In lower-third fractures of shaft of femur, the proximal fragment undergoes which displacement ?
**Core Concept**
In lower-third fractures of the shaft of femur, the displacement pattern is influenced by the intact adductor magnus muscle, which plays a crucial role in stabilizing the proximal fragment. The proximal fragment tends to displace posteriorly due to the pull of the adductor magnus, leading to a characteristic displacement pattern.
**Why the Correct Answer is Right**
The adductor magnus muscle, which is attached to the proximal fragment, contracts and pulls the fragment posteriorly, resulting in posterior displacement. This occurs because the muscle fibers of the adductor magnus are oriented in a way that they exert a posterior force on the proximal fragment when they contract. As a result, the proximal fragment tends to displace posteriorly, leading to a characteristic displacement pattern in lower-third fractures of the femoral shaft.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the displacement pattern in lower-third fractures is not primarily due to the pull of the quadriceps muscle.
* **Option B:** This option is incorrect because the displacement pattern in lower-third fractures is not primarily due to the pull of the hamstrings muscle.
* **Option C:** This option is incorrect because the displacement pattern in lower-third fractures is not primarily due to the pull of the gastrocnemius muscle.
**Clinical Pearl / High-Yield Fact**
In lower-third fractures of the femoral shaft, the intact adductor magnus muscle can lead to characteristic posterior displacement of the proximal fragment, which is an important consideration in fracture management.
**Correct Answer: B. Posterior displacement.**