**Core Concept**
The triple deformity of the knee joint refers to a combination of flexion, posterior subluxation, and external rotation of the tibia in relation to the femur. This complex deformity is often seen in conditions that cause significant knee instability, such as severe ligamentous injuries or osteoarthritic changes.

**Why the Correct Answer is Right**
The triple deformity is characterized by a flexion deformity of the knee, which is often due to a disruption of the anterior cruciate ligament (ACL). The posterior subluxation of the tibia occurs due to the loss of posterior cruciate ligament (PCL) integrity, allowing the tibia to sublux posteriorly relative to the femur. The external rotation of the tibia is often a result of the associated meniscal injuries or the loss of medial or lateral collateral ligament stability. The combination of these deformities results in a significant loss of knee function and stability.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the triple deformity of the knee joint.
**Option B:** This option may be related to a different type of joint deformity, such as the "genu valgum" deformity seen in conditions like rickets or Blount's disease.
**Option C:** This option refers to a different type of joint deformity, such as the "genu varum" deformity seen in conditions like rickets or Blount's disease.

**Clinical Pearl / High-Yield Fact**
A mnemonic to remember the components of the triple deformity is "F-P-E" for flexion, posterior subluxation, and external rotation.

**Correct Answer:** C. Genu recurvatum