy may be necessary for definitive diagnosis and treatment.
**Correct Answer:** B. Dislocation of the patella.