Knee rotation is possible when the knee is positioned at 90 degrees or more of flexion mainly because in this position the

Knee rotation is possible when the knee is positioned at 90 degrees or more of flexion mainly because in this position the

• A. Condyles of the femur glide posteriorly on the condyles of the tibia
• B. Hamstrings act as rotating force
• C. Patella deviates inferiorly
• D. Tension on the ligaments is decreased

Answer: (D)

When the knee is flexed to about 90 degrees or more, the passive restraints inside the joint become less taut, especially the cruciate and collateral ligaments. This release of tension frees the tibia to rotate relative to the femur, allowing tibial rotation at that joint angle. In contrast, near full extension these ligaments are tight and the screw-home mechanism locks the knee, limiting rotation. So the main reason knee rotation is possible at 90 degrees of flexion or more is the decreased tension on the ligaments. The other ideas aren’t the primary driver: the posterior glide of the femoral condyles happens to accommodate flexion but doesn’t explain rotation; the hamstrings can contribute to rotation if they’re actively contracting, but rotation can occur passively when ligaments are lax; and patellar position doesn’t govern the ability of the tibia to rotate.

When the knee is flexed to about 90 degrees or more, the passive restraints inside the joint become less taut, especially the cruciate and collateral ligaments. This release of tension frees the tibia to rotate relative to the femur, allowing tibial rotation at that joint angle. In contrast, near full extension these ligaments are tight and the screw-home mechanism locks the knee, limiting rotation. So the main reason knee rotation is possible at 90 degrees of flexion or more is the decreased tension on the ligaments.

The other ideas aren’t the primary driver: the posterior glide of the femoral condyles happens to accommodate flexion but doesn’t explain rotation; the hamstrings can contribute to rotation if they’re actively contracting, but rotation can occur passively when ligaments are lax; and patellar position doesn’t govern the ability of the tibia to rotate.