A patient with a two-week-old complete posterior cruciate ligament tear who has not undergone surgery—which muscle can assist with knee stability and reduce posterior translation?

• A. Quadriceps femoris
• B. Popliteus
• C. Biceps femoris
• D. Semimembranosus

Answer: (B)

When a posterior cruciate ligament is torn, dynamic stabilizers around the knee become crucial for limiting posterior tibial translation during movement. The popliteus is a key posterior structures muscle that sits behind the knee and attaches to the posterior tibia and the lateral femoral condyle. Its contraction helps stabilize the knee by guiding tibial position and supporting the posterolateral corner, which reduces the tendency of the tibia to translate backward relative to the femur when the PCL is injured. This makes it a particularly important aid for knee stability in the early rehab setting, as it provides posterior stability without relying on the compromised PCL.

In contrast, actions of the quadriceps tend to pull the tibia forward (anterior translation), which can help oppose posterior sag only indirectly, and the hamstrings (such as semimembranosus and biceps femoris) tend to pull the tibia posteriorly, potentially worsening posterior instability in a torn PCL. Thus the popliteus stands out as the muscle whose function most directly supports posterior knee stability in this scenario.